OS LA 15 Helping me get good at deadstick landings - RC Groups
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Sep 07, 2009, 12:08 PM
Just a guy.

OS LA 15 Helping me get good at deadstick landings

Help! I have an OS LA 15 installed in a Mini Funtana X. I think that I have only landed it under power once all year. It runs fine for the first third of a flight then it quits on me. It doesn't really give me any warning before I get to practice my short notice landing. The engine will run just fine if it is sitting on the ground - it idles well too. Last summer the engine ran fine. It should have enough time on it to be mostly broken in.

I have a 4 oz tank and I only ever manage to fly half a tank at a time. I have a 3 line setup for fueling. I have run both 5% and 15% nitro in it and I have the same response from both.

I took in off and cleaned out the needle valve and carb but that changed nothing. The plastic backplate was a little loose but tightening it up hasn't made a difference.

A club member had suggested maybe putting some gasket material on the backplate and the carb in case it leaks (which I plan to try when I have time).

I am mostly an electric flyer so I don't know engines very well (give me a soldering iron any time). Anybody have any suggestions on what is wrong?
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Sep 07, 2009, 01:03 PM
quick, stretch into a monster!
Mr.Me's Avatar
how are you tuning it? seems lean and over heating to me. do you back it off 3-500 RPM rich when you tune it?
Sep 07, 2009, 01:48 PM
Just a guy.
I did back it off - I did not tach it. I did notice the problem get worse when I tried a leaner run. The motor is cowled it but it does have some intake holes (and the bottom is wide open for the muffler.

One of my buddies out at the field is still breaking his LA 15 in (he has less than a third of the time I have). He is getting a much higher RPM out of his. I should tach both of them to really see. We are running the same diameter prop (8x4 for me and 8x5 for him). I don't think that I am getting what I should out of this motor.
Sep 07, 2009, 04:07 PM
Registered User
Have you changed the glowplug? a new os #6 will do. After break in I recommend a new plug.
Sep 07, 2009, 04:23 PM
Just a guy.
Originally Posted by lucasavaitor
Have you changed the glowplug? a new os #6 will do. After break in I recommend a new plug.
Of course I haven't - because that would have made sense. Looks like I have one more thing to add to the list.

The glowplug is still drawing current (according to my buddy's power panel). The plane does run and idle fairly well on the ground.

Sep 07, 2009, 04:32 PM
Since you seem to end up with a half a tank of fuel left when it cuts, have you checked your clunk line in the tank to see if its fallen off or split?
Sep 07, 2009, 05:25 PM
Registered User
Even if it is drawing current, the glowplug may be bad. Even if it isn't the problem, you probably need to change it by now anyways. As stated above, check fuel lines and clunk.
Originally Posted by Aber
Of course I haven't - because that would have made sense. Looks like I have one more thing to add to the list.

The glowplug is still drawing current (according to my buddy's power panel). The plane does run and idle fairly well on the ground.

Sep 07, 2009, 11:18 PM
Registered User
I have had some of the same problems with an older os .40.. when I learned to fly on my trainer I was taught to rn engine wide open, open throtle till the engine speed starts to decrease, the turn the screw back in 2 to 3 clicks. and sometimes it would die just like yours does. I thought of the same, (clunk, trash, old fuel line.) Then I tried the advice on tuning your engine on the other post, to run your jet out till the engine starts to slow down, then go out 2 to 3 more clicks. It made the engine sound rough but once i made a couple of passes it cleaned itself out,and ran great! I've only ran 3 tanks this way but so far i have gotten more flying time out of each tank. however it does get a little messy with the richer fuel setting..

Sep 07, 2009, 11:30 PM
Just a guy.
Well, I did half of the things I planned. I put some gasket material on the backplate and carb. Took apart the fuel system and the clunk was just fine. Changed some older fuel tubing to a cleaner setup. I remounted the engine and put the cowl back on. I did not have a new glowplug so I stayed with the old one. (Since it idled well I suspect that the glowplug is fine anyways. Wouldn't a bad glowplug have a poor idle?)

I got out to the field and discovered a whole new problem. Some fool forgot to hook up the throttle cable........

Gonna have to find that guy and have a conversation.

Too bad the I have to take it half apart to get that linkage back on.
Last edited by Aber; Sep 07, 2009 at 11:32 PM. Reason: To few elephants in the soup.
Sep 08, 2009, 07:36 AM
Registered User
Couple of suggestions:

If it's dying mid-tank it's likely overheating or leaning out. The general rule for cowls is that outflow need to be 2 - 3 x's as big as the inflow. One way to check if you're over-heating is to try a few flights w/o the cowl. If the problem goes away then there's your problem!

For possible leaning out issues, check your tank height. The center line of your tank should be approx the same height as the spraybar in your carb. If you're slightly lean at full tank, you'll be substantially lean at 1/2 tank. I've had several planes where an extra 1/2" of tank height made all the difference.

You may want to put it on an engine stand until you get it figured out. That removes the temptation to just fly the danged thing...

Sep 10, 2009, 01:31 PM
Registered User
Flyer 495th's Avatar
Take the backplate off and use some red RTV on it. Then put it back on and use some blue locktite on the screws. I have corrected all my LA problems because of this leaking. Good Luck!
Sep 10, 2009, 05:04 PM
Registered User
earlwb's Avatar
I would tend to agree with the others about the clunk or fuel pickup isn't working, since it quits at around 1/2 tank or so.
Try adjusting the engine with 1/4 tank of fuel in the tank. Then fill it up and see what happens. You might have a longer than normal fuel line as well as a odd fuel tank position in relation to the carb on the engine and the engine has trouble sucking the fuel up to the carb. Ideally one wants the fuel tank as close to the engine as possible along with as short of a fuel line as possible. The fuel line size should be chosen to match the engine as well. For a 15 small or maybe a medium size fuel line at the most should be used. I have seen people try using large fuel line on a small engine, and it doesn't work well most of the time.
I assume you are using a muffler pressure tap to help pressurize the fuel tank a little. But sometimes if one is using a racing type of muffler, there is little to no pressure from the muffler to help pressurize the fuel tank. ideally you want a pressure fitting that tends to act more like a rocket nozzle, where it lets muffler pressure in but tends to resist letting the fuel tank depressurize quickly (at least until the engine stops). One could test the muffler pressure, with the engine at a fast idle, pull the fuel line off and note how long the fuel dribbles out after the engine stops. It should dribble for a second or two or three. If the fuel stops dribbling immediately, then you have no muffler pressure or a problem with the fuel line someplace.
Sep 10, 2009, 08:28 PM
Larry Jasmann
I had a very similar problem on an OS 46 AX a week ago. Tried all of the things you tried and it still quit when I got to about 50% fuel. I replaced the line to the clunk and to the engine, changed the plug, ran it richer.. all to no avail.

I finally took a close look at the length of the line to the clunk... of course, when I replaced it I made it exactly as long as the old line.. and it was a plane that I inherited, so I had not put the fuel tank together in the first place. Turns out that the line to the clunk was just a tad too long, so the clunk would hang up on the back of the fuel tank sometimes.. not every time, but about 80% of the flights. Wouldn't do it on the ground as there was not enough motion of the plane to make it move around and risk getting above the fuel level of the tank as it drained out.

I shortened the line by about 3/8 of an inch and my problems went away..

Take the stopper out of the fuel tank, and line it up on the outside of the tank and see where the clunk is with respect to the end of the tank. In the case of my tank, the end of the tank is concave (facing inward), so if the clunk moves up, it is closer to the end wall of the tank. Make sure that you have a bit of distance between the end of the clunk and the back wall of the tank.

L. Jasmann
Sep 12, 2009, 01:01 AM
Lost it again!!!!!
dirtman's Avatar
The clunk being to long sounds like a winner. All the advice here is good.

What I would like to know is....what are you doing when it dies? acelerating from low idle? decelerating? WOT? If it stutters right at 1/2 throttle or just above...Probably to lean on top. If it stalls as you hit the stick before 1/2 throttle, the bottom is to rich or lean(hard to tell unless you hear it)

You say it Idles fine. But what is fine to you? You should be able to idle for over a minute and hit the throttle and it should snap right up.

One other thing...how responsive is the motor to the stick inputs? Any lag, more noticeble in deceleration, it it takes a second or two to idle down, or RPM fluxuates at WOT you got an air leak.

What is your flying style? Lots of loop, rolls and 3D. Any fuel pick-up problems will cause a problem. Also with that type of flying you have a lot of throttle transitions, a poorly tuned motor, or a bad glow plug will give you a problem.

Check you glow plug by starting your engine, and removing the ignitor with the motor at an idle. If the idle drops, or it dies the glow is bad.
Sep 19, 2009, 12:56 AM
Just a guy.
Thanks again for all of the help. I have not had the chance yet to run the motor (again). Last time I forgot the throttle linkage. This time it was a bit too windy to fly ( I did fly other planes but I was not willing to chance a deadstick in that wind).

I have a new glowplug (which I will try).

Muffler and muffler tap? I have the standard ones that came with the LA engine. I made no modifications there.

As for my definition of a fine idle? Well I normally fly electric so anything less than instant throttle response doesn't seem quite right to me. That being said, if I idle it for a little while there is a shade of hesitation before it will throttle it up.

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