- Oct 18, 2003
- Saline Michigan
Hmm, so you are willing to manually control the vane setting and fuel flow setting while watching the manifold pressure? The human engineering guy in me rebels at the thought. For a while, Piper sold a turbocharged Cherokee variant (Arrow, IO-360, retract gear) with a fixed wastegate and you trimmed power with the throttle (gas engine, has a throttle plate, can adjust manifold pressure with it) to keep manifold pressure in bounds. If you got sloppy, you overboosted the engine or went short on power. It made the pilot look at the power settings, which might be OK when at cruise, but it sure complicates things during the go part of a rejected landing. And it was only one lever to trim power.If there is one thing I've learnt about diesels over the last couple of days it is to forget everything I know about petrol engines. Thanks Bilski and PMD, you have increased my understanding 100 fold, along with a load of other reading I've done.
I also received a reply from Serge. He says at take-off to have a maximum pressure which does not make you lose engine revs at take-off throttle, so no more air than needed. At cruise, you do the same thing, set the cruise revs then reduce the turbo pressure to just above where revs decrease. So from this I gather I would find a setting (distributor pump and boost) that gives maximum HP (little smoke) that can be used for take-off at sea level (most of Australia). When flying I would reduce throttle (a misnomer) to cruise speed then back off the turbo until it starts to decrease in revs. As altitude increases, I dial in more boost keeping an eye on revs and EGT. Have I got that right?
I guess there will also be a setting I could use to 'set and forget' that will give me enough boost for adequate take-off power and OK in cruise, one that can be used by other pilots without special instruction, similar to a non-variable turbo.
BTW, my basic medical doesn't allow cruising at altitudes above 10,000 feet in Oz and our highest airport is 4000ft with a vast majority being less than half that. though it can get very hot.
You will have both a fuel lever and a manifold pressure lever, and it sounds like you will have to manipulate both. You might be well served in this area by putting in three adjustable detents in each linkage, one for take-off power, one for climb power, and one in the middle of cruise. Mark the manifold pressure gauge similarly. Then during high workload events, you can just go to the appropriate detents. When you get settled down a little, you can check manifold pressure and trim the manifold pressure and fuel flow settings.
This all still sounds like a human factor nightmare - Imagine another airplane intrudes on the runway while you are a quarter mile out. You have to transition from approach to climb configuration of the airplane, the fuel flow, and the manifold pressure. Many folks have their hands full just getting the airframe changed and cobbing the throttle. Maybe you can, when you retard the fuel lever on final, shove the manifold pressure lever forward counting one, two, three clicks, so that advancing fuel puts you there. Or maybe that forces enough power that descent and land becomes a long floaty thing... I do not know, but you should definitely find out.
I again emphasize that instead of making and flying something that is already known, you seem to be entering the arena of invention, with both benefits and risks.