charles.harbert wrote:
Paul, for Mike P:
Scott, I'm using a combination of a manual and automatic control over my
wastegate to control boost at high altitudes. I haven't flown the plane higher
than 4K' yet, but it was designed to operate effectively abv 15K'. All AC
turbo's are much larger than ground based turbo's, so that they don't overspd to
destruction (per HMac AC section) by going over roughly a 3:1 pressure ratio.
Normal wastegate control is a feedback system that opens the waste when the
compressor (intake) side reaches a predetermined spring pressure (i.e.3-20 psi).
The method used to increase the intake pressure, which you will need to do at
higher altitudes, is to increase the spring pressure, or you can manipulate the
feedback pressure to the waste so that it thinks there is less pressure in the
intake manifold (which is what I did). The line from the intake side goes thru a
small pressure regulator that I can manually adjust (based upon an AC manifold
pressure guage in the panel). For example, if you want to maintain 3 psi of
boost at sea level (and at altitude) that is really roughly 18psia (absolute),
but when you go to 15K' where the outside air press is roughly half of sea
levels 15 psia, or 8 psia, then you'll need 10 psi from the turbo ( about 3
times the boost) to get back to 18 psia. I just reduce the air pressure going
back to the waste so that it thinks it only has 3 psi and it won't go abv this.
The 2 critical items are that you know the compressor map and how much you can
boost (blw 3:1), and second that you remember to screw the pressure regulator
back out when you descend. I've used this system a couple times in low level
flight and it works. It's a pretty simple system which I think will not fail.
I'll let you know what I find when I take it to higher altitudes, hopefully in
the next 6 months. I'm sure there are other systems that are better, but this is
how I did it.
The Aircraft Rotary Engine Newsletter. Powered by Linux.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org