Holy crap, I lost my engine last night...

[urflyingme?!]

i KNEW it

I guess I learned something in school

 

[aucfi]

The bottom of the green arc is lower in the Piper than in the Cessna, but isn't it the same engine?

I know the green arcs on tachometers represent normal operating speeds for the engine/prop on a constant speed setup. If your operating (engine making power) in the green arc, the engine is working to turn the prop. If you are out of the green arc, the relative wind is turning the prop, not the engine. I used to think the green arc was the "safe zone" as far as no carb ice but my mechanic showed me otherwise. Ever seen a yellow arc on a tach? Thats what made me question it.

My question is, does the same apply for fixed pitch setups? The green arc on my cub covers the entire dial up to the redline and I can assure you that it is not immune to carb ice.

 

[mtrv]

The mentality that carburetor ice is less likely on engines which attach the carburetor to the sump is flawed. Carburetor ice isn't forming as a result of conductive heating or lack thereof via the carburetor body; it's forming in the airstream, and adjustment of the carburetor airstream temperature is what creates or prevents it.

Forget about lycoming this and continental that. If it has a carburetor, it's susceptible to carb icing, period.

You might make a good preacher for a bunch of sheep, but I'd suggest that anyone who is really interested in this subject, to do research across the internet, including forums, Lycoming, Piper, etc.

There are many ideas, reasoning, explanations and answers. Some agree with Avbug, and many don't. To except Avbug's gospel as the total last word, is in effect---flawed. This is, and has been a highly debated suject. You can read and read, and read, and still not get a positive for sure, no mistake about it answer.

Regarding carb heat as a habit; without, having to re-write a quote from a Piper's POH, I'll just paste a copy thats already posted.

GROUND CHECK
...
Carburetor heat should also be checked prior to take-off to be sure that the control is operating properlyand to clear any ice which may have formed during taxiing. Avoid prolonged ground operation with carburetor heat ON as the air is unfiltered.
...

CRUISING
...
The continuous use of carburetor heat during cruising flight decreases engine efficiency. Unless icing in the carburetor are severe, do not cruise with the heat on. Apply full carburetor heat slowlyand only for a few seconds at intervals determined by icing severity.
...

APPROACH AND LANDING
...
Carburetor heat should not be applied unless there is an indication of carburetor icing, since the use of carburetor heat causes a reduction in power which may be crifical in case of a go-around. Full throttle operation with heat on is likely to cause detonation.

The idea that carb heat should be all or nothing is flawed, and applies a very un-airman like and very unprofessional sense of guesswork to what really is science; carb air temperature. Lacking a gauge, your best guess is full heat or none, but it's still a wild, rough guess.

Properly applied, partial heat is appropriate, in order to put the carb air temp in it's proper place.

That's correct. If you have a gauge, then fine. But without, it's all or nothing. At least that's what the majority seems to believe.

 

[Amish RakeFight]

You can keep the carb heat on continuously during cruise. Just lean it out.

 

[Dr Pokenhiemer]

You are correct RakeFight--same goes for higher altitude takeoffs to a certain extent. Apply carb heat, the lean the mixture to get the rise in RPM.

 

[avbug]

My, my, MTR. You're quite the five hundred hour expert.

The poster who started the thread posted because he lost his engine. Seems that he found out carb heat ought to be used, didn't he?

Carb heat is a tool. It's there to be used as needed. The assertion that it's all or nothing is an ignorant one. It's a blanket idiot statement, much like assertions regarding minimum altitudes for leaning...and operations lean of peak.

Sounds to me like you're a book warrior...probably think that ground effect is a cushion of air beneath the wing, that lean of peak operation is hotter than rich of peak, that the downwind turn doesn't exist, and that the wrights were the first in flight. Believe what you will.

As for the green arc representing anything to do with carburetor heat, it doesn't. Nor does the yellow arc, which is typically an RPM range to avoid under certain conditions due to blade harmonics.

Additionally, being in the green arc doesn't suggest the engine is driving the prop, as it doesn't take into account slipstream velocity and it's effect on the propeller. A dive at idle may place the prop well into the green arc, while clearly the wind is driving the prop and not the engine.

As for MTR's assertions regarding POH/AFM use of carburetor heat...I said nothing about ground operations, and the discussion here speaks nothing toward prolonged use of carb heat on the ground. Accordingly, your introduction of this into the discussion is an effort to cloud the issue, not contribute. Likewise, your includsion of information regarding detonation on a go-around serves nothing to address the topic.

Yes, full carburetor heat may lead to detonation at power settings above 75%...assuming the pilot is an idiot. But partial carburetor heat may not...and that's your beef here...you don't have the experience to know that it's far from always full or nothing. Have you ever used a carburetor air temp gauge? Have you ever experienced an engine failure due to carburetor icing? Have you ever operated an aircraft with each kind of carburetor installation out there, and been able to make the comparison? Have you ever had proper instruction in the use of carburetor heat?

It's a misunderstood topic, and one in which most pilots don't get proper training. That you don't understand it isn't surprising.

 

[Amish RakeFight]

Avbug brought up some common fallacies pilots have on some issues. Since he only mentioned them, I thought I'd clarify them for anyone who isnt familiar with them.

The assertion that it's all or nothing is an ignorant one. It's a blanket idiot statement, much like assertions regarding minimum altitudes for leaning

Leaning may be accompished at ANYTIME as long as the power is below 75%. While taxiing, leaning has NO effect if the throttle is at idle. At Idle, a separate fuel jet is suppling fuel to the engien and moving the mixture lever does nothing.

...probably think that ground effect is a cushion of air beneath the wing

It's a misconception that the wing is compressing air below it and allowing the wing to rest on it. When the wing is within its wingspan of the ground and more so closer than this, you will encounter a decrease in upwash, downwash and wingtip vortices. This has the effect of decreasing the induced drag generated by the wing and consequently cuts the drag associate with it. The reduction in drag allows the wing to develop a greater coefficient of lift at the same angle of attack, therby allowing this additional lift to create a "floating" over and down the runway.

that lean of peak operation is hotter than rich of peak

Sounds like a paradox, but rich of peak is hotter than lean of peak. Since rich causes more fuel to enter the cylinders for combustion, it creates higher operating temperatures. This is no different that observing engine temp rise with an RPM going from 500 to 2300. More power equals greater heat combustion translating into higher temps. At lean settings you deprive the engine of fuel and thus increase the economy. Intially, the temp will rise while leaning, but then drop down as engine is deprived of fuel. Lower temps require less additonal fuel for cooling.

Additionally, being in the green arc doesn't suggest the engine is driving the prop, as it doesn't take into account slipstream velocity and it's effect on the propeller. A dive at idle may place the prop well into the green arc, while clearly the wind is driving the prop and not the engine.

When the plane is on the ground during a runup, the tach needle goes from outside to inside of the green arc. There is no wind component turning the blade on the ground. The engine is turning the prop outside fothe arc. Not sure who told the original poster this, but the green arc has nothign to do with whether the wind or engine is turnign the prop in a constant speed propeller.

 

[Ralgha]

that the downwind turn doesn't exist

You think it does???????

 

[nosehair]

You think it does???????

Don't you??????

 

[minitour]

My, my, MTR. You're quite the five hundred hour expert.

I thought it was about experience, not hours. What ever happened to the "if you want hours, buy a good pen" (paraphrased) posts?

-mini

 

[avbug]

Sounds like his pen ran out. Buy a better pen.

 

[aucfi]

When the plane is on the ground during a runup, the tach needle goes from outside to inside of the green arc. There is no wind component turning the blade on the ground. The engine is turning the prop outside fothe arc. Not sure who told the original poster this, but the green arc has nothign to do with whether the wind or engine is turnign the prop in a constant speed propeller.

FAA's Airplane Flying Handbook Page 11-6 & 11-7

Some important points to remember concerning constant-speed propeller operation are:

• The green arc on the tachometer indicates the normal operating range. When developing power in this range, the engins drives the propeller. Below the green arc, however, it is usually the windmilling propeller that powers the engine. Prolonged operation below the green arc can be detrimental to the engine.

I am pretty sure they mean while in flight.

 

[barnyard]

Avbug, are you below average height?

 

[Amish RakeFight]

FAA's Airplane Flying Handbook Page 11-6 & 11-7

Some important points to remember concerning constant-speed propeller operation are:

• The green arc on the tachometer indicates the normal operating range. When developing power in this range, the engins drives the propeller. Below the green arc, however, it is usually the windmilling propeller that powers the engine. Prolonged operation below the green arc can be detrimental to the engine.

I am pretty sure they mean while in flight.

I learned something new. Thanks.

 

[joe_pilot]

First of all, I'm NOT getting into the mud-slinging and name calling. Please don't take this as a personal attack.

You can keep the carb heat on continuously during cruise. Just lean it out.

I don't like this because what happens if you do get carb ice? Now what do you do? It would be tough but still possible to get carb ice with the heat on, but it takes away an option. All of my flying with carbureted engines has been in TX, OK, CA and PA not in high lattitudes. All of my friends and students who flew in Alaska said they would never leave carb heat on all the time unless there were severe conditions and they were in the process of landing.

My $.02.

-JP