Major vibration noise!

[brookfreeman71]

When I fly at altitude (20-400ft) and during take-off (not so much at landing), I hear a pulsing vibration noise coming from my prop. This noise NEVER happens during a motor test on the ground.

I fly a Mini Ultra Stick, with an E-Flite 450 motor, APC 10X7 prop, an E-Flite 20 amp ESC and 2000 mah batt. This noise has happened since I built my plane.

This happens with 2 other props; an E-Flite 10X7 and an APC 10X7 Slo-fly. The prop tracks true (one blade follows the other), and there is no play in the motor.

I am at a loss to understand what is happening. What really baffles me is this ONLY happens in flight (which leads me to believe it is an aerodynamic issue [but what?]).

If anyone has any ideas, please let me know. Thank you for your help.

Brook

[Wendi Smol]

Hi
can it be true that no one has any ideas? It should but would not surprise me.
Vibration is caused by an unbalance in the drive train - usually the prop.
At certain revs the vibration from the prop is amplified by resonation of other parts, particularly long thin structural parts (U.C. struts). It may sound like it's the prop but the real noise comes from the resonating part(s).

Balance the prop first and see if it helps.

Have fun

W.

[vintage1]

Probably cause by the prop turbulence hitting the airframe.

[brookfreeman71]

Hi
can it be true that no one has any ideas? It should but would not surprise me.
Vibration is caused by an unbalance in the drive train - usually the prop.
At certain revs the vibration from the prop is amplified by resonation of other parts, particularly long thin structural parts (U.C. struts). It may sound like it's the prop but the real noise comes from the resonating part(s).

Balance the prop first and see if it helps.

Have fun

W.

Wendi, Thanks for your input. I had this comment about the noise on another forum, and a few people on there said they had the same issue. I have tried three different props and still get the noise issue. I will double check my prop tonight.
Brook

[brookfreeman71]

Probably cause by the prop turbulence hitting the airframe.
Vintage- I think it is a combination of turbulence and resonance. Another mini stick pilot said it sounds like an angry hornet. Thank you for your input.

[MCarlton]

Could it be that the props, being light and more flexible than IC props, are flexing, so what you are hearing is a sort of "prop flutter"?

Try a lower pitch prop and see what happens

[Brandano]

If the noise is particularly more noticeable through pitch or yaw changes it could well be the blades flexing due to gyroscopic precession forces

[MCarlton]

Thats the word, gyroscopic precession, sounds better than "prop flutter"

Is this somewhat akin to "blade slap" ?

[brookfreeman71]

You guys (and girls) are great for posting your input. Thanks.

[Wendi Smol]

You guys (and girls) are great for posting your input. Thanks.

Hi

so did you resove your problem? What was it?
It's always interesting to hear whether our assumptions were right or wrong.

Have fun

W.

[brookfreeman71]

Hi

so did you resove your problem? What was it?
It's always interesting to hear whether our assumptions were right or wrong.

Have fun

W.


Wendi,

Thanks for your inquiry.

I bought a Great Planes fingertip prop balancer at Hobby Town

(here it is at Tower Hobbies:
http://www3.towerhobbies.com/cgi-bin/WTI0001P?I=LXK247&P=8)

and the prop balanced perfectly.

My assumption is the noise is caused my resonance in the model, and perhaps turbulence. had a slight problem the other day, and had to switch back to a 10X7 Slow fly prop (which is balanced also), and the noise is still there, albiet not as pronounced. So that made me think it wasn't the prop. I don't think its flutter either, because a fast and low fly-by revealed no control surface movement.

When I asked on the Mini Stick forum, some other pilots chimed in and said their planes did the same thing (and some said theirs did not). Several things were mentioned: wheels not being tight; stock wheels make the noise; wing resonance etc.

What puzzles me is it happens on some models and not others. I have not noticed any performance problems due to the noise.

Thank you very much for your help, Wendi. What do you fly? Besides my Mini Stick I have an E-Flite MCx and am working on combining two models into one (long story).

Brook