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HELP - GP P47 clunk doesnt work!

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Old 03-17-2011, 11:30 AM
  #1  
cjbotox
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Default HELP - GP P47 clunk doesnt work!

Only someone else out there with this plane and set up can answer this problem...

I just finished my son's great planes P 47 thunderbolt and ran ground tests yesterday. Only one big problem, the tank / clunk system. We're using a 25FX for power and the engine has been in other planes and runs flawlessly. But in this plane something was wrong - after topping off with fuel, it started right up (had to invert to do this) turned the plane right side up and ran full bore. So far ,so good. I picked up the screaming demon and tilted it nose up - still screamin - then nose down. In a second, it sputttered and quit. After numerous start ups, we found that as long as the plane was situated horizontal or nose up, it ran the tank dry!

I did everything short of disassembling plane. Pressurized lines & checked for pin holes, you name it. Finally I removed the tank and lines and used the fueler to diagnose - voila! I found the clunk was unable to even touch ANY fuel once the tank was (more than) 3/4 full tilted downward. This particular tank is unlike any other I've seen before. In order to fit it inside, a small rectangular 120 cc tank was used, sized 31/2" L X 1 7/8" W X 1 3/8" H. The 1 3/8" H leaves less than 1/4" top and bottom of stopper. The following sugestions were from other club members:

Suggested: turn stopper soclunk(to carb) is at top of tank - no better

Suggested: use smallest thin wall tubing inside tank - only draws down 1/2 tank

Suggested: shorten the brass tube at back of stopper to 3/8" - I made down to 1/4" - NG

Suggested: install a bigger, better tank like a dubro 6 oz. - possible option but requires extensive modification to wing support bulkhead.

Suggested: call GP tech support - quote "we aint never had anyone complain about this before, don't know why it doesn't work for you.

Ideas, anyone? And no, EP is not an option.

Thanks, John.

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Old 03-17-2011, 12:47 PM
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Default RE: HELP - GP P47 clunk doesnt work!

I think I understand your problem....with the tank 3/4 full....and tilted downward the clunk is out of the fuel and the engine dies...correct?
Why did you have to invert the airplane to start?....Is this engine mounted inverted? and inverting the airplane actually putting the engine right side up?
I believe pointing straight down the engine is going to die......the clunk is out of the fuel and at full throttle it will die quickly......your clunk should move around some but not point back to the fire wall.......
by the way how is idle once the airplane is started and right side up?
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Old 03-17-2011, 12:49 PM
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Default RE: HELP - GP P47 clunk doesnt work!

You have a very short clunk line, with a stiff, short chunk of hose.

Buy some very flexible hose. The ½A line is small and very flexible, use it.

Shorten the tubing nipple inside the tank so only ¼ inch sticks inside the tank. If necessary buy smaller diameter tubing. The ½A fuel line needs no more than a quarter inch to hang on to.

Another method: Just bend a length of tubing to pick up off the bottom of the tank, and don't roll the plane over (unless you want to kill the engine.) Some ½A people do this routinely.

Good luck,
Dave Olson
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Old 03-17-2011, 01:04 PM
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Default RE: HELP - GP P47 clunk doesnt work!

John,
My only suggestion, since you've already tried most things I can think of: Find a heavier clunk, or find a way to add weight to the one you have.
Dubro http://www3.towerhobbies.com/cgi-bin...?&I=LXAHF0&P=0
Sullivan http://www3.towerhobbies.com/cgi-bin...?&I=LXBWL1&P=0

Carrell
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Old 03-17-2011, 03:16 PM
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Default RE: HELP - GP P47 clunk doesnt work!

I just assembled a 2 ounce tank and had to do as Scar mentioned. The tank is so small there isn't enough room to get a lot of stuff in there. I'm lucky and have a box with a lot of different clunks so I got one that weighed a lot more then the one that came with the tank. The main line was very stiff and being short it didn't drop like normal so I had to change lines. About a year ago I noticed tanks are now coming with regular line like we get from the hobby shop, before that the lines they gave us were much softer. I looked at three hobby shops and found a spool of the soft line like we used to get with the tanks. I didn't ask but after Scar mentioned it the line could be for 1/2A planes? The tricks Scar mentioned will do what you need. A bigger tank would be the answer though, even a .25 will drink a lot of fuel if flown hard.
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Old 03-18-2011, 05:41 AM
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Default RE: HELP - GP P47 clunk doesnt work!

OK, first in reply to jetmech05: I have to invert to start because that's the way it is designed. We (had) a P 40 - same installation, ran no problem - until it made an unscheduled landing. The broken plane was put in my warehouse, this weekend I will go get it and see what the difference is between tanks, BTW it also is a GP combat sized like the P 47. Idle is fine, a little on rich side. I'd say you understand most part except for the clunk orientation when nosed down. All but 2 of our small fleet are glow and (they) run exceptionally reliable in any orientation.

To carrellh: I will try your suggestion if the following posts don't work from -

To scar and greybeard: I think the tubing I put in last is what you"re talking about. The >*&# clunk bends around more but still only gets 1/2 way! Keep in mind this is a very small tank, about 4 oz and like I said, a larger tank might be the only way out but will require modifying the main bulkhead to a point that concerns me.

I want to thank you all for your suggestions and add this; when one encounters a problem, set back, troubling matter, etc. look at it as an opportunity and use that noggin until the light bulb turns on. When the GP tech didn't have an answer I told him I'd post this in forums until someone else can address and fix this. I'm not a whiner that wants to bash this product. In fact the tech encouraged me to post this and let him know how it is fixed so they will have the answer the next time someone like me calls.

Will be back Monday, thanks again

John
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Old 03-18-2011, 05:49 AM
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JohnBuckner
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Default RE: HELP - GP P47 clunk doesnt work!

Try the Hayes three ounce the and neoprene clunk line is of an approprate flexiblity to the tank size and the O ringed plug point is lower in the tank. The three ounce tank is a perfect capacity for the twentyfive engined sport plane.

Your could of course completely eliminate the clunk all together with a Tetra Bubbless tank and these have many advantages over a conventional tank especially with that size airplane. With these it does not matter attitude and the fuel pickup remains dead center of the tank. The smallest Tetra is 4.5 ounce. Correction they now also have even smaller ones.

http://www3.towerhobbies.com/cgi-bin...?&I=LXK826&P=7

http://www.centralhobbies.com/Fuel/fueltnk2.html

John
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Old 03-18-2011, 06:14 AM
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Default RE: HELP - GP P47 clunk doesnt work!

I have flattened out a fishing weight before and wrapped it around the end of the fuel line to get the clunk to move right in a line that was too stiff. That let me get at the corners of the tank well enough to fly in any attitude. It's not good for it to be able to move forward though. It can get stuck and that will give you deadsticks on takeoffs and up lines.

If you think about it, there aren't any scenarios in flight where you're going to have the situation you are simulating. If he's in a full throttle dive, the plane will be accelerating, which puts the fuel at the back of the tank. Most of us dive at idle which does let the fuel go forward, but at idle the engine can run quite a while on the fuel left in the lines. If yours can't, a loop of extra fuel line can give you a safety margin. After the dive, the line fills back up quickly when the air bubble reaches the fuel inlet. I'd check the idle time at nose down before changing anything. If you can get 7-8 seconds, that's longer that he'll likely be in any decelerating attitude and will be good enough to fly the plane.
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Old 03-18-2011, 06:24 AM
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Default RE: HELP - GP P47 clunk doesnt work!

saw your post and was wondering _ if you tip the tank when it's empty does the clunk fall to all corners s you rotate the tank.

if not:

1. make sure the clunkpickup is heavy eough to pull the fuel line inside the tankto all corers. add weight if needed
2. make sure the clunkpichup is not touching the back of the tank. 3/16" min clearece for fuel delivery and so fuel will dragclunk with it as it movesround the tank.
3. a slight bend of about 5 degrees up inside the tankon the engine fuelsupply on smaller will allow the clunk to move easier.


hope this helps
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Old 03-18-2011, 06:46 AM
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LesUyeda
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Default RE: HELP - GP P47 clunk doesnt work!

I don't believe that you have a problem. When you are in flight, the forward motion of the aircraft will automatically force the fuel into the rear of the tank, where the pickup is.

Les
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Old 03-18-2011, 08:04 AM
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cjbotox
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Default RE: HELP - GP P47 clunk doesnt work!

Well I had a dumb idea, before the last 4 posts appeared and I immediately returned to the forum only to find several other guys hit it on the head.

I pulled two tanks out of my larger 60 sized planes and guess what? Neither of the clunk lines are any softer than the one I thought I had a problem with. So... this means that in the air while the aircraft has momentum (and believe me, this engine hauls) the fluidity (?) and G force should PUSH the fuel to the back and maintain fuel feed (except in DOD?).

For new planes or engine tweaking, I have always tilted the planes up (lean run) and downward (rich run) to see if corrections of the needle valves are necessary. Never before did this happen probably because the tank in the P 47 is so flat. But now we will reassemble everything and go flying (with caution). My son found the P 47 on U Tube, powered by a 25 LA and it few a lot longer than I expected this tank would last.

Lastly, I like the idea most of replacing this tank with one of those bladder types. DARN! I thought I was going to have to invent something and get a patent - wouldn't be the first time.

Thanks all

John
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Old 03-18-2011, 09:00 AM
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Default RE: HELP - GP P47 clunk doesnt work!

There was a thread for a video from Germany I think where the fellow had a clear tank mounted to the outside of the planes fuse and a video camera on the wing pointed at the tank. He took off and did a bunch of stunts so you could see what the fuel is doing in the tank during flight. It was a big surprise and an eye opener. The fuel goes all over the place in flight, the G forces do not keep it at the back of the tank. I have the thread in my favorites but it isn't working any longer. The other thing you will notice is how well the anti foaming agents in our fuel works. Hard mounted and not a bubble or sign of foaming. I showed this to a lot of pilots and it was a surprise to us all. I hope someone has a thread of this video that is working and will post it for us. It's one of the better videos I have seen.
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Old 03-19-2011, 07:21 AM
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LesUyeda
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Default RE: HELP - GP P47 clunk doesnt work!

We're talking about "flying", not whatever 3D acrobatics is:-)))))))))))

Les
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Old 03-21-2011, 05:21 AM
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Default RE: HELP - GP P47 clunk doesnt work!

> the forward motion of the aircraft will automatically force the fuel into the rear of the tank, where the pickup is. ,

In level flight at a constant speed there is no force to move the fuel backward. Only acceleration would do that.
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Old 03-21-2011, 06:30 AM
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Default RE: HELP - GP P47 clunk doesnt work!

"In level flight at a constant speed there is no force to move the fuel backward. Only acceleration would do that."

I'll buy that. In which case the clunk will be lying right in the rear bottom of the tank, where it belongs.

Les
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Old 03-23-2011, 06:29 AM
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Default RE: HELP - GP P47 clunk doesnt work!

UPDATE!!- GOODNEWS

Finally made time to fly yesterday and put the P 47 in the air. It flies just fine with the original clunk set up. Now I regret jumping to premature conclusions I made in this post. If anyone is still interested, I would be happy to download some pictures of this peculiar shaped tank with its unbelievable potential. By that I mean that in addition to feeding fuel reliably in any orientation, the little 4 oz tank ran the 25 FX for at least 10 minutes. That was the longest flight time we tried pushing and even after that, we disassembled wing to see about another oz left in the tank.

It was a great day for my son who put in a dozen flights on it. It performs VERY well and would undoubtedly make for a good combat plane.

3 things I've learned from this, 1 - Tilting some planes for 'tweaking' won't work. 2 - I didn't know our fuels contained anti foaming agents (as mentioned by greybeard). 3 - The clunk tubing inside your tank should NOT bend or reach to front - because it usually will STAYTHERE when you don't need it to!

Thanks everyone for input

John
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Old 10-18-2015, 07:14 PM
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66carsandguitars
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Just purchased a used Great planes P-47 .25. Any possibility you could take a picture of this fuel tank when you get a chance? Someone was going to do an electric conversion and pitched to fuel tank. plane also came with an OS 32. Is this to much motor for this bird? Appreciate any help I can get! Thanks
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Old 10-19-2015, 11:35 AM
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Our P-47 wore out a long time ago. However, the unusual design of the glow tank was one of a kind, if you give me a couple days to check in my warehouse I'll see if there's one left in storage. We also had a GP P-51 with same tank config so it might be there.

As for .32 engine is it O.S.? The difference between the .25 and .32 were very little if memory serves me correctly. It would not be too much engine for that plane as the O.S. .25 was high performance... and light.
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Old 10-22-2015, 07:30 AM
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OK I found one in warehouse. It says FLIGHT MODEL on top, 120 cc.

Measures 3.5" L X 1.5" high X 1 15/16" wide.

From front of stopper to back = 3 7/8" + 1/2" aluminum tubes.

2 - clunks inside for O.S. rear connection config (one line permanently connected to engine, other used for filling)

This it?
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