John Rcflyer

Hi Guys.
I just installed a tuned pipe on my Viper. It will turn 15400 rpm on the ground with a 40FX and a 9x8 APC pylon prop. Before the pipe I was getting around 13000 rpm or so. Now I have a problem with leaning out in high speed turns. It really flies like a rocket. If I make a wide turn or climb vertical no problem. Only when I yank the stick for a fast turn. Any body know how to fix this problem? I am not really to familiar with racing set-ups.
Thanks
John

combatpigg

My Feedback: (3)

If the G forces on the fuel system get too extreme it will cause fuel starvation, nothing can beat a pressure bladder for high G fuel delivery. Most flyers would rather jump off a bridge than jump through all the hoops to rig up a bladder system though. I would say to do your high speed needle with the nose pointed straight up, with 1/3 tank of fuel. Forget about the idle, richen up the low end enough to allow a good mid to high transition. A crankcase pressure and cylinder leakdown test could also reveal why your engine isn't drawing well enough to keep up with it's own needs. The first thing to rule out is [of course] everything from the needle valve back to the tank, and tighten all screws. The fuel tank should be well padded in soft foam. I read recently that GE silicone is good for isolating the tank from vibration. Rule out foamy fuel. When you find the problem, let us all know what it was.

BTW, if you are running borderline too lean, all it takes is a momentary pinch of the fuel line to kill the engine when setting the high speed needle.A good working pipe system should have a very healthy spray of unburnt fuel

John Rcflyer

Combattpigg,
I will check out the fuel system and try to pad the tank better and see what I can find out.
I have heard of a bladder system, where can you find one and how does that work?
Thanks,
John

bob27s

My Feedback: (19)

What you decribed is not an uncommon condition. In a high-g turn the fuel flow is affected, while at the same time you end up loading the engine. Makes for a tricky balance setting the needle.

For racing, we use to set the engines a tiny bit rich to avoid going lean in the turns. More currently, the vast majory of racers use bubble-free fuel tanks. These tanks use regular muffler pressure that you normally use, but they prevent the introduction of air into the fuel (foam), and the internal fuel bag provides consistant fuel system pressure throught the flight. Added benifit is that you can run the tank completely dry without ever seeing a change in fuel flow or needle setting (no toasted engines).

Such tanks are available from Jett (bubble-jett tanks) and Tetra tanks (available from performance specilaties and others)

combatpigg

My Feedback: (3)

Loading the engine in a tight turn.... yes, that alone can shut things down. Just a prop change to one with a slightly lower load can work wonders, if there are no other problems anywhere else.

John Rcflyer

Combatpigg,
I have a 9x7.5, not a 9x8 like I originally thought. What kind of props are you guys using?
John

combatpigg

My Feedback: (3)

John, you are right there with your prop sizing, if you are running wood or carbon you can work on thinning the blades, and doing a super balance job. 8.5" could be tried. If you get a JETT tank, fresh glow plug, and good needle setting, you should be able to yank those sticks all you want. The pressure bladder system is an extreme deal, because you lose your throttle, and you have to rig a fuel shut off for safety. It is made out of latex tubing, and filled with a syringe. It doesn't sound like you are in a rpm range yet that induces a lot of vibration related problems, but the faster the engines goes, the worse it gets.. Extreme vibration causes HEAT between mated parts and premature wear. My question though is why does vibration always back screws OUT, why doesn't doesn't it sometimes TIGHTEN stuff for us? How does it know which way is counter clock wise? Even with reverse threads, vibration knows which way is loose!

Rudeboy

Good one there CP...

But vibration DOES tighten screws... its the ones that don't come loose that are tightened! LOL (obviously you only notice the loose ones... generally when it's too late)

I have actually seen seen wooden dowels become scorched due to high rpm vibes... wooden dowels in wooden fuse formers that is... metal dowels do not appear to have this problem.

John Rcflyer

CP
I will have to gat a bladder tank and see how that works.
Thanks for the help

daven

My Feedback: (1)

Definately go with the bladder tank. I prefer the Tetra tanks, but the jetts are already assembled. Also, as to the syringe, the Jett definately is the easiest to use.