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Prop question? - 9/21/2004 4:00:17 AM   
Zeroman


 

Posts: 121
Joined: 6/13/2003
From: Vancouver Island, BC, CANADA
Status: offline 		Can a prop fly faster than its calulated speed?
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RE: Prop question? - 9/21/2004 10:21:58 AM   
der_steuermann



Posts: 238
Joined: 11/7/2002
From: Stolberg, GERMANY
Status: offline

No, even if considering an ideal environment (no draggy airframe/engine, no air resistance) the theoretically calculated speed would be the best possible one.

From experience a very good speed setup reaches about 90% of the theoretical prop speed at given rpm (rpms of an unloaded engine during a powerdive derived from Doppler effect measurements).

Boundary conditions are:

- low drag airframe supporting the engine/prop combo to unload with ease after the first dive
- low drag speed prop designed for a certain rpm and target speed
- an engine swinging the prop within its highest efficiency
- preferably subsonic prop tip speeds
- speed measurements in both directions, headwind and downwind


(in reply to Zeroman)
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RE: Prop question? - 9/21/2004 3:25:40 PM   
Zeroman


 

Posts: 121
Joined: 6/13/2003
From: Vancouver Island, BC, CANADA
Status: offline 		Thanks for the info der-steurmann, there has been quite a discussion about this.Some club members say they fly faster than the calculated speed all the time.Chris.

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RE: Prop question? - 9/21/2004 4:19:57 PM   
daven



Posts: 6908
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		I'm not convinced that a prop CAN'T fly faster than its calculated speed.

I think its possible, but it may be due to incorrrect pitched props.

I've seen APC 10x7 props go faster than what they should be capable of going.

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Dave Norman

klasskote.com
supertrc.com

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RE: Prop question? - 9/21/2004 5:59:23 PM   
Mike Connor



Posts: 1384
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline 		Since a typical prop starts developing forward thrust at a negative 3* pitch I would have to say yes. The calculated forward speed of a 0* pitch prop would be 0 but under the right circumstances it may even get a plane off the ground. This advantage is usually lost to drag as speed increases.

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Mike
http://www.mikesrc.us/

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