engine stalls after takeoff!! Please Help!

[DigitalBurn]

Hi.

I have a Super Chipmunk that I built out of a kit. It came out real nice, but I have a weird problem.

It has a Magnum .45 engine in it that stalls everytime it gets airborne. Before takeoff, we run it, shake it up, turn it vertical, and the engine runs great! No problems. But seconds after my friend throws it, it stalls! Everytime!!

I'm getting tired of fixing the gear and never flying it. We can't figure out why it stalls after he lets go and it gets airborne. It's almost like someone is playing a joke on us.

:confused:

[rcflier]

It sure sounds like it is leaning out in the air, which is fairly normal. The next time you try a flight set the engine as you normally do on ground. Then after you have it set like you normally do, richen it 3 or 4 clicks.

Also double check that your vent line is connected to the muffler pressure. And make sure your vent line isn't plugged or kinked. Not only check the vent line itself but also check the pressure nipple in the muffler it may be plugged with carbon build-up. It's possible your tank isn't venting and your building up a vacuum in the tank as fuel is draw out.

And last try a new and possibly different style glow plug. Maybe you have a bad plug or wrong style plug.

[DigitalBurn]

Thanks for the suggestions.

I hope you're right about it leaning out in the air. The engine reacts badly to being slightly lean, I've noticed thru tuning. Maybe that's the problem. However, it's blowing some pretty good smoke already. But, I'll definitely try a little richer.

As for the pressure fitting, it doesn't have one. This has been sitting on my mind as well. Because I'm thinking maybe the G's exceed the sucking of the carburator at a certain point, and pressure in the tank might solve that. Keep in mind, I AM a novice though. Feel free to shoot that idea down.

The muffler is a Pitts style muffler, and from what I read, you don't need a pressure fitting with this type of muffler. If I could easily fit the stock muffler(with pressure fitting) that came with the engine, on the plane, I'd try it.

And the glow plug. Hmmm, . . .the manual says you should use R/C Long. The guy at the local RC shop said the Standard Long plug should work fine. They didn't have R/C Long so I got what he recommended. I did get ONE 10 minute flight off this plane with the Standard Long plug.

The only thing that has changed since the day I got my 1 good flight is the fuel mixture setting (I can't help but play with it). Maybe it really is leaning out in the air.

Anyone have more suggestions?

[rcflier]

I would defintely put a pressure tap in your pitts muffler. My CAP 232 has a pitts muffler and it has pressure tap. Typically all r/c engines will run better and more consistently with muffler pressure. Pumped engines such as my OS 1.20FS pump don't require muffler pressure as the pump and regulator meter the fuel.

If the engine requires a R/C long you should run it. A standard glow plug probably won't reach far enough into the combustion chamber to get good a burn.

[Dave Robelen]

Hi DigitalBurn,
This is kind of a long shot, but I once had exactly the same experience test flying a buddies scale model. It seems the carb was located inside the cowl which was plenty open in the front, but there was very little opening in the rear for air to flow thru. What was happening was the plane would accellerate to flight speed, lift off, and die shortly after in level flight. The problem turned out to be a build up of air pressure inside the cowl which had the effect of choking the carb just a neat as putting a finger on it.
If it is possible to make a flight without the cowl, that might provide a clue.
Teake care, Dave

[DigitalBurn]

Ah, thanks for the replies.

I bought some R/C Long plugs, and I'll give it a shot this weekend, if weather permits.

The guy at the RC shop thinks it's leaning out in the air, too.

And, Dave, thanks for the tip. I'm running it without the cowl, but that is certainly an interesting pitfall I will keep in mind in the future.

In case you're curious, I'll post the results.

[Dave Robelen]

Hi Digitalburn,
There is still another possibility. The fuel may be foaming in the fuel tank and causing a leaner run. I check for this by putting some hefty rubber bands around the wings chordwise. Crank up the engine, and with help support the model in this "rubber sling". It may be that there is a resonant vibration that only occurs when the model is free to vibrate in flight.
Cheers, Dave

[DigitalBurn]

Wow! Thanks. That is certainly another interesting possiblity. I will definitely try producing the in-flight effect before we try sending that plane sailing again. I'm really tired of seeing it auger in.

[Dave Robelen]

Hi DigitalBurn,
I just remembered, there is still another possibility. The glow plug may be too cool, or the fuel too cool (low in nitro) for the engine/plug combo. A test that works well for me is to crank up at idle, leave the booster battery connected and advance the throttle to the midrange. Now remove the battery. Does the rpm drop? The firing point of these little glow plug engines is set by the compression ratio, plug temperature, and fuel nitro content.
If the engines slows when you remove the battery, it probably will get even cooler in flight causing it to quit. This is especially true if the engine is mounted inverted where droplets of raw fuel can accumulate on the plug filament.
I found that the K&B plugs are among the hottest R/C plugs, while the Fox brand run very cool. If you do have this sort of problem, you might see if you can borrow a small amount of hotter fuel or switch to a hotter plug. When all is well, there should be no change in rpm with the battery on or off.
Regards, Dave

[DigitalBurn]

Again, thank you very much for the reply. That is a very distinct possiblity, since I had to use a Standard Long plug, instead of the recommended R/C Long.

I have been wondering if a drop in RPM is normal when you remove the glowplug clip, because when I remove it, it does drop. Also, the plug I was using is a Fox.

I will set all these little things straight before I try to takeoff again.

Thank you very much for the info. I appreciate your time.:)

[DigitalBurn]

Well, I was here and just thought I'd update the thread.

I haven't flown the chipmunk since. I have bought a Magic fun-fly ARF and put my Magnum 45 engine in that. The engine works okay in that, and I do mean just okay. The Magic is absolutely incredible! Those are for other threads though.

I used an O.S. no.8 plug, and that cured the rpm from dropping when you remove the glow plug.

I have simply been running the engine a little richer. We'll see what happens when I put it back in the Chipmunk.

[jmaxwell]

Hi, DigitalBurn

I have a Magnum .46 and had the same problem. The engine would seem to run fine on the ground but would then deadstick all the time. Luckily, I was always able to bring it home in one piece! Yikes...

Anyway, I got a tip from someone very close to the manufacturer who said that the rubber O-ring on the needle valve was not very good and seating the needle valve. Solution - Put a small piece (1/8") of fuel tubing around the needle valve where it enters the housing. NOTE: You have to gently lift the clip that sits in the ridges on the outside of the needle valve as you are screwing it in.

The engine has run perfectly ever since. It was like a miracle!!:)

BTW, I also think that the advice about the pressure filter on the muffler given earlier in this thread is very pertinent.

Hope that helps.

[Taylorcraft]

DigitalBurn:

From what your last post says, I suspect your problems with the Super Chipmunk are either caused by:

* Fuel foaming
* Lack of fuel pressure
* Incorrect height of fuel tank
* Pick-up clunk in tank jamming against rear tank wall during take-off.

Fuel foaming will be noticed as bubbles in the fuel line. This may not be seen during the ground run, because the RPMs will pick up when you let go the plane, causing the tank and fuel to come into resonance, wich will cause this problem.
Solution: Ensure the tank is properly padded. More doesn't neccessarily mean better.

Lack of fuel pressure and incorrect height of tank can combine to cause problems, since the engine will starve out and quit.
Solution: Use muffler pressure and ensure the middle of the tank is approx. lined up with the venturi, not lower than 1/4 inch when the plane is level.

Acceleration during takeoff can, in some rare cases jam the clunk against the rear wall of the tank, and cause fuel starvation.
Solution: Cut approx. 1/8 inch of the clunk tube and try again. (learned that one from Clarence Lee some time ago...)

Hope this will help.
Anyway I hope you will get your Super Chipmunk up where it belongs, boring holes in the sky.

Good luck my friend!

BRG

Taylorcraft
_____________________________________
Given enough power even a brick will fly.
But, the lighter the brick, the better it flies!

[DigitalBurn]

Thank you all for the info.

I have been wondering about some accumulating fuel around where the needle valve assembly fits into the carb, and thinking about replacing o-ring or gasket. I like the silicone fuel line patch idea, jmaxwell. Wow, is that stuff versatile!

I also have the stock muffler (with pressure fitting) on the engine now, and I think that is helping things a lot. My friend came over, and we finally got it tuned to a nice melody.

One thing we noticed that probably really helped a lot, as well, is that the main needle valve was turning as the engine was running! Apparently my engine didn't come with a little 'clicker' thing (don't know what it's called) on the main needle valve knob to keep it from spinning. We tuned it to where we wanted it, cut the engine, then hit the gap under the main needle valve knob with a little CA. This worked, but makes it difficult to change the high speed mixture again.

And Taylorcraft, I've got all those kinks worked out, but thank you very much for the input.