I worked on a 3/8" copper pipe coupler for my GMS .32 and it's done a decent job of minimizing stand-off fuel. Figured I'd do the same for my OS .46AX on my spad sickle.

This time I used a piece of 1/2" copper pipe and between boring this out to squeeze onto the carb and sanding things smooth it lightend up a bit. Used some aluminum polish to polish it up.



Looking forward to seeing if this minimizes stand-off fuel.

somegeek

You do nice work

wOW, nice job! What did you use to adhear it to the carb so you don't loose it?

Thanks
Al

OK, dumb question alert. What do you mean by "stand off fuel"? The stack looks fantastic though.

Hello:

Yes, the stack does look wonderful. I'm also curious about how it's attached so it doesn't vibrate loose.

To answer the question about "stand off fuel", the timing of the intake opening in the crankshaft is a compromise. For part of the rpm range, the fuel air mixture is puffed **out** of the carby, wasting fuel. It may be possible to see a slight haze around the carby when the engine is running, however, I always keep my face well away from the spinning propeller.

The idea behind this stack is to always keep the puffed out fuel air mixture in a place where it can be sucked back into the engine again. The engine doesn't puff the fuel air mixture very far.

I hope that helps.

Bye, Ian

I Dremeled out the inside a bit at a time until it fit snugly down to 1/8" left to be fully seated. After polishing it, I tapped it into place... so friction is holding it there. I'd be a bit skeptic if this was my first time installing this, but I installed a stack with this same method on a GMS .32 and it's held well after 20 or so flights(not wandered a bit) and the stack tube on that .32 is not as snug.

Thanks for the kind words. ianwynne explained it well - here is another reference regarding this:

http://en.wikipedia.org/wiki/Velocity_stack

Only dumb question is the one left unasked.

somegeek

have you seen better fuel economy with the velocity stack? do you have any hard figures? one minute longer flights might be worth the effort of making one of these?

Geek,


As Julian hinted, the only advantages your piece of work will bring to you, is less wasted fuel (and a cleaner plane).

Even this is true only if you use an unusually large prop that would 'promote' spit-back (the term 'stand-off' is not right here...).


And it is beautiful, but could be bothersome (in a gashing way...[:@] ), if you flip-start your engine...

Well worth the effort or not, I copied the design onto my 55AX tonight (mounted on a Pulse XT). Took all of 10 minutes from start to finish, and that's only because I couldn't find my flare tool. Even if it only helps a little, I'm looking forward to taking it to the field Sunday for a chorus of "What's that!?"

Thanks for the idea, somegeek. I love trying new things, especially if I learn something in the process.

Nice to see this inspired someone else to give it a go.

I finally got my spad sickle up with this stack installed. I had much less fuel deposited on my plane than before. The majority stayed in the carb where I want it. Gonna make one of these now for my Sig Somethin' Extra. I have the same engine on that.

somegeek