I have three gas planes in the very near future. I am working on two of them right now, and will receive the third in mid December.
I have a 3W24 in a 1.20 size Sukhoi 31M, it should come out at around 11-12 lbs. I figure an 8-10 oz tank will be enough for 10-15 min. flights.
I also have a zdz80 in a 30%Cap231EX, should come out at 21 lbs. I figure a 24 oz tank should be good for 10-15 min. flights.
Finally I have a zdz40 for which I'll receive a DiablotinXL in a few weeks. I don't know if this plane come with a tank, but if not, I guess a 16 oz tank should be fine for 10-15 min. flights.
Please let me know if I plan to carry to little/much fuel for my planned 10-15 min. flights.
DKjens

I think you are pretty close, provided the throttle is not wide open all the time, and you don't expect the thing to hover for 15 minutes...

Run an experiment...
I use a graduated beaker to check fuel draw rate... fire the engine up on a stand & run it for several minutes at different throttle settings to approximate your flying style and measure it...
3minutes 6oz... 15 minutes 30oz's

obviously this is an approximation, so you should do this and then add a 20 - 30% saftey margin or so...
(once you get flying, do a real experiment with inflight conditions)

erik

Can't comment on anything except the zdz40. I have one in my DP Extra and am in the process of switching the tank out for a smaller one. I have a 24oz tank right now (I know...but I never had a gas engine before ). After a ten minute flight of various throttle settings I have half a tank left or more depending. I think I will switch it for a 16. Should have a good safety margin after each flight that way and take up much less fuel. No point in flying around with twice as much fuel as I have to. Going to use the 24oz for my new Extra with ZDZ80....should be perfect.

I don't have any of the specific engines mentioned, but I can tell you that an 800 cc (27 oz) tank is at least double what you need for 12-15 minute flights with an FPE 3.2 (52 cc) on a WM 27% Extra. I used the tank that came with the plane, but that tank was supposed to feed the design-intended engine, an O.S. 1.60 glow 2-stroke. I will most likely be replacing the tank; a 16 oz would seem about right. It appears the 52 cc FPE uses less than an ounce per minute while flying aerobatics, to include some WOT (vertical) maneuvers. My first gasser... live and learn.

you are correct in your fuel tank sizes 10 - 12 minutes flights with a touch 2 spare.

I have a 3w24 in my Katana with a 16 oz. tank.I really could go with a 10-12 oz. tank.The 16 oz. tank will run it for over 20 minutes.I'm just carrying extra weight that I don't need.

In the 3W 24 you should use 12oz and try to get the plane under 12lbs for get good power.Other things this engine need more time than other 3w engines for breaking.

If you use a tuned canister you can use a mejzlik 20/8