Topic: ASP 52 2-stroke overheating in La7

Ok ok ok. Calm down... I know this hurts in some ears out there. But I'm ok a tight budget ok?
I put an ASP 52 2-stroke (with 90 degree in cowl exhaust) in my Warbirds La7. And I'm having problems with the engine dying due to overheating :(

I followed the instructions and turned the engine so it sits right in front of the rear blowout. I even cut a bit of the cowl in front of the carburator to let some more air in.
Got a 12x6 2-bladed prop on the engine. And the engine has been working great since day 1 (ran the engine in a trainer the first couple of hours).
There is a 56mm Thunder Tiger plastic spinner fitted. And the engine runs good when I remove the spinner and run prop only 

Any suggestions?  What spinners did you use in yours?
And will a 4-stroke run cooler?

Oh and by the way I'm using 10% nitro and 20% oil (10% of that beeing synthetic) in my fuel.

Two suggestions spring to mind:

• an aluminium spinner should help carry some of the heat away
• add ducting to ensure that what cooling air there is flows through the engine cooling fins. I've used thin plastic sheet, balsa/ply and fibreglass for this and they all work well

This shows the cooling arrangement on my RCV 91CD in a Spitfire - the duct is less than 1mm from the ends of the fins on all sides and the air has to flow through the fins.


Hope this helps.

Richard

You only need a small hole for the air to get in and one about 4x greater for the air to get out. Cutting a bigger inlet usually makes things worse. If the air cant get out then the air gets hotter and expands which means it has a more difficult time trying to get out and thus stops any cool air getting in. the engine then gets hotter making the air hotter even greater volume needs to get out and so onand so on.

Try blanking off some of your intake and opening up your outlet.

    Tom

Posting some pictures of the installation

Try and blank off most off the front ring behind the cowl, exept for a small section in front of the engine, that will force air over the fins. If you could get a bit more exit that would help as well.

Steve

Try dropping the nitro content too. The 52 will run fine on 2-5% nitro.

Gerry

Dropping the nitro content to 5% will also mean the engine is running as intended as the ASP's/SC/Magnum's are timed to run with 5%. Any more and you will be suffering preignition, which may be one of the reasons for the heat. As said above, blank off the cowl ring to reduce the air in significantly.

The silencer inside the cowl isn't helping and there isn't any way out for the hot air. I would cut a big hole in the bottom rear of the cowl and blank some of the front off.

   Tom

Regarding your question about a four stroke:

Yes a four stroke would run cooler, but it would still probably need less air in and more out.

    Tom

What Tom meant is You need to make a baffle plate so all the air being forced into the front of the cowl passes closely to the cooling fins on the engine . At the moment the air is coming into contact with a hot silencer before it's forced out the cooling hole at the rear of the engine cowling.

A plate is on its way into the cowl. Thanks for the advice

I'm also thinking of creating small walls inside to make some sort of corridor for the air. Would that be a good idea?

I'm also thinking of creating small walls inside to make some sort of corridor for the air. Would that be a good idea?

Yes, that's what I meant by a 'duct' in my post - channel all the air over and through the engine cooling fins.

I'd be inclined to block off the opening leaving from 8 - 10 o'clock open then add sides behind the baffle to direct the incoming air at and through the cylinder cooling fins. Try to keep it close to the fins all the way around (or at least for the front half). This page http://www.aerocorsair.com/id108.htm demonstrates this approach on a microlight where it resulted in a 30 degrees C reduction in temperature.

Microlight cooling duct (in pusher mode hence low pressure zone marked):


I find that wrapping some brown packing tape covered cardboard around the cylinder makes a good plug for laying up one or two layers of glass fibre for these ducts and really keeps the cooling air in contact with the fins. You can also use metal for the ducts but be careful to avoid metal-metal contact which can produce interference.

As the effective inlet hole will be the size of the gaps between the duct and the fins, you may find that you do not have to increase the size of the exit hole as the existing ones may be the required 3-4 times the size of the effective inlet hole.

If the model can stand the extra nose weight, an aluminium spinner will also help. The one on my Spitfire is warm after a flight so I know it is helping draw heat away from the engine.

Hope this helps.

Richard

Tight ducting would normally mean that your exit hole is big enough as it is, if the silencer was out in the breeze. However as your silencer is inside the cowl you need to provide some cooling for it, as well.


    Tom

Sorry to hear your having overheating problems Zeno.Having flown over 1000 "missions" with the beloved La7 , without overheating, I would try this option first.
Take the cowl off. Add some weight to compensate . Fly on 10% as before (I do) , if that don't work, phone just engines.
Luv Richard Wills.
Let me know what happens.

I removed the 52 2-stroke and bought myself an ASP 61 4-stroke. Installed it together with a baffle-plate.
Seems to be running better, and sounding a lot better as well!
Just need to learn to adjust the engine... For some reason it runs better without the pressure line connected to the exhaust.
But the engine is new and has only been ran in a bench for break in precedure, so I'm not getting the full revs yet. But so far so good except for the pressure line.
Richard, can I bother you with some pictures of one of your engine installations?
I'm a bit curious on how people without overheating-problems mount their silencer. That thing becomes very very warm.
Do you route it out at the side on the cowl or do you point it downwards and make hole at the bottom of the cowl (the La7 instructions and construction calls for the engine to be mounted at an 8'oclock angle)??

Zeno,
I archived some previous La-7 builders piccies

Here's Trebors (Rob I think) installation using a flexi-pipe to extend the silencer under the cowl (very neat IMHO :ww)...

More...







HTH,
Steve

P.S. Zeno, any idea how much your La-7 weighs ready to fly? Cheers.

Oh great!
I was looking around at the previous build threads and wondered why the images was gone.
That installation looks great, moving the hot silencer away from the hot engine.

Yes, I know the weight of my La7, it comes in around 3,3kg (fuselage 2kg, wing 1,3kg). I don't know how and why. And I don't have any lead in it. The battery sits just above the tank on the firewall.
This was my first build so I was counting on some overweight, but not as much.
Can't really think of any way to lighten her up either, except removing the wing, and that won't work
I know Richard uses mechanical retracts, I bought the Eurokit ones (spring air copies), and I think these are heavier than a mechanical installation.

Hi Zeno
 We have seven ASP fs engines, and only the 53 will run well on pressure.
 The others, 61,80,80,90,90,120,120 180, run very poorly on pressure. I allways use a three-line tank, one to the carb, one to fill, and one fixed to a small-bore pipe facing forward. The fill pipe can be blocked with the usual horrible screw etc, or,  drill a 2mm hole under the bulkhead to suit the shank of a blind rivet-roughen the shank of the rivet- and epoxy in the hole. Then instead of a pipe and screw dangling about just push the fill pipe onto the rivet head, nice tidy, doesent catch on anything, and you cant lose the screw in the grass. Leave the forward-facing pipe open and facing FORWARDS to lightly pressurise the tank.
 allways works for me, give it a try.

 mokiman

Wow thats quite a collection!
Thanks for the suggestion, will give it a go tomorrow if the weather allows it   

Interesting stuff about the ASPs. I havent had one myself, but have seen several that surge all through the flight, which could well have been pressure problems.
Regarding the silencer and overheating issue , give me call next week, after monday if you get a moment and maybe we can come to a usefull conclusion.

Mokiman is talking about 4 strokes but Zeno is using a 2 stroke engine that is unlikely to run well without the pressure pipe connected.

zagi: He is on the correct path. I'm making things more confusing by changing from a 2-stroke to a 4-stroke somewhere in the middle of this thread   :ww

Oh my, just realized that I should update this thread... as promised.
I removed the preassure line and attached it to a small piece of plastic tube that I'd glued to my new baffleplate. This didn't work out that well. The engine quit on me when pointing the nose up for more than a couple of seconds. So I put the preassure line back again.
I got to try the following setups, with and without preassure line, and with or without cowl. The engine now runs the same during all these configurations.
I'm fumbling in the dark a bit here. Cause this is my first 4-stroke, and at the local field everyone runs 2-strokes... There aren't any 4-stroke-gurus around.
The engine runs fine on the ground but as soon as the plane comes up in the air and starts to move around things get funny. As soon as I give full throttle it starts to wander in RPM. Hard to explain... Thought this was the engine dying on me, but its not, it keeps running but sounding odd. A guy at the field told me that the engine might be like this for a while before it loosen up. Sounds a bit odd to me.


Richard: How much do your La7 differ from the weights I posted earlier (fuselage 2kg, wing 1,3kg)?

Zeno,

is it running rich ?   I have an ASP180 which did this.  At full throttle it was hunting when the nose was raised. Bringing the throttle back to 3/4 increased and stabilised the revs. I leaned out the mixture ( 1 1/2 to 1 1/4 turns out ) at full throttle to remove this and then adjusted the idle in by 1/8 of a turn. She now runs sweet as a nut. It's also worth checking the valve clearances - mine were twice what they should have been !

I've tried both leaning and running it richer, same thing. The needle is very sensitive.
Gonna check the valve clearence, bought things to measure with today 
Read that it should be between 0,04 and 0,1mm... Never done this before, does this mean that I should be able to get the 0,1mm blade between the valve or that it should be tight just enough to not allow the blade to go between?     

the gauge should be a sliding fit, not tight.

Okidoki, thanks!