DLE 2-strokes

[Bruce Collinson]

Thinking of putting my toe back into the water, with another DLE, 30 or 35. The issue is noise.(The last one, a 20RA, got recycled due to the difficulty in getting it anywhere near 82dB without strangling it).

The airframe for this one is a large F3A with the customary provision of a hefty pipe recess plus more in-cowl space so there may well be room for a can/pipe which there wasn't with the 20.

The question is, has anyone got either of these reliably down to 82dB and if so, would you share the details with me, starting with the exhaust/silencer/header etc., the prop and anything else e.g. soft mount etc.?

Bruce Collinson

[alec james]

I will be watching this with interest, I want to know myself how we can get a 20cc petrol motor under 82dB.

[Bruce Collinson]

Harder with a 20; far fewer after-market options, less room around the front to smuggle in something big enough to make a difference. Hence I ditched mine, put a Saito 125 in place but haven't flown it yet.

Let's hope for eager and positive replies!

B

[cymaz]

Glad you raised this and I’m sure I can help. I have a new DLE 20ra, standard exhaust box. It’s running a Graupner 16x8, 32:1 mix.

At WOT it was about 8100 on straight through silencer. 86dB at 7m. Field limit is 84dB.

With 2 of #THESE# , much better. Only lost 400rpm at WOT, now 83dB....pass . RCWorld also stock the DLE30 size.

 

I know it’s not 82dB but I haven’t screwed on the lower cowl yet, to completely encase the engine.

Edited By cymaz on 03/04/2019 17:43:42

[Ron Gray]

Whilst I haven't gone that small with gassers, my DLE 35s and 55s run a lot quieter when fitted with a can, it's the volume of the 'silencer' that makes the biggest difference!

[Bruce Collinson]

Ron, help us out with the 35; what’s it silenced by?

Cymaz/Peter, you did better with those than I did. When I alluded to strangulation, it was with those and I think it was nearer 800 rpm. Whatever it was completely took the edge off its performance. How’s your Infinitelycomplex going? I had a rush of blood, a small bonus and a birthday all coincident and acquired its big brother, a Collaboration ( hence sniffing after another another DLE!). 2 m span but the box is HUGE.

Bruce.

[Ron Gray]

Picture here Cannister

[Bruce Collinson]

Ron,

thanks.

Have you obtained an absolute dB reading? That’s pretty much what I envisaged.

B.

[bert baker]

Go for the biggest engine you can get., and don’t run it at full throttle,,

[Ron Gray]

@Bruce - no readings I’m afraid but am just about to build an SBach for the 35ra so will be testing it in a couple of week’s time (the 35s are between ‘planes at the moment!).

@Bert - good advice Bert but most tests have to be conducted at WOT. Maybe a mechanical throttle stop would get over that issue?

[bert baker]

The important bit is to keep the noise down to whatever you need it to be at.

Get the set up as quiet as possible and then ATV the last bit,

it’ll be a sad thing if a club insists the carb has to actually be wide open.

even if you made a mechanical restriction all these things can be removed when you get home

[cymaz]

Posted by Bruce Collinson on 03/04/2019 18:20:47:

Ron, help us out with the 35; what’s it silenced by?

Cymaz/Peter, you did better with those than I did. When I alluded to strangulation, it was with those and I think it was nearer 800 rpm. Whatever it was completely took the edge off its performance. How’s your Infinitelycomplex going? I had a rush of blood, a small bonus and a birthday all coincident and acquired its big brother, a Collaboration ( hence sniffing after another another DLE!). 2 m span but the box is HUGE.

Bruce.

The weather has been too windy each weekend. I’ve only managed a quick flight with it in 13/15mph winds. Hopefully will try again Sunday.

[Peter Jenkins]

I have a DLE35RA in a 2 mtr Majestic aerobatic airframe. There is a large belly pan in which to hide a canister. The first canister was a cheap (£35) off Ebay but a much better option is a JMB Can which I got from IAD Designs. The difference in sound is quite impressive. The engine was turning an 18x10 Falcon Beechwood prop at around 8,000 rpm. On the day I did the noise test, the only reading over 82db was with the airframe facing the noise meter. I think that was primarily due to a strong wind blowing into the back of the prop. It would have been interesting to have swapped around so the wind was blowing into the front of the prop and re-tested but time was short so we didn't. Vertical performance was not unlimited!

Having said that, there is much more power with a 17x10 which pulls 8,400 static and gives good vertical performance but not quite up to my electric 2 mtr standard. The engine has now accumulated a lot more running since the test and I may try the 18x10 and 19x 8 for performance again before submitting them to a noise test. It would be really helpful to have a sub 82 db machine for the noise sensitve field I sometimes fly at but there is no point in doing that if the vertical performance is poor. The empty weight of the airframe is 5.4 Kg and it has a 12 oz tank that is good for 14-15 mins. I'll post the results when I get them.

[Peter Jenkins]

I should have said that it might take a little while before I can get the noise test re-done!

[cymaz]

I do the noise tests at our club. The fact that you had a strong wind and the nose pointed at the meter would not help the dB . At our testing the measurements are from the sides if rear mounted exhaust , and primarily from the exhaust side if side discharge.

A stiff breeze can add to the level by 1-2 dB.

Though, I realise, each club has varying noise limits and methods of measuring.

I have all my tests on a record book. Date, pilot, airframe, engine, exhaust type, prop. Each aircraft then displays a visible pass sticker on the wingtip.At the same time a failsafe check is recorded. I also record when I calibrate the meter.....roughly check this every 6 months.

[TigerOC]

I run a DLE 30 and had to get it under 82db.

Bought a Pitts muffler from HK and got a welder to turn the discharge cylinder and pipes through 90 degrees so it discharged back instead of down. Bought 2 of these;

Stainless steel mufflers

Connected them via the supplied connector pipes and suspended them with a sprung bracket.

The test results were 79db front and 75db sides and 77db back at 7m. The tone of the engine is much deeper and less raucous. All at low cost. The stainless steel mufflers add are heavier than Al but the model is very over powered anyway.

Rob

[Michael Black]

Hi Tiger have you a photo of this set up interested

mick

[TigerOC]

I don't have a picture of the finished article after the welder turned the exhausts from the Pitts but here is picture of the test rig;

Note the Pitts exhausts have just been cut shorter. There is a barrel chamber welded to the manifold section. The welder cut the barrel where it joins the manifold and then turned the barrel 90 degrees so the exhaust is discharging back under the fuselage. The 2 canisters were then connected using the silicone pipe. The outlets from the Pitts exhaust are 16mm diameter so they matched the inlet of the canisters quite well.

I made up another Al bracket that tucks up under the fuselage and this uses springs to reduce the stress forces from the vibration on the canisters.

[Michael Black]

Thanks for that Tiger May give that a go

mick

[Paul Marsh]

I have a DLE 40 rwin, so it's 2 x 20cc cylinders. Not measured it, but very quiet. It's hard to muffle a petrol engine, but do-able. It's a shame there aren't many after marked unit available for them, or are hard to obtain.

[Michael Black]

So what have you done there looks like a can on one cylinder and standard on other I suspect I am wrong but that’s what it looks like.

mick

[TigerOC]

Michael, here are some pics I have taken today for you;