I just can't seem to get a straight answer on this one....
I've always been taught apply carb heat on any carb engine as part of pre-take off, FREDA and downwind checks. This is how I've always operated and continue to operate.
I have the CAA AIC on carb icing and from time to time consult to remind myself of the most dangerous conditions for ice formation.
But I have heard different stories (this has been covered before on here) about the use of the carb heat on the carbed PA28s....
Considering the above imagine my shock at being told by my IR instructor in Florida upon seeing me reach for the carb heat during a FREDA check "nah it's too hot for carb heat" mentally I just said to myself WTF?!! (Temp about 30 dew point about 25). He also seemed to think that oil temperature had a bearing on whether ice would form or not....again something that really surprised me.
Reading the POH however revealed this:
The mixture control should be kept in full "RICH" position to ensure maximum acceleration if it should be necessary to open the throttle again. Carburetor heat should not be applied unless there is an indication of carburetor icing, since the use of carburettor heat causes a reduction in power which may be critical in the case of a go-around. Full throttle operation with carburetor heat can cause detonation.
Still not convinced I asked the examiner during my checkride "would you use carb heat now" when we where descending with about 1900RPM set and in close proximity to yet not actually in clouds. "No I would not" came to reply; he had asked the factory and in there opinion during normal descents the use of carb heat was not recommended.
This left me with the impression that Piper are pretty confident that the O-320 engine doesn't really suffer carb icing in normal conditions. How do they know this though? I've never seen a graph that describes ice forming conditions for the PA28....does one exist and what do other people think of this?