LS1 Engine for aircraft?

Discussion in 'Chevy' started by Brohawk, Feb 9, 2008.

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  1. Feb 9, 2008 #1

    Brohawk

    Brohawk

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    This past week I was talkiing with a friend at work who is into cars. He was telling me about the Chevy LS1 aluminum block engine. That got me thinking...

    From what he said, it's a pretty light weight package for the power that's delivered.

    A couple days ago I found a performance chart (rpm/hp curve) and if I remember correctly, it put out around 200 hp @ 2,000 rpm (peak hp is around 340 out of the crate).

    Here's where the wheels got to turning...

    - For most of the ideas I'm running in my head, I wouldn't need more than 200 hp.

    - Would it be possible to set the rev limit at around 3,000 rpm? (I don't know much about the computers controlling car engines - I miss point ignitions ;)).

    - How hard would it be to fabricate a roughly 1:1 belt drive (to isolate the prop from the crankshaft).

    - It seems that running at what would be "highway rpm" rather than near-peak would make for an extremely long engine life.

    Eagerly awaiting opinions...
     
  2. Feb 9, 2008 #2

    orion

    orion

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    The GM engines are about the most popular in the industry and the install should be relatively straight forward but in going this route, you have to coordinate the power requirement with the installation weight. Aluminum block or not, by the time you have the engine ready to bolt up to your firewall that assembly is probably going to weigh well more than 500 pounds. That's a lot of mass for 200 hp.

    But in order for this to work well in an airplane, you'll most likely want to make a few modifications in order to maximize the torque capability of the engine. The two easiest modifications include the installation of a long stroke crank and a cam timed for max torque at low rpm. Essentially what you're looking for is a truck engine or possibly a marine one.

    Assuming I ever get the time, my own personal goal is something similar to what you describe but I want to run inverted with the output in-line with the crank. The output shaft, bearings and its housing will be designed for the flight imposed loads and will be separated from the crank by a isolator coupling.
     
  3. Feb 10, 2008 #3

    Midniteoyl

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  4. Feb 10, 2008 #4

    PTAirco

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    I for one would love to see more on that inverted direct drive idea; keep us posted.
     
  5. Apr 28, 2008 #5

    CJ#3

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    The new LS7 would be an ideal canadate. It is built with titanium rods, forged crank, aluminum block, and sodium filled exaust valves. Not to mention the dry sump system. At 427 ci. it has plenty of displacment.400hp for take off and 300hp for cruse is not unresonable. But, on the down side they are a little on the pricey side for an auto convesion.
     
    whiteknight likes this.
  6. Aug 19, 2008 #6
    There are several companies manufacturing items to use an LS series engine. Most of them use a reduction drive. This seems to be one of those situations where everyone follows the same lead and assumes it must be the only/best way. I'm not saying its wrong, but to my way of thinking, it may not be the best way...at least in my set of circumstances.

    If you use a reduction drive, what do you gain?

    1. You gain the ability to run the engine at a higher RPM and create more HP
    for takeoff. You will also need more HP to carry the weight.
    2. You can run the engine at a somewhat higher RPM level and increase cruising speed. This along with the added weight will reduce the distance you can travel before landing, and may be greater than the airplanes maximum speed. You'll get to the gas pump quicker....
    3. You increase the cost and complexity of building the airplane and reduce the TBO. You place added strain on the engine components at higher rpms.
    4. You may have to compensate to get your weight and balance to offset the added weight. You lose cargo capacity, and gliding distance, increase stall speed.

    My opinion (and its just that...an opinion) is that trying to mimic an airplane engine is the best way to go. If 160/200 hp is sufficient to fly the airplane, then what good is having 300 hp? When cruising, you will probably only require a 100HP or so, and if you want to fly at top speed, figure how many HP you need and shoot for ...say 20 more than that and direct drive.

    How do you get there? My opinion again...cubic inches. Everyone wants to purchase a readymade factory engine and plug and play. A 427 cu in LS7 doesn't weigh anymore than a 346 cu in LS1...but it sure costs a lot more.
    (About $13K) Its 505 hp right out of the crate and GM sells a computer and harness that you can plug and play for under $1K. But...the 505 HP is at an RPM well above where you need to run. The LS1 5.7 Liter may meet your needs, but why not look at getting more cubic inches in an engine that weighs the same. To increase your power down low (2000-2800 rpm) the best way is to add cubic inches. Look at buying a 427 LS7 block and putting a stroker in it. You can actually build them even bigger than 427and for a whole lot less than a factory titanium rod version.

    Now, back to the direct drive scenario. Everyone is throwing up their hands and saying the engine is not designed to deal with the thrust, the harmonics, or the prop twisting and flexing.

    OK, how many of you have ever looked at or measured a crankshaft in a Lycoming? The crank has a 2.375 diameter crankshaft main journal and they use it on O320/O360/O540......even a 540.

    An LS1/LS7 has a 2.650 diameter main bearing. Thats over a 1/4 inch larger than a Lycoming. (Also, a conventional smallblock Chevy has a 2.65 diameter on the 400 cu in block, and 2.45 on a 350 cu in block)

    Thrust face...the Chevy won't handle the thrust. Well there is where the "rub" comes in. The LS1/LS7 engine has the thrust face in the middle of the crank instead of at the rear. My opinion, thats not good, because a propellor will be pulling on the back half of the crankshaft with no thrust face supporting it. (My solution later) On a conventional smallblock Chevy the thrust bearing is at the rear of the engine. The thrust of a Lycoming is applied directly against the face of the aluminum engine case. Look at one and you will see that its not an extremely large contact area....and its directly against the aluminum....hmmmm. So while I don't know if the Chevy will handle the thrust with no problem, I've never seen any factual information showing it can't.
    (Hopefully someone will jump in here and provide that info if I am wrong)

    The Lycoming does have an elongated snout which contains the equivalent of two rod bearing surfaces with a space in between.This purportedly provides the strength to resist the prop side loading. It does a good job. It would seem that if a small housing were made that could support a set of those bearings and an oil supply and return routed to it, then one would have a virtual equivalent of the Lycoming . A short shaft would have to be made to bolt to the Chevy and protrude thru the housing for mounting the prop.

    The LS1/LS7 also has a crankcase which extends down past the crankshaft and uses 6 bolts to retain the main bearing caps...as opposed to 2 or 4 on a conventional smallblock or 2 thru studs on a Lycoming.

    Another important factor here is cylinder filling. Its hard to get enough air into an engine at the lower rpms so you need air velocity. My opinion again...some generic LS1 heads will probably accomplish that task better with small intake passages than some more expensive high flowing (upper rpm) heads. That means you can buy em cheap. Am I right in this assumption...I dunno, but it sounds good. Also, Chevy is experimenting with some 3 valve heads because they can flow much more air than two valve heads...even at lower rpms. If it ever happens, it would be a nice upgrade.

    Oh, I almost forgot...the crank will break. Well maybe it will and maybe it won't. They break off airplane engines so some will probably break off some auto engine conversions...if they aren't done properly. Both types of crankshafts can be bought made from the same materials, so I don't see a problem there. As for harmonics...some airplane engines are not supposed to be run in certain rpm ranges...or they may break. Auto engines may suffer the same problem, but there is equipment available to test them. Also you can put a harmonic damper on an auto engine. Everyone calls them "balancers" but the truth is that they are dampers that are designed to absorb harmonics. They are designed to work in a certain range and the rubber absorbs the harmonic vibration. Aftermarket units can be purchased which work over a broad range of rpms. The rubber absorbs the vibration and prevents it from increasing. Ever see one for an airplane engine? I haven't, but there probably is one somewhere.

    As for information on conversions, Contact Magazine is a great nuts and bolts source of information, and Mick Mayall has some books out that has combined all the articles from the magazine. If you are serious about conversions, thats where I would reccommend starting.

    I've rationalized a lot of things here because its what I want to make happen. If you disagree or have other ideas, feel free to state them. I'm always willing to learn...like I said, this is just my opinion.


    Last comment...Weight

    I purchased a 98 LS1 Firebird and removed the engine. On a scale I own it weighed 399.5 lbs without the starter and alternator, but with the power steering pump still attached and some water in its block. The starter and altenator showed 21 lbs. It had the factory welded tube exhaust manifolds attached also. No flywheel. I had the scale calibrated a few years ago and assume its accurate as I have only used it a few times....again I could be wrong but at least it something other than speculation.
     
  7. Aug 19, 2008 #7

    PTAirco

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    Well, that is more of less my plan for my biplane - a direct drive Chevrolet. I designed the airplane around the small block 350 with various modifications to handle some of the problems you mentioned. I am looking hard at the LS engines, but they are still pricey. A crate ZZ4 engine with aluminium heads and a steel crank etc, can still be had for just under $4000, so that is my plan. My idea for handling propeller loads is to use a short stub shaft from the flywheel end, supported at the hub end by a BIG bearing, all of it supported by an off the shelf bell housing.

    The folks building those scaled down Hawk P6's have been using a direct drive version of similar engines, with nothing more sophisticated than a spacer/prop hub bolted to the flywheel. I have read that some main bearings wore out very quickly, but that other (Federal Mogul) held up well. Hard to find any more info on that. Of course, thrust loads are reversed from what the engine was designed for.

    I agree about all the engineers throwing up their hands and predicting imminent self-destruction, but if such crude conversions hold up well, then something a little more sophisticated should work fine. As far as harmonics go - I don't care how much FEA analysis or reams of paper you use to calculate if it will occur; it's still educated guessing, considering the huge number of variables involved. It is not impossible to tune out harmonics, if they even occur, but the only way to find out is to go ahead and try it.
     
  8. Aug 19, 2008 #8

    Midniteoyl

    Midniteoyl

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    Test for it then get a custom dampner built.. TCI and ATI will even do the testing/building for you (at a cost ;)). But, they can design one for both ends of the crank to isolate it completly.

    Seems easy enough to me.
     
  9. Aug 20, 2008 #9

    orion

    orion

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    Your idea and reasoning behind it are good and in line with my own thoughts on the process, except that in my case I still want the baseline amount of power and ideally, I'd like to run the engine upside down in order for it to fit within a fairly normal cowl. My own reasoning for this is based on the need for a simpler system and the fact that in my opinion, many of the manufacturers out there don't have sufficient engineering behind their products to cover all the bases of the redrive's design requirements. Some of these drives you can just glance at and see that they would be unable to sufficiently cope with the flight environment - not for any significant length of time anyway.

    The LS series is a good choice in that it is a reliable configuration with a wide after-market for a variety of improvements and configurations. But making those choices, especially for direct drive, requires a specific bit of knowledge and experience since not all aspects of the engine relate directly to this application.

    This seems to be one of those situations where everyone follows the same lead and assumes it must be the only/best way.....

    Depends on what you're trying to achieve. The bottom line of the choice is simply that if you're going to put 500 pounds of engine on your airplane, ideally you'd like to see more than 150 to 200 horsepower out of it. With that power-to-weight you might as well go out and get a moderate timed Lyc or Continental since those engines will deliver a better ratio. True, the aircraft engines might set you back a bit more but in the end you'll know that you have an engine specifically designed for flying, not something that had top be modified to work in the particular situation.

    If you're like one other member of this board who is installing the V-8 in a vintage biplane design, then the amount of power is not that critical since the old engines of the orignal airplanes had relatively low power ratios to start with. As such, the V-8 will come close to providing the airplane with the proper amount of power and mass balance. But if you're looking for at least some level of efficiency, then the redrive will allow you to operate the engine somewhat higher on the power and torque curves, and within more normal operating envelopes so that you can still use an off the shelf prop.

    1. You gain the ability to run the engine at a higher RPM and create more HP
    for takeoff. You will also need more HP to carry the weight.

    At this power level, the weight of the redrive is relatively minor as compared to the performance you might gain. Furthermore, the power gain is not just for takeoff - while you yourself may want to cruise at 100 hp, the more common applications of this power and weight class would barely stay in the air with the throttle set that low.

    As far as the weight is concerned, the 70 pounds or so that the redrive might cost you is fairly negligible where airplane performance is concerned, especially given the torque and power benefit its use will generate.

    2. You can run the engine at a somewhat higher RPM level and increase cruising speed. This along with the added weight will reduce the distance you can travel before landing, and may be greater than the airplanes maximum speed. You'll get to the gas pump quicker....

    Nothing says you have to run with the throttle full open. But the increased power provides the airframe with much more flexibility. Also, if you encounter a situation where you might suddenly need the power, it's certainly nice if it's there in the first place. In a general sense, limiting your available power when you don't need to is a compromise in safety and efficiency. In the end, you'll pay a much greater weight-based penalty in installing this heavy engine configuration without taking advantage of the performance it is capable of providing you.

    3. You increase the cost and complexity of building the airplane and reduce the TBO.

    Huh? If your use of a redrive reduces your TBO and so significantly increases the cost of the airplane, you've chosen the wrong product or approach. But engines and airframes need to be matched. This is not something to be simply eyeballed.

    4. You may have to compensate to get your weight and balance to offset the added weight. You lose cargo capacity, and gliding distance, increase stall speed.

    To a point, true. But again, the added weight of the redrive as compared to the airframe's operational or gross weight is fairly small. All you'll most likely need to do is shift the battery or configure the cooling system other than in front of the firewall.

    My opinion (and its just that...an opinion) is that trying to mimic an airplane engine is the best way to go. If 160/200 hp is sufficient to fly the airplane, then what good is having 300 hp?

    True, but if all you need is that small amount of power, why would you install a 450 pound engine on the nose? Talk about inefficiency and weight penalty.

    Despite claims otherwise, most airplane owners fly at 75% power or higher. If all you need is 200 hp max, there certainly are more efficient choices.

    How do you get there? My opinion again...cubic inches. Everyone wants to purchase a ready made factory engine and plug and play. A 427 cu in LS7 doesn't weigh anymore than a 346 cu in LS1...but it sure costs a lot more.

    Excellent point and quite true. But cubes is not all there's to it. You can also gain tremendous benefit by employing boost (turbocharging, not super charging - lighter), improving the timing through a more optimal cam, and of course, better breathing (intake and exhaust design).

    Everyone is throwing up their hands and saying the engine is not designed to deal with the thrust, the harmonics, or the prop twisting and flexing.

    These are not opinions - these are simply the base physics of the situation. Ignore them at your own peril. I'd equate this to something like making light of designing your wing structure. You do it wrong and things might go crunch at the worst possible time. And for an airplane, the worst possible time is each time you get more than ten feet off the ground.

    OK, how many of you have ever looked at or measured a crankshaft in a Lycoming? The crank has a 2.375 diameter crankshaft main journal and they use it on O320/O360/O540......even a 540.

    Comparing an aircraft crank to a mass produced automotive product is downright foolish. The manufacturing processes for aircraft products are substantially different than for automotive ones, resulting is significantly different structural properties, especially when considering issues of fatigue, notch sensitivity, and yes, even strength. Just because it's steel and measures about the same is no comparison.

    Thrust face...the Chevy won't handle the thrust. Well there is where the "rub" comes in. The LS1/LS7 engine has the thrust face in the middle of the crank instead of at the rear.

    There's much more than thrust to worry about, and certainly more than just the crank. First off, the loads imposed by the prop are not only axial (thrust) but also radial (out of plane shear) and moment based (gyroscopic). These can be quite substantial, especially the latter, imposing loads on the structure possibly orders of magnitude higher than anything an automotive product is designed to handle. Keep in mind that the automotive crank only sees pure torsion, nothing else. Introduce even a small variation to that and all the original design assumptions go out the window.

    And of course the loads have to go somewhere. The next area then to investigate is that associated with the crankcase since that will be the primary stress transfer medium that will transfer the flight loads into the airframe. Now you need to consider the strength and durability of the block, which if it's cast aluminum, will be very poor in fatigue, will be notch sensitive (sensitive to stresses in areas of abrupt geometry change or left over machine marks created during manufacturing), and will have generally low structural properties to start with. Again, keep in mind that the basic engine is designed to output only torque - introduce flight loads and you're out of the original design envelope. And yes, it is very significant and not to be taken lightly.

    The thrust of a Lycoming is applied directly against the face of the aluminum engine case. Look at one and you will see that its not an extremely large contact area....and its directly against the aluminum....hmmmm. So while I don't know if the Chevy will handle the thrust with no problem, I've never seen any factual information showing it can't.

    The Lyc case is designed to carry flight loads associated with the props it is certified for. The Chevy crankcase is designed to carry a stationary bell housing and a drive system that transfers no axial and/or no bending moments into the crank. The trust bearings in the automotive engine are there to only carry positioning loads that the engine sees as a result of expansion due to heating - that's why the thrust bearings are in the middle of the crank.

    The Lycoming does have an elongated snout which contains the equivalent of two rod bearing surfaces with a space in between.This purportedly provides the strength to resist the prop side loading. It does a good job. It would seem that if a small housing were made that could support a set of those bearings and an oil supply and return routed to it, then one would have a virtual equivalent of the Lycoming . A short shaft would have to be made to bolt to the Chevy and protrude thru the housing for mounting the prop.

    It's not that simple but in essence you're right. The key to this is to make sure that you isolate the prop loads from the engine and an externally supported shaft in a proper housing is pretty much the only solution.

    Oh, I almost forgot...the crank will break. Well maybe it will and maybe it won't. They break off airplane engines so some will probably break off some auto engine conversions...if they aren't done properly.

    The only aircraft crank failures that I know of happened either due to ground impact or due to a manufacturing flaw. If you mount a prop directly to an automotive crank you can almost bank on it failing.

    Both types of crankshafts can be bought made from the same materials, so I don't see a problem there.

    No! Different processes of manufacturing, heat treat, machining, and finishing.

    As for harmonics...some airplane engines are not supposed to be run in certain rpm ranges...or they may break.

    This is not solely an engine issue - the engines are specifically tested and certified for particular props. It is that combination of engine and prop that sets the green arc. Outside of that arc the combination can encounter harmonics that can be damaging. Considering that a relatively wide range of harmonics off of the primary natural frequency can damage the system, this is also something that needs to be addressed in any new development, either through testing or through proper isolation design.

    Also you can put a harmonic damper on an auto engine. Everyone calls them "balancers" but the truth is that they are dampers that are designed to absorb harmonics.

    Inapplicable - these small harmonic dampers are designed to only take care of the engine's internal vibrations caused by the physical characteristics of the engine's rotating components - these have absolutely nothing to do and no ability to deal with any external components you install.

    Ever see one for an airplane engine? I haven't, but there probably is one somewhere.

    Airplane engines are designed so that they don't need them, although there is some evidence that their use might be beneficial when using a wood prop. I have seen one made for the four cylinder Lycs that incorporates into the ring gear.

    I've rationalized a lot of things here because its what I want to make happen. If you disagree or have other ideas, feel free to state them. I'm always willing to learn...like I said, this is just my opinion.

    You're on the right track but I'd guess that you'll need to take your considerations deeper than just this simplistic analysis - after all, your life depends on it.
     
  10. Aug 21, 2008 #10

    Lee Schaumberg

    Lee Schaumberg

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    Good posts by ekimneibo and orion. Many things I've learned that I didn't know. There is a guy in the LA area that has a bored and stroked tall block on his 75% scale mustang. A LS7 has a dry sump. So if you can't fly like Hoover did you won't have a problem.
     
  11. Aug 21, 2008 #11
    You make some excellent arguments but I think maybe some of what I said was misconstrued or looked at in the wrong light. I'll respond to them individually.

    Your idea and reasoning behind it are good and in line with my own thoughts on the process, except that in my case I still want the baseline amount of power and ideally, I'd like to run the engine upside down in order for it to fit within a fairly normal cowl. My own reasoning for this is based on the need for a simpler system and the fact that in my opinion, many of the manufacturers out there don't have sufficient engineering behind their products to cover all the bases of the redrive's design requirements. Some of these drives you can just glance at and see that they would be unable to sufficiently cope with the flight environment - not for any significant length of time anyway.

    The LS series is a good choice in that it is a reliable configuration with a wide after-market for a variety of improvements and configurations. But making those choices, especially for direct drive, requires a specific bit of knowledge and experience since not all aspects of the engine relate directly to this application.

    This seems to be one of those situations where everyone follows the same lead and assumes it must be the only/best way.....

    Depends on what you're trying to achieve. The bottom line of the choice is simply that if you're going to put 500 pounds of engine on your airplane, ideally you'd like to see more than 150 to 200 horsepower out of it. With that power-to-weight you might as well go out and get a moderate timed Lyc or Continental since those engines will deliver a better ratio. True, the aircraft engines might set you back a bit more but in the end you'll know that you have an engine specifically designed for flying, not something that had top be modified to work in the particular situation.

    As you say, it depends on what you are trying to achieve. I would like to achieve 250 hp at 2700 rpms. I would be satisfied if I can attain 210 hp or more. I believe that to be easily attainable. I don't see the need to produce
    400 hp because it will be unusable most of the time (in a 4 seat high wing with 160 mph max speed 2500 lb gross) A Lancair or some very fast airplane might make use of this, but when you throw all that horsepower at the airframe to save you from a situation,I don't think its necessary or advisable.

    The reason I want to use something other than a Lyc is the high cost of parts and maintainance,thermal shock concerns, rusty cam problems,and disbelief that all those log books for used engines are accurate.


    If you're like one other member of this board who is installing the V-8 in a vintage biplane design, then the amount of power is not that critical since the old engines of the orignal airplanes had relatively low power ratios to start with. As such, the V-8 will come close to providing the airplane with the proper amount of power and mass balance. But if you're looking for at least some level of efficiency, then the redrive will allow you to operate the engine somewhat higher on the power and torque curves, and within more normal operating envelopes so that you can still use an off the shelf prop.

    I'm not sure what you mean by "normal operating range" and "some level of efficiency" but just because an engine is capable of operating at a higher rpm level doesn't mean it should be, or that it is inefficient when operated at a less demanding rpm.My S10 with a 4.3 V6 turns about 1800 rpm when I am driving 65 mph. It virtually never operates at 4000 rpm for other than a momentary burst into highway traffic. So to me operating at 2200 wouldn't be much different as a normal operating range.
    To produce horsepower requires burning a specific amount of fuel. If you run an engine at a higher rpm range and produce more horsepower you will burn more fuel. My son had an LT1 Camaro/6 speed. In 6th gear (2 overdrives) it would go about 70/75 mph at 1500 rpm and get high 20s mpg (27/28).






    1. You gain the ability to run the engine at a higher RPM and create more HP
    for takeoff. You will also need more HP to carry the weight.

    At this power level, the weight of the redrive is relatively minor as compared to the performance you might gain. Furthermore, the power gain is not just for takeoff - while you yourself may want to cruise at 100 hp, the more common applications of this power and weight class would barely stay in the air with the throttle set that low.

    As far as the weight is concerned, the 70 pounds or so that the redrive might cost you is fairly negligible where airplane performance is concerned, especially given the torque and power benefit its use will generate.

    The weight of a redrive is very consequential in many airplane designs, especially when placed way out on the nose of the airplane. In many instances that additional weight may be the difference in whether a conversion is even possible. On the






    2. You can run the engine at a somewhat higher RPM level and increase cruising speed. This along with the added weight will reduce the distance you can travel before landing, and may be greater than the airplanes maximum speed. You'll get to the gas pump quicker....

    Nothing says you have to run with the throttle full open. But the increased power provides the airframe with much more flexibility. Also, if you encounter a situation where you might suddenly need the power, it's certainly nice if it's there in the first place. In a general sense, limiting your available power when you don't need to is a compromise in safety and efficiency. In the end, you'll pay a much greater weight-based penalty in installing this heavy engine configuration without taking advantage of the performance it is capable of providing you.

    Doesn't matter whether you are running wide open or not, if you are producing more horsepower you are burning more fuel.I don't feel that you are "limiting" your available power,only deciding what you need and then building to that need.Lycoming proved that an O320 would produce more power at a higher rpm by gearing the propellor down, but they went back to direct drive. So, while its possible to produce more HP, its it needed?



    3. You increase the cost and complexity of building the airplane and reduce the TBO.

    Huh? If your use of a redrive reduces your TBO and so significantly increases the cost of the airplane, you've chosen the wrong product or approach. But engines and airframes need to be matched. This is not something to be simply eyeballed.

    An engine has only so many cycles in its lifetime before it has to be overhauled. If an engine has a 2000 hr TBO and runs at an average of 2500 rpms, it will complete 300,000,000 reveloutions.At 4000 rpm it will only take the engine 1250 hours to comple that many revolutions....so the lifespan of the engine has been effectively shortened even though it has completed the same number of revolutions. Also, the stresses placed upon the crankshaft,con rods, bearings, pistons, has more than doubled. Couple this with higher operating temps within the cylinder and their possible effect on the exhaust valve and spark plug and you have lessened your safety factor
    even further. You are right that running an engine at less than peak hp is limiting it, but I prefer to look at it as increasing the safety factor by insuring that the engine isn't stressed. Its really just the way either of us wish to view the situation.
    .





    4. You may have to compensate to get your weight and balance to offset the added weight. You lose cargo capacity, and gliding distance, increase stall speed.

    To a point, true. But again, the added weight of the redrive as compared to the airframe's operational or gross weight is fairly small. All you'll most likely need to do is shift the battery or configure the cooling system other than in front of the firewall.

    Yes, I agree that other items can often be shifted to compensate for the added weight in relation to your Center of Gravity....but it is still weight that can't be compensated for in the overall weight of the airplane.Weight is weight.......




    My opinion (and its just that...an opinion) is that trying to mimic an airplane engine is the best way to go. If 160/200 hp is sufficient to fly the airplane, then what good is having 300 hp?

    True, but if all you need is that small amount of power, why would you install a 450 pound engine on the nose? Talk about inefficiency and weight penalty.

    Despite claims otherwise, most airplane owners fly at 75% power or higher. If all you need is 200 hp max, there certainly are more efficient choices.

    I think the term "75% power is kind of arbitrary. RPM wise you may reduce your rpm from 2700 to 2200, but the horsepower being produced is not exactly linear. As rpm increases hp climbs more radically than at lower rpms.
    So I think when you cut back to 75% you are refering to rpms not HP.
    If I'm correct in that assumption, cutting back a 180 hp Lycoming to 75%
    would not mean you are operating at 135hp, but at something less than that.
    The 100 HP statement may have been a little low, but not falling from the sky unreasonable.....at least in the type of plane I'm interested in.


    How do you get there? My opinion again...cubic inches. Everyone wants to purchase a ready made factory engine and plug and play. A 427 cu in LS7 doesn't weigh anymore than a 346 cu in LS1...but it sure costs a lot more.

    Excellent point and quite true. But cubes is not all there's to it. You can also gain tremendous benefit by employing boost (turbocharging, not super charging - lighter), improving the timing through a more optimal cam, and of course, better breathing (intake and exhaust design).

    You are correct that there are other ways, but what I'm looking for is simplicity and reliability...not complexity and additional weight. But it is a fact that those are other ways to do it.


    Everyone is throwing up their hands and saying the engine is not designed to deal with the thrust, the harmonics, or the prop twisting and flexing.

    These are not opinions - these are simply the base physics of the situation. Ignore them at your own peril. I'd equate this to something like making light of designing your wing structure. You do it wrong and things might go crunch at the worst possible time. And for an airplane, the worst possible time is each time you get more than ten feet off the ground.

    Every propellor powered airplane deals with these factors. Do you have any hard evidence that shows that the engines will not perform satisfactorily?
    If not, then it is an opinion....just like mine. If the crankshafts were totally unsuited to this, then virtually every one of them would fail. Since there are examples out there flying successfully I must assume (don't say it) that they will work if done properly. The question is"what is "prop erly" (pun intended).
    I just think that well intended people scare people away with worries about unquantified unknowns..........








    OK, how many of you have ever looked at or measured a crankshaft in a Lycoming? The crank has a 2.375 diameter crankshaft main journal and they use it on O320/O360/O540......even a 540.

    Comparing an aircraft crank to a mass produced automotive product is downright foolish. The manufacturing processes for aircraft products are substantially different than for automotive ones, resulting is significantly different structural properties, especially when considering issues of fatigue, notch sensitivity, and yes, even strength. Just because it's steel and measures about the same is no comparison.

    Thrust face...the Chevy won't handle the thrust. Well there is where the "rub" comes in. The LS1/LS7 engine has the thrust face in the middle of the crank instead of at the rear.

    There's much more than thrust to worry about, and certainly more than just the crank. First off, the loads imposed by the prop are not only axial (thrust) but also radial (out of plane shear) and moment based (gyroscopic). These can be quite substantial, especially the latter, imposing loads on the structure possibly orders of magnitude higher than anything an automotive product is designed to handle. Keep in mind that the automotive crank only sees pure torsion, nothing else. Introduce even a small variation to that and all the original design assumptions go out the window.

    If both crankshafts are made from the same composition of metal and the automotive one is thicker, it would seem that it can handle the same loading even if an engineer didn't say so........



    And of course the loads have to go somewhere. The next area then to investigate is that associated with the crankcase since that will be the primary stress transfer medium that will transfer the flight loads into the airframe. Now you need to consider the strength and durability of the block, which if it's cast aluminum, will be very poor in fatigue, will be notch sensitive (sensitive to stresses in areas of abrupt geometry change or left over machine marks created during manufacturing), and will have generally low structural properties to start with. Again, keep in mind that the basic engine is designed to output only torque - introduce flight loads and you're out of the original design envelope. And yes, it is very significant and not to be taken lightly.

    The case of an LS1/LS7 is much stronger than previous Chevy alum blocks and has cross bolted mains. The LS7 has steel main caps while the others have powdered metal. To my knowledge no one has broken any engine cases but I'm not going to say its impossible....but not probable. As far as the flight loads go, I would think that all the torture engines go through in offroad racing and airboat racing would demonstrate their ruggedness.



    The thrust of a Lycoming is applied directly against the face of the aluminum engine case. Look at one and you will see that its not an extremely large contact area....and its directly against the aluminum....hmmmm. So while I don't know if the Chevy will handle the thrust with no problem, I've never seen any factual information showing it can't.

    The Lyc case is designed to carry flight loads associated with the props it is certified for. The Chevy crankcase is designed to carry a stationary bell housing and a drive system that transfers no axial and/or no bending moments into the crank. The trust bearings in the automotive engine are there to only carry positioning loads that the engine sees as a result of expansion due to heating - that's why the thrust bearings are in the middle of the crank.

    I don't know why they put it in the middle, but most thrust bearing failures in automobiles are caused by ballooning of the torque converter which forces the crank into the thrust bearing further than its mechanical limit.



    The Lycoming does have an elongated snout which contains the equivalent of two rod bearing surfaces with a space in between.This purportedly provides the strength to resist the prop side loading. It does a good job. It would seem that if a small housing were made that could support a set of those bearings and an oil supply and return routed to it, then one would have a virtual equivalent of the Lycoming . A short shaft would have to be made to bolt to the Chevy and protrude thru the housing for mounting the prop.

    It's not that simple but in essence you're right. The key to this is to make sure that you isolate the prop loads from the engine and an externally supported shaft in a proper housing is pretty much the only solution.

    Lycoming doesn't isolate prop loads from the engine...........




    Oh, I almost forgot...the crank will break. Well maybe it will and maybe it won't. They break off airplane engines so some will probably break off some auto engine conversions...if they aren't done properly.

    The only aircraft crank failures that I know of happened either due to ground impact or due to a manufacturing flaw. If you mount a prop directly to an automotive crank you can almost bank on it failing.

    And you know this for a fact..........how?




    Both types of crankshafts can be bought made from the same materials, so I don't see a problem there.

    No! Different processes of manufacturing, heat treat, machining, and finishing.

    Do you know what the differences in manufacturing are? I think that you are making an assumption without intimate knowledge of the available products.
    What manufacturing step makes a crankshaft resist torsional twisting? Can you make a blanket statement that all crankshafts produced by aftermarket manufacturers are unworthy of consideration? I have a maching background and have investigated some of the newer processes for crank manufacture. I was pretty impressed. So the crankshafts and metalurgy of Lycoming crankshafts designed and produced 60 years ago are better than what any automotive crank maker can do today.............. I don't agree at all.



    As for harmonics...some airplane engines are not supposed to be run in certain rpm ranges...or they may break.

    This is not solely an engine issue - the engines are specifically tested and certified for particular props. It is that combination of engine and prop that sets the green arc. Outside of that arc the combination can encounter harmonics that can be damaging. Considering that a relatively wide range of harmonics off of the primary natural frequency can damage the system, this is also something that needs to be addressed in any new development, either through testing or through proper isolation design.

    Also you can put a harmonic damper on an auto engine. Everyone calls them "balancers" but the truth is that they are dampers that are designed to absorb harmonics.

    Inapplicable - these small harmonic dampers are designed to only take care of the engine's internal vibrations caused by the physical characteristics of the engine's rotating components - these have absolutely nothing to do and no ability to deal with any external components you install.

    Isn't the purpose of the 5th order weights that Continental places inside their
    engines to combat internal harmonics? And riding or reducing these harmonics is what prevents you from destroying your engine.When an engine destroys itself harmonically its because a vibration has been allowed to reach a resonance that built until it became catastropic. At least thats my understanding. A dampner continually absorbs harmonic vibration and prevents it from building.



    Ever see one for an airplane engine? I haven't, but there probably is one somewhere.

    Airplane engines are designed so that they don't need them, although there is some evidence that their use might be beneficial when using a wood prop. I have seen one made for the four cylinder Lycs that incorporates into the ring gear.

    Again I'll refer you to the counterweights that Continental installs...same principal.

    I've rationalized a lot of things here because its what I want to make happen. If you disagree or have other ideas, feel free to state them. I'm always willing to learn...like I said, this is just my opinion.

    You're on the right track but I'd guess that you'll need to take your considerations deeper than just this simplistic analysis - after all, your life depends on it.

    We seem to be at opposite ends of the spectrum on this subject, but I enjoy the give and take .........

    __________________
     
  12. Aug 22, 2008 #12

    Midniteoyl

    Midniteoyl

    Midniteoyl

    Well-Known Member

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    An engine is most efficient at Peak Torque. Any time you run it at any other RPM, your efficiency goes down. You very well might get better GPH's of flow due to the lower RPM's, but the BSFC (Hp per gallon burned) goes down.

    Equating 'highway rpm's' in car use to RPM's in plane use is not accurate. That Camaro, in 6th @ 70mph is only producing about 30-40 hp. Not the 100hp or so you would need to maintain the same speed in a plane.

    75% power is exactly that - 75% of your max HP, not RPM. The RPM at which that 75% power is depends totally on your torque curve. If you have a 'peaky' torque curve that lays flat till 2000 RPM, then suddenly rises, your HP curve will do the same thing. If, on the other hand, you have a torque curve that rises gradually, peaks, the lowers (like a bell curve) then that is what your HP curve will do, only narrower. A flat torque curve produces a HP curve that rises linearly with RPM's.

    75% power for a 180hp Lyc is 135hp.

    He's saying that there are NO gyroscopic loads or significant weight on the bellhousing-to-block mating surface/bolts in an auto situation. In cars/trucks, the end of the transmission is held in place at the tail shaft. This removes cantilevered loads from the bellhousing, and limits the amount of 'twist' the mating surface sees. In fact, in off road use, the rubber mounts are replaced with solid ones - as are the engine mounts - precisely because they break, which allows the tranny to twist, which breaks bellhousings and blocks.

    A search of the net, mags, groups, etc, will find many examples. You wont find LS7's, simply 'cuase they are new.. :)

    However, they are not the same. Even so, your ignoring the torsional feedback from the prop - totally different than in a car.

    Um, the same type of forces a direct drive prop would do? :) The reason for the failure is it wasn't designed for it - not strong enough nor wide enough to carry the loads.

    Because its designed for them. :)

    To a point, then it will fail and damage will occur. However, your ignoring the massive increase in torsionals created by the prop as compared to even a clutch/tranny system in car. Take a look at large truck/diesel dampeners, clutches, and converters, you'll see a massive increase in the amount of torsional control that needs to be provided.



    Don't get me wrong here, I am currently in the design/build stage of an LSx engine for the plane in my sig. I agree that if done properly, you can come out ahead with a much better engine. But, do not ignore the problems in converting what was built for a car for plane use. To do so invites perils...
     
  13. Aug 22, 2008 #13

    orion

    orion

    orion

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    This seems to be one of those situations where everyone follows the same lead and assumes it must be the only/best way.....

    There is one other aspect to this observation: When decades of development in connection with any technological aspect lead to product lines in a particular form, it can usually be concluded that that form is being used over and over again simply because it works, and usually, works well. This is not arbitrary or simply following the herd, usually there's much more to it.

    The idea of automotive-based direct drive for aircraft has its roots going back to the late 50's and early 60's. In those days the developers did not have advanced tools for the design so a few went the trial and error route, investing their time and money toward developing an "affordable and simple" solution to the aircraft power-plant. To the best of my knowledge, all failed. I recall one in particular in the mid 70's in Northern California - the gentleman was working with a RPO GM 350 and a fixed pitch McCauley (don't recall the size). The prop mounting was on a shaft that extended from a lightened flywheel, past the end of the bell housing, to a standard prop flange. The shat was supported on external dual row ball bearings (in a separate body within the bell housing), but was rigidly mounted to the crank (this was the aft shaft support also).

    To make the long story short, the assembly failed during the ground tests - the shaft sheared off the crank just aft of the flywheel.

    The second set of test then used an aftermarket drop forged 4340 crank and interestingly enough, the failure was nearly as quick except that this time the failure was just inside the engine between the bearing surface and the first eccentric.

    The failure was determind to be a result of slight bending loads imposed on the crank end caused by the prop generated moment transfered trough the supporting outer bearing. I don't know if that program went any further - I lost contact shortly after the second failure.

    As you say, it depends on what you are trying to achieve. I would like to achieve 250 hp at 2700 rpms. I would be satisfied if I can attain 210 hp or more. I believe that to be easily attainable. I don't see the need to produce
    400 hp because it will be unusable most of the time (in a 4 seat high wing with 160 mph max speed 2500 lb gross)

    True and it probably would not be advisable to try for that 400 hp anyway, not for any length of time. I think my comment was in response to an earlier statement where you indicated a need for 160 hp, at which point I think there would be better solutions than using 450 pounds of engine for that low level of power. But yes, I do understand that sometimes it is reasonable to trade cost for efficiency (in this case I mean weight per horsepower), especially in this arena where the industry standards cost about as much houses used to.

    The reason I want to use something other than a Lyc is the high cost of parts and maintenance,thermal shock concerns, rusty cam problems,and disbelief that all those log books for used engines are accurate.

    I can certainly relate here - I just had to do a major due to a cam and lifters that looked something like the surface of the moon. The log books, although relatively accurate, were not able to clearly indicate that the airplane sat for several years, getting less than 10 hours per year of flight time. Talk about sticker shock!

    I'm not sure what you mean by "normal operating range" and "some level of efficiency" but just because an engine is capable of operating at a higher rpm level doesn't mean it should be,

    In this case I'm referring to operating ranges that would allow you to use relatively conventional props. No sense in doing all this work and then having to spend through the nose getting a custom prop made. Furthermore, the efficiency of engines is based on temperature differentials (temperature of the working fluid - air). The highest efficiency is based on the highest level of differential between the incoming air and combusted mixture. The further you operate the engine from the "ideal" range, the less efficient the engine becomes. The result is that your fuel consumption may not be as good as you might think since on a unit basis (fuel flow per unit of power - specific fuel consumption), your sfc throttled back will be higher than at full throttle - it is not necessarily linear with rpm.

    My S10 with a 4.3 V6 turns about 1800 rpm when I am driving 65 mph. It virtually never operates at 4000 rpm for other than a momentary burst into highway traffic. So to me operating at 2200 wouldn't be much different as a normal operating range.

    Unfortunately, comparisons to automotive consumption and power levels is generally meaningless - flight requirements are unique, if for no other reason than the fact that in the air, even throttled back, you will still need to be generating substantially more power then what the car needs, even in a high speed freeway cruise.

    An engine has only so many cycles in its lifetime before it has to be overhauled. If an engine has a 2000 hr TBO and runs at an average of 2500 rpms, it will complete 300,000,000 revolutions.At 4000 rpm it will only take the engine 1250 hours to comple that many revolutions....so the lifespan of the engine has been effectively shortened even though it has completed the same number of revolutions.

    The life of an engine and its internal components is not determined by rpm, especially considering that high rpms actually result in less wear than what the parts see at low rpms. This is addressed by two phenomena: 1) Lubrication is a function of surface speed. The lubricating film works through a protective layer that is generated as a function of shearing forces on the fluid, created by the relative motion of the rotating and stationary components. The faster the relative motion, the more stable and functional the lubricating film is, thus minimizing any issues of wear. 2) The higher the relative speed of two surfaces the lower will be the kinetic friction factor. And of course, the lower the friction, the lower the amount of wear. This is why when most engines start up, they immediately go to a relatively high rpm. After sitting, most of the lubricating oil is gone from many of the internal surfaces. As such, the high rpm after the engine starts creates relatively high surface speeds and thus, low amounts of friction. After a few seconds the rpm drops to a more normal idle but by that time the oil is already circulating.

    Also, the stresses placed upon the crankshaft,con rods, bearings, pistons, has more than doubled. Couple this with higher operating temps within the cylinder and their possible effect on the exhaust valve and spark plug and you have lessened your safety factor

    True, more power creates higher internal stresses (due to rpm, pressures of combustion, centripetal acceleration of rotating components, etc.) but in most cases the engines are designed to handle these loads but admittedly, within limits. Pushing the engine beyond those limits will shorten the life so applications like racing will often see the engines inspected and often rebuilt in relatively short cycles. That's why virtually all engines leaving the manufacturer have a duty cycle rating, although the consumer rarely sees this data.

    Yes, I agree that other items can often be shifted to compensate for the added weight in relation to your Center of Gravity....but it is still weight that can't be compensated for in the overall weight of the airplane.Weight is weight.......

    True, and here it depends on how you're approaching your airplane. If you're building an existing design then yes, it is engineered for a particular weight so installing additional mass will result in a lower payload and the need for a distribution that addresses the added mass up front.

    If however, you're doing a new custom design, then you have the flexibility to design it for whatever you need so if it needs a bit more weight because you're after certain amount of performance, you can take that into account up front and deal with it with little penalty.

    I think the term 75% power is kind of arbitrary.

    No. These ratings and published numbers are very specific since they relate directly to the aircraft's capabilities. Designing airplanes with arbitrary numbers would make absolutely no sense. Providing these numbers arbitrarily to aircraft owners would make even less since a misinterpretation could be quite fatal. When reading off of the published airframe or engine spec manuals you can pretty much depend on the rating.

    You are correct that there are other ways, but what I'm looking for is simplicity and reliability...not complexity and additional weight. But it is a fact that those are other ways to do it.

    Yes, simplicity is a good thing in airplanes and a very reasonable trade-off. It's one reason that I'm looking to follow a similar path, if I ever get the time.

    Every propeller powered airplane deals with these factors. Do you have any hard evidence that shows that the engines will not perform satisfactorily?
    If not, then it is an opinion....just like mine. If the crankshafts were totally unsuited to this, then virtually every one of them would fail. Since there are examples out there flying successfully I must assume (don't say it) that they will work if done properly.

    True, it is an opinion but it is one based on experience, both practical and theoretical. As such, I'd be willing to put it up against most. Just FYI, many years ago I started work as a mechanic in a rebuild shop for exotics and high performance applications (I specialized in engines), including racing. Later I was a machinist for Boeing and then went back for a degree in Mechanical Engineering and Aeronautics. That was followed up by work in aerospace (configurator and structural designer) and as a sideline, about a ten year involvement in the SAE (Society of Automotive Engineers).

    The state of the art in automotive design and manufacturing depends uniquely on a particular set of conditions that are vastly different when compared to those required for flight. Trying to adapt automotive engines to aircraft does work but it is of paramount importance that the engines operate in the same manner as they do on the ground and the first and foremost consideration of that requirement is simply that the internal components (namely the crank and its bearings) be isolated from all the flight loads generated by the prop.

    If both crankshafts are made from the same composition of metal and the automotive one is thicker, it would seem that it can handle the same loading even if an engineer didn't say so..

    Both may be made from similar base materials but the manufacturing is different. The airplane engine crank is not only made for strength but also for toughness, a feature that the automotive crank does not need to as great a degree since it does not see loads other than simple torsion. Furthermore, the aircraft component is made under much higher quality control levels, including everything from how the metal is formed to detail inspections after each and every process along the way. The inspections do not depend on a statistical process - each and every part goes through a rigorous inspection procedure. Automotive products however use statistics where only one part out of twenty or a hundred get inspected, so the chance of something less than ideal slipping through is much higher than with the aviation counterpart.

    Regarding whether you believe engineering data or not, that's at your own peril. No, we don't know everything and can't predict every iota but ignoring basic engineering concerns just because it "looks or feels" stronger is the ultimate combination of ignorance and arrogance, a combination that at times leads to a substantially shortened life. Keep in mind that the engineer's ultimate duty in this arena is simply to keep you alive. Furthermore, given that in over fifty years of these types of development there has not been any significant successful applications of a prop being directly bolted to a automotive crank (I can't think of one anyway) should be an indication that there might be something wrong with your assumptions.

    As far as the flight loads go, I would think that all the torture engines go through in off-road racing and airboat racing would demonstrate their ruggedness.

    Most racing teams go through in-depth inspections and/or rebuilds after nearly every race. Furthermore, the way the engines are mounted and operate, even in off road racing, the loads are not what you're going to encounter in flight.

    I don't know why they put it in the middle

    It's in the middle because the motion due to expansion is smaller when measured from the middle to the end than it would be if you tried to absorb the motion over the entire length of the block. This allows the engine to be built to tighter tolerances, which generally result in better service and improved life.

    Lycoming doesn't isolate prop loads from the engine...........

    They don't have to - their engines are specifically designed for the loads. Car engines are not.

    And you know this for a fact..........how?

    Over twenty five years of structural engineering experience and quite a few in automotive, both from the practical and from the theoretical sides.

    Do you know what the differences in manufacturing are? I think that you are making an assumption without intimate knowledge of the available products.

    As I indicated, I know the products quite well. True, I don't have hands-on experience in actually fabricating an aircraft crank so I don't have the intimate knowledge of every iota of the process, but I know enough to state my concerns with conviction and experience to back it up.

    What manufacturing step makes a crankshaft resist torsional twisting?

    As indicated before, axial torsional twisting is not the issue here. It is a combination of thrust loads several orders of magnitude greater that what the automotive components were designed for, of gyroscopic loads (generated when you combine the rotation of the prop with rotation of the airplane along a perpendicular axis) capable of generating a moment that wants to peel the prop off the flange in the hundreds of foot pounds, and of shear loads encountered as a result of accelerations generated in flight maneuvering and when flying through turbulence.

    Can you make a blanket statement that all crankshafts produced by aftermarket manufacturers are unworthy of consideration?

    Pretty much, yes. Although high performance after market products are often substantially superior to the mass produced units, they are still designed for the conditions of the road, not flight. As such, at best their use would still be highly suspect.

    So the crankshafts and metallurgy of Lycoming crankshafts designed and produced 60 years ago are better than what any automotive crank maker can do today.............. I don't agree at all.

    Since aircraft engines get periodic rebuilds, the internal components are generally updated as time goes on. Given the stricter requirements of liability and certification, the engine companies have been updating their own manufacturing processes as new technologies become available. Very few engines today are flying with the old components.

    When an engine destroys itself harmonically its because a vibration has been allowed to reach a resonance that built until it became catastrophic. At least thats my understanding. A dampener continually absorbs harmonic vibration and prevents it from building.

    Yes, you got it but keep in mind that these vibrations are only those that occur within the engine due to the engine's own vibratory response to the internal cycles. These have nothing to do with anything you bolt on to the outside.
     
  14. Aug 25, 2008 #14
    Reply to midnite toy


    Quote:
    I'm not sure what you mean by "normal operating range" and "some level of efficiency" but just because an engine is capable of operating at a higher rpm level doesn't mean it should be, or that it is inefficient when operated at a less demanding rpm.My S10 with a 4.3 V6 turns about 1800 rpm when I am driving 65 mph. It virtually never operates at 4000 rpm for other than a momentary burst into highway traffic. So to me operating at 2200 wouldn't be much different as a normal operating range.
    To produce horsepower requires burning a specific amount of fuel. If you run an engine at a higher rpm range and produce more horsepower you will burn more fuel. My son had an LT1 Camaro/6 speed. In 6th gear (2 overdrives) it would go about 70/75 mph at 1500 rpm and get high 20s mpg (27/28).

    An engine is most efficient at Peak Torque. Any time you run it at any other RPM, your efficiency goes down. You very well might get better GPH's of flow due to the lower RPM's, but the BSFC (Hp per gallon burned) goes down.

    Equating 'highway rpm's' in car use to RPM's in plane use is not accurate. That Camaro, in 6th @ 70mph is only producing about 30-40 hp. Not the 100hp or so you would need to maintain the same speed in a plane.

    Reply: Yes, any engine is most efficient at peak torque but no one runs their engine at only peak torque. The point is that as you increase the rpm of an engine you will increase horsepower.If you increase horsepower you will burn more fuel because it takes an increase in fuel to create that horsepower.
    If you are flying at a speed that does not require more horsepower, then why burn more fuel to generate power you are not using or are wasting.

    As for the comparison to my son's car and my truck...my point there was about "normal" operating ranges of automotive engines. No where in normal driving does the average driver run his engine at 4,000 rpms for extended periods of time. The engines usually operate in a range below 2700 rpms, so that is what I would consider normal.

    Also, if you check out the graph below you will see that a Lyc never reaches peak torque in its operating range.......






    Quote:
    I think the term "75% power is kind of arbitrary. RPM wise you may reduce your rpm from 2700 to 2200, but the horsepower being produced is not exactly linear. As rpm increases hp climbs more radically than at lower rpms.
    So I think when you cut back to 75% you are referring to rpms not HP.

    75% power is exactly that - 75% of your max HP, not RPM. The RPM at which that 75% power is depends totally on your torque curve. If you have a 'peaky' torque curve that lays flat till 2000 RPM, then suddenly rises, your HP curve will do the same thing. If, on the other hand, you have a torque curve that rises gradually, peaks, the lowers (like a bell curve) then that is what your HP curve will do, only narrower. A flat torque curve produces a HP curve that rises linearly with RPM's.


    Reply: That description doesn't remind me of any graph I've ever seen showing HP and Torque representation.
    The best torque curve is usually the flatest one you can get. HP starts out much lower than torque and rises much faster since torque is already higher. As they progress across the graph the horsepower will cross paths with torque. Torque will begin to fall off and HP will continue to rise. I can only imagine that something like a peaky torque curve might exist in a fuel dragster or formula 1 vehicle, but most torque curves are reasonably flat with maybe a slight rise as they progress...





    Quote:
    If I'm correct in that assumption, cutting back a 180 hp Lycoming to 75%
    would not mean you are operating at 135hp, but at something less than that.

    75% power for a 180hp Lyc is 135hp.

    Reply: Thats what I said, 75% of 180 HP is 135 HP, but when you throttle back to 2250 RPMs for cruising, you are below 135 HP. I have a graph of a test run by Lycoming to verify the output of some aftermarket exhausts. As a baseline, they tested the factory exhaust. The test engine produced 185HP
    /370 ft lbs @ 2650 rpms (Lyc AEIO360). 135 HP was at appx 2450 rpms
    and at 2250 rpms the power out put was appx 110HP. Remember, this test was conducted by Lycoming. Remember to check out the fact that a Lyc never reaches its torque peak while in its operating range....

    E:\Engines\Dyno Lycoming\aircraft exhaust systems.htm


    Quote:
    The case of an LS1/LS7 is much stronger than previous Chevy alum blocks and has cross bolted mains. The LS7 has steel main caps while the others have powdered metal. To my knowledge no one has broken any engine cases but I'm not going to say its impossible....but not probable. As far as the flight loads go, I would think that all the torture engines go through in offroad racing and airboat racing would demonstrate their ruggedness.
    He's saying that there are NO gyroscopic loads or significant weight on the bellhousing-to-block mating surface/bolts in an auto situation. In cars/trucks, the end of the transmission is held in place at the tail shaft. This removes cantilevered loads from the bellhousing, and limits the amount of 'twist' the mating surface sees. In fact, in off road use, the rubber mounts are replaced with solid ones - as are the engine mounts - precisely because they break, which allows the tranny to twist, which breaks bellhousings and blocks.

    Reply:I'm not exactly sure what this statement means. What I attempted to say was that I know of no automotive engine being used in an airplane that had the block break as the result of gyroscopic forces. If a crank breaks due to gyroscopic forces, it may then break the block...even a Lycoming.
    In a conventional smallblock Chevy engine there are two bolts retaining the rear main bearing, and 2 or 4 retaining the rest of the mains. In an LS1 you have six bolts retaining each main bearing.Also the engine case is extended so that it supports the main bearings on each side, and the oil pan is also a structural member providing additional strength. A bellhousing or machined plate or even a redrive will bolt to the block and the oil pan and you can even use holes in the rear of the head for strength and support.







    Quote:
    Every propeller powered airplane deals with these factors. Do you have any hard evidence that shows that the engines will not perform satisfactorily?
    A search of the net, mags, groups, etc, will find many examples. You wont find LS7's, simply 'cuase they are new.. [​IMG]

    Reply:You will also find examples of Lycoming and Continental engines which have failed. You can read about case fretting, exhaust valve problems,cylinder cracking, and even crankshaft cracking. How often have you seen the comment that a crank had a prop strike but still dials zero on the indicator. This really doesn't tell you that the crank is OK. Due to the high cost of airplane engine crankshafts, you can bet that many a crank has been reused when it should be replaced. Lycoming and Continental have a myriad of things that go wrong with them, and when you put them all together there are a lot of things that can make them fail. So far all I hear about automotive engines is that the crank won't work. I'm not convinced that this is true if you research and then buy a quality crank.
    Quote:
    If both crankshafts are made from the same composition of metal and the automotive one is thicker, it would seem that it can handle the same loading even if an engineer didn't say so........
    However, they are not the same. Even so, your ignoring the torsional
    feedback from the prop - totally different than in a car.

    Reply: Are Continental and Lycoming crankshafts made from exactly the same materials using exactly the same process? Apparently there is more than one process and composition that will work. When Continental went to the VAR process to manufacture cranks, they changed from a different process. Many of those old cranks are still flying...so more than one process and composition will work. I don't see how people feel they can make blanket statements on the reliability of every crank out there today. The processes some of these specialty crank manufacturers use today is "state of the art".


    Quote:
    I don't know why they put it in the middle, but most thrust bearing failures in automobiles are caused by ballooning of the torque converter which forces the crank into the thrust bearing further than its mechanical limit.
    Um, the same type of forces a direct drive prop would do? [​IMG] The reason for the failure is it wasn't designed for it - not strong enough nor wide enough to carry the loads.

    Reply: Nope, I disagree. The reason most automotive thrust bearings fail is because they have a small freeplay area engineered into them and when an attached component fails (torque converter) it forces the crankshaft forward farther than the mechanical limit that its engineered for. It pushes against the transmission (which you explained was ridigidly attached to the engine)
    and since the transmission can't move,it pushes the crank forward further than its mechanically designed limit. A propellor is only pushing or pulling against air, so that is a different situation. Also, the fact that a Lycoming is pulling against an aluminum surface (crankcase face) with no bearing makes me wonder just how much thrust is actually applied.


    Quote:
    Lycoming doesn't isolate prop loads from the engine...........
    Because its designed for them. [​IMG]

    Reply: Yes, they are designed for them. It doesn't mean that nothing else will work. If you subscribe to Contact Magazine check out what NASA has to say about the subject.Issue 69 page 4. They mention that the thrust bearing is somewhat more beefy but don't call it a catastrophic problem. They also say that they don't believe a redrive is necessary or even desirable...and in their opinion a direct drive is preferrable. I can't imagine them saying this if the crankshaft was a definite deal breaker. They even reference the LS1 as an example.





    Quote:
    A dampner continually absorbs harmonic vibration and prevents it from building.
    To a point, then it will fail and damage will occur. However, your ignoring the massive increase in torsionals created by the prop as compared to even a clutch/tranny system in car. Take a look at large truck/diesel dampeners, clutches, and converters, you'll see a massive increase in the amount of torsional control that needs to be provided.

    Reply: I would think that a semi would have extreme cyclic loadings due to the large engines and huge loads they move. I don't think thats a fair comparison.




    Don't get me wrong here, I am currently in the design/build stage of an LSx engine for the plane in my sig. I agree that if done properly, you can come out ahead with a much better engine. But, do not ignore the problems in converting what was built for a car for plane use. To do so invites perils...
    __________________
    Jim
    Reply: OK Jim we obviously have different points of view here, but I encourage anyone to give it a shot instead of listening to why things can't work. I'm sure Orville and Wilbur heard the same things. Please don't interpret my steadfastness as a lack of concern for the perils involved, but I just think it can be done in a manner other than what the popular belief is....
     
  15. Aug 26, 2008 #15
    Reply: All engines have cyclic vibrations due to the natural combustion process and varying cylinder pressures. What needs to be done is to prevent the component from reacing a point of reasonance.If you can provide dampening which prevents resonance inside the engine you have at least duplicated what Lycoming does..if not exceeded it. Then you have the same propellor issues to deal with that Lycoming has....so, it becomes an issue of whether your design will survive similar forces.
     
  16. Aug 26, 2008 #16

    PTAirco

    PTAirco

    PTAirco

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    Reply:Huh? So if my engine is running at 2200 rpm and meeting the needs of the moment, it will make a difference in whether its pulling an airplane or a truck?

    Strictly speaking, it does: The analogy would be that the engine in an airplane , is subjected to the same kind of loading as pulling a truck up a steady incline, constantly.

    It is not simply the RPM that matters, it is the BMEP developed. You can be be turning the engine at 2200 in neutral, 2200 going up a steep hill or 2200 going downhill. It's clear that it won't be subject to the same strain under all three conditions, even if the RPM's are the same.

    A good reason to set up the engine to be a "towing" engine as far as cams and valves are concerned.
     
  17. Aug 26, 2008 #17
    Yes I agree that setting up the engine for lower rpm power is different. Someone previously mentioned that an LS7 might be a good idea. I don't think its the best idea for the very reason you mentioned. The engine has large intake passages and valves and somewhat higher compression so even though its a fantastic engine (and would probably work fine), I have a different way to proceed.

    I like the LS7 block because it has steel main caps unlike the other blocks in the LS series. It also has replacable liners where other LS engines can only be slightly overbored or require boring the liner out of the block. It gives you the ability to have 427 or more cubic inches. If you buy a bare block and build it you can select the crankshaft of your choice and use high quality aftermarket rods. (LS1-6 uses powdered metal rods and main caps...LS7 uses Titanium $$$$) You can select the cam of your choice to improve the lower rpm power/torque (as you referenced). The factory LS7 uses a dry sump oiling system but I would go with a conventional oiling setup. Also, I think I would use readily available LS1 heads as they flow well and have smaller passages and valves than an LS7. That should keep costs down and the smaller passages should keep velocity up when a 427 is drawing air thru them.(I bought a used low mile set with valves and rockers for $120 off
    ebay) By building the engine from scratch I can use forged pistons and set the compression where I want it.(Note there are also some cheap truck heads which flow extremely well right from the factory.)
    I have an article from Hot Rod Dec 2003 where they built an engine for low end torque.They used a Rocket block version of a smallblock Chevy and built it to 450 cu in. Using a very mild cam (Comp Cams XE270HR) they built an engine with a 9.3 compression ratio that runs on 87 octane gas.
    It produced ....500 ft/lbs of torque from 2000 thru 5000 rpms. Impresive when you consider that many people believe that torque...not Horsepower moves the airplane. At any rate, there was plenty of HP to go around also.

    190hp @ 2000 RPM 247 hp @ 2500 RPM 267hp @ 2700 rpm

    Consider that it stacks up well against an O540, but I'm wanting it to weigh less and compete against an O360. An LS engine will have 15 degree heads instead of the 23 degree used on a conventional smallblock, so it may produce even more HP/Torque. (Note LS7 heads are 12 degrees)

    So I agree wholeheartedly that you build the engine to provide power where you need it.

    The anology about going up hills, down hills , or running 2200 rpm in neutral.
    Yes, the BMEP will be different in each of these situations at 2200 rpm, but it will also do the same thing when rising during takeoff, descending during landing, or idling on the taxiway. So the engine doesn't know if its in an airplane or a truck, it only knows its turning 2200 rpm and either has a load or not.
     
  18. Aug 26, 2008 #18

    Midniteoyl

    Midniteoyl

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    As a side.. the LS9 block will be available as a replacement for ALL LS series engines in 2009. The LS9 block is about 20% stronger with less voids and stress risers, and able to handle larger bore sizes.

    ekimneirbo: its funny, really.. You have all the same arguments I had when first undertaking this project. Experience has taught me that not all is so simple...
     
  19. Aug 28, 2008 #19

    plncraze

    plncraze

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    As I was following this thread I remembered reading about Steve Wittman's V-8 conversion for his Tailwind, Chris Beachner's V-8 Special and Ron Vanderhart's V-8 conversion in his Stits Playmate. All these conversions had some things in common:

    All three isolated the engine from the prop, either by using a bellhousing on the engine with bearings to support the prop or with a reduction drive

    All kept their horsepower expectations low and regarded the published performance figures provided from the manufacturer with skepticism due to the engine's new operating application

    All used a eight cylinder engine (Olds/Buick/Rover aluminum block)

    Vanderhart had some funny stories about flogging a four cylinder Ford Escort engine around the pattern firewalled because it would not stay in the air otherwise and moving up to a Chevy V-6 before he finally put in a V-8 and figured that he was getting approx. 135 hp from the V-8. He made a point of saying that he was not getting the figures quoted in car magazines for this engine.
    For some reason it seems that car engines do not give the horsepower in an airplane that performance specs suggests they should.
     
  20. Aug 28, 2008 #20
    There has been much skepticism over the years about automotive HP ratings
    Back in the 50s car makers used to say "wins on Sunday sells on Monday".
    Ford started over rating their HP while Chevy began under rating theirs. Since cars were assigned to a racing class by advertised HP, guess who won.

    Eventually a new standard way for calculating HP was put into effect and the advertised HP went down and became more authentic. No matter how you look at it, an engine is an air pump and the more air and fuel you can get into it, the greater power you may produce.

    I have heard different rationales about why a Lyc will outproduce an automotive engine...and there are some things that have a major effect on the power produced by a given engine. When you look at a Lyc, it has huge pistons. Some people equate that as a major reason that automotive engines can't compete. Another myth in engines is that an engine with a longer stroke will produce more torque than an engine with the same cubic inches that has a shorter stroke.

    There are a lot of pros and cons that affect every choice. My feeling is that all aircraft engines are anchient technology, but they do work reasonably well.They are simple to manufacture,build and maintain.

    Personally, I find it difficult to believe that with all the improvements and refinements made in the last 60+ years that an automotive engine cannot match the power output of an airplane engine. I think many automotive engines are poor choices for various reasons, but if you select wisely you can find a few that deliver what you need. Even Model T engines were once used to power airplanes.

    Just think about the design of these engines. Huge loose fitting pistons that pump oil like a sieve,and hard to start when hot. Inadvertantly shock cool one and your compression and your bank account will both go down...drastically. Flood one, and it just ain't goning to start. Engine castings are crude by todays standards. If you only fly your Lyc once a month or less in the winter your cam will rust and destroy other internal parts.Cylinders crack,cases fret, and magnetos get ADs relegating them to the scrap pile. Continental had a program in cooperation with Honda to produce water cooled engines, but I guess liabilities must have ended that.
    Yes its old tech but if properly maintained($$$), they are pretty reliable.
    On the other hand, they get annual inspections and frequent replacement of expensive parts such as cylinders in order to maintain reliability. Automobile engines with minimal (oil changes and 1 tune up) routinely go 150K or more.
    So which is actually more reliable today?



    I had one of the all aluminum Buick 215 V8 engines and put it in a Luv pickup truck many years ago. It was a nice little engine. The high performance cars of today are equaling and exceeding the outputs of much larger high performance engines of yesteryear. Muscle cars such as Camaro and Chevelle and even Corvette had heavy BIG BLOCK engines with 427 cu in. Today you can get a 427 in a SMALLBLOCK . It will weigh appx 150lbs less and make more HP than the old engines. Thats why they deserve a new look for being viable airplane alternatives.

    Its really difficult to know what to believe, what is fact and what is fiction.
    All you can really do is investigate what you are told and see if you can find a true basis for it. Then decide what what you believe and go with it.Most people want to be helpful, but there is a lot more fiction than fact in much of it.
     

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