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Mark,
I think this is a valuable tool - thanks for
doing it. Not sure I can add anything to your list since you arent naming names.
:-) Although I think that may result in some repeats on your
list.
Of course the other part of this still
missing is flight hours and thats going to be hard to accumulate. Documenting
problems and trying to determine MTBF without knowing how many hours are
flown is obviously a problem.
You've already established a pretty
significant list of issues. My guess is that as a group the rotary crowd
probably spends more time tinkering and tweaking than flying compared with our
LyCont counterparts. Al least initially. Which would make the stats look
even worse. Just a guess.
Mike Wills
RV-4 N144MW
----- Original Message -----
Sent: Sunday, April 12, 2009 9:30
AM
Subject: [FlyRotary] Re: Gary Casey was
[FlyRotary] Re: Rotary Engines
Al & Tracy,
Thanks for providing the additional
history for my files. I have started a spreadsheet of incidents which I
will be happy to share at the Texas Rotary Fly-In on May 29-31. The list
has grown to 14. If anyone has any "incidents" to share, please contact
me off-list and I will add them to my spreadsheet. To put everyone's
mind at rest, I am not listing names or tail numbers. They don't have to
be catastrophic failures, only something (related to the engine install) which
could have seriously affected the safe outcome of the flight. Please
provide date, description of incident, type a/c, and a description of what
went wrong.
Just to make it perfectly clear, I'm not doing this to
scare anyone, or point fingers, only to help us to learn from others mistakes
and learn how to build safer rotary-powered aircraft.
Thanks,
Mark
On Sun, Apr 12, 2009 at 9:19 AM, Tracy Crook <tracy@rotaryaviation.com>
wrote:
Good
list idea Mark. I'll add my 2 to the list.
1. Carb
overheat (boiled fuel out of bowl) due to radiated heat from nearby
exhaust pipe. (added heat shield to fix) I was in process of emergency
landing but was able to restart engine so no actual forced landing.
2. Loss of coolant due to coolant cap malfunction. (the
cap fitting had been modified so my fault again.)
Tracy
On Sun, Apr 12, 2009 at 7:45 AM, Mark Steitle <msteitle@gmail.com> wrote:
Mike,
Has anyone ever tried to document the rotary incidents resulting
in a forced landing?
Here's what I recall from memory, so it likely
is missing a few;
3 forced landings due to
ruptured oil coolers
1 forced landing due to apex
seal coming out of its slot (rotor out of spec)
1
forced landing due to improper assembly of engine (seal wedged between
rotor & side housing)
1 forced landing on
highway due to catastrophic overheating of engine
2
forced landings (one fatal) due to probable fuel system design flaw
1 forced landing on highway due to ingestion of
FOD.
There were a few others, such as turbo failures which
allowed for continued operation at reduced power, so we may or may not
wish to include those here.
While a number of these
incidents date back quite a few years, and we have made excellent
progress, it says to me that we still have room for improvement in the
peripheral department. The good news is that out of all of the
incidents listed above, none of them were caused by a true engine
failure. That's where the rotary has really earned my respect as a
viable a/c engine.
Pay attention to the details!
Mark S.
On Sat, Apr 11, 2009 at 9:22 PM, Mike Wills <rv-4mike@cox.net> wrote:
This has been an interesting thread. In the
end, it doesnt really matter how many "major" parts you have - even a
minor failure can bring you down. While I believe the basic rotary
engine itself is more fault tolerant than a recip, the peripherals used
in the typical rotary install are a lot more complex than a typical
recip install. Since we rotary fliers dont have the benefit of 70 years
worth of experience flying behind the typical LyCon farm implement I
think overall our odds are considerably worse. Comes down to how well an
individual engineer's his installation and there is a tremendous amount
of variation here.
The dependence on electronics in the
typical rotary install is a good example. I may be a
little sensitive to this issue since I've been trying to find an
intermittent glitch (2 times in 22 hours of engine
testing).
Mike Wills
RV-4 N144MW
-----
Original Message -----
Sent:
Saturday, April 11, 2009 7:31 AM
Subject:
[FlyRotary] Gary Casey was [FlyRotary] Re: Rotary Engines
Good analysis
and logic, Gary.
You’d make a
good addition to the “rotary community”. I have noticed over the
10 years I have been flying my rotary powered RV-6A that the problems
have decreased considerably, the success rate and completion rate has
gone up and first flights are now occurring without significant
problems – even cooling is OK {:>). I believe most of this
improvement can be attributed to folks sharing their knowledge,
problems and solutions with others - such as on this list.
I know that
fewer parts count is often touted as one of the rotary benefit – and
while it is true that the part count is lower, the most significant
thing (in my opinion) is not only does the lower part count help
reliability (if it is not there – it can not break), but if you look a
the design of the eccentric shaft (for example) you notice the absence
of the jogs in a typical crankshaft and their stress points. The
thing is over 3” in diameter at some points and does not have the same
inertia loads born by a piston crankshaft. The parts that are
there are of very robust design. Finally, the rotary is (I
believe) more tolerant of damage and tends to fail “gradually and
gracefully”, it can take a licking and keep on ticking as the old
saying goes. Only extended time and numbers will provide the
true MTBF for the rotary, but I believe it looks very
promising.
Failure of
rotary engines are extremely rare, but unfortunately, as with many
alternative engine installations, auxiliary subsystems such as fuel
and ignition frequently being one-off designs have been the cause of
most failures – with probably fuel the prime culprit. The good
news is that for some platforms (such as the RVs) we have pretty much
established what will make an installation successful. The
Canard crowd is fast approaching that status with their somewhat more
challenging cooling requirements being over come.
Having
lost a rotor during flight due to putting in high compression rotors
with worn apex seal slots worn beyond specs (found this out later – my
fault for not being aware of this spec limit and checking it) which
led to apex seal failure and consequence lost of most of the power
from one rotor, I was still able to maintain 6500 MSL at WOT and fuel
mixture knob to full rich – flowing 14.5 GPH – a lot of it undoubtedly
being blown through the disabled rotor. Flew it back 60
miles to a suitable runway and made a non-eventful
landing. There was a small increase in vibration due to
the power strokes no longer being balanced, but nothing bad and you
could still read the needles on the gauges. Other folks have had
FOD damage to a rotor and also make it to a safe landing. Two
folks lost cooling (one loss of coolant fluid , one lost of water
pump) and while they did cook the engines, both made it back to a safe
landing. So all things considered, I think the rotary continues
to show that if the installation is designed properly, it makes a very
viable and reliable aircraft power plant.
Failure of
rotary engines in aircraft are extremely rare, but unfortunately, as
with many alternative engine installations, auxiliary subsystems such
as fuel and ignition frequently being one-off designs - have been the
cause of most failures. The good news is that for some platforms
(such as the RVs) we have pretty much established what will make an
installation successful. The Canard crowd is fast approaching
that status with their somewhat more challenging cooling requirements
being over come.
My rotary
installation cost me $6500 back in 1996, the primary cost being a
rebuilt engine $2000 and the PSRU $2900. I have since purchased
a 1991 turbo block engine from Japan for $900 and rebuilt it myself
for another $2200. My radiators (GM evaporator cores) cost $5.00
from the junk yard and another $50.00 each for having the bungs welded
on. So depending on how much you buy and how much you build the
price can vary considerably. Today, I would say it would take a
minimum of around $8000 and more nominally around $10000 for a
complete rotary installation in an RV – some folks could do it for
less, some for more.
But,
regardless of the technical merit (or not) in someone’s mind, the
crucial thing (in my opinion) is you need to address two personal
factors:
1. What
is your risk tolerance? It doesn’t really matter how sexy some
“exotic” engine installation may seem – if you are not comfortable
flying behind (or in front) of it, then it certainly does not
makes sense to go that route. After all, this is supposed
to have an element of fun and enjoyment to it.
2. What
is your knowledge, experience and background (and you don’t have to be
an engineer) and do you feel comfortable with the level of involvement
needed.
So hope you
continue to contribute to expanding our knowledge and understanding of
the rotary in its application to power plant for
aircraft.
Best
Regards
Ed
From:
Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Gary
Casey
Sent: Saturday,
April 11, 2009 8:36 AM
To: Rotary motors in
aircraft
Subject:
[FlyRotary] Re: Rotary Engines
Just to add a few more comments and answers to
the several excellent comments posted:
How many parts does it take to make a rotary
rotate? Well, "parts aren't parts" in this case. Mark was
right in that there are maybe 4 "major" components, but you have to
define major. A piston engine certainly has far more major
parts. Is a valve a "major" part? I think so. Is a
rotor corner button a major part? Not sure, but probably not.
Is each planet gear in the PSRU a major part? I say yes,
and the PSRU is an integral part of the rotary engine. As
someone correctly pointed out, it's not how many parts, but the
reliability of the total system that counts. Just looking at the
history of the rotary (which, from the implication of another post)
it's not that good, but I don't think it has anything to do with
reliability of the concept. It's more to do with the
experimental nature of the builds and installations. My original
point, perhaps not well expressed is that to say there are just 4
parts is an oversimplification. But let's face it, to put in an
engine that has had many thousands of identical predecessors is less
"experimental" than one that hasn't..
Are we ES drivers more conservative?
Probably so, since the ES is probably one of the experimentals
most similar to production aircraft, and not just because the Columbia
(can't force myself to say Cezzna :-) was a derivative.
Therefore, it tends to attract conservative builders and owners.
Not surprising then that almost all ES's have traditional
powerplants, with the most excellent exception of Mark. While
there may be more, I know of only two off-airport landings caused by
engine failures in the ES in almost 20 years of experience. One
was caused by fuel starvation right after takeoff (fatal) and one was
caused by a PSRU failure in an auto engine conversion. So our
old-fashioned conservative nature has served us pretty
well.
Yes, I was assuming that the rotary had
electronic fuel injection and ignition, but that by itself doesn't
change the inherent fuel efficiency of the engine. Direct
injection does have a potential to improve BSFC because the fuel
charge can be stratified. It will probably decrease available
power, though. I think the best rotary will be 5% less efficient
than the "best" piston engine(same refinements added to each).
But I stated that as a simple disadvantage - as Mark pointed
out, it isn't that simple. The rotary already comes configured
to run on auto gas. The piston engine can also be so configured,
but the compression ratio reduction would reduce its BSFC and maybe
durability advantage. The total operating cost is certainly
significantly less if auto gas can always be used to refuel. I
assumed in my assessment that it will only be available 50% of the
time. The real disadvantage, which I failed to state, is that
the extra fuel required for a given mission might be 5 or 10% higher
and that negated the weight advantage, if only for long-range
flights.
Is the engine less expensive? I did a
thorough analysis of a direct-drive recip auto engine installation and
my conclusion was that if the auto engine were equivalent in
reliability to the aircraft engine it would likely cost just as much.
Is the same true of the rotary? I'm not sure, but you have
to consider the total cost, including engineering of all the parts in
the system, not just the core engine. I would love to do a
rotary installation, but I don't think I could justify it by cost
reduction.
It wasn't mentioned in the posts, but some
have claimed the rotary is "smoother" than a recip. I at first
resisted that notion. Sure, any rotary given sufficient
counterbalancing, is perfectly balanced. A 4-cylinder opposed
recip is not - there is a significant secondary couple. The
6-cylinder opposed engine is perfectly balanced, but only for PRIMARY
and SECONDARY forces and couples - higher order forces have never
really been analyzed, although they would be very small. And
then consider the forces within the engine that have to be resisted by
that long, heavy, but flexible crankshaft. So it isn't the
mechanical balance that gives the rotary an advantage. Let's
take a look at the the torsional pulsations, comparing the 3-rotor
against the 6-cylinder: A 6-cylinder engine has 3 power impulses
per rotation, as does the 3-rotor, so they are the same, right?
Wrong. They both incorporate 4 "stroke" cycles, meaning
that there separate and sequential intake, compression, power and
exhaust events so that is the same for both. The power event,
which is the source of the torque impulse, takes 1/2 of a crank
rotation for the recip. In the rotary the power event requires
1/4 of a ROTOR rotation, but the rotor rotates at 1/3 crank rotation -
the result is that the power impulse lasts 3/4 of a CRANK rotation,
50% longer than in a recip. Therefore, the torsional excitation
delivered to the propeller, PSRU and to the airframe is significantly
less than for a recip. And if you analyze the actual forces
imparted, they go down by the square of the rpm. The torsional
vibration amplitude goes down by a factor of 4 just because the rpm of
the rotary turns about twice as fast. If you've skipped to the
bottom of the paragraph, as you probably should have :-), yes the
rotary is "smoother" - a LOT smoother.. (my apologies to rotary
purists, for simplicity I used the word "crankshaft" for both
engines)
But just because you can burn auto gas should
you? The biggest problems with auto gas in recip aircraft have
nothing to do with the engine, but with the high vapor pressure of the
fuel - it is more prone to vapor lock. The fuel systems of
certified aircraft are not particularly well designed with regard to
vapor lock. "Fortunately", rotary engines typically have no
mechanical fuel pump and are forced to rely on electric pumps.
Fortunately because the pumps can be located at the very bottom
of the aircraft and close to the fuel tanks, making vapor lock much
less likely. I would caution any builders to consider vapor lock
possibilities very seriously, much more so if you intend to run auto
gas. when I was going to do this I planned to put one electric
pump in the wing root of each wing, feeding the engine directly(the
check valve in the non-running pump prevents back-feeding).
Redundancy was by a "crossfeed" line that could connect the
tanks together.
And thanks, Mark for - probably incorrectly -
referring to me as a "good engineer". I'll have to put that in
my resume!
(do you allow us outsiders in your events?
I'll park well away :-)
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