Helicopter Urban Myths
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Helicopter Urban Myths
Time to start the arguments and get this web site fun again! The below was generated by some informal consensus about 2 1/2 years ago:
Helicopter Urban Myths
These Urban Myths pervade our understanding of helicopters and how they operate. Each is fundamentally incorrect, but most are generally held as gospel, because training, lore and reference documents have repeated them long enough that they are simply accepted.
1) Vortex Ring State (VRS) can happen at as little as 300 foot per minute descent, it does not have to be a higher descent rate
2) VRS is more likely at high altitude and high gross weight
3) Hovering with the nose off wind consumes much more power
4) Blade stall is always preceded by vibration
5) Winds affect the power we require when we are in forward flight
6) Downwind takeoffs are absolutely forbidden
7) The Height Velocity curve is a precise guide to the engine failure danger zone
8) Engine failure is the most common accident cause, so full CAT A is the most cost effective safety enhancement we can incorporate into new helicopters.
9) The legal definition of VFR is sufficient to assure flight control and safety using outside references
10) "They" sometimes hide things from us. We should not trust them, the only reliable information we can trust is our own wits.
11) The helicopter is perched on a ball of high pressure air when close to the ground, and "falls off" this ground cushion when it moves forward.
12) Phase lag is cause by gyroscopic precession, and is always exactly 90 degrees
13) LTE is when you run out of power pedal and can be experienced by any single rotor helicopter.
14) NVG are dangerous and should only be used by gifted military pilots.
15) You have to first learn to fly fixed wing before you take helicopter training
16) Torque limits, overspeed limits, temperature limits, hours and airframe limits have huge safety factors built into them by the engineers, so it is OK to bust them every now and then.
Helicopter Urban Myths
These Urban Myths pervade our understanding of helicopters and how they operate. Each is fundamentally incorrect, but most are generally held as gospel, because training, lore and reference documents have repeated them long enough that they are simply accepted.
1) Vortex Ring State (VRS) can happen at as little as 300 foot per minute descent, it does not have to be a higher descent rate
2) VRS is more likely at high altitude and high gross weight
3) Hovering with the nose off wind consumes much more power
4) Blade stall is always preceded by vibration
5) Winds affect the power we require when we are in forward flight
6) Downwind takeoffs are absolutely forbidden
7) The Height Velocity curve is a precise guide to the engine failure danger zone
8) Engine failure is the most common accident cause, so full CAT A is the most cost effective safety enhancement we can incorporate into new helicopters.
9) The legal definition of VFR is sufficient to assure flight control and safety using outside references
10) "They" sometimes hide things from us. We should not trust them, the only reliable information we can trust is our own wits.
11) The helicopter is perched on a ball of high pressure air when close to the ground, and "falls off" this ground cushion when it moves forward.
12) Phase lag is cause by gyroscopic precession, and is always exactly 90 degrees
13) LTE is when you run out of power pedal and can be experienced by any single rotor helicopter.
14) NVG are dangerous and should only be used by gifted military pilots.
15) You have to first learn to fly fixed wing before you take helicopter training
16) Torque limits, overspeed limits, temperature limits, hours and airframe limits have huge safety factors built into them by the engineers, so it is OK to bust them every now and then.
Welcome to the party, gents.
Where does no 5 say anything about maintaining a constant groundspeed? 
Those 300/30 numbers are one of the very reasons for the growth of these myths. But no, Davy, you can't get VRS at 300ft RoD and 30kts.
Those 300/30 numbers are one of the very reasons for the growth of these myths. But no, Davy, you can't get VRS at 300ft RoD and 30kts.
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Davy07,
The books say so, but they are quite wrong. VRS can only be induced by descending at least as fast as 75% of the downwash velocity of the helicopter and at a forward speed of not more than about 8 knots. For a Robbie this is at least -750fpm rod. For an S76 it is about -1500 fpm.
Why is 300 taught? Because one can start a VRS event by entering a hover with too little power, slip into an overpitching event and in short order, enter VRS. In a helo with scads of OGE hover performance, the 300 fpm is truly a myth, in one without, it is misleading as a VRS cue, but good word as an overpitching warning.
Manfrom Uncle, what you are correctly saying is that going faster uses more power. The wind has nothing to do with it. 80Kts airspeed uses the same power both up and down wind.
The books say so, but they are quite wrong. VRS can only be induced by descending at least as fast as 75% of the downwash velocity of the helicopter and at a forward speed of not more than about 8 knots. For a Robbie this is at least -750fpm rod. For an S76 it is about -1500 fpm.
Why is 300 taught? Because one can start a VRS event by entering a hover with too little power, slip into an overpitching event and in short order, enter VRS. In a helo with scads of OGE hover performance, the 300 fpm is truly a myth, in one without, it is misleading as a VRS cue, but good word as an overpitching warning.
Manfrom Uncle, what you are correctly saying is that going faster uses more power. The wind has nothing to do with it. 80Kts airspeed uses the same power both up and down wind.
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Hi Guys.
What would be the downward velocity of my Bell-47.
I was also taught the 300/30 rules, it put the willy's up me every time I land? Which I know it shouldn't... so I end up making very long low landings, which are often not ideal.
Cheer
Kevin.
What would be the downward velocity of my Bell-47.
I was also taught the 300/30 rules, it put the willy's up me every time I land? Which I know it shouldn't... so I end up making very long low landings, which are often not ideal.
Cheer
Kevin.
14) NVG are dangerous and should only be used by gifted military pilots.
Well, I would cut this one to
14) NVG should only be used by gifted military pilots.
With lack of proper training, correctly adapted cabin/cockpit it could be dangerous.
Arrakis
Well, I would cut this one to
14) NVG should only be used by gifted military pilots.
With lack of proper training, correctly adapted cabin/cockpit it could be dangerous.
Arrakis
Last edited by ARRAKIS; 18th Nov 2007 at 18:30.
Aye cheers for that nick, just checked the Principles of Flight book there..
Vortex State Ring can develop when the helicopter has:
1 A low or zero airspeed (below translational lift speed)
2 Some power in use (collective input) 'As you mentioned'
3 A rate of descent that is in the region of 400 to 800ft/min, depending on aircraft type!
Duno were i got 30 Knots out of!
Vortex State Ring can develop when the helicopter has:
1 A low or zero airspeed (below translational lift speed)
2 Some power in use (collective input) 'As you mentioned'
3 A rate of descent that is in the region of 400 to 800ft/min, depending on aircraft type!
Duno were i got 30 Knots out of!
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Addressing the myths
1) Vortex Ring State (VRS) can happen at as little as 300 foot per minute descent, it does not have to be a higher descent rate
- If you are in a hover, I could buy that. Just can't imagine that happening with forward airspeed, above ETL.
- Possibly, however, demonstrations in the 407, with half a bag of gas, myself and the Instructor were the only two in the aircraft, it was very easy to get it into VRS once the airspeed was at ETL or below.
- Much more? Where is the wind? Less power with right pedal application, because you are using the engine torque (in Bell aircraft that is).
- Haven't the slightest idea, I'm not a test pilot and hope I never find out...got to be honest and know my limitations!
- Doubt it...fuselage and tail will weather vane into the wind during slight crab angles...if the wind is 90* off the fuselage, there wouldn't be any further power requirements, and if the wind was off the tail, we would have a higher ground speed.
- Well, it's not a smart thing to do with smaller A/C (206B,L, schwietzer 300's, MD 500"s, etc.) If you've got an A/C with good power, I see no big deal. I see Blackhawks, 53's, 47's do it all the time. Fact is I was taught to use the wind to your benefit, and it is a safety concern in the A/C I fly.
- Not precise, just a limitation by the manufacturer to prevent lawsuits
- Nope, Pilot error is the most common. CAT A is a relatively safe way to take-off and depart, but Pilot error could still screw that up.
It's a great discussion on the subject, in the U.S anyway...
10) "They" sometimes hide things from us. We should not trust them, the only reliable information we can trust is our own wits.- "They" need a life and perhaps get laid.
- I could by that...the reason for adding a tiny bit of collective on takeoff before and during ETL.
- Sure, in a two bladed helicopter.
- I am sure some will come on and say "only in Bell OH-58, Bell 206B,L etc. etc.) But I have seen videos of other manufacturers experiencing the same thing, especially the Aircrane video, that's at the top of my list! So yeah, it can happen with single rotor heli's with a tail rotor.
- What a crock...that's an improvement on safety...especially when the Pilot receive proper training.
- I didn't...and quite frankly, fixed wing Pilots have the hardest time, having seen those coming through the Academy.
- Well, I'm in it not only for flight, but to live to fly again. If I am in flight and exceed the flight time, or my survival depends on it, that I can live with...but anything intentional or my survival option is within my boundaries, I trust the engineers, having seen what they do to test those limits.
Simul8,
Here's one of the many definitions of 'myth' that Google just threw up:
"Something not true, fiction, or falsehood. A truth disguised and distorted."
Here's what wiki has to say about 'urban myths':
"An urban legend or urban myth is similar to a modern folklore consisting of stories thought to be factual by those circulating them."
In light of that, do you understand what Nick's point is?
Here's one of the many definitions of 'myth' that Google just threw up:
"Something not true, fiction, or falsehood. A truth disguised and distorted."
Here's what wiki has to say about 'urban myths':
"An urban legend or urban myth is similar to a modern folklore consisting of stories thought to be factual by those circulating them."
In light of that, do you understand what Nick's point is?
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Sure do...however, Nick first stated "Time to start the arguments and get this web site fun again! The below was generated by some informal consensus about 2 1/2 years ago:"...so Bravo73 have you got any arguments to state based upon my submission?
Nick then went on to say:
However, from a lot of your 'arguments' it would appear as if you believe that the majority are true. The 3 words, 'hook', 'line' and 'sinker', spring to mind!
PS LTA is different to LTE.
These Urban Myths pervade our understanding of helicopters and how they operate. Each is fundamentally incorrect, but most are generally held as gospel, because training, lore and reference documents have repeated them long enough that they are simply accepted.
PS LTA is different to LTE.
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When the RAF taught using 30kts for vortex ring, it was for a very good reason. The ASI on Gazelle started reading accurately at 30, so anything below was classed as zero. We were told the figure was MUCH lower, but that was the lowest speed we could read.
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"When the RAF taught using 30kts for vortex ring, it was for a very good reason. The ASI on Gazelle started reading accurately at 30, so anything below was classed as zero. We were told the figure was MUCH lower, but that was the lowest speed we could read."
I got told the same thing.
However, this VRS rumor thing confuses me a bit. I read up everything out there on VRS and how to get into it, and really believed that you'd have to be falling at a great rate with low airspeed to get into VRS (think 900fpm vertical descent), until I went out with the instructor and got full blown bucking bronco VRS that started with pulling collective at 200fpm descent rate indicated (figure 300-400 with the VSI lag) and maybe 0-5kts airspeed in a robbie. After seeing that, I'm a firm believer of <300fpm at <30kts. Granted, it's still that elusive goblin that's gonna come and git'cha, but without complete practical experience and understanding, and only what I've seen during training evolutions, I'm convinced that the point at which you could get into it is a lot closer than some make it out to be.
Anybody's thoughts?
Mike
I got told the same thing.
However, this VRS rumor thing confuses me a bit. I read up everything out there on VRS and how to get into it, and really believed that you'd have to be falling at a great rate with low airspeed to get into VRS (think 900fpm vertical descent), until I went out with the instructor and got full blown bucking bronco VRS that started with pulling collective at 200fpm descent rate indicated (figure 300-400 with the VSI lag) and maybe 0-5kts airspeed in a robbie. After seeing that, I'm a firm believer of <300fpm at <30kts. Granted, it's still that elusive goblin that's gonna come and git'cha, but without complete practical experience and understanding, and only what I've seen during training evolutions, I'm convinced that the point at which you could get into it is a lot closer than some make it out to be.
Anybody's thoughts?
Mike
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5) Winds affect the power we require when we are in forward flight
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.
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But no, Davy, you can't get VRS at 300ft RoD and 30kts.
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Without going into individual myths, Nick is right in suggesting that a lot of helicopter activities are carried out without much analysis as to why they are done.
I would add "a shallow approach is the only one to use in mountains (or anywhere else)" to the list.
Phil
I would add "a shallow approach is the only one to use in mountains (or anywhere else)" to the list.
Phil
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Hi all,
Shouldn't the myths read:
1) Vortex Ring State (VRS) can only happen when gifted military pilots are conducting NVG operations
2) VRS is more likely when the operaor has drunk 4 pints of heavy (preferably NOT warm) mixed with tequila chasers while going down the back stairs to the carpark.
3) Breaking wind with the nose off wind consumes much more power from the chilli night
4) Blade stiffness is always preceded by vibration of the 1R variety on the mattress
5) Winds affect the power we require when we stick our heads out the window
6) Downwind farts are absolutely forbidden
7) The Height Weight (BMI) curve is a precise guide to the heart failure danger zone
8) Alcohol is the most common accident cause, so a breath analysiser ignition lock thingy is the most cost effective safety enhancement we can incorporate into new helicopters.
9) The legal definition of a bundy (rum) and coke is sufficient to assure your flight control and safety using outside references
10) "They" always hide things from us. We should not trust them, and insist that the water always comes from a bottle.
11) The socially lubricated helicopter pilot is perched on a ball of high pressure air when close to the ground, and "falls off" this ground cushion when he/she moves forward to chat up the bird.
12) A midnight stagger is always caused by gyroscopic precession, and is always exactly 90 degrees out from where you are attempting to get to
13) LDE (Loss of Drinking Effectiveness) is when you run out of your allowances (either from work or from the home financial controller) and can be experienced by any single or married helicopter pilot.
14) NVG are dangerous when driving home to avoid detection by the local plod, and should only be used by gifted pilots with good insurance coverage.
15) You have to first learn to not take yourself too seriously before you take helicopter training
16) Head spins, vomit, and damage from jumping out of buildings (seemed like a good idead at the time) limits have huge safety factors built into them by the engineers, so it is OK to bust them every now and then.
Shouldn't the myths read:
1) Vortex Ring State (VRS) can only happen when gifted military pilots are conducting NVG operations
2) VRS is more likely when the operaor has drunk 4 pints of heavy (preferably NOT warm) mixed with tequila chasers while going down the back stairs to the carpark.
3) Breaking wind with the nose off wind consumes much more power from the chilli night
4) Blade stiffness is always preceded by vibration of the 1R variety on the mattress
5) Winds affect the power we require when we stick our heads out the window
6) Downwind farts are absolutely forbidden
7) The Height Weight (BMI) curve is a precise guide to the heart failure danger zone
8) Alcohol is the most common accident cause, so a breath analysiser ignition lock thingy is the most cost effective safety enhancement we can incorporate into new helicopters.
9) The legal definition of a bundy (rum) and coke is sufficient to assure your flight control and safety using outside references
10) "They" always hide things from us. We should not trust them, and insist that the water always comes from a bottle.
11) The socially lubricated helicopter pilot is perched on a ball of high pressure air when close to the ground, and "falls off" this ground cushion when he/she moves forward to chat up the bird.
12) A midnight stagger is always caused by gyroscopic precession, and is always exactly 90 degrees out from where you are attempting to get to
13) LDE (Loss of Drinking Effectiveness) is when you run out of your allowances (either from work or from the home financial controller) and can be experienced by any single or married helicopter pilot.
14) NVG are dangerous when driving home to avoid detection by the local plod, and should only be used by gifted pilots with good insurance coverage.
15) You have to first learn to not take yourself too seriously before you take helicopter training
16) Head spins, vomit, and damage from jumping out of buildings (seemed like a good idead at the time) limits have huge safety factors built into them by the engineers, so it is OK to bust them every now and then.