Laser Engines - Technical questions

[J D 8]

Thanks for confirming my thoughts Martin.   John.

[Nigel R]

I think N4 is a med hot HSP brand plug... Standard two stroke plug, give or take. 

Edited April 25, 2022 by Nigel R

[Nigel R]

I have one or two of the enya four stroke plugs... Cannot tell the difference between that and an os f.

Edited April 25, 2022 by Nigel R

[J D 8]

   I was wondering what that plug is, thanks for the info,

[Jon H]

5 hours ago, Gary Spicer 1 said:

Hi Jon

On the Laser70 carb is all the fuel metered by the main throttle asembly? i.e. does all the fuel go through thoses two small holes or does an amount bypass the main needle via the outer chamber and go down the spray bar to the idle needle?

I ask, because if all the fuel is metered by the main needle why isn't the idle mix also affected when I set the main needle?

Just curious

Gary

 

 

When that brass part is screwed in it bottoms out and seals the chamber. Fuel passes through the holes into another chamber which is filled with the needle. 

 

The main needle does effect the slow run but only in so far as it can prevent all fuel entering the carb. 

 

Think of it like this. The main needle is a tap with a length of hose on it (the hose being the spraybar in the carb). The more you open it, the more you can draw through it and you adjust it to meet the fuel demand of the engine at full power. However at lower rpm you do not need that much fuel so you need to block the flow. This is done by the slow run needle and you will notice that as the barrel closes it also moves inward. This inserts the tapered slow run needle into the spraybar, reduces its area, and limits the amount of fuel that can come through it. The taper is there to approximate the fuel demand of the engine as the throttle is opened. hope that makes sense, its kinda late and i am tired. 

[Gary Spicer 1]

Hi Jon

Many thanks, that does make total sense. One of my Lasers 70s had been behaving erratically when applying power, 95% of the time it was fine, but then suddenly it would stop. I knew it wasn’t the tank position and plumbing as nothing had changed in 2 years and it was the first thing I checked over.  It had always been 100% reliable until now it wasn’t!  No fuel filters on the model, but two plastic housed filters on the fuel caddy. When I opened the main assembly (as in my photo) it had a few bits of what looked like tiny shards of plastic, no idea how it got there, but I think it was enough to occasionally interrupt the smooth flow of fuel.  I have done two flights since the clean and its 100% again.

 

[Nick Somerville]

Had a strong tailwind gust of wind taxiing my rather tippy Taylor P47 last week and put a split in the prop. Rummaging about I found an unused APC 18x8  Wide Sport propellor I bought some time back but is as yet unused. Anyone tried one on a Laser 180 in a warbird?

[Jon H]

I am told they work well on 180's in acrowot xl's so i would not expect the P47 to be any different. 

 

Also if the model is a little tippy perhaps tweak the c/g back a little at a time until you find a better balance. Remember to reduce elevator rate as you move the c/g to keep it from getting over sensitive. 

[Nick Somerville]

Thanks Jon. Yes c of g moved back would be a good idea as it clearly needs a bit more elevator authority on the ground to compensate for the nose over tendency. I am mot able to tweak the gear with shims as the wheels are so snug in the wells. I would have to buy 1/4” smaller sized wheels and they wouldn’t look good at all.

[Jeffrey Cottrell 2]

Hi Guys
Hope you don't mind me joining the party, but I noticed a couple of posts which might help with an issue I have.
I have started a thread here but long story short I have bought a second hand model with an ASP80 mounted inverted in it.
The engine position is determined by the moulded cowl, and the tank position by the bottom of the g/f fuz.
Trouble is, as installed the centre of the tank is some 25-30mm ABOVE the c/l of the carb, not helpful.
Can't raise the engine enough without half the crankcase being above the fuz top, and can't lower the tank except by cutting away the lower fuz floor which would compromise the strength and also the u/c mount which bolts to it.
Wondering whether a chicken hopper tank might be a solution.
Your thoughts?
Jeff

[Don Fry]

I have used, and use chicken hopper systems. 
1. They work, and work well, if you learn the foibles about pipe sizes, flow gradients, and accept there are higher maintainability issues.

2. They are not a replacement to hacking if possible to get it right, KISS applies.

3. By possible even if difficult, hack, and then replace the structure with glass, carbon fiber, whatever.

[Jon H]

Put my reply on the OP thread

[Mike Mc]

I need some opinions for my next Sport Aerobatic airplane.

 

I am in the US and am thinking of getting a Hanger 9 Tiger 30cc ARF from Tower Hobbies. I want to put a FT-200 on it. 90 inch wingspan and 16-18 lb. Probably a little more with a FT-200. Will the FT-200 have enough power for sport aerobatics?

 

Is there a better ARF choice?

 

[Mike Mc]

Jon,

 

What RPM can I expect from a FT-200 with 18x6 and 18x8 props.

 

Edited September 21, 2022 by Mike Mc

[Jon H]

Hi Mike

 

The FT 200 should provide more than enough power for that and i would expect a very sprightly performance. 18x6 is a bit small for the FT 200 with 18x8, 19x8, 19x6, 20x6 and even 20x8 being options. I am told by customers than 18x10 has also been used without trouble. Generally, as long as its revving in the 7-8000rpm range its well set for aerobatic flying. You can run it faster, upto 8500 say, but its not really very efficient like that. 

[Chris Walby]

22 hours ago, Mike Mc said:

I need some opinions for my next Sport Aerobatic airplane.

 

I am in the US and am thinking of getting a Hanger 9 Tiger 30cc ARF from Tower Hobbies. I want to put a FT-200 on it. 90 inch wingspan and 16-18 lb. Probably a little more with a FT-200. Will the FT-200 have enough power for sport aerobatics?

 

Is there a better ARF choice?

 

IMO go for it and you won't be disappointed at all. I have a FT200 in an old Eurobat (84 inch wingspan) that's solidly built and the FT200 just sounds great and pulls it around a treat. As Jon says its at its best when not at WOT, but will rev if you want it to. Hope the airframe does the engine justice and it will be a great combination for sports aerobatics.   There is only one problem...its so much fun its difficult to pick another model to fly after it!

 

Let us know how you get on.

 

PS - Laser recommend running on the lower oil content fuel and most times after flying I either give it a quick wipe or don't bother, that's how little residue there is. 

[Mike Mc]

22 minutes ago, Chris Walby said:

 

PS - Laser recommend running on the lower oil content fuel and most times after flying I either give it a quick wipe or don't bother, that's how little residue there is. 

I have a FT-160 so I know all about low oil fuel. The 160 is also a fantastic engine. It gets many flights every week!

 

BTW what prop are you using on the FT200?

 

Edited September 22, 2022 by Mike Mc

[Chris Walby]

Hi Mike,

 

I am running an APC 18 x 8 W and although I have not tried any other props for comparison it seems to run well. Plenty of progressive pull from idle to 3/4 throttle on take off +  seems to rev out ok.

 

AUW is 15lbs

 

Video of short test run, Jon at Laser Engines has a more comprehensive one on YouTube 

 

[Ron Gray]

The APC 18x8W seems to be ideal, I’m using one on my 200FT powering a Wots Wot XL and that gives it near unlimited vertical.

[Andy J]

Have an old Laser 70 engine (manufactured I assume at least pre 2000) mounted inverted in a warbird which is now running in an most unreliable manner. On the last flight the engine having ran fine in the pits started to surge after the model climbed out of the circuit so decided a quick return was required.  Unfortunately this resulted in an untimely landing on the top of a high thorn hedge which proved very painful to get it down.  So something needs to be done to improve the situation as several of its proceeding engine stops in flight have also resulted in damage to the model.

Having removed the engine,  suspected the carb could be the reason but the compression is also poor and fuel drips from the HS needle.  Changed the O ring on the carb intake that sits inside the engine block and tightened the retaining screws as the carb could be turned with a little hand pressure. Also pumped fuel through the carb intake just to ensure any foreign body or dirt was removed from the inner workings.

So having reinstalled the engine in the model it took quite some time to establish a needle setting that allowed the engine to run as the engine would easily start and then almost immediately stop. Any way after trying the HS needle both turned in and out from the initial position I then found a position that the engine continued to run at a high throttle setting but reducing the throttle caused the engine to stop. Then played with the slow speed needle trying an initial 1/4 turn in which did not improve the situation and then a 1/2 turn out which seemed to work with the engine having a steady idle and accelerates with only a slight hesitation.

So whilst I am happy to give it another flight should I be opening the engine to see the state of its inner workings as certainly I have not had it apart in the 8 years I have owned it.

Also should I be doing something about the dripping fuel which leaks from the carb body? Unfortunately cant see the source of the leak so did wonder if replacement carbs or parts are available from any source.

If I did remove the engine head and valves what method should be used to re-seat each valve to see if the compression can be improved.

Alternatively am I just better sending the engine to ebay haven and starting again with a new Laser.

[Alan Gorham_]

Nothing to be lost by quickly checking the tappet gaps? 

[Martin Harris - Moderator]

I’d check the tank and plumbing before anything more drastic and pop in a new plug perhaps. 

[Jon H]

Hi Andy

 

Fair bit to unpack there so one at a time. 

 

Poor compression. This could be a ring worn out or a leaking valve. The valve might have debris in there, a damaged seat, castor contamination, or a broken valve spring. 

 

Leaking needle. This one tends to cause confusion as a leaking needle will rarely drip fuel. The engine sucks through the carb so if there is a leak it will be air going in and not fuel coming out. Usually fuel dripping off the needle is coming from somewhere else and the needle is just the lowest point so it drips from there. 

 

That neatly brings me to fuel tank placement. I am putting money (or a beer at least) on it being too high. Warbird, likely an inverted engine..tank is probably too high. The fuel will gravity feed through the needle, leak out of the carb intake and drip down the needle. If i had a quid for every time i had seen it i would be a far richer man. 

 

Carb settings. These should be fairly quick to dial in if the rest of the engine is working as it should. An engine that starts and immediately stops is lean on the slow run as you subsequently found. Again, this brings me back to the tank. Tank too high, fuel leaks into carb, engine fires but slow run is too lean (likely to prevent fuel dripping??) so it stops after this accumulated fuel is used. Rinse and repeat. Opening the slow run needle is fine but half a turn is a massive adjustment. I wouldnt recommend adjustments more than 1/8 turn at a time and as tiny as 1/64 turn if you really want to dial in a slow run needle. 

 

I would check the fuel tank placement and sort that out if its not right. If that makes no odds or its already set correctly and the engine is still not running well then by all means pop it back for service. Be aware that if the engine needs valve springs (very likely) it could be into the new year before i am able to do the work as we are very short of valve springs at the moment and i am not processing any repairs that need them. Even when the springs arrive i already have 2-3 weeks work backed up on repairs alone so the sooner i get it back the sooner it will land itself a place in the queue. 

[Andy J]

Thanks for the quick reply Jon.  Think you are correct about the tank being too high as pictures I have dating back to 2017 after a lipo fire seem to suggest the bottom of the tank is in line with the carb intake. So the tank outlet would be above the carb.

Having said that, back in 2017 the installation seemed to work fine but will see if I can lower the tank although the outlet feed will have to go up and then down to go around the battery which sits in front of the tank.

[Andy J]

45 minutes ago, Martin Harris - Moderator said:

I’d check the tank and plumbing before anything more drastic and pop in a new plug perhaps. 

Did change the plug whilst the engine was on the bench but it was second hand one from another engine as it was the only OS F type I could find at the time.

 

Having just had a look at the tank it will be impossible to lower as it currently sits flush with the wing seat.  So assume I will have to live with the dripping fuel from the carb.

Edited September 27, 2022 by Andy Joyce