Wright Stuff C

[CrayolaCrayon]

So I just received some broad blade flaring props. I have seen some talk about sanding them down. Would the purpose of sanding be to decrease their weight? Also, how should they be sanded to achieve the purpose of sanding?

Thanks

Flaring props are sanded behind that thing that holds the blade so that they actually flare.

[bjt4888]

Crayola,

Good job, you hit the nail on the head. The part that the blades are attached to is called the spar.

I think it’s safe to say that 100% of AMA national records and national championships used flaring propellers for low ceiling sites (low ceiling being less than 8 meters, in most cases; in some cases, flaring props are successful up to 15 meters plus). Blade shape, blade area, softness of flaring and method for achieving flaring are all items to research and test (research Hip Pocket Aeronautics; all airplane classes, not just SO; research Indoor News and Views; research the archives of this wiki). And of course, matching the flaring propeller to the rubber density and length.

Brian T

[Alke]

Today, we were able to test in a draft-free environment which allowed us to notice some peculiarities with the plane. We used a standard Freedom Flight model airplane, symmetrical 24 cm. Ikara prop, and 18.5" of .094" rubber weighing 2.38 grams. We winded our rubber motor to 1,575 turns with a max torque of 1.1 ounces per square inch. Our launch torque was always .4 ounces per square inch. However, the number of rewinds differed. Most importantly, on some runs, the peak height was ~16 ft while on others, the peak height was ~40 ft. Both differed in the number of circles to peak. Flight time scaled with peak height. The first run on a fresh rubber band produced a low peak height. The third produced a high peak height. The rubber motor broke after that. We replicated the flight with other rubber motors and the peak height inconsisties continued.

Why does the peak height change so much? Can it be that our torque meter produces inaccurate torque measurements since its 15" long and the rubber band is 18.5" long?

Constants: Angle of incidence of all surfaces, winding technique, rubber band motor, 2 o-rings, launch torque, max winds, no/little drafts in room, torque meter, symmetrical 24 cm Ikara prop with both surfaces at the same pitch, launching technique

Thanks,

Ethan

[bjt4888]

Ethan,

By “number of rewinds differed” are you referring to backoff winds to reduce from max torque of 1.1 to get to launch torque of 0.4 in oz.?

Did you make your own torque meter, or is it the Freedom Flight meter?

Brian T

[bjt4888]

How much did the backoff turns differ on these flights?

[Alke]

Ethan,

By “number of rewinds differed” are you referring to backoff winds to reduce from max torque of 1.1 to get to launch torque of 0.4 in oz.?

Did you make your own torque meter, or is it the Freedom Flight meter?

Brian T

Hi Brian,

Yes, "Number of rewinds differed" should refer to the backoff turns to reduce the max torque to achieve a launch torque. Also, we're using a Freedom Flight torque meter (ordered last year). The distance from the winder's hook to the torque meter hook is ~15 cm.

Thanks,

Ethan

[Alke]

How much did the backoff turns differ on these flights?

Bjt,

When there was a high peak height, the backoff turns were ~150 turns. Conversely, when there was a low peak height, it was ~600 turns. However, the max turns, max torque, and launch torque were all the same.

Thanks,

Ethan

[DarthBuilder]

Hello,

This is a bad question but can you go in depth to what a flaring prop is and is it allowed this year for Div C?

[Alke]

Hello,

This is a bad question but can you go in depth to what a flaring prop is and is it allowed this year for Div C?

Hi DarthBuilder,

These are good questions and I'll try to answer them to the best of my limited knowledge!

1. With Wright Stuff, there are two main types of propeller styles: non-flaring and flaring. Take a look at these pictures and try to notice the differences.
Non-flaring: https://freedomflightmodels.com/images/ ... pLarge.jpg
Flaring: https://freedomflightmodels.com/images/ ... pLarge.jpg

As you can observe, the non-flaring propeller is symmetrical about the length of the propeller. However, the flaring propeller is not symmetrical in this regard. This propeller's symmetrical nature changes the behavior of the propeller. In non-flaring propellers, the pitch (angle) does not change. However, with a flaring propeller, the unsymmetrical shape allows the pitch to temporarily increase at the beginning of the flight because of the higher torque. Consequently, the temporarily increased pitch slows down the climb, conserving winds. After this initial spike of torque, the blade will flex back to its original, flatter pitch. To my knowledge, this behavior is useful in low-ceiling conditions.

2. Yes, this is allowed for Division C as non-flaring propellers do not have moving components that change the pitch.

Hopefully, that helped! Please feel free to correct me.

Ethan

[bjt4888]

Ethan,

150 backoff turns vs. 600 backoff turns is a very large differential to arrive at launch torque. A variance of 15 or 30 (one or two winder turns of the usual 15:1 winder) is typical.

It sounds like something is binding or rubbing in your torque meter setup. Is the pointer needle dragging on the readout dial? Or possibly the hole in the white nose button is too small and there is friction there. Probably you are already doing this, but you do want to keep the rubber level with the torque meter so that the meter dial pretty much rests on the piece of wood it is mounted on (this is as you finish winding and are reading the meter and slowly backing off). We use my digital meter and two of my self made meters and a couple of the FF meters for my four HS teams that I coach. The FF meters have been very consistent and accurate for us. Look your meter over carefully for issues.

Brian T