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#21
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Chevy LS2 and Trans??? any real issues besides weight
"Charles K. Scott" wrote in message ... On 10 Nov 2005 12:41:25 -0800, "MrV" wrote: Hey guys i'm a new pilot that really wants to build his own craft. help me with this one issue. I want to use a chevy ls2 or ls7 as the power plant in my craft. now looking at everything including the hp/torque curves i've decided running the engine around 3100 rpm should give me around 250 hp with good torque now getting that power to a propeller seems to be an issue. I'm wondering besides weight would there be any real issue using the associated transmission locked in gear maybe 3rd/4th/5th gear whichever is just under 1:1. it would seem the car tranny has been engineered to convert the engine motion into the spinning i would need to propel the propeller. plus running the engine at 3100 rpm it would prob last longer than i will. the aircraft i want to design is a very cab foward design with a pusher prop and the engine would be mounted approx mid craft. i'm new at this and besides having an engineering background i really have no exp building an aircraft so any opinions would be helpful Mrv, you should understand that homebuilders have been thinking that auto engines should work fine for airplane powerplants from the very beginning of the homebuilt era. Not only homebuilders, but a number of qualified aeronautical engineers thought likewise and have tried through the years, with varying degrees of success, to convert auto engines to spin propellers. Toyota actually managed to get a Lexus based V-8 conversion certified with a Hamilton prop designed specifically for it. But they withdrew the engine from the market without attempting to put it into any airframes, other than the test bed. There is absolutely nothing inherently wrong with almost any auto engine's ability to run at aircraft flight power settings for a long time. That fact has been proven for years. What IS a problem is fabricating a reliable prop speed reduction unit, and managing to engineer adaquate cooling for the engine. The litanny goes, it's not the auto engine that fails, it's everything else. And there is a lot of everything else that can go wrong and stop the prop from spinning. From an aviation stand point, using an auto transmission for a PSRU is not a great idea. For one thing, it's carrying around a bunch of gears that add to the weight and aren't being used. That's just crazy. Also, with the transmission in the car, the drive train is locked solidly in place and does not impose any side loads to the transmission at all. All it does is transmit torque as it spins. But the propeller produces ENORMOUS side loads on the prop drive every time you turn, hit turbulence or climb or dive. The auto transmission, as it comes from the car manufacturers simply is not designed to withstand that kind of side loading. As mentioned previously, the lower gears in the transmission are designed to be operated for only short periods. They do not have the heft and thrust bearing support to manage sustained pressure at high torque loads. Finally, while belted PSRU's are fairly well understood at this point, they tend to be marginal for high output engines. The only PSRU I'd recommend at this point would be the Geschwender type. See: http://www.alternate-airpower.com/ for details. Corky Scott To me, it's interesting to note that in the automotive role, the engine is isolated from the load to the maximum extent possible. In other words, the engine is coupled to the wheels with cardan shafts that have U-Joints and sliding splines such that engine vibrations, other than torque pulses, don't get transmitted to the wheels and wheel vibrations don't get transmitted to the engine. The engine just rocks and rolls in it's own rubber mounts and transmits only torque to the drive line. The engine bearings see neither thrust or radial loads. The vision is that everything is isolated with rubber mounts to eliminate all possible vibrations. That seems to be a successful formula for cars. I'd suggest this is a good path to take in auto-engine conversions. Don't just mount the prop to the crank or mount the PSRU rigidly to the engine. Separate them and let the prop, PSRU and engine each live in their own isolated vibration environment. So, how to do this? First, think of a prop attached to the airframe turning in it's own bearings that carry the thrust and radial loads with the bearing carrier on elastomer mounts. Drive the prop with belts that absorb some torque pulses and drive the belt with a pulley block mounted to the airframe like the prop that is itself driven through a elastomer flex coupling by an engine riding in isolation mounts. This way the prop won't see engine vibrations and the engine won't see prop vibrations. The airframe itself should see neither. In drive line systems, there's no such thing as 'good vibrations'. Bill Daniels |
#22
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Chevy LS2 and Trans??? any real issues besides weight
I've been around homebuilts and homebuilders since 1973, and have
learned much from the mistakes of others. The old guys will tell you that you never design both an airplane and a powerplant at the same time, and that you never design an airplane without training or extensive research unless you are simply copying something else to a great extent. I've met or read about fellows with odd ideas about some "new" airframe who have either bankrupted themselves trying to make it work, or nearly killed themselves trying to fly it. The majority of these people weren't even pilots yet, just guys full of preconceived notions. They spent an enormously frustrating amount of time and money to no good purpose. Auto engine adaptations are very time-consuming, and while there are a few that run well enough, many of their builders wish they had just bolted a Lyc to the firewall in the first place. Would have been cheaper and they could have gone flying. I was also into boats for some years, and knew a guy who did the auto transmission thing; didn't last long at all. Those gears just won't take the high power levels for very long. Cars don't cruise at 75% power, and that's all there is to it. Detroit doesn't design stuff any stronger than it has to. The OP would be wise to read EVERYTHING he can find on the subject, which is a lot more than I had available in the '70s, what with the 'Net and all. No excuse to make the same mistakes all over again. Dan |
#23
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Chevy LS2 and Trans??? any real issues besides weight
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#24
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Chevy LS2 and Trans??? any real issues besides weight
As i stated earlier i'm an engineer and building/designing things is
something i burn to do. I've given myself 10 years to buid this thing. My problem with airplane engines is cost they are far to costly for what u get and are about as reliable as my lawnmower. the tranny i'm talking bout is a chevy tremec tranny built for the corvette. looking at the specs its about as bullet proof a gearbox as anything i've ever seen. now the tranny things is just an idea, use cheverolets billion dollars of research to get something going. the only semi-const is the engine which will more than likely be an ls2 as the ls7 i originally wanted is up there with airplane engines in cost. well lower end airplane engines. prob by the time i need the drivetrain it'll be cheaper. the question is if the engine/tranny is isolated from the thrust/sideloading/vib of the prop and besides weight would it be reasonable to assume this would be okay. it really shouldn't be all that difficult to completely isolate the drivetrain from the prop. now some other details that i would like to get input on: now the craft is essentially a kevlar covered steel tube frame. reason being i'm good at welding but have worked very little with composites( built speaker enclosures and spoilers for my car). but i really like the finish of the composite aircraft. and kevlar because its cheaper than graphite and lighter than fiberglass. 1. i only intend to run this thing at approx 50% power while i could spin it up higher i just can't see a reason to do it. 400lbs for 200+hp seems like a good trade to me. Plus i can buy another one or rebuild it myself for far less than the rebuild of an aircraft engine. 2. I"m not trying to build the most efficient fastest cruising thing in the world. i want something reliable, simple kinda speedy(150 - 160kts) and without the prop, massive front end and massive instrument panel infront of me. 3. 2 seater also maybe 3 but most likely 2. 4. also what is a good way to keep the sound of the engine/prop/gears in back where it belongs ? massive noise in the cabin would completely ruin the effect i'm trying to achieve. hey guys i'm only hunting for ideas now so please feel free to respond with anything u can come up with pro/con. also hopefully you aren't annoyed hehe cause prob get realy frustrated when i start asking about wing construction hehe. |
#25
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Chevy LS2 and Trans??? any real issues besides weight
It has to be said also the fastest way into the air is indeed the
museum piece Lycoming engine-securely mounted to the firewall of an already built certificated production aircraft. Even at today's high prices, they still are a Good Deal for most people who really want to fly. |
#26
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Chevy LS2 and Trans??? any real issues besides weight
"MrV" wrote: A page displaying his total lack of knowledge. To you, I put out the following possibilities. You a 1) A kid playing on the computer. If I am wrong, stop using the text message type of shorthand. 2) So completely ignorant of what works, what does not, and what might work, that you need to get into the books, and/or Google, and do some homework. The things you are proposing are ALL so far from reality, it is hard to know where to start giving advise. I doubt you are going to get many responses, because of this. 3) A plain and simple troll. -- Jim in NC |
#27
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Chevy LS2 and Trans??? any real issues besides weight
yes i did and that is why i posted it here asking for comments. if u
notice a number of times i have stated this is just for info and if it is reasonable. I'm guessing you are just an idiot that doesn't bother to read complete post. from the replies i've received the only thing i can see wrong with my idea is 1 weight and 2 vibration everything else can be solved readily with some planning. instead of posting something stupid like this why not give reasons why i'm TOTALLY off base. |
#28
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Chevy LS2 and Trans??? any real issues besides weight
In article .com,
"MrV" wrote: from the replies i've received the only thing i can see wrong with my idea is 1 weight and 2 vibration everything else can be solved readily with some planning. instead of posting something stupid like this why not give reasons why i'm TOTALLY off base. I think cooling was mentioned also. And, those pesky details are not trivial. I believe you also stated that your objection to Lycon is cost. The knowledgeable people here have pointed out that you will spend *far* more engineering your own airplane and powerplant than you would by buying off the shelf. I don't think they're referring to percentage, but orders of magnitude. And then you alluded - in a somewhat mocking tone IMO - to some new ideas you have for a wing. I think you can understand why it might be easy for some of us to assume you're a troll. You might be some sort of engineer, as you claim, but without the merest hint of any background in aviation, that isn't going to buy you much in the real world. Now, this is RAH, so I'm not going to suggest that you're off base. But chatting here isn't research. Go spend several thousand hours studying the issues, and then come back with *specific* questions based on a real understanding. Even the Wright brothers started by learning everything they could about what everyone before them had done. I'll give you one "out." If your objective is to design the next Moller skycar in order to bilk investors, then of course you don't need any real understanding of the issues at all. That's an objective that requires a completely different set of skills. |
#29
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Chevy LS2 and Trans??? any real issues besides weight
from the replies i've received the only thing i can see wrong with my
idea is 1 weight and 2 vibration everything else can be solved readily with some planning. instead of posting something stupid like this why not give reasons why i'm TOTALLY off base. Why you're TOTALLY off base: 1. Weight. You do want to fly, don't you? 2. Design. You do want to live, don't you? Get some understanding of aircraft. It can't be solved "readily." 3. Vibration. Kills mechanisms like you are proposing. Vibration is a science all its own, and few there are that understand it. 4. Gyroscopic loads. We haven't even touched on that one yet. 5. Money. Hope you have lots to throw away. There are plenty of people that will take it. 6. Reality. I can't recall anyone who entered this field, non-aviation engineering background or not, that has designed a successful airplane and powerplant combination from the ground up. Most of them crashed a few times and learned from that; the rest died. Since there's lots of info available now, there's no excuse to do the macho-ego-designer thing anymore. 7. A Lycoming is a lot more reliable than a lawnmower engine. Witness the average age of the lightplane fleet using them: something like 35 years? We don't want another ignorant newbie killing himself and discrediting the homebuilt movement. Please listen up. Dan |
#30
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Chevy LS2 and Trans??? any real issues besides weight
Smitty Two wrote: In article .com, "MrV" wrote: from the replies i've received the only thing i can see wrong with my idea is 1 weight and 2 vibration everything else can be solved readily with some planning. instead of posting something stupid like this why not give reasons why i'm TOTALLY off base. I think cooling was mentioned also. And, those pesky details are not trivial. I believe you also stated that your objection to Lycon is cost. The knowledgeable people here have pointed out that you will spend *far* more engineering your own airplane and powerplant than you would by buying off the shelf. I don't think they're referring to percentage, but orders of magnitude. This assumes every user of a non-LyCon engine has to engineer his own conversion from a clean sheet of paper. If you are going to apply that standard you should insist every LyCon using homebuilder make his own crankcase and cylinder patterns, pour sand castings himself, and machine them. Instead of buying a reduction drive, mounts and so forth pre-designed from a reputable supplier and attach them to an engine core with good history of results, using plumbing and systems as other successful operators have. That's the common sense solution. Find someone making a redrive and mounts for a reasonable price, reflecting only a small percentage for engineering since it's hardly a Skunk Works project and amortizing it over many units. The _best_ solution to auto engine cooling and cost is to buy a "real aircraft engine" that is "proven". What does a new PT6A series P&WC engine cost? That's a real aircraft engine, a LyCon is an overgrown Volkswagen. Unfortunately, for me a new Pilatus PC-9 is outside the range of affordability. (A L-39 is a third or fourth the price, and that's too expensive by far for most of us.) The sport boating industry exists to a large extent because of affordable marinized auto-derivative engines and sport flying can use them as well if some good simple engineering and common sense are applied. In fact, it has, since the days of Bernie Pietenpol and Steve Wittman, who flew reasonably well on commodity general purpose engines. |
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