fuel tank

Guys. Have a rather silly question. I'm needing to make / alter or get a couple new tanks.

Size is two ounces. I'm planning on running standard venting. I have noticed that all the standard vent tanks have the vent out the top, fill(vent) at the bottom.

The question is. Because of the configuration of the tank compartment on the Pond Racer, can I simply make the tanks with all tubes forward, just like the uniflow ATF's. ? If I use standard vent ( up and down ) it'll cause grief shimming the tanks.

Any experiences ? Pros and Cons ???

The Pond racer is my new ship that I'm just teething. It's a twin with Saito 30's. My reason for re-tanking (!!!!) is the 2 1/2 oz tanks that I'm presently using are far to much capacity and the little Saito's ( mounted sidewinder ) really don't prefer uniflow ( based on my bench tests) and with muffler pressure I don't like how sensitive the needle is.

Hence the silly question.

One of the tank makers offered a particular variety of his tanks plumbed just the way that you suggested. Those apparently worked just fine. I know that when I have re-plumbed a couple myself to accomplish the same thing, those worked as well as my clumsy soldering allowed - - (I had to keep on working with one of the two over an extended, frustrating period of time, because I had a bad seam that seemed to only get worse the more I kept on trying to fix it!).

The K.

Wouldn't it be a whole lot simpler to fill your 2.5 oz tanks and then take out .5 oz of fuel with a syringe?

We use a hand crank pump and do the same thing. Fill the tank all the way, then take a number of "turns" back out of the tank and fly. You can easily adjust by half a turn, three fourths a turn, whatever to get quite precise in the length of run.

Yes, I can put less fuel in the tanks. But, the tanks are still uniflow. What I'd like is standard vent all tubes forward.

Anyhow, this evening opened up two 3 oz standard vent wide profile tanks. Cut off 1" to make an even two ounces. Cutting off the 1" took out the existing vent holes on the tank body. Drilled the cap for standard vent configuration out the front. One in the upper corner and one in the lower corner. And resoldered.

I hope I have more luck with my soldering job than Kiwi and its good news that he had some luck.

As mentioned, the little Saito's just don't seem to run as crisply on uniflow. Hence the reason for going to standard vent. Standard vent was a recommendation of Bob Z and I found on the bench running they prefered standard vent, even that to muffler pressure. I used the uniflow cause that just happened to be the tanks I had in inventory.

Pressure tested tanks. Soldering ( knock on wood ) is okay. Just need to clean out with acetone and run a bit of fuel through them to flush.

If anyone is interested, I have set up some photos of the pond at http://www.agroponic.com/pond.htm. It's pretty radical looking. Swept forward wing. All in line ( engine/wing and stab ). Molded top and bottom blocks on pods and fuse. Carbon fibre cowls and cheek cowl and landing gear struts. All done up pretty much with Brodak candy colors. It is basically a Card 60 in disguise.

The nice thing I have enjoyed so far, is no problem with noise, but the sound of both engines running at 8,500 to 8,700 RPM is awesome.

VERY nice bunch of pics and planes. The Pond Racer is kewl, but needs two more engines . WAY back when...I found that adding a washer around the solder joint where a tube pokes into a tin tank is a good investment to avoid future difficulties. Gives more surface area and spreads the loads. Steve

To convert a uniflow tank to a standard vented tank all you have to do is leave the cap off the vent. Instant standard vent tank.
Nils

I just now had a chance to look at your web site. Very, very nice! I can't wait to hear how it flys. I'll bet those twin .30's sond really great!
Nils

It seems odd to me that 4-strokes would not prefer a steady fuel supply. Does anyone have an hypothesis as to why this should be?

>It seems odd to me that
>4-strokes would not prefer a
>steady fuel supply. Does
>anyone have an hypothesis as
>to why this should be?

The fuel suction on most 4-strokes with the stock carbs appears to be very marginal compared to most 2-stroke stunt engines. The fact that the tank position is super-critical is a read flag.
The only reason that I can think suction would be better is that the slightly higher (but dropping) fuel pressure somehow mitigates that.

Current best guess is that a much smaller equivalent venturi with maybe a plenum will improve this.

Hi Guys.

Thanks for all the advice. Have been on the road last few days with real work.

My reason for wishing to use suction is basically to widen the needle range. What I found with bench testing last fall, winter and spring is showing to be true. With both engines pressure and uniflow provided both very narrow needling ranges. Whereas with suction one had a good 1/4 fine tuning on the needles to play with. Also on both presure and uniflow, the engine characteristics changed as fuel was consumed. ( This held true with all tanks mounted at CL to needle on carb ). Both engines are really run in well and each have about 2 gallons of fuel through them.

I believe it true what Brett mentioned. With low carb/manifold suction being a 4 stroke, the needles do become real real sensitive as they are closed. Ie on muffler pressure engines ran best when the needles were about 1 - 1/4 turn open and at that one klick one way or the other sagging or rich run. Whereas on suction, the needles were close to 2 1/2 turns open to achieve the same engine run. Being a twin I wished to have the widest range of needle as possible for fuel metering and sync.

Now the kicker. I'm up at 4,100 to 4,200 feet above sea level. Now with less air density, one has to wonder how much of a factor that presents. ??? .

I guess I'll find out tomorrow when I put in the suction tanks that I built. Isn't life fun, it's always a challenge.

The sound of both engines running is incredible for sure. Prop whirl over engine noise. Its like white silence. Must have had the engines running for a couple hours each day right in the back yard and not a complaint. I could actually hear the nieghbors lawn mowers over the twins running.

Ken

I guess I'm missing something. The fuel draw of an engine certainly doesn't depend on whether the tank is normal vented or uniflow---especially on the bench. All uniflow does is to give a constant flow over the entire run--you set the flow with the needle.
Now when you start flying that plane, the normal venting is going to lean out on you as you continue to fly. You won't see that in bench running, or at least not as extreme as in flying (this does depend upon the tank width).

>I guess I'm missing something. The
>fuel draw of an engine
>certainly doesn't depend on whether
>the tank is normal
>vented or uniflow---especially on the
>bench. All uniflow does is
>to give a constant flow
>over the entire run--you set
>the flow with the needle.

The thing you may be missing is the fact that with identically-shaped tank in the same position, the absolute fuel pressure out of a uniflow tank is lower than an equivalent suction tank, at least at the beginning. The suction tank pressure starts out higher and falls to the uniflow pressure at the end.

The odd thing is that you would think that if the engine was so sensitive to fuel pressure, you'd think that running suction would be a diasaster. But it isn't. I don't really understand what's going on. I just offered the observation.

>Now when you start flying that
>plane, the normal venting is
>going to lean out on
>you as you continue to
>fly. You won't see
>that in bench running, or
>at least not as extreme
>as in flying (this does
>depend upon the tank width).

My bench tank is much deeper than the airplane tank. It's uniflow to avoid having to chase the needle around during the break-in.