ORIGINAL: p40hawker
I have a new Thunder Tiger Pro 46 which cuts out in a 3D move. Such as a roll or loop. Does the fuel in the tank stay at the back of the tank when performing a loop or a dive.
If you're getting flameouts during rolls, what happens during a loop or other downhill maneuvers doesn't really matter.
I was told that the fuel line inside your tank needs to be flexible enough to move to the front of the tank when the nose is down, as in a dive. But I don't think this actually happens.
Add me to the growing list of people who do not think the fuel tubing should ever move forward. I've used the setup Ken drew. On smaller tanks, I've even gone so far as to solder a small section of brass tubing directly to the klunk so I only needed one piece of flexible line in the tank.
Pull your tank and confirm that the klunk can easily move to all 4 rear corners and that it can't move forward, and potentially pinch closed, when the nose is down. Also confirm that the klunk doesn't hang up on the rear of the tank as it's moving around.
I think that centrifugal force keeps the fuel at the rear of the tank.
I think the whole discussion about the fuel being in the front or back of the tank is a red herring. If you're having trouble with rolls, there's something else going on.
For most maneuvers, there will be enough fuel at the rear of the tank to keep the engine running. There are a few things to keep in mind:
1) It's not a good idea to do long, steep descents as the fuel is getting lower. Aerobatics should be done while the tank has a good amount of fuel in the tank. If you're going to do descending maneuvers, get used to the idea that you're not gong to be running the tank nearly dry during your flights.
2) Most (all?) descending maneuvers should be done with reduced throttle. This drastically reduces the fuel flow. Even if a small bubble gets in the line, the duration of a typical downhill maneuver won't be long enough, due to the low fuel flow because of being at reduced throttle, to reach the engine. By the time the bubble, if there even is one, gets to the carb, the engine will be powered back up and would barely notice it, unless...
How do you set the high speed needle on your engine? Do you just peak it and back off a bit? Do you then perhaps give it the famous "pinch test" and figure it's ok? Following is my suggestion for tuning. I learned this somewhere around 25 years ago from my instructor, who flew masters pattern. I figured if it was good enough for him, it was good enough for me:
Tuning – High speed needle
The following method is designed for sport flying where one wants reliable engine performance (minimum deadsticks) and long engine life (part of which comes from avoiding lean runs).
I’ll start off with a reminder that all needle adjustments should be done from behind the engine and that the plane should be firmly anchored or held. Never attempt to adjust the needle while holding the plane in the air. A small engine blip or wind gust could result in fingers in the prop.
Begin by gradually leaning the engine until you find the peak RPM. Once you find this, turn it several clicks rich. Once you’ve found this slightly rich setting, with a firm two handed grip on the plane, point the nose straight up. While you are doing this, remember to keep the propeller arc out of anyone’s face. When you raise the plane’s nose, one of three things will happen to the engine RPMs.
If the engine speeds up slightly and holds that speed for 10 to 15 seconds, pat yourself on the back (after you put the plane down), you’ve got the needle set pretty well.
If the engine slows down, or does not speed up a bit, it’s too lean. Lower it immediately, turn it a few clicks richer and try again.
If the engine speeds up significantly, it could probably be a bit leaner. Put it back down, set it a bit richer and try again.
End of tuning guide.
PS. My instructor was also the one who taught me that the klunk should NEVER go to the front of the tank and that a piece of rigid tubing would help prevent such a thing.
