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Rusty,
Consider the following.
If you had a 'supercharger' (belt driven) instead of a turbocharger, you
would agree that the supercharger is sucking power from the engine to do it's
job. Friend of mine has one, and estimates that it takes about 30
horsepower to run the supercharger. If you were driving this supercharger
, and keeping the manifold pressure to 30", then you would be getting *less*
power from the engine-supercharger combination than a NA engine.
The same may be happening with your turbocharger. It is sucking power
by increasing exhaust backpressure, but you are restricting the manifold
pressure that needs to be higher in order to generate more power. You have to
generate your net power *plus* the work the TC is doing.
Does this make any sense to you?
Bill Schertz
KIS Cruiser # 4045
----- Original Message ----- From: Russell Duffy Sent: 9/15/2003 9:36:44 AM To: flyrotary@lancaironline.net Subject: [FlyRotary] Re: Good news, Bad news
1. The BUC is draggy, even worse than
we thought (but doesn't really explain the lousy climb rate)
This is a given, and the new cowl is being mentally
designed as I type.
2. The Warp Drive prop is never going
to be an optimum high speed stick. (but hell, you're not even to moderate
speed yet) My gut feel is that you should be running at least 17 degrees
at tip. Anything less than 16 is a waste of time unless you are resigned
to flying a draggy RV-3 which I'm sure you are not. This is assuming about
a 68 - 69" prop length.
Your gut feeling is pretty accurate. Warp
originally estimated that I'd need 18 degree (3 blade, 68") for a 200 HP
engine. I just got off the phone with them, and they're going to be
calling back later today with some real numbers. Off the top of his head,
he said these sound a whole lot like what the gyro guys get with their 120
HP Subaru's. Sadly, that's about what I expected to hear, but I
guess the good news is that I may have identified the largest issue.
The turbo's really becoming more trouble than it's worth (Tracy, this is
where you say "I told you so").
3. Your CG is near the fwd. limit which
generates a LOT of trim drag.
4. You may be underestimating the
effect of gearleg & wheel fairings (I think you mentioned you don't
have them yet) I found that I could not make ANY final decisions on
airframe/engine performance, prop pitch or even cooling until these were in
place.
On the RV-8, the gear fairings and pants made about 12 kts
difference at cruise speed, but didn't change climb performance that I
could tell.
Turbo stuff:
I have no turbo experience but my best guess is
that the air temp sensor should be up-wind of the turbo. Let the MAP table
programming take care of the temp rise due to adabiatic (Sp?) heating from the
turbo. This should work at low levels of boost like you are running
and will eliminate the big mixture difference between A & B
controllers. With this setup in a worst case scenario, the mixture might
go too rich at high boost, a much better thing than too lean.
I'll have to think about this some. You're correct that it
would be the safer way to go. On the 3rd gen, the temp sensor is in the
intake manifold, which is a large chunk of aluminum. Unfortunately,
the sensor isn't well isolated from the heat of the manifold itself, so it tends
to read the heat of the manifold almost as much as the air that passes through
it. One almost certain way to blow up an engine is to drive
your car for a while in the winter, then park it for a few minutes.
By the time you get back in, the temp sensor is reading some really high, heat
soaked temp, and will continue doing so for about the first 10 minutes of
driving. The air getting to the engine is freezing cold, so when
you jump on the throttle, you get fuel to go with 150 degrees, but have 30
degree air. Boost + lean mixture = new apex seals, and maybe new
turbos.
Thanks,
Rusty
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