inverted instalation of a laser engine

[Phil 9]

does anyone have a diagram or photo showing the ideal tank position for an inverted laser engine

[Scott Edwards 2]

Just stick the centre of the tank roughly level with the carb intake and you'll be fine. There's no black magic to it, and as long as you don't tell it, a Laser doesn't care if it's upside down back to front or sideways.

Edited By Scott Edwards 2 on 18/08/2017 21:33:33

[Don Fry]

Arf way up the tank, is centred on the venturi of the carbi.

[Phil 9]

Scott the carb intake level is where I have put the red line is that correct? where the fuel nipple is?

 

Edited By Phil 9 on 18/08/2017 21:45:09

[Phil 9]

Don I have no idea what that means

[J D 8]

The venturi is where the air enters the carb.

[Scott Edwards 2]

That will be fine, but ideally raise the tank a smidge so the centre line of the tank is in line with the centre of that big black hole that sucks the air in.

[Phil 9]

ok thanks got it now.

Om my model that puts the centre line of the tank about 10mm above the ideal. will that affect the engine running at all?

[Jon H]

ideally you want the top of the tank level with the carby. The c/l of the tank will as a result be a touch lower. if your tank c/l is higher than the carb that is not ideal and could cause issues. I recommend lowering the tank as much as possible and removing anything that's in the way as long as its not too important!

[Phil 9]

thanks Jon that answers the question of an ideal setup. but leads me onto another question.

That the ideal inverted tank position puts the bottom most tanks lower than the cylinder head.

on your model (correct me if I'm wrong) this tank looks to me to be higher than ideal. This situation would be common to the majority of models

[Jon H]

Hi Phil

you are right but the picture does make it look higher than it actually is. Remember too that its the c/l of the carb and not the inlet nipple which is important.

In any case, the tank in the Hurricane is a shade on the high side which is why I mounted the tank so that it is wider than it is tall. This reduces the head change as the level drops and prevents the engine leaning off. In the Hurricane the engine works really well and I do not have any problems as long as I don't do anything really stupid. If I was to try and outside loop with a low tank level I don't think the engine would appreciate it, but as its a Hurricane I never have that trouble. If the model was of an extra then I would mount the tank a shade lower and as the engine would be side mounted in an extra it would be really easy to do.

I will grab a tank and engine from the shed in a minute and lay them out on the bench. Hopefully that will clear things up. At some stage it would be nice to get this info into the instruction sheet as it is probably the issue I see most with inverted engines, especially now artf models are in proliferation and many modellers are less than enthusiastic when it comes to cutting into their new toy. I can understand their point of view, but equally it will be a great deal more hassle if the engine wont work because its being drowned with fuel.

[Phil 9]

thanks for the explanation Jon

A fellow club member has a laser 155 mounted inverted in a wots wot xl. it seems to run just fine. he has the tank as low as possible in the model but that still it puts the tank a shade above the ideal position,

I wanted to try the same in my acro wot. it would probably run fine but from your comments I can now see it may cause issues during some of the more violent aerobatic manoeuvres or problems when the fuel level is low.

[Jon H]

yea it varies between the engines too. The 155 is a large engine and has a strong draw, the 70 being smaller is less able to cope. If you think back to old 1 and 2cc engines they were very fussy with tank position for the same reason.

In the acrowot I would mount it sideways as the tank position is spot on, cooling is good, the carb is easy to access and routing the exhaust is easy too. Its win's all round.

[Phil 9]

Posted by Jon Harper - Laser Engines on 19/08/2017 13:29:05:

yea it varies between the engines too. The 155 is a large engine and has a strong draw, the 70 being smaller is less able to cope. If you think back to old 1 and 2cc engines they were very fussy with tank position for the same reason.

In the acrowot I would mount it sideways as the tank position is spot on, cooling is good, the carb is easy to access and routing the exhaust is easy too. Its win's all round.

I have it like that now but I always thought it would look nice inverted I should learn not to mess with something that is already working well

[KimVlasblom]

I'm finishing the design of a model and choosing the position of the tanks for a Laser 200-V. I was about to line up the top of the tank with the carb intake but then I realised that if I do that, when the model is flying inverted, the tank will be way above the carb and that worries me. I suppose that lining up the centreline of the tank with the carb is then the safest bet... Is that right, or will it then give me problems?

[KimVlasblom]

I'm finishing the design of a model and choosing the position of the tanks for a Laser 200-V. I was about to line up the top of the tank with the carb intake but then I realised that if I do that, when the model is flying inverted, the tank will be way above the carb and that worries me. I suppose that lining up the centreline of the tank with the carb is then the safest bet... Is that right, or will it then give me problems?

 

The image shows the tank lined up with its top at the carb intake height, which I am worried about when flying inverted.

Edited February 25, 2023 by KimVlasblom
Wanted to delete double message and then saw that I could add an image. Added image.

[Jon H]

The alignment vertically is fine as the worst that will happen when inverted is the engine may go a little rich which is no problem. If you were to raise the tank you risk the engine going lean when inverted and this is far more likely to cause it to stop. i would see if you can move the tank forward though as it looks a long way back. 

 

What sort of model is it you are building? 

[KimVlasblom]

Thanks for your reply Jon! (I just tried to call, to ask you about this. I also need to sort out (purchase 😉)some bits to enable scale fitting my exhausts. 

It's a 25% SAAB Safir 91D. So you'd leave the tanks down this low? 

 

The exhausts on the prototype are shown in the below pictures, luckily two of them which should make life a little easier for me. I think I need to place the silencers just above the cowl, possible get a couple of yours with longer outlets? Otherwise add a small length of correct diameter tube to my existing ones somehow. And then some sort of extension from the ports to the silencers. I'm open to your suggestions. I could turn a fitting on the lathe to pop into the ports with your O-rings, and use flexible or plumber's tubing to extend down to the silencers...

[John Stainforth]

Kim,

 

I am having some difficulty interpreting the relative levels of tank and engine in your perspective drawing. The tank and the red line appear to be angled downwards towards the front, and the engine and firewall give the impression of being set up with a very large amount of right thrust, which (in the angled view, rather than side view) also makes it difficult to tell the relative levels. Maybe these effects are just optical illusions.

[KimVlasblom]

They are indeed optical illusions. The tank (red line) is level with the 'shelf' you see at the top of the wooden box and the engine thrust line. The engine has no side thrust set up.

 

[Chris Walby]

Looks spot on to me and as Jon mentioned if you can move the tank forward and closer to the engine then all the better.

[John Stainforth]

Kim,

 

Thanks for posting the excellent top and side views. All looks fine. The distance between the tank and the carb also looks fine and rather ordinary - certainly not excessive.

[Jon H]

On 25/02/2023 at 12:47, KimVlasblom said:

So you'd leave the tanks down this low? 

 

Its a common view that tanks in the position are low, but they arent. This where tanks should be and the image below is lifted from an OS manual. They show the tank above the carb but also an air space we never use so in effect the top of the tank is the fuel level line in their drawing. 

 

 

If you use a long exhaust extension in metal you will need to make clamps and brackets to secure it back to the engine mount. Do not tie it to the firewall as the engine and exhaust need to move as one unit. Attaching to the fixed firewall will introduce flex and eventual fatigue failure. 

 

With the tank placement, if you can shove them forward a bit it would be good but as this model looks like it will be moderately aerobatic at best it is not as big an issue as something more exuberant. 

[KimVlasblom]

Thanks everyone. I'll move the tanks forward, but first need to ensure that I have space for a bell-crank for the throttle servo. (I don't have space for the servo in that area so will place it up on that top shelf/lid of the box. But it was the height of the tank that I was concerned about, and that question is resolved. 😃