I have a trainer that has a 6 ounce tank and a Thunder Tiger .40 PRO turning a 10x6 prop. About how long of a flight time should I get at full throttle?

Maybe 8 minutes or so? An 8oz would be better.

Burn a tank thu'er on the ground and time it. Should run at least a tank thru it before flying anyway to help break in the engine anyway, with it set a bit rich. This will give you a pessimistic run time (because the engine is rich) that you can use as a "safe" guideline flight time. Be sure to use a restraint of some sort to keep the plane from moving.

J

Some of the guys at my club tell me I should put a 14 or 16 ounce tank in it. Seems a bit much to me. What do you think?

There is nothing more useless than air above the plane or an empty fuel tank. You want lots of air beneath the plane (altitude) and landing with fuel remaining in the tank. For a new pilot, dead-stick landings can be a challenge. It's one of those things you want to practice doing... but not forced to do because you miscalculated the fuel remaining in the tank. Add the extra size and don't worry about it. If you have fuel remaining at the end of the day, pump it back in your fuel bottle and use it the next time out.

CGr

I've got a 12oz tank in my .46 AX powered Mustang. I can get about 17 minutes or so WOT with that, but at that speed, 10 or 12 is enough for me. Your .40 should be a bit less thirsty than my 46AX.

Good rule of thumb. Put as big a tank as you can fit in there and still have some foam around it.

I like the mouldable sullivan tanks, you can make'em fit with a heat gun and a few minutes. Very handy for maximizing fuel range.

J

Oh yeah, Jburry. I forgot about those tanks. Great idea. I gotta look that one up and put one in one of my planes that has a tank that I do not like. I hate cramming the tank into a location that was not necessarily designed to fit.

CGr.

Excessively large tanks frequently are the cause of running problem for lots of fellows and generally a bad idea. Yes it can work if you set everything up perfect but more often than not I see folks complicate poor installation problems with oversize tanks and the result is often flameouts and never really being able to uitilize the full capacity anyway.

A substancially larger tank than the norm for any give displacement will experiance a greater fuel head pressure variance from full to empty and the engine will spent more time with weak fuel delivery problems than neccessary.

John

Thank you all for all the great information. It has been really helpful. I am going to try the 14 ounce Sullivan flex-tank.

A fourteen ounce tank is an excessively large tank for a TT .40 Pro especially in a trainer besides causing a greater CG change during the flight to the rear it will also change fuel head pressure during the course of a flight causing needling changes and its doubtfull you consistantly ever be able to use all the fuel.

A more reasonable tank size for the .40 pro is eight ounces and no more than 10.

John

Do you really fly full throttle all the time? Your flight times will be much more then 8 minutes if you are flying normaly with most time spent around half throttle. I personaly wouldnt go above 10 oz in that model. I try and keep my tanks as small as possible while still giving me half a tank after 10 min flight time.

8 oz is about 'normal' for a 40 size engine. You can make do with 6 oz. Fly for 5 minutes with your normal throttle setting and land, then pump out the fuel and see how much is left. Then increase the 5 minutes accordingly.

I fly a 3D profile on a 6 oz tank with a .50 size engine. I get 10 minute flights, but the tank is strapped to the side of the fuse so the remaining fuel level is visible.

As JohnBuckner said, sometimes too large a tank can present problems. I'm not sure why, maybe it has something to do with muffler pressure. I have had engine problems on two different models that were solved by decreasing the size of the thank.

I just started flying with a Thunder Tiger .36 and a 6 oz tank.
I timed the tank at 10.5 min. on the ground. Most of the time at half throttle up to full for awhile..
I set my timer for 8:min. I havent measured what was left in the tank yet.
I just got back from my 6th flight on my 2nd weekend flying...No landings yet!

I've been a little concerned about the 6 oz tank.
I want to do more tests to know my limits. Maybe go to an 8oz tank..

Pop

Yes, I now agree with the larger sized tanks being too much. While comparing the size of the 12, 14, and 16 ouncers; I decided on a 10 ounce. Those other were just way to big. I know on my T-Maxx the difference it makes from full to empty on the way it runs, I could only imagine what would happen in the air with more tank than the exhaust could fill. So do you guys think I made the right choice with the 10? And thanks again for all the great help. I hope that soon in the future I can return the favor.

Hey, good thing about our R/C planes is that the tank is almost always removable.

Stick the 10oz in there and go fly it. If you decide it's too small (which I'd bet against) you can put a bigger one in.

The most excellent thing about our hobby is that it ALWAYS provides us with strong reasons to buy our next model. If you discover that the 10oz is either too small or too large, what is your only alternative? To buy a "proper size" tank. And then what will you have sitting there??? A TANK THAT NEEDS ANOTHER MODEL AIRPLANE to keep you from wasting money on that now unused tank. TAA DAA !!!!!!

Ain't this an awesome hobby !!!!

BTW, one way to decide on tank size is look at the specs of a number of models that use the size engine you plan to use.

There is a reason the models come with certain size tanks. It's because they are designed around an engine size. And engine size determines tank size. You won't find a chart anywhere, but you don't need one.

Tower Hobbies is about the most dependable "specs" provider. They almost always describe in detail everything they sell. They're a good place for research of the sort.