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Laser Engines - Technical questions

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Chris Walby01/01/2019 21:39:10
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894 forum posts
213 photos

Flying the Acrowot 70 today (7 degrees C and a bit of a wind chill) and I don't think I was getting the best from the engine (nothing wrong with the engine, just the nut on the end of the needle)!

I warmed it up and set max revs by turning towards lean and then backing it rich (to get max revs). for the first couple of flights, but it didn't quite seem to rev right out. Only talking 3/4 to flat out.

Then tried it a little richer for a couple of flights, but not to affect max revs and it seemed better.

Might just have been me, however does anyone else employ a slightly different technique for winter or have I been doing it wrong all summer!

Jon - Laser Engines01/01/2019 22:05:25
4507 forum posts
164 photos

when its cold engine rpm can drop a bit as the air is denser and so drag on the prop rises. The cooler air charge can also cool the plug a bit and retard ignition slightly.

The effects are all quite small but can add up. Generally though they are not an issue.

As for tuning, i dont do it any different in the cold. Warm up engine, tune for max speed, go fly.

J D 801/01/2019 22:05:43
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1088 forum posts
65 photos

I had an Enya that needed a scarf on a cold day. The only way it would fly properly at low temps was to tie a rag around the base of the cylinder!

Chris Walby02/01/2019 10:01:46
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894 forum posts
213 photos

Jon,

I was definitely flying, wink the Acrowot and Laser 70 are very well suited, Great fun even in the blustery conditions.

Just preparing for the winter conditions when it will be sub zero and the heated gloves will be needed and the ground is hard with frost.

Denis Watkins02/01/2019 10:07:48
3559 forum posts
166 photos

Check your OS F plug Chris, if it has done a season or two, the cold weather will show up if the coil is less than good

Chris Walby02/01/2019 11:15:55
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894 forum posts
213 photos

Denis,

You mean they don't last forever.... I'll try a new one and see what happens, but I suspect it might be on its way out and an easy swap to see if it makes a difference.

Jon - Laser Engines02/01/2019 11:16:04
4507 forum posts
164 photos
Posted by J D 8 on 01/01/2019 22:05:43:

I had an Enya that needed a scarf on a cold day. The only way it would fly properly at low temps was to tie a rag around the base of the cylinder!

My enya 53 is not a fan of being cold. If i give it the big one too soon after starting it there is a long bang and the prop shoots over the horizon. It demands a good 30-40 seconds at over 1/3 throttle to get it warm enough to be happy at full power.

Chris, i think the weekend is going to be a bit nippy so the gloves will come in handy!

Rocker03/01/2019 20:16:35
341 forum posts

A person in our club is building a Seagull Stuka (90 inch ) he has 50 cc petrol engine to put in the Stuka .Just a thought anyone tell me if the Laser 180 would be powerful enough to fly the Stuka .I know Seagull recommend a 50 cc petrol engine for the Stuka,I know the Laser 180 is not a 50cc engine but sometimes the manafactures over power there models ( a good example is the Seagull Gipsy Moth ,Seagull recommend a 120.4 stoke for the Gypsy Moth and I fly it on a Laser 80 and it is perfect )I I have always like the Stuka but I do not like big 2 stroke petrol engines .To noisy for me much prefer the sound of a Laser 4 stroke and what with the Laser twin not being in production at the moment just thought if a Laser 180 would do the job but I think I might be asking a bit to much from the Laser 180 ?

Edited By Rocker on 03/01/2019 20:18:29

Martin McIntosh03/01/2019 20:42:57
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2774 forum posts
1037 photos

In my opinion you really would be asking too much here. My 180 powers a rather heavy (18lbs) 72" Spitfire and is just right for this. An 18" prop would also look rather silly on yours. My 96" Hurricane is adequately powered by a 50cc petrol and as you say the noise is unacceptable. I recently re engined an Extra 540 at 2m span from 52cc petrol to a 30 but this is a very light model indeed. Just be patient and hang out there for a Laser twin.

Jon - Laser Engines03/01/2019 21:03:07
4507 forum posts
164 photos

Rocker it will come down to two factors:

1. The actual flying weight (the quoted 17lbs is suspiciously light)
2. Your performance expectation for the model.

If we assume a likely weight of 20lbs then the 180 will fly the Stuka and will give it scale performance. By that i mean it will have the performance of a heavily laden ground attack aircraft. It will not fly like a fighter.

If you are prepared to fly the stuka as a stuka, and run the 180 for maximum thrust (use 20x6 prop) then i do not think you will have any trouble.

If however you want a more dynamic model with a performance that is more than scale then you will need more power.

To give an idea of the performance available from the 180 we have several in 80'' span Hurricanes from YT and seagull. The seagull version is just shy of 18lbs and the YT version about 20. Both fly well on 180's in the 2/3-3/4 throttle area for scale performance. I also used the 180 in my 80'' La7 of 19lbs and it flew fine. I have since changed the engine in the la7 but only because the 180 did not give the vertical performance i wanted for a 1944 fighter.

Beyond that my stampe is light at 16lbs but has quite a bit of drag from an effective 160'' wingspan. 1/2 throttle is all i need here.

So while i understand Martin's hesitation i personally think it will work as long as you are happy to fly the Stuka as a Stuka and not pretend its a 109

Martin McIntosh03/01/2019 21:06:54
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2774 forum posts
1037 photos

Fair comment Jon.

Rocker03/01/2019 21:53:37
341 forum posts

Thanks that has answer my question

Jon - Laser Engines03/01/2019 23:20:46
4507 forum posts
164 photos

No worries.

If you have never seen the stuka they have at Hendon i think you should go take a look. I was staggered just how big they are and understand fully why its rate of climb was worse than a tiger moth at less than 500ft/min. For comparison, a Hurricane climbs at up to 2800ft/min and that was nothing compared to the 109 and other later fighters.

I am very keen to see the restored example they have in the US fly again in the not too distant future.

Andy Shailer04/01/2019 16:15:57
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358 forum posts
374 photos
Hi all, firstly apologies for a silly question, l have two Laser engines both look same size, one l believe is a 120 the other a 150, no markings on both to say what is what, silly question time.....would the 150 be heavier then the 120, many thanks for any info.
Andy.
Manish Chandrayan04/01/2019 17:19:36
553 forum posts
65 photos
Andy, logically the 150 should be heavier than the 120. Why not post pictures of both? That should make things easier
Andy Shailer04/01/2019 17:35:00
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358 forum posts
374 photos
Just trying to work out how to on my phone as no lap top
Andy
Jon - Laser Engines04/01/2019 20:09:45
4507 forum posts
164 photos

Its not a silly question, in fact its pretty common. Assuming you can beat the tech into submission then some photos are all we need for an ID

you will happy to hear all current engines come with the size on them

Andy Shailer04/01/2019 20:14:43
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358 forum posts
374 photos

20190104_173242.jpg

20190104_173236.jpg20190104_173231.jpg20190104_173311.jpg20190104_173317.jpg

Andy Shailer04/01/2019 20:17:14
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358 forum posts
374 photos

Hi Jon, sorry l couldn't rotate pictures

Jon - Laser Engines04/01/2019 21:18:16
4507 forum posts
164 photos

No problem Andy. The taller engine with the square rocker cover is a 1998 vintage 150. The shorter engine is a 2000 vintage 120.

Both are still supported for spares and service.

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