Originally Posted by
Glowgeek
Concept
Using checked crankcase pressure with the solenoid tee'd into the line between the check valve and fuel tank. Crankcase oil would drain through both the check valve and the solenoid to provide lube. The solenoid would serve as an adjustable pressure relief valve. Our existing fuel channel curve would become a tank pressure curve, tied to throttle position.
I have no idea of validity of the idea but it seems like it would provide varying fuel pressure just as muffler pressure does. The final pressure curve would be tuned in flight, just as with our current configuration.
The headroom for additional fuel during unloading is an unknown to me. It seems there would be additional tank pressure/fuel pressure available as the prop unloads, above ground peak rpm, without further adjustment of the solenoid/relief valve but I'm not sure if it would be enough to meet fuel demands. It may require some compromises.
As usual, I've probably over simplified the whole thing and I really don't think the concept will control engine fueling with the granularity of the current setup. It may however work good enough, getting rid of the severly over rich midrange common to glow/gas conversions and get rid of that pesky crap trap.
No, it would not... It would provide variable fuel pressure, but NOT like the muffler does. The difference is that the electronically controlled pressure does not follow the RPM (unloading), ONLY the throttle position. It would basically be the same as a fuel curve without muffler pressure.
This is an important difference.
The thing is, there are TWO corrections on fuel: One for the throttle position, which is now our fuel curve, the other correction is "automatic" by means of the muffler pressure, and it corrects for unloading. The issue with that one is, that I have no idea how that "unloading-correction" works WRT numericals. I know it works, but I have no idea if that pressure is linear to RPM, squared to RPM or maybe even cubed. Or maybe it is none of the above. So I would not know how to describe that correction mathematically. And that is a problem, which can only be solved with LOTS of testing, and it might even require a LUA script ecause a Taranis can do a lot, but it does not have mathematical functions.
And let's face it, that craptrap, it really is not such a monstrosity that avoiding it would justify all that testing and programming. One of the principal goals was mainly to keep things SIMPLE...