Fred, The twist of a blade along its length is fairly critical to engine
cooling. Changing from a Woodcomp SR2000 with 12 degree twist to an SR3000W
with about 26 degrees of twist has transformed my 914 cooling , totally
eliminating the overheating on delayed take off or prolonged climbs. It has
also added 4 kts to top speed and improved fuel consumption.
As you can see from the attached mathematical analysis a 12 degree
twist is optimised for air flow through the prop of about 40 kts, which is
what you get sitting on the ground at about 1/2 throttle, before take off.
At 100kts + you have negative AoAs in the central portion of the propeller,
which doesn't help anything. It's no coincidence that all really fast planes
(Spitfires, Red Bull racing planes, turboprops, etc) have props with twist
more than 20 degrees. Regards, David Joyce, G-XSDJ
----- Original Message -----
From: "Fred Klein" <fklein@orcasonline.com>
Sent: Saturday, March 21, 2009 1:12 AM
Subject: Re: Europa-List: Constant Speed Props, etc.
>
>
> On Mar 20, 2009, at 2:00 PM, Paul McAllister wrote:
>
>> I am not an aerodynamicst, not even an amature one but I was wondering
>> why you didn't think the Kiev blades will be much of an improvement
>> over the Warp Drive blades.
>
> Bud,
>
> I too was surprised at your apparent skepticism as to whether those Kiev
> blades may offer improvement over the current WD blades in the Airmaster
> hub.
>
> I had several long emails w/ Martin on the subject...perhaps 2 years
> ago...and my recollection is that he was quite candid about the WD blades
> being less than optimal given the flight envelope and length limitations
> of the blades for the Europa. My understanding is that the WD blade
> stock is much longer, and when cut down to length required, they lose
> much of their twist...to such an extent I've read that the inner portions
> of the blades create negative thrust under certain conditions. I've
> speculated that the relative lack of twist may be a factor in engine
> cooling...just speculation, I have, of course, no direct experience.
>
> Assuming that the "432" references a new hub, I hope it's available with
> other than a Rotax flange.
>
> Fred
>
>
>
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