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Old 09-23-2017, 10:17 PM
patchntx's Avatar
patchntx patchntx is offline
Cozy III Ch. 9
 
Join Date: Jul 2011
Location: Savannah, Texas, United States
Posts: 143
Default Metal Constant Speed Prop

Metal Constant Speed Props: 30 or 40 years ago Rutan may have warned people that a metal CSP will fail on the back of a canard. Confused air, strake interference blah, blah, yaddah, doom. Since then the community warns against metal CSP's specifically and CSP's in general. I think it's all hearsay and thought experiments without any evidence.
1. Is there any data developed by anyone in the community?
2. Has anyone ever had a metal CSP fail on a canard?
3. Is there anything at all other than hearsay and anecdotal evidence?
The Defiant I posted a few days ago has 2 blade metal CSP props on both ends. Takes off and climbs like a bat out of hell. Cruises at 175 kts TAS on 15gph. I think we were at 8500ft.
Keep the metal CSP's?
Put a Hoffman 3blade composite CSP on the back?
Cato fixed pitch on both ends?
Why change at all?
I love Rutan Designs but I think he is full of crap on the prop thing.
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  #2  
Old 09-24-2017, 06:05 PM
LEZ1675 LEZ1675 is offline
Bill Welter
 
Join Date: Feb 2010
Location: Colorado Springs, CO
Posts: 544
Default Re: Metal Constant Speed Prop

In a tractor configuration, the prop sees more or less, a constant and even load. Burt felt that since the air coming over the strakes and around the engine was disturbed, this would cause the metal prop to fail.

Burt is an aircraft designer and a heckuva smart guy, and felt that wooden props could handle these conditions better, and had liabilities to worry about.

Props have come a long way since the 70s, might work OK. Maybe someone (you) could try a metal prop and see if it does work.

Might...might not
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  #3  
Old 09-24-2017, 07:00 PM
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TMann TMann is offline
Got Foam?
 
Join Date: Mar 2007
Location: Omaha, NE
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Default Re: Metal Constant Speed Prop

The metal fatigue issue is huge for a metal prop in a pusher configuration. It's hard on the blades as well as the hub.

Worst case scenario, you loose a blade followed by a severe out of balance situation. That sets up a violent vibration that if an immediate shutdown doesn't occur (in time) the engine will be ripped from the airframe.

If the engine departs ......... well, time to do a new weight and balance.
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