Commonsense attitude to Carburettor Icing
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Sure, dust will accrete, but it won't erode anything much. The only moving part that's exposed to this unfiltered airflow is the throttle butterfly, and I struggle to see how dust in a fast-moving airstream is going to find its way into the butterfly bushes. All the other moving parts are exposed to the dust to the same extent whether the carb heat is selected or not, so they are irrelevant.
You might get some blocked jets (although the air pressure is, by definition, pushing against the incoming dust rather than sucking it into the jets), but even if you did it would only need an overhaul (strip & clean) and wouyld not justify scrapping the carb.
So I still don't see it.
PDR
You might get some blocked jets (although the air pressure is, by definition, pushing against the incoming dust rather than sucking it into the jets), but even if you did it would only need an overhaul (strip & clean) and wouyld not justify scrapping the carb.
So I still don't see it.
PDR
Mostly I have found worn butterfly bushes - these neither give full power or a proper idle - without other adjustments if possible to do it.
Amazing how many people who previously flew Cessnas would use the same technique for application of carb heat in a PA28 or PA38. When asked why this was done instead of following the POH the response 99% of the time was simply "My last instructor told me to"
Learning by rote is about the highest level of understanding in many instances.
Learning by rote is about the highest level of understanding in many instances.
Folks,
Long time ago, now, but we always fitted warm air filters, where available, either as an OEM option, or an STC.
I was always impressed with the difference in an engine at overhaul in the UK, vesus Australia, we still had warm air filters there, but there was never anything like the dust we got in our VH- aircraft. Indeed, in western NSW and FNQ we often did filter and oil changes at 50 hours, for air filters, sometimes less, depending on how fast they loaded up.
UK versus AU certainly showed up in overhaul costs.
Tootle pip!!
Long time ago, now, but we always fitted warm air filters, where available, either as an OEM option, or an STC.
I was always impressed with the difference in an engine at overhaul in the UK, vesus Australia, we still had warm air filters there, but there was never anything like the dust we got in our VH- aircraft. Indeed, in western NSW and FNQ we often did filter and oil changes at 50 hours, for air filters, sometimes less, depending on how fast they loaded up.
UK versus AU certainly showed up in overhaul costs.
Tootle pip!!
Thread Starter
When asked why this was done instead of following the POH the response 99% of the time was simply "My last instructor told me to"
Yet the only before landing checks in the manufacturer's POH (Cessna 172 for example)
are: Seats, belts, Harnesses secure, Mixture Rich, Carb heat on.
Comment: Note seats secure in the POH but not mentioned in "what my last instructor told me to". Note nothing either in the POH about brakes, undercarriage or master switch or mags on. I recall asking one instructor why he taught Masters and Mags as part of the before landing items. Because they start with "M" he said.
PUFF checks on final. Whatever mnemonic takes your fancy. All inventions of some instructors who blindly adhere to 'My last instructor told me to"
Centaurus, I was staying in a town on business and spontaneously went for a bash in a C152 late one summer evening. As I was unfamiliar with the area I went with an instructor who showed me the sights. It was an awesome flight over the coast and I asked if we could return to the field for a few touch and goes.
On turning base I completed the checklist from memory and verified against the written one in the aircraft (as is my habit). Naturally before pulling the throttle back I applied full carb heat.
On very short final I went to push the carb heat to COLD. The instructor balked at this and immediately pulled it back out to ON. I didn't say anything and touched down, retracted the flaps, then went to push the carb heat back to cold again before applying full throttle. He practically smacked my hand away and said "leave it on". He left the carb heat on until approx 300ft AGL and then he set it to COLD.
I was confused by all of this. His explanation was that it was their standard operating procedure and that it reduced the likelihood of carb ice accumulation during the critical take-off phase. Clearly there was no arguing with him so we finished up the next circuit with a full stop.
Who was right or wrong in this situation? The C152 POH says that any normal takeoff should be with carb heat COLD, and as part of the BEFORE LANDING checklist it should be set ON. It doesn't make mention of if it should be set to COLD on short final!
On turning base I completed the checklist from memory and verified against the written one in the aircraft (as is my habit). Naturally before pulling the throttle back I applied full carb heat.
On very short final I went to push the carb heat to COLD. The instructor balked at this and immediately pulled it back out to ON. I didn't say anything and touched down, retracted the flaps, then went to push the carb heat back to cold again before applying full throttle. He practically smacked my hand away and said "leave it on". He left the carb heat on until approx 300ft AGL and then he set it to COLD.
I was confused by all of this. His explanation was that it was their standard operating procedure and that it reduced the likelihood of carb ice accumulation during the critical take-off phase. Clearly there was no arguing with him so we finished up the next circuit with a full stop.
Who was right or wrong in this situation? The C152 POH says that any normal takeoff should be with carb heat COLD, and as part of the BEFORE LANDING checklist it should be set ON. It doesn't make mention of if it should be set to COLD on short final!
Who is correct here? The engine rebuilders when they marvel at the worn cylinders and wonder where the air filtration system went wrong. Stupid instruction, stupid policy.
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Certainly not the way I was taught. Aside from the various other reasons given in previous posts, you also get rid of the carby heat on short final so that you have FULL power available should you need to go around or if you're doing a touch & go you have FULL power for takeoff. 
He practically smacked my hand away and said "leave it on". He left the carb heat on until approx 300ft AGL and then he set it to COLD.
I was confused by all of this. His explanation was that it was their standard operating procedure and that it reduced the likelihood of carb ice accumulation during the critical take-off phase. Clearly there was no arguing with him so we finished up the next circuit with a full stop.
I was confused by all of this. His explanation was that it was their standard operating procedure and that it reduced the likelihood of carb ice accumulation during the critical take-off phase. Clearly there was no arguing with him so we finished up the next circuit with a full stop.
Since the use of carburetor heat tends to reduce the output of the engine and to increase the operating temperature, carburetor heat should not be used when full power is required (as during takeoff) or during normal engine operation, except to check for the presence or to remove carburetor ice.
Read more Carburetor Heat
Read more Carburetor Heat
It seems to me that if carbie heat has been applied properly before the reduction in power, the probabilities of ice accumulating during the approach are extraordinarily low. However, it should be noted that the rote-learned procedure is usually to apply carby heat immediately before pulling the throttle. But it takes time for carby heat to heat the carby. If the probabilities of icing are high, carby heat should be applied up to 30 seconds before the throttle is pulled.
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The C152 POH says that any normal takeoff should be with carb heat COLD, and as part of the BEFORE LANDING checklist it should be set ON. It doesn't make mention of if it should be set to COLD on short final!
As another example of instructor personal ideas confounding common sense, I was undergoing a dual check in a Navajo. The instructor insisted the cowl flaps should be set to fully open on final in case (in his own words) we had to go-around. The fact that it would take us only 45 seconds to get back to circuit height went over his head and the CHT was never going to be a problem in that time.
It is up to the operator if they want to add things like brakes off to pre-landing checks. It's quite another to ignore the POH and just lazy to adopt a one size fits all instead of reading the POH for different types.
POH for Tomahawk and Warrior state in section 4:
APPROACH AND ANDING
Carburetor heat should not be applied unless there is an indication of carburettor icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburettor heat on can cause detonation.
Section 4 of POH for C152 states:
BEFORE LANDING
1. Seats, Belts, Harnesses -- ADJUST and LOCK.
2. Mixture -- RICH.
3. Carburetor Heat -- ON (apply full heat before reducing power).
AFTER LANDING
1. Wing Flaps -- UP.
2. Carburetor Heat -- COLD.
BALKED LANDING
1. Throttle -- FULL OPEN.
2. Carburetor Heat - COLD.
3. Wing Flaps -- RETRACT to 20°.
4. Airspeed -- 55 KIAS.
5. Wing Flaps -- RETRACT (slowly).
So, similar to the "in case of a go-around" reasoning that people give for opening cowl flaps on final, where for example C182 POH says to open them for a baulked landing; it shows that people are just parroting rather than learning.
POH for Tomahawk and Warrior state in section 4:
APPROACH AND ANDING
Carburetor heat should not be applied unless there is an indication of carburettor icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburettor heat on can cause detonation.
Section 4 of POH for C152 states:
BEFORE LANDING
1. Seats, Belts, Harnesses -- ADJUST and LOCK.
2. Mixture -- RICH.
3. Carburetor Heat -- ON (apply full heat before reducing power).
AFTER LANDING
1. Wing Flaps -- UP.
2. Carburetor Heat -- COLD.
BALKED LANDING
1. Throttle -- FULL OPEN.
2. Carburetor Heat - COLD.
3. Wing Flaps -- RETRACT to 20°.
4. Airspeed -- 55 KIAS.
5. Wing Flaps -- RETRACT (slowly).
So, similar to the "in case of a go-around" reasoning that people give for opening cowl flaps on final, where for example C182 POH says to open them for a baulked landing; it shows that people are just parroting rather than learning.
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go with the aircraft/engine ops manual.
Rotax manual in my aircraft, Use carby heat when required to keep airbox temp at 21Deg C. so, in winter, its not uncommon to fly the entire flight with carby heat on... and the reason rotaxe's should always have an airbox, so heated air is added before the filter.
only ever had carby ice once in a rotax, on a long descent from 8500 to sea level mid winter. and of course, i forgot to keep carby heat on in cruise.
And what exactly are you trying to do when "Clearing the carby" clearing it of what exactly?
Rotax manual in my aircraft, Use carby heat when required to keep airbox temp at 21Deg C. so, in winter, its not uncommon to fly the entire flight with carby heat on... and the reason rotaxe's should always have an airbox, so heated air is added before the filter.
only ever had carby ice once in a rotax, on a long descent from 8500 to sea level mid winter. and of course, i forgot to keep carby heat on in cruise.
And what exactly are you trying to do when "Clearing the carby" clearing it of what exactly?
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It is up to the operator if they want to add things like brakes off to pre-landing checks. It's quite another to ignore the POH and just lazy to adopt a one size fits all instead of reading the POH for different types.
POH for Tomahawk and Warrior state in section 4:
APPROACH AND ANDING
Carburetor heat should not be applied unless there is an indication of carburettor icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburettor heat on can cause detonation.
Section 4 of POH for C152 states:
BEFORE LANDING
1. Seats, Belts, Harnesses -- ADJUST and LOCK.
2. Mixture -- RICH.
3. Carburetor Heat -- ON (apply full heat before reducing power).
AFTER LANDING
1. Wing Flaps -- UP.
2. Carburetor Heat -- COLD.
BALKED LANDING
1. Throttle -- FULL OPEN.
2. Carburetor Heat - COLD.
3. Wing Flaps -- RETRACT to 20°.
4. Airspeed -- 55 KIAS.
5. Wing Flaps -- RETRACT (slowly).
So, similar to the "in case of a go-around" reasoning that people give for opening cowl flaps on final, where for example C182 POH says to open them for a baulked landing; it shows that people are just parroting rather than learning.
POH for Tomahawk and Warrior state in section 4:
APPROACH AND ANDING
Carburetor heat should not be applied unless there is an indication of carburettor icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburettor heat on can cause detonation.
Section 4 of POH for C152 states:
BEFORE LANDING
1. Seats, Belts, Harnesses -- ADJUST and LOCK.
2. Mixture -- RICH.
3. Carburetor Heat -- ON (apply full heat before reducing power).
AFTER LANDING
1. Wing Flaps -- UP.
2. Carburetor Heat -- COLD.
BALKED LANDING
1. Throttle -- FULL OPEN.
2. Carburetor Heat - COLD.
3. Wing Flaps -- RETRACT to 20°.
4. Airspeed -- 55 KIAS.
5. Wing Flaps -- RETRACT (slowly).
So, similar to the "in case of a go-around" reasoning that people give for opening cowl flaps on final, where for example C182 POH says to open them for a baulked landing; it shows that people are just parroting rather than learning.
If the POH is written such that we can assume pilots can learn to do things correctly, it SHOULD read like this.
BEFORE LANDING
1. Seats, Belts, Harnesses -- ADJUST and LOCK.
2. Mixture -- LEFT ALONE IN A LOP CRUISE SETTING or at a ROP Cruise position.
3. Carburetor Heat -- ON (apply full heat before reducing power).
AFTER LANDING
1. Wing Flaps -- UP.
2. Carburetor Heat -- COLD.
BALKED LANDING
1. Throttle -- FULL OPEN.
2. Mixture RICH THEN Carburetor Heat - COLD.
3. Wing Flaps -- RETRACT to 20°.
4. Airspeed -- 55 KIAS.
5. Wing Flaps -- RETRACT (slowly).
And yes folks that is how it should be done! Zero harm to engine and airframe, less chance of icing and less than the POH method. Does everything it should and nothing it shouldn't and yes I have generated the data personally.
LAST OF ALL......A MASSIVE OLD WIVES TALE TO KILL OFF.
Please do not start saying the OEM should know........This one is BULL**** of the highest order. I have participated in more detonation testing than anyone on PPRUNE, on the worlds most advanced aero-piston engine dyno. I declare this to be an OWT of the highest order.
Full throttle operation with carburettor heat on can cause detonation.
Simply cannot happen. Not unless you advance timing well out of spec, run on crappy low grade mogas, have oil temps in the 245dF range, CHT's in the 440dF or much higher range (unlikely prior to landing) and you are at 34" MAP with a mixture accurately set at 35-40dF ROP.
If anyone at Piper can explain how a pilot can do that in one of those planes (Chieftain is another matter but still take a bit of effort) and even if they did it would be so mild to begin with the GA and subsequent climb to circuit height would barely clean the cylinders let alone damage anything.
So......any more OWT's need busting?
So......any more OWT's need busting?
Hey whoa Jaba, I'm just the messenger here.
OWTs to bust?
Well, there's the people who turn the PA28 electric fuel pump off at 300 feet after take off
"Because you will wear it out",
The one about the MP number should always be lower than your RPM number "Or you will blow up the engine"
The ones who fully open cowl flaps on final no matter what the CHT is "in case you need to go around",
The one who told me "a localiser will only work correctly if the runway number is put on the top"
That you must NEVER use a rotating card on the ADF "in case it gets stuck"....
Putting a variable pitch prop to coarse on a single engine piston to "glide further in the event f an engine failure"
The signature on part 3 of a maintenance release is always signed by the pilot in command...
OWTs to bust?
Well, there's the people who turn the PA28 electric fuel pump off at 300 feet after take off
"Because you will wear it out", The one about the MP number should always be lower than your RPM number "Or you will blow up the engine"
The ones who fully open cowl flaps on final no matter what the CHT is "in case you need to go around",
The one who told me "a localiser will only work correctly if the runway number is put on the top"
That you must NEVER use a rotating card on the ADF "in case it gets stuck"....
Putting a variable pitch prop to coarse on a single engine piston to "glide further in the event f an engine failure"
The signature on part 3 of a maintenance release is always signed by the pilot in command...
Putting a variable pitch prop to coarse on a single engine piston to "glide further in the event f an engine failure"
If the engine has failed there is no oil pressure to act against the spring and it would go to the stops, most will default to full fine.
That's quite an overstatement, Clare. If the engine has stopped or lost all its oil (and oil pressure is necessary for the pitch control on the specfic propellor) then: Yes.
But if the engine has "failed" because of fuel starvation or exhaustion (the usual cause) or (unusually) both mags have failed, the propellor is windmilling and the resulting oil pressure is perfectly adequate to drive the prop to full coarse. And it makes a profound difference to glide range.
But if the engine has "failed" because of fuel starvation or exhaustion (the usual cause) or (unusually) both mags have failed, the propellor is windmilling and the resulting oil pressure is perfectly adequate to drive the prop to full coarse. And it makes a profound difference to glide range.
I think the significant part is "...in case of an engine failure..." ie not yet trying to glide. After the failure then, yes, prop to coarse, otherwise as required i.a.w. the POH/AFM.
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Seems to me that the post from Ex FSO Griffo was perfectly reasonable. He said the engine was scrapped due to dust abrasion/scouring in all 4 cylinders. Maybe he really meant just that, the cylinders had to be scrapped. Seems many have over-read Griffo's post. Regardless, why use unfiltered air in a mustering environment. Not too much time spent at low power settings I suspect.