Quiet Props

Acroduster · Nov 2, 2017

This is a welcome development. Hopefully the aftermarket propeller designers can emulate this...

DJI’s quiet new drone could be easier to integrate into everyday life

RichWest · Nov 2, 2017

It is interesting, I'm hoping the same from the aftermarket. I had read an article over the last year of improvements to airfoil design for helicopter blades. I'd wondered if the back swept tip design could improve efficiencies and reduce noise for our application. It is an interesting thought and science, seems it's closer to reality now.

I've pondered the thought to mod some 11" APC props down to 10" in an attempt to incorporate the back swept tip. Just haven't reasoned for being an up or down design. Then I woke up and realized I've got no background in airfoil design....

Maddog · Nov 2, 2017

I've noticed the same thing comparing stock to Master props. The Master props just sound less annoying.

Just so Rich knows, their tips are turned up also. Wonder if DJI took a lesson from them?

Maddog · Nov 2, 2017

RichWest said:
It is interesting, I'm hoping the same from the aftermarket. I had read an article over the last year of improvements to airfoil design for helicopter blades. I'd wondered if the back swept tip design could improve efficiencies and reduce noise for our application. It is an interesting thought and science, seems it's closer to reality now.

I've pondered the thought to mod some 11" APC props down to 10" in an attempt to incorporate the back swept tip. Just haven't reasoned for being an up or down design. Then I woke up and realized I've got no background in airfoil design....

You could just heat your props with a heat gun and bend the tips up. Might work or Solo might behave like a buckin' bronco.

RichWest · Nov 2, 2017

Maddog said:
You could just heat your props with a heat gun and bend the tips up. Might work or Solo might behave like a buckin' bronco.

It's on the "back burner" at the moment, but I do have some broken APCs I'll test later this winter. There are several thoughts as to why tips up or down. So more reading is required.

The cool thing from the DJl's offering is that it will help expand the conversation and solutions to other platforms.

andrew.baker.142 · Nov 2, 2017

Reducing noise on (full scale) helicopters has been a topic of research for many years.
The key is to reduce disk loading (larger props), lower tip Mach number (lower RPM) and reduce/avoiding flying through your own tip vortex (tip shape helps here).
The DJI article specifically discusses reducing the rpm (and frequency) to make the quad noise less objectionable.
I would definitely NOT recommend the DIY solution of bending the prop tips. It will only make things worse aerodynamically and your chances of getting the props balanced again are pretty low.

RichWest · Nov 3, 2017

andrew.baker.142 said:
I would definitely NOT recommend the DIY solution of bending the prop tips. It will only make things worse aerodynamically and your chances of getting the props balanced again are pretty low.

I do agree a DIY effort would be filled with issues, even reaching marginal results. In either case it's an interesting topic, prop tech. Here's to stealthier props.

banjopad · Nov 4, 2017

RichWest said:
I do agree a DIY effort would be filled with issues, even reaching marginal results. In either case it's an interesting topic, prop tech. Here's to stealthier props.

Well -- 3DR dos'nt have any R & D now like DJI, so it's going to have to be DIY. My Mavic dos'nt record sound anyway -- Completely silent after it get 10 ft away.

RichWest · Nov 4, 2017

banjopad said:
Well -- 3DR dos'nt have any R & D now like DJI, so it's going to have to be DIY. My Mavic dos'nt record sound anyway -- Completely silent after it get 10 ft away.

True, but there is both MAS and APC that could develop better as that is their business. Like I said, could just be the kick start needed to further the idea.

Looking for adhesive backed stiff plastic film of about .020". Anyone with some ideas on where to source? Just need about 4" worth...

Maddog · Nov 4, 2017

RichWest said:
True, but there is both MAS and APC that could develop better as that is their business. Like I said, could just be the kick start needed to further the idea.

Looking for adhesive backed stiff plastic film of about .020". Anyone with some ideas on where to source? Just need about 4" worth...

I have a roll of UHMV that is 3" wide, about .020" thick, 5' long. You can find it online- woodworkers us it to make jigs that slide easily, etc. Comes in many thicknesses.
UHMV stands for Ultra-High Molecular Viscosity

I can send you some if you like.

RichWest · Nov 4, 2017

Maddog said:
I have a roll of UHMV that is 3" wide, about .020" thick, 5' long. You can find it online- woodworkers us it to make jigs that slide easily, etc. Comes in many thicknesses.
UHMV stands for Ultra-High Molecular Viscosity

I can send you some if you like.

I have a wood crafters near a Fry's I wanted to get to today...will try there... Thanks!

RichWest · Mar 17, 2018

Hey Maddog, I did try to mod a prop with an extended flap tip. Had about an 1/8" flap on the trailing edge of about 1/4" wide inside the tip. I followed the pitch of the prop. At low idle rpm was no problem, as throttle was applied it maintained and then it went crazy. The flap, at flight rpm, was causing the blade leading edge to rotate down forcing the blade down and then back up on the rebound. The blade tip developed maybe an inch of flutter. It was quite spectacular, obviously I stopped the test.

Yes just one motor and on the ground with me holding down Solo.

This video reminded me to followup.

Maddog · Mar 21, 2018

RichWest said:
Hey Maddog, I did try to mod a prop with an extended flap tip. Had about an 1/8" flap on the trailing edge of about 1/4" wide inside the tip. I followed the pitch of the prop. At low idle rpm was no problem, as throttle was applied it maintained and then it went crazy. The flap, at flight rpm, was causing the blade leading edge to rotate down forcing the blade down and then back up on the rebound. The blade tip developed maybe an inch of flutter. It was quite spectacular, obviously I stopped the test.

Yes just one motor and on the ground with me holding down Solo.

This video reminded me to followup.

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Definitely not something for us amateurs.
Some time ago I saw an old high-speed video of a helicopter rotor blade in motion. I couldn’t believe all the “gyrations” it went through in normal flight. It almost looked like a flapping bird wing.