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Wing tanks? - 8/19/2003 1:31:55 AM   
Dukester


 

Posts: 804
Joined: 7/25/2003
From: Houston, TX, USA
Status: offline 		So there I was shoe-horning the throttle servo for thye norvel 061, fuel tank (2 oz), receiver, battery, etc into the front of the fuse for this hummingbird I am building (designed for CL 049). I got it all in there, but man was it tight. The whole time I'm cussing myself for not just following the dang plans.

So then I happen to spy two small plastic bottles lying on the backside of my workbench in the 'you never know when you might meed some obscure piece of plastic' pile. Well, after seeing DB's post on the octo-Cox Spruce Goose and it having wing tanks that has got me thinking about why couldn't I use those two little plastic bottles as wing tanks instead of one big tank in the fuse.

So here is what I am thinking about doing and what I would like to ask for comments on. The bottom of the wing is approximately level with the carb on the big mig. So the centerline of the tanks in the wing would be about 1/2 inch high to the carb. I figure with this I wont need the exhaust tap pressure. I was thinking to Y the two tanks together at the top and bottom of the tanks. The bottom for fuel feed and top for venting. To prevent fuel starvation to the engine I was thinking to use a slightly larger piece of tubing and have the fuel and vent lines run to that tube on one side and have a feed line continue out the engine to the other. The vent line would be Y'd off to the tanks and to the outside of the plane. The idea is that gravity would feed fuel into the feed line until it self levels in the vent line at the level of the fuel in the tank. Once you start the engine, any air drawn into the feed line would be allowed to escape back into the vent line rather than being drawn down into the final feed line. This way you have a small stock of fuel in the tube so that if both the fuel feeds are uncovered in the tanks, the engine would still be able to draw fuel until the planes attitude allows normal fuel flow. Now obviously, this won't work for inverted, vertical, or other such sustained flight, but I won't be doing that with this plane at least.

Picture shows the setup I'm considering plus a generic pic of a hummingbird.

Anyway, let me know if yall think this may be a workable deal?

Thanks,
Dukester

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Wing tanks? - 8/19/2003 2:21:54 AM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Duke:

Parallel feed from multiple tanks has never been made to work well. What has been used with success is one tank feeding into the second, with the second tank feeding the engine. But if you have these tanks located one in each wing your lateral balance will change as the fuel burns off.

I also question the engine's ability to draw the fuel that great a distance without assistance. I think you'll at least need muffler pressure.

It would be easy enough to set it up on a stand and try it, see if there are any problems, correct them, then put it in the plane and find more problems.

Bill.

_____________________________

Real Airplanes have Two Engines
AMA 25139 - More than 40 years.

(in reply to Dukester)
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Wing tanks? - 8/19/2003 8:01:00 AM   
BMatthews



Posts: 8951
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Sorry dukster but this is a non starter.... or at least a non runner. The tanks may be that little bit lower than the carb when it's sitting still but as soon as there's any diving, climbing or other accelleration it'll flame out like an old time reporter's flash bulb. The only way it would work would be if the tanks were a bladder pressure type or some other pressurized container and the little jokingly labels doomahicky was actually a precision regulator located close to the engine. And even if it IS a regulator you'd need much more than the gentle puff from a muffler tap. We are talking serious "squirt a yard or better" type pressure if you want to ensure proper feed at the engine. On top of all this you'd need some way to regulate the pressure even lower during idle.

Our engine and gas tank arrangements don't have float bowls to provide a closely controlled source for the carbs to draw on. We get around this problem by keeping the tank close at hand so it actually sort of acts like a float bowl. But that means that reliable runs come from smallish tanks located very close to the carb.

I've gotten some horribley long fuel lines to run fine on a test stand but I would never think to put them into a model that way.

If you're really stuck for room then put the receiver and batteries into the wing. Electrons don't care how long the wire is.... within reason anyway.


_____________________________

Bruce-
Proudly wasting balsa since 1965.

Free Flighters go that extra mile........

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       Post #: 3

Wing tanks? - 8/19/2003 10:03:01 AM   
Dukester


 

Posts: 804
Joined: 7/25/2003
From: Houston, TX, USA
Status: offline 		These hose runs are not actually going to be that long, maybe 6-8 inches at maximum. During run testing with the plane held vertical, the big mig would draw fuel from the bottom of the 2 oz tank through the fuel line which is about 4 inches right now with muffler pressure. So there seems to be a fair amount of suction. I figured that the small reserve of fuel where the vent and fill tubes come together should act like a mini tank a few inches form the carb. As a minimum it should have atmospheric pressure on the backside of the fuel and the big mig should be able to suction the fuel from that distance as long as the height is approx the same as the carb.

For fuel pressure, i was thinking to place the vent either in the prop wash directly or possible on the leading edge to provide a small amount of boost pressure into the tanks.

Anyway, I think I am going to just follow Bill's advice and put together a fuse mockup and try it out and see what happens.

(in reply to Dukester)
       Post #: 4

Wing tanks? - 8/19/2003 10:54:28 AM   
BMatthews



Posts: 8951
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		I'm not just making all this up. It's been tried by either myself or other folks I flew with back when we didn't know any better and I had hair. 6 to 8 inches is about 4 to 6 too many. In other words you don't want more than about 1/2 inch from the end of the tank to the back of the engine.

Boost pressure from flight speed isn't enough to bother with. I've used slant cut or bent forward breathers almost forever and all it does is ensure that you don't get a vacumn situation to draw the fuel out of the tank. A plus to be sure but no where near enough to presurize the tank to the point that it constitutes a pressurized fuel delivery system that you can use I'm afraid.

But it's an easy thing to bolt an engine to a 2x4 and sit the tank back what you think you'll need. Tune it up in level and then point it up and down and you'll see what's what.


_____________________________

Bruce-
Proudly wasting balsa since 1965.

Free Flighters go that extra mile........

(in reply to Dukester)
       Post #: 5

Wing tanks? - 8/20/2003 5:39:43 PM   
C. McManamay


 

Posts: 40
Joined: 4/29/2003
From: clarksville, TN, USA
Status: offline 		Hey Dukester What kind of plane is a hummingbird who makes it and where can I getl one? Its a good looking plane.Thanks

(in reply to Dukester)
       Post #: 6

Wing tanks? - 8/20/2003 8:35:35 PM   
Dukester


 

Posts: 804
Joined: 7/25/2003
From: Houston, TX, USA
Status: offline 		C.

You can e-mail Lee Stangel at [email]lee@stangel.com[/email]. I got mine off of E-bay for $10 as a pre cut balse kit. He has a 049 and a 40 version.

I did a number of mods to my plane including conversion from 049 CL to RC with big mig 061, plus I have just removed the single servo called for in the plans for aileron control and replaced with 2 mini servos mounted to the sides of the fuse so I can play with flaperons.

Here is a pic of my plane.

Duke

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(in reply to Dukester)
       Post #: 7

Wing tanks? - 8/20/2003 9:53:56 PM   
2fast4u



Posts: 924
Joined: 3/2/2002
From: LITTLE ROCK, AR, USA
Status: offline 		It is true that the tanks must feed in-line. The loop would run from the muffler to a vent in tank 1, tank 1 clunk to tank 2 vent, then tank 2 clunk to the carb. That works just fine, but the distance is a bummer.

Try this..... Hook up 2 tanks this way, but place them on either side of the fuse, up front. Might look a bit funny, but it could lead to a whole new design. Ya just neva know!! Use the smallest line you can from T1 to T2, from one side to the other, and let'er rip!!! It will really work well if you run no throttle and a pressure tap back plate. Good luck and post your progress.


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       Post #: 8

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