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Car Engines vs. Aircraft Piston Engines


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#1 lelebebbel

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Posted 25 October 2007 - 22:39

this is something that I've been thinking about since I first learned what kind of engines most GA piston aircraft and helicopters use.
So far, I haven't found anyone who could give me a really conclusive answer. So here's the question:

Why do piston helicopters and airplanes still use old fashioned, huge single cam push rod type engines and burn leaded fuel?
Modern cars and motorcycle engines (DOHC, 4V per cylinder, water cooled) have a much higher power output per liter/displacement. They burn less fuel and even the maintenance times are off the scale!
Sure, there are differences:
1) Obviously, in a helicopter the engine runs at a constant speed, so that makes a difference.
2) Then there is the weight issue.
3) And, probably the most important thing - reliability.


so:

1) would it be really that hard to adapt the technology common in any modern car engine for a fixed rpm aircraft engine?

2) are car engines, even those in regular family cars, really that heavy? From the numbers I've found, modern R4/V6 up to 3 liters are pretty much in the same weight range or lighter (w/o transmission) than your average Lycoming O-320 B2C (5.3 liter) as found in an R22 beta, but some of them have way more power.
So, does the added technology really come with a weight penalty like some people have told me? considering the power output, of course.

3) reliability. This one leaves me guessing. Modern car engines may have much high power outputs, but they are rarely operated near full throttle for longer periods. But couldn't you just build or adapt an engine like that for fixed speed, and de-tune it a little bit to make it more reliable at full throttle?


Now I'm not suggesting one could develop a cabable 3 liter 300lbs DOHC aircraft engine with 240hp in a few months and stick it in a helicopter. I'm merely wondering why the engines in piston aircraft have hardly changed for like 40 years, and no one seems to be adapting even parts of the available technology.
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#2 apiaguy

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Posted 26 October 2007 - 00:24

Great question, it tends to come up often in aviation circles.
Let me say right off the bat I'm all for technology improvements in aviation... I own a highly modified mooney M20C (fixed wing) that has an after market turbo kit, lasar electronic ignition, numerous speed modifications and can cruise 175kts at 12,500 or close to 190kts at 20,000 while burning 10 gallons per hour.

Lets get right to it..
Aviation engines are not all that antique or old fashioned... sure they are based on 1950's technology but they have been constantly improved for reliability. Yes they use single cam push-rod design.... this is actually preferred in lower rpm power output... a pushrod engine will out perform a overhead cam engine in low rpm torque and power.

We burn leaded gas because we use air for cooling... the air cooled engine runs hotter than a water cooled engine... 400' vs 200' average temps... those hot cylinders require an anti-detonating fuel with a high octane to handle the compression and hot temp. So why not a liquid cooled engine.... complicated... adds weight, less reliable with more components to fail... the air-cooled engine works fine.

Those modern engines don't really have a "much higher output per displacement" Nearly all engines of comparable size are going to put out comparable power (when designed for a constant output high reliability application) Those modern engines derive their high power from either higher compression or higher RPM or a combination of both.... adding either to an aircooled engine can give the same result.. more power produced by the same displacement = less reliable, shorter life.

Definitely disagree that those other engines maintenance times are "off the scale" if equated to an aviation standard those engines wouldn't make it 500 hrs before needing overhaul.

1)No it wouldn't be that hard to adapt an automotive engine for an aircraft application... but it would be heavier and less reliable. Also if it were to be certified it would cost alot more than the currently available aircraft engine.
2)nope... the auto engine is heavier... steel block, all those accessories and puts out less power at the necessary rpm range. Even an aluminium block engine by the time you add a power reduction unit to use the rpm is going to weigh similar and you're zinging the rpm making the engine less reliable. (unfortunately with the design of a reciprocating engine the higher rpm leads to higher failure, more wear and shorter TBO.
3)again, they only have higher power because they are higher strung and that power rating cannot be maintained for long periods of time... it will wear out quickly.

On the final note... Bombardier already converted their engine for aircraft use then dropped the program when they realized it would be near impossible to change current manufacturers to incorporating them in new designs thus the market for sales is flat or dead unless they produce the conversion for currently manufactured aircraft and they didn't want to get into that. I think the way of the future will be diesel in GA. I've already talked too long so I'll skip how that is going to happen. But on a final final note..... the toroidial intersecting vane machine sounds like the sweetest new engine!!!!

Edited by apiaguy, 26 October 2007 - 00:25.

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#3 500E

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Posted 26 October 2007 - 08:35

Personally I think vested interest is a large part of the problem with engine development.
Another reason is the cost of certification, on existing equipment
I think your comment on Bombardier was the telling paragraph in your post.
We would not accept the engine life in our auto so why do we accept it in aero environment.
I would dispute existing aero engines cannot be made more efficient \ reliable, with minimum cost, but as long as we the users put up with low MTBF we will get more of the same.
Sticky valves went the way of the dinosaurs years ago on auto engines
The power cycle could be less of a problem than you think the Porsche Subaru auto engines can produce very high specific outputs, so de tuning + mods to the design could provide more torque with lower gross HP and longer life
I would also dispute life of high stressed air cooled motors had had numerous Porsche, VW cars and the alloy motors were real reliable for high mileages 250,000 hard driven on the ones I have owned and were still going when sold, all be it serviced beyond the manufacturers requirements.
As most light helio piston engines drive through belts the gearing should not add to weight appreciably.
The life of engines can be upset by a no of factors some years ago a heavy plant firm with an impeccable reputation for longevity of its engines started fitting to lorry's and the head gaskets & I believe valves started to fail on a percentage that was higher than in the plant.
Plant motor= constant rev +- small variation Lorry motor =up and down the rev range = Problem till sorted, most light helio\aircraft constant rev range +-slightly larger rev range than plant, but not the vast difference of road use.
The wear in most engines is at its highest in first minutes from cold, short running times( acid build up in crank case\oil). and the continual load of varying RPM, so longer run times low RPM fluctuation mandatory service scheduling should be not to much trouble.
I do not know how many Subaru VW engines are in autogiros, experimental aircraft, but am led to believe it runs to thousands world wide + these are Cheap! automotive engines
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#4 Gomer Pylot

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Posted 26 October 2007 - 09:47

It basically comes down to one word: bureaucracy. It's simply too expensive, and not profitable enough (same thing in the end) to go through the FAA's certification process to get a new engine approved. It would require an STC to install the engine in every aircraft, even after the years of effort it would take to get the certification done. Modern automotive engines are far more reliable than aircraft engines, and generally as light, if not lighter, and the computer integration allows them to be used at any altitude. Honda has done some work in using auto engines in aircraft, but it hasn't caught on. In some ways pilots and aircraft manufacturers are incredibly conservative. Every helicopter I've ever flown leaks water into the cockpit whenever it rains. We would never allow that in even a cheap car, but we accept it in a multi-million dollar helicopter. We accept seats that are grossly uncomfortable in a helicopter, but would never buy a Yugo with seats that bad. We accept unreliable engines with many decades-old technology, which we would never buy in a cheap car. The combination of the FAA's incompetence and unwillingness to actually do anything, and our willingness to accept whatever we get, is killling us, and costing lots of money.
Best Regards,

Gomer

#5 500E

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Posted 26 October 2007 - 15:33

With you again GP. regarding engines and the water ingress
A 500 that don't leak has not been made, even with gutters doors leak, usually on your leg.
The best thing I have found for the canopy leaks, is Captain Tolleys Creeping crack sealer, starts like water and flows for a short period, then thickens to a soft jelly and with perseverance we have stopped the screens leaking BUT the Doors!!!!!!!!
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#6 lelebebbel

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Posted 26 October 2007 - 16:50

thanks for your replies. Apiaguy, thanks for the insight - your technical explanations are far more conclusive than what I had heard so far.

Good point about the operating temperature. But, as GP said, there are plenty of air cooled motorcycle and car engines, too. Do these run at much higher temperatures, too? Or do they have more effective oil cooling instead? I know that it is somewhat harder to keep the engine temp. steady in an air cooled engine, which makes it harder to use an effective catalytic converter - probably one of the reasons why they are disappearing from cars and motorcycles.

The advantages of the older design when operating at low RPM is another good point. But, does this have anything to do with the push rod design? Or is this about valve size / 2 valves vs. 4 valves per cyl.?

Anyways, I see that you can't really increase the power output per displacement much if you don't want the engine to run at higher RPM.
So, about the reliability vs. speed.
What is it that limits the reliability at higher RPM? As far as I know, it's piston speed, and valve actuation. I agree you can't run a push rod engine at 4000rpm fixed and expect it to live very long, but isn't that problem solved by overhead camshafts? 4000rpm is not even that fast for a car engine and certainly doesn't cause any reliability issues - if you cruise down the Autobahn* at 90mph, you will be in that range or higher in most cars (and at a pretty high power setting, too), and there are plenty of people who do just that for hours every day - in cars that have factory approved oil change intervals of 12.000 miles or even more, and don't ever get an overhaul.

So, I still think that if someone would design an aircraft engine for a small helicopter from scratch today, it wouldn't look anything like, say, a Lycoming 360. That must mean it's really mostly cost of certification and development holding things back, like 500 and GP said.


*Yes, I'm from Stuttgart, so please imagine a german accent while reading this post!

Edited by lelebebbel, 26 October 2007 - 16:55.

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#7 67november

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Posted 26 October 2007 - 21:53

there are 2 distinction between a/c engines and auto engines.
1) a/c engines are operated at the rated 100% RPM from the factory and the components used to operate the a/c are manipulated to make the a/c fly.
auto engines are operated at variable speeds to make the basicly non manipulitive components operate the vehicle.

2) internal engine tolerances are far different from a/c to auto.
a/c engines are build with looser internal tolerances to allow for the large flow of oil thru out the engine for the cooling purposes are of course lubrication.
auto engines are built with much tighter tolerances which requires a cooling system other than air to keep them from overheating, thus adding to the weight and bulk. auto engines are NOT designed to run at the rated 100% RPM for this reason.

in general the a/c engine tolerance averages .040" where an auto engine averages .015".

the "old fashioned" engine style of the a/c engine is tried and true and will continue to remain basicly unchanged, the technoligy is in the parts that are in the engine.

hope this helps shed a little more light on the picture.

Edited by 67november, 26 October 2007 - 21:54.

spinning wings are better than fixed.

#8 Scarab

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Posted 27 October 2007 - 15:21

I saw a Rotorway with a Mazda rotary engine in it near Dallas, back in 03. It wasn't flying at the time. the builder was working on a governor but I don't know how reliable it turned out other than he sold it and the new owner ended up in the NTSB records. I think it was fuel pump problem that made him set it down. It was a pretty good looking installation, three power pulses per rev would make it mighty smooth compared to piston engines. Electronic ignition is not forgiving in a low/dead battery situation.

The small pistons with gravity feed fuel are pretty darn safe when you get down to it. Low rpm, redundant mags, no fuel pump. Gas/spark/go

I'm sure there are homebuilts out there with all manner of engines, mostly in the airplane/ultralight market. I guess I'd rather not be a test pilot for some really good idea on the drawing board that doesn't workout in the air.

Anyone know what happened to the R-22 with the turbine conversion in progress, that was on ebay around 03? It looked pretty awesome but again I didn't sign up to be a test pilot.
Flying a helicopter is the most fun I've ever had with my clothes ON!

#9 delorean

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Posted 27 October 2007 - 17:44

As GP said.....with all the liability involved.....Example: Precision Airmotive. They're the company that manufactures and overhauls the carburators on Lycoming and Continental engines (Previously called Bendix, Marvel, etc., but always the exact same carb.)

-They are a very small company. Ten people, or which two are lawyers.
-The occupy a small, leased shop in which they have some leased tools and a few test benches.
-They recently took their $50 carb overhaul manual and raised the price to $1300 to "encourage" more people to factory overhaul.
-At anytime, they usually have 5-7 lawsuits going.
-Very nice people, but fighting to stay alive.

This is why aviation is so f'd up and so freakin' expensive.

#10 500E

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Posted 27 October 2007 - 17:50

67
You are talking old technology, modern design materials etc. can work for aircraft, The No. of VW engines in motor gliders and home built planks seem to work & this is a basically 60 year old design.
The 100% power is a design criteria, not a insoluble problem, as for tolerances When I was heavily into vintage cars, tolerances were pretty loose by today's standards, by using newer materials with closer tolerances & having better wear characteristics, power and reliability could be increased, I am sure Porsche would be interested in your hypothesis that air cooling dos not work to well, 430 Hp. 390Lb\Ft torque on the last air cooled motor, air cooling is noisier than water due to fan, & no water jacket but in an aero engine is this a problem, the Subaru boxer engine is water cooled and is fitted in a no of autogiros light planes & in the Aerocopter.
http://www.copter.co...ak13_photos.php
Subaru boxer diesel motor. a new engine for 2008.
www.autoblog.com/2007/02/08/subaru-diesel-boxer-to-debut-in-geneva/
The loads that modern engines will stand are phenomenal if you follow the WRCar championship you will only begin to understand the stress that 300\400 Hp. engines are going through, the shock loads as wheels look for grip, all wheels off ground for 100s ft on rev limiter then bang with full throttle time after time and we worry about over revving the lycasorus by a few hundred RPM and
the bill $ ************* .
GP is correct we accept old technology that is way beyond its sell by date
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#11 Jack Poller

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Posted 28 October 2007 - 22:41

2) internal engine tolerances are far different from a/c to auto.
a/c engines are build with looser internal tolerances to allow for the large flow of oil thru out the engine for the cooling purposes are of course lubrication.
auto engines are built with much tighter tolerances which requires a cooling system other than air to keep them from overheating, thus adding to the weight and bulk. auto engines are NOT designed to run at the rated 100% RPM for this reason.

in general the a/c engine tolerance averages .040" where an auto engine averages .015".

the "old fashioned" engine style of the a/c engine is tried and true and will continue to remain basicly unchanged, the technoligy is in the parts that are in the engine.


I think (actually, I'm quite sure) you're wrong.

Tolerances may be different between aircraft and auto engines -- I don't know. If they are, it is more than likely because the Lycoming engine is a very old design, is manufactured in low numbers (compared to auto engines) and uses old manufacturing techniques, old manufacturing technology, and old tooling.

Regardless, tolerances do no dictate the type of cooling required.

Most aircraft engines use air cooled because, 99% of the time, the engine is moving through the air, and air cooling is cheap, easy, light weight, uses less parts, and, did I mention, it's light weight.

Auto engines use liquid cooling because they have to endure long periods of running with zero airflow in very hot conditions. And, there's very little weight penalty (relatively speaking).

Tolerance of components does not dictate cooling.

Tolerance of components is a design factor, and is dictated by cost, type of component, use, wear allowances, technology of materials, etc.,

Jack

#12 67november

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Posted 01 November 2007 - 22:26

I think (actually, I'm quite sure) you're wrong.

Tolerances may be different between aircraft and auto engines -- I don't know. If they are, it is more than likely because the Lycoming engine is a very old design, is manufactured in low numbers (compared to auto engines) and uses old manufacturing techniques, old manufacturing technology, and old tooling.

Regardless, tolerances do no dictate the type of cooling required.

Most aircraft engines use air cooled because, 99% of the time, the engine is moving through the air, and air cooling is cheap, easy, light weight, uses less parts, and, did I mention, it's light weight.

Auto engines use liquid cooling because they have to endure long periods of running with zero airflow in very hot conditions. And, there's very little weight penalty (relatively speaking).

Tolerance of components does not dictate cooling.

Tolerance of components is a design factor, and is dictated by cost, type of component, use, wear allowances, technology of materials, etc.,

Jack


Well Jack I'm gonna haffta rebut your post. ;)

tolerences will dictate the cooling factor, as I stated a/c engines run the majority of their life at the 100 % rated RPM, auto engines are NOT designed to run at the "red line" designed by that maker.
a/c engines will always have an air cooling factor flowing over them as the auto engines will not even if you put them in an a/c, if you look at the VW bug engine it also has a larger tolerence than a water cooled engine.
auto engines have never been designed to run the majority of thier life at 100 % of the rated RPM and until they develope an engine that can do that we are stuck with whats available as the FAA will not approve anything without substancial testing and red tape.

the only a/c engine that is water cooled that defies the theory is the merlin engine that was use in the P51 mustangs, it also had looser tolerances than a standard liquid cooled engine.
there are other liquid cooled a/c engines that were tested/used but never had an equal time in service to the merlin.
spinning wings are better than fixed.

#13 Eliot Cross

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Posted 02 November 2007 - 20:49

Being brand new to this site, still brand new helo pilot, & computer stupid, I jump in anyway. Interesting stuff. Assuming 67N's reference to "standard liquid cooled engines" meant automotive ones, I think the tolerance differences in the Merlin in comparison are common to aircraft recips in general. Even if it doesn't last as long as its automotive counterpart, the aircraft engine manufacturers don't need their motors locking down because of anything being too tight. Reliable is #1.
Don't forget the Allison V 1710, They used the heck out of them, & they were great engines too.
My experience w/ auto engines in aircraft (fixed wing), hasn't endeared me to them. Yes the 360 & 540 Lycs are not new technology. But I think they're darned reliable. My experience behind them in fixedwing machines comforts me in a type of aircraft new to me, in which I don't need a lot of real emergencies right off the bat. Eliot Cross SGJ

#14 Jack Poller

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Posted 18 November 2007 - 19:16

Well Jack I'm gonna haffta rebut your post. ;)

Sorry for the late reply -- I've been traveling.

tolerences will dictate the cooling factor, as I stated a/c engines run the majority of their life at the 100 % rated RPM, auto engines are NOT designed to run at the "red line" designed by that maker.

First, RPM and tolerances are related but are not the same thing.

Second, tolerances do not dictate cooling factor. In fact, temperature is one of the factors that affects tolerances. There are hundreds of moving parts in a piston engine, and tolerances are different for each one, depending on material, load, temperature, lubrication, etc. Don't believe me - do the research - look up the tolerances yourself. As an example, a VW Type IV 2.0 Liter air-cooled motor has a crankshaft bearing minimum clearance of 0.0008" whereas the Continental IO-520 minimum is 0.0018. And both are air cooled. The big difference is the operating temperature - the Continental has to live in -50F temperatures that the VW will likely never see.

Third, auto engines are definitely designed to be run at 100% of rated RPM (redline) -- in places such as on the Autobahn, in addition to Porches loafing at low RPMs at 120MPH, you'll find Peugots and Citroens and VWs all happily bouncing off their rev limiters at 120MPH. (If the manufacturers didn't design for this, the lawsuits would be horrendous.)

a/c engines will always have an air cooling factor flowing over them as the auto engines will not even if you put them in an a/c, if you look at the VW bug engine it also has a larger tolerence than a water cooled engine.

You're mixing things up here. First you say auto engines will never have air cooling, then you site an air cooled auto engine. And you say auto engines will not have air cooling even if you put them in an aircraft. What type of logic is this?

If you put an engine into an aircraft, you have to be able to cool it. If you're putting a liquid-cooled automotive engine in an airframe designed for an air-cooled engine, clearly you have to make some modifications - either to the engine to convert it to air cooling, or, more likely, to the airframe, to add ducting to a radiator.

Now, let's get down to facts instead of opinions - Crank bearing clearance
  • 1991 Acura (Honda) Integra (Liquid Cooled, Fuel Injected Inline 4): 0.0007"-.0017"
  • VW Type-4 (Air Cooled Horiz. Opposed 4) 0.0010 - .0027"
The difference is much more likely attributed to 40 years of materials science and computer controlled manufacturing than Air Cooling vs. Liquid Cooling.

auto engines have never been designed to run the majority of thier life at 100 % of the rated RPM and until they develope an engine that can do that we are stuck with whats available as the FAA will not approve anything without substancial testing and red tape.

Please site a reference regarding auto engines at 100% RPM. Bet you can't because it's just not true. If it was, the manufacturers would be facing trillions of dollars of class-action lawsuits.

And the FAA red tape and approval process is completely unrelated to the design of the engine - it exists for all engines and all manufactures.

the only a/c engine that is water cooled that defies the theory is the merlin engine that was use in the P51 mustangs, it also had looser tolerances than a standard liquid cooled engine.
there are other liquid cooled a/c engines that were tested/used but never had an equal time in service to the merlin.

I wish you could state some facts, rather than throw platitudes around willy-nilly.

There were many successful liquid cooled (not water cooled) motors developed during the WWII era. I leave it to you to come back with clearance and tolerance numbers that show differences between air cooled and liquid cooled (hint - there aren't any significant differences).

The motivation during WWII was the same as it is today. The rate of heat transfer of of a radiator is much greater than that of fins for air cooling. This means that a much smaller frontal area is required, contributing to better (in general) aerodynamics.

To date, you have shown little comprehension for the question at hand, little comprehension of design choices for motors, automobiles, and aircraft, and a complete lack of ability to string together two sentences into a cohesive non-contradictory paragraph. Please come back and play once you find the shift key, the spell checker, the grammar checker, and, of-course, the fact checker.

Jack

#15 500E

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Posted 19 November 2007 - 08:37

Jack Poller, Bit strong even if you don't agree with post
I would in the main agree with your comments.
There are a lot of ways the Lyc can be made more reliable & cost effective, but why waste time on a design 50 + years old the technology\Materials have moved on the main reason no new engines is COST to certify, there is no real pressure from users to supply newer, lighter, more fuel efficient designs, the user is still expected to pick up the bill for poor\ outdated design problems.
Oil consumption, Valve sticking, just for a start, and if you over rev don't even think about the bill, and all at RPM that make most engine designers laugh.
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#16 apiaguy

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Posted 19 November 2007 - 23:42

Yeah, maybe a little extreme Jack... but it's ok..

I understand where 67 is coming from... his thoughts maybe a little scattered but they all come from reputable industry knowledge.

An air-cooled aircraft engine will have a "loose" tolerance not because the design and science or material science is so outdated. It is more to do with thermal expansion of the materials inside the engine when operated at very high temperatures in a high-load environment... ie.. that continental or lycoming is fine operating at 475+ CHT...
It is unlikely that the VW engine will attain that operating temperature with its consistently lower output and load factor.
All these statements about RPM have gotten out of hand a little... I believe 67 is trying to relate the power settings that aircraft use as "normal operating".... it isn't specifically RPM driven but a combination of RPM, manifold pressure and air temperature. These aircraft engines are tested and operated day in and day out at 100% power (wide-open throttle, full manifold pressure.... or nearly so)

This is quite different from auto engines that can cruise down the autobahn at 120 mph using probabally less than 50% rated power... The auto engine routinely uses less than 35% power when cruising at highway speeds... Sure, it can produce full power and high RPM and not blow apart.... but it is NOT designed to operate at 100% power all the time.

It is well known in racing and building high output engines that engine tolerances and clearances are greater in such engines to allow for the greater thermal activity and expansion that occurs. I believe this is a design in aircraft engines due to the continued high output and high operating temperatures...

#17 500E

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Posted 20 November 2007 - 07:43

I built engines and the cars for race & rally, on a professional \ paid for basis with some success using the latest materials, techniques, and machinery, building to less exacting standards was not an option.
The main thrust of this post is, If the Auto engines design was locked in the 40\50 & 60s we would still have cars that did 25\30 Mpg instead of 50\60+ Mpg still used oil at a pint every 300\500 Miles or less, still have engines with average life of 60 \100 Thousand miles or less .
We have aero engines designed in the 40\50\60 with little or now development since, with high on going costs being borne by GA.
The MTBF if designs had been moved forward on par with Automobile\motorcycle\AG would be at least double what we have today, I will not say poor design because when they were conceived they were state of the art.
I also appreciate the development is slowed by Type approval \ certification and volume,
but there is a limit.
Fly the dream fly 500

#18 apiaguy

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Posted 20 November 2007 - 11:37

I built engines and the cars for race & rally, on a professional \ paid for basis with some success using the latest materials, techniques, and machinery, building to less exacting standards was not an option.
The main thrust of this post is, If the Auto engines design was locked in the 40\50 & 60s we would still have cars that did 25\30 Mpg instead of 50\60+ Mpg still used oil at a pint every 300\500 Miles or less, still have engines with average life of 60 \100 Thousand miles or less .
We have aero engines designed in the 40\50\60 with little or now development since, with high on going costs being borne by GA.
The MTBF if designs had been moved forward on par with Automobile\motorcycle\AG would be at least double what we have today, I will not say poor design because when they were conceived they were state of the art.
I also appreciate the development is slowed by Type approval \ certification and volume,
but there is a limit.



Are you suggesting that the aircraft engine is a "less exacting standard" because the bearing clearances and tolerances are greater?
If so, I believe you are mistaken

I'd also like to know what pizza cutter automobile gets 50-60+ mpg that isn't a hybrid....

Edited by apiaguy, 20 November 2007 - 11:48.


#19 67november

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Posted 26 November 2007 - 10:50

Yeah, maybe a little extreme Jack... but it's ok..

I understand where 67 is coming from... his thoughts maybe a little scattered but they all come from reputable industry knowledge.

All these statements about RPM have gotten out of hand a little... I believe 67 is trying to relate the power settings that aircraft use as "normal operating".... it isn't specifically RPM driven but a combination of RPM, manifold pressure and air temperature. These aircraft engines are tested and operated day in and day out at 100% power (wide-open throttle, full manifold pressure.... or nearly so)

This is quite different from auto engines that can cruise down the autobahn at 120 mph using probabally less than 50% rated power... The auto engine routinely uses less than 35% power when cruising at highway speeds... Sure, it can produce full power and high RPM and not blow apart.... but it is NOT designed to operate at 100% power all the time.


yes that what I was trying to convey, running at full power

I'd also like to know what pizza cutter automobile gets 50-60+ mpg that isn't a hybrid....


my buddies wife's car is a Volkswagon Jetta Deisel that gets 50 MPG hwy, my 93 Saturn gets better gas mileage (31MPG hwy) than most hybrids out there.
spinning wings are better than fixed.

#20 500E

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Posted 26 November 2007 - 16:06

I use a 1996cc. diesel van every day that returns 50 +Mpg driven hard, will cruse at 70Mph+ at 52 Mpg and the last two vehicles I owned did 50 +, at 1.06 per Ltr you don't want a US guzzler the helio cost enough without adding to the expense.
What I am saying about the OLD aero engines is development has not been pushed forward at anywhere near the auto engine pace I understand the volume argument, but the aero people have been left behind and it is you and me that pick up the tab for poor life, what real advance has lycasorus brought in other than injection in last 30 years ?
Fly the dream fly 500




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