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Engines and Reliability



 
 
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  #1  
Old June 29th 04, 08:32 AM
Dylan Smith
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Default Engines and Reliability

Things that make you go 'hmm'.

The accepted wisdom is that aviation engines are tough, because they can
be run at full rated power for hours on end, and auto engines are
fragile, and must not be thrashed or they won't last very long. It was
even mentioned in a thread in the last couple of weeks - I don't
remember who said it, but they said "operate your car engine like that
and it wouldn't last half an hour".

I've never really thought about it, but this weekend I learned how to
drive the winch at the glider club. After a few launches it got me
thinking - this thing about aero engines vs car engines is probably an
old wives tale, possibly promulgated so people don't feel so bad about
spending so much money on aircraft engine parts when yet another
cylinder is cracked.

The winch. Basically, the winch is a method of launching gliders. At one
end of the runway, you have the glider. At the other end, attached to
the best part of a mile of steel cable is the winch. This consists of a
take-up drum which reels the cable in, and a power plant and
transmission of some sort. Our winch is a 'homebuilt'. The power plant
and transmission came straight off a car - a mid-70s Jaguar XJ6.

In this era, Jaguar quality was at its worst. Jaguar was part of British
Leyland, a nationalised car making monstrosity, beset by problems with
trade unions and appaling quality control. The engine is a 4.2 litre
inline six with dual overhead camshafts, and dual SU carburettors. The
transmission is the standard 3-speed automatic.

Winching a glider means you go from idle, rapidly increase the power,
then as you see the glider pitch up to about 45-50 degrees nose up,
floor it. The glider rockets skywards. Wide-open throttle is held, with
the transmission in drive which will select the appropriate speed for
the drum. As the glider starts getting towards the top, power is eased
back, eventually reaching idle. The cable then comes down on a
parachute. A little power is required (especially if there's a
crosswind) to bring the chute and cable in and make sure it lands on the
runway.

The engine is tortured by this idle - wide open - idle cycle maybe 30
times a day when we're operating. Since 4-star leaded fuel (98 octane)
which the engine was designed for is no longer available,
the engine is now run on regular unleaded. The engine and transmission
is nearly 30 years old, it's been in the winch for a few years and it
hasn't missed a beat. It starts easily, and runs sweetly despite the
abuse it gets - and it was built during Jaguar's worst years.

Perhaps auto engines aren't as feeble as people like to make out?

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"
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  #2  
Old June 29th 04, 09:47 AM
Peter Duniho
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"Dylan Smith" wrote in message
...
[...]
Perhaps auto engines aren't as feeble as people like to make out?


I've never seen anyone claim that auto engines were "feeble" or "fragile".

What they ARE is complex, and lacking in the necessary redundancy to be
operated in an airplane. They are generally too heavy, as they are made
stronger by adding material. They also lack an interested party to go to
the effort to certify them for aviation use.

Even with those impediments, some auto engines are being translated into
aviation use. Of course, the aviation-certified ones are significantly
different from their auto-based ancestors in some respects, but in many
other respects they are very similar. And of course, in the homebuilt
arena, many people operate auto engines for extended periods of time quite
successfully.

Now, all that said, one engine does not a proof or disproof make. Just
because your Jaguar engine running your winch has held together for 30
years, that doesn't mean that engines generally do well under that kind of
stress. Also, I seriously doubt that the engine has been left unmaintained
for its entire lifetime. In fact, I'd guess that someone is taking care of
it, and an engine that's being properly maintained can survive quite well.

Finally, without a doubt there are *some* auto engines that would never
survive in an aviation environment, and which *would* self-destruct in a
short period of time if operated for hours at a time at 75-80% power, with
extended 100% power climbs.

Perhaps your strawman was every bit as flimsy as one might have expected
from a strawman.

Pete


  #3  
Old June 29th 04, 10:25 AM
Stefan
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Default

Dylan Smith wrote:

The accepted wisdom is that aviation engines are tough, because they can
be run at full rated power for hours on end, and auto engines are
fragile, and must not be thrashed or they won't last very long.


It all depends what "full power" is.

I remember a marine diesel (forgot the brand, maybe Volvo), which was
available in two variants: Heavy duty and light duty. Both were
basically the same engine, only the heavy duty model developed about 40%
less power. Of course it could be run at "full power" the whole day long!

Now imagine a car with a 360 cubic inch engine that develops a mere 180hp!

Stefan

  #4  
Old June 29th 04, 01:14 PM
external usenet poster
 
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Default

On Tue, 29 Jun 2004 07:32:04 -0000, Dylan Smith
wrote:

Perhaps auto engines aren't as feeble as people like to make out?


Maybe it's time for me to post the article written by a Detroit auto
engineer about exactly what kind of torture auto engines go through
during their development and testing. He was in charge of GM's
"Premium Engine Program" and wrote this article for "Contact!"
magazine about 8 years ago.

Begin article:

"PERFORMANCE

The engine in production form for 1999 develops 215 HP at 5600 RPM and
230 foot pounds of torque at 4400 rpm. As a routine part of an engine
development program we tested the engine at full power, maximum RPM.
We ran it at 6000 RPM, pulling 215 HP at wide open throttle, for 265
hours. That's a continuous 265 hours of wide open throttle, far worse
than autobahn driving, because even on the German Autobahn, you
wouldn't be at 6000 RPM. THAT IS A STANDARD DURABILITY TEST.
(emphasis mine) We run many engines through this test as a matter of
course.

Specific development focus is on the crank, pistons, rods, block
structure, timing drive wear; we get a lot of full load cycles in a
hurry. It isn't necessarily designed to replicate customer driving
but to get development answers. Wear and fatigue are accelerated.
The test is particularly applicable in proving out dampers and their
effectiveness. If the damper is not properly tuned to the engine the
crankshaft will inevitably break in that time period. (note, this is
evidence you should not discard the stock damper when using the auto
engine for aircraft power)

A number of other engine tests are utilized. We use a variety of
specific tests to accelerate engine wear and to look at fatigue
failures. The cyclic endurance test is now called PTED (power train
endurance). It closely approximates cyclic durability. The engine is
cycled from its torque peak to its horsepower peak, at wide open
throttle, then down to idle, then accelerates up to shift points, then
back down to the torque peak and then horsepower peak. This test is
run for 400 hours. Once again, it's a wide open throttle test for 400
hours. The RPM for this engine, ranged between 4400 and 6000 RPM,
back and forth in about a 5 minute cycle. The dyno computer will
occasionally bring the engine down to idle, up to 6500 RPM shift
points, and then back to the 4400 - 6000 RPM 5 minute cycle.

Thermal cycle tests are run to define engine capability under cold
weather condition. We run the engine at full throttle at 4000 RPM,
bring it down to idle, stop it, switch the coolant valves to drain the
hot coolant, pump the chilled coolant from the chiller until the metal
temperature stabilizes at 0 degrees F. Frost forms on the outside of
the block, as the cold coolant rushes into the engine. When it
stabilizes at 0 F, we motor the engine, start it, come to full
throttle at 4400 RPM, the valves switch and the coolant temperature
starts to climb. It climbs back up to 260 degrees F. It takes 10 -11
minutes to complete one cycle. The engine must pass 600 cycles
without any sign of failure. We typically run 1200 cycles and a probe
test will run 1600 cycles. That's a (sic) excellent gasket killer
test. Head gaskets are the first to fail because of the rapid
expansion and contraction.

A powertrain endurance test simulates in-vehicle operation. The
Ypsilanti plant uses it for testing transmission. We, of course, use
it to look at engine performance. The equipment consists of an
engine/transmission combination, which sits on a dyno with large steel
inertia wheels. The inertia wheels are being driven by the
transmission output shaft, just like in a car. They cycle is brutal;
the engine is at idle in gear. The engine accelerates wide open to
6200 RPM, upshift occurs, 6200 RPM is reached, upshift occurs to 3rd,
6200 RPM is reached, upshift occurs to 4th, the wheels turn up to 135
MPH depending on the application. The second half of the cycle calls
for a closed throttle down to 70 MPH, then wide open throttle with a
downshift to 2nd, the engine goes back up to top speed, coasts down so
that the transmission selects down to a lower range. The engine is in
an overrun condition all the way down to idle; i.e., the engine is
being used for braking. That's one cycle. One transmission life
cycle is typically 12K - 13K cycles of the above test. We will run an
engine through 4 or 5 transmissions. This is a very harsh schedule
for the engine, particularly because of the overrun braking.
Cylinders and rings suffer the most on this test.

We run some idle tests to verify low speed operation. The engine is
run at idle for about 2000 hours to make sure of adequate oil flow at
idle.

We use all those engine tests in addition to fleet tests and extensive
vehicle road testing. The customer can be assured that the PV6 engine
is a thoroughly tested advanced design that matches or exceeds
competing offerings."

End of article

This is merely typical of auto engine development, all the
manufacturers run some variation of this kind of torture. BMW and
Mercedes probably beat up their engines even worse.

As Peter Duniho pointed out, auto engines have been in use in the
homebuilt community for many years now. One guy managed to run his
Ford 3.8L engine to 2,000 hours before tearing it down for a rebuild.
He found no significant wear in any of the engine components, but he
replaced the Gates toothed belt for the PSRU anyway. The engine tear
down and rebuild, including the belt, cost him around $1,000 if I'm
remembering correctly.

Corky Scott


  #5  
Old June 29th 04, 01:47 PM
Bill Denton
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Posts: n/a
Default

It's called "operating parameters"...

An aircraft engine is designed to meet one set of parameters, a land vehicle
engine is designed to meet another set, and a marine engine is designed to
meet still another set.

And you can have additional sets of parameters within these broad
categories: economical operation in a passenger automobile, towing capacity
in an SUV, sustained high speeds in a NASCAR racer.

Obviously, other power train components have to be factored into the
equation.

You can "sledge hammer" just about any engine into just about any vehicle
and "Rube Goldberg" it into operating, but the results will probably not be
very satisfactory.

The key to long life and satisfactory performance from an engine is to use
it within it's design parameters. Aircraft engines are designed for
sustained, high RPM operation, automobile engines for a mix of stop and go
driving and sustained high speeds. And as long as the engine is operated
within it's design parameters you should receive satisfactory service.



"Dylan Smith" wrote in message
...
Things that make you go 'hmm'.

The accepted wisdom is that aviation engines are tough, because they can
be run at full rated power for hours on end, and auto engines are
fragile, and must not be thrashed or they won't last very long. It was
even mentioned in a thread in the last couple of weeks - I don't
remember who said it, but they said "operate your car engine like that
and it wouldn't last half an hour".

I've never really thought about it, but this weekend I learned how to
drive the winch at the glider club. After a few launches it got me
thinking - this thing about aero engines vs car engines is probably an
old wives tale, possibly promulgated so people don't feel so bad about
spending so much money on aircraft engine parts when yet another
cylinder is cracked.

The winch. Basically, the winch is a method of launching gliders. At one
end of the runway, you have the glider. At the other end, attached to
the best part of a mile of steel cable is the winch. This consists of a
take-up drum which reels the cable in, and a power plant and
transmission of some sort. Our winch is a 'homebuilt'. The power plant
and transmission came straight off a car - a mid-70s Jaguar XJ6.

In this era, Jaguar quality was at its worst. Jaguar was part of British
Leyland, a nationalised car making monstrosity, beset by problems with
trade unions and appaling quality control. The engine is a 4.2 litre
inline six with dual overhead camshafts, and dual SU carburettors. The
transmission is the standard 3-speed automatic.

Winching a glider means you go from idle, rapidly increase the power,
then as you see the glider pitch up to about 45-50 degrees nose up,
floor it. The glider rockets skywards. Wide-open throttle is held, with
the transmission in drive which will select the appropriate speed for
the drum. As the glider starts getting towards the top, power is eased
back, eventually reaching idle. The cable then comes down on a
parachute. A little power is required (especially if there's a
crosswind) to bring the chute and cable in and make sure it lands on the
runway.

The engine is tortured by this idle - wide open - idle cycle maybe 30
times a day when we're operating. Since 4-star leaded fuel (98 octane)
which the engine was designed for is no longer available,
the engine is now run on regular unleaded. The engine and transmission
is nearly 30 years old, it's been in the winch for a few years and it
hasn't missed a beat. It starts easily, and runs sweetly despite the
abuse it gets - and it was built during Jaguar's worst years.

Perhaps auto engines aren't as feeble as people like to make out?

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"



  #6  
Old June 29th 04, 01:53 PM
Bushy
external usenet poster
 
Posts: n/a
Default

Now imagine a car with a 360 cubic inch engine that develops a mere 180hp!


Now imagine a car with a 1200 cubic inch engine that develops a mere 1800hp!

At 2200rpm..........., and only the first little bit of boost!

;)

Peter


  #7  
Old June 29th 04, 02:08 PM
Dylan Smith
external usenet poster
 
Posts: n/a
Default

In article , Peter Duniho wrote:
"Dylan Smith" wrote in message
...
[...]
Perhaps auto engines aren't as feeble as people like to make out?


I've never seen anyone claim that auto engines were "feeble" or "fragile".


The inference was certainly there. (A recent thread, to paraphrase, one
poster wrote "if you operate your car engine at 100% rated power, it
would be toast in less than half an hour". That certainly suggests the
poster thought auto engines were a bit fragile).

What they ARE is complex, and lacking in the necessary redundancy to be
operated in an airplane. snip


That's not part of the discussion; the discussion is whether auto
engines can be operated as 'harshly' as aircraft engines and survive.

other respects they are very similar. And of course, in the homebuilt
arena, many people operate auto engines for extended periods of time quite
successfully.


Which also demonstrates that at least those auto engines (I know the
opposed Subaru engines are quite popular, as some Ford type, the Mazda
rotary and Volkswagen air cooled engines) can be operated at high power
outputs for long periods of time.

stress. Also, I seriously doubt that the engine has been left unmaintained
for its entire lifetime. In fact, I'd guess that someone is taking care of
it, and an engine that's being properly maintained can survive quite well.


Of course it's being maintained. Again, maintenance was not something I
mentioned in the original post. (I strongly suspect our winch engine
spent some time sitting in a rotten-out Jag that nobody had driven for a
while though, I don't know as I wasn't there when it was put in the
winch).

Finally, without a doubt there are *some* auto engines that would never
survive in an aviation environment, and which *would* self-destruct in a
short period of time if operated for hours at a time at 75-80% power, with
extended 100% power climbs.


I'm not sure there are, certainly in the 100-200hp category. I certainly
can't think of an auto engine that's too fragile to be operated at high
power for hours on end in that bracket. Certainly not fitted to any
modern car.

Perhaps your strawman was every bit as flimsy as one might have expected
from a strawman.


It wasn't a straw man - the thrust of the argument was that maybe it's
an old wives tale to generalise that auto engines can't be run at high
power for prolonged periods or run in punishing regimes without
self-destructing, which seems an oft-repeated Usenet "truism" (which
tends to surface in the auto-vs-aero engine debates on r.a.h)

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"
  #8  
Old June 29th 04, 02:16 PM
Bushy
external usenet poster
 
Posts: n/a
Default

Aircraft engines are designed for
sustained, high RPM operation, automobile engines for a mix of stop and go
driving and sustained high speeds. And as long as the engine is operated
within it's design parameters you should receive satisfactory service.


Even my old Ford "tractor motor", a pushrod 250 cubic inch six, purrs along
the highway at a designed (and legal in most of Australia) 100kmh (55%
cruise) at about 3000rpm in 4th gear, drop it back to a economical 5th gear
(look, a variable pitch prop!) and I can crank it out to a whole lot more
than that for a good highway run, even without the speed cameras it will do
200kmh (Vne?) and sit on 160 kmh (75% cruise?) in the long roads in the
Northern Territory (unrestricted speed limit) even in summer, overtake many
another vehicle and plenty of hills that cause it to climb and descend, from
full throttle back to idle.

Mind you, it has had the odd problem over the years, but most of them have
been expected items for motor cars like: water pump, fan belt, spark plug
leads, alternator, flat tyres and so on. If it had the same work done to it
that most aircraft get, like a 100 hourly service, if it received a proper
runup in the morning before heading off to work, (Bloody hell, I'm late
again! Better hit the loud pedal!), or had the oil checked more often than
once a month if I remember, or when the oil light comes on, whichever occurs
first, if it had a fresh batch of pretty green coolant and a fresh radiator
hose or two, at least every other year, then it would have run as nicely as
any aircraft engine that I've played with.

The only reason I'm not going to put one in my homebuilt is that I don't
feel like coming in for a forced landing strapped to that dirty great big
chunk of steel!

Hope this helps,
Peter



  #9  
Old June 29th 04, 02:20 PM
EDR
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Default


The limiting factor in continuous high power engine operation is
cooling.
If you put an auto engine in PARK, depress the accellerator and run the
engine at high RPM, the heat will build up and the engine will self
destruct in (I'm guessing) less than an hour.
Take that same engine and head down the interstate with the cruise
control on and the temperature gauge will stay in the middle of the
range and the engine will run as long as the fuel lasts.

Guess what happens to your aircraft engine during ground operations?
Get it up in the air with the air flowing through the cowling and it
will be happy, too.
  #10  
Old June 29th 04, 06:21 PM
Michael
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Default

Dylan Smith wrote
The accepted wisdom is that aviation engines are tough, because they can
be run at full rated power for hours on end, and auto engines are
fragile, and must not be thrashed or they won't last very long. It was
even mentioned in a thread in the last couple of weeks - I don't
remember who said it, but they said "operate your car engine like that
and it wouldn't last half an hour".


In reality, that's nonsense and everyone knows it. The standards of
testing used by Detroit (never mind the Japanese) are way tougher than
anything the FAA ever thought about doing. This has been discussed
extensively on rec.aviation groups. Check out this link, or just
google it yourself:

http://groups.google.com/groups?hl=e...30% 26hl%3Den

I've never really thought about it, but this weekend I learned how to
drive the winch at the glider club. After a few launches it got me
thinking - this thing about aero engines vs car engines is probably an
old wives tale, possibly promulgated so people don't feel so bad about
spending so much money on aircraft engine parts when yet another
cylinder is cracked.


That's basically it. The aviation engines we use are obsolete. Sure,
they're more reliable and have better power-to-weight ratios than auto
engines - as long as you compare them to contemporary auto engines.
That's contemporary to the design age - meaning somewhere in the
1950's-1960's. At that point, real aviation went to gas turbines, the
designs of aviation piston engines were basically frozen, the
engineering talent went away, and no further progress was made.

When was the last time you heard of a modern (made in the last 10
years) auto engine that just died without giving weeks (or months, or
years) of warning? Not got stalled by a ham-fisted shifter or run out
of gas, but actually died? I'm sure it's happened, but it's a huge
rarity (whereas in 1955 it wasn't). On the other hand, I don't know
ANYONE with more than 2000 hours in piston GA who hasn't had an engine
failure. These things eat valves, they crack jugs, they throw rods,
their carb floats sink - you name it.

The truth is that aviation and auomotive use are very, very different.
They have very different duty cycles, cooling requirements, and
performance requirements. It really should not be a viable
proposition to adapt automotive engines to airplanes - you will wind
up with engines that are overdesigned in some areas and underdesigned
in others. However, automotive engines have advanced tremendously in
the past half century; piston aviation engines have not. Now we even
have manufacturers actually using autmotive cores (which are optimized
for a completely difference application), dressing them up for
aviation, and selling them - that's how Thielert works. It's very
much suboptimal - but the existing engines from Lycoming and
Continental are such disasters that even this is a viable business
plan.

Homebuilders have been adapting automotive engines for years. The
safety record has been abysmal. Oddly enough, it's never the engine
core that fails. It's always fuel systems, ignition systems,
reduction drives - all the stuff it takes to make the conversion. In
other words, all the stuff that is amateur-designed rather than
professionally engineered. That's why I'm not a great fan of auto
conversions. It's not that there's anything wrong with the engines -
despite being suboptimal for aviation, they're way out in front of the
crap Lycoming and Continental are selling, even for aviation
applications. The problem is that adapting the engine for aviation
use is a major task, and not something to be done by a garage mechanic
on the cheap.

Michael
 




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