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Old Mar 01, 2013, 08:12 PM
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farmington, mn
Joined Sep 2003
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7 minutes to short to fly with?

I am converting my Pby from electric to gas 4 strokes. All I can manage to get in the wing are two 3.5 ounce tanks. Doing a bench test all I can get is almost 8 minutes at 80% throttle before its bone dry. Should I look at trying to fit some 1 oz header tanks in the wing for is 7 minutes enough to really fly with its a pby so I don't plan on going anything to exciting. Also I am using the standard tank type with the round rubber stopper and the three brass tubes with a clunk. All I can fill it up is 80% before it comes out the exhaust is this normal or should I be able to fill it all the way up, as you can tell I normall don't fly gas
Thanks jeff
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Old Mar 01, 2013, 08:40 PM
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United States, SD
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3.5oz tanks are kinda small. Are we talkin gas or nitro?
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Old Mar 01, 2013, 09:00 PM
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farmington, mn
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Nitro is running a .26 4 stroke
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Old Mar 01, 2013, 09:54 PM
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miltac's Avatar
United States, NC, New Bern
Joined Dec 2011
99 Posts
you should be able to fill the tank till its completly full. The line going to your muffler should be bent up inside the tank until its about just shy of touching the tank.
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Old Mar 02, 2013, 10:19 AM
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United States, IA, Rockwell
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IMO 7 minutes is not a "short" amount of time. A PBY is not an aerobatic plane. I take it you will mostly just be tooling around the sky. You might find 7 minutes is a long time to just fly in circles. Go for the 3 1/2 oz tanks. You can always add the header tanks if you feel the need.

Ken
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Old Mar 02, 2013, 10:39 AM
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United States, NY, Ithaca
Joined Sep 2007
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When I got a minute flight with a rubber powered plane I could hardly believe it. It seemed like it would never come down. It's all in the frame of mind. I wouldn't complicate it.

Are you really going to fly a PBY around at 80% throttle? Seems like for a scale type you'd be throttled back more, and I would expect to get much better than 7 minutes from 3 1/2 oz on a 26 4 stroke. Probably you'll want to do touch and goes. But even for take-offs models almost always take off way too fast for realism, so even there you might not use full power. And as soon as you're up you throttle back, right? Scale models usually look terrible at anything close to full power, unless it's a WWII fighter type.

Jim
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Old Mar 02, 2013, 11:49 AM
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farmington, mn
Joined Sep 2003
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Thanks for the input I'm normally flying electric so I'm still not sure how much fuel gets used in starting and taxi. But I should be able to get more run time if I get the exhaust tube bent correctly to fill the tank all the way up, another question is with this small of a tank should I use a clunk since it really doesn't have much movment with that short of a tube and just use the brass tube and bend it down towards the rear of the tank? Next question is in small tanks do I want to use a ball type fuel filler or a hand crank filler
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Old Mar 02, 2013, 08:55 PM
The Prez....... again
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United States, IA, Rockwell
Joined Jul 2011
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You will want to use a clunk. Find some small fuel line though. It will be more flexible. In fact you should use small line all the way to the carb. It will help with fuel draw a bit. The engine will lift a small column of fuel better than a large column.

Sounds like a neat project. Post some photos of your progress.

Ken
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Old Mar 02, 2013, 09:52 PM
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Once you get airborne, you can very likely throttle back to 1/2 to 3/4 throttle and fly the plane. So at reduced throttle you should be able to make it go 10 minutes or longer even.
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Old Mar 03, 2013, 11:29 PM
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USA So. Cal.
Joined Sep 2010
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Quote:
Originally Posted by earlwb View Post
Once you get airborne, you can very likely throttle back to 1/2 to 3/4 throttle and fly the plane. So at reduced throttle you should be able to make it go 10 minutes or longer even.
For sure. And by the way 10 minutes is longer than Many electrics fly. It is a nice comfortable flight time.
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