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

Questions regarding my first speed delta

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Old 12-11-2007, 09:34 AM
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BlackB12
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Default Questions regarding my first speed delta

I'm looking at Mike's RC Screaming demon to be my first fast plane. I'm primarily a 3D pilot and I want to have something to fulfill the need for speed. The screaming demon looks perfect. I have 3 engines I'm considering using on a demon. They are, a supertigre 51, supertigre 40, or a OS46ax. I realize this will not be a missile like something powered by a Jett engine, but it would be a start. My fastest plane right now is a beater Skyraider Mach 2 with the Supertigre 51 on it. I'm sure it doesn't top 70mph so if I can get into the 100's that would be good. What engine would be best. I emailed mike and he didn't have first hand experience with either engine on a demon, but he thought the ST51 would be fastest. A friend gave me a 60 sized tuned pipe so maybe that could be adapted to the 51. Or maybe it's too much pipe for the smaller engine. I don't know. The ST51 will turn an APC 10x7 at 13,500 rpm. What's the max rpm I should run this engine to? Lots of questions I know, but if anyone can help my move to speed planes, I'd greatly appreciate it.

Mike
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Old 12-11-2007, 09:49 AM
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bob27s
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Default RE: Questions regarding my first speed delta

Hi Mike... welcome...

There is no real mystery here. You have a collection of good engines. You just have a different application, thus different props, and slightly different performance setups.

Any of those engines will be suitable for the speed application.

Easiests way to get some added fun/speed/performance is by adding a jett-stream muffler to the engine. Inexpensive investment. Your engine will thank you for it. Any of the engines listed respond great.

Do not concern youself with rpm "limits". You will be quite ok with any of the engines listed using a practicle flying prop.

The ST51 and ST40, with the stock muffler, both perform great turning between 15,000 and 16,500 ground peak rpm. Select a prop accordingly. The APC 9x6 and 9x7 are good places to start. For the ST51, after some flight time at speed, you might also try a 9x8.

The OS46AX prefers to run a bit slower due to design and port timing, so you want to go more along the lines of a 9x8 - target around 15,000 - 15,500 ground peak rpm with the stock muffler.

The larger pipe can be used, but for the engines you listed, you really want a 6.5cc pipe - the 10cc pipe may be difficult to get the length short enough to support the rpm targets.

And do not kid yourself ... Mikes Demon with any of the above engines, propped as suggested, will very likely reach 100 mph. With the jett-stream muffler added, no doubt you will exceed 110 mph in level flight.

Since you havbe been running the engines low and slow with big props, it may take a few flights for them to become aquainted with the higher rpms. Be patient. Find peak rpm before launch - back off 500-600 rpm from there for flight.

I hope this is helpful

Bob
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Old 12-11-2007, 03:44 PM
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Default RE: Questions regarding my first speed delta

My favorite plane combo was a Diamond Dust with an OS .32SX. The Screamin Demon is similar to a Diamond Dust, but a bit more streamlined. For a first speed plane I think you'll like a delta with either a .32SX or .46FX. Neither is too heavy, they run very easily, and the .32 loves high RPMs.
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Old 12-11-2007, 08:12 PM
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Default RE: Questions regarding my first speed delta

After e-mailing to Bob (bob27s) I tried a JettStream muffler. Now I have 3 of them. For many years I ran tuned pipes. I ran engines on the bench and tached and trimmed the header time after time. It sure is a lot easier to bolt on a Jett. If you have an OS .46AX, get the Jett for it. Use a 10-7 or 9-8. They don't turn as much as the older FX, but will turn a bigger prop. You'll probably gain 1500 rpm with the Jett.
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Old 12-11-2007, 09:46 PM
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Default RE: Questions regarding my first speed delta

BlackB12,

SET the CG correctly, if you are nose heavy you will need a lot of UP elevator to hold the landing flair. I hope you have a radio with dual rates and Expo. High rate elevator with 30-40% expo should be a good place to start .
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Old 12-12-2007, 03:21 PM
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Mike Connor
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Default RE: Questions regarding my first speed delta

It all looks like good advise to me. If you build it clean and can turn a 9x7 around 16,000 rpm it will be an easy 120 mph in level flight. My last one with winglets, no engine cowl and the TT 46 was even faster.
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Old 12-12-2007, 09:15 PM
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Default RE: Questions regarding my first speed delta

The RPM limit should be set at 1 rpm below whatever RPM the engine blows up at.
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