Had the opportinity to take to the air yesterday. The mission was to meet Paul Fisher at DVN for lunch.
Had flown once since signing off my condition inspection and all went well.
Forecast was sunny and 41F winds light and variable.
Arrived at the AP and started the pre heater (hair dryer), did the pre flight, had full fuel. All is good
Fired her up, taxied to 11, did the runup, into position, full power, lift off at 80, All is good.
Climb out at 100, start a right hand turn on coarse, ALL IS BAD!!! Lost partial power! Applied cab heat, cough, sputter, gaining RPM, seems to be full power.
Carb heat off while changing from right turn to left turn (trying to find the AP) to a downwind, still climbing slightly. Power loss again to 2000, 2100 rpm.
Again with the carb heat, off with the fuel pump, PRM increases slowly, but getting better. Back to full power with carb heat on, about 2400 rpm.
200’ below pattern altitude, power back to 1700 rpm (that makes you pucker as well) a bit fast on final, but not a problem. Nice touch down, brake hard to get speed down. Make first intersection and clear the active.
Carb ice is bad shit! Thought I had a handle on this problem a few years back. I had problems then, because the cabin heat box had an overflow hole to let hot air escape. When I applied carb heat, the air would draw from the overflow hole, across the top of the heat muff and into the carb, rather than from the fresh air inlet in the baffling, through the length of the heat muff and into the carb, taking the path of least resistance. When this happened, the air was not warmed sufficiently, and ice could form. Solution. Cover the overflow on the top of the cabin heat box. No problems since.
Back to the story. Did passes down the runway full power. Chopped power and did the second and third. Forth the pass, climb out at 100 to 3000’ and fly around the airport for about 15 min. No sign of that nasty bastard ice! Got on coarse and headed for DVN. Every little noise or bump gets your attention, RIGHT NOW! Took about half the flight to get the edge off. Fair landing at DVN. Taxied to Paul’s hanger. Had a nice lunch. Played with some wires and annunciator boards that Paul had made. Paul got his pre heat going. We both took off from runway 21. Paul followed me for about half the trip home, (just because he could) and turned back. Engine ran fine all the way home and made an excellent LDG at DEH.
Now the to conclusion. Remember the cabin heat box? Wellll, I had turned on cabin heat before taxiing to 11 on my first attempt. Thus allowing the engine to pull air from the cabin, across the heat muff, instead of through the muff, and was not getting hot air on runup. Started to form ice and by the time I was 400’ off the ground bad things happened. When I left DVN, I closed the cabin heat on TO and left it that way all the way home, as it wasn’t too cold. A bit chilly when I got there.
You can draw your own conclusions, but be aware of carb ice. It will make you sit up and take notice!
TriQ 200 N7868B 445 hrs