Previously I wrote about the temperature of lower cowl air entering the
induction system.
In my airplane, the temperature probe was placed away from the exhaust
pipes, but measuring the total temperature of the air used to cool
the ENGINE and OIL cooler exit air (TOTC) - that is, the probe is
located aft of all 4 cylinders rather the ahead of the cylinders where the
induction air might be drawn from. Remember that I am talking about
injected Lancair 235/320/360s with the throttle body mounted on the forward
face of the oil sump.
Baro 30.18, OAT 86F, Airport is 710 MSL, Palt 450, Dalt 2400:
8 min after start, TOTC 176F (90F rise)
During 135 KIAS climb (WOT, 2600 RPM) TOTC went from 167F to 158F when the
OAT was about 81F or a rise range of 86F to 77F.
Level at 4500 MSL, 25 squared, 180 KIAS, 194 KTAS, OAT 75F, (TAT 68F), CHTs
360F-380F, TOTC 149F (rise from OAT of 74F)
On taxi in after landing, Oil temp 200F, TOTC 190F to 203F for a rise
of 104F to 117F above OAT.
So....Take off and climb might indeed see a difference from
OAT of under 100F, but actual induction air temps of 150F to 175F. Is
that bad? Oh, I forgot the impact of passing thru the oil sump and then
hitting the hot cylinders after being cooled by fuel vaporization........
In any event, software from Sacramento Sky Ranch calculated a loss of 5% - 8%
power if the induction air temperature is raised by these amounts.
I then went to move the probe to the air exiting the heat muff (just like
carb heat air) and in doing so I finally broke my probe. Maybe it wouldn't
matter because the display is limited to 210F (99C) although I would have liked
to show that the "carb heat" air is always hotter than the lower cowl
air.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
OK, I replaced the temperature probe and put it where the heat muff air
exits. This is the same air that would be "carb heat" air.
Baro 29.89, OAT 72F:
8 minutes after startup, 167F (95F rise)
Runup, 198F (126F rise)
During 135 KIAS climb (WOT, 2600 RPM) in excess of 210F (probe display
limit), OAT 68F, rise > 142F.
Level at 6500 MSL, 25 squared, 174 KIAS, 196 KTAS, OAT 66F, CHTs 360F-390F,
203F (rise of 135F)
The heat muff air is quite a bit hotter.
I believe the carb air temp probe is located after the fuel has been mixed
with the air - thus lower temps from the vaporization process are seen on
the cockpit display. The same thing happens after the injectors in an I/O
engine.