Use of Carb Heat

[Andrew Foster]

Hello all,
Was flying in solid IMC the other day. OAT about 45, and carb temp around 28F

I decided to use a bit of carb heat to raise temp to 38F. Do you think this was a good idea or not?

This on a 61 250 carb.

Thanks for the feedback

Andrew
N7533P

[Zach Grant L1011jock]

I am of the opinion that carb heat is better used as deice, than as antiice. This is especially true when you have already frozen moisture that would pass through easily, but with heat gets partialy melted and sticks to everything. Running WOT greatly reduces your chances of carb ice, as well as does the location of the carb bolted to the oil pan on the Lycomings. This transfers some heat to the body of the carb and helps keep things thawed out. If the carb does start to ice, it is very obvious as a MP drop, at which time apply full and carb heat and wait for the MP to rise and the engine to run smooth again. Once this happens return to cold, and keep an eye on the MP. Only in extream conditions should continuous carb heat be necessary. This is both Piper and Lycoming recomondation.
-Zach

[15384]

Zach: Since the Servo on a Twin is not located directly on the body of the oil pan or the engine but it gets air after it goes into the nacelle and over the cylinders where it must pick up some heat, how susceptible is the Twin's servo of icing up. I know we have the alternate air source. I have seldom heard or read of anyone complaining of servo icing on our Twins. Have you ever known a NTSB conclusion that a PA30/39 came down due to servo ice? I know that it would be very unlikely to have both engines suffer servo ice. I read all the time about carb ice being the conclusion of an engine stoppage resulting in off airport landings.

Are our servos susceptible to icing period?

John

[Zach Grant L1011jock]

John,
Induction icing on any fuel injected aircraft is extreamly rare simply because the lack of fuel evaporating does not cause a temp drop like it does in a carb type system. With the fuel not introduced until essentially the intake valve, it doesn't get the ice buld up on the throttle plate. This is not to say that it cant happen, but it is rare. The alternate air doors on the PA-30 are both automatic and manual. They will open with significant vacuum and supply air to the engine, but notice the alternate air is designed to bypass an induction problem well before the servo. The truth is that on any PA-30/39, turbo or not, the chances of induction icing is VERY VERY rare, and you would probably ice up the engine cooling inlets before you had toworry about the induction system!
-Zach