I just bought a fuel tank for the trainer I'm building.
Looking at it, I can see how the engine would be supplied fuel at any stage in a roll. However, it seems to me that the fuel level would be too low for the tube if the plane was in a dive.

Is that true, or is there something I'm missing?

yes, in an extended dive, when the tank is nearly empty, the clunk will draw air. In the real world that seldom happens, because you are generally not in a dive long enough to kill the engine. If some air gets drawn into the line, it will not always kill the engine. And when you are pointed down, the throttle is usually at idle, so only a miniscule amount of fuel is being used.
Also, when you first point the plane down, the fuel does not immediately drop to the front. Picture you drop the plane (in a vacuum) and the plane rotates to the nose down position. The fuel drops at the same rate as the plane and stays where it is. But in real air, the plane does not continue to accelerate downward but is slowed by the air. And the fuel does fall to the front of the tank.

Good question, but I wouldn't worry about it.

If you are in a dive long enough for it to make a difference, then fuel starvation would be the least of your problems!

Let's see . . 60 mph (about the speed your trainer is plummeting) is 88 feet per second isn't it?

Lets say you are almost 200 feet up in the air, it only takes just over 2 seconds to meet that hard flat object, which is scarcely long enough to make the engine starve too much.

-David C.

I for one, can attest to the fact that in a prolonged dive the engine will run dry.

Here I am right, having a good time flying the good ol' trainer and decide to climb up real high and go into a dive straight down. No problem, I thought, I'll pull out real slow so as to not rip the wings off. So now I'm pulling out of the dive, leveling out at about 20 feet or so and figure I've got just enough speed left to do a tight loop. Right about at the top of the loop, the engine went dry and sputtered. The landing gear actually brushed the tall grass exiting the loop. Just about had to check my shorts on that one.

I vowed to never pull that stunt again. It didn't last long though, tried it again and this time hit one little pine tree in the middle of the field. The plane lived though...

So yeah, the engine will die after a while.

But look at it this way. A 40 or 46 size engine in a trainer, which usually has an 8 ounce tank, will fly for nearly 10 minutes at wide open throttle. (A 40FP when using throttle, will run about 20 minutes on an 8 oz tank.)

10 minutes is a long flight (national average according to a survey is 6 minutes). So, you'd have to be pushing the limits of flight time for your tank to be that empty, and not many people are going to climb high enough (at the end of a long flight when you know fuel's getting low), to be able to dive far enough to starve the engine. :stupid:

Whew! That being said, don't worry about it!
Dennis-

I wasn't talking about being in a dive for any long duration. Think though, nose down and the clunk is at the top of the tank with the fuel level below it. The fuel line will not bend back towards the neck of the tank.

It won't take all that long to burn through the fuel in just the fuel line from the clunk to the carb. If that even makes sense the way I wrote it, I'm no English major...

I understand what you're saying nbc, but I've been flying for eight years and have done any number of long dives. Haven't had an engine quit yet.
Dennis-

when your engines running its amazing how long that little bit of fuel in the line lasts, we can cut engines in fast planes on the dives, but the trick is to make the dive just about right so it still accelerates and the fuel stays at the back, sometimes you can catch it and not cut, or even restart!