X-Mozilla-Keys:
Jeff Spitzer wrote:
Ken Powell wrote:
Help!
I don't understand the theory behind this. Do you size the turbo for
a max boost (say 6 lbs) at sea level?
Yes, that is the theory. As I have never actually done this before I'll
have to see how well it works in reality. It is not a new idea and has
been done before by others.
Does this mean that you cannot
overboost the engine?
No. The boost will always be a function of RPM when using no wastegate.
If you have a variable pitch prop and overspeed the engine you will also
overboost.
What kind of boost will you get at 15,000 ft
(does the boost drop with air density)?
The "boost" should increase with altitude in order to maintain approx. the
same MAP. That's the whole idea of "turbo-normalize". The exact result
will be a function of turbo and engine details that are yet to be worked out.
How much boost is 'safe' for
a rotary if running an intercooler? What is the recommended timing?
Is a timing retard device necessary? Do you have to run a richer
mixture at cruise to promote cooling? What else do I not know?
For these questions I refer you to the Paul Yaw posts.
Paul lamar wrote:
I personally am going to try for the maximum boost I can get at sea
level with a TO-4 turbo charger at 6200 e-shaft RPM and then limit
the throttle opening to about 230 HP or so for longetivity.
I will monitor things like turbo RPM, intake manifold temperature
and turbine inlet temperature to insure the engine does not;
A:detonate
B: the turbo does not overspeed or
C: the turbine wheel does not melt.
I don't think you want to go for "max boost at S.L." as you say, Paul.
That will make the turbine housing too small. The result will be overspeed
at altitude and too much back pressure. If you design for max boost at
S.L. the turbo will try to add boost at altitude which you restrict with
the throttle. Even if you maintain the MAP you want the pressure upstream
of the throttle may be too high (for the turbo) and the overall efficiency
will be poor.
I think we all sorta want the same thing. That is
sufficient boost at S.L. for 200+ hp, flat rated to about 10,000 ft, and
try to avoid the wastegate. We should all be running pretty much the same
turbo then. OTOH, your request for high altitude operation will require a
bigger turbo which will reduce your boost at S.L. Just seat of the pants,
I don't think you can go to 30K with no wastegate and get any substantial
boost at S.L. So, take your pick...reduce your altitude, reduce your S.L.
boost, or add a wastegate.
On a related but off topic note: Didya see in Sport Av the article about
the Pushy Galore guy wanting to take his Exxon Rocket (or whatever he calls
it) to 60K. This guy has no chance and no clue. There is no way in hell
he'll ever cool the IO-540 at that altitude. He thinks he can just pour in
nitrous for oxidizer and he's home free. He's got A LOT to learn about
thin air. The article also mis-states that the piston record remains
unbroken. We've broken it and so has Aurora with the Perseus drone. There
just weren't any "officials" around to certify it. I guess NASA Dryden
tracking radar doesn't count.
Jeff Spitzer
Thanks for your comments on this Jeff. I stopped off at Turbonetics
this morning but did not get to talk to Bob Keller the aviation guru
and president of Turbo N. I did glean some useful information however.
The guy I talked to was Bill Boro General manager.
The good news is Inconel turbines are almost no extra cost.
The maximum turbine inlet temperature for Inconel is 1850 F
instead of 1700 F for GM-R. They do have
some trick new material called MAR M. A turbine wheel made of this
2200 degree F material is $1500. The other good news is Turbonetics is
in the process of coming out with a turbo tachometer so we can monitor
the turbine RPM at high altitudes.
They are pushing their ceramic ball bearings made from silcon nitride.
Even though only one bearing out of the two required is ceramic they
are still claiming a longer life for the turbo. The ceramic bearings
are ABEC-9 and made by Barden in Germany. Bill gave me a couple
of SAE papers on why there is only one ceramic ball bearing used.
SAE 942530 and 962500 in case you are interested in the tech
details. Ceramic BB's are $400 extra and my gut is they are not
worth it for aviation use.
They also have water cooled bearing housing which is what I am going to
opt for. No extra cost. They recommend synthetic oil for the turbo.
The ash remains in suspension and does not coke out on the bearing
surfaces or shafts. Mobil 1 is fine.
I picked up the latest catalog.
They are a little behind in computer tech so no email yet but they
are working on it.
BTW Bill recommended Sperco... George Spears (818) 901 7851 for info
on intercoolers he is in Panarama City so I will drop by there
and see what I can find out.
I got a tour through the factory and experimental NC Machine shop.
They are a small company so our orders are welcome.
I suggested a rotary as a good test engine because of the extra
heat in the exhaust.
We might contact them on machining that SS exhaust manifold.
They may offer it to others which would lower our cost.
As soon as you get it finished I will show them copies
of the drawings with your permission.
Paul Lamar
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