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Laser Engines - Technical questions

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Robert Hay 406/10/2018 12:56:17
48 forum posts
6 photos

Great, thanks for your answers Percy and Jon.

Braddock, VC13/10/2018 00:24:55
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Will an old laser hundred fly a 12lb plane, 2 metres span and slow to boot?

David Davis13/10/2018 06:01:36
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Posted by Braddock, VC on 13/10/2018 00:24:55:

Will an old laser hundred fly a 12lb plane, 2 metres span and slow to boot?

It should do. A old 90 has flown my Senior Telemaster.

stm with laser 90.jpg

Denis Watkins13/10/2018 07:27:17
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Posted by Braddock, VC on 13/10/2018 00:24:55:

Will an old laser hundred fly a 12lb plane, 2 metres span and slow to boot?

As a rule of thumb Braddock, for any I/C motor

.08 will fly 1lb therefore

.46 will fly 5lb

1.00 will fly 12.5lb

This is an old assumption from the 1940s literature, so with modern motors and synthetic fuel, we do even better

Edited By Denis Watkins on 13/10/2018 07:30:45

Jon - Laser Engines13/10/2018 07:29:00
5510 forum posts
268 photos
Posted by Braddock, VC on 13/10/2018 00:24:55:

Will an old laser hundred fly a 12lb plane, 2 metres span and slow to boot?

Yea it should be ok. We have had guys use the 100 to pull 1/4 scale DB gypsy moths and they are more than 12lbs

Former Member13/10/2018 10:43:05

[This posting has been removed]

Rocker15/10/2018 13:33:11
351 forum posts

I have a Laser 80 and have just ordered the Seagull P47 Thunderbolt (63" Snafu ) It does say it is for a 120 four stroke but I am sure the Laser 80 will power it OK .My question is " How does everybody fit the Laser engines inverted .When I try I always have big problems with getting the fuel tank right .Because the carp is on the top of a Laser engine when you invert the engine the carp is very low and to get the tank right you almost have to have the fuel tank under the fuselage But seeing all the great photos of model powered by Laser a lot of people have them inverted .How do they get the tank right ?????.I do not want to install the Laser 80 at right angles to get any chance of installing the fuel tank right .It spoils the look of the model with the engine install at right angles

Chris Walby15/10/2018 14:03:23
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1240 forum posts
303 photos

Rocker, with my limited experience I would say its a case of moving the engine or the tank to get them to line up.

There are a few threads where you can use a small tank in the correct position fed from another tank in a less optimal position.

Sort of depends on how much wood work mods you want to do, but there have been a few issues with build quality and my seagull Mossie came apart a bit to easily (to move the bulkhead back). Made the mod easy and once beefed up all has been ok.

Tim Flyer15/10/2018 14:13:59
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1289 forum posts
236 photos

Rocker you might be interested in my thread and album photos on putting in a Laser 100 into a p47 Thunderbolt. It’s very easy. Fuel tank just goes below fuel tank floor . I also have an album of photos on it on this site,

Tim Flyer15/10/2018 14:20:26
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1289 forum posts
236 photos

**LINK**

Jon - Laser Engines15/10/2018 15:32:41
5510 forum posts
268 photos

Dont worry about it too much Rocker. There is loads of space in the P47 to get the tank down nice and low. You can either fit it from inside the fuz, or cut a hole through the firewall below the engine mount box and insert it from the front. I would probably go in from the top though as it leaves the firewall sealed and prevents goop getting inside the fuselage.

Rocker15/10/2018 15:36:01
351 forum posts

Hi Jon I am right about the Laser 80 being OK to fly the P47 .I am sure it will ? ( It is the Seagull 63 " )

Edited By Rocker on 15/10/2018 15:36:49

Jon - Laser Engines15/10/2018 18:07:14
5510 forum posts
268 photos

Yea it will fly. the 100 would be better but its not going to be an issue. Certainly its not going to lumber around like a wounded elephant. Start with a 14x6 prop then try 15x6

Martin McIntosh15/10/2018 18:51:46
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3419 forum posts
1213 photos

Rocker, do not worry about a high tank. I expect that you have seen the pics of my Stampe with twin tanks. With the throttle closed there is very little syphoning of fuel between flights and you will see that the supply line can be closed off when not in use. Inverted is no problem because these things suck fuel like hell. Outside loop problems are easily solved with a silencer pressure tapping if needed.

ASH.15/10/2018 22:20:59
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334 forum posts

The easiest way to prevent or stop any kind of syphoning is to loop the carb line up over the engine mount first.
I do that with all installs - works without fail.
I don't prescribe to "the carb line has to be short as possible".
Jon - Laser Engines15/10/2018 23:08:00
5510 forum posts
268 photos

In general we recommend tanks are located on or below the centreline of the carb and are kept as close to the engine as possible. It will work in other configurations for sure, and some models are more sensitive than others, but we recommend the above as its one less thing to give you grief in the long run.

The other thing to remember is that we cant guarantee the operation of the engine if you deviate from our recommendations because its an unknown for us. The things i always ask when someone calls with a problem are what prop, what rpm at full power, what fuel, what plug, and where is the tank. We make recommendations for all of these things, and know the performance we should see in return. Any deviations make it hard to diagnose faults.

As an example, say you call me with a problem with fuel flow, or the engine dies during some aerobatic figure, or the engine cuts after X minutes in the air. If your tank setup is not as recommended, the first thing i will do is tell you to change it to the recommended configuration as i know the engine works like that, which is why we recommend it in the first place. If the tank is wrong, then that could be the whole problem, or it could be unrelated. Until its setup in a way that i know will work i cant really offer advice as it could just be the tank.

i would say that by far the largest number of running problems i deal with are due to incorrect tank placement. so many people get drawn in as they think its not that critical, and they will probably get away with it because dave from the club two fields over did it so lets save ourselves some work. In practice, its far more effort to go back and rehash it all once its gone wrong so its best to bite the bullet and get it right first time, especially when it as easy as it will be in the P47.

 

 

Edited By Jon - Laser Engines on 15/10/2018 23:12:20

Tim Flyer16/10/2018 09:25:13
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1289 forum posts
236 photos

As John said is easy on that model. The thread I linked above was for My 63in Seagull P47 Snafu, it’s just the one you asked about. All that is is needed is to put the tank under the fuel tank floor. Access is easy and it just requires a couple of zip ties . You also need to cut a new hole for the fuel and vent pipes in the bottom part of the firewall. There are plenty of photos in the link but I’m happy to post more tonight if needed.

Tim Flyer16/10/2018 09:38:45
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1289 forum posts
236 photos

There is no problem with correct tank on this model . The thread I linked was for this same Seagull P47 Snafu. All is needed is for the tank to be zip tied UNDERNEATH the tank floor rather than on top. A new hole needs to be cut In the bottom part of the firewall for the repositioned fuel and vent pipes. There is plenty of space. Make sure you fuel proof first! If you need more photos I can post them tonight. The engine is mounted inverted at around 7pm.

Tim Flyer16/10/2018 09:40:01
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1289 forum posts
236 photos

Oops double post!

Chris Walby21/10/2018 21:32:34
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1240 forum posts
303 photos

I have an Acrowot with a Laser 70 in it...it really is just too much funsmiley

Aanyway its on a 13 x 7 prop and I was wondering if a 13 x 6 would better suit it? It just seems a bit laboured at times, but perhaps that's just me!

I don't mind giving it a go, just needs another noise test before reaching for the sky

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