Since quite a few people have asked me about this, here it is.

I generated this computer model of the tank I made for my SAITO .30 powered Argus.
It starts as a stock 2-ounce wedge, modified as follows:

I put in two vertical tubes from the bottom as shown.  The vent, which gets muffler pressure, goes to the forward upper inboard corner of the tank. The filler is about ½ inch outboard – capped after filling.

   I drilled a 1/8 inch hole in the back, and extended the pickup tube out ¼ inch.
(note that the pictures show two positions for the pickup tube – put it wherever    you want)
I drilled two 3/32 holes into the tank as shown. They are approximately ¼ inch in from the pickup and 3/8 inch on centers. The fuel feeds into the auxiliary reservoir through these holes.

I made the reservoir from a 9/16 long piece of 5/8 OD brass tube, shaped to the tank, with the rear blocked off with a piece of brass shimstock. The reservoir is simply soldered to the back of the tank, flush to the outside. All fuel that gets to the engine comes in through the reservoir.

I was totally pleased with this setup. The engine gave a perfect run through the entire pattern. Then, it ran lean for the last four or five laps.

Questions?

         Bob Z.

Bob,

I understand the chicken hopper layout. I've used various kinds of chicken hopper setups forever. What I don't understand is, you show two vents entering the bottom of the tank and another vent exiting the tank on the upper side of the outboard wedge. Then add in the fuel supply exit and that's 4 exit tubes. One goes to the engine, one to muffler pressure (which?) and one is the overflow and capped. What is the last one?

Any chance of an internal view of the vent layout.

As there has been some recent discussion on tanks for 4-S engines, I decided to bring this up.

Bob Z.

Hi, Kim - excellent question.

First off, the functional length of the "hopper" is really 1/2 inch, since the shimstock plug is recessed 1/16 inch.

But, in my line of thinking, I wanted a change in engine speed to act as a warning - it worked out because the last few laps are always a bit lean, indicating the forthcoming shutoff.

One thing that I find a bit disconcerting about 4 stroke engines - there is absolutely no warning of shutoff - it just plain stops. This tank changes that as it allows the engine to pull in some bubbles, temporarily leaning the mixture.

I could not be happier with the way it works - the runs are PERFECT!!!!! 

Thanks for your comment.

Bob Z.

Bob - if you heard my Argus run at Brodak's, you know how well this setup works.

Bob Z.

Had an interesting experience last weekend.. One of our club members had a p-40 profile slightly overweight and powered with a Thunder Tiger 36.. We pulled the TT and discovered a Saito 40 bolted right up.. Used the same uniflow, GRW wedge tank he was running with the TT and bolted on the Saito off my TwistMaster..

Probably the best way to describe the run was, the very next day he ordered a Saito 40 from Horizon.. It ran great and as consistant as it did with the clunk tank on my TwistMaster.

I'm rethinking what has been a pretty hard stand on using clunk tanks with 4 strokes. I believe when I went through my hard tank tests I really didn't have the other important pieces of the puzzle in place. I now believe the two most important pieces are the venturi size and prop. You either have to match a prop to a fixed venturi or be able to adjust the venturi to match the prop.

What program did you use to draw the 3D model.
How long did it take to draw,  assuming you are an experienced user ?

And the best part about Solid Edge is that its so very cheap,, or uh NOT  lol
I am a tried and true Cad guy, sure wish I could step up into parametric modeling at least as an experiment, but man all this software is a years worth of modeling budget and then some! Guess I will stick to my Autocad,,,

Bob Z.  The "sump" tank is very clever.  I think with it you can eliminate the "wedge" part of the tank, as the sump will drain the last of the fuel without having to resort to the wedge trick to urge the fuel to the pickup tube.   I generally build rectangular tanks because (1) you get max fuel volume in the often cramped space available (2) it's easier to bend up and solder.

Floyd in OR

Here is a picture of a tank I was working on for a twin Saito 30 Heinkel  . In theory after a half of the fuel was gone the engine would cut off after about 10 laps flying level. You have too keep doing the pattern to keep the hopper full. The intake holes are in the top of the hopper and would fill the hopper in a climb or flying inverted. It worked pretty well but I couldn’t stand the worry that it might cut off at the top of some maneuver.
Willis