Carb heat

kevin47881

kevin47881

Final Approach
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Time to fly!
While getting checked out in a PA28-180 last evening, the CFI and I had a difference of opinion regarding carb heat.

When I did my PPL I was flying a Warrior and the POH stated not to use carb heat except when needed (paraphrased of course).

I then transitioned to a C172 with the "same" 160 hp. Cessna's POH states to use carb heat with RPM below about 2,000 RPM.

When we landed the CFI looks in the Cherokee POH and sure enough it confirmed my memory regarding carb heat usage.

So the question became...why does the same engine in two different aircraft have different operating procedures for carb heat?

If you know, I'd sure like to understand the reasoning and any difference between the set ups that cause the difference in using carb heat.

Regards,
 
The exhaust gas in the Cherokee is routed in such a way that it heats up the carb housing so there is less chance for icing. At least that is what I have been told and I have not had a chance to dig under the cowl of a Cessna that was not fuel injected to verify the correctness of that statement.
 
In a C172 I use carb heat from 15 degree F up to 70 degree F. Any warmer or colder and I don't use it.

My experience in Pipers is limited. When I did fly them it was the middle of the summer and I never had to really worry about it.

I seem to remember someone saying that the oil cooler in the Piper is right by the carb which helps keep it warm. I don't know this for sure though.
 
jesse said:
I seem to remember someone saying that the oil cooler in the Piper is right by the carb which helps keep it warm. I don't know this for sure though.
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In the Warrior that is not true. The oil cooler is on the pilot side of the engine behind the cylinders. The carb is on the center bottom of the engine. The two are at least 12 inches away from each other.
 
my understanding is that it had to do with the routing of exhaust pipes near the carb on Pipers.
 
Pipers place the exhaust at the rear of the engine compartment, no wheres close to the carb.

Its just an engineering thing left over from the days that Cessna was running engines with a remote mounted carb,such as the C-65/85/0-200/0-470, piper does not use those engines because they are known ice makers in the carb venturies, due to the carb not being influenced by the hot oil sump to which all other engines mount their carb.
 
NC19143 said:
Pipers place the exhaust at the rear of the engine compartment, no wheres close to the carb.
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To which Pipers are you refering?

My Warrior has it all up front and running near the carb

Here is a pic that shows this to be the case.
 
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NC19143 said:
Pipers place the exhaust at the rear of the engine compartment, no wheres close to the carb.

Its just an engineering thing left over from the days that Cessna was running engines with a remote mounted carb,such as the C-65/85/0-200/0-470, piper does not use those engines because they are known ice makers in the carb venturies, due to the carb not being influenced by the hot oil sump to which all other engines mount their carb.
Click to expand...
This is NOT true Pipers place thier exhaust systems all over the place check the Piper parts Manual for the pA-28 151/161 Wa rrior Fig 44 In FRONT of the Carb

YOU GOTTA SAY WHICH PIPER
 
jesse said:
In a C172 I use carb heat from 15 degree F up to 70 degree F. Any warmer or colder and I don't use it.

My experience in Pipers is limited. When I did fly them it was the middle of the summer and I never had to really worry about it.

I seem to remember someone saying that the oil cooler in the Piper is right by the carb which helps keep it warm. I don't know this for sure though.
Click to expand...

Not true depending on the aircraft try a long Throttel closed decent in warm humid gulf airAnd most PA-28 sieries A/C have the oil cooler in front of the #4 cyldinder
 
NC19143 said:
Pipers place the exhaust at the rear of the engine compartment, no wheres close to the carb.

Its just an engineering thing left over from the days that Cessna was running engines with a remote mounted carb,such as the C-65/85/0-200/0-470, piper does not use those engines because they are known ice makers in the carb venturies, due to the carb not being influenced by the hot oil sump to which all other engines mount their carb.
Click to expand...

Pipers place the exhaust at the rear of the engine compartment, no wheres close to the carbThis is NOT true either MOST all of the Cherrokie a/c have the muffler in the front of the carburetor</p>
 
c170bm said:
Pipers place the exhaust at the rear of the engine compartment, no wheres close to the carb

This is NOT true either MOST all of the Cherrokie a/c have the muffler in the front of the carburetor</p>
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Nope that's not true either. Depends on the model. Some up front some out back.

Look at the inlet ducting on Piper vs Cessna. The 172s I've opened up jam the air straight into the air box and into the carburator. The Pipers I've seen have the inlet air routed around somewhat before it gets to the airbox and then the carburator.
 
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This thread is an excellent example of why the NTSB (several years ago) recommended that pilots use full carb heat whenever power is pulled back from cruise power no matter what kind of plane/engine was involved. In their opinion, the risks of being wrong or remembering the right procedure but for the wrong airplane were just too great. You're not going to hurt the engine by applying carb heat at the relatively low power settings used in descent or in the pattern, so just get in the habit of using it every time. :)

Bob Gardner
 
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