Originally Posted by
RTN11
It's all down to the engine.
In Lycoming engines the carb is usually located close to, if not attached to, the oil sump. Therefore a lot of heat is automatically transferred reducing the overall risk of ice. Students are still generally taught to liberally apply carb heat, and in a lot of schools to use it for every approach. This is completely unnecessary with a Lycoming engine, but for the average PPL it's probably good to get into a habit which will work on every aircraft, and there are engines out there that will simply stop if you reduce power without carb heat. For more on use of carb heat see this thread
http://www.pprune.org/flying-instruc...carb-heat.html
With older continental or rolls royce engines, the carb was positioned further infront of the engine leaving it much more exposed. I believe this was also the case on some older Gipsy engines found in Chipmunks and the like, but my experience on these types is fairly limited.
The main area of risk is from 5 - 20 degrees C, and the big danger is that it will happen in clear air if it is humid enough.
The only time I've had serious carb ice with a Lyco is taxiing on wet grass with a typical OAT of +8 to +15. Ultimately you have to know your engine and it's own dangers.
While it is generally true that Continentals are more prone to icing than Lycomings, I think one has to be careful to avoid making absolute statements.
The design of the cowling and air intake are also a factor. In my experience the worst 2 airplanes for carb icing were the BN Islander and the Piper Apache , and both are powered by Lycoming engines.
Carb ice is where you find it. I fly a little Grumman AA1B with a Lycoming O 235. The West Coast of Canada spends pretty much all of the winter sitting right in the max carb ice danger zone yet in over 10 years of flying I never once experienced carb ice...until last year. I was cruising at 6500 feet on a beautiful clear October afternoon with an OAT of about + 8. The engine starting loosing RPM and was sightly rough. I at first assumed it was plug fouling, a common problem with low compression engines run on 100 Octane AVGAS, but a mag check didn't make show any difference. However going to full rich made the engine run even rougher. It was at that point the penny dropped
and I selected full carb heat. After a few HARRUMPS from the engine it roared back to full power
.
Any engine will give you warning that it is icing first with a loss of power and then rough running so pay attention and icing will never be a problem.