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Thread: LS1 Engine for aircraft?

  1. #31
    Registered User Dan Thomas's Avatar
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    Re: LS1 Engine for aircraft?

    The damper on an auto crank is to stop the "ringing" of the crank set up by torsion loads applied by the con rods as the various cylinders fire. At harmonic RPM the rwisting can accelerate to the point that the crank twists apart; the vibratory loads are much higher than the engine's torque output. Vibration analysis is a huge and complex field all to itself, and engineers have earned doctorates studying it.
    An aircraft engine's internal counterweights are mounted rather loosely on the crnk and are to absorb and later reinsert the torque pulses. Not the same thing at all as the rubber-mounted damper pulley ring found on your car.
    Steve Wittman adapted an aluminum Buick V-8 to his Tailwind, inverted direct-drive. He used the bell housing to support a bearing and shaft assembly to isolate thrust and gyroscopic loads from the crank. However, this is not as simple as it sounds; the crank needs a flywheel of some sort, and if the propeller is it, then that shaft has to take severe forward-reverse torque loads from the crank and damp them out. Every time a cylinder fires there's a forward lurch; every time there's a compression load there's a reverse braking. The flywheel absorbs and returns those, and if those loads have to pass through a shaft, that shaft had better be REALLY stout. If we use a flywheel on the engine, then the shaft to the prop, the prop and flywheel have different ideas about damping and they get into an argument at certain RPMs and place huge loads on that shaft, which usually gives up and separates.
    The PSRU has to deal with those loads. The old V-belts used years ago would slip and release the worst of the overloading. Toothed timing belts will get their teeth torn off if the designer doesn't get it right, and the PSRU we had on the Glastar's Soob told us that 1400 engine RPM was something to avoid. Spur gears suffer the worst, since only one tooth, maximum of two, is taking the load much of the time. Planetaries are much stronger and much heavier. Geschwender used the Morris Hy-Vo self-tensioning chain to good effect and those engines (Ford 351s) saw service in crop sprayers like the Pawnee.
    Steve Wittman, as I heard it, eventually gave up on that Buick and put a Lyc in the airplane. Too much hassle, not the least of which is draining the oil out of the case and back to the tank without getting excessive oil bleed past the rings after shutdown, which can promptly flood the plugs (no restart, see?) and can cause hydraulic lock. Properly-designed inverted aircraft engines have the cylinder sleeves extending into the case an inch or so to act as oil dams, and also have several scavenge pumps to draw the oil out.

    Dan
    Last edited by Dan Thomas; September 18th, 2008 at 01:57 PM.

  2. #32
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    Re: LS1 Engine for aircraft?

    Well written Dan. I virtually agree with everything you said, but like always there are some things I see slightly differently. I like your explanation of how the harmonic resonance can tear the engine apart and that there is a difference between the weights used in aircraft engines and bolt on dampners. Am I correct in assuming that these counterweights only target a specific order of resonance? In other words if you have a 5th order counterweight, it will have no effect on other resonant orders? On the other hand my understanding of a bolt on harmonic dampner is that it contains a fluid or solid that absorbs vibrations occurring in any range. Hartzell is now marketing propellers which have harmonic dampners which are following the absorbtion type of dampening train of thought.
    So I guess my question is, if something has the ability to absorb vibration and prevent harmonics in all ranges, isn't that preferable to something that only works in one resonant range? (Didn't Continental or Lycoming chage the counterweight dampners to a different order after years of being at another order?) I'd really like to see your ideas on this thought, as I only have an opinion and am trying to reconcile this in my mind.

    Second, your explanation of what the direct drive shaft is dealing with was well done also. My thought is that whatever the propellor is attached to...that thing will be addressing all the same problems that the front end of the LYC is dealing with. The front end of the Lyc crank is basically an extension shaft to attach the propellor. So, if the extension shaft has the equivalent metalurgy or better, and simalar or greater strength to the front of the Lyc, and sufficient bearing support.....what is it being subjected to that the Lyc output shaft isn't dealing with? Why should it be subject to failure any more than the reliable Lycoming?

    Third, Steve Whitman was a pioneer who I feel we all owe our gratitude to.
    I personally have never felt that inverting an engine was a good thing, but its been done...sucessfully. I just always felt that rings weren't designed to prevent oil seepage when sitting for long periods, and then there is the exhaust valve thing. How does it get sufficient oiling when the oil settles
    into the valve cover instead of on the valve stem? Also, I wonder about condensation settling inside the distributor cap.

    Anyway, I appreciate what you wrote but I still have unresolved issues/thoughts on the subjects above.
    My reference to dampners that cover a wide range of vibration absorbtion means something on the order of a Fluidamper or Rattler...not an OEM which covers only one or a narrow band of vibration.

    (My understanding of resonance is that "order" means an event that occurs in each revolution and the number of times it occurs ....a 5th order would therefore occur 5 times in one revolution?????)
    Last edited by ekimneirbo; September 18th, 2008 at 08:20 PM.

  3. #33
    Registered User Dan Thomas's Avatar
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    Re: LS1 Engine for aircraft?

    I'm no expert on vibration, but these guys try to make the crankshaft pendulum counterweight idea understandable:
    http://www.sacskyranch.com/power_limitation.htm

    As for the orders:
    http://www.vibratesoftware.com/html_...ed_Related.htm

    The nose of a Lyc's crank is pretty heavy and is part of the whole forging. A shaft attached to the crank will have attachment points, changes in cross-section, and other features that represent points where stress accumulates and failure may occur if one of those points can't take it. If the shaft is too flexible, it may fracture or heat to the point that it loses strength. In systems that use longer extension shafts, some sort of clutch may be employed to dissipate those stresses.

    Don't get me wrong. Auto conversions can be workable, and many have flown. But many more have been a disappointment and their limitations often cause the builder to abandon the project. The best thing, as far as as I can see after reading and observing for a long time, is to use some sort of PSRU to do three things: (A) It allows the engine to generate power at RPMs that it was designed to do it at. Just remember that the manufacturer's redline is not the same idea as Lycoming's redline; the auto can be run to that point occasionally but consistent operation at that speed will shorten its life, maybe catastrophically. Lycoming certifies their engines to operate as long as you want at redline unless there's something like a 5-minute takeoff power limitation, as some engines have, but even then the max continuous rating is very high. At any rate, the geared or belted engine can generate much more power for a little more weight. (B) The PSRU get the thrust line up where it should be, if it's a spur gear or belt. (C)The PSRU removes the prop's thrust and gyroscopic loads from the crank. The PSRU should be designed to remove radial loads, too; a belt or spur gear will place radial (sideways) loads on the crank end and the main bearing will fail, so most PSRUs incorporate a bearing to support the driving pulley and to take the belt's tension loads.

    Dan

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    Re: LS1 Engine for aircraft?

    The thing I don't understand is, why everybody keeps comparing auto conversions to lycomings. It is like comparing apples to oranges. If you want a fair compairison why not compair it to a Merlin.

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    Re: LS1 Engine for aircraft?

    Quote Originally Posted by CJ#3 View Post
    The thing I don't understand is, why everybody keeps comparing auto conversions to lycomings. It is like comparing apples to oranges. If you want a fair compairison why not compair it to a Merlin.
    Because Lycomings (and Continentals) are the only things available for aircraft in a similar power range to those that the auto conversions are aimed at. To be generally successful, the conversion would have to offer at least comparable performance and reliability, and do so at a cost advantage that makes the development effort worthwhile. As has been said, there are special cases, such as WWII replicas, where the shape of a flat opposed air cooled engine just doesn't work well at all and thus the auto conversion has a significant advantage even if it is more work and just as expensive.

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    Re: LS1 Engine for aircraft?

    What I ment was comparing a liquid cooled V engine to an air cooled flat engine as far as viability as an aircraft engine. The general architecture is similer to a Merlin, not to the perfrmance, size, or complexity.

  7. #37
    Registered User djschwartz's Avatar
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    Re: LS1 Engine for aircraft?

    Quote Originally Posted by CJ#3 View Post
    What I ment was comparing a liquid cooled V engine to an air cooled flat engine as far as viability as an aircraft engine. The general architecture is similer to a Merlin, not to the perfrmance, size, or complexity.

    In my opinion, the viability is in the overall design of the powerplant system, of which air vs. water cooling, and opposed vs. V configuration are only small parts. The bigger issues revolve around what type of service the powerplant is designed for:

    * continuous output at moderate to high power vs. efficient operation over a very wide range from short bursts of very high power to long operation a very low power

    * tradeoffs between power-to-weight, life expectancy, noise and vibration levels, fuel efficiency, and manufacturing cost.

    * type of mechanical system the powerplant is designed to deliver power to: car transmission vs aircraft propellor.

    Sure, it's possible that very similar engine cores may be adaptable to both applications and maybe even some parts used directly in both. But there will be a lot of differences as well. While the Lycs and Continentals may be different from auto engines in configuration, they are the engines that have been designed for the aircraft application. Automotive engines, by definition, have been designed and optimized for that application. It is certainly possible to utilize automotive parts in an aircraft powerplant; but, as the old saying goes, the devil's in the details.

    As just one example of the many design tradeoffs that one might face: sticking a 10 lb torsional damper on the crankshaft of an engine to solve a resonance problem may be a perfectly acceptable solution for automotive applications where weight isn't that critical. Especially if the resonance occurs at an RPM that the vehicle will see only occasionally so the damper doesn't need to be that good. For an aircraft application weight is much more of an issue and it might be worth the effort and cost to re-design the crankshaft.

  8. #38
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    Re: LS1 Engine for aircraft?

    Aircraft engines and automotive engines are very different. I have worked on plenty of both. Aircraft engines were designed very weight conscious. I have been amazed by how thin the material of the rotating assembly is. The reason a Lycoming has the rolling counter weights is to smooth out the power pulses. An IO-540 is only a 6 cylinder. Where an automotive engine is not designed with weight as one of the primary focuses. But, not all auto engines are the same. I will expand more on this at my next break.

  9. #39
    Super Moderator Midniteoyl's Avatar
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    Re: LS1 Engine for aircraft?

    [QUOTEWhat I ment was comparing a liquid cooled V engine to an air cooled flat engine ][/QUOTE]

    So lets compare it to a Briggs & Stratton...?
    Jim

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  10. #40
    Registered User PTAirco's Avatar
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    Re: LS1 Engine for aircraft?

    On the topic of LS 1 and 2 engines, these guys are working on a STC for theirs:

    Quiet Aviation - Programs - Quiet Technology [QT] Powerplant

    They quote a cost of less than $20,000 for the whole setup, including ground adjustable prop! For the cost of Rotax 914 , you get almost 400 hp. I'm sure this price will creep up quickly if they ever get into production, but it's a bargain if you can lay your hands on that kind of change.
    "Aeronautical engineering is highly educated guessing, worked out to five decimal places. Fred Lindsley, Airspeed."

  11. #41
    Registered User Dan Thomas's Avatar
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    Re: LS1 Engine for aircraft?

    Quote Originally Posted by ekimneirbo View Post
    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.
    I've been rereading this thread and realized that there are things not yet mentioned here.

    60 years ago most small opposed aircraft engines were typically in the 65 to 125 hp range, with a few 150 hp models. Most larger engines were radials, with very stout cranks. In the early '50s larger opposed engines began to show up.

    Even at that, though, crank failures were not unknown. An aircraft crankshaft has to be exceptionally strong, and any flaws at all or any errors in metallurgical mix or heat treatment or machining can result in a failure. In the last ten or 12 years there have been numerous Airworthiness Directives against numerous cranks, each one dealing with a somewhat different cause of failure.

    ADs 2000-23-21 and 2000-08-51 deal with certain Continental cranks that were made from improperly mixed metal. Several failed. Owners had to drill out a bit of metal from the flange and send it in for analysis.

    AD 99-19-01 had to do with faulty installation of counterweight bushings. The tool lightly nicked the crank and cracks formed from those nicks. Continental, again.

    AD 97-26-17 had to do with the VAR manufacturing process. Those cranks had to be junked. Continentals.

    AD 98-02-08 was about Lycoming cranks that suffered corrosion pitting in the crank nose. One or two of those broke. Many were found with serious pitting. IIRC, pits more than .010" deep junked the crank.

    AD 2005-19-11 forced the removal of numerous Lycoming cranks from service. This AD resulted from reports of 12 crankshaft failures in Lycoming 360 and 540 series engines rated at 300 HP or lower. Just not strong enough. They were cranks made by contracted firms, I think. AD 2006-16 was a similar problem.

    AD 2006-20-09: This AD resulted from reports of 23 confirmed failures of similar crankshafts in Lycoming Engines 360 and 540 series reciprocating engines. More inadequate metal.

    AD 2002-19-03 2002-17-53 applied to Textron Lycoming LTIO-540 and TIO-540 series engines, rated at 300 horsepower (HP) or higher. That action required replacing certain serial-numbered crankshafts that were hammer forged with crankshafts that were press forged.

    Even the rebuilding of cranks is critical. AD 98-17-11, for instance, refers to crankshafts overhauled by Nelson Balancing Service. They screwed up somehow in the nitriding or heat-treatment process. Cracks were found and a whole lot of cranks had to be junked. A similar AD was issued against cranks overhauled by a California company.

    Here's the point: Aircraft engine crankshafts are very highly loaded and are operating much closer to their limits of strength than automobile cranks. Any deficiencies in a crank can lead to failure real quick. Auto cranks are not designed for high thrust loads, gyroscopic loads or heavy acceleration loads due to the inertia of the prop, and so the manufacturers certainly don't need to pay a lot of attention to detail in order to minimize failure from those factors.

    I tend to be sensitive to crankshaft flaws. I had a crank break in flight some years ago due to some sort of propstrike many years previous. In the smaller Continentals, a propstrike will often cause cracking of the crank through the cheek between the #1 and #2 rod journals, which is at the opposite end of the engine from the propeller. Explain that one. That's where mine broke, too.

    Dan

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    Re: LS1 Engine for aircraft?

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    If anyone is interested in the actual horsepower they are getting when reducing power back to the 2200/2300 rpm range, go to Superior engines and check out their graph for a 360 engine. You will see that at that rpm range you are getting about 110 hp.


    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.


    Reply: Thats really kind of twisting the intent of the statement. 200 HP is small only when you compare it to say 500 HP. Its still a significant amount of power and won't be found in most smaller engines. Actually, I've seen graphs showing that stroked LS blocks can make 250/260 HP at 2700 RPMs. So rather than try to stretch the comparison to the maximum (and rival a O 540) I picked an easily attainable figure and any excess HP would be a bonus. Most people can't use 300-500 hp, so its useless to try to attain that figure (in most instances). You also have to be aware of the fact if you design a reduction drive to utilize high rpmsfor takeoff, when you cruise, you can only reduce the engine rpms to a moderately high range.....not a low rpm because the prop only has a useful range of maybe 600/800 rpm change. Your 5000rpm
    takeoff would become a 3700/4000 rpm cruise. Thats hard on an engine.



    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.


  13. #43
    Super Moderator Midniteoyl's Avatar
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    Re: LS1 Engine for aircraft?

    ekimneirbo ???
    Jim

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    Re: LS1 Engine for aircraft?

    Jim, I saw ekimneirbo??? on your last post. Did you want to contact me?
    I've been involed in some other things and haven't checked until today.
    How is your project coming? mike_obrien@raytheon.com

  15. #45
    Super Moderator Midniteoyl's Avatar
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    Re: LS1 Engine for aircraft?

    Sorry.. I just saw your post and it seems it was just quotes from previous replys... wondering what was up?
    Jim

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