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Bob, I presume you are using a 2.85:1 PSRU to get 6600 with your 68x78 prop which would give you approx 2300 prop rpm. I flew with a 68x72 and a static of 5600 would give me a prop rpm of 2580. At 7000 rpm your prop would be swinging at 2456 rpm. My point is that assuming your are using the 2.85 then I agree with your assessment, you are a bit "under propped", if you are using a 2.17:1 then I want to know your secret {:>).
I found that with a 2.85 gear box and going to a 74x88 prop, the take off and climb out performance improved tremendously over using the 2.17 and my 68x72 prop.
Also if my old 68x72 would turn 2580 at 5600 engine rpm and yours 2456 at 7000 rpm then I think you will find that your fuel burn is going to be a bit higher for the same prop rpm.
Ed
----- Original Message ----- From: "Bob White" <rlwhite@comcast.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, April 28, 2006 9:24 PM
Subject: [FlyRotary] Engine Run and Static RPM Report
I've been trying to finish up all the little nitpicking details and a
few big details so I haven't ran my engine for quite a while. I made
up my mind to get some time on it today. The weather was a bit nasty
today with the winds kicking up to 20-30 kts (it wasn't that bad when I
started). I fired it up, and the first problem showed up - No
charging. The new alternator mount from Pineapple racing is power
coated and insulating the alternator from the block. I rigged up a
jumper to fix that problem, and started the engine again. All was
well. After taxiing around for 1/2 hour or so, I hit 4 hours run
time. Bruce T.'s break in instructions was to run the engine 5 hours
below 4500, but I couldn't stand the suspense any longer. I really
wanted to find out what my static RPM was. So, I stopped it heading
into the wind and gave it full throttle. I saw 6400 RPM and backed off.
The mixture was going a little lean, so I turned up the mixture and got
6600 RPM. Max manifold pressure was a little over 23. (Don't forget
that I'm at 6000 ft.) That's a little over the 6000 RPM limit Bruce has
for the 5 to 15 hour segment, but his regime seems quite a bit more
conservative that some of the other break-in schemes I've heard on
here. :) With this prop, I suspect I could exceed my RPM redline of
7500. If everything is looking OK, I may increase that to 7700.
It seems like I'm a little under propped. This prop is 68 in. dia, with
a 78 in. pitch.
I also found out that a little air flowing over the rads is a good
thing. As I mentioned earlier, the wind was kicking up to about 30
knots toward the end. While taxiing downwind, the water temp started
climbing above 200 F. I shut the engine down, got out and pushed the
plane around into the wind. After starting the engine back up, the
temps dropped down to 160F.
Now the next big question is how badly will my new cowling and cooling
plenum screw up the cooling. I'm only about 1/2 done with the cowling
mods and getting ready to jump back into some more fiberglass work.
Apparently according to the checklist my DAR sent, I need to do a high
speed taxi test. I'm not going to do that until I think the plane is
airworthy, even if I don't have the paperwork!!
Bob W.
-- http://www.bob-white.com
N93BD - Rotary Powered BD-4 (first engine start 1/7/06)
Custom Cables for your rotary installation -
http://www.roblinphoto.com/shop/
--
Homepage: http://www.flyrotary.com/
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