Helicopter Urban Myths
The question is badly phrased in that 'winds affect the power we require.......' - to do what?
Any movement of air in relation to the disc will alter the relationship of IF/RAF and therefore the maximum potential of lift will also be affected corresponding to that and pilot induced variations. So you will only need more power if you are trying to maintain datums precisely. This of course assumes W/V is constant in value and origin and it never will be. So the answer is NO.
Any movement of air in relation to the disc will alter the relationship of IF/RAF and therefore the maximum potential of lift will also be affected corresponding to that and pilot induced variations. So you will only need more power if you are trying to maintain datums precisely. This of course assumes W/V is constant in value and origin and it never will be. So the answer is NO.
Well done, 'Ace'. The answer to most of the statements (if there is actually an 'answer') is 'NO'. They are myths, ie NOT TRUE.Well, yes MSP, that is obviously the exception that proves the rule. But for Davy's sake (considering that he's got a couple of hours training under his belt and is currently getting his answers from Wagtendonk), being at 30kts and 300ft RoD will not get you into VRS.
sunnywa -
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Outstanding. LOL.
I thought 12 - 'midnight stagger' - was actually an inverse square law. The ability to get where you want to stagger is adversely affected (inverse) by the square of the number of beers consumed. This in turn is affected by the gyroscopic progression described but which can act at any angle both in a vertical and horizontal plane.
I thought 12 - 'midnight stagger' - was actually an inverse square law. The ability to get where you want to stagger is adversely affected (inverse) by the square of the number of beers consumed. This in turn is affected by the gyroscopic progression described but which can act at any angle both in a vertical and horizontal plane.
Damn, looks like I got most these questions wrong... now dont anybody tell the ol bovines that or they may think I dont know how to fly and decide to ignore me buzzing over head. 
Nick,
You forgot to mention the 'low-skid-in-hover-due-to-the-main-rotor-and-T/R-not-being-on-the-same-plane'. You raised up that one a while ago. I will keep believing it until otherwise demonstrated.
point #3: in Utopia, considering the rotor only with nothing underneath, no, the wind direction does not influence the required power. In reality try to maintain hover with a 30 Kt crosswind and then look at the engine parameters.
Another one that woud be worth discussing is the pitch down attitude when entering auto. Many think it's the airstream pushing up the horizontal stabilizer.
Cheers
ATN
You forgot to mention the 'low-skid-in-hover-due-to-the-main-rotor-and-T/R-not-being-on-the-same-plane'. You raised up that one a while ago. I will keep believing it until otherwise demonstrated.
point #3: in Utopia, considering the rotor only with nothing underneath, no, the wind direction does not influence the required power. In reality try to maintain hover with a 30 Kt crosswind and then look at the engine parameters.
Another one that woud be worth discussing is the pitch down attitude when entering auto. Many think it's the airstream pushing up the horizontal stabilizer.
Cheers
ATN
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manfromuncle,
You could simplify No. 13 to ' With a new CPL and low hours your chances of getting any job are good'
Or my all time 'favourite' from some flying schools ' With 2000+ hours TT in a Robbo you are at a stage where the industry feels any job would be open to you'
When what they really mean is ' We'd love to sell you an FI course'
You could simplify No. 13 to ' With a new CPL and low hours your chances of getting any job are good'
Or my all time 'favourite' from some flying schools ' With 2000+ hours TT in a Robbo you are at a stage where the industry feels any job would be open to you'
When what they really mean is ' We'd love to sell you an FI course'
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I had the pleasure of meeting Bell man OK Moore in the early nineties. What he said in conversation was "We've been flying around in single-engined helicopters for forty years and suddenly they're dangerous!"
Found the piece below in my archives regarding Singles and Twins, just to add to the mix!! It was written in 1994. The Tables didn't paste in as saved, I hope they make sense.
************************************************************ ********
There are two important studies in the matter, both carried out by Bell Helicopter over the last 24 years.
The first considered the number of fatal accidents involving Bell helicopters during the period January 1970 to March 1987. The survey covered 19,700 single turbine and 1,800 twin turbine helicopters supplied to both military and civil customers and divided the causes of fatal accidents into three categories of Accident Initiator. They were, Engine Material Failure, Non-Engine Material Failure and Non-Material Failure (Pilot Error, usually). 6% of single turbine helicopter fatal accidents were caused by Engine Material Failure, 3% in the case of twins. However, Non-Engine Material Failure was the cause of 12% and 22% of fatal accidents in singles and twins respectively. Thus the total percentage of fatalities for all mechanical failures was 18% for singles and 25% for twins.
The table illustrates these figures clearly:
Accident Initiator
Engine Material Failure
Non-Engine Material Failure
Sub-Total
Non-Material Failure (Pilot Error, Usually)
82%/75%
It is apparent, therefore, that any advantage offered by the presence of the second engine is more than offset by the reduction in reliability of the aircraft as a whole brought about by the additional and more complex systems to be found aboard the twin-engined helicopter.
18% and 25% represent a ratio of 4:5 for accidents involving singles and twins respectively.
The second study counted the number of accidents per 100,000 flight hours for single turbine and twin turbine helicopters. These show that accidents, all caused by mechanical failure, were at the rate of 5.49 for singles and 4.37 for twins.
The ratio of 5:4 for accidents involving singles and twins respectively is almost precisely the reverse of that shown above.
Found the piece below in my archives regarding Singles and Twins, just to add to the mix!! It was written in 1994. The Tables didn't paste in as saved, I hope they make sense.
************************************************************ ********
There are two important studies in the matter, both carried out by Bell Helicopter over the last 24 years.
The first considered the number of fatal accidents involving Bell helicopters during the period January 1970 to March 1987. The survey covered 19,700 single turbine and 1,800 twin turbine helicopters supplied to both military and civil customers and divided the causes of fatal accidents into three categories of Accident Initiator. They were, Engine Material Failure, Non-Engine Material Failure and Non-Material Failure (Pilot Error, usually). 6% of single turbine helicopter fatal accidents were caused by Engine Material Failure, 3% in the case of twins. However, Non-Engine Material Failure was the cause of 12% and 22% of fatal accidents in singles and twins respectively. Thus the total percentage of fatalities for all mechanical failures was 18% for singles and 25% for twins.
The table illustrates these figures clearly:
Accident Initiator
Single/Twin
Engine Material Failure
6%/3%
Non-Engine Material Failure
12%/22%
Sub-Total
18%/25%
Non-Material Failure (Pilot Error, Usually)
82%/75%
It is apparent, therefore, that any advantage offered by the presence of the second engine is more than offset by the reduction in reliability of the aircraft as a whole brought about by the additional and more complex systems to be found aboard the twin-engined helicopter.
18% and 25% represent a ratio of 4:5 for accidents involving singles and twins respectively.
The second study counted the number of accidents per 100,000 flight hours for single turbine and twin turbine helicopters. These show that accidents, all caused by mechanical failure, were at the rate of 5.49 for singles and 4.37 for twins.
The ratio of 5:4 for accidents involving singles and twins respectively is almost precisely the reverse of that shown above.
Combine Operations
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It is apparent, therefore, that any advantage offered by the presence of the second engine is more than offset by the reduction in reliability of the aircraft as a whole brought about by the additional and more complex systems to be found aboard the twin-engined helicopter.
Careful, Heliski. You know what they say about lies, damn lies and them other things.
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Farmer 1
Like Nick said at the start, the idea is a little debate!
Sitting fat'n'happy, fully coupled in a corporate twin, clear blue sky above, cotton wool to the horizon just below, it's easy to look back on the "good old days" of powerline patrols and aerial photography/filming in an old JetRanger which fit like a well-worn boot!
And remember -
"Old men like to give good advice when no longer able to give bad example!"
Like Nick said at the start, the idea is a little debate!
Sitting fat'n'happy, fully coupled in a corporate twin, clear blue sky above, cotton wool to the horizon just below, it's easy to look back on the "good old days" of powerline patrols and aerial photography/filming in an old JetRanger which fit like a well-worn boot!
And remember -
"Old men like to give good advice when no longer able to give bad example!"
Last edited by heliski22; 20th Nov 2007 at 13:57.
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13) LTE is when you run out of power pedal
Please forgive my ignorance but I thought this was the case.
And Bravo 73 what is the difference between LTE and LTA?
SB
Please forgive my ignorance but I thought this was the case.
And Bravo 73 what is the difference between LTE and LTA?
SB
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LTE and LTA
From recent discussions with our pilots, I was told that LTA is the precursor to LTE. Meaning you will first loose the authority of the pedal, however I understand this could lead to LTE, but could happen by itself without experiencing LTE... I have been told you will experience LTA first before LTE...
After Bravo73 pointed it out, I had to investigate...
After Bravo73 pointed it out, I had to investigate...
scooter boy and simul8,
re LTA vs LTE
This is how I summed up the difference a couple of years ago (in another thread):
This thread, however, covers the topic in much more detail:
http://www.pprune.org/forums/showthread.php?t=143383
HTH
re LTA vs LTE
This is how I summed up the difference a couple of years ago (in another thread):
There's a difference between LTE (Loss of Tail Rotor Effectiveness - in it's simplist terms, the TR is not 'big' or effective enough to provide control within the entirety of the flight envelope) and LTA (Loss of Tail Rotor Authority - TR doesn't have enough RPM to maintain control due to mechanical problem or the pilot 'overcooking' things).
This has been covered in depth in previous threads.
The B206A was particularly prone to LTE whilst most helis can be subjected to LTA if the pilot allows the RRPM to droop too far.
This has been covered in depth in previous threads.
The B206A was particularly prone to LTE whilst most helis can be subjected to LTA if the pilot allows the RRPM to droop too far.
http://www.pprune.org/forums/showthread.php?t=143383
HTH
Last edited by Bravo73; 20th Nov 2007 at 21:27.
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VRS
Like Twin Huey Man I got my VRS education in a Robbie.
At the factory instructor course I happened to mention, in flight, that I could only occasionally achieve this elusive VRS at >300' + <30kts. to teach my own students.
"Follow me thru!" And the factory pilot used (from memory), 16" with AIS flickering10-20kt, and yep it is the bucking bronco ride. A great demonstration, and confirming what I had earlier learned with my own dangerous experiments. It is not only autorotation entry that gets you out; transitioning fwd with cyclic movement will do just as well with much less height loss.
thekite
At the factory instructor course I happened to mention, in flight, that I could only occasionally achieve this elusive VRS at >300' + <30kts. to teach my own students.
"Follow me thru!" And the factory pilot used (from memory), 16" with AIS flickering10-20kt, and yep it is the bucking bronco ride.
A great demonstration, and confirming what I had earlier learned with my own dangerous experiments. It is not only autorotation entry that gets you out; transitioning fwd with cyclic movement will do just as well with much less height loss. thekite
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High pressure bubble under helicopter in hover
I was wondering if anyone could elabortate on this myth. I am new here and I read this thread this morning then went out and hovered and noticed my altimiter reading lower in a hover than when on the ground. It seems that my altimeter is showing higher pressure when in a hover. Also, why do you get that dip in altitude after accelerating just prior to ETL? It seems like it takes more power at that point than any other during take off.
Statistics....oh Lordy!
If it takes 22 Cobra crashes to kill the same number of people as can be killed in 1 Chinook Crash....does that make the Cobra 20X safer than the Chinook? Does that mean Cobra pilots have 20X less chance of buying it than does a Chinook pilot?
How many crashes of two engined helicopters occurred due to a second engine failure as compared to the number of crashes that occurred in single engine helicopters which had a single engine failure?
If it takes 22 Cobra crashes to kill the same number of people as can be killed in 1 Chinook Crash....does that make the Cobra 20X safer than the Chinook? Does that mean Cobra pilots have 20X less chance of buying it than does a Chinook pilot?
How many crashes of two engined helicopters occurred due to a second engine failure as compared to the number of crashes that occurred in single engine helicopters which had a single engine failure?
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Bravo73, Nick, Shawn Coyle, and everybody:)
I've seen many videos which claim to be LTE, and it's quite a wide range...OH58, 206 series including the 206LT, Dauphin in the ice next to the ship (is that really considered LTE if it doesn't have a conventional tail rotor?), the Aircrane, AS350, Sea King just offshore, darn it's really hard to remember all of them...So, this leads me to think not many aircraft have a tail rotor effective enough, or big enough, to prevent LTE...(I haven't heard of or found any incident with the 407, does the asymmetrical airfoil of the TR blade have anything to do with that? Have not heard of any L models with the High Altitude tail rotor either, but I am not familiar with other manufacturers)
Bravo73 thanks for the links...I was interested in the CAA document...Looks like they regurgitated much of what Don Bloom found back when the Army was having problems. Which leads into my next example...I know he had found that LTE can be initiated by two distinct causes (amongst others)...The main rotor vortex produces a downwash that disrupts the airflow into the tail rotor (washing out the effectiveness of the thrust produced?), and the second to mention, is the prevailing winds themselves can cause the tail rotor to experience VRS. I have seen a video of those wind tunnel tests and it was quite convincing...however, after PPRune, I am:
1. Somewhat convinced the true cause is still a myth, or
2. Not all causes have been discovered, and last but not least
3. The pilot had a brain fart
Back to investigating those other posts...repetition is the key you know
Bravo73 thanks for the links...I was interested in the CAA document...Looks like they regurgitated much of what Don Bloom found back when the Army was having problems. Which leads into my next example...I know he had found that LTE can be initiated by two distinct causes (amongst others)...The main rotor vortex produces a downwash that disrupts the airflow into the tail rotor (washing out the effectiveness of the thrust produced?), and the second to mention, is the prevailing winds themselves can cause the tail rotor to experience VRS. I have seen a video of those wind tunnel tests and it was quite convincing...however, after PPRune, I am:
1. Somewhat convinced the true cause is still a myth, or
2. Not all causes have been discovered, and last but not least
3. The pilot had a brain fart
Back to investigating those other posts...repetition is the key you know