Noisey electric models

[Paul Jefferies]

My first electric model was a foam Wot 4 and I was struck by how quiet it was. It was followed by an MX2 which was also pretty quiet. I have subsequently designed and built a pattern (aerobatic) model and also bought a HK Bixler2 for aerial photography and both these latter models seem to make almost as much noise as some ic models and can certainly be heard from some distance away.

In the good old days when I flew aerobatics fairly seriously, we found that the propeller made a big difference to noise level and I can only assume that the noise from these electric models is due to the prop. Has anybody noticed that some designs/makes of electric flight propellers are quieter than others and if so, which are the quiet ones?

I know that electric motors have a kv rating and need to run at a certain speed but would it be disastrous to use more pitch to load it up more and slow the prop down? Does anyone have any other suggestion as to how to make electric models quieter?

Paul

[Pete B]

I too have a Bixler 2 and it is certainly the noisiest of my leccy models. It's a function of the high Kv and small prop - no chance of increasing the prop size on the Bixler though. A small increase in pitch, carefully monitored to avoid exceeding the system limitations, may be enough to reduce the RPM without affecting the performance too much.

Disastrous is a good way to describe the result of just increasing the pitch of the existing prop - unless you have a wattmeter to establish exactly what is going on. Increasing the diameter/pitch will mean that the motor will still attempt to run at its designed RPM and this will possibly be too much for the motor and ESC, both of which have a maximum amp rating.

I'm sure different makes of prop will produce different levels of sound, although I can't recommend one over another. I tend to use the APC 'E' range. The Master Airscrew range look very nice but I find they don't seem to be anywhere near as efficient as APC's.

In general, with tractor setups, reducing the motor Kv and increasing the prop diameter/pitch will result in quieter running.

Pete

[Erfolg]

I am not sure that the majority of noise comes from the prop at all.

Many of my models rev in the 10,000 rev min-1 region. They make very little noise.

I have one model that revs at 21,000 rev min-1, it makes a little more noise.

I have fitted IC props to electric models, as a consequence of a number of mistakes. I cannot say they made any more noise than the others. The main difference was that the revs were slightly down, discovered subsequently.

From observation and qualitative assessment. you have to work hard to make a electric model make noise. To do this, you need revs and the placement of the propeller very close to say the trailing edge of a pusher type model.

As for propellers used, I increasingly use APC style propellers, quite a few "Master electric" and some electric/IC propellers. As I have said, I have used IC props such as JXF and JM, they work, reduce revs, as such not ideal, although others have used them on electric models. In addition for gliders

I have used both Graupner and Aeronaut for folders. I have used unbranded Chinese propellers of this type and shed a blade with disastrous results, destroying the front of the model.

To sum up, for most ordinary applications, I am not sure that it matters to much, on every day models and set ups, although weight appears to reduce performance. For folders, it is Graupner or Aeronaut.

[Biggles' Elder Brother - Moderator]

I watched an electric powered Weston Mini Magnum last weekend down at the field - bot was that noisy! The noise was almost certainly a combination of motor rotor and propeller noise. These models are usually fitted with very high speed brushless in-runners with kV's in the region of 3000 and 5 or 6 cell battery - so max rpm is approaching towards 50-60k! V=Lots of fun, incredibly fast, but very noisy for an electric model!

BEB

[Erfolg]

As I wrote BEB, you have to work very hard to make a lot of noise with an electric. 50-60k revs min-1 is not a rev range for many models, perhaps other than DF.

I do believe that my Komet

which is fitted with a HXT 2835, 2700kv on a 3s is at all noisy, although it never reaches its theoretical revs, topping out at 23,700 rev min-1 (from my record book), using a 7*4. What noise there is not motor related. Although I emphasis, it is essentially quite.

The only electric models I have noted to be noisy have been close mounted propellers to the trailing edge, mounted as pushers. Move it away, and the noise drops very significantly (which I did with my flying wing).

[Martin Harris - Moderator]

Apart from interference effects from pushers in close proximity to trailing edges, I believe a common cause of noise is from out of balance props and spinners.

[Bob Black]

If the above apply with new motors ,ignore my post completely .......But if they are not new and have been laying around a wile unprotected from sanding dust, filing any metal etc they can also become quiet noisy. those magnets are good attractors would you believe!

[Mart49]

My Bixler2 was also the noisiest in my fleet, however it more down to the fact the bearings in the stock motor were nearly square! I changed it for an NTM 1400, put on a 7x5 and its now very smooth and a lot less noisy. I also wondered if the engine mount and the hollow area just behind it amplified the noise as well! Mart

[Alwyn Gee]

I'll second Martins post above with regards to balancing the prop and if at all possible the spinner. (Some are easier than others). I've had several occasions when a model that was usually quite quiet when it has had the prop changed for a brand new one (usually APC electric) has then become rather noisy and required the prop balanced to get it back to normal.

I have managed to get a semblence of balance on some of the plastic spinners, using my Great Planes magnetic balancer, by pushung one cone right to the end of the pin to support the pointy end as it were and fitting this through the backplate and then assembling the spinner and use the other cone to hold the backplate centered and finally giving the pin a push to ensure it is right through to the end of the front cone and the magnet is just strong enough to hold some of them. Don't forget to mark the sinner and backplate so that you always assemble it the same way after balancing. I have to say this does not work with all spinners but as they are nearer to the hub it is a little less important than the prop.

Hope this helps

Alwyn

[Mowerman]

Many electric models with rear mounted 'pusher' props are noisy due to the interaction of the air flow from the wing trailing edge, the closer the prop is to the trailing edge the noisier the model.

[Erfolg]

I certainly always balance my props, with electrics, there is no good reason for vibration, other than being out of balance. I have found to date, that a coat of WBV is all it takes to balance. I am not sure how I would manage without quick drying varnish now.

The noisy bearings interests me, I have had only the once, on a Cf 2812 on my Delta. The rear ball race had collapsed, although I noted the change in note, rather than thinking that is noisy. There is a certain beat with the twin motors on the Delta.

I do not balance spinners, principally because I do not know how to do it and secondly, I have concluded that the mass being so near the rotating axis, it hopefully is not significant

I have just been to find out what a Bixler is, I can now understand to some extent what one is. Yes, these are noisy, I very recently had the unfortunate task to ask a group of freelance flyers to not fly on one of our (club) fields, they were flying either Bixlers or the Graupner original. Yes, I take it all back, they are noisy, sound like a high reving 2 stroke motor cycle being rode with a death wish. Totally unacceptable at our field, in part due to flying on NT land, and the noise can be antisocial however you look at it. How such a model can be so noisy baffles me!

[malcolm woodcock 1]

Whatever the motor mount is fastened to can resonate quite loudly especially at max revs such as take offs, aerobatics etc.

[Paul Jefferies]

Many thanks all for your comments, I'm glad mine is not the only noisy Bixler. I had not heard the theory about proximity of the prop to the trailing edge but it would certainly explain why a pusher delta I had many years ago was as noisy as it was!

Prop balance is certainly something I need to look at. Unfortunately my balancer broke some time back and so far I haven't replaced it........ ebay here I come.

As for Erfolgs comment of " you have to work hard to make a electric model make noise.".......... Er, not really but I am trying quite hard to reduce the noise!

Thanks again to all for taking the trouble to reply.

Paul

[Shaunie]

Balancing of prop and spinner is important in my view. On one recent occasion I wasn't looking for lower noise but trying to reduce jello on my onboard camera. I am using a Thunder Tiger trainer as a camera ship with a very low kv motor (not deliberate, it was what I had). I took lots of time to balance the prop and spinner. I then adjusted the relationship of prop to motor in small increments until I got the lowest perceived vibration. I now have a plane that gives almost no vibration on the camera. The side effect of this is that at "low pass" speeds I think the unwary could walk in front of it as it's almost silent. The prop I am running is a 12X10 APC as a result of the low kv.

Shaunie.

[Ben B]

I think it is easy to underestimate the noise created by the ratcheting effect of a high kv inrunner. Just my gut instinct but they're far less smooth than an outrunner.

[YakMad]

I have used good quality inrunners as well as outrunners with no perceived noise difference, I have a Multiplex Acromaster which has an outrunner in it (Great Planes Rimfire), it was very noisy, I could not figure out why as I had balanced the prop, it has a foam spinner and the motor mount design spreads the load over a wide area of the fuz, it actually sounded like flutter but that was ruled out as well. I played around with the esc motor timing to no avail. I decided to change the esc (Hyperion) with a different make (Dymond) as a last resort and suddenly all was almost silent, I have since used the original esc in other models and I have not encountered the same effect.

[Dave Bran]

Anyone who feels that you have to work hard to make EP models noisy clearly has only explored a tiny fraction of their potential!

As to noise per type, I can't agree on the inrunner being noisier per se than the outrunner. I assume the ratcheting noise mentioned is the magnetic push/ pull effect of the rotor passing the fixed magnets, more usually called "cogging", and if so, outrunners normally are worse than inrunners, though from my experience there is no direct relationship from this into emitted running noise.

EP models with a prop "chopping" close past a flat surface are inherently noisy, be it pusher or even worse, prop in slot. EP pylon and fast wings can easily reach very high sound levels, as per one of my fast wings, which produced an extremely loud multiple echo off a tree line 1/4 mile away when first "aired". EPP "sound plate" Chevron wing, inrunner pusher running at extremely high revs meant a plane capable of 150mph plus and likely losing flying rights if continued. And that was balanced to perfection, motor and composite with prop, etc.

BTW, A friend had a EP model he wanted me to quieten down................it WAS very very noisy...............but then the wheels were vibrating on their axles and the push rods in their horns...............he'd spent some time trying various props............. DOH!!

In my opinion the noise annoyance issue with EP is amplified (!) by the high pitch of the noise, just like a Jet Ski is an annoying noise over a trad outboard drive boat, though usually not any more measuered noise dB wise.

[Martin Harris - Moderator]

The noisiest models at our club (by a country mile) are electric powered F5b "motor gliders" operated by one of our members, which use 5 to 6 kW motors driving enormous carbon props with massive pitch. The noise at launch or if the speed has decayed too far during the "pylon race" phase has to be heard to be believed as the prop blades are fully stalled but thankfully there are only a few sub 2 second blasts of these during the flight so can be tolerated as "silent flight"!

[Erfolg]

Martin

There were a number of models of the type you describe in our club. Not one has made the noise as described. In our club such a noise could not be tolerated, as it would put our field at risk. Although in the past being restricted to a 30s motor run now a 200m height limit, there performance in the climb, or going for height and distance have not been compromised.

Perhaps the two clubs I am a member of are exceptions, in that motor noise is not an issue, particularly when compared to IC motors (at one club).

We have even had a electric pylon racer being tested out, the simple boxy type, which did not make much noise.

Or is it that I am going deaf?

It could be, knowing that excessive (IC type) noise, cannot be tolerated, causes members to ensure that they have performance without excessive noise.

[Erfolg]

The point is there is no good reason why an electric model should be noisy. It is not necessary even at the extremes of performance.

Yes, you can make it noisy, is it necessary, even to obtain that extra bit of performance? I would argue no!

In this age, the generation of noise, particularly when avoidable, will often lead to further loss of flying sites, produces a negative image of models in much of the publics mind, adversely effects opinion.

[Paul Jefferies]

"The point is there is no good reason why an electric model should be noisy"

"Yes, you can make it noisy"

Erfolg, from the tone of your replies you seem to be blaming people because their electric models are noisy. Nobody is MAKING their models noisy deliberately. Some models, and the Bixler seems to be one of them, just ARE noisy as supplied out of the box and one of my OD models just turned out to be noisy. I don't know why and the purpose of my question was to try to find out WHY, in order to reduce the noise.......

That said, many thanks to all for your responses. Propeller diameter, pitch, blade shape and balance are all relatively easy to experiment with. I was particularly interested in Yakmad's comments about the esc. I will try switching the wires round and I do have another suitable esc that I could try in the Bixler.

Thanks to everyone, there is much food for thought

Paul

[Trevor Crook]

Re. prop noise, yes, I'd agree that close proximity of the prop to a trailing edge or other part of airframe is the main culprit, coupled with high rpm. A few years ago I had a Multiplex Funjet which was much quieter than most others I had seen, because I used a larger prop turned by a relatively low kv motor. Unfortunately, looking at the Bixler it doesn't seem possible to go this route because of the layout. Somehow moving the motor a bit further back, perhaps by fitting a tube in the pylon, would probably help, at the risk of c of g problems.

For modestly sized (up to .60 glow equivalent) tractor prop models, I'd agree that you'd be doing something extreme to make them noisy.

[YakMad]

I meant to say in my previous post that I acquired an Axion Laser Arrow from a club member who won it at our annual Club Fun Fly but he is not interested in fast delta type models. It flies well and is fairly fast but was noisy, the motor is in the nose and sounded more like a four-stroke than an electric motor. The prop was out of balance, but even after balancing the prop it was still noisy. I flew it a couple of more times until I noticed that the motor was loose, I figured the bolts holding the motor had become loose as I had this problem when I got it first, anyway when I got home the bolts were tight but the plastic plate which the motor is bolted to and which itself is held onto the tube motor mount with four self tappers had split in two. Not having easy access to a replacement I made one out of piece of 1/8 inch ply, when I ran the motor to test my fix, the droning four-stoke noise was gone. Tthe plastic engine mounting must have been flexing and causing the strange resonance noise.