Fuel tank idea works good.

LAST EDITED ON Dec-24-03 AT 02:59 PM (CDT)
 
I have always had consistant run problems with my engines. I have switched engines and still have the same problem. I have switched glow plugs and still have the same problem. I have switched props and fuel and added more oil. The engine would run out of fuel and stop in a really tight loop. The fuel tank is the problem!!!

Centrifical force keeps the fuel to the outside of the fuel tank during level flight. During a turn the fuel moves form the outside of the tank to the top/outside or bottom/outside of the fuel tank. During a very sharp turn or sudden turn like a square loop the fuel moves to the top of bottom of the tank for a split second.

I designed a fuel tank with baffles. The tank has 3 baffles to stop the sudden movement of fuel during a turns. The baffles are soldered in to the tank in several places but not a continious solder connection. I also have 6 very tiny holes drilled in each baffle. Centrifical force will keep the fuel to the outside of the tank. When the airplane makes a sudden turn the fuel can not flow away from the fuel pick up because its trapped behind the baffle.

My engine now runs consistance all the time during all the turns, inside loop, outside loop, vertical figure 8, horizonal figure 8, over head figure 8, upside down, sudden turn square corners. Even a really tight loop it keeps right on running. When I know the fuel tank is getting low and I know I should be careful not to kill the engine in a loop its no problem I can still do loops in either direction. The engine runs like I am flying staight and level all the time.

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The fuel tank holds 80 CC's of fuel. I think one baffle might be enough but to play it save I used 3 baffles on this experement. I might experement with 1 baffle later.

Using a chicken hopper tank accomplishes the same thing.

A single baffle should be plenty and has been used before. Some of the baffles were installed at an angle to the outlet instead of straight as you have them.

Are you still able to kill the engine at the end of the flight by performing a tight loop as you can do with a tank without baffles?

If you were desinging a tank to keep you from flaming out with a sudden manuever, why would you then want the plane to shut off with a sudden manuever.

Fuel management my man, fuel management.

Sides, with my luck, I'd get through my first nearly perfect pattern, do a shutoff manuever and something that had just barely held on the whole flight would go flying off making the flight a wash.

You get to decide where in relation to the wind the engine quits.

Prevent over run if a little lean.

Have seen several top 20 fliers use it during practice.

>You get to decide where in relation to the wind the engine
>quits.
>
>Prevent over run if a little lean.
>
>Have seen several top 20 fliers use it during practice.

Do it all the time. The combination of the Y-axis acceleration, the low fuel level, and the outboard yaw of the airplane during inside maneuvers moves the fuel away from the pickup long enough to cut it off.

>I have always had consistant run problems with my engines.
>I have switched engines and still have the same problem. I
>have switched glow plugs and still have the same problem. I
>have switched props and fuel and added more oil. The fuel
>tank is the problem!!!

In this case, yes. A square tank will generally not work as well as a stunt tank, for stunts, anyway, for reasons you mention. Yours is particularly bad since the pickup is not all the way against the outer wall of the tank.

I don't know if you are aware of this or not, but tanks fur stunt typically have a wedge shape at the outer edge. This keep the fuel near the pickup without having to use a baffle at all.

>
>The fuel tank holds 80 CC's of fuel. I think one baffle
>might be enough but to play it save I used 3 baffles on this
>experement. I might experement with 1 baffle later.

There have been many baffled tanks made over the years, and it has been well-proven that you probably don't need them if the tank is shaped right to begin with. And they are much easier to make than baffled tanks.

If you insist on continuing, then I would suggest a single baffle made from a 3/8 brass tube, split lengthwise, and soldered up against the outer tank wall, with the pickup in the middle, will be the easiest and mode effective baffle for a square tank.

Tanks are a long-solved problem. 10's of thousands of stunt flight are made each year with tanks no more complex than a Veco T-21 tank that was designed in probably 1950.

Whatever works for you. I'd suggest soldering your pickup tube to to outer wall of the tank, else it is eventually going to either vibrate the solder joint loose at the front of the tank or crack from vibration. Guess how I know.

So far as kill-the-engine maneuvers go. I defy you to kill your engine so long as there is enough fuel to cover the uniflow. Once you can uncover the uniflow, then you can kill the engine. I use a big @ 80 degrees inside loop, which doesn't always work.

Gary,
If you are going to make your own tank you might also look at George Aldrich's "Pinch Corner" tank. He included it on a lot of his plans.
Perhaps add uniflow plumbing.

>Gary,
> If you are going to make your own tank you might also look
>at George Aldrich's "Pinch Corner" tank. He included it on a
>lot of his plans.
> Perhaps add uniflow plumbing.

He already has that, assuming he plugs the right vent. The vent tube towards the back terminates near the pickup.

Jim T is of course correct that the suspended end of the tube should be soldered to the outside edge of the tank, or it will fatigue and break loose after a while.

Gary, why don't you just use a stunt tank and not reinvent the wheel?? Your set up is not unlike a uniflow, minus the outside wedge. Veco made baffle tanks in the 50's, only the baffle was perpinducular (across the tank) and about 1/2 inch from the end. Until the advent of the uniflow, these worked pretty well.

LAST EDITED ON Dec-25-03 AT 01:20 AM (CDT)
 
It's heavy, I bet. Why is the fuel pickup away from the outboard wall of the tank? That will just leave fuel in the tank after every flight, diluting your fresh fuel after the model sits for some weeks. Lots of stock tanks work well, tho I bet it was a lot of fun to make that puppy. Well, maybe not. I have a drawing of GMA's pinch corner tank on my computer, and would be happy to email it to you. Steve

I discovered that the jpeg of GMA's pinched corner tank was only 35kb, so I am posting it here. No baffles! Not Uniflow! K.I.S.S.!

Steve

If one can live with a 3.5 ounce tank there are probably a bunch of the stock tanks around that were not used in ARF Noblers.

>I discovered that the jpeg of GMA's pinched corner tank was
>only 35kb, so I am posting it here. No baffles! Not Uniflow!
>K.I.S.S.!

Steve

>
>http://www.nwskyraiders.com/index.html

If I can make a simple observation, there is nothing magical about George's tank. It is simply a wedge tank with a square front. And since it is not uniflow vented, it suffers from all of the same problems as any other standard vented tank. A standard wedge is actually K.I.S.S. simpler, and either one benefits equally well with uniflow venting.

Absolutely. Probably not as easy to make, either. GMA claimed that this tank, without uniflow, required no shimming to get equal upright/inverted lap times, just put the CL of the tank on the CL of the NVA. Whatever. I like a uniflow for the steady run, but I also want a strong indicator of impending glide mode. Pulling the uniflow tube away from the feed tube should do that. My other problem is that unless the overflow is in plain view, I'll leave the cap off and have a non-Uniflow vented tank all too frequently. Does a check valve work reliably enough? Anybody use a check valve instead of a cap on the overflow vent? Steve

As I understand it, George was managing (manipulating?) the lean-out as the flight progresses with his tank shape. I'm not clear on what he was trying (successfully?) to accomplish. George was always very complimentary of Bob Palmer's engine runs; and, of course, the Palmer tank is a uniflow.

I don't see why you couldn't use a one-way valve on the overflow. I use one (pointed the other direction) on the uniflow if not running muffler pressure. Back when I was running Foxes with muffler pressure, the engine would go rich when the uniflow was uncovered, then go lean and die. I don't see the phenomenon much with other engines.

>Absolutely. Probably not as easy to make, either. GMA
>claimed that this tank, without uniflow, required no
>shimming to get equal upright/inverted lap times, just put
>the CL of the tank on the CL of the NVA. Whatever. I like a
>uniflow for the steady run, but I also want a strong
>indicator of impending glide mode. Pulling the uniflow tube
>away from the feed tube should do that. My other problem is
>that unless the overflow is in plain view, I'll leave the
>cap off and have a non-Uniflow vented tank all too
>frequently. Does a check valve work reliably enough? Anybody
>use a check valve instead of a cap on the overflow vent?
>Steve
>
>http://www.nwskyraiders.com/index.html

The engine should run differently if the tube is not capped. It will run richer with the cap off, leaner (need to open the needle more) with the uniflow cap plugged. Just put it in plain sight where you can see it.

The check valve idea won't work because if you use it to fuel (fuel flows in) then it will vent in, also. If you put the check valve the other way, you might just as well plug it and leave it plugged.

Oh, and no tank is dead on as George described it. Back in those days no one really thought of shimming a tank. He was using a Fox 35 blubbery rich and just didn't notice the difference. His tank was not magic. If it were, don't you think you would see a few around among the top competitors? Just a few? Someone? Anyone?

Does a check valve work reliably enough? Anybody
>use a check valve instead of a cap on the overflow vent?
>Steve

I tried that once Steve. I was using some little surgical grade one-way valves from Small Parts Inc.
As I recall it worked but it wasn't dead reliable & the fuel ate the little rubber flapper gizzit fairly quickly. I still have a couple if you want to try one.
Oh yeah, here's my solution: when you remove the cap from the vent for fueling, put it between your lips, that way you'll remember to put it back on. Works for me.

>>I discovered that the jpeg of GMA's pinched corner tank was
>>only 35kb, so I am posting it here. No baffles! Not Uniflow!
>>K.I.S.S.!

Steve

>>
>>http://www.nwskyraiders.com/index.html
>
>
>If I can make a simple observation, there is nothing magical
>about George's tank. It is simply a wedge tank with a
>square front. And since it is not uniflow vented, it
>suffers from all of the same problems as any other standard
>vented tank.

For the most part, the magic pixie effects sometimes claimed for this tank are mythical. In particular, the "doesn't need shimming" thing is just not accurate - it needs the same relationship to the needle valve as any other tank. Nor does it cure the "Fox Burp".

But, depending on where you put the vents, it's at least constant pressure for part of a tank. As drawn, it's about a 30% uniflow, with constant pressure for about the first 30% of the run, then steadily increasing for the rest of the run.

It does work fairly well, with a decent amount of volume for the external dimensions, and decent cutoff characteristics. Ted and David have used a squared-off version of this tank (made by Kenn Smith, or by myself copied from Kenn's design) for years. I prefer the tapered wedge tank (that is copied from a design by Ed Robbert) and I think it cuts off even better - if you fly around level at the end, it runs dead steady, then leans out and quits in less than 1/8 lap. Perfect for FAI.

The shape of course means essentially nothing until you get to the end.