Crazy howling noise on two mini planes

Gazoo

Well-known member
I recently built a mini-guinea using two Emax 2204s with 6X3 GWS props (3S). It was pretty fast for my thumbs but plenty of fun to fly. Weird thing is that when I put it into a dive at WOT, when the airspeed increased, it would start making this crazy howling noise.

At first I thought it was because of the rubber bands I was using to hold the nose on with so I twisted them to eliminate any vibration. Still had the howling noise at high airspeed. Then I thought it might be the ping-pong ball I had recessed into the nose for a front wheel or just the air frame itself.

After folding the wing and firmly planting the MG into the earth, I ended up using the 2204 (with a different 6X3 prop as the former one was turned into a fine powder) on a modified FT Scout. I cut in ailerons and it had no rudder.

The scout is very nice to fly and it moves along nicely. When put into a dive at WOT, it too emits the same howling noise. It actually sounds cool but I can see where others at the park may be annoyed by my audible foolishness. Like the couple trying to play a relaxing game of tennis.

It makes sense that the noise is coming from the prop. Anyone else have this noise? Can anyone venture an explanation?
 

earthsciteach

Moderator
Moderator
I can't say definitively, but since these planes are foamboard, it could be caused by paper vibrating along cut edges. Or, maybe its vibrations caused by openings in the fuselage. Or, and this is quite possible, you are getting flutter due to the high speed.
 

French

Construire Voler S'écraser Répéter
What props are you using? Since it's happening on two different planes, maybe it's power system related. What speeds are you talking about in these dives?
 

Gazoo

Well-known member
What props are you using? Since it's happening on two different planes, maybe it's power system related. What speeds are you talking about in these dives?

The motor is an Emax 2204 and it has a GWS 6030.

Edit: I don't really know how fast it goes. The Mini-Guinea was faster than the Scout. The Scout is pretty draggy.
 
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SlingShot

Maneuvering With Purpose
My mini Mustang has an aileron push-rod that has a distinct buzz as it vibrates against the control horn..
 

Hai-Lee

Old and Bold RC PILOT
The noisy motor/prop combinations I have currently have two separate sources depending on the noise type or base frequency.

The low "Motor like" sounds are normally attributable to the motor'prop combination being out of balance of the motor having a slightly bent shaft.

The higher pitch sounds which can sound like a jet engine spooling up are normally due to propeller tip speed on high revving motors especially when unloading in a high speed dive followed by a flt past.

The noises seem to be amplified or far more noticeable in the aircraft using the mini power pod as the power pod can move, (vibrate), as it is only held in by the skewers and is not glued to the larger mass of the fuselage.

Whilst I cannot suggest what the noise you are hearing is attributable to I have traced the noise generators in my own hangar. I suspect that you are using noisy props or have a slight out of balance condition in your setup.

Have fun!
 

kdobson83

Well-known member
Are the props flexible? I was watching a review on props the other day, mrsteele, he was talking about noise coming from the thinner more flexible props. I'm assuming at higher speeds these thinner props vibrate and make more noise. My cheap 6030's were super loud at WOT but my heavier 5x4x3 and 6045 are pretty quiet, well, quiet compared to the 6030's. Lol Try a higher quality prop, or something stiffer.
 

JimCR120

Got Lobstah?
Site Moderator
I've always noticed a different sound when using prop savers vs bolted prop adapters.

Does it make the noise with the engine spinning before you launch it into flight?
Does it make the noise without a prop on?
 

Gazoo

Well-known member
After flying it again, it is definitely the props I'm using. The prop is mounted directly to the motor with a nut. Initially (with a fresh 3S battery) it would make the noise. After a while (when the voltage on the battery was lower) I could not get it to make the same noise.

Using the same prop/motor combo on the mini guinea made the same noise but double because it has two motors.

The props are definitely flexible.

And, it does not make the noise with a fresh batt at WOT when I hold it. Or on takeoff. Only when there is a high airspeed.

Either way, the problem is solved as I silenced it by sticking it into a tree.

I need to shrink the size of the video to get it to upload...if anyone is interested.
 

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kdobson83

Well-known member
Well, the props/motors will spin faster when the plane is moving compared to you holding it on the ground. It's not pushing as much air when it's moving allowing the props to spin faster. Sounds to me like it's noise from the flexable props. Put a stiffer HQ prop or something of the sort, same size just stiffer, and I bet money it doesn't make that sound anymore.
 

dayve

Member
I had the exact same issue on my Mini Arrow. Whenever I used a 6x3 or 7x3.5 cheapo GWS clone prop on a 2204, it would make that howl at WOT. Once the pack was about half used, it would only happen in a dive. It's pretty clearly related to RPM, but I'm not sure exactly what the issue is. I did a bit of math. With the 7" prop, the tips are approaching supersonic. I figure it's either the tips going supersonic or just a matter of the cheap, flimsy props getting some sort of flutter going at very high RPM. I switched to a HQ 5x4x3. Never heard it again.

Edit: You posted the video while I was typing this. Yes, that's the exact noise mine made.
 
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Gazoo

Well-known member
Thanks guys. Nice to get some input on this. I have the plans for the Mini Cruiser that I am going to put the 2204 motors on. I also have some carbon fiber 6X3 multi-rotor props to put on it. It will have both CCW and CW motors and props. I'm guessing the CF props will not emit that noise...
 

mrf

Member
I've had some cheap and nasty flexible props vibrate themselves to death on the mini arrow before! I heard a funny noise and then lost power. Glided the thing to the ground and found the propeller had exploded and blades lodged in the foam board!

I've found that if you search for "durable props" on ebay you'll get some nicer results. Carbon Fibre works too, but is a bit more expensive.

I don't know if anyone with more experience can confirm, but I've also heard a whirring sound if there's a big enough chip in one of the blades from a previous crash. It's probably related to the propeller being out of balance as was mentioned in a post above.