Prop blade cutout drag

[Ron Lee]

Someone mentioned that this area can cause drag. Currently I do not have the aft side cutouts installed. I am working on fiberglass inserts. With three openings in this area, can someone approximate the speed loss?

Will I pick up 2-3 knots for each part that I fill in?

[DakotaHawk]

Ron, I've never filled in my aft side cutouts either. I'd be interested in seeing a true test of before/after speeds when the cutouts are installed. Maybe Bob A. has already done the tests?

[Bob Axsom]

It has been mentioned by Paul Lipps in this forum. I do think about it from time to time but I have not attempted it yet. I would guess that the total increase in speed would be on the order of the gain I got from my NACA vent covers - almost 1 knot (0.9 kt in my test). That is enough to cause me to think about it with my C/S prop. With a fixed pitch prop I would have done it already. If you do it Ron I would like to know your test results.

Bob Axsom

[SteinAir]

Paul certainly would be the guy to comment on this with authority - that's one of his many areas of expertise. The only thing I have to add is that some time ago we worked on a SX-300 (very slick plane) and everything you can imagine (and things you wouldn't think of) on that plane was sealed up. Cutouts for the spinner, the cowl to the crank even had a seal and the cowl to the spinner itself. I've never seen more attention to sealing up stuff than on that plane, but it was a fast devil!

Cheers,
Stein

[elippse]

I recommended to one of the people who races in the Sport Class that he seal his CS prop to the spinner. He made a rotary seal which gave him a 1.6% speed increase, which is like having 4.9% more power.

I was told the other day by someone that an SX300 picked up about 5 mph by putting stream-lined cuffs over the root section of his CS prop.

I just sent off a Hartzell blade to a fellow where I added hardening clay to his blade root with a nice airfoil and the proper twist, then covered it with two ply of fiberglass so that he can make a plug and make some cuffs for his prop. If everything goes well, I'm sure he will tell of his results, good or bad.

I notice that at least Strega and The Galloping Ghost P-51s at Reno this year had streamlined cuffs on their blades. Reno guys wouldn't put something on their blades unless it worked.

As far as the little triangular filler on the spinner behind the blade, I have no idea what the percentage increase will come about from having it on, but I would never consider my spinner-prop installation complete unless I had the prop completely sealed to the spinner. I even make a fillet from the spinner on to the front and back of the blade to get smooth flow. Why would you put thousands of hours taking care of every little detail and not fill in that hole?

Keep in mind that the total velocity of that hole in back of the prop is the combined forward speed and rotational velocity. With a rotational velocity of 104.4 mph at 2700 rpm on a 13" spinner and a forward TAS of 200 mph, the edges of that hole are going 225 mph!

I have some testing to do with my new prop, such as trying 0.002" nickel tape on my prop's LE, and if I think of it I will try to do a test with those fillers off.