Wright Stuff C

[lechassin]

Basically the prop blades are held by their trailing edge so the blades flex to higher pitch under the higher launch torque.

It's too many steps to write out effectively so we made you a video: https://www.youtube.com/watch?v=BCXz3t8Q-8I&t=5s

Good luck!

[CrayolaCrayon]

Basically the prop blades are held by their trailing edge so the blades flex to higher pitch under the higher launch torque.

It's too many steps to write out effectively so we made you a video: https://www.youtube.com/watch?v=BCXz3t8Q-8I&t=5s

Good luck!

Very good explanation. I like the jig you've set up!

I must ask, are you an engineer?

[lechassin]

Mmm, no. I wasn't good enough at math. I'm a retired surgeon.

Today is the quest for just-right thinner bottles.

[xiangyu]

Basically the prop blades are held by their trailing edge so the blades flex to higher pitch under the higher launch torque.

It's too many steps to write out effectively so we made you a video: https://www.youtube.com/watch?v=BCXz3t8Q-8I&t=5s

Good luck!

Wow! Thank you so much! I will for sure use your tips in the future with my team.

[xiangyu]

Xiangyu,

See reply #125 and after here for flaring prop ideas:

https://www.hippocketaeronautics.com/hp ... =23474.125

Also, instead of creating twisting flexibility in the prop spar, you can us a flexible material for the prop blade to cause flaring. Orienting the blade so that most or all of the blade area is forward of the spar is typical. You can use a number of different materials for the propeller spar; carbon rod, basswood, hard balsa, etc. I would suggest copying a successful style and building the prop and try it. Then test as many variations and as many rubber motor densities as you have time for.

Brian T

Thanks! I will try this out with my team soon.

[lechassin]

I'm curious to see how much math and/or design software can optimize things. To be sure, the shape of my blades and the amount of helical pitch is un-scientific (but not bad looking IMO).

My approach now is to first set the relaxed pitch based on remaining knots, starting at 30 degrees at the tips and tweaking the paper clips as needed.

Then we keep making thinner blades until the flaring is detrimental. Our best rigid prop had 0.017" thick blades, yesterday's time improvements were with 0.010" blades, and today I found a suitable water bottle and made a prop with 0.008" blades.

We'll compare it to the 0.010" prop next Sunday and hopefully get good video(s).

[bjt4888]

Eric,

Good job experimenting with softer and stiffer flaring. You can also accomplish this by sanding certain plastic blade material. The Chris Goins “Double Trouble” design (in Hip Pocket) and previous posts of mine in this Forum’s 2015 WS section describe the process.

Keep up the good work. There are still more best practices to discover.

Brian T

[lechassin]

Here's what I found: https://www.hippocketaeronautics.com/hp ... c=17412.75

About half way down the page is a drawing of a sanded blade and interestingly it's in the same ball park as the blades I made today, although the prop and plane specs are different so we'll have to see.

[bjt4888]

Eric,

Yes, that’s the Ikara propeller sanding diagram from the Double Trouble Plan. My team’s sanded flaring prop method is in the 2015 WS thread and is a little simpler and still very effective. That year, my best team flew 3:46 in a 22 ft scrubbable ceiling and won the Michigan State Championships. The team we beat was Northville HS, the eventual National champion (they flew 3:18).

We used this same propeller last year for part of the season to fly a best of 3:51 in a 30 ft ceiling (after this, we finished testing a better prop that did 3:58 at 18 ft; capable of much more in higher ceilings but our States is in a very low ceiling so we weren’t testing for high ceiling at that time).

Brian T

[lechassin]

We went to the well-lit parking lot near our house with one of the first planes I made, very little breeze, and torqued the 0.008" thick prop to 0.3 in.oz, our usual launch torque.

The prop works, um, great...

...the plane climbed above the lights (25-30 feet) and just plain disappeared into the night sky. It surely came down somewhere but I absolutely cannot find it.

Soooo, that's two planes that have flown away outside testing improved props, without intentionally over-torquing the launches. We're down to the plane Luke made and the plane I made with the shifting wings, so in addition to me making another 0.008" thick prop, now's a good a time for Luke to make himself another plane.

Note to self: stop over-doing it outside