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Hi Mark,
I can understand being conservative –
particularly in a Lancair – dead sticking an RV into a field is one thing,
doing it with a Lancair is not something I would care to do.
Well, being an engineer then Gary can
pretty much see the advantages of the rotary – but, as I noted his claim of “more
parts on a rotor than a piston” needs to be seen in the context of a rotor
really being equivalent of three pistons – then the part difference is not what
it first appears.
Yes, my plans are to attend, hopefully
everything will work out and I’ll see you there again.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mark Steitle
Sent: Friday, April 10, 2009 10:39
AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re:
[Lancair_ES] Re: Rotary Engines
Thanks Ed. The Lancair bunch tend to be pretty conservative when
it comes to their choice of engines. They can think of a hundred reasons
why it is better to go with a certified engine, all of them based on the past
100 years. ;-)
Gary is a very sharp engineer, so I need to be careful what claims I
make because he will be checking to see if I'm embellishing the facts, not that
I would ever do that, mind you.
Are you planning on attending the Texas roundup in May? It would be good
to talk to you again. Bobby hopes to have his supercharged
RV-10 flying by then (dependent on Tracy
getting the mods finished to his EC-2). I plan to be there as will Dennis
H. and a number of others. It should be fun.
On Fri, Apr 10, 2009 at 9:29 AM, Ed Anderson <eanderson@carolina.rr.com>
wrote:
Good run down, Mark.
Gary does mention the numerous parts on the rotor
itself – and while each rotor does have a high part count, you have to consider that each rotor is the equivalent
of 3 pistons – so in that context the parts count is actually lower,
not higher – its very seldom you ever hear of any failure of rotor parts other
than the occasional apex seal – wear yes, failure – seldom.
plus I have never heard of a rotor coming through the block
{:>) So, good questions and good answers from you.
One saying does come to mind – from our good friend, Tracy
Crook. “…If you’re
asking if you should do it, you probably shouldn’t. If you should be doing it,
nobody can talk you out of it..”. For 90% of homebuilders,
its probably not appropriate.
Ed
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net]
On Behalf Of Mark Steitle
Sent: Friday, April 10, 2009 9:26
AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re:
[Lancair_ES] Re: Rotary Engines
Thanks
for adding a more technical tone to this discussion. Yes, I was not
accounting for all the misc pieces needed to make the rotary run, but then I
wasn't considering all the little pieces needed to make a conventional piston
engine run either. Of the pieces that normally fail and end up poking out
through the engine case, I think you'll agree that the rotary has significantly
fewer of those. In fact, I have never seen a rotary with a thrown
connecting rod. ;-)
Having a
liquid cooling system is a two-edged sword, but its not anything that
can't be overcome with good engineering. For coolant lines on my
installation I used aluminum tubing connected to the engine and
radiator via "Wiggins" couplings. I monitor coolant
pressure, coolant level, and coolant temperature. Of course, if I catch a
Canadian goose in the radiator, it will likely loose its ability to cool the
engine, but then you have the same risk with an air-cooled engine.
As for
the bsfc, do your numbers reflect the modern EFI systems, or
carbureted engines. Tracy Crook realized a significant improvement
in bsfc when he switched from carburetors to EFI. The new
"Renesis" rotary engine has a better bsfc due to the side
exhaust ports. Anyway, I prefer to consider it
in "dollars per air-mile". By the time you factor in the
cost savings for purchasing and maintaining a rotary engine over a
certified engine, and that the rotary runs happily (prefers) on 89 UL fuel
(half the cost of avgas), the cost per mile tips significantly in favor of
the rotary. (Reading
the recent post about the $2300.00 oil pan practically brought tears to my
eyes.) I guess its the German in me that caused me to seek
out something better, or different.
Ahhhh...
you mentioned the magic word, "turbo-charger". I built my
engine with the intention of turbo-charging as it was initially
turbo-charged in its former life. After much thought, I decided
to follow the KISS principle and go N/A. But there's a little
voice in my head that keeps whispering "turbo-charge". With the
rotary's high energy exhaust gasses, turbo's are a natural solution.
Yes they add weight, but not much more than my current exhaust system.
Stay tuned...
One thing
that I hadn't mentioned that could be considered a negative for the rotary engine
is that very few A&P's know anything about rotary engines. Heck, very
few auto mechanics know how to work on a rotary engine. But, if I'm there
with my repairman's certificate in hand, who needs an A&P? Also,
rotary parts are less plentiful if you get stuck in some hole-in-the-wall
town. But there is always UPS overnight.
Gary, thanks
again for your thoughtful post. I'm not trying to convert
anyone to a rotary engine, I only want to see it get a fair
shake.
P.S.
I've CC'd the Fly Rotary group as they need something to talk about (the list
has been rather quiet lately).
On Fri,
Apr 10, 2009 at 7:13 AM, Gary Casey <casey.gary@yahoo.com> wrote:
I'll certainly have to commend Mark on the great work
with the rotary engine. I agree with his comments on almost every count.
But...
You probably should count ALL the parts in and around
the engine to have a fair comparison. For example, the air-cooled
aircraft engine cooling system has essentially no moving parts, unless you
count the vernitherm. Yes, the 3-rotor engine has only 4 MAJOR moving
parts, but each rotor has about 50 components. While that's not
necessarily good or bad, it's not an inherently simple solution. It rejects
more heat to the coolant and more of that to the oil (rotors are oil-cooled),
making the cooling system larger and potentially more complex. And the
exhaust is hotter and contains more aggressive pressure pulses, which have to
be taken care of by some sort of muffling. The ideal muffler is probably
a turbocharger, which can work very well on account of the pressure pulses, but
it probably takes a special high-temperature turbo that can tolerate the up-to
2000 degree exhaust. The turbo adds weight and complexity, but perhaps
not more weight than an effective muffler. The fact that the engine is
inherently round and concentric with the output shaft is a good thing, but
probably more attractive for a wing-mounted engine than one in front of the
fuselage. The rotary engine almost requires a speed reduction unit to
make the power/weight come out favorable, and I was not impressed with the
design of the then-currently available units, although they seem to work okay
in practice. One big thing that bothered me is that the efficiency is
inherently lower than that of a good piston engine, partly because the
compression ratio is limited to less than about 9 and the surface-volume ratio
the combustion chamber is higher. This penalty is probably 5 to 10%.
All that being said, the big attraction to me was, as Mark said, the
rotary will rarely completely fail, even if the coolant is lost. The apex
seals might disintegrate and parts warp, but it will most likely continue to
produce power for some time, unlike a piston engine. A long time ago we
were testing many rotaries and occasionally we would see a loss in power.
When the engine was shut down it welded itself together even though it
was still producing power. And the very things that make it less efficient
contribute to the fact that it can tolerate a variety of fuels. And with
boosting it can be made to produce a lot of reliable power.
I seriously looked at 3 different approaches - a
standard aircraft engine, a direct-drive automotive piston engine, and a
rotary. The eventual deciding factors were that the automotive engine
came out heavy and the rotary engine burned more fuel. I really do like
the rotary, though.
From: Mark
Steitle <msteitle@gmail.com>
To: Lancair_ES@yahoogroups.com
Sent: Thursday, April 9, 2009 2:27:21
PM
Subject: Re: [Lancair_ES] Rotary
Engines
Since there were no other replies, I figured I would
give my 2-cents worth.
I have been flying a 3-rotor Lancair ES for almost 2
years now with a total of 110 hrs on the Hobbs.
While it hasn't been without some teething pains, all-in-all, it has been a
very positive experience and I would choose a rotary again if/when the
opportunity presents itself.
While I did the FWF myself, my installation and
the Mistral are both closely related. As an example, I could bolt a
Mistral intake and/or exhaust directly to my engine, and probably
interchange many parts with the Mistral 3-rotor. The Mistral folks have
taken much of the rotary engine technology, and refined and pakaged
it into a (soon to be) certified product.
My reasoning is based on my belief that the rotary is
inheretly a stronger engine (pistons are cast iron vs.
aluminum), with only 4 moving parts. If you read the
recent AOPA story about the Cessna 400 blowing an engine over Pennsylvania in the night, well, I had a
similar experience in a Cessna 152, only not at night. Like the chap in
the AOPA story, we too just barely made it to the nearest airport, with
oil pouring out from the cowl onto the runway. Since that incident, I have
been very leery of all conventional piston engines. Hence my
decision to go with a rotary.
Gross weight on my ES was 2060 lbs. I typically
climb out at 7000 - 7200 rpm (2400 - 2500 prop rpm), climbing at between
1000 fpm and 1300 fpm, burning 16 - 18 gph, 15 gph in regular cruise (6000
rpm) and around 10 -12 gph in economy cruise (5100 rpm). (Keep in
mind that the pistons (rotors) turn at 1/3 the speed of the crankshaft, so they
are only turning 1733 rpm in economy cruise.) I can run either 100LL
or mogas (w/o alcohol) without worry and can lean the mixture aggressively
without worry of hurting the engine (no exhaust valves to burn). I can
pull the throttle to idle whenever and not risk shock cooling
the engine. Being fuel-injected, it will start cold, hot, or
anywhere in between. What's not to love?
I mentioned some teething pains... those consisted of
an early cooling problem which was solved with an auxilary water-to-oil
exchanger and a cowl flap. I have also had a series of oil leaks, all
from the oil pan not being properly sealed. I finally pulled the pan,
cleaned and resealed it. Problem solved. The
toughest issue to resolve has been finding a muffler that could withstand the
pounding of the rotary's exhaust. I'm pretty sure that issue
has been resolved by switching to a DNA racing muffler, but I don't
have enough hours on it yet to state for certain.
Hopes this helps answer your question(s).
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