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How do I get my Laser 80 below 82db

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Martin Harris12/04/2017 11:51:26
7564 forum posts
188 photos

That's not always an option. I don't know where Andrew flies but most people enjoy their clubs and want to operate responsibly to ensure their continuing existence. Most reasonable sized models can get through the DoE noise test (unfortunately it is flawed but can be used to demonstrate a reasonable and responsible attitude) with a little fine tweaking - hence this thread which asks for advice.

Reading back, I was a little concerned about seeing advice on "fiddling" the test - it shouldn't be about finding ways round it, rather finding ways to legitimately pass the test - even though it's arguable that the perceived noise in the air may reduce due to unstalling the propeller and other factors, this is subjective and can't be quantified as evidence of reasonable behaviour. Conversely, a model can pass the test but cause a noise nuisance - even "silent flight" electrics can be guilty here - and a club might need to limit their use to avoid complaints.


Since posting this, I've seen Andrew's last 2 posts which I thoroughly agree with and demonstrate very well the responsible attitudes which I hope are common. 

As for APC props, we've always found them to give excellent results in noise tests - the only downside is the big jump in price once past 13" diameters but they can be worth paying the extra for.

Edited By Martin Harris on 12/04/2017 11:58:39

Jon - Laser Engines12/04/2017 13:39:14
3764 forum posts
147 photos

I also dont really agree with a fiddle to get through the test, but in the case of the front noise reading i would fiddle it any day of the week as its a meaningless measurement.

But, i had a go at measuring the noise of a laser 100 i was running earlier. It was doing 9200rpm on an apc 14x7 and was 80-82 db from the front at about 5m when surrounded by buildings, skips and mounted to a steel test bench sat on concrete. However, i did only have my phone app to measure with so take it all with a pinch of salt.

In my results are in any way accurate then something is not right with the 80 in the OP.

My money is still on 14x6 or 14x7 apc props i have to say and any tweaks you can make that prevent things like the cowl from resonating will be a good thing.

Denis Watkins12/04/2017 14:56:07
2724 forum posts
137 photos
Posted by LYKA on 15/09/2014 14:43:11:

Have just brought a second hand Laser 80 to put in a Wots Wot. Just noise tested it and it comes out at 84db,it has the quiet silencer on it and I have put a 16x6 prop to try and get it below the club's 82db but it still comes out at 84db.Would a 3 blade prop be any quieter and get it down below 82db Any suggestions how I can get this Laser 80 below 82db

The OP regarding a second hand laser 80

The motor does want looking at closely, as it is of uncertain history

Luckily they are solid and should have survived a previous owner, but everything needs checking for tightness or wear

When a 4 stroke glow is due for a noise test there are usually never any concern, and they do sail through

Andrew Ray12/04/2017 15:08:00
612 forum posts
19 photos

Denis, the OP posted in 2014, he had overpropped the engine, he went to a 14x7 and the model passed the test.

I have picked up this thread nearly 3 years later, it is not the engine but the propellor and the airframe causing the noise. I am finding the process interesting and Jon is spot on in his advice.

Nigel R12/04/2017 15:14:52
1219 forum posts
275 photos

APC props were a complete revelation when they first appeared, against the competition at the time of plastic black master airscrews (flexible, noisy, inefficient) and the graupner gray (far better than MA but still a bit noisy, although OK at lower revs) props. An object lesson in how a decent tip design can improve the whole wing, in much the same way the recent boeingbus airliners now all feature some variety of swept and highly tapered tip in order to minimise tip vortices and drag (coincidentally our props tip speed is not dissimilar to the airspeed of an airliner although the Re is a bit different!)


Edited By Nigel R on 12/04/2017 15:15:29

Jon - Laser Engines12/04/2017 15:49:48
3764 forum posts
147 photos

Props are a minefield and they can make or break a model in terms of performance.

I currently fly one of our 80's in a hurricane and i first flew it on a 14x6 apc for running in. I then switched to a 3 blade 14x7 master, lost 1000rpm but the whine of the prop on the ground is really noticable. In the air however, nothing. Its quiet and nice to fly with even if its pushing the poor old 80 to its limits

Andrew Ray13/04/2017 18:17:00
612 forum posts
19 photos

Right, the APC props arrived today. While I have been waiting for them to arrive I have fixed a resonance from the cowl, I have fettled the wing struts so they are a firm fit to the wing and, although there was no play in the ailerons there was lateral movement in the link between the top and bottom ailerons that rattled when I tapped them.

The results are what I hoped for.

  • G-Sonic 14x7 9500 rpm at 83dB, still over but a 2dB improvement
  • G-Sonic 14x7 9000 rpm at 82dB so an improvement of 300rpm for the same noise level
  • APC 14x7 8500 rpm at 82dB but 500 rpm less than the G-Sonic for the same noise level
  • APC 14x6 9200 rpm at 83dB similar noise level to the G-Sonic at similar rpm

So the noise levels are down by about 2dB on the G-Sonic at max rpm and all for fixing areas of vibration causing noise, this propellor also allows the engine to achieve higher rpm than the APC 14x7 by 1000 rpm, this will account for the greater noise level from the G-Sonic but does that extra rpm result in a greater performance?

Something else I noticed, all the tests I have carried out are fitted with an exhaust deflector, the exhaust deflector was angled between the upper and lower wings (the exhaust exits the side). I removed this and found that the noise level with the APC 14x7 reduced by about 1dB.

The next job is to reposition the exhaust to exit underneath the airframe.


I meant to add that it appears that for the same rpm the G-Sonic might be a quieter prop than the APC props.

Edited By Andrew Ray on 13/04/2017 18:20:35

Jon - Laser Engines13/04/2017 19:08:28
3764 forum posts
147 photos

Very methodical testing!

As you rightly point out though rpm is not a measure of thrust and its thrust that will pull your model. Master airscrew props rev well but do nothing other than turn rpm into noise. You are clearly tuning your engine well too as you are slightly exceeding the rpm I normally expect from the engine on those props. Clearly the engine is on song and I would take the apc props up and test it at the site and go from there.

I am still slightly surprised the levels are so high as my admittedly crude test revealed lower noise from a larger engine at a closer distance with less favourable surroundings.

Andrew Ray13/04/2017 22:00:35
612 forum posts
19 photos
Posted by Jon Harper - Laser Engines on 13/04/2017 19:08:28:

I am still slightly surprised the levels are so high as my admittedly crude test revealed lower noise from a larger engine at a closer distance with less favourable surroundings.

I am sure the airframe is responsible, when I find time I intend putting the engine in my old Acro Wot, foam wings and solid 1/4 balsa sides (or something like that) and taking some measurements.

cymaz13/04/2017 22:09:24
7594 forum posts
981 photos

The effects of airframe drumming can have a real effect on the noise test. Also try not to do the noise test in windy weather. The noise made when wind is crossing the detector can be an extra 2-3 dB.

Andrew Ray14/04/2017 12:40:56
612 forum posts
19 photos
Posted by Jon Harper - Laser Engines on 13/04/2017 19:08:28:

I am still slightly surprised the levels are so high as my admittedly crude test revealed lower noise from a larger engine at a closer distance with less favourable surroundings.

Well Jon, you were not wrong to remain surprised.

Because of the length of the cowl the Laser is hard up against the bulkhead, I have had to relieve the bulkhead to clear the silencer. Removing the engine to look at repositioning the silencer there is evidence that the end of the silencer has been touching the bulkhead, probably the main cause of the high noise levels.

Denis Watkins14/04/2017 12:58:43
2724 forum posts
137 photos
Posted by Denis Watkins on 12/04/2017 14:56:07:

When a 4 stroke glow is due for a noise test there are usually never any concerns, and they do sail through

If noise becomes an issue, just have a clubmate look over the installation

Jon - Laser Engines14/04/2017 20:39:11
3764 forum posts
147 photos
If the exhaust is touching that's not going to help. It will also damage the exhaust and can even damage the head and break the head bolts over time. It's amazing the loads involved when you get into that sort of situation.
Andrew Ray20/04/2017 19:39:56
612 forum posts
19 photos

I have made adjustments to the exhaust and now with an APC 14x7 I am getting a reading of 80dB at 8700 RPM. I tried the G-Sonic 14x7 and that is now at 82dB at 9400 RPM.

This has been an interesting and fun exercise to see how the changes I have made have affected the noise reading, now I am wondering what difference isolating the mount from the airframe would have. Maybe in the future I will play with that idea but for now I am going to enjoy flying the Wots Wot and thank you for all the input, much appreciated.

Jon - Laser Engines21/04/2017 08:38:24
3764 forum posts
147 photos

8700 on a 14x7 apc? good grief what have you done? thats 300rpm up on what i expect!

Either way, good to hear its all sorted and if you wish to damp the sound further then you can try putting some thin rubber mat behind the mount but i would not really recommend it as the engine can move about a little more and eventually the bolts will come loose on the firewall.

Also the engine flapping about is not good for it and we dont recommend those du bro vibration damping mounts for that reason. It causes more problems than it removes.

Andrew Ray21/04/2017 09:43:06
612 forum posts
19 photos

I'm using a Turnigy Micro Tacho and maybe it's not that accurate but then I checked it against a fluorescent light tube and it gave exactly 3000 RPM so it seems accurate (unless my logic is wrong).

Must admit this engine is sweet, starts easily, idle is nice and steady at just a smidge under 2000 RPM. One seriously chuffed Laser owner. I'm actually thinking of selling my petrol 2 strokes and replacing them with a couple of Lasers.

As it's at 80dB I'll probably end up leaving the installation as it is.

Jon - Laser Engines21/04/2017 09:58:01
3764 forum posts
147 photos

And now you have two 80's to play with as well! And your trick for checking is the tacho is the same one i use, and rpm can vary day to day and my testing has always been with brand new engines and they do come up a bit with some running.

What size are the petrols you are thinking to replacing??

Andrew Ray21/04/2017 10:10:51
612 forum posts
19 photos

Those that are currently flying are a Zenoah G26 (with a magneto) in a Hangar 9 Taylorcraft and a Roto 35vi in an Acro Wot XL. I also have an Evolution 20GX, an Evolution 26GT which is the same as the MVVS and a NGH 17. Thinking I might try my Laser 120 in the Taylorcraft but the Acro Wot would need something bigger than the 155 I have.

Jon - Laser Engines21/04/2017 11:24:01
3764 forum posts
147 photos

The acrowot XL is a great performer with a 155 and so is the wots wot xl. We have a number of guys flying those combinations and noone has said they are short of power.

In terms of power output the 155 should be at the very least on par and likely ahead of the 20-26cc two strokes. Its certainly ahead of the DLE 20 a friend has.

i cant find alot of info on the roto in terms of its rpm on a given prop. Some are saying 20x10 at 6300rpm which is not as fast as our 300v on the same prop, but the idea of a 300 in the acrowot is madness as i use it in WWII models of the same span but at least 5lbs heavier without any problem.

The 120 or 155 will be nice in the taylorcraft and the 155 would be my choice as it can turn 18 inch props when used in a model like that.

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