> > Bill Eslick has run a bunch of interesting prop tests and
> > published the data on his web site.
http://www.weslick.com/
> > I reproduced some of it here and added some comments.
> > The airplane is running into a brick wall at 165 MPH.
> > Increasing the power does not help and just burns more
> > fuel. It does not result in an increase of airspeed.
> >
> > My theory is the prop tips are stalling and running
> > into the high drag transonic region at the same time.
> >
> > Quoting Bill:
> > "I used a Props, Inc. 67 x 68 wood prop, a Felix Bi-Cambered
> > 68 x 72 wood prop, and a Warp Drive three-blade ground adjustable
> > carbon-fiber prop."
> >
> > Quoting Jordonoff:
> > "If the propeller were turning in solid material, as is the case with
> > a screw in wood, it could act without slipping, and so the distance
> > traveled in one revolution would be equal to the theoretical travel
> > of the propeller. Inasmuch as the propeller is turning in the air,
> > however, there is a certain amount of slip; there fore its actual
> > travel distance falls short of its theoretical travel distance."
> >
> > The ratio of how far it would screw into wood to how far it would
> > screw into air is called the Advance Ratio. IMHO these props are
> > at the limit of the advance ratio.
> >
> > The Warp Drive have no twist so the tip drag is higher.
> >
> > The tip thickness is as follows.
> > Felix: 0.235" Props, Inc: 0.420" Warp: 0.272"
> >
> > I am guessing here. The solution might be more blade area with
> > a shorter prop. The Warp drive blades can be modified by
> > cutting off the aft part of the blade at an angle and sanding
> > them in such a way as to reduce the tip angle of attack and hence
> > the drag. However one would probably have to add another blade.
> > I'll do a 3D shortly
> >
> > What is your theory on what is happening?
>
> > Paul Lamar
>
>
> The Warp Drive prop has very little twist - about 13 deg and was
designed
> and
> optimized for ultralights and 100 mph operation. At higher speeds, the
> inboard
> sections of the prop are actually going into reverse thrust. Look at the
> prop
> and see if you have any bugs on the forward face of the prop. There
should
> be none, only on the back of the prop (this is near the hub).
> I had the same problem with my 125 hp Soob EA81 powered Europa and
> after doing the research went to a Catto custom fixed pitch. WOT speed
> instantly jumped from 150 to 175 mph with no other changes. Climb
stayed
> the same.
> The Catto has 40-45 deg twist at the root. This is so at higher
speeds, the
> hub area is still at a positive angle of attack to the relative wind.
> I had no idea what was going on and I emailed Stuart Gort at Powerfin
> Props and he was
> very helpful with the following:
>
> 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 achieving
> equilibrium - 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 accommodate your plane.
>
> Stuart Gort
> Powerfin Props
> GLENN CROWDER
>
>
> The point here is modifying the Warp drive prop
> you might have instead of spending big bucks on
> new props until you find one that works.
> That is if you can even find a properly twisted all carbon
> blade with sufficient blade area to absorb the rotary HP
> that can be ground adjustable in pitch.
>
> The Warp Drive blade can be set up in a mill at just the right
> angles and the bottom milled off flat. If you keep
> the set up support you could mill all four blades
> which is what I think one is going to need for blade area
> when you cut the prop down to about 64 inches dia. or so.
> (To lower the tip Mach number.)
>
> No doubt about it. It is a compromise and far from
> perfect. Final shaping can be done with a block sander.
>
> I am not sure this is going to work but it might be worth
> a try. Cheaper than up grading one's PSRU to a 2.85:1.
>
> BTW Perry Mick do you think you can duplicate Bill Eslicks
> test with your current prop? As I recall you are also
> running a 2.17:1 PSRU. That will give us some more data
> to go on. These airplanes should be going
> faster with all that HP.
>
> Paul Lamar ...No rotor no motor.
>
Warp Drive offers a prop blade with a modified tip. I'm not sure what
it looks like, but I suspect it's similar to what you are proposing.
It allows a higher pitch setting for the same static rpm. According to
the guy I talked to at Warp Drive, they recommend it for engines that
need lower pitch settings but it isn't beneficial if you can already use
the high pitch settings.
There seems to be a consensus that the Warp Drive prop doesn't have the
right "twist" at the right places and that is producing the "brick
wall" at 165 mph as seen by Bill Eslick. The constant speed props
don't appear to have any significant twist either. Should it be any
harder to make a blade for a ground adjustable prop that will perform
well at EITHER climb or cruise than it is to make a blade for a CS prop
that can operate in both regimes? Of course the CS give you both but it
seems to me that if the blade looked like a CS blade, I should be able
to set it for one or the other, or somewhere in between. What is the
deficiency in the Warp Drive blade compared to a typical CS blade?
Bob W.
N93BD - Rotary Powered BD-4 -
http://www.bob-white.com
First Flight: 11/23/2006 7:50AM - 1.7 Hours Total Time
Cables for your rotary installation -
http://www.roblinphoto.com/shop/
*******************************************************
Constant speed props do have twist and some air racers have
the twist optimized by prop services for their airplanes
top speed.
If one could some how design a variable pitch hub for a variable
>>>TWIST<<< IVO blade it would be a perfect prop :)
OK all you engineers out there, lets have a design contest.
Must be scale 3D. I'll entertain REALLY good ideas and do
a 3D for you if I think your idea has real merit.
Paul Lamar ...No rotor no motor.
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Please don't overlook the fact that the same phenomenon is apparent in
my charts even using wood props with lots of twist.
That is why I believe I am just out of power.
Bill Eslick
Good point Bill so it is not just a twist problem.
Given that fact IMHO blade area becomes an issue.
What are the widths of the blades Bill?
Paul Lamar ...No rotor no motor.
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
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Copyright 1998-2006 All world wide rights reserved.