Helicopter Urban Myths
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From the propulsion support group:
The limitation placed upon the engine is a combination of the effects of cooling, mass airflow and fuel burn. These effects are different dependant upon whichever turbine we are talking about. A turbine requiring a large cooling factor, generally the older turbines will react badly in a hot environment due to the restrictive cooling and the restrictive throttle. A more modern engine with less cooling requirements will perform poorly with a greater emphasis placed on the restrictive throttle position caused by reduced the thermal expansion range.
SO! After a long and labourious thread it would seem that there is no winner or loser. The system reacts slightly differently dependant upon the aircraft, engine fit and age. Some aircraft, generally the older, respond poorly to cooling, hence not reaching their torque limits before the temperature. Others, with more efficient cooling systems reach the limit by running out of 'combustion space'.
It is a broad range of aircraft, situations and scenarios that we have and to flame someone for looking from a different view point as having no knowledge is a dangerous thing. There are very few 'black and white' situations in our profession.
Nick, thanks at the end I can see it from your point of view as well as my own and after flying the S-61 for too many years I have also learnt that there are other factors out there. The performance and limitations that I use have served me well in ops around the globe and I will continue to use them but I will also now include your theorys as well. It is interesting to see that a quick canvas of opinions at work resulted in 1. Blank looks, 2. Arguments for both ideas.
So..... Thanks all, I'll wait to see what comes up.
The limitation placed upon the engine is a combination of the effects of cooling, mass airflow and fuel burn. These effects are different dependant upon whichever turbine we are talking about. A turbine requiring a large cooling factor, generally the older turbines will react badly in a hot environment due to the restrictive cooling and the restrictive throttle. A more modern engine with less cooling requirements will perform poorly with a greater emphasis placed on the restrictive throttle position caused by reduced the thermal expansion range.
SO! After a long and labourious thread it would seem that there is no winner or loser. The system reacts slightly differently dependant upon the aircraft, engine fit and age. Some aircraft, generally the older, respond poorly to cooling, hence not reaching their torque limits before the temperature. Others, with more efficient cooling systems reach the limit by running out of 'combustion space'.
It is a broad range of aircraft, situations and scenarios that we have and to flame someone for looking from a different view point as having no knowledge is a dangerous thing. There are very few 'black and white' situations in our profession.
Nick, thanks at the end I can see it from your point of view as well as my own and after flying the S-61 for too many years I have also learnt that there are other factors out there. The performance and limitations that I use have served me well in ops around the globe and I will continue to use them but I will also now include your theorys as well. It is interesting to see that a quick canvas of opinions at work resulted in 1. Blank looks, 2. Arguments for both ideas.
So..... Thanks all, I'll wait to see what comes up.
SASles: Ah, but it must be a true story as it's in colour!
Paul:
"Gas turbines work well in cold temperatures because the Torque limitations are reached first"
Now you've really lost the plot.
Paul:
"Gas turbines work well in cold temperatures because the Torque limitations are reached first"
Now you've really lost the plot.
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Paul
'Unhinged? don't think so look at a video from Rolls Royce doing a PPI check on a gas turbine and watch it glow white!'
This made me chuckle somewhat? Okay Unhinged was a bit strong...sorry. It's been a very interesting debate though.
As a final if somewhat moot point. I've no need to watch videos of Rolls Royce engines since I worked on making enough of them during my apprenticeship not to mention much larger gas turbine and nuclear reactor chambers. Try going beyond white hot - to a point where the castings become so translucent that you can literally see through them!
This is real enginering - practice meeting science!
'Unhinged? don't think so look at a video from Rolls Royce doing a PPI check on a gas turbine and watch it glow white!'
This made me chuckle somewhat? Okay Unhinged was a bit strong...sorry. It's been a very interesting debate though.
As a final if somewhat moot point. I've no need to watch videos of Rolls Royce engines since I worked on making enough of them during my apprenticeship not to mention much larger gas turbine and nuclear reactor chambers. Try going beyond white hot - to a point where the castings become so translucent that you can literally see through them!
This is real enginering - practice meeting science!
212man....
Does that mean things that are Black and White are not necessarily true? We must colour our perceptions to see reality?
Oh dear....back to watching the freight trains roll by.
Does that mean things that are Black and White are not necessarily true? We must colour our perceptions to see reality?
Oh dear....back to watching the freight trains roll by.
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Paul said:
p.s. on the afterburner thingy look at the back of most military aircraft and you'll see a moveable shroud. This reduces the cross section of the afterburning exhaust output to increase the available thrust.
WHAT!
After an excellent landing you can use the airplane again!
p.s. on the afterburner thingy look at the back of most military aircraft and you'll see a moveable shroud. This reduces the cross section of the afterburning exhaust output to increase the available thrust.
WHAT!
After an excellent landing you can use the airplane again!
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R1 Tamer, thanks
I found it fun as well!
SASless, wasn't the whole world black and white before they invented colour?
Flash, ahhh, then convergent duct to increase thrust, think I mentioned that.
Thanks all.
I found it fun as well!
SASless, wasn't the whole world black and white before they invented colour?
Flash, ahhh, then convergent duct to increase thrust, think I mentioned that.
Thanks all.
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These statements are true:
Turbine maximum engine power output can be accurately told by using pressure altitude and outside air temperature.
Turbine engine maximum power varies greatly if operated at identical density altitude, but at variable outside air temperature.
Turbine maximum engine power output can be accurately told by using pressure altitude and outside air temperature.
Turbine engine maximum power varies greatly if operated at identical density altitude, but at variable outside air temperature.
Well if we are going to start taking off downwind now we might as well begin learning our downwind auto's as well.
We would be able to relate to the fixed wing boys as well....
Powered pedal turning: super idea. Start doing the RH pedal turns lads and see how long you last. Like it was said, you can push in all the RH pedal you want but can you stop it? Very imperitive that you understand the concept for operations in bush and remote areas or at altitude.
Get ready to write an overtorque report.
We would be able to relate to the fixed wing boys as well....
Powered pedal turning: super idea. Start doing the RH pedal turns lads and see how long you last. Like it was said, you can push in all the RH pedal you want but can you stop it? Very imperitive that you understand the concept for operations in bush and remote areas or at altitude.
Get ready to write an overtorque report.
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Steve76,
You are right mostly, and sometimes not. The aircraft will not fall out of the sky if you take off downwind, and it can be perfectly safe. In fact, it can be perfectly safe to take off vertically, and tell the wind that you just don't care. Lots depend on the power margins and options available. I think our military brothers who fly attack helos or medevac can relate to those times when hovering downwind and shooting, or landing downwind and pcking up injured was the only way to do the job.
The idea behind this "urban myths" thread was to spark the value judgments that allow us to discuss these optons, and open the debate where the maneuver envelope of the helicopter is understood, and used when necessary.
You are right mostly, and sometimes not. The aircraft will not fall out of the sky if you take off downwind, and it can be perfectly safe. In fact, it can be perfectly safe to take off vertically, and tell the wind that you just don't care. Lots depend on the power margins and options available. I think our military brothers who fly attack helos or medevac can relate to those times when hovering downwind and shooting, or landing downwind and pcking up injured was the only way to do the job.
The idea behind this "urban myths" thread was to spark the value judgments that allow us to discuss these optons, and open the debate where the maneuver envelope of the helicopter is understood, and used when necessary.
Landing downwind is no problem....have done thousands of them...a few intentionally. The planned ones always seemed to work out much better than the impromptu version. Tail wag on the impromptu method seems to be common but missing on the planned. Torque consumption seems to increase on the downwind landing vice into to wind variants of the technique.
Torque deviations always seem to be more prevalent when doing faster...flatter approaches rather than the steeper, slower approaches.
From my experience flying offshore with pilots from both sides of the green pond....our Gomer buddies faint at steep approaches whereas our tea drinking compadres panic at Gomer style flat approaches.
Wonder why there is such variation in making a landing to an elevated deck in the same type aircraft such as the Bell 212?
Lets add one more myth....QFE altimeter settings are more accurate than QNH altimeter settings. Particularly for use around and aerodrome (think airport for you Rednecks out there).
Torque deviations always seem to be more prevalent when doing faster...flatter approaches rather than the steeper, slower approaches.
From my experience flying offshore with pilots from both sides of the green pond....our Gomer buddies faint at steep approaches whereas our tea drinking compadres panic at Gomer style flat approaches.
Wonder why there is such variation in making a landing to an elevated deck in the same type aircraft such as the Bell 212?
Lets add one more myth....QFE altimeter settings are more accurate than QNH altimeter settings. Particularly for use around and aerodrome (think airport for you Rednecks out there).
Avoid imitations
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Jellycopter,
Pse check PMs.
Pse check PMs.
Lets add one more myth....QFE altimeter settings are more accurate than QNH
Gentleman Aviator
quote:
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Lets add one more myth....QFE altimeter settings are more accurate than QNH
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If it's an airfield QNH, then there should be no difference in accuracy, but a regional QNH is a forecast figure, so only as accurate as the Metman.
And of course the accuracy of the altimeter is (presumably) optimised for "normal" figures. So using QFE at Nairobi (if you could dial it up) probably wouldn't be terribly accurate. - Just guessing on the latter point though...
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Lets add one more myth....QFE altimeter settings are more accurate than QNH
--------------------------------------------------------------------------------
If it's an airfield QNH, then there should be no difference in accuracy, but a regional QNH is a forecast figure, so only as accurate as the Metman.
And of course the accuracy of the altimeter is (presumably) optimised for "normal" figures. So using QFE at Nairobi (if you could dial it up) probably wouldn't be terribly accurate. - Just guessing on the latter point though...
Forecast Regional QNH? Fly around using an altimeter setting based upon some boffin's best guess? Why not use an altimeter setting for an airfield nearest your location , say within 100nm's? Would that not give a more accurate setting than a mere guess?
Avoid imitations
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SASless,
I prefer to use a local airfield QNH whenever possible as it is measured / calculated rather than estimated / forecast.
However, in UK it is allowable to fly IFR below TA on an airfield QNH ONLY up to 25 nms from the source, it's not up to personal choice.
Outside that, the regional QNH is a forecast supplied to ensure that a pilot doesn't come to grief with regard to MSA.
If flying beneath (or over) controlled airspace, then obviously one should obtain the actual QNH to make sure an altitude bust doesn't occur....
BTW, incorrect altimetry is the most common cause of a failure in the CAA IR test.
I prefer to use a local airfield QNH whenever possible as it is measured / calculated rather than estimated / forecast.
However, in UK it is allowable to fly IFR below TA on an airfield QNH ONLY up to 25 nms from the source, it's not up to personal choice.
Outside that, the regional QNH is a forecast supplied to ensure that a pilot doesn't come to grief with regard to MSA.
If flying beneath (or over) controlled airspace, then obviously one should obtain the actual QNH to make sure an altitude bust doesn't occur....
BTW, incorrect altimetry is the most common cause of a failure in the CAA IR test.
FWIW, in some parts of the globe (Australia being one) QFE is almost unheard of. All our altimetry is based on QNH, be it airfield, forecast or area.