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

K&B 7.5 on Diamond Dust

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Old 06-17-2009, 10:30 PM
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med601
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Default K&B 7.5 on Diamond Dust

I'm planning on building a DD with a K&B 7.5 DF.
Has anybody done this?
If so please share your info. How did you balance it? what size prop works best? what speeds are you getting? and what pipe are you using?
Thanks
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Old 06-18-2009, 01:22 AM
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Default RE: K&B 7.5 on Diamond Dust

It's been done before. Most 45/48 DF engines run fine with Macs tuned pipes #1150 pipe, #1250 Muffled or the #1050 Quiet pipe.
The later K&B 48s are close to a OS 46 VXDF in power and should run only carbon props.
If it's a 7.5, try a APC carbon 7.4X8.25 #LP74825C if it's less than 23,500 with that prop, than you may get away with a steep pitch pylon prop but re-tune the pipe for lower working range.
You could run a carbon of less pitch on the 7.5 to get into the 24.5k range,I may be wrong, but I don't think it will unload well, so go with the greater disk area of a pylon and run lower rpms. Stay away from the narrow pylons for this. Good prices and nice list: http://www.pspec.com/details.asp?ProdID=47&category=6 The one at the top of the list and the three at the bottom look promising.

Balance the Dust as per instructions, I put my batteries aft of the rear spare because the OS is so heavy. You can split the pack too if need be.

Good luck.
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Old 06-18-2009, 09:59 PM
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Default RE: K&B 7.5 on Diamond Dust

Thanks,

The 7.5 hasn't been broken in yet (not sure what prop or procedure)

I can't find #LP74825C on that sight or carbon props.

I have no header, so i was thinking of using a piece of tubing that woud go over the tank to a Bud Light mouse can. What do you think?

what kind of speed are you getting with the OS?

Medwin
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Old 06-18-2009, 11:57 PM
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Default RE: K&B 7.5 on Diamond Dust


ORIGINAL: med601

Thanks,

The 7.5 hasn't been broken in yet (not sure what prop or procedure)

I can't find #LP74825C on that sight or carbon props.

I have no header, so i was thinking of using a piece of tubing that woud go over the tank to a Bud Light mouse can. What do you think?

what kind of speed are you getting with the OS?

Medwin
Here's the manual: http://www.mecoa.com/kb/87/9101.htm I lists an even bigger pipe to use than I would have guessed. Break-in with a 9 pitch pylon rich two stroke sound, don't peak it, and stay out of the prop arc. A cold run on K&B engines will kill the connecting rod, just too hot to hold the head with your fingers is about right at the start.

I noticed that APC has quite a few props that I like missing, Give them a call and I think they have it, if not do a search some on-line stores have them.

I'm not a fan of mouse can exhausts on speed planes, too much drag and fiddling around to get it right. You can hurt a new engine engine like that.

The OS gets an easy 170mph and on a good day 175+ and on some days that just seems too fast for me so I take it up and away from the deck.
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Old 06-19-2009, 01:06 AM
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Default RE: K&B 7.5 on Diamond Dust

The APC site is not very easy to navigate, so just call them directly and they will take care of you.
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Old 06-19-2009, 04:43 PM
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Default RE: K&B 7.5 on Diamond Dust

Performance specialties caries a good variety of racing props. Check them out at www.pspec.com.
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