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HeliTorque :: View topic - Carb Icing
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HeliTorque Forum Index » Flight Dynamics

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WhirlyGirl
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PostPosted: Sun Feb 15, 2009 10:28 pm    Post subject: Reply with quote

Heliwhore wrote:
No no, it's true. You can even take your hand off the cyclic if you have enough friction on it as well. At times like that, I like to put a brick on the pedals. Rolling Eyes


Laughing Laughing

Now I bet you're going to tell me you've let down into a field, put the frictions on rotors running and gone to take a pee behind a bush!

Sarah
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PostPosted: Sun Feb 15, 2009 10:28 pm    Post subject: Reply with quote

Does anyone have a cockpit picture of the R66, would like to see their instrument layout/types.
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PostPosted: Sun Feb 15, 2009 10:29 pm    Post subject: Reply with quote

WhirlyGirl wrote:
He has recommended that RHC redesign their MAP limit chart based taking into account the carb temperature as opposed to simply calculating it on OAT. Sarah


Sarah,

Does the Robinson have the same limitation on the CAT gauge as does Schweizer 300s.....that it is unreliable below 18' mp?

This could be reason not to base the MAP limit chart on CAT rather than OAT.

Just a thought.

AB
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PostPosted: Sun Feb 15, 2009 10:37 pm    Post subject: Reply with quote

Quote:
Now I bet you're going to tell me you've let down into a field, put the frictions on rotors running and gone to take a pee behind a bush!

Sarah


I actually do know someone who did that.. except his was a no.2 at the Santa Fe dam. Sure Lars will even remember the student's name Smile

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PostPosted: Sun Feb 15, 2009 10:37 pm    Post subject: Reply with quote

R66... sadly not. Haven't seen it in action yet.

To respond to whoever asked about why I might be pulling close to max MAP in the hover, it's not that difficult in a Beta if you're teaching hovering and the stude inadvertently goes a bit heavy on his left boot. I'm only a modest 130lb - I can take full fuel with many of my students and still be well within weight and CofG limits (not that I tend to fill it up to the brim for training), but even with only the main tank full it can on occasions get close to that limit.

Sarah
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PostPosted: Sun Feb 15, 2009 10:42 pm    Post subject: Reply with quote

afterburner wrote:
Does the Robinson have the same limitation on the CAT gauge as does Schweizer 300s.....that it is unreliable below 18' mp?

This could be reason not to base the MAP limit chart on CAT rather than OAT.


Yes is is unreliable below 18", but I suspect that even on the "new" placard, if it ever does come out I imagine the rule of full carb heat below 18"MAP will still apply.

In the R22 the position of the sensor is not in a good place in relation to the throttle butterfly which adds to the unreliability.

Another tip... if you don't already do so, make checking the carb gauge reading part of your A-Check. Before the first flight of the day it should read the same as OAT. If it reads significantly higher then your reading once the engine is running probably won't be accurate and you may think you're out of the yellow band when you're actually not.

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PostPosted: Sun Feb 15, 2009 10:57 pm    Post subject: Reply with quote

WhirlyGirl wrote:
Another tip... if you don't already do so, make checking the carb gauge reading part of your A-Check. Before the first flight of the day it should read the same as OAT. If it reads significantly higher then your reading once the engine is running probably won't be accurate and you may think you're out of the yellow band when you're actually not.Sarah


Good suggestion for all carb engine helicopters with CAT gauges.
(One of the reasons I only fly the fuel injected models Laughing )

Thanks Whirlygirl.

AB
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PostPosted: Sun Feb 15, 2009 11:32 pm    Post subject: Reply with quote

i found this

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

quite interesting if not applicable
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PostPosted: Sun Feb 15, 2009 11:38 pm    Post subject: Reply with quote

I think it is very appropriate and puts things in simple terms.
Added another safety tip to my repertoire.

Good article.
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PostPosted: Sun Feb 15, 2009 11:40 pm    Post subject: Reply with quote

The "below 18" MAP" restriction is due to a large pressure differential (and therefor temperature) over the throttle butterfly when at a low power setting. The carb temp sensor is only taking the temp from one side of the butterfly where it is maybe all hunky dorey, however ice may be forming on the opposite side.

This was brought in to force after two R22's both suffered engine failures due to icing when recovering from autorotation in the US.

First one occured, EOL in to field. FI contacted his school and the CFI flew out to the site in another R22, for convenience and time saving he conducted an auto to the same field, upon power recovery the engine stopped, again due to icing.

Both pilots has simply been maintaining carb temp out of the yellow band during the auto.

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PostPosted: Sun Feb 15, 2009 11:49 pm    Post subject: Reply with quote

yeh we looked at that on the robinson safety course - not a problem on the R44 as the temp sensor is other side of the valve Very Happy
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PostPosted: Mon Feb 16, 2009 12:10 am    Post subject: Reply with quote

HaggisHunter wrote:
the CFI flew out to the site in another R22, for convenience and time saving he conducted an auto to the same field, upon power recovery the engine stopped, again due to icing.


For convenience and time saving! Your kidding, right? Why would you want to intentionally conduct an auto into a field, unless you are training. Wouldn't a steep approach/confined area approach profile due? and be a safer way to conduct the operation?

I don't think that was a very wise decision on the part of the FI , especially as it turned out. He thought power would be available on the recovery. Surprise! He is lucky he did not slam into the ground.

or am I not understanding the post (again. Laughing )

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PostPosted: Mon Feb 16, 2009 12:42 pm    Post subject: CAT during 'A' check Reply with quote

I've been taught to look at the CAT during my 'A' check, I even thought about snagging the A/C the other week...

Outside Air Temp Gauge reading 2C
CAT reading 30C

Now I know it should be reading 2C or somewhere very close... I was all for ringing my instructor back in the office when it dawned on me, when was the A/C last flown?

Yup - I'd cracked it by the time I'd opened the cowlings... The engine was still hot from the previous flight hrs before and the carb had heat soaked to the engine block temp!

I continued with the start and watched the CAT shoot downward before the warmth of carb heat raised it back up.

Moral of the story is not to always believe what you see on first inspection - verify with another source if possible.

Jeff Hall
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PostPosted: Mon Feb 16, 2009 1:03 pm    Post subject: Reply with quote

Jeff,

Funnily enough just posted this in Check A thread! Tech log is always a good source of info as to when it was last flown.

Sarah
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PostPosted: Sat Sep 12, 2009 9:55 am    Post subject: Reply with quote

The CAA AIC relating to Carb ice has just been redone

http://www.nats-uk.ead-it.com/aip/current/aic/pink/EG_Circ_2009_P_077_en.pdf
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