Combat training is going well. abut 10 flights on my battle axe. I'm having a problem with the OS .15LA sputtering during flight, and on the ground.
Starts fine runs fine then I can see bubbles coming out of the fuel tank heading towards the remote NV.
This is a new tank with new lines, I'm thinking it may be fuel foaming?
If you dont know the battle axe, the engine is bolted to two aluminum rails ( home depot product used to edge 1/4" ply. ) The fuel tank is sitting on foam padding and zip tied to the aluminum rails. This seems to transfer allot of vibration to the fuel??

The engine breaking down looks to be related to the air bubbles... How best to deal with it?

I have another 3 oz tank I'm going to try..


Thanks

Steve

Thry this stuff: http://www3.towerhobbies.com/cgi-bin...?&I=LXE101&P=7

If there is room, try adding more foam padding and zip-tying slightly looser- add some foam under the zip-ties as well. This should dampen the vibrations some.

I believe there is also a product you can add to fuel to lessen the foaming, but I cannot remember what it is... I want to believe it was windex or something similar, but I'm not sure... Perhaps someone else will remeber what the mystery liquid is.

I also would look for some kind of pin hole in the fuel system. Does it do it all the time in flight?

If you are serious about your combat flying then you need to convert to Bubbless type tanks avaliable from central hobbies (Tetra) or Dub Jett. That is the only way to totally eliminate the problem and no serious combat pilot or pylon racer would ever use anything else. I also use them in some controlline applications.

John

Bubbless types are hard mounted and no foam is use nor is a clunk used Foam is impossible to form and they provide the best unpumped/unregulated fuel delivery possible in high 'g' conditions.


John

This is an interesting topic, Iwonder why the Nitro Helicopters don't have foaming issues? Their tanks are hard mounted, they go through gyrations that no fixed wing could possibly do and at G forces that would snap the wings off most planes, and they don't have any foaming issues. They burn the same fuel for the most part that we do in our planes. Granted that they have a small slave tank (wrong term?) but it gets shook up the same as the primary tank. Iwould guess that all of the comercial fuels now have an anti foaming additive. Iknow the Omega and Cool Power does.

My guess is that if you are seeing air bubbles in the line, you have a hole in the supply line, and look all the way back to the clunk. A sharp end on the brass tubing is like a razor blade to the fuel line. I use a stone setting bur, 45 degree taper to clean the IDof hte brass tubing and the a very fine file to knock off the sharp edge on the OD and also to dress the end. After fighting this problem on my first few planes, I found it easier to fix before the first flight on a tank. Also, the bung will sometmes loosen up after a little use and shoud be retightened,

Don

Header Tank

..............Plus a bubbleless clunk:

http://www3.towerhobbies.com/cgi-bin...&I=LXXF25&P=RF

Foam cannot isolate the tank from vibration if:
1) It is crunched.
2) There is another non-isolating connection to the airframe (tie-down, velcro, etc.)

JohnBuckner explained the radical solution to fuel bubbles, assuming the silicone tubes are hermetic to air sucking.[sm=thumbs_up.gif]

Actually to a combat pilot and many forms of pylon racers trying to screw around with a conventional tank 'IS' the radical approach and oh so much more complicated

John

Sorry if I used the word "radical" wrongly; English is just my second language.[sm=red_smile.gif]

I just tried to say:
1) These tanks are the solution designed to remove the root of all the bubble problems.
2) They are an excellent, cool solution, with no trade-offs'.
3) Fuel is not in contact with any air, which is the raw material for bubbles.

No, there is no problem and you did not use the term inappropriately I just used the opportunity to express my enthusiasim for the bubbless tanks for certain types of aircraft.

John[8D]

hey steve, I have the same set up. I do get a little bubbling also but it really isnt enough, I have done a few things to eliminate it. first, I use the foam under the tank also, I use a few rubberbands to hold the tank on and just one zip tie, I balance the props and I make sure the system is good.

you can also use a scintered clunk and a few drops of armor all to you fuel can. those will also help eleminate foaming

you will get the issues worked out, have fun!