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Laser Engines - Technical questions

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tigerman01/03/2019 15:05:14
159 forum posts

I thought the 14/7 was a good choice but when you get down the flying field everyone is an expert .I think the 14/7 is OK but I wait and see what the real expert thinks

Geoff Sleath01/03/2019 15:54:34
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3239 forum posts
247 photos

I tried a 13x4 on my (electrically powered) DB 58" ws Tiger Moth on the grounds that it's a slow flying aircraft and doesn't much pitch speed. It took off very quickly as it was effectively in a low gear. I swapped it for a 12x6 and, whilst the take off was a bit longer, it seemed to fly better.

I know it's a different 'engine' but there's a bigger difference between 14x7 and 13x4 than what I tried. I would have thought the Laser 80 would be very under propped on 13x4.

Geoff

Denis Watkins01/03/2019 16:05:03
3600 forum posts
166 photos

14 x 7 is way over propped Tiger

13 x 6 more likely

Percy Verance01/03/2019 17:59:55
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7918 forum posts
152 photos

Not for a Laser 80 Denis. A 14x7 is ( I think) the recommended prop. I never owned an .80, but the suggested prop for the .100 was originally the Graupner Super 15x8 and for the 1.60 v twin it's the 16x8. Lasers have a bit more torque than the *buzzier* jap/chinese four strokes.......

I did own a Laser .70, and the suggested prop for that is a 13 inch.

 

Edited By Percy Verance on 01/03/2019 18:04:41

Jon - Laser Engines01/03/2019 18:08:45
4581 forum posts
171 photos

Cat?

Check

Pigeons?

Check

For a laser 80 in a model like that you are looking at 15x6, perhaps 16x6 or 16x5? You might even get away with 17x4 or 5 if you really want to go large.

To make life easy though i would use a 15x6 and just forget it. They are easy to get and should run around 8000. I use one on my Hurricane as its pretty over powered with the 80 on any other prop.

13x5 is small even for the 70 and i have used 13x5 master props on 50 size 4 strokes and they work very well. chap i used to fly with had an ASP 52fs in a wot trainer with a 13x5 master on it and the performance was excellent. I even run a 15x5 turnigy wood on my saito 45, not that it does many revs mind you.

To bring it back to the 80, i would say 14x6 for sport models (acrowots etc), 14x6/7 or 15x6 for WWII scale, and 15x6 or 16x5/6 for slow scale or vintage. Below 14x6 you are just revving like mad and while the engine will gladly take a 13x6 into the mid 10000 range its really not good for noise or efficiency.

Jon - Laser Engines01/03/2019 18:10:59
4581 forum posts
171 photos
Posted by tigerman on 01/03/2019 15:05:14:

when you get down the flying field everyone is an expert

Aint that the truth!

tigerman01/03/2019 19:43:38
159 forum posts

Ok thank you Jon I will try a 15/8 prop on the Gipsy Moth .Just out of interest how different will the 15/6 be compared with the 14/7 prop,will it make it slower ,faster ,better to loop the Gipsy moth etc

Jon - Laser Engines01/03/2019 19:54:29
4581 forum posts
171 photos
Posted by tigerman on 01/03/2019 19:43:38:

Ok thank you Jon I will try a 15/8 prop on the Gipsy Moth .Just out of interest how different will the 15/6 be compared with the 14/7 prop,will it make it slower ,faster ,better to loop the Gipsy moth etc

15x8 is a little too much pitch. It will run, but it might not work as well.

15x6 will give you more thrust without the feeling of the model trying to run away with itself and fly too fast. you will also have better propeller braking which will help slow down for landing and prevent overspeed when coming out of a loop. Think of the 15x6 as 3rd gear in your car and the 14x7 as 4th. Its that sort of thing

tigerman01/03/2019 20:04:58
159 forum posts

Thanks Jon for explaining that. The 3rd gear and 4th gear was a good way of explaining it

Martin McIntosh01/03/2019 20:07:28
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2785 forum posts
1045 photos

My 80 has an APC 14x7 on my Mustang. Perfect for the model.

Ken Lighten01/03/2019 21:08:34
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241 forum posts
40 photos

Hi Jon, is it possible to get the type of sleeved nut supplied with the 180 (M10 thread) for the 150 which I think is a M8 thread?

Jon - Laser Engines01/03/2019 22:28:07
4581 forum posts
171 photos
Posted by Ken Lighten on 01/03/2019 21:08:34:

Hi Jon, is it possible to get the type of sleeved nut supplied with the 180 (M10 thread) for the 150 which I think is a M8 thread?

Yes in theory, i need to see if i stall have some. I think they are on the long list of things to make.

Martin, 14x7 is a good choice for a mustang

Paul james 802/03/2019 10:44:08
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126 forum posts
23 photos

I'm making up some of the sleeved nuts shortly, need one to fit my 200 with aluminium spinner.

Manish Chandrayan02/03/2019 15:50:58
558 forum posts
65 photos

Paul

If you would be willing to make a couple for 150 i would be very interested.

Ken Lighten02/03/2019 16:29:02
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241 forum posts
40 photos

Hi Paul, if you are making some and you are willing then put me down for one for the 150 please

Paul james 803/03/2019 22:35:17
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126 forum posts
23 photos

There are various ways of doing the sleeve nuts, the simplest is with a sleeve that goes back inside the prop, for these a washer with an oversized bore to suit is required. The other one I make up as required has both the sleeve to go into the prop and a protrusion at the opposite end of the nut with a thread to take a spinner centre bolt.

When making these for my own use I obviously have the engine and prop I'm going to use so can measure up from that to make the required parts. i don't have all the data for all the engines so if anyone wanted one or two I'd need info from them.

Typically for an engine with a crankshaft thread of 8mm or 5/16" UNF I make the outside of the sleeve 10mm diameter, with a 10mm thread the outside is 12mm diameter. Lengths of sleeve need to be considered so that with any given prop hub thickness the thread in the nut sleeve doesn't bottom out on the step on the crankshaft.

I don't want to tread on the toes of the guys at Laser and it is unlikely that in batches of 1 or 2 I could meet their very reasonable price of £8.50 for nut and washer. Not sure if they do one with a front extension for a spinner screw?? It is pretty basic machining work but I can understand if the guys at Laser are pushed for time to get some made.

Jon - Laser Engines04/03/2019 08:56:43
4581 forum posts
171 photos

Im in the position where there are far higher priority jobs that need attention. The M8 sleeve nut is only supplied with the 160v and 240v..both of which are out of production.

I would like to do a complete overhaul of the accessories we offer but i have to get the engines sorted out first

Paul james 804/03/2019 10:17:26
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126 forum posts
23 photos
Posted by Jon - Laser Engines on 04/03/2019 08:56:43:

Im in the position where there are far higher priority jobs that need attention. The M8 sleeve nut is only supplied with the 160v and 240v..both of which are out of production.

I would like to do a complete overhaul of the accessories we offer but i have to get the engines sorted out first

Makes perfect sense to prioritise your workload, easy for folks to lose sight of how many bits and pieces are involved when making a range of products like yours

I'm not looking to make parts on a commercial basis, just happy to help people out where I can for non standard or hard to get parts.

Chris Walby08/03/2019 17:24:33
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907 forum posts
220 photos

Jon,

Do you have a recommendation regards the method for starting Laser engines?

Electric starter, chicken stick or by hand and does engine size make any difference?

... you can tell the weather is rubbish wink

Tim Flyer11/03/2019 10:51:39
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962 forum posts
158 photos

I will be making up a flex exhaust outlet for my Laser 70 in my Acrowot ARTF soon . As the firewall to spinner distance is short at 120mm I have already made a carburettor scoop/vent similar to the one in the “ Acrowot laser” thread on this forum. For my exhaust pipe I am using some stainless steel flex tubing and will braze a sleeve formed by some 7/16” brass tube on the end. This seems to push fit fairly snugly into the cylinder head exhaust outlet and I was just going to wipe a very fine smear of high temperature silicone on that to ensure a good seal. What I was wondering is whether I might need to make two narrower sleeves and use two o rings between them to provide an even better seal as per the stock exhaust? The exhaust will be properly clamped lower down and I don’t think the noise will be bad without a can ( our site us not noise limited).

Edited By Tim Flyer on 11/03/2019 10:55:53

Edited By Tim Flyer on 11/03/2019 10:59:38

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