Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

MAGNUM VIDEOS

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Old 01-23-2006, 12:17 AM
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cobratraxxas69
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Default MAGNUM VIDEOS

Hi guys,

Here are some videos shot this past weekend, I was running a 8x9 prop:


http://www.resume-connection.com/Pas...estLanding.mpg

http://www.resume-connection.com/Pas...BackGround.mpg

http://www.resume-connection.com/MagnumDay2Montage.mpg


Here's a video running a 8x10 prop:

http://www.resume-connection.com/Pass8x10Prop.mpg


BTW, I was only turning max 17400 RPMs on the ground with the 8x9 and 8x10 (nowhere close to the 20000 RPM others have reportedly turned with the West .50)


-Mike
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Old 01-23-2006, 12:37 AM
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Default RE: MAGNUM VIDEOS

Have you shortened your header yet? You need to cut it back to get better RPM's with the steeper pitched props. Also, how many runs does it have, it takes about 20 or 25 to really start to come alive. I can get better than 21,000 with an 8x8 no problem, I find the 8x8 to be the best prop I've found on this engine at my previous altitude of 3000' asl. Now that I'm closer to sea level I haven't had an airframe to run it on.
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Old 01-23-2006, 01:01 AM
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Default RE: MAGNUM VIDEOS

Thanks for the reply Jeremy,

I personally haven't modified the header yet. I read from a previous posting that you could leave it the original size with a 8x10.


9x7 prop use normal pipe lengths.
8x8 prop cut half inch off header and half inch off pipe.
8x9 and 8x10 use original pipe lengths.
I bought the plane from RCU, so I'm not sure if the header has already been cut. How long is the tuned pipe/header combo supposed to be? Between what 2 points is it measured (very tip of exhaust to midway through engine seems like a reasonable way)

After I leaned out the motor a bit, I heard it "surging" at full throttle when flying. It sounded like someone was playing with the throttle (moving it up or down slightly). Also, when I went from idle to full throttle quickly, the motor would die. Not sure what was happening, as tuning is not my forte

Thanks,

-Mike
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Old 01-23-2006, 02:02 AM
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Default RE: MAGNUM VIDEOS

I might have it backwards on the shortening for steeper props now, haven't had to do that for a long time. I just always had teh best luck and fastest speeds with the 8x8, not to say that's the best prop, but it's what has always worked well for me

If I remember I can measure my pipe/header length tomorrow at the shop.
Jeremy
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Old 01-23-2006, 07:59 AM
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Default RE: MAGNUM VIDEOS

Weston recommend cutting 1" of off for running 8x8, leave it as is for 8x9 and 8x10. I run an 8x10, and its ballisitc, definitely the best prop I've had for outright speed, but maybe a bit trickier to tune (more sensitive on the needle). Trick is not to run too lean on the ground, as when it unloads in the air, it leans out a bit more (must be volume of air being forced into the carb at 180mph+)!
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Old 01-23-2006, 12:05 PM
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Default RE: MAGNUM VIDEOS

I'm still wondering why I'm giving up 3000 RPMs


I hadn't touched the tuned pipe/header and I thought I was running as lean as I could make it (and then backed off a few clicks).
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Old 01-23-2006, 12:33 PM
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Default RE: MAGNUM VIDEOS

A 9-6 or 8-8 might turn that fast on the ground, but I am not sure that the 8-10 will, but it will sure unload in the air. Has anyone else reported 20k static on an 8-10? Mine does a bit over 20k static on a 9-6, but I would not expect that on the 8-10. Could be wrong.

Re pipe/header, Weston's recommendations to me were: 8x10 - stock length, 8x9 - maybe 1/2" off, 8x8 - 1" off.

They said their best speeds are with the 8-10 but launches are trickier, which is logical as that prop would likely be cavitating like a son-of-a-gun off the launch.

I can measure mine tonight if I remember so you can compare lengths to see if yours has been altered or is stock.

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Old 01-23-2006, 02:03 PM
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Default RE: MAGNUM VIDEOS

Great thanks!
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Old 01-24-2006, 11:48 AM
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Default RE: MAGNUM VIDEOS

Here's what I measured. Bear in mind I did not remove the silicone coupler but did my best to ID the junction underheath. If I am off, the sum of these two measurements will still be accurate, but one might be a hair more and the other a hair less.

Exhaust centerline to end of header - 2-1/2"

Front of pipe to high point of pipe (the first and largest "ridge" on pipe heading from front to back) - 8-15/16"

So, exhaust centerline to pipe high point should measure about 11-7/16" on a stock pipe/header.

MJD
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Old 01-24-2006, 01:05 PM
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Default RE: MAGNUM VIDEOS

ct69: where is that awesome location you are flying at?
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Old 01-24-2006, 01:16 PM
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Default RE: MAGNUM VIDEOS

Hi MJD,

Thanks for doing the measurements. I measured my plane and found that it is very similar to your set-up.

Exhaust centerline to end of header - 2-1/2" (Mine was 2-1/2" also)

Front of pipe to high point of pipe (the first and largest "ridge" on pipe heading from front to back) - 8-15/16" (Mine was 8-15/16" also)

Exhaust centerline to pipe high point should measure about 11-7/16" on a stock pipe/header. (Mine was 11-7/8" -- 7/16" longer than yours-- difference must be in the sillicone adapter)

-Mike
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