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Old 25th Nov 2008, 18:09   #1 (permalink)
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Join Date: Jul 2003
Location: Port Townsend,WA. USA
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shrouded prop for improved static thrust

I found this old 1960 paper by Dr. August Raspet http://4wings.com.phtemp.com/lib/files/Raspet_c.pdf
about shrouded propellers and how he improved the static thrust by almost double over an open prop. This would apply to VTOL lift and helicopter fenestron type tailrotors that are mostly static thrust devices .


Is this possible?

slowrotor

Last edited by slowrotor; 25th Nov 2008 at 18:12. Reason: correct website
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Old 26th Nov 2008, 00:47   #2 (permalink)
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Thanks Nick,
Your confirmation of the theory requires that I do additional research!

I am working on a lift fan for a slow airplane, the drag is not a big factor in this case.

So far, I think the design requires a large bellmouth inlet, and the largest possible diameter two bladed prop and a divergent outlet duct around 20% of fan diameter as you suggested.

I think a wide blade tip might help reduce the need for a close clearance, but I have no data about tip clearance yet for a shrouded prop. I think the ducted fan information does not apply.
This is interesting! Double the thrust!
slowrotor
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Old 26th Nov 2008, 01:38   #3 (permalink)
 
Join Date: Dec 2003
Location: Melbourne, Australia
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I recently came across this unusual old design for a channeled wing / prop airplane. You might find it interesting:

Welcome to the Custer Channelwing Website.
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Old 26th Nov 2008, 15:25   #4 (permalink)
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The Custer Channelwing is controversial. I think the channelwing is a form of deflected prop thrust. Nick told me once that deflected thrust is not as good as direct vertical lift. I think he is probably right. Some people think the channelwing works.

I watched an experimenter flying a single engine channelwing of his own design. It was a pusher with a channelwing behind the cockpit. The problem, as I saw it, he could not descend for landing without reducing power and so he had no lift gain while landing. Might have helped for takeoff but I did not see any better performance, maybe worse than a stock Cub.
slowrotor
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Old 26th Nov 2008, 17:40   #5 (permalink)
 
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Location: Vancouver, BC, Canada
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slowrotor,

There may be some information of value in here.

Tip Fin Propeller
Shrouded Propeller
Ducted Fan

Dave
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Old 26th Nov 2008, 18:16   #6 (permalink)
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Dave,
Your shrouded prop links do not work anymore. I am not interested in ducted fans, only shrouded props.

The bent tip prop will not help control the reverse flow of a static prop in my opinion.
slowrotor
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Old 26th Nov 2008, 19:33   #7 (permalink)
 
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slowrotor,

This page has been revised.
Shrouded Propeller

A couple of the previous NACA reports were found.

Also included is the search on NACA for "Shrouded Propeller"


Hope this helps.

Dave

________________

PS

We're going to get banned from this forum, since we are both currently working on winged craft.

Here is my project;





VTOL - AeroVantage - 1x2 Overview

D

Last edited by Dave_Jackson; 26th Nov 2008 at 19:44. Reason: PS added
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