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Ok, Mark
I think I see one (or more) of my “events”
in your list. However, none actually required a forced landing – in other words,
I could have remained airborne should I have choose to do so. In fact, I did -
until a suitable and safe landing site was reached. Well, Ok, the lost rotor
really did beg for a landing as soon as safely feasible {:>)
Event 1:
I lost the apex seal in my worn high
compression rotors at 160 hours on the block from a complete rebuild of a
Japanese imported 1991 turbo core.
Probably most important decision during
the incident was:
- Immediately
turn for closest good air field when the engine started to act abnormal
- Recognizing
that the EGT on rotor 1 going to minimum indicated lack of useful
combustion in that rotor
- Realizing
that power (or lack thereof) was going to be an issue, I reached over and
turned up the manual fuel mixture to maximum rich – that move the fuel
flow from 7 gph up to over 14 gph. Needless to say a lot of expensive
fuel was not providing much power on the bad rotor. But, I managed to maintain
6400 MSL fully loaded with fuel and camping gear.
- After
landing, I found it took much more throttle to taxi up hill on one rotor.
After loosing the rotor on way to 2005 Sun
& Fun I landed at what turned out to be a derelict airport (FB0) had just
left and radios were being stolen from aircraft on the field. A county
investigator informed me after checking me out because I was “disassembling” my
aircraft to get the engine off to take home to repair.
Event 2:
Because (in part) of my concern for my
aircraft on said airfield, I hasten (too hastily it turns out) rebuild my
engine with new rotors. I had the engine buttoned up and turned it over – it was
indeed a bit harder to turn over than I recalled from previous rebuilds – but there
was no scraping sound and compression was good, so convinced myself just a damn
good tight rebuild! So reinstalled the engine. Even after it was running, I
noted that for the first hour - anytime I reduced the rpm below 2000 rpm the
engine would quite. (Did I fail to mention that I had plenty of warning from
the engine as well as from Bruce Turentine and Tracy Crook). But, after the
engine had “loosened up” a bit, it ran fine.
One the way to Charlie England’s
Mississippi Rotary fly in later that spring, I noticed my coolant pressure was
very slowly increasing – like about 1 psi each hour of flight. It started out
at around 10-12 and by the time I got to Charlie’s place it was up to 18 psi.
Well, I pretty much knew that I had a leak between coolant galleys and
combustion chamber. Flew on to Louisiana to visit Kin folks, upon departing
one week later, I got up to just about lift-off speed but the engine was
missing a bit. Nothing serious, power was good, but still….. I aborted the
take off. Had brake line failure, hydraulic fluid fire and went off the runway
into a ditch (fortunately slow speed and shallow ditch). Thanks to Laura and
Tracy Crook was able to rebuild the engine (without haste this time) during
which time I found that one of the small triangular end pieces of apex seals
was missing from the front rotor, instead there were two silver dollar size
blue spots on the iron side housings (that was also the vicinity where the TES
O rings had failed (due to the clear localized high temps). Apparently the
apex part fell into one of the milled lightening holes in the side of the rotor
– if it had not fallen into the hole which provided just enough clearance for
the engine to rotate – I am certain I would not have been able to rotate the
assembly by hand or starter.
So in this case, no forced landing – never
got airborne. Then there was the 12 mile engine-out glide – but that had
nothing to do with the engine and everything to do with the pilot, so I won’t
go there {:>)
So here is some meat for your project
{:>)
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mark Steitle
Sent: Sunday, April 12, 2009 7:45 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Gary
Casey was [FlyRotary] Re: Rotary Engines
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).
----- 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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