Carb Heat
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Carb Heat
When I was learning to fly on a C-150 the procedure was on downwind the carb heat comes on and stays on until landed. Then it was modified to carb heat on whenever RPM is below the green arc (2000 rpm if I remember correctly). I've met plenty of pilots who do that on all carbureted aircraft they fly but I've never seen it in an AFM anywhere. If you checked for carb ice throughout the flight and none is forming, and you check again on downwind and there isn't any, can you be sure there won't be any once you close the throttle? Or is this something that only applies to the O-200 and other small engines?
Re: Carb Heat
I've many times experienced significant carb icing in a 150 while doing, er, "extended" runups at about 1600 rpm on the ground on cool October mornings in Toronto. It feels just like the throttle is slipping out, so you keep pushing it open, then the penny drops and you hit the carb heat, and - whoosh - you get back all the RPM that you were missing, all at once.
On the basis of that experience, and the speed the ice formed (too slowly to notice an instant issue, too fast to get away with for more than 30 seconds), in the 150 I'd definitely take care to keep the carb heat on when flying with RPM near that value. That includes from the downwind, until landing.
On the O-235 equipped C152, I've never seen it. Wiser people than I have told me it's because of the different geometries of the carburettors in the two engines. So the practicalities are quite engine-specific.
The green arc on the tach isn't there specially to remind you to apply carb heat at any particular rpm but as an aide-memoire it doesn't appear to do any harm.
On the basis of that experience, and the speed the ice formed (too slowly to notice an instant issue, too fast to get away with for more than 30 seconds), in the 150 I'd definitely take care to keep the carb heat on when flying with RPM near that value. That includes from the downwind, until landing.
On the O-235 equipped C152, I've never seen it. Wiser people than I have told me it's because of the different geometries of the carburettors in the two engines. So the practicalities are quite engine-specific.
The green arc on the tach isn't there specially to remind you to apply carb heat at any particular rpm but as an aide-memoire it doesn't appear to do any harm.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
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Jungle Jim
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Re: Carb Heat
My old Stinson with the Franklin engine, which had the intake tubes separate from the sump would for ice real fast when conditions were right. I got into the habit of pulling the carb heat on downwind every time.
Frequently I would see the effects of carb ice in cruise and had to apply heat. I guess it depends on the engine, but adding on the downwind is a good habit to get into.
Regards,
Jim
Frequently I would see the effects of carb ice in cruise and had to apply heat. I guess it depends on the engine, but adding on the downwind is a good habit to get into.
Regards,
Jim
Re: Carb Heat
Small Continentals are more prone to Carb Ice than Lycomings.
Lycoming Carbs are attached to the oil pan and get quite warm. In addition, the induction air tubes pass through the oil pan, warming the intake air.
Continentals get better fuel economy from the cooler intake air.
Lycomings can startle you with unexpected Carb Ice under certain conditions; cool air with high humidity. In those conditions, Lycomings need almost continuous Carb Heat; surprising the unwary, because normally Lycomings seldom ice up.
Small Continental engines definitely need Carb Heat regularly; especially at lower power settings.
Lycomings can fool you; watch for decreasing power or Manifold Pressure in cool air with high humidity or rain.
ALWAYS check Carb Heat on downwind; put it on when reducing power.
Lycoming Carbs are attached to the oil pan and get quite warm. In addition, the induction air tubes pass through the oil pan, warming the intake air.
Continentals get better fuel economy from the cooler intake air.
Lycomings can startle you with unexpected Carb Ice under certain conditions; cool air with high humidity. In those conditions, Lycomings need almost continuous Carb Heat; surprising the unwary, because normally Lycomings seldom ice up.
Small Continental engines definitely need Carb Heat regularly; especially at lower power settings.
Lycomings can fool you; watch for decreasing power or Manifold Pressure in cool air with high humidity or rain.
ALWAYS check Carb Heat on downwind; put it on when reducing power.
Re: Carb Heat
Good tip. I have a 0300D powered 172. I use carb heat at reduction of throttle before my base turn and push it in before I flare in case I need to do a go around. My CFI made this an evolution to do every time before landing. Never had any Carb ice this winter but I expect I will see some this spring
Re: Carb Heat
I have a 172P POH handy and it says carb heat on when you reduce power. The 152s and 172s I've flown had a green marker on the tach, carb heat on below that mark.
The Cherokees I learned to fly in called for a shot of carb heat on downwind and any other time you reduce power, but don't leave it on. You can tell if the engine needed it. My Musketeer has the same engine (O-320) and the carb heat use is the same.
...laura
The Cherokees I learned to fly in called for a shot of carb heat on downwind and any other time you reduce power, but don't leave it on. You can tell if the engine needed it. My Musketeer has the same engine (O-320) and the carb heat use is the same.
...laura
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Cat Driver
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Re: Carb Heat
The need for carb heat varies from airplane to airplane.
The worst problem with using excessive carb heat is higher fuel burn.
Which is better than less fuel burn because the engine quit when you needed it most.
The worst problem with using excessive carb heat is higher fuel burn.
Which is better than less fuel burn because the engine quit when you needed it most.
The hardest thing about flying is knowing when to say no
After over a half a century of flying no one ever died because of my decision not to fly.
After over a half a century of flying no one ever died because of my decision not to fly.
Re: Carb Heat
Leave the carb heat on until after you've reached full throttle for a few seconds. Then put in the CH on the go around.Kejidog wrote:Good tip. I have a 0300D powered 172. I use carb heat at reduction of throttle before my base turn and push it in before I flare in case I need to do a go around. My CFI made this an evolution to do every time before landing. Never had any Carb ice this winter but I expect I will see some this spring
These continentals can collect ice at reduced throttle and especially at idle while on final.
Make sure you always apply CH fully.
Another tidbit and can be used in any aircraft but especially prone engines, before take off in conditions conducive to icing, CH on, full throttle, wait a few seconds and then CH off.
You can collect a surprising amount between taxiing from the ramp to the runway.
Always safe than sorry.
