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

ducted fan engines

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Old 10-12-2004, 10:04 PM
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willflyforfood
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Default ducted fan engines

What rpms do the ducted fan engines run with standard props. I've heard of guys using DF engines for speed planes and was wondering if they were in the 30,000's and what pitch props they are turning. I am working on some future designs and I am trying to get an idea of the engines/ RPM's. Any help woud be great. I am looking to get just the absolute maximum out of a prop engine combination.


Thanks,
Joey
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Old 10-13-2004, 01:06 AM
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LGM Graphix
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Default RE: ducted fan engines

Not even close, typically most fan engines turn less RPM's with a prop than with a fan, at least from what I've seen and read, Not because the engine isn't capable of turning those speeds, but because most guys with a brain realize you best prop them in a range where the props won't explode. The biggest challenge with larger props is not exceeding their safe RPM's. Sure you might get close to 30,000rpm with a 7x8 pylon prop, but you will get that with a Nelson QM40 or JETT QM40 too and not have to deal with the weight issue. Once you start getting up to a 14" prop which you might get some use out of an OS91VRDF you really don't want to exceed probably 16,000 or 17,000 RPM.
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Old 10-13-2004, 06:06 PM
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Default RE: ducted fan engines

Hi,
I beg to differ. My OS 91 vrdf does 22k static with an 11x8 apc. It is scarry though.

randy
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Old 10-13-2004, 08:47 PM
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Default RE: ducted fan engines

I have a K&B 82 that is currently hooked up to a fan in an ex-Garland Hamilton, Agressor. Since I'm thinking about putting a turbine in the Agressor, using the K&B in a prop plane sounds interesting. I haven't even looked at how it is attached to the fan. Will I need a different prop nut or spacers or what ever? Has anybody out there tried this engine with a prop? I have a 60 size P51B that looks like it would make a nice new home for this motor.
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Old 10-14-2004, 12:06 AM
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Mike Connor
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Default RE: ducted fan engines

ORIGINAL: r-c-guy

Hi,
I beg to differ. My OS 91 vrdf does 22k static with an 11x8 apc. It is scarry though.

randy
That would put the tip speed at over 700 mph and exceed mach after unloading. Hmmmm
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Old 10-14-2004, 12:42 AM
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Default RE: ducted fan engines

ORIGINAL: r-c-guy

Hi,
I beg to differ. My OS 91 vrdf does 22k static with an 11x8 apc. It is scarry though.

randy

No need to beg to differ, you're doing exactly what I said you can do, and you're exceeding the safe tip velocity, I've seen APC's come apart, it's not pretty, just be damn careful with it. They come apart without warning so always make sure you are not in the pit area, and not in line with that prop when you run it up.
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Old 11-10-2004, 05:25 PM
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Default RE: ducted fan engines

Hi,
You havent mentioned what size of DF-engine you wanna use? My rossi 105 turns a APC 10x10 about 17000rpm. The tuned length must be longer than on the fan pipe. I am using it on a 11LBS airplane 80" wingspan and geting about 120mph. On a smaller airplane it should give you at least 160mph.
Good luck, Amir
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