Air Racing

[paul330]

Thanks Michael.

That's just the sort of info I need. I find that surprising but scratch one idea. Saves me all the time and effort taking the cowls off, making the adjustments, testing it .......

How about the other 2........?

Last year there were 5 RV-10s. We were all pretty much equal in speed - the 2-bladers might have had 1/2kt on me. Except one who was about 4 knots faster and came in 3rd out of 115. Supposedly stock build with standard engine and mags - nobody could work out why he was so quick......

[rv8ch]

Originally Posted by paul330

...

- rig ailerons (say) 1 degree up. Less lift produced in the outboard wing section and more inboard so reduction in tip vortex drag.
...

I've heard that this can help, might want to consider the same for flaps, if it's possible on the -10.

Can you restrict intake or exit air? Build a cowl flap? Smaller tires and smaller wheel pants?

[rv8ch]

Originally Posted by MConner

I have heard that racers clean and wax their prop daily.

Not going anywhere near that one!

[DanH]

Ok, not allowed to tape gaps. Anything in the rules about sealing them from the inside? Sealant, foam tape, flap seal?

Some gap and fairing joggle drag is external, but some of it is excrescence drag, jets of air escaping from inside the airframe. The jets are similar to hard parts sticking out into the airstream.

Same problem; different aspect: airflow through the interior of the airframe is exactly like cooling drag, i.e. drag = mass x loss of velocity. Reducing the mass flow or the velocity loss is a drag reduction.

Cooling drag itself can be big factor. Given a typical GA cooling system, any air which enters the front and exits the rear suffers a loss of velocity. Mass required for cooling is, well, required. However, any which bypasses a trip between hot fins is pure drag; it did nothing useful. So examine your engine compartment sealing very carefully, in particular if you have flap seals. Most leak badly. Reduce leaks to reduce mass flow.

Is your propshaft sealed?

Now address loss of velocity. Fair any structure in the cooling outflow, like nose gear support tubes. Remove or move garbage hanging in that flow.

Do you have any cooling headroom? If CHTs are low, reduce the cowling exit area.

Want to get serious? There is very likely some energy loss at the underside of the cylinders and heads, where the two cooling streams (imagine one from each side of a cylinder) meet at the exit of the baffle wraps. Decreasing that loss would result in higher exit velocity. It's one of the reasons the water cooled guys can get less cooling drag.

[Alan Carroll]

Originally Posted by paul330

ballast in the baggage hold. Reduces trim drag by shifting CG aft. However, ups the gross weight.

I did some experimenting with this years ago in the RV-8. In theory it should work, but I could not measure an improvement.

[paul330]

Sealed everything I can in the cowl. CHTs run at just around 400F during racing so I don't want to reduce cooling any more. This is meant to be fun and I don't want to compromise the life of the engine. I experimented last year with putting in a bigger oil cooler and reducing the flow from the #6 baffle. Oil temp is fine and I reduced #6 (highest) temp by about 15F - so I can run a bit leaner ie closer to best power. Nothing else to be done there ...... I'll put a boroscope in the cowl and make sure all the seals are good - pretty sure they are but worth a look.

I agree that aft ballast should help but can't quantify it.

I will try rigging the ailerons up a bit - that's easy to do and to undo. Flaps can't be changed.

Thanks for the inputs!

[DanH]

It's a matter of adding up little improvements here and there. Racing has always been like that. You can find more.

Back in the 80's I had a friend with an identical production racebike. All season long, I could draft past him with about a half a mile per hour to spare, which had him muttering and throwing things in the pits and threatening to file a protest, as surely I was cheating. At the end of the season I showed him a photo another friend had taken of us on the main straight at Roebling Road. We looked like twins, both tucked tight...except I was sliding my feet back so just my toes were on the pegs, then pulling my heels in tight. Tony's toes were in the breeze, like little speed brakes

[rvbuilder2002]

Originally Posted by rv8ch

I've heard that this can help, might want to consider the same for flaps, if it's possible on the -10.

The RV-10 airfoil is designed in such a way that in high speed flight angle of attack the ailerons and flaps are already in a reflexed position.
At high speed they are very slightly loaded on the upper surface already. Reflexing them any more would probably be adding drag, not reducing it.

[paul330]

Originally Posted by rvbuilder2002

The RV-10 airfoil is designed in such a way that in high speed flight angle of attack the ailerons and flaps are already in a reflexed position.
At high speed they are very slightly loaded on the upper surface already. Reflexing them any more would probably be adding drag, not reducing it.

Thanks Scott

The idea was to re-rig the ailerons only up by 1 degree. The thinking was that this would effectively slightly reduce the AoA and lift at the outer wing thus reducing the tip losses. Of course, it would be necessary to increase the inboard lift slightly to compensate but, again, the thinking was that the inboard section of wing is more efficient.

But you are the expert and if you think it would be counter-productive......