More P-Nut capers

[Dave Robelen]

Hi All,
Just about when you though I might stop messing with this little bird, I pop up again. As a result of the stiff competition in the pylon racing, I decided to use other means to measure performance. For speed, my daughter and I set up two poles 100' apart in a small pasture, and timed runs back and forth. Meanwhile I had been working wih several maneuvers to measure the aerobatic potential.
At this point the poor little bird has gained an inch of wingspan, new gearing (8-1) and a new prop (a 5 X5 with helical pitch).
So what? Well, I now have a little bird that cruises at 23 mph in level dlight, can pull large loops, multiple rolls, and a recognizable Cuban eight. What this means to me is that I am getting more freedom to fly my little micro in weather that is not calm, and can begin to enjoy real live aerobatics where power is a factor. Some fun numbers are the prop rpm at cruise=4,000, and that means a motor rpm of 32,000. Sort of reminds me of when I was pushing the GWS EDF motor around with a gearbox. Take a low resistance motor, tall gearing, and ample prop, and you have a formula for performance. The picture will show the 72t large gear sort of poking through the top of the nose. These gears came from one of thse battery alarm clocks, and are terrific for our use.
Cheers, Dave

[Fwilly]

whats your thrust gain with your new gearing and prop?
thanks
mike

[Dave Robelen]

Hi Mike,
You are reminding me of something that I have not been doing. Instead of measuring static thrust, a numbr that is dubious at best, I have been comparing performance in flight. This little bird P-Nut, benefits from a pretty high pitch because of the range of flying speed. Usually, the high pitch props like this one do not look all that great in a static thrust measurement. While things are still together, I will try to get a reading of a couple of props on this motor/gear setup.
Regards, Dave

[bmutlugil]

Hi Dave,

The racer/aerobat looks good, as well as the performance specs. Is the wing made of the foam type that is used for insulation in building construction? If so, it should be quite strong, once I chucked a piece of this foam in the lathe and turned a 4" long part for a handle. Is the model without any finish on the surface - or will the finish come later? If so, how will the wing be finished?

I was thinking of using this material for the wings of a J-3 Cub to be used as a trainer - using the 3-views you sent.. For this size wing, is there any need for spars or other reinforcement with a Clark Y profile, do you think?

Best regards,

Bulent

[Dave Robelen]

Hello Bulent,
Yes, the wing is made from insulation foam. There is one 1/4" wide strip of strapping tape on the lower surface that extends to 1/2 of the span on either side.
At this point the model is completely without finish. The foam wing weigh 3.5 grams for the 14" X3" wing, and the fuselage/tail weighs another 3.5 grams. If I were to put any finish on the wood, I would use RA Microlite plastic film. I do not have a satisfactory method for finishing a foam wing this size without a serious weight penalty. If I were to improve the cosmetics, I would use a framed wing covered with RA Microlite. Weight is so critical with these small models, that I was willing to exchange appearance for performance in this case.
The Clark Y airfoil is a very poor performer at small chords in this range. I am using the MA409 with good results (I found it in PROFILI), the Benedeck be6365b is another that worked well for me. A thin (6%) flat bottomed airfoil would be a reasonable alternate, especially if the last 10% of the chord were tipped down to create a drooped trailing edge.
Regards, Dave

[bmutlugil]

Hello Dave,

Do you mean be6356b or be6365b? I can not find info on the 6365b, but the 6356b is a profile I am accustomed to, from Wakefield days.. The Ma409 looks good also, has less undercamber..

Bulent

[Dave Robelen]

Hello Bulent,
You caught me! The correct answer is Be6356b. I have no idea if that "other one" exists except in my keyboard.
Regards, Dave