Small block Chevy Ideal Setup

[RJW]

I apologize if the paragraph about the weight of an iron-block SBC was not clear enough to facilitate understanding. Here is the important part again:

The weight of a running on the stand/dyno iron-block SBC WITH AS MANY CHEAP ALUMINUM/AFTER MARKET PARTS AS IS PRACTICAL is very close to 425 pounds.

Yes, an all iron SBC with iron exhaust manifolds, gigantic starter, 40-pound flywheel, huge alternator, and all the other stock parts as pulled from a car weighs about 575 pounds. But nobody would put an engine like this in a cheap weekend street machine let alone an airplane.

It is amazing to me that I have to keep saying how much something weighs. I am building my airplane to use a 425-pound SBC (about a dozen of which I have lying around the shop). Others are free to use the 575-pound version.

I also apologize for the short comment about torque. Feeling a bit testy about the weight thing I guess. It’s a gross oversimplification. Still, the claim is correct but not for the reason I gave. As Hot Wings pointed out it has more to do with piston speed, rod/stroke ratio etc.

The comment about death is only meant to point out that these problems/questions are decidable and understandable. This is the strength of systematic investigation. It has nothing to do with “open mindedness”. In fact being open minded when working with a well thought out system is exactly what you don’t want. Being “open minded” or “thinking outside the box” or allowing differing “opinions” destroys the point of systematic investigation. It is nothing more than incoherence. I own my mistakes. I’m proud of them. I do all I can to weed them out though I sometimes fail. Anybody who doesn’t do this will only succeed in something like airplane design by sheer luck. I won’t have anything to do with that kind of thinking. It is suited to TV ads, politics, religion, etc., not engineering. Again I thank the careful and thoughtful folks here for keeping me on track.

Rob

 

[ekimneirbo]

You're not missing anything.

Torque = force X arm
Displacement = stroke X piston area
Piston area relates directly to force. (assumption)

Displacement A = Stoke A X Piston area A ....................... Torque A = Piston area A X Stroke A
Displacement B = Stoke A/2 X 2 X Piston area A .............. Torque B = Stroke A/2 x Piston area X 2
Displacement A = B
Torque A = Torque B

There are other factors such as flame front velocity/piston velocity (the real reason for dual ignition) and rod to stroke ratio that influence peak torque.

Reply: I agree that there are tuning factors which can affect the ability of a stroker to produce more power at lower rpms, but the mechanical portion of the equation is equal. With a longer stroke, you do have to use a shorter rod if compression heights remain equal, so thats a negative for the long stroke, Also the smaller bore may cause smaller valves to be used or have valve shrouding. The normal thing is that when someone strokes an engine they increase the size/capacity of the engine and due to added mass reduce the ability of the engine to rev. The added capacity then has its most major effect at the lower rpms. Other than a racer trying to find the magic best combination while staying in the confines of the rules set by some racing organization, no one decreases the bore when they add stroke.Hence the feeling that stroking makes a torque engine.

 

[ekimneirbo]

I apologize if the paragraph about the weight of an iron-block SBC was not clear enough to facilitate understanding. Here is the important part again:

The weight of a running on the stand/dyno iron-block SBC WITH AS MANY CHEAP ALUMINUM/AFTER MARKET PARTS AS IS PRACTICAL is very close to 425 pounds.

Yes, an all iron SBC with iron exhaust manifolds, gigantic starter, 40-pound flywheel, huge alternator, and all the other stock parts as pulled from a car weighs about 575 pounds. But nobody would put an engine like this in a cheap weekend street machine let alone an airplane.

It is amazing to me that I have to keep saying how much something weighs. I am building my airplane to use a 425-pound SBC (about a dozen of which I have lying around the shop). Others are free to use the 575-pound version.

I also apologize for the short comment about torque. Feeling a bit testy about the weight thing I guess. It’s a gross oversimplification. Still, the claim is correct but not for the reason I gave. As Hot Wings pointed out it has more to do with piston speed, rod/stroke ratio etc.

The comment about death is only meant to point out that these problems/questions are decidable and understandable. This is the strength of systematic investigation. It has nothing to do with “open mindedness”. In fact being open minded when working with a well thought out system is exactly what you don’t want. Being “open minded” or “thinking outside the box” or allowing differing “opinions” destroys the point of systematic investigation. It is nothing more than incoherence. I own my mistakes. I’m proud of them. I do all I can to weed them out though I sometimes fail. Anybody who doesn’t do this will only succeed in something like airplane design by sheer luck. I won’t have anything to do with that kind of thinking. It is suited to TV ads, politics, religion, etc., not engineering. Again I thank the careful and thoughtful folks here for keeping me on track.

Rob

Hello Rob, seems you and I got off on a bad footing. Rereading my posts, I do feel I should have worded them differently. My apologies for that. We see things somewhat differently, but I'm really here to discuss rather than debate things, and I want info from knowledgeable builders. I do feel that we need to just agree to disagree with each other sometimes, but respect one anothers opinions.

 

[ekimneirbo]

My experience with aircraft engines is somewhat limited but I have been building auto and boat engines for a lot of years. Compression provides the combustion pressure that acts on the piston area which moves the crank throw to produce torque. You have to limit compression only to the point where it encourages preignition or detonation. Since, as I understand it, an aircraft engine operates under full load at all rpms, like a boat, then higher compression gets risky beyond safe cylinder head temperatures and fuel octain ratings.
Over-bore engines can spin faster because the average piston speed is slower in the same cubic inch displacement but in an aircraft engine you like lower rpm - 2200 - 3000 which favors the smoother under-bore lay-out. The smaller piston area works over the longer stroke with less peak pulse cutting down on the vibration that is transmitted to the airframe. That is not to say that an engine cannot use mounting and different configurations (boxer style engine) to elieviate a majority of the vibration that comes from an over-bore design.
Nothing about the engine - or any part of the aircraft - operates in a vacuum. They can be configured to work together or work toward failure. It is my opinion that one should work to minimize all the adverse affects and then combine the components in a manner that further smooths the operation of the assemblies.

I believe it is farsical to believe that the cranks own thrust washer is enough to hold a direct drive prop and survive. I have seen too many thrust washers fail with only the use of a mechanical clutch in daily use on the street. To operate a direct drive prop you must add a strong thrust bearing and higher axial load bearing to take the loads of the propeller.

submitted with all due humility,
Paul

Reply: Hello Paul, welcome to the discussion. Like you, I don't think mounting a prop directly is the best way to deal with thrust or harmonics...........

 

[Wagy59]

Alright..I have a question...I was reading about the DH Hornet and it had Rolls Royce merlins ....130 and 131 variants I believe ...one had an idler gear to drive the prop opp hand to the other to improve handling at low speeds etc...each engine turned the same direction but one side had the idler gear to turn the prop opp. the other side....OK...all is good everybody gets that...makes a lot of sense to do that. so my question is based on hearing so much about harmonics and piston impulses , blah blah blah, because I've never actually run across anything describing a real problem experienced by a real person using a v-8 conversion..people talk about different ways to isolate the prop from the engine impulses etc etc. Well, the merlins in those days pretty much had gears on the front of the crankshaft driving the prop...worked great..still works...and I'm pretty sure my ole 283 ci chevy in my 63' 4 wheel drive surburban had the smoothest idle on the planet and was extremely smooth on up through 3000rpm......I used to watch it a lot....that engine never moved,,you could set a nickle on it while it idled and the nickle would just sit there....and that was after the engine had gone 150,000 miles....so whats the deal? I hear a lot of other worldly theories and a bunch of "ya gotta do this or that" Seems to be a lot of BS about it...does anybody really know? Anything documented on problems with harmonics and piston impulses on gears and props?

 

[Toobuilder]

... Well, the merlins in those days pretty much had gears on the front of the crankshaft driving the prop...worked great..still works...and I'm pretty sure my ole 283 ci chevy in my 63' 4 wheel drive surburban had the smoothest idle on the planet and was extremely smooth on up through 3000rpm...

Not quite that simple. The Merlin had plenty of trouble keeping the gearbox together, as did the Allison, and for that matter, the R2800. It's easy to look back 70 years and think it was a simple fix, but the fact is these were "perfected" by wartime needs and mountains of money. The gearbox problems on the R2800 are well documented and nearly doomed the entire program.

 

[Wagy59]

Yeh , I get that...not sure why the R2800 has anything to do with it..radial engine with planetary gears, which are known to be extremely durable by the way, due to the loads getting sread out among more gears....R2800's are famous for still running after canon shells got rid of 2 or 3 cylinders etc....and I'm old enought to know it's "not quite that simple"...I just was looking for an answer to my question

 

[orion]

The answer to your question lies in the nuances of the system, not simply what one can observe. for instance, yes, the engine can idle in your car or truck and look like it's perfectly smooth and not moving. But that system has been very refined and has numerous balancing components within and down the line, all of which act in harmony to dampen out any damaging vibrations. A rotary engine is a great example - they too can run and idle with a near turbine like smoothness. But in aircraft, virtually everyone who has worked with rotary applications has witnessed catastrophic failures happening seemingly with no warning - one moment the engine is running fine, the next you have pieces all over your dyno or test cell.

The issues that cause the damage are not the ones that cause some engines to run rough or shake - most of those are internal and only in a few occasions do those have any effect on the components down the line. The phenomena that cause aircraft failures are those that are not easily felt or measured without the use of more advanced equipment. Furthermore, the failures occur not simply due to the characteristics of the engine but more so the characteristics of the system that includes the engine, the gears and the prop. When all these things play together there are forcing functions and feedback that cannot be felt or predicted by the good old eyeball or even trial and error testing. You really have to know what you're doing, both, at the theoretical level and the practical one also.

Some time ago I wrote two very basic articles on this subject - neither is a work of science but both attempt to familiarize folks with some of the practices I've personally seen in the industry and look at some of the issues of redrive design. The articles are here: https://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/10768-articles.html

 

[Wagy59]

Thanks..I'm downloading the articles..I started to read one and said. ok ..time to download!..LOL I guess it boils down to how much less reliable is a chevy Ls series engine with a gear reduction than a run of the mill IO-540 with equal amounts of care and maintenance?...I mean everyone I've ever known had to spend a lot of money to keep their "aircraft engine" from cratering on them... whether it was an O-200 or an IO 540 of cont 480 or whatever...they ALL seem to be full of problems even if your really careful with them... and they ALL break and fail on a regular basis and cost owners thousands to maintain..I'm just having trouble seeing much difference in reliability/life expectancy/cost..based on my personal experience, which isn't as extensive as yours I suspect..But I have rebuilt a couple lycomings in my day as well as some GM engines..certainly nothing more magical about airplane engines than automotive engines...funny thing about lycomings and continentals is the basic design hasn't changed in 60 years or more whereas auto engines today are a far cry away from what was being produced that long ago....but then the "airplane" engines work..if ya have money..so why change??

 

[Toobuilder]

Yeh , I get that...not sure why the R2800 has anything to do with it..radial engine with planetary gears, which are known to be extremely durable by the way, due to the loads getting sread out among more gears....R2800's are famous for still running after canon shells got rid of 2 or 3 cylinders etc....and I'm old enought to know it's "not quite that simple"...I just was looking for an answer to my question

As Orion pointed out, it is not a simple answer like brute strength that gets you through something as complicated as gearbox harmonics. The early P-38 engines had "epicyclic" (sp) (planetary) gears also, and were just awful. It took a major gearbox redesign (spur gears) to give them any kind of reliability.

Getting everything to play well together is just flat out tough. And even in a "perfected design", one seemingly minor change in the engine, prop or gearbox itself may set up a condition which simply eats the gearbox alive. Heck, it's possible that a Merlin gearbox would self destruct if hung on the front of a Chevy V8 just because of the difference in resonance between the core engines.

 

[Wagy59]

FYI...In light of my previous post, I HAVE done some fooling around and can always revert back to using a couple IO-540's on my twin without destroying the whole design..I can widen the nacelles about 4 inches from what they are and and reshape them a bit and get creative on air inlets/cooling and it will still look just as good..:ban:

Well maybe not quite as good.
By the way I made the stool...I may quit my real job..Everyone I know wants some..I've refined the design..about to make a couple out of walnut

 

[Toobuilder]

FYI...In light of my previous post, I HAVE done some fooling around and can always revert back to using a couple IO-540's on my twin without destroying the whole design...

I feel for you. If I ever get around to finishing and building my design, it will also accept the 540 just in case my direct drive LS doesn't work out.

 

[Wagy59]

I feel for you. If I ever get around to finishing and building my design, it will also accept the 540 just in case my direct drive LS doesn't work out.

Yep..thanks!..Man, I feel for you too...It is all just so challenging!!!....What bugs me is I want this thing to be something I can jump in and go fly or go somewhere in without worrying about and engine/prop combination self destructing & falling off the airplane..within reason anyway..I'll worry about it all the time, but I don't want to start every flight intending to use the parachute or put it in a field! I want it to be somewhat reliable enough not to have to treat it like I'm in the X-15 or something

 

[ekimneirbo]

Re: Small block Chevy Ideal Setup..... Engine Reliability

About a month ago I went to pick up a frame for a 49 Chevy pickup. I drove about 200 miles round trip. It was one of those dreary days when little rain storms populated the area and I was continually passing in and out of the rain. Often it rained so hard you could barely see, other times it rained lightly ,and ocassionally not at all. I was driving a little V6 S10 and pulling a 16 foot steel floored trailer with the truck frame and suspension loaded on it. As it purred along oblivious to the changing moisture and cold, I noticed how much traffic there was on the road that day, thousands of cars going where I had just been, and thousands more going along the way I was. I believe in all that soupy mess I saw one car parked alongside the highway for some unknown reason.
It occurred to me just how dependable todays vehicles really are........that tens of thousand of people every day get into their vehicles and set out in virtually any kind of weather and never give a second thought about their vehicles ability to "get them there". Most of these people have no concept of how the vehicle makes this happen. Many of them virtually never service their vehicle.Others perform routine maintaince without the benefit of any licensed mechanic to sign em off, yet day after day all these engines, once started tend to give unwavering service. They are more dependable than the family dog.
Then, on the other hand you have the aircraft engine.Even, a good one sucks more oil than a worn out car engine. They run rough, are hard to start when cold, hard to start when hot, have outrageous parts costs,rust up when not used regularly,usually have a leak somewhere, don't transfer heat consistantly, and require an annual testing to make sure they are fit for service. If they required all of that in a car, they would be called a lemon............yet everyone swears by them and tells you to beware of car engines. Go figure....
Anyway, if you can make a reliable and efficient drive system, I think they are the way to go.

 

[Toobuilder]

Well, if there were 10 million airplanes sold every year, and the same number of consumers who demanded such things, then aircraft would have that too. Cars were unreliable, difficult to operate, and required lots of maintenance too. It was the consumer who demanded (by purchasing the "better" car) that they become this way. There is a lot of engineering and development cost wrapped up in creating the trouble free car - the aircraft market simply isn't big enough to recover that cost. So we're stuck with what we have.

 

[Dan Thomas]

I mean everyone I've ever known had to spend a lot of money to keep their "aircraft engine" from cratering on them... whether it was an O-200 or an IO 540 of cont 480 or whatever...they ALL seem to be full of problems even if your really careful with them... and they ALL break and fail on a regular basis and cost owners thousands to maintain..

I was a Director of Maintenance for a flight school operating seven aircraft, thousands of hours per year, and every engine reached TBO. Continentals sometimes needed valve work maybe 1000 hours along, Lycomings never did. The only failure we ever had (in about 60,000 hours!) was a partial power loss in an O-200 that swallowed a valve. Aircraft engines that are cared for as the manufacturer recommends will behave themselves just fine. The auto conversions will make far more trouble in 60,000 hours, believe me. The difference is that they are driving a rotating mass with much more resistance to changes in angular momentum than the original flywheel, and so an engine that's firing every so many degrees of rotation and compressing or exhausting or sucking the rest of the time will have a crankshaft that is NOT turning really smoothly. That's why it has a flywheel there, after all, and even then it doesn't get the rotation perfectly smooth. Now we connect that thing, often with a much lighter flywheel, to a PSRU and try to drive a prop. The engine's crank wants to go slow-fast-slow-fast as it runs through even one revolution, and the prop wants to turn at a really steady rate. that's where the arguments arise and something often ends up broken. Violently. A direct-drive setup avoids much of that, but then we have precession and thrust that has to be managed somehow.

Turning a transmission to run wheels on pavement is another deal entirely, but with a heavy flywheel and either springs in the clutch plate or a torque converter (fluid coupling) and the ability of the driveshaft and/or axles to absorb such pulsations, it works OK. We can't compare the millions of cars on the freeway to the aircraft engine at all. Different animal. Different dynamics altogether.

And car engines rust out, too, if they are run for an hour every three or four weeks or even less than that. They'll rust a little slower because there's less blowby in a liquid-cooled engine where the tolerances can be tighter, but they'll still corrode. It's the water vapor and corrosive combustion byproducts getting into the crankcase that do it, far more than any atmospheric water.

Dan

 

[RJW]

Well, if there were 10 million airplanes sold every year, and the same number of consumers who demanded such things, then aircraft would have that too. Cars were unreliable, difficult to operate, and required lots of maintenance too. It was the consumer who demanded (by purchasing the "better" car) that they become this way. There is a lot of engineering and development cost wrapped up in creating the trouble free car - the aircraft market simply isn't big enough to recover that cost. So we're stuck with what we have.

Not to mention that your typical car engine does almost nothing compared to even an archaic O-200 (how many times has this been said/proved?). How many words (or rather engines) will it take to convince folks that even half a horsepower per cubic inch wears out an engine? In reality car motors never see this kind of power production. All you have to do is build a few car motors that make a half horsepower per cubic inch, use them at that power level and note how long they last. You’ll notice pretty quickly how wonderful crappy airplane engines really are. And I like car motors.

Rob

 

[orion]

Two facts we've discussed here before: Auto engines develop only about 20% of their rated power for the vast majority of their anticipated life. Airplane engines are asked to develop well in excess of 80% power for most of their lives and in many cases, more. Auto engines are commonly used every day. Aircraft engines tend to sit for long periods of time, after which point they're brought up to 100% power very quickly. Historically flight school and commercial operations see engine lives easily reach TBO, and higher. Use the airplane and keep it maintained and the engine will last a long time. Let it sit and it is unlikely that you'll reach 50% of TBO.

 

[Toobuilder]

Yep, aircraft engine failures are like most aircraft crashes - due to operator error. Cars have evolved far enough to actually be "foolproof", not "better"... Aircraft still require some knowledge and skill to manage. But when they are managed well, aircraft engines generally give exemplary service. There are more than a few Lycoming operators who have applied for TBO extensions far in excess of factory numbers and routinely get them.

 

[stol]

xxxx