> > True, nobody really knows the ultimate limit for continuous power but
the
> > phenomenon I described has been demonstrated well beyond the point of
> > "myth". Do you really mean that what water does or doesn't do
temperature
> > wise is not a factor? A bold statement in a water cooled engine.
>
> As you can see from the Continental chart the temp at the hottest spot
> in the combustion chamber was not reduced by dropping the coolant temp
> from 290F to 250F.
>
> > The "oil
> > coking" was not a factor in what I was describing but it may be an
> > > indicator.
> >
> > I have determined experimentally at what point nucleate boiling begins
in
> > the 13B on my plane (about 165 HP continuous). What I don't know is
how
> > much higher it will go before nucleate boiling can no longer handle the
heat
> > flux. Auto applications (even racing) don't duplicate the aircraft
> > environment because if the engine is throttled back even momentarily
(like
> > for corners) the heat flux is reduced long enough for nucleate boiling
to
> > re-establish and bring CC wall temp back under control.
> >
> > Jusy my opinion, FWIW.
> >
> > Tracy Crook
> > tcrook@rotaryaviation.com
> > www.rotaryaviation.com
>
> How do you know you had nucleate boiling and where it began?
> In other words how did you separate this phenomena from all
> the other variables? Nucleate boiling is a local phenomena.
> The tiny bubbles are carried off by the main flow and
> dissipate.
>
> I am still waiting to see some real temperature numbers. I
> would also like to see a melted rotor housing or one that showed
> any kind of failure between the steel liner and the aluminum.
> We have plenty of rotor housings that have been severely
> over heated and NONE show failures in this area.
>
> Cracks have been known around the spark plug holes but
> that could be caused by a high temp gradient. In other words
> TOO MUCH cooling on the back side of the combustion chamber
> wall. Just about all one rotor NSU Spyder engines cracked
> around the spark plug holes. Mazda themselves removed metal
> from around the spark plugs on the late turbo rotor
> housing by a simple single cut of the mill on both sides.
>
> Until I see some failed rotor housings or some real world
> temperatures exceeding 500 F at the junction between steel
> and aluminum I am still going to consider this a myth.
> Even if the temp exceeds 500 F in this area does not
> mean the rotor housing will necessarily fail to function
> normally. Aluminum does not melt until about 1100 degrees.
>
> The signs of combustion chamber wall failure in air cooled
> aircraft engines is a pock marking or cratering of the surface.
> In WW II B29 engines that showed this effect in the exhaust port
> where automatically changed out. Jeff Auckland and I had a long
> talk about this when he was using a Chev big block engine in the Legend.
> He saw the same phenomena in the Chev combustion chambers.
>
> Paul Lamar
-billdunn wrote:
This is all very, very interesting but empirically I have heard the
sustained high HP climbouts can lead to overheating and boiloff of coolant,
perhaps due to exaggerated nucleate boiling ?
It seems some physical phenmenon is at work otherwise boiloff would not
occur,,,no ? Cars don't see those sustained loads that a climbing aircraft
does.
Very interesting
bd-
I think what you are seeing is a cooling system not up to the job.
Has nothing to do with the rotary per se. You would see the
same problems with a liquid cooled piston engine with an equally
inadequate cooling system. If you don't cool the coolant it
is going to boil. Extra is having problems cooling the liquid
cooled Continental Voyager engine in the 400. So is Cool Jugs
with their prototype Cherokee. It is not easy designing a
liquid cooling system for an aircraft.
Paul Lamar
I have driven my RX7 at 6000 rpm in second gear for twenty minutes
without overheating and without any damage as far as I can tell.
This was to simulate aircraft use. Of course it was not generating
200 hp so I don't know if this test counts. I do think the rotary
should be able to operate at the rpm levels that we are talking about
without problem. I don't recall a warning in my owner's manual
prohibiting sustained operation at any level below red line. Also,
while racers don't stay on the throttle all the time, I think that
most of the time the engines stay above the 6000 rpm level with
frequent trips to the 9000/10,000 rpm range. It seems to me this
would generate more heat than an engine running a sustained 6000.
Just guessing. Another guess is that cheek rads become less
efficient as speeds increase because of higher pressure building up
behind the rads. That would put a limitation on sustained high speed
cruising! Lots of cooling air available at 200 mph, if we can figure
a way to use it. Jerry
Tailwind & Rotary Engine Support
http://www.j-winddesigns.com
mailto:j-winddesigns@thegrid.net
This does not simulate aircraft use. Any engine can run at
6000 RPM and be generating little or no HP. What matters is
both RPM and the load on the engine.
HP required is proportional to the cube of top speed while cooling
air flow only increases with the square of speed. That is the
fundamental problem cooling an aircraft engine running flat out.
That is also why we offer an Everett Hatch Memorial Fund $500
prize to the first NA 13B averaging over 200 MPH in a sanctioned
cross country race of at least 100 miles. If your cooling system
works well enough for this I would consider the problem solved.
Tracy claims his RV4 goes 214 MPH which should be sufficient.
However he has declined in the past to enter the annual Sun 100 race
at Sun & Fun in April. :) How about this year Tracy?
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2002 All world wide rights reserved.