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

New to speed.

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Old 11-04-2007, 11:38 PM
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kbear
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Default New to speed.

I have recently been bit by the speed bug. I'm running a old OS 50 FSR and was wanting some prop suggestions. Here's my plane.




She had her first flight today. I had a MAS 11x6 on her for the first shake down flights. I was thinking of trying an APC 10X8, but figured you guys would have helpful info.

Here is a link to some video.

http://www.youtube.com/watch?v=Dj71id5SQEs

My two best runs were 100 mph and 101 mph, so I' m hoping to get above 120 mph with the right prop.
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Old 11-05-2007, 12:13 AM
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Mike Connor
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Default RE: New to speed.

On my PC the picture is a little dark and I can't tell much about the plane. If it is clean enough I would drop down to a 9 x 8 or 9 x 9 for more speed.
What did you use to check your speed? I did a Doppler speed check from the video and it was consistent in the 120 mph range.
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Old 11-05-2007, 12:26 AM
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Default RE: New to speed.

What RPM does a plane with an 11x6 prop have to turn to do 120?
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Old 11-05-2007, 01:16 AM
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Default RE: New to speed.

I used a Doppler program. I'm just learning how to use it. I didn't know to change the Temp. After I changed it to 24 C (75F) I too Got 119 - 120. I'll get some better pics for you. It Weighs in at 4.5 lbs. dry. The 11x6 really makes it easy to launch as you can see. I'll put a tach on it this coming weekend with various props. Do you think I might be able to hit 150? Guess we'll see. For what it's worth, The launch is directly into the wind, so it's a bit of a cross wind on the speed passes. Thanks for running it through for me, as I said, I'm just learning to use the software, and it's all in German. Here is one of the results I got. See if I need to change anything.

Click here to watch Flipper-D-o1

http://www.putfile.com/pic.php?img=7019968
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Old 11-05-2007, 01:33 AM
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Mike Connor
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Default RE: New to speed.


ORIGINAL: combatpigg

What RPM does a plane with an 11x6 prop have to turn to do 120?
21,000 rpm would have a theoretical speed of 120.

kbear,
Your picture looks like what I got. Like combatpigg I am a little confused how you got that speed with that prop. If is hard to tell by looking at the video but it seems to be moving right along.
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Old 11-05-2007, 01:48 AM
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Default RE: New to speed.

Maybe the 3" Spinner on the front is making a difference in drag. I don't know enough about it yet, but it sounds like I'm in good shape so far.
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Old 11-05-2007, 09:11 AM
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Default RE: New to speed.


ORIGINAL: kbear

Maybe the 3" Spinner on the front is making a difference in drag. I don't know enough about it yet, but it sounds like I'm in good shape so far.
It may well reduce drag but pitch speed is pitch speed nonetheless, the best you can do in that case is to reduce drag allowing the prop to unload a little more as the airspeed comes up a bit. But you'll hit a wall somewhere around pitch speed and I bet two donuts and a coffee it ain;t 120. Not to shoot down the fact this thing probably moves out, I am sure it does, but this makes me wonder about the accuracy of these audio Doppler analyses.

That said, you likely have the horsepower to do 120 or so, maybe a tad more, and I agree a 9-8 is a good next step. An 11-6 is great for larger slower aircraft but is a total mismatch for this aircraft - although yes, it will sure make launches easy. You'll launch easily enough with a 9-8 or so. If you wanted to step gradually along the pitch/dia path, perhaps run a 10-7, then 9-8, and observe the changes in flight characteristics. Or not, and just go right to the 9" - whatever floats your boat. [8D]

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Old 11-05-2007, 01:53 PM
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Default RE: New to speed.

MJD, thanks for the info. I didn't tach it on the ground, but I don't think it's running 21,000. I will do as you say and try a 10-7 and then the 9-8. I want to add a little at a time both to make sure I don't have problems piloting her and that she can handle the speed. We have several Police officers that fly out here, and they stop by from time to time on there brakes. Maybe I can get one to put a radar gun on here and check the results on the Doppler against that. The doppler usually gives me a margin of error of around 4 or 5 kpm. That's a bit of a difference.
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