This suggests that maybe I ought to look into making up some sort of duct that runs directly from the peripheral intake to the oil cooler; at present the oil cooler duct takes in a mixture of deflected cold air from the peripheral duct and warm air from the plenum.Incidentally, these data were collected while cruising at 4,500 feet at 144 ktas on 6.8 gph -- another example of the airplane doing better than expected at very low power settings -- 25/2100 and way LOP, in this case.The bypass is only 3/4" in diameter, and so even at low power a significant amount of exhaust gas is going through the blower, which is pumping against a partially closed throttle.This is an inefficient arrangement, obviously, but by using low rpm (these tests were run at 2,300 rpm, but I often go lower) I can open the throttle fully at 8,000 feet or so.I'm not sure what the politics of splitting the inner channel of a NACA scoop are, but I'll find out.The most difficult part of the whole project, I think, will be making the induction-air tanks, which have to withstand both heat and pressure.I had thought about constructing a pitot-style inlet with a boundary layer channel, but I decided it would be rather complicated and possibly draggy, so my present thought is to replace the existing NACA scoop in the cowling side panel with one about three times larger.
Here's another plot of the same data, this time temperature rise versus net boost pressure above (or below) ambient.(I am reluctant to attach such a large, relatively massive object to the engine.) I have not yet found out how much cooling air the intercooler requires.A turbonormalized Bonanza has a ram air intake about 3 or 3.5 inches in diameter, but unless the velocity ratio in the duct happens to be 1.0, that tells me little about the actual mass flow.Different altitudes produce scatter, but on the whole the points line up fairly well.Yesterday I collected some baseline data that will allow me, at some future time, to assess the effectiveness of the putative intercooler.
The first time I tested it in flight I got the impression that it had had a remarkable effect; but as time went on the effect appeared to vanish.