Fuel tank 'clunk" question

Hi there,
I am new to this NG and working on my 4th RC airplane. I am building a
1/6th scale Dh2 Beaver on floats (96" span) and am in the process of
installing a Du Bro 24 oz fuel tank to go with a Super Tiger .90 -2 stroke.
Tank is aproximately 2-1/2" x 2-1/2" by about 8 inches long with the stopper
and lines at one end .....The problem I see is that the Clunker stays to the
bottom of the tank every which way I turn the tank like it is supposed to
except if I put the plane into a nose dive...the clunk dosen't slide itself
to the front (towards the stopper) of the tank as I think the fuel tubing
that came with the tank is too stiff to allow this.... I think the engine
would stall if I had half a tank of fuel and was decending with the plane...
I am thinking of putting the tank in on a slope upwards towards the firewall
to perhaps counter this problem...or... cut the tubing so the clunk sits
about half way down the tank?...
Reply to
Jim & Lil
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What he said is correct, and another point that could be made is to use a big enough fuel tank that you don't burn more that 2/3rds of the tank on a normal flight. That is usually enough to keep it running.
Another choice is to use a header tank. You have your 12 oz or whatever tank feed into the vent of a 2 oz tank, then into the carb. The small tank never leaves full until the big tank sucks air. -- Jim in NC
P.S. Don't let that clunk go to the front of the tank. The bend will cut off the fuel flow.
Reply to
Morgans
Hopefully you won't be in a full power dive long enough to use all the fuel in the line!
Reply to
Paul McIntosh
Jim, You definately don't want the clunk to go to the front of the tank. If you are in a dive long enough to empty the fuel line you will be taking a trip to China to find yr plane...In fact you should take steps to prevent it, as it may go to the front in a hard landing and give you all sorts of grief feed wise. There are two ways to do this: 1. Slip a length of spring over the pickup tubing so it can't bend forward. 2. Where the copper/brass tubing exits inside the tank only use a piece of fuel tubing that is about 3/4" long to provide a pivot. Now, take the clunk and solder a length of brass tubing into it that is long enough to push into the 3/4" piece -with the clunk at the rear of the tank- and still provide nice free movement. BTW, I have a 96" Beaver on floats with an OS120 FS and a 20 oz tank. The whole mess weighs 19 lbs. Once in the air it flies at 1/4 to 1/2 throttle and a 15+ min flight only uses about 2/3 of a tank so you are going to have loads of time with the 24oz tank. I don't think that you have to worry about the line running dry. A word of warning about the Beaver. If you try to horse it off it will immediately stall to the right and carwheel. I have flown/watched quite a few at various float flys and they will all do it at some time. If you have put flaps on yours, always take off with about 5 to 10' down -no more. Let the A/C run out on the step until you see light under the floats and then establish a nice gentle climb. Take the flaps off when you reach altitude. Be prepared for the nose to drop a bit when you do.
I think that you will really like the plane. Good luck with it. Gord Schindler MAAC6694
Jim
Reply to
Gord Schindler
Thanks to all that replioed to my question...The tank is installed and fuselage is sheeted over...I did put the tank in on a bit of an upward angle though just to set my head at ease.... Thanks again to all that replied....a very knowlegable group!...Jim
copper/brass
Reply to
Jim & Lil
You all are forgetting that in a dive, if the dive is faster than fuel can free fall, the fuel will remain at the back of the tank. Most all manuvers will keep the fuel at the back.
Dan Thompson (AMA 32873, EAA 60974, WB4GUK, GROL) remove POST in address for email
Reply to
Dan Thompson
Indeed you are right. In fact, in almost all except inverted flight, the fuel doesn't move. There is a marvelous video taken from the back seat of an Aero Commander, over Bob Hoover's shoulder as he pours a glass of water from a pitcher while doing a roll. The glass is sitting on the top of the instrument panel. He then proceeds to put the A/C through the most amazing sequence of manouvers and the water never moves. Of course, we are not likely to be as co-ordinated in our flying as he is but it makes the point. Gord Schindler MAAC6694
Reply to
Gord Schindler
The Aero Commander is NOT rated for much negative Gs. All the flying he did was ALL at positive Gs. We modelers quite frequently pull significant negative Gs.
David
Reply to
David AMA40795 / KC5UH
You have to be accelerating faster than the acceleration of gravity for that to be true. In a 15 second dive, you would add 32 + 32 .... fifteen times and that would be your vertical speed in feet per second. That would only keep[ up with gravity.
Reply to
Paul McIntosh
.. Thanks in
-> Felt clunc!
Reply to
René
I think a 24 oz tank is too big for a .91. The fuel draw may not be adequate when the clunk is so far from the engine, due to the size of the tank. 14 oz would be more realistic, unless you have a pump. (now I'll go back and read the original post again to check on that).
Reply to
John R. Agnew

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