quote:

ORIGINAL: Malcolm H

Brian/Brenner,

About 100 years ago when I was actively into control line teamrace we habitually used to washout the tips of our 7 x 8'' Bartels glass props by removing some material from the last inch of trailing edge towards the tip in a triangle as viewed in plan and then using a flat sanding block thin back the trailing edge keeping the back of the prop as flat as possible and washing out the tip.

The result was more revs than the standard prop without losing dia and h99opefully an increase in efficiency. The problem I see with modifying a standard pair of props in this way will be an increase in revs and hence noise both static and airborne. I believe the only way this approach will bear fruit is with an increase in dia which isn't really desirable or a redistribution of blade area which might be worth experimenting with.

Malcolm

quote:

ORIGINAL: underdw

Sorry to interrupt a great discussion.....

Brenner, back to the new Neu adaptor: do you have an estimate as to when it will be available?

I took apart my drive tonight and found that 4 of the 8 teeth are almost gone. (1 season of flying, and it should be noted that my motor is one of the ones with the swapped spacers resulting in less engagement distance)
From Neu's website, an estimated repair cost to the motor is $126 + 2x shipping. So, I'm not excited about putting a newly repaired motor on the existing adaptor.

The good news it that it seems like I'll be able to get additional life from the current pinion by carefully assembling it so that the unworn teeth now engage the drive.

Another reason I'm looking forward to the new adaptor, is that I've always suspected that the clatter in that interface contributes significantly to the overall noise.
( it sounds really bad at startup)

Thanks, Dan

quote:

ORIGINAL: Jason Arnold



One would think that if it's a manufacturing defect then the repair would be free....

Cheers,
Jason.

quote:

ORIGINAL: Brenner

There are also a couple of things to note about the current Contra props, that might be of use to consider:

1/.. The ''disk power loading'' for each prop (W/mm^2) is close to half the disk power loading that a single prop setup has. This improves efficiency, and it also changes the angle of attack that each prop runs at in a steady state condition. For instance. my calculations show that at maximum horizontal speed a 22x22 setup is running at a theoretical pitch speed of -11 mph, and a 22x18 setup is running at a theoretical pitch speed of -3 mph, which in and of itself is perhaps a good argument for higher pitch props, but it also suggests to me that additional washout isn't going to improve noise or efficiency much during high speed flight. However, static noise testing on the ground is a different matter.

2/.. When the Contra is run at full throttle on the ground, (like during noise testing..) the front prop is stalled, and the rear prop is probably partially stalled, so under these conditions, I think that anything that can unstall the blades is probably going to help with efficieny and noise. Here additional washout near the tip could perhaps help.

Brenner ...