Design a Duration RC : Must Fly for 2 Hr. Min.

[Texas Buzzard]

In 2000 I built a Telemaster-Type 10' w.s. (11.6 sq ft) spruce stick/ply plane to fly carrying a 0.60 P.A.W. Diesel and a 1 gal. metal tank. On the bench the engine ran about an hour on a quart of diesel fuel.

I wanted to fly from my field to Padre Island ( 75 miles into a 15 mph wind). On the bench all was well. But, in the plane the engine suffered from being too rich with a full tank and no gravity flow to the "header tank" when half full.

I didn't use a fuel regulator ( maybe a small motorcycle carb bowl would work).

Some engineering help or suggestions are needed. I had an 8 oz. header tank right by the engine. The bottom of the 1 gallon tank was maybe 2 inches below the header tank when the plane was in flying attitude.

Any takers? Thanks. :) :rolleyes:

[HugePanic]

small fuel engines use the exaust pressure to "pump" the fuel to the engine...

[BMatthews]

small fuel engines use the exaust pressure to "pump" the fuel to the engine...

The pressure from those is very minimal.

Buzzard, your problem was that the tank wasn't high enough. The whole tank has to be above the header. Gravity won't let fuel go UPHILL. Also ensure that the main tank and header both have vent lines to let air in as the fuel flows out. And the same on the header tank but in that case it let's air OUT so that fuel can flow in.

Also you just plain do not need a big header tank. All your fuel flow issues were most likey related to the size of that header tank. And just to clear this up did your header tank have a float and control valve in it to only allow fuel from the upper tank when required or was it just a "wide spot in the line"?

The right way to do a long duration tank setup like this is to have a small one oz float bowl tank right beside the needle valve or just behind the engine and equip it with a float and closer needle and seat as used in motorcycle carbs. That way the fuel level is always the same as far as the engine carb is concerned.

[Texas Buzzard]

Bruce Matthews wrote a very good suggestion...."The right way to do a long duration tank setup like this is to have a small one oz float bowl tank right beside the needle valve or just behind the engine and equip it with a float and closer needle and seat as used in motorcycle carbs. That way the fuel level is always the same as far as the engine carb is concerned."

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Yes my header tank was just a wide spot in the fuel line. Yes I had air vents in both tanks. When main tank was full , fuel ran out the air vent of the header tank and made needle setting BAD.

I have two small motorcycle carbs with a float and fuel shut off, etc. I didn't use them because they looked so big. But maybe I have to use the float mechanism in a cobbled up (brass tank) to get results.

I will not start cutting wood until the fuel problem is solved. Hey BMatthews, thanks. (I agree that exhaust pressure is minimal.)

[Yukonho]

I am not sure if this is an effective solution, but I will put it forth anyway.
I recall the "Perry Pumper" or something along those lines. Would this type of fuel pump not completely solve your problem?
Here is a link to their products page. Carbs, pumps and valves...http://www.perrypumps.com/products.htm
Colin

[BMatthews]

Looking at the Perry products they seem to have come a long way. One of their solutions may well work.

Either way I'd suggest you do what Maynard Hill did with his long duration model design. He tested them first on the ground and got the bugs out.

A model sized float bowl would not need to be all that big. A Fuji 35mm film container would be just fine and the vertical cylinder would offer up a nice chamber to add a float to it. What to make it out of is the question. It would need to be totally fuel proof, light and not soak up any fuel so any sort of raw foam is out.

You may want to email Perry about how their stuff could possibly work with your needs.

[vintage1]

Why not go electric? 2 hrs is easily achievable.

I've got 45 minutes stuff here that would easily take 4x battery weight.

60" span and around a pound of battery should work..around 200W total, maybe 3 1/2lb AUW..should fly all day on 40W or so...2 hours=80watt hours..about 8 ampere hours at 10v.

Not hard.

[Texas Buzzard]

I am not sure if this is an effective solution, but I will put it forth anyway.
I recall the "Perry Pumper" or something along those lines. Would this type of fuel pump not completely solve your problem?
Here is a link to their products page. Carbs, pumps and valves...http://www.perrypumps.com/products.htm
Colin
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I wnet to that site and wanted to ask if the VP-30 Regul. Pump worked off of crankcase pressure and did they supply the tap.

I used their e-mail address and it was sent back by the mailer-demeon.

Do you know if that pump operates from crankcase pressure??