Hi All

Have a new TT Pro .46 and am very pleased with its performance and ease of tuning. However,
I realized on the second or third flight (it's mounted on a SPAD Debonair) that if I sustain a steep angle of attack, the engine stalls after several seconds and I end up having a deadstick landing. After this happened the first time, I started the plane, held the nose up vertical and observed. After several seconds (five to eight, maybe) I notice that the fuel line fills up with air bubbles and shortly thereafter the engine dies. The fuel tank is a Dubro and I installed the supplied hardware per the instructions. The clunk is all the way at the bottom (and rear) of the tank and this does not change when the plane is vertical. Can anybody give me suggestions about where the air in the line is coming from? The tank sits just aft of the firewall so there isn't a lot of distance between the pickup and the carb. The centerline of the carb sits slightly above the centerline of the fuel tank. The only time the airbubbles appear is when the plane is vertical, otherwise the thing runs great and has good zip for pulling the plane around the sky. Any suggestions, tips, hints, etc. would be appreciated. Thanks in Advance!

Steve

Sounds to me like there is a hole in the fuel line inside the tank. If the hole is near the front of the tank, it would be open to air when the tank is tipped up. I would try replacing that line to the clunk.

Yep, sounds like that might be the problem. I had the 46 AX on my Tiger 2 cutting out last week. It wouldn't do it all of the time - plane flew fine 99% of the time. Rolled over to inverted and the engine died. My first deadstick - no damage - but I later found the fuel tubing inside had split and the klunk fell off.

So, I replaced the tubing and the next flight engine still cut out while inverted but only toward the end of the flight. The new line I had put in was too stiff and wouldn't allow the klunk to move freely. So, put in a more flexible line and going to try it out next flight.

Steve,

The clunk line and other fuel lines should be checked as has already been suggested.

Bubbles in the fuel line are always bad. Bubbles in the fuel line have almost always meant fuel foaming in my airplanes. If the problem persists after checking the other things you might suspect fuel foaming. If the tank is against a structure sometimes a small amount of chafing might be seen on the tank. Latex foam rubber around the tank and loose tank mounting has always been my solution to fuel foaming.

Bill

Thanks everyone for the diagnosis/suggestions. I will pull the tank and run new fuel line. Bill, this was something that I thought about initially, however the air in the line is only evident when the plane is oriented vertically. If foaming is the problem, do you think it would be apparent when the plane is sitting level? Also, I have the tank wrapped in foam and slid into the fuse for a snug fit...a very snug fit. I suppose the fit is tight to the point that it may be defeating the cushioning effects of the foam as it is compressed very tightly. I am using an 8 oz. tank and aside from going to a smaller tank, I don't see any way around this except to maybe try a Great Planes or Hayes 8 oz. tank. As mentioned before, aside from the cutout with the plane vertical, the engine runs impressively. I will check the line, fittings etc. to see if the problem is cured. Thanks again.

Steve

Not necessarily.

Foaming is hard to find and cure because it can vary:
1. with engine RPM.
2. with the amount of fuel in the tank.
3. with the attitude of the airplane.
4. with the addition or removal of a structural member.
5. by simply holding the airplane rather than flying.

A loose fitting tank protected by latex foam rubber is the best insurance against foaming.

The upside is that you may get very good at dead stick landings.

Bill

For what it is worth I have been working on an engine problem that started with foaming for about two weeks. Along the way three other engine problems were found and are now fixed. A smaller tank and liberal foam was used but the foaming problem still exists. The bubbles are much bigger than the pinhead size bubbles initially observed. Just cut a structural member for more clearance. Really hated to do that. The original 4-stroke engine did not have a problem with the original tank.

Be sure your props are balanced, that can also cause foaming. ENJOY!!!!
Red

One thing that was unclear. Does your engine have a rear needle valve? If it does, then are you looking at the fuel line before fuel goes into the needle valve. The problem may be that you are setting the needle too lean on the ground. You may want to revisit your engine manual and make sure you are needling correctly for flight.

On new airplanes, I only put between a quarter and half a tank of fuel in, then rough set the needles. Once I am satisfied, I fill the tank and fly it with the setting at half full. Any time I varied from this, I usually ended up dead stick about half way through the flight, especially with a new engine. It is very easy to set a highspeed needle too lean on the ground. Many folks try to get the most RPM's out of the engine with the nose pointed up, and think they are good to go. This is a big mistake. With the nose up, tank full and throttle open, you should be able to pinch the fuel line and hear a slight increase in RPM,s. If you experience a decrease or no increase, you are too lean. Remember, the plane will lean out once in the air and the fuel level drops in the tank. With trainers, deadsticks are just frustrating, usually, but with warbirds and biplanes, they can be downright costly, since most fly like an aerodynamically designed brick with no power.

If all the other checks prove fruitless, then this might have helped. Happy Landings (with power, hopefully)

Thunder Tigers don't have those silly rear needle valves & they seldom suffer from carburation problems. Assuming that the clunk is not stuck at the forward end of the tank (you did hold it nose up & give it an almighty shake up & down didn't you?), my guess is a pinhole in either the clunk line inside the tank, or the feed line from the tank to the needle valve.