Four Strokes Only Please

[Dai Fledermaus]

I spotted this Irvin .53 on Ebay this morning and was interested/concerned to see that the seller is saying that he has joined a club which only flies four stroke ic engines, hence the need to sell it.

I understand that noise is an issue these days but is this club unusual or a growing trend?

LINK

[Mowerman]

The Brighouse club (W Yorkshire) rules out two strokes. Again noise is the issue.

Luckily my club allows both but IC is fast becoming a minority after noise complaints from a neighbour who also complains if he can see the models by standing in tiptoe.

Edited By Mowerman on 08/07/2014 09:56:25

Edited By Mowerman on 08/07/2014 09:56:56

[Cuban8]

Gave my old Hanger 9 Aresti 40 fitted with an ASP 61FS an outing last week after the model had been laid away in my 'hanger' ( too much electric flying lately ).Several remarks from club mates about quiet the model was and I must admit I'd forgotten how so much quieter the model was over its two stroke counterparts.

Unusual to have a ban on two strokes, but if it's a case of otherwise losing a field then a correctly propped FS can easily be made very quiet and less intrusive. Not saying that a two stroke can't be muffled effectively, it's just that doing so can turn out to be very expensive given the cost of custom silencers that do actually work, and that the (annoying ?) quality of the sound emitted from a two stroke (silenced or not) will always tend to be more inclined to attract the attention of those living nearby.

[Biggles' Elder Brother - Moderator]

I think that whilst still relatively uncommon this is a growing trend.

BEB

[Bob Cotsford]

Four strokes often give the impression of generating less noise but our club noise tests prove otherwise. However the lower tone of a four stroke is generally less offensive, possibly it carries less distance so generates fewer complaints?

[Cuban8]

Posted by Bob Cotsford on 08/07/2014 10:25:40:

Four strokes often give the impression of generating less noise but our club noise tests prove otherwise. However the lower tone of a four stroke is generally less offensive, possibly it carries less distance so generates fewer complaints?

Yes, quite agree. Certainly no expert in acoustics, so I suppose the amount of sound energy is broadly similar between the two types, but is perceived quite differently in terms of annoyance factor (similar issue with turbine models?). It does throw up a weakness in the noise test though.

[Jon H]

4 strokes without doubt make a similar amount of noise as a two stroke, but as previously stated it is less annoying due (I believe) to the lower frequency. Model diesel two strokes (doing normal rpm not crazy control line rpm) are similar. If you think about all the noises that annoy you or set your teeth on edge, like the white noise from a tv, a dentist drill etc etc they are all high frequency/pitch. Also passers by are more used to the sound of a 4 stroke flying over head in a full size aircraft so its less noticeable and blends into the background.

We have only had 2 noise complains in recent times. one was for a 50cc petrol that was audible over a mile away (face palm) and the other was a zagi with an electric motor doing massive rpm. While making less noise the zagi was so annoying that it caused a complaint. None of my 4 strokes (from saito 45, laser 150, laser 300v asp 64cc radial etc) have ever attracted any complaints even though the saito and the asp were totally unsilenced.

I think a perceived noise test should be introduced, ie if its over 82db but sounds quiet in the air then let it fly. The opposite should be true as well, if its 78 but really nasty in the air then get it down!

 

Also, all two strokes should be banned anyway as four strokes are just better

Edited By Jon Harper on 08/07/2014 11:53:47

[john stones 1 - Moderator]

I agree lads I love all glow engines, but 4 stroke noise don't seem to carry or be so noticeable.

John

[Former Member]

[This posting has been removed]

[Jon H]

Personally I wouldn't touch one of those dubro mounts with a barge pole. They cause more problems than they ever solve and can damage your engine as it flops about all over the place. The big mistake people make with 4 strokes is running small props. They seem to forget that 4 strokes can swing bigger props and don't need to be doing 12000rpm. My little saito 45 is turning a 13x5 turnigy prop at 8200 and is lovely in my flair nieuport. Most of my other 4 strokes (mainly Laser) run between 7000 and 8500rpm and are not an issue noise wise.

[Bob Cotsford]

Jon, I have used the Dubro mounts and I'm puzzled by your description of them allowing the engine to flop about. It sounds like the rubber buffers were either worn out, damaged or just not clamped tight on the example you describe. Certainly the DuBro jobs allow a lot less flex than eg Hyde mounts.

[Former Member]

[This posting has been removed]

[Jon H]

Hi Bob

While I have no doubt that user error is often a part of it, I have never seen one of the DB mounts work in the intended way. The engine always flops about all over the place and basically rattles itself to death. Given the outrageous cost of the mount it is, to me anyway, a total waste of time and expense. A good quality (read as, not the cheap crap often supplied with ARTF kits) glass nylon mount is perfectly satisfactory and has enough flex to reduce vibrations.

If you have them working well then fair play and good luck to you

As for props, in the old days a 10x6 would have been great for something like a 40fp or LA. But the newer gen engines (ball raced abc especially) are much more oomphy without doubt. I am a little critical of many engine manufacturers here for not listing larger diameter props but instead ones with really high pitch. This is mostly an issue with 4 strokes as we were discussing above.

Edited By Jon Harper on 09/07/2014 16:28:08

[Allan Bennett]

A few years ago, before I went all electric, I replaced the OS120FS in my XtraWot with an OS120AX because the 4-stroke was too noisy! The pitts-style silencer that came with the AX was probably what made the difference. I used Dubro mounts with both engines, by the way, and never noticed any flopping around.

It seems to me that setting a lower dB limit is surely the answer if noise is a potential issue, then let members prop their engines appropriately, and use decent silencers, to stay within the limit.

[Cuban8]

I've always thought that the noise test was rather a blunt instrument and only really useful as a general indicator or where locally imposed regulations required one. Dogmatically banning a model because a noise meter shows that it exceeds an arbitrary maximum, but is perceived in the air as acceptable and not likely to cause complaint is just daft.

Most of us know when a model is particularly quiet or indeed a bit on the 'barky side', so by all means use the noise test as a start, but only give a model the OK (or otherwise) after it has been demonstrated in flight.

[stu knowles]

I agree with Cuban *8 above and would also add that so much depends on how the model is flown too. Some people fly flat out all the time and / or wander all over the county just in visual range. Others use full power only when going uphill and stay close.

Over the years I have found arbitrary noise limits and testing to cause nothing but trouble, as does an attempt to control noise by 'rules' against this that or t'other. No two strokes, no petrol nothing over 'x' cc engine size, even 'No pattern ships' are all things that have been implemented at various times. All have caused much debate and invariable not addressed the model / pilot that still manages to cause a nuisance.

stu k

[Cliff Bastow]

My club has a DB limit imposed so as long as you dont exceed this you can fly any type of power you like,

we are lucky that our site is quite remote and so far we have had no problems.

I would also add that to my ears some electrics can emit lots of not very plesant noise. some models with high kv motors and small props can really scream and some ducted fans are loud! and not very pleasant.

Edited By Cliff Bastow on 11/07/2014 11:12:35

[John Olsen 1]

The "A" curve that is usually used to weight noise measurements is supposed to take into account the sensitivity of the human ear to noise at various frequencies. However, I wonder if it only takes into account the perceived loudness and not the unpleasantness of the noise. Noise measurements are fraught with all sorts of problems and are not always very repeatable. One gotcha with our situation is that we take noise measurements fairly close to the model, while the people who are likely to object tend to be much further away. If the particular noise is one that carries well over a distance, it will sound worse to the complainer than one that does not carry as well, even though they were both at the same level in a noise test close to the model.

There are of course a few tricks to minimise the reading from a given model. For instance, make sure it is over grass, long if possible, rather than concrete or tarmac. Keep it as high as possible to reduce the sound reflected off the ground, eg on a starting table rather than on the ground.

Electric pushers can create a lot of noise, especially when the prop is quite close to the trailing edge. This causes a sort of siren effect, eg the air off the top of the wing is hitting the prop at a different speed to the air off the bottom. You can duplicate this effect by blowing a jet of compressed air into a prop at one point.

We've had one complainer who has claimed that we were overflying her house. This seemed odd, because her house is far enough away for a model to be nearly out of sight. It has taken us a while to realise that the problem is not actually us. We are quite close to a full size general aviation aerodrome, and she happens to be dead in line with the runway. They can and will overfly her house frequently, and it is unlikely that complaining about them will do her any good.

John