tank height in builtup fuse

[Chris Belcher]

The last two planes I have assembled (arf nobler and UHP Gieseke Nobler) suffer from the same issue. I mount the metal tank on the beams and use 1/16" plates under the motor. First time I go fly and flip it inverted...sure enough it goes rich, even while I'm saying "don't go rich...don't go rich". So I know the tank needs to be raised (sitting on wheels) but one cannot always get to the bearers to dig them out and the Gieseke has a tank floor. I can't lower (sitting on wheels) the motor more on the Gieseke as the nose cone won't align. I dont' really like using plastic tanks as i have not had good success with the adjustable uniflow tube...it seems to want to migrate back to it's own location under vibration i guess. IF i was building from plans or scratch I could make these adjustments ahead of time..like taking an eighth or so off of the bearers in the tank area.
Maybe i should take the back off the tank and move the uniflow tube up or down as needed? Suggestions??

[Mark Scarborough]

I tended ( when I flew glow) to build my own tanks and set the uniflow/pickup tubes a bit higher in the tank to allow more shim room

[Tim Wescott]

Do what Mark says.  There's an active thread on uniflow tanks that explains why: raising the uniflow vent inside the tank has the same effect as raising the whole tank.

If you don't want to build your own tank, then pop the back off of a store-bought tank , raise the uniflow vent (don't forget to tack the end down with a bit of solder -- and do the pickup if it's not done), button the tank up, and go.

[Motorman]

can you lower the needle valve?

MM

[Tim Wescott]

can you lower the needle valve?

One could, but it's probably less work to modify the tank.

[Mark Scarborough]

AND lowering the needle valve comes with its own set of complications,, what do you do with the old hole,, how will it affect airflow into the port,, on and on,, nope I would recomend against tweaking the motor,, do the tank, its much cheaper,, and if you screw it up you are out a few bucks worth of tin and copper tubing ( you do use copper tubing instead of brass dont you?)

[Steve Helmick]

Most important, it has been proven that moving the NV doesn't do a darned thing. It's the engine itself, the tank, and the relative position of the two. In the case of the tank, we know it's the position of the uniflow tube inside the tank. Ted Fancher and Al Rabe both did tests that involved moving the spraybar up & down the venturi, and reported in their columns in AAM (?) that there was no change in effective "tank height". 

The mysterious part is the reason why one engine design is different than another. Probably related to crankcase volume, Ted Fancher gave this characteristic a name, "Pumping Center", IIRC. This has been written about previously on Stunthanger. Maybe a search would turn it up. It's not April 1st.    Steve

[Chris Belcher]

But how do you pros build for this? Do you relieve the bearers in the tank area to allow for shimming? Do you leave the tank floor out and install later after tank height is established. I have designed this in my head but never applied...basically a "tank box" with shims on bottom and top that could be switched from bottom to top as needed until optimal. i guess my real issue is I have never had to move a tank DOWN (sitting on wheels) only UP...the only way it can't go! (unless the bearers are relieved).

[Steve Helmick]

Lots of guys make their own tin tank and move the point of the wedge upwards. Sometimes, it takes making more than one tank to get it into the ballpark where shimming works. Once experienced with an engine, it'll transfer to the next plane with the same engine.

I am curious to find out if two engines with different displacements built on the same crankcase casting would be the same...or different. Such as the Magnum XL .40 and XL .53, Enya .40 and .45, or ST .51bb and .60bb?  Steve