>Hey Tom!
> The problem for me (and also for any Warp Drive users on higher
>performance aircraft) is that
>the Warp Drive blades do not have enough twist to be efficient at (or
>allow) higher speeds.
>Every propeller has a designed in "pitch speed" that it is most efficient
>at.
> The WD prop was originally designed as a prop for ultralight aircraft.
>Ultralight aircraft are typically
>too draggy to go faster than 100 mph. It is a very fine propeller for this
>application and for speeds
>up to about 135 mph. Higher speeds than this require a large amount of
>pitch in close to the
>hub to avoid going into reverse thrust in this area. The WD is very
>efficient at its designed speed
>but it is a one size fits all approach. One can obtain higher performance
>(at least at higher speeds)
>by designing a prop with more twist. At the same time, you need a wider
>blade to absorb higher
>horsepower.
> As far as the Airmaster goes, I'm sure its a very fine propeller, but it,
>the NSI CAP 140 (which I
>have), the Kremen and others all use the WD blades. I think the Arplast
>uses their own blades.
>The big benefit I observed with the NSI CAP 140 was a shorter takeoff roll
>and slightly better initial climb, but I played with it for minutes at a
>time at WOT and there was no improvement at higher speeds over a ground
>adjustable WD prop. How could there be, they are the same blades!
> I did some research a while back and received the following reply from
>Stuart Gort Sr, owner of
>PowerFin props. He is a very helpful fellow.
> Let me know if I can be of further help!
>
>>From: "Stuart Gort Sr." <info@powerfin.com>
>>To: "GLENN CROWDER" <gcrowder2@hotmail.com>
>>Subject: Re: powerfin prop for Subaru powered Europa
>>Date: Tue, 6 Jan 2004 19:00:47 -0800
>>
>>Hi Glen,
>>
>>The Powerfin B-model has only about 2 more degrees of twist than the Warp.
>>The twist is important on your application because as you approach the
>>fast part of the flight envelope, the inboard sections of the prop begin
>>to go into beta mode. This means the air is being accelerated over the
>>lower camber faster than over the upper camber, essentially making reverse
>>thrust (or at least making enough drag to be the main factor in acheiving
>>equilibium - no more acceleration). Our prop, because of the 2 more
>>degrees might have some positive effect but I wouldn't bet the farm on it.
>>Chances are that any improvement would be negligible. For airplanes in the
>>135 mph range, a proper design might have about 40 - 50 degrees of twist
>>from the tip to the most inboard definable sections. A Warp, at 64" has
>>about 13 degrees. So, the lack of twist on the Warp and the resulting drag
>>on the inboard stations is certainly slowing you down but there is no off
>>the shelf design out there yet that can well accomodate your plane.
>>
>>It's not moment of inertia that is making vibration for you. It's
>>resonance typical to running a two blade prop with a reduction ratio near
>>2:1. The blade is almost in the exact same postion every time the engine
>>fires. Having a ratio that is near 2:1 but not exactly helps this a little
>>but 2.04:1 is pretty close and the fact that 204 is divisable by who know
>>how many factors isn't helping either. It takes some time to fully
>>explain, but in a nutshell; the more factors 204 has, the less number of
>>revolutions the propeller makes before the blade blade is in the exact
>>same postion as the engine fires. It's complicated but if 203 was a prime
>>number (I don't know if it is), then a 2.03:1 gear drive would result in
>>the blade going around 203 times before it was in the exact same postion
>>as the engine fires, reducing the propensity to resonate. Not eliminating
>>it but minimizing it to its lowest possibility.
>>
>>In short, you're stuck with a little vibration if you want that speed
>>because the two blade, fixed pitch prop guys are the only ones making
>>props with more twist. That's why you're getting the desired speed with
>>just about every one. You could hope to find a slightly different ratio
>>that meets the above requirements (doubtful). You could try a Powerfin
>>B-model 64" and see how it does but it's a weak premise to buy a prop on
>>unless you enjoy experimenting. I wouldn't sell you one by making any
>>grand claims though.
>>
>>Our Apex 912 hub will fit your flange perfectly. You are correct. The
>>pattern is exactly the same as the 912, 912S. and 914 pattern.
>>
>>Thanks,
>>
>>Stuart Gort - Powerfin Inc.
>>
>>
>>From: GLENN CROWDER
>> To: info@powerfin.com
>> Cc: gcrowder2@hotmail.com
>> Sent: Tuesday, January 06, 2004 10:47 AM
>> Subject: powerfin prop for Subaru powered Europa
>>
>>
>> Hello Stuart and HAPPY NEW YEAR!
>> I'm looking for a better prop for my Subaru EA81 powered Europa. I
>>am
>> currently using a 3 blade 64" dia Warp Drive and is doing OK but I
>>would
>> like to improve cruise speeds if possible.
>> My field elevation near Denver is 5100 ft and I typically fly at
>>around
>> 7000 ft. With the Warp Drive
>> at this altitude, I typically attain about 130 kts GPS on a still day.
>>Climb
>> rate is about 1000 fpm.
>> The WD is very smooth if you tweak the blades extremely carefully. It
>>takes
>> a lot of time to set
>> the blades.
>> I have tried a couple of two bladed wood props and get better speed
>>and
>> climb but I get an
>> unacceptable level of vibration or resonance. It is similiar to flying
>>in a
>> twin engine plane and having
>> the engine speeds out of synch. I have a Warnke 64 x 62 prop that
>>climbs
>> very well and gets about
>> 10 kts better at the top end. I also tried a GT (Italian) prop that
>>also
>> improved speed and climb
>> but also had the same resonance problem.
>> The WD prop is a one size fits all approach but has very little twist
>>on
>> the blades and very
>> narrow chord width (4 1/4"). If I keep increasing the pitch of the
>>blades,
>> I get to a point where
>> I don't go any faster but climb rate is much worse. I think I need a
>>blade
>> that is slightly wider in
>> chord and has more twist like the Warnke and GT props I have been
>>trying.
>> I found the Bolly Prop website from Australia and like that because
>>their
>> blades seem wider with
>> more twist and fit my WD hub but I can't get any response from them
>>after
>> several emails.
>> My motor is about 120 hp at 5100 ft, (was dynoed at 137 hp at 1000
>>ft),
>> has a Marcotte gear
>> drive with 2.04 ratio, redline is 5600 rpm, top speed with WD is about
>>130
>> kts, cruise speed
>> 115 kts, prop dia 64". The prop hub is the rotax 4.000" pattern, 6
>>bolts
>> 8mm dia with drive
>> lugs .505" dia that protrude out .505". Centering boss is 1.850" dia
>>and
>> protrudes out .500".
>> This is the identical pattern used on the Rotax 912 and 914 I believe.
>>I am
>> very interested in your
>> props due to the low inertia which I think contributes to prop
>>resonance.
>> If the WD prop is
>> smooth, it seems like yours should be even better and easier to adjust.
>> Thanks for your help!
>>
>> Glenn Crowder
>> 740 Braun St
>> Golden, Co
>>80401
>> 303-520-3659
>>
>> gcrowder2@hotmail.com
>>
>> _________________________________________________________________
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