Aircraft engine certification FAR's

The information below comes from our resident informational
wellspring, Ron Wattaja. He stepped into a "debate" between Craig
Wall and an auto conversion believer and set the record straight about
what was and was not required in the aircraft engine certification
test with the following information. You will see by reading below
that the FAA requires a FAR (pun not intended) less rigorous test for
aircraft engines than Detroit does voluntarily for their street
engines. I say voluntarily, but Detroit understands that if they do
not produce engines capable of withstanding incredible abuse, the
buyers will go elsewhere and take their money with them and it will
take a long time to overcome the bad publicity, which tends to smear
all models.

*** Begin Quote ***

From FAR 33.49:

b) Unsupercharged engines and engines incorporating a gear-driven
single-speed supercharger....the applicant must conduct the following
runs:

(1) A 30-hour run consisting of alternate periods of 5 minutes at
rated takeoff power with takeoff speed, and 5 minutes at maximum best
economy cruising power or maximum recommended cruising power.

(2) A 20-hour run consisting of alternate periods of 1.5 hours at
rated maximum continuous power with maximum continuous speed, and 0.5
hour at 75 percent rated maximum continuous power and 91 percent
maximum continuous speed.

(3)A 20-hour run consisting of alternate periods of 1.5 hours at rated
maximum continuous power with maximum continuous speed, and 0.5 hour
at 70 percent rated maximum continous power and 89 percent maximum
continuous speed.

(4) A 20-hour run consisting of alternate periods of 1.5 hours at
rated maximum continuous power with maximum continuous speed, and 0.5
hour at 65 percent rated maximum continuous power and 87 percent
maximum continous speed.

(5) A 20-hour run consisting of alternate periods of 1.5 hours at
rated maximum continuous power with maximum continuous speed, and 0.5
hour at 60 percent rated maximum continuous power and 84.5 percent
maximum continous speed.

(6) A 20-hour run consisting of alternate periods of 1.5 hours at
rated maximum continuous power with maximum continuous speed, and 0.5
hour at 50 percent rated maximum continuous power and 79.5 percent
maximum continous speed.

(7) A 20-hour run consisting of alternate periods of 2.5 hours at
rated maximum continuous power with maximum continuous speed, and 2.5
hour at maximum best economy cruising power or at maximum recommended
cruising power.

That's 150 hours total, including 85 hours at maximum continuous power
and speed, and 15 hours at rated takeoff power. The longest runs at
max power are the 2.5 hour ones in para. 7. According to para (a) of
FAR 33.49, for at least 35 hours of the max runs, the engine must be
operated with one cylinder at redline temperature and the others
within 50 degrees of redline.

To my eternal shame, I don't have the regs that cover the primary
category. However, I seem to recall that they include reciprocity to
other country's certification rules. The CAM-100 engine, for
instance, was tested to JAR 22 (European motorglider) standards:
Fifty hours on the test stand, with short low-power cycles and 1-hour
full-power ones.

*** End of quote ***

Ron, I hope you will forgive me for re-posting this information you
dug up.

Corky Scott

In article , Corky Scott
wrote:


FAR 33.43 is also relevant here. It requires a torsional and bending
vibration survey, using a prop (and of course a PSRU if applicable) at
up to 110% of max continuous rpm.

The requirement to test the PSRU is important, as they can be the
weakest link in the power chain.

It is difficult to compare the aviation engine type certification tests
with the automotive durability tests, as the two tests are doing
different things. The automotive test is trying to find problems that
will cause the manufacturer grief in automotive service.
Unfortunately, the configuration tested may be quite different from the
one we would use in an aircraft, as there is no PSRU, and there may be
substantial differences in ignition and fuel delivery systems. The
aviation engine test is supposed to test the whole engine, PSRU, etc,
in a configuration that is suitable for airborne use.

Continuing airworthiness issues also come into play here. The aviation
engine manufacturers are required to inform us about any major problems
they learn about. For automotive engines you may only learn about
problems and fixes through the grapevine (e.g. Ford V-6 coolant leaks
into the oil system).

So, in the end, the only way to figure out whether a given automotive
conversion will work is do fly it and find out. Eventually we'll have
enough service history to know what works, and what doesn't.

I'm not anti-automotive conversion - I'm considering a Mazda conversion
for my next project (please don't tell my wife I'm considering another
project - she still expects to get the garage back once my RV-8 is
flying).

======================

Section 33.43: Vibration test.

(a) Each engine must undergo a vibration survey to establish the
torsional and bending vibration characteristics of the crankshaft and
the propeller shaft or other output shaft, over the range of crankshaft
speed and engine power, under steady state and transient conditions,
from idling speed to either 110 percent of the desired maximum
continuous speed rating or 103 percent of the maximum desired takeoff
speed rating, whichever is higher. The survey must be conducted using,
for airplane engines, the same configuration of the propeller type
which is used for the endurance test, and using, for other engines, the
same configuration of the loading device type which is used for the
endurance test.

(b) The torsional and bending vibration stresses of the crankshaft and
the propeller shaft or other output shaft may not exceed the endurance
limit stress of the material from which the shaft is made. If the
maximum stress in the shaft cannot be shown to be below the endurance
limit by measurement, the vibration frequency and amplitude must be
measured. The peak amplitude must be shown to produce a stress below
the endurance limit; if not, the engine must be run at the condition
producing the peak amplitude until, for steel shafts, 10 million stress
reversals have been sustained without fatigue failure and, for other
shafts, until it is shown that fatigue will not occur within the
endurance limit stress of the material.

(c) Each accessory drive and mounting attachment must be loaded, with
the loads imposed by each accessory used only for an aircraft service
being the limit load specified by the applicant for the drive or
attachment point.

(d) The vibration survey described in paragraph (a) of this section
must be repeated with that cylinder not firing which has the most
adverse vibration effect, in order to establish the conditions under
which the engine can be operated safely in that abnormal state.
However, for this vibration survey, the engine speed range need only
extend from idle to the maximum desired takeoff speed, and compliance
with paragraph (b) of this section need not be shown.

--
Kevin Horton - RV-8
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/

On Fri, 25 Jul 2003 15:22:20 GMT, Kevin Horton
wrote:


It is difficult to compare the aviation engine type certification tests
with the automotive durability tests, as the two tests are doing
different things. The automotive test is trying to find problems that
will cause the manufacturer grief in automotive service.

I would say that any manufacturer of aircraft engines would be looking
for the same thing, only in aviation service.

Unfortunately, the configuration tested may be quite different from the
one we would use in an aircraft, as there is no PSRU, and there may be
substantial differences in ignition and fuel delivery systems. The
aviation engine test is supposed to test the whole engine, PSRU, etc,
in a configuration that is suitable for airborne use.

I agree. I guess I'm reacting from the old Paul Lamar episodes where
he declared that the short block itself by dint of it's V type
configuration, use of a cast steel crank and close cast cylinders was
inherently fragile and that the crank would "crumble to dust" and the
engine be unable to cool properly. What shocked me about this
attitude was that he used to work with Chaparal racing when this
little group was standing sports car racing on it's head with it's
innovation in aerodynamics and transmissions. He was an aerodynamics
engineer (I think) who's job was to make what Jim Hall dreamed up
happen. They made racing history. Now, 20 years later, he was
declaring that the very same type of engine that ran successfully in
his race cars (V engines), sometimes for 24 hours, cooling all the
way, would now not cool for even five minutes of climb at greatly
reduced rpm from the race track. It didn't make sense. I knew of no
crankshafts that had broken as he declared they would at that time,
and now almost 10 years later, I still haven't heard of any.

The engines themselves appear robust enough to handle the power
requirements. As you say, it's the ancillary components that can be
problematic.

Continuing airworthiness issues also come into play here. The aviation
engine manufacturers are required to inform us about any major problems
they learn about. For automotive engines you may only learn about
problems and fixes through the grapevine (e.g. Ford V-6 coolant leaks
into the oil system).

So, in the end, the only way to figure out whether a given automotive
conversion will work is do fly it and find out. Eventually we'll have
enough service history to know what works, and what doesn't.

Well how many hours should that necessarily be? Bruce can cite two
examples that have reached 2,000 hours and beyond. There are many
models of aircraft engines that must be overhauled long before then.

I'm not anti-automotive conversion - I'm considering a Mazda conversion
for my next project (please don't tell my wife I'm considering another
project - she still expects to get the garage back once my RV-8 is
flying).

We've been walking around the fuselage in the shop for so long that
it's become a fixture. It keeps getting more stuff put on it from
time to time.

Corky Scott

In article , Corky Scott
wrote:

On Fri, 25 Jul 2003 15:22:20 GMT, Kevin Horton
wrote:


It is difficult to compare the aviation engine type certification tests
with the automotive durability tests, as the two tests are doing
different things. The automotive test is trying to find problems that
will cause the manufacturer grief in automotive service.

I would say that any manufacturer of aircraft engines would be looking
for the same thing, only in aviation service.

Well, we are comparing tests that the automotive industry does at
their own discretion against tests that the aviation industry is
required to do. The aviation industry does many, many hours of
discretionary testing over and above the FAR 33 minimum standards. For
example, the turbine engine manufacturers that I deal with will use
flight test aircraft to conduct hundreds of hours of airborne testing -
this testing is over and above the FAR 33 requirements, as far as I can
tell (caveat - I am not a powerplants engineer, so I am not intimately
familiar with FAR 33 and the associated Advisory Circulars).

Continuing airworthiness issues also come into play here. The aviation
engine manufacturers are required to inform us about any major problems
they learn about. For automotive engines you may only learn about
problems and fixes through the grapevine (e.g. Ford V-6 coolant leaks
into the oil system).

So, in the end, the only way to figure out whether a given automotive
conversion will work is do fly it and find out. Eventually we'll have
enough service history to know what works, and what doesn't.

Well how many hours should that necessarily be? Bruce can cite two
examples that have reached 2,000 hours and beyond. There are many
models of aircraft engines that must be overhauled long before then.

Just because two examples have done 2,000 hours doesn't mean that you
or I will be able to achieve the same, unless we can gain the benefit
of all the lessons that were learned by the folks who had the success.

As I read on RAH recently, we really need access to some sort of
cookbook that explains exactly which engine and accessory configuration
has been show to have a good service history, and how it must be
installed, operated and maintained to achieve that good service
history. With an aviation engine, we can use the manufacturer's
installation manual + AC 43.13B + Tony Bengelis' (SP?) stuff + the
manufacturer's operating and maintenance instructions.

--
Kevin Horton - RV-8
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/

Earlier, (Corky Scott)
wrote:

...You will see by reading below that
the FAA requires a FAR (pun not
intended) less rigorous test for
aircraft engines than Detroit
does voluntarily for their street
engines.

And I will make the obligatory observation that Detroit tests it's car
motors for car service, and the FAA dictates tests that validate (to
some degree, at least) suitability for aviation service. The qualities
of one _may_ carry over to the other, but there are absolutely no
guarantees of that.

I happen to like auto conversions, because I think that they're
interesting and because I value resourcefulness. But I don't think
I'll be an early adopter. As soon as we see entire FWF auto conversion
packages that pass these tests (Detroit's or the FAA's), I'll sit up
and take notice.

Thanks, and best regards to all

Bob K.