Carb Heat

[WhatItTakes]

The R22's operating book lists visible moisture when detailing conditions for carb ice. There are certain things to be done under these conditions. Do you do these only when actually flying through visible moisture, or even whilst in dry air with clouds/rain ect about?

[Charbuque]

If you are ever uncertain put the carb heat on anyway - it doesn't hurt anything.

[Hello Pilots]

If you are ever uncertain put the carb heat on anyway - it doesn't hurt anything.

Can only lead to detonation......absolutely nothing to worry about there!!

[Robinsondog]

The visible moisture is hopefully above you with the clouds, at and above dew point. you can easily induce dew point in your carby by lowering the atmospheric pressure there, which is what happens. Always check carby air temp prior to take off and especially prior to decreasing power after take off.

I.E. My post take off check list.

1. Take off safety climb speed - check,
2. Cross check, altimeter increasing against VSI, climb established - check
3. Carby air temp safe range, - check,
4. Safe to reduce power to max continuous or desired climb power, - check

If in F/W then I would, 5. Raise wheels. - trim.

[bman]

Can only lead to detonation......absolutely nothing to worry about there!!

????? Please explain, I would love to know how it can lead to detonation

[harold]

Hello Pilots...what a load of....maybe on a 40 degree C day pulling max power for 20 minutes but otherwise,

[Hello Pilots]

From a manufacturer
"Consistently high temperatures are to be avoided because of a loss of power and a decided variation of mixture. High charge temperatures also favor detonation and preignition, both of which are to be avoided if normal service life is to be expected from the engine"
http://www.lycoming.com/support/publica ... I1148C.pdf

[ring gear]

If I remember correctly,
The manual says to keep the CHT needle out of the yellow, and I would of thought clouds are visible moisture ???
Also not a silly idea to apply a little carb heat before pulling out of a confined area if you've been idling for a while. (push in for take off obviously).

My 2 Bob's worth.

RG

[cassidy_copter]

Icing Conditions:

-10 to +10 degrees Celsius, Visible Moisture, less than 2 miles visibility. It is possible for carburettor ice to form in high ambient temperature, high humidity and clear sky.

However, the carburettor can form ice in the throat, especially during low power settings.

Due to the venturi effect and concomitant lower pressure, plus additional cooling due to fuel being vaporised, carburettor ice will form.

If there is any water in the fuel, ice will also form.



Some good information:
http://www.aopa.org/asf/publications/SB09.pdf

[muppet]

push in for take off obviously

Why's that Ring Gear? You operating near FTH? HINT: I am opening a can of academic worms regarding Carb Heat application. (but won't comment further yet cos can't recall last time I flew a piston...) The question is: Does applying carb heat really cause you any problem for take-off?????

[robbiedan]

2 cents from someone who's only flown piston. R22's (beta 2 engine) don't mind carby heat on a cool day with pilot only - takeoff or otherwise. Anything above 30 degrees, full fuel, both seats occupied and there is a noticeable power loss. R44 (raven 1) is similar but will let you get closer to MTOW before it starts complaining.

Important note is the in an R22 carby heat should only ever be applied in full or not applied. In an R44 you can apply an amount of heat to stay out of the "yellow ". The difference is due to the position of the temperature sensor in the carby - nice design consistency Frank!

Both R22 and R44 (except astro and alpha) have a lock on the carby heat lever. When unlocked the carby heat is linked to the collective by a friction thing. Collective down (below 18" MAP) then carby heat comes on but won't come off when collective comes up.

Never experienced precognition or detonation with 'inappropriate' carby heat addition but have noticed a bit of a power loss at times. Had it on startup on a 45 degree day - carby heat off at the time. Power loss primarily due to less air mass flow into engine - in my opinion.

If in doubt fly a raven 2 - fuel injected, no carby heat required.

[fly123]

If you read safety notice 25 that actually says you should use some carb heat during takeoff.

I've just done the Robinson Safety Course with Tim Tucker who is Robinson's chief flight instructor and he said that we should use carb heat on take off. The reason he said was that the temperature will increase by pulling on carb heat therefore your manifold pressure limit will also increase. Now i know that the manifold limit is taken from the OAT, but if you think about it, that air is then being heated by the carb heat which is stopping the carb ice, but is also going into the engine at a warmer temperature.

As for using carb heat in cloud, if there is a lot of cloud around and if you know that the dew point and temperature is close together, use the carb heat and make sure the needle is out of the yellow. Even if you weren't flying through the rain, I would still use it just encase. And i agree with Charbuque, i think there would have been far more helicopter crashes due to carb heat not being used than detonation...?

[AussiePride]

Carby Heat causing detonation????? Correct me if I am wrong but application of Carby Heat increases the temperature of the air being induced into the cylinder and hence decreases the pressure (or amount of air molecules) present in the charge. Detonation or pre ignition occurs upon leaning of the mixture as it takes longer for the charge to burn creating higher CHT. This therefore meaning if the fuel flow remains unchanged and Carby heat is applied the charge will become richer and a decrease MAP will be noted. I would think detonation would be the last of your worries.

[harold]

Hello Pilots....The Defence Rests......

"Consistently high temperatures are to be avoided...........

There have been far more accidents/engine failures/deaths caused by carburettor icing than detonation in helicopters! Now with the use of governors the problem for the inexperienced can actually be 'masked' by the governor (a phenomenom known as Automative Dependency where we fail to recognise the problem onset or expect the technology to fix the problem). In the event of detonation, simply reduce the amount of carby heat being used and the problem is fixed.....detonation takes time to have a detrimental effect on an engine (minutes) whilst carby icing can bring a machine to a complete engine failure with little to no warning!

[100ft]

Piston engines, needlessly complicated.

[kiwiflyer]

Detonation I wouldn't be worried about. Carb heats not going to cause it.

The lack of power due to carb heat being used inappropriatly I would be worried about.
It's about an inch to an inch and a half of manifold pressure.
In winter I will do the run up etc with full carb heat do the carb heat test backwards( ie push it off and the watch the carb heat gauge drop) then when ready for take off push the carb heat away and then adjust it in flight after a few hundred feet and the power req reduces.
Same on landing carb heat full away after 200 ft ice will not form in a few seconds that the butterfly may not be full open and the chances that you will need that extra inch or so of manifold pressure are a lot higher than carb icing.
We have always used partial amounts of carb heat here in NZ and has worked for a lot of people for a long time but Snds like its wrong , the things you learn.
I think a lot of people overcook the carb icing thing there is a gauge to look at and a window to look out off.
But I guess if you are not sure pull it on as there's been a few accidents due carb icing.
Personally I would still not be using carb on take off or landing

[Baby Ag Flyer]

Hey Guys.

Just completed the Factory safety awareness training (for foreigners as RHC puts it). Quite a discussion on carb heat. RHC & Tim Tuckers take on it is that due to the de-rating process on the engine (131 Hp 5 minutes/124 Hp MCP), carb heat application has no bearing on power loss as long as the MAP limits are calculated using the temperature on the CAT gauge instead of the OAT. Which makes sense as power available is proportional to the temperature entering the cylinders as opposed to OAT. HOWEVER, you will experince a power available loss at or near full throttle height when using carb heat due to the throttle butterfly being fully open and only able to produce 131 Hp maximum in the ambient conditions. If the density of the air entering the carby is decreased due to the application of carb heat, power available will also decrease. (Less tham 131 Hp available). It takes the same amount of horsepower to maintain hover height regardless if Carb heat is on or not. During the flying stage of safety awareness training, Tim set the carb heat out about 1 inch and didn't touch for the next hour even though we spent 90% of that time in autorotation with no problems. Still advocate proper use of carb heat though. Keep it out of the yellow, and full on below 18" MAP.

Just my 2 cents worth. Really good thread and comments. Just want to say if any of you get the chance to attend the factory safety awareness course with Tim Tucker then I strongly recommend it. I found it to be really informative as both a commercial pilot and LAME.

Cheers

[Tony Carmody]

My two bobs worth:

http://brumbyhelicopters.com.au/carbheat.htm

and

http://brumbyhelicopters.com.au/r22engine.htm

Tc

[Tony Carmody]

missed one:

http://brumbyhelicopters.com.au/Rotax912uls.htm

Tc