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Thanks, Doug
Some good thoughts and insight from a guy who's been with a big OEM engine
maker.
However, Just remember while your Lycoming has not failed there are plenty
of Lycoming failures out there. What I think you should read into this is
had a lycoming lost 1/2 of its cylinders to foreign object damage would it have
done any better (or as good) as the rotary did? I agree that our poor
attempt at R&D can never remotely match that of OEM developers - on the
other hand, a lot of their development is for an engine with different operating
conditions which may or may not translate to good aircraft requirement
match.
I agree and have long stated that what is good for a Racing rotary is not
necessarily good for an aircraft usage - on the other hand it may not be bad
either. The racers do us a service in my opinion in that they generally
take an engine to its breaking point - you never know the limits until you
exceed them. While not all of their lessons are germane to our
needs, I for one appreciate getting some insight to where the "real" limits
are. I am not fond of exceeding the limits in aircraft usage - it ruins
seat cushions {:>).
I don't think your insights or views paint you as a "stick in the mud",
caution in this hobby is a life prolonging trait in my opinion - however, even
the big OEM engine developers show they can get it wrong - i.e. one example in
the news recently are the crankshaft failures that Lycoming is being sued
over. So I think it unrealistic to think we small guys will never have
"incidents" that we would rather not have.
Fortunately, I believe that we are reducing the likelihood of incidents by
such mediums as this list. Engines are always going to break - we just
want to get it down to the bear minimum and eliminate those approaches which
seem to hasten such incidents {:>)
It is not an area suited to everyone - perhaps not to most people.
While I don't think of myself and other rotary fliers as written in one national
flying magazine as "Hairy Chested Heroes of today's aviation", I do think you
have to have confidence in your ability and the knowledge to handle
such incidents. I don't mean press-on regardless, but to quickly
assess the situation and then make decisions that favor a good outcome.
Its a pucker factor when that old engine starts to rattle, but knowing the
engine is likely to stay together and continue to produce some power if you stay
with it can make a difference.
For the new guys, and to put the record straight, I have had three
incidents where I ended up forced to land at airport. Of the three, one
had to do with a fuel tube that separated from a fitting in the fuel tank, the
second one was when my muffler separated from my header and I deemed it prudent
to land, and the only one involving any part of the engine was this latest
incident. So must keep things in their proper perspective. Take
Tracy Crook over 1600 hours and never one forced landing to my knowledge.
Therefore, my conclusion is the engine is a keeper - no question in my mind or
else I would not be looking for replacement/alternative parts for a rotary - I
would be shopping for a used Lycoming.
Best Regards and thanks again for you comments and insight
Ed A
----- Original Message -----
Sent: Thursday, April 14, 2005 11:45
AM
Subject: [FlyRotary] Rx-8 Rotors
Hi Ed:
I hate to always appear to be the "stick in the mud" re: the wonderful
"great" ideas that some have to circumvent the $$millions that Mazda spent
over years of R&D.
The concept that creates the most anxiety for me re: my fellow EAA'rs is
the reliance on "racers" (Lynn in Columbus excepted) whose objective is
maximum HP for a very short period of time when our usage is continuous
moderate HP over a very extended time. The issues and
constraints are very different.
My research into OEM irrigation engines shows that they last from
25,000-30,000 hours TBO producing approximately 0.5 HP/cubic inch at 24"-26"
MAP. Most run just off WOT at 1,200 - 2500 rpm depending upon
size.....bigger slower, smaller higher rpms. I recall that I calculated
mean piston speed for several and that seems to be the key issue which
determines "specified" rpm. Even when one reduces the TBO by the
cube of the rpm which we desire to use to account for higher BMEP and
rotational forces (squared function), the TBO still comes out to in excess of
3,000 hours, if someone doesn't muck with the "complete"
system.
The point: OEMs have spent $$millions to insure these engines will
produce SPECIFIED HP under an unbelievable range of difficult
conditions. Why would one want to add any single element which would
negate that effort?? Make it produce more HP....of course, but all
durability expectations are Null and Void. Make it produce less HP for
longer....of course, but the price will be high and again, even though more $$
will have been spent, the expectations are a SWAG....and from my experience, a
very poor result is a high probability.
The 13BT will produce....what 250 HP as specified by
Mazda??? That means as designed, it will cool adequately, will function
over a large range of conditions at maximum efficiency at 250 HP. Why
would we be so arrogant as to suppose that we can improve upon that, and for
what reason?? Do not even guess,....that 13BT was run at WOT for
many hours at Maximum HP without failure.....and even worse was cycled back
and forth from max torque rpm WOT to max HP WOT, dumped to idle then back to
max HP, etc....on and on and on! There are hundreds, if not thousands of
combinations of the various components which over hundreds of thousands of
hours of R&D are continuously refined to successfully pass these
tests. I'm certainly not smart enough to know how to improve upon
that. Perhaps that is my issue?
If I'm not mistaken you have written a bit on this and have endeavored to
follow "change as little as possible of the major components" as one of your
guidelines. Remove the emission components? Seems OK! Change
the plug wires, perhaps? Change the waterpump when we run at less that
max "specified" rpm? That makes zero sense to me. Change the rotor
seals/materials/oil pump/waterpump/oil flow.......??, go ahead....but pain
hurts like ____, and my insurance rates go up when an EAA'r crashes and kills
themselves!
Pardon my passion in this, but too many "experimenters" are ruining the
possibility of success in the use of low-cost, high production, automotive
based engines in aircraft and it is a shame because there is no fundamental
reason that today's modern automotive engines won't perform admirably, IF
utilized properly. Work on the installation, not on the basic
engine. Installed in this manner, the accessories will be the issue, not
the powerplant.
IMO for your engine.....Best: buy some new rotors designed for your
housings. Next best: Buy three wreck engines with relatively low
mileage ($300/ea. around here) and measure and pick a rotor which meet Mazda
specifications. Last and probably best and least expensive in the long
run, go purchase an RX8 from a rear-end wreck and put it in, Stock
innards/major components.
Keep up the super work and communication. We are counting on you to
be successful. Your latest escapade really threw water on my excitement
re: my project. I had hoped you would process fuel like crazy for a
thousand hours while we watched your R&D/durability results from our
shops!!
Continued good luck and POR,
Doug in Colorado
In a message dated 4/14/05 8:35:12 AM Mountain Daylight Time,
eanderson@carolina.rr.com writes:
Hi Doug,
Some good thoughts and questions, of which I would like to know the
answers to as well. I believe the reason the experts are recommending
milling the RX-8 rotors for the older seals (when used in the older rotor
housings with peripheral exhausts) is that the RX-8 seal was not designed to
withstand the forces of crossing the exhaust port (in the Peripheral wall)
opening unsupported. Its rather skinny and long. Mazdatrix
reported the RX-8 seals warped as a consequence of the the hot exhaust gas
blowing over them and primarily the lack of wall support at the exhaust
opening(on the older housings). The combination of the additional heat
and lack of wall support appears to be more than the 8 seal can take.
However, I am in basic agreement with you why machine the rotor
when perhaps a new/modified seal is the answer. I want to check with
Tracy Crook since his seals are reportedly 800% stronger than stock apex
seals to see whether the seals could be machined down/created so that they
fit in the RX-8 rotor standard apex slot and still be strong enough -
say 300% stronger than stock {:>). Since they are not made of
typical "gray iron" alloy that the stock and most other seals are made and
chill/case hardened, they may be amenable to machining.
Yes, having airports scattered around in just about every county and
sometimes three or more in a county, the geography is much kinder to
engine-out excursions here on the east coast. Fly High, Glide
long! Better yet, keep running on both rotors.
Ed A
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