Pitot heat
Thread Starter
Joined: Apr 2002
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From: Hartford, CT USA
Pitot heat
Hello all, a question came up in a recent ground school with my intructor. We were discussing pitot icing and I asked if having the pitot heat on affected the inst. readings at all. He said that he wasnt sure but at the speed most helicopters are operating he didnt think it was an issue.
Although most of the CFI's at the school agreed few had any actual experience flying IFR. So is anybody aware of the effects of pitot heat on IAS readings?
Thanks
Although most of the CFI's at the school agreed few had any actual experience flying IFR. So is anybody aware of the effects of pitot heat on IAS readings?
Thanks
Approx 10 degrees on S76A+ sby compass.
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
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From: EGDC
One thing is certain though - if you are flying in icing conditions with the pitot heater off it definitely affects your ASI reading!!
SODPUD is the mnemonic for ASI over/underread with pitot/static blockage. Static Overreads in Descent - Pitot Underreads in Descent.
SODPUD is the mnemonic for ASI over/underread with pitot/static blockage. Static Overreads in Descent - Pitot Underreads in Descent.
Gatvol
Joined: Jun 2000
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From: KLAS/TIST/FAJS/KFAI
It will also affect one if exiting the aircraft and touching it right after flight. Easy to do in helicopters, most difficult in a 747..
Bell products usually never on unless needed, Eurocopters, just the opposite.
Bell products usually never on unless needed, Eurocopters, just the opposite.
Joined: Jul 1999
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From: UK
B Sousa - now you mention it why do Aerospat flight manuals ask for the Pitot heat to be on all the time? Maybe to save burning out the warning light bulb on the Caution panel?
Another thing - why do so many pilots put their Nav lights on in daylight? The bulb manufacturers must love it and think of the waste of electricity!
Another thing - why do so many pilots put their Nav lights on in daylight? The bulb manufacturers must love it and think of the waste of electricity!
Gatvol
Joined: Jun 2000
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From: KLAS/TIST/FAJS/KFAI
MBJ
Without doing any french bashing here( In fear of banishment to New Zealand.) I think you will find that at least the A-Star is allowed to fly into a certain amount of Snow. Therefore instead of two things to concentrate on (one being why the hell should you fly a helicopter into Snow) and (second remembering to turn on the Pitot Heat ) They just say leave it on. And your right it also cleans up the Light Panel.....
Lights on in daytime is a Male thing. It makes the helicopter stand out a bit more with all those flashes, girls like that. And they dont have to remember to turn them on at night, thus no requirement to know official sunset OR sunrise.
We now have Pulse Lights, another extension for visibility. I just cant wait to turn my Pulse Lights on before takeoff.
Im just having too much fun flying.
Without doing any french bashing here( In fear of banishment to New Zealand.) I think you will find that at least the A-Star is allowed to fly into a certain amount of Snow. Therefore instead of two things to concentrate on (one being why the hell should you fly a helicopter into Snow) and (second remembering to turn on the Pitot Heat ) They just say leave it on. And your right it also cleans up the Light Panel.....
Lights on in daytime is a Male thing. It makes the helicopter stand out a bit more with all those flashes, girls like that. And they dont have to remember to turn them on at night, thus no requirement to know official sunset OR sunrise.
We now have Pulse Lights, another extension for visibility. I just cant wait to turn my Pulse Lights on before takeoff.
Im just having too much fun flying.
Joined: Dec 2001
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From: Philadelphia PA
Personally, I like the 'pitot heat on all the time' method. The system will tell you if the pitot heat has failed, something you would want to know if you fly in colder climates, or even wet climates.
Why we don't have pitot heat on all the time in other machines would be the better question.
Why we don't have pitot heat on all the time in other machines would be the better question.
Gatvol
Joined: Jun 2000
Posts: 4,197
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From: KLAS/TIST/FAJS/KFAI
Good point Shawn. I can say for a fact that I have frozen my butt off flying a Huey onto Straw Peak to re-supply the Air Force. Thats a stones throw away from where your located in the Mojave Desert......
Thread Starter
Joined: Apr 2002
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From: Hartford, CT USA
I remember reading a discussion somewhere where a pilot suggested leaving the pitot heat off, especially if you thought you might be flying in an area of icing. That way when you got the pitot icing you could turn on the heat and do a 180. What do you guys think? Would the water/vapor from the ice effect the funtioning of your instruments? Also how hot do they get exactly?
Joined: Feb 2003
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From: Harwich
Let me show my ignorance here - don't you turn on the flashing lights before rotor start, to let everyone close by know that you ARE going to start the rotor? Similarly, they don't go off until the blades have stopped? Or am I confusing beacon / nav lights / strobes / discotheques? That's a question for B Sousa, above.
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From: uk
PITOT HEAT.......The Pitot Head is so positioned to enable dynamic pressure to show Indicated Air Speed. It does this by pressure variation within the instrument, the faster the greater pressure the higher IAS. Slowing down will reverse the effect.
Pitot heat is provided to ensure that the air within the pipes/instrument is unhampered by the restricyion that will result should icing occur. Static pressure port is either part of the Pitot Head or as a separate port elsewhere.
The pitot heat generally is unlikely to heat up all of the trapped air which is within the system and therefore unlikely to have any 'mechanical' effect upon the IAS reading. There are other effects which will effect the rading. Flying out of ballance, whether climbing or descending, accellerating or deaccellerating.
In your Flight Manual, in the Performance Section there will be a Airspeed Calibration Curve (level flight) chart which shows the relationship between IAS and Calibrated Airspeed(CAS). IAS corrected for position error equals CAS.
To my knowledge there are no charts or data for helicopters below 2835kg AUM which suggests that pitot heat has an effect in IAS.
Pitot heat is provided to ensure that the air within the pipes/instrument is unhampered by the restricyion that will result should icing occur. Static pressure port is either part of the Pitot Head or as a separate port elsewhere.
The pitot heat generally is unlikely to heat up all of the trapped air which is within the system and therefore unlikely to have any 'mechanical' effect upon the IAS reading. There are other effects which will effect the rading. Flying out of ballance, whether climbing or descending, accellerating or deaccellerating.
In your Flight Manual, in the Performance Section there will be a Airspeed Calibration Curve (level flight) chart which shows the relationship between IAS and Calibrated Airspeed(CAS). IAS corrected for position error equals CAS.
To my knowledge there are no charts or data for helicopters below 2835kg AUM which suggests that pitot heat has an effect in IAS.
Joined: Jun 2002
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From: home and abroad
MBJ,
considering the sudden swing that affects the sby compass on the S76 when the pitot heat is switched on, I presume that having them on at all times like on French helicopters makes it easier to callibrate the sby compass.
About nav lights, at my school I was taught that nav lights on when stationary indicated that the cockpit was manned so engines could be started any second. Strobes indicate (imminent) rotation of parts, but may fail and then the nav lights provide some redundancy.
As I don't have to pay for the bulbs, why not switch them on?
considering the sudden swing that affects the sby compass on the S76 when the pitot heat is switched on, I presume that having them on at all times like on French helicopters makes it easier to callibrate the sby compass.
About nav lights, at my school I was taught that nav lights on when stationary indicated that the cockpit was manned so engines could be started any second. Strobes indicate (imminent) rotation of parts, but may fail and then the nav lights provide some redundancy.
As I don't have to pay for the bulbs, why not switch them on?
Guest
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Pitot heat exists, of course, to keep ice off the probe, since this ice would disrupt the shape of the lip (or block it entirely) and make airspeed indications very inaccurate, or reduce airspeed to zero, and then increase it as the aircraft climbs above the altitude where the pitot plugged.
The heated air trapped in an otherwise properly functioning pitot would not have any affect on the airspeed reading. The air itself would be a bit less dense, because it is hot, but it is being packed into that tube by the same dynamic pressure from the airspeed, so it will read exactly the same speed as if it were cool.
The compass swings in many aircraft (those with dc electric pitot heat) because the significant amperage it draws changes the cockpit's magnetic field, and the compass is a fine field indicator.
The heated air trapped in an otherwise properly functioning pitot would not have any affect on the airspeed reading. The air itself would be a bit less dense, because it is hot, but it is being packed into that tube by the same dynamic pressure from the airspeed, so it will read exactly the same speed as if it were cool.
The compass swings in many aircraft (those with dc electric pitot heat) because the significant amperage it draws changes the cockpit's magnetic field, and the compass is a fine field indicator.
Joined: Jul 1999
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From: UK
Barannfin
You asked how hot they get? Well in Indonesia we used to have an Engineer who would stand by the nose of our Puma, which had two pitot tubes at a convenient height for him hang on to while starting up.
In a spirit of curiosity, and also because I didn't want him hanging on, I switched the heaters on. 4 second time lag - then a very agitated engineer clapping his hands in his armpits, while pilots wet themselves!
S76Heavy
You're quite right - I was really thinking day VFR, ISA + 20 when I made my comments!
You asked how hot they get? Well in Indonesia we used to have an Engineer who would stand by the nose of our Puma, which had two pitot tubes at a convenient height for him hang on to while starting up.
In a spirit of curiosity, and also because I didn't want him hanging on, I switched the heaters on. 4 second time lag - then a very agitated engineer clapping his hands in his armpits, while pilots wet themselves!
S76Heavy
You're quite right - I was really thinking day VFR, ISA + 20 when I made my comments!
