>Paul,
>We are converting our Team Steadfast Yak from a modified super DC3 prop
>to a S2F Tracker prop. We came up with 6 blades (so I can make 2 styles)
>to work with as well as a serviceable hub.
>I will be cutting the blades 4? from the tip to get the diameter down to
>124?. Anyone have any information on the most efficient tip design for
>high speed props?
>We have 2 gear reduction cases and can turn this prop at either .7 mach
>or .9 mach. Target indicated airspeed is 380 knots at 7000 ft density.
>Engine PW R2000.
>There are a few tip designs that have been tried, but I am open to any
>great ideas.
>Thanks,
>Larry
> Super thin is in. You want to have the twist such that the tips
> are running at a low angle of attack with a very thin airfoil.
> Swept back helps too.
--
> Paul Lamar ...No rotor no motor.
Hi Larry, In another life I worked with blade design engineers at
Hamilton Standard. There is a ton of history and calculation in a blade
as the airfoil shape progresses from the hub to the tip. (all
essentially automated today). I can assure you that cutting anything off
the tips will NOT porvide a better blade. If it hits the ground because
it's too long---well mabe that's an exception : ) What you will wind up
with is a blade that does not have the proper twist over its length and
has a tip thickness that is thicker than optimum. Since it is virtually
impossible to retwist a blade you will have to accept this ineffiency.
Also, if you try to dress down the thickness at the tip you would have
to carry that material removal all the way to the hub to even approach a
proper blade again. I know people cut blades down every day but most of
them don't take the time to understand the entire story. I hope you will
as the blade tip controls extreemly important aspects of blade
performance. RPM-wise the only blades that H.S. developed that were
efficient at almost supersonic speeds were banana shaped in profile and
were a well guarded propietary section shape. Therefore the .7 g'box you
have available is probably the best choice. Hope this helps in your
decisions. Dave M
Lots of guys re twist the CS blades at Reno.
Paul Lamar
Thanks Dave,
We did have to cut 4 inches off the tips for ground clearance....
Pilot wanted 5.5 inches cut, I told him to start 3 pointing the landings!
Need the diameter to go faster!
We copied the tips from another Yak that has the same engine and blades and
has a history of going fast. I will upload a picture when I get one.
There was only a very slight twist difference in that area, and these blades
have about 10 deg more twist than our old blades. They are headed to
Stockton Propeller (one of our sponsors) for finishing and balance.
I'll let you guys know how fast it is when we get it installed.
Larry
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