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

GP Viper 500

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Old 04-16-2007, 02:22 PM
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Destiny-RCU
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Default GP Viper 500

Hello all

I'm looking for opinions on engine size for this plane. I've always flown aerobatic planes and i'd like to lean into some faster stuff. This will be my first "speed plane" so i'm looking for opinions on what the plane is like with say a .25, .32, and up....Is a .25 a good start to learn the plane or...?

Thanks in advance
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Old 04-16-2007, 03:20 PM
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Default RE: GP Viper 500

the plane with fly with pretty much any engine on the nose. If you have anything from a .25 to a .46, use it. Plane will fly nicely.

For simplicity and basic setup, I suggest using a Thunder Tiger 40 pro - inexpensive, and this is the engine used for 424 racing (should you wish to... there is some 424 racing down at Markam Park). It has a throttle - just throttle back or mechanically limit the engine to 3/4 throttle to start with. When you want to go faster, again, you know where the throttle is.

Bob

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Old 04-16-2007, 08:14 PM
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Default RE: GP Viper 500

What sort of speeds would you expect with the 40? 46?
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Old 04-16-2007, 08:20 PM
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Default RE: GP Viper 500

110 mph - 120 mph with a sport 40/46 is realistic.
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Old 04-16-2007, 08:24 PM
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Default RE: GP Viper 500

What's the speed difference between a "sport" engine and a Jett?...In the future I would like one of these with a good engine
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Old 04-17-2007, 06:57 AM
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Default RE: GP Viper 500

Ohhhh, several thousand RPM. Instead of a mass manufactured engine you're dealing with a handfit engine. Its comparative to taking 70's muscle car down to the specialist and having them pull out the stock engine and putting a balanced, blueprinted motor on it with a blower.
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Old 04-17-2007, 10:37 AM
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Default RE: GP Viper 500


ORIGINAL: Destiny-RCU

What's the speed difference between a "sport" engine and a Jett?...

Jett makes Sport Jett and a racing engine. The Sport Jett will give you 2000+ rpm and 10+ mph over a similar engine from O.S. or Thunder Tiger.
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Old 04-17-2007, 11:19 AM
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Default RE: GP Viper 500

A Jett 40/50 on the same plane will get you to 150mph pretty easily.
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Old 04-17-2007, 07:16 PM
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Default RE: GP Viper 500

A 6" prop has to spin at 17,600 to reach 100 mph without any loss or drag, so for speed you might look at a 8" pitch.
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Old 04-18-2007, 12:24 PM
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Default RE: GP Viper 500


ORIGINAL: buzzingb

A 6" prop has to spin at 17,600 to reach 100 mph without any loss or drag, so for speed you might look at a 8" pitch.
Dont be so sure.... There is more to a prop than its pitch - its not 100% related to the flat surface pitch

A Q-500, TT40, 9x6 prop, 16,500 at launch ... lets say maybe 17000 in flight --- does fly at 120mph
By your calculation there this is impossible. But it is known to be true.
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Old 04-18-2007, 01:10 PM
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Default RE: GP Viper 500

How about a 10x7 at 14,500 (on the ground) that does 125 in the air straight and level, no wind.
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Old 04-18-2007, 02:03 PM
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Default RE: GP Viper 500

what is the formula to figure speed vs. pitch?
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Old 04-18-2007, 02:13 PM
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Default RE: GP Viper 500


ORIGINAL: Destiny-RCU

what is the formula to figure speed vs. pitch?
point here, is that prop pitch and rpm are not the only things that determine potential speed.

Lets leave it at that. It took a year of aero courses to understand prop theory.
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Old 04-18-2007, 02:23 PM
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Default RE: GP Viper 500

Yes, i'm sure there are a lot of variables to determin the performance of a prop.
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Old 04-18-2007, 02:29 PM
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Default RE: GP Viper 500

being that I know little about prop design. Also makes me curious, is there room for "out of the box" thinking with making a prop? Or is what we use today as far as it can go?
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Old 04-18-2007, 03:56 PM
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Default RE: GP Viper 500


ORIGINAL: Destiny-RCU

being that I know little about prop design. Also makes me curious, is there room for "out of the box" thinking with making a prop? Or is what we use today as far as it can go?
If you are participating in competition or speed trials.... dealing with rpm, tip speed, aircraft design for this specialty application, and aircraft flight regeims that are at the extreme, there are a probably a number of designs to be tried yet. If you are interested in some prop theory, look up supercool props (do a google search). Some good info there.

For sport use.... don't give it a further thought. Use an off the shelf APC standard blade or D1 series on the Q-500, and you will be much, much better off.

Just in closing here... you can get a far greater speed increase with drag reduction and refinements on an aircraft, than you can achieve with tweeking a prop. For a Q-500, take it for what it is... a box with wings.

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Old 04-19-2007, 05:09 PM
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Default RE: GP Viper 500

Yes, there are many variables with propellers and you are probally correct. However, as a general reference without considering the airfoil etc. it easy to get close to the rpm to reach a certain speed. I don't know if you could get an extra 20mph out of an air foil or not but thanks for pointing that out.
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Old 04-19-2007, 07:42 PM
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Default RE: GP Viper 500


ORIGINAL: buzzingb
I don't know if you could get an extra 20mph out of an air foil or not but thanks for pointing that out.
Yes, you can. Just like a sailing ships can travel faster than the wind speed.


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