BO105 fatal accident back in 2006(?)
With all respect to Dennis and all display pilots I think the thread has moved away from the reality of the crash... With over 3500 hours on 105's and years of crop spraying, that turn was BOLD to say the least 
I wonder about if it's not time to bring out the old Aerodynamics notes from PPL ground-school.
Why did we learn to keep collective pitch constant during our first hours?
Cause: The amount of power needed for hover, will allow acceleration and climb away once passed 12-15 kts (ETL) as the whole disc area is now more efficient, generating more lift over drag, than in a hover also making the disc more responsive/controllable.
Why do I drag this into the discussion?!
Well, in his manoeuvre he would turn from up-wind to down wind while decelerating, climbing, and bank hard. About 98 deg. if I remember correctly, so A BIT steeper than your average steep-turn
All of you know that operating down-wind is less favourable than up-wind, and the importance of maintaining IAS. However, if you fly with reference to the ground (in this case for practise for a film-shoot) you might unintentionally loose too much of your IAS, and even loose ETL. Now your disc is generating less lift for drag and it is far less responsive for your recovery actions.
IF in this case, he in fact lost ETL at the top of the manoeuvre, WITH the extreme bank-angle he had (his disc is NOT producing lift vertical to the ground at this point, but acted upon by earth's gravity generating a fairly high ROD), the only thing that could let him recover was to regain ETL by loosing ALT, which in this case he did not have much of...about 70 ft.
Back to the question about the down-wind/up-wind, if that has any effect. If he had done the same manoeuvre opposite direction, I am fairly sure the outcome would be much different as I am sure he wouldn’t have lost ETL and by that maintained control throughout the manoeuvre.
My 2 cents...
There are old pilots and there are bold pilots, but there are NO old bold pilots....
RIP
Why did we learn to keep collective pitch constant during our first hours?
Cause: The amount of power needed for hover, will allow acceleration and climb away once passed 12-15 kts (ETL) as the whole disc area is now more efficient, generating more lift over drag, than in a hover also making the disc more responsive/controllable.
Why do I drag this into the discussion?!
Well, in his manoeuvre he would turn from up-wind to down wind while decelerating, climbing, and bank hard. About 98 deg. if I remember correctly, so A BIT steeper than your average steep-turn
All of you know that operating down-wind is less favourable than up-wind, and the importance of maintaining IAS. However, if you fly with reference to the ground (in this case for practise for a film-shoot) you might unintentionally loose too much of your IAS, and even loose ETL. Now your disc is generating less lift for drag and it is far less responsive for your recovery actions.
IF in this case, he in fact lost ETL at the top of the manoeuvre, WITH the extreme bank-angle he had (his disc is NOT producing lift vertical to the ground at this point, but acted upon by earth's gravity generating a fairly high ROD), the only thing that could let him recover was to regain ETL by loosing ALT, which in this case he did not have much of...about 70 ft.
Back to the question about the down-wind/up-wind, if that has any effect. If he had done the same manoeuvre opposite direction, I am fairly sure the outcome would be much different as I am sure he wouldn’t have lost ETL and by that maintained control throughout the manoeuvre.
My 2 cents...
There are old pilots and there are bold pilots, but there are NO old bold pilots....
RIP
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An odd quirk of physics seems to be that a really dense cloud layer will apparently cancel out "inertia" and all those other nasties that wait to pull us into the ground during a "downwind turn".
For a demonstration of this phenomena, simply note the wind direction, climb thru the layer, once on top take up a heading into the wind previously noted and then commence a turn onto a reciprocal heading without any reference to the ground. Notice anything?
Or you could perhaps do a series of continuous 360's under the hood and try to establish which direction the wind is coming from.
STL
For a demonstration of this phenomena, simply note the wind direction, climb thru the layer, once on top take up a heading into the wind previously noted and then commence a turn onto a reciprocal heading without any reference to the ground. Notice anything?
Or you could perhaps do a series of continuous 360's under the hood and try to establish which direction the wind is coming from.
STL
Avoid imitations
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Again, if the helicopter is being "pedalled" round the turn, i.e. not in balanced, banked flight, the rules for balanced, banked flight don't fully apply.
As usual, take the extreme example to illustrate the point.
Imagine a helicopter in straight flight.
The pilot keeps the altitude and applies no bank whilst rapidly pedalling the aircraft round 180 degrees. Just because it's now pointing in the opposite direction doesn't mean to say it's now flying in the opposite direction.
Any turn where the helicopter is yawed with pedal into a turn, to a degree more than that needed for balanced flight, as sometimes happens at low IAS, remaining forward airspeed can be rapidly lost, especially in a gusty wind.
Quite strong "negative" flapback can occur where IAS rapidly decreases through zero and to a negative value. This could pitch the aircraft rapidly nose down to a situation where possibly insufficient aft cyclic control remains to recover, until forward airspeed is regained and positive flapback occurs, naturally bringing the nose up. Negative airspeed over the horizontal stabiliser (now a de-stabiliser) can make this nose-down pitching worse. Close to the ground that could be catastrophic.
I saw 120 to 130 degrees nose down with no airspeed in a Puma HC1 a couple of times, once with at least one hydraulic pump briefly screeching as it cavitated; it's quite enlightening.
As usual, take the extreme example to illustrate the point.
Imagine a helicopter in straight flight.
The pilot keeps the altitude and applies no bank whilst rapidly pedalling the aircraft round 180 degrees. Just because it's now pointing in the opposite direction doesn't mean to say it's now flying in the opposite direction.
Any turn where the helicopter is yawed with pedal into a turn, to a degree more than that needed for balanced flight, as sometimes happens at low IAS, remaining forward airspeed can be rapidly lost, especially in a gusty wind.
Quite strong "negative" flapback can occur where IAS rapidly decreases through zero and to a negative value. This could pitch the aircraft rapidly nose down to a situation where possibly insufficient aft cyclic control remains to recover, until forward airspeed is regained and positive flapback occurs, naturally bringing the nose up. Negative airspeed over the horizontal stabiliser (now a de-stabiliser) can make this nose-down pitching worse. Close to the ground that could be catastrophic.
I saw 120 to 130 degrees nose down with no airspeed in a Puma HC1 a couple of times, once with at least one hydraulic pump briefly screeching as it cavitated; it's quite enlightening.
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Ok, my 2 penneth, which will be quick as I'm having breakfast. If you look at the shape of the turn as viewed by us i.e. the radio controller pilot guy on the ground, it looks pretty symmetrical. This was mentioned before about trying to make the turn look good for the camera. By doing this with the tail wind present, he's got to lose airspeed halfway through. Bang.
Do this above 8/8 of cloud (as already mentioned) with 15 knots of breeze whilst using a particular cloud for a reference point, you'll be home and dry - your reference point is moving at 15 knots.
I find it hard to believe that wind will affect your IAS. Great discussion tho!
Cheers, DM
Quick edit here - look at the vid, doesn't look like the chopper was out of balance during the turn
And another edit - for the record, I agree that an out of balance maneuver would/could have significant inertia issues.
Do this above 8/8 of cloud (as already mentioned) with 15 knots of breeze whilst using a particular cloud for a reference point, you'll be home and dry - your reference point is moving at 15 knots.
I find it hard to believe that wind will affect your IAS. Great discussion tho!
Cheers, DM
Quick edit here - look at the vid, doesn't look like the chopper was out of balance during the turn
And another edit - for the record, I agree that an out of balance maneuver would/could have significant inertia issues.
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The thread has polarised into the believers and non believers in the relevance of the wind direction and I'm not going to persue that further as I said. I now have it clear in my own mind.
To throw more into the bubbling pot, refer back to the video. It is conveniently time stamped. As the aircraft enter the turn it climbs and reaches the highest point of the turn at 11.06.12. At this point the aircraft is banked to 90+ degrees and runs out of momentum opposing gravity. Any thrust from the main rotor (probably little) is added to gravity pulling the aircraft earthwards at 10 m/s2.
At best the aircraft begins to accelerate downward as would any object in free fall as there is no thrust vector to oppose gravity. The pilot probably has his left boot to the floor but its not enough to keep the nose up. He has whacked in left cyclic and by 11.08.10 is just getting some response, but still has a bank angle of about 60 deg.There is not enough downthrust to overcome the momentum the aircraft has acquired earthwards. The result is inevitable at 11.08.12.
The aircraft was doomed achieving that angle of bank at that height.
Just 1 second of no force opposing gravity means you will end up descending at approx 10m/s or 1980ft/minute.
I would estimate the windspeed at no more than a few knots by the speed of the smoke and at no point does the aircraft look as though it got anywhere near losing translational lift. He was motoring all the way round. He lost lift 'cos his rotor was pointing in the wrong direction.
Just my interpretation of the video.
Thoughts anyone. I'll get me coat...
EDIT: I'm not testing this in my Enstrom (once was enough) nor my RC model but trying it in a reasonably good RC simulator I can't recover from bank angles over 90 degrees without losing significant height.
To throw more into the bubbling pot, refer back to the video. It is conveniently time stamped. As the aircraft enter the turn it climbs and reaches the highest point of the turn at 11.06.12. At this point the aircraft is banked to 90+ degrees and runs out of momentum opposing gravity. Any thrust from the main rotor (probably little) is added to gravity pulling the aircraft earthwards at 10 m/s2.
At best the aircraft begins to accelerate downward as would any object in free fall as there is no thrust vector to oppose gravity. The pilot probably has his left boot to the floor but its not enough to keep the nose up. He has whacked in left cyclic and by 11.08.10 is just getting some response, but still has a bank angle of about 60 deg.There is not enough downthrust to overcome the momentum the aircraft has acquired earthwards. The result is inevitable at 11.08.12.
The aircraft was doomed achieving that angle of bank at that height.
Just 1 second of no force opposing gravity means you will end up descending at approx 10m/s or 1980ft/minute.
I would estimate the windspeed at no more than a few knots by the speed of the smoke and at no point does the aircraft look as though it got anywhere near losing translational lift. He was motoring all the way round. He lost lift 'cos his rotor was pointing in the wrong direction.
Just my interpretation of the video.
Thoughts anyone. I'll get me coat...
EDIT: I'm not testing this in my Enstrom (once was enough) nor my RC model but trying it in a reasonably good RC simulator I can't recover from bank angles over 90 degrees without losing significant height.
Last edited by Gaseous; 8th Apr 2008 at 01:08.
It's really sad watching that video knowing how it's going to end. Whatever maneuver Ziggy was trying to pull off there looked improvised and unrehearsed. I'd imagine that once he got up to the apex he probably said to himself, "Oh sh*t. This is not good." His airspeed must have been very, very low and his lift/thrust was pointing in the exact wrong direction. He was, as has been pointed out, at the will of gravity at that point.
Obviously he would have had to roll out of that steep bank and then recover from the dive. He probably did have the cyclic all the way to the left stop but the ship just wasn't responding what with the combination of low airspeed, bank angle and power applied as we know Bolkows are prone to (not) do. And there wasn't enough altitude to dive for more speed.
A long, long time ago when I was a mere private pilot, I'm ashamed to say that I crashed a ship doing something similar: an ill-advised ag-turn which I had seen done but never had demonstrated to me. Had I started with 60 mph it probably would've worked out okay. But I only had about 45 on the clock. At the end of the field I pulled the cyclic back. The nose came up and the ship...just...sort of...stopped, hardly climbed at all. I pedal-turned around, pointed straight at the ground now and went, "Oh sh*t, this is not good." Luckily I managed to get it more or less level before Bell 47 parts and pieces started flying everywhere. Result: One Bell 47G-2 destroyed. Completely my fault. I've lived with it ever since.
Difference between me and the Bolkow pilot was that he knew what he was doing...or so he thought.
Obviously he would have had to roll out of that steep bank and then recover from the dive. He probably did have the cyclic all the way to the left stop but the ship just wasn't responding what with the combination of low airspeed, bank angle and power applied as we know Bolkows are prone to (not) do. And there wasn't enough altitude to dive for more speed.
A long, long time ago when I was a mere private pilot, I'm ashamed to say that I crashed a ship doing something similar: an ill-advised ag-turn which I had seen done but never had demonstrated to me. Had I started with 60 mph it probably would've worked out okay. But I only had about 45 on the clock. At the end of the field I pulled the cyclic back. The nose came up and the ship...just...sort of...stopped, hardly climbed at all. I pedal-turned around, pointed straight at the ground now and went, "Oh sh*t, this is not good." Luckily I managed to get it more or less level before Bell 47 parts and pieces started flying everywhere. Result: One Bell 47G-2 destroyed. Completely my fault. I've lived with it ever since.
Difference between me and the Bolkow pilot was that he knew what he was doing...or so he thought.
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To the believers of the downwind turn I offer the following experience. Where I flew 60-70 knots of wind was not uncommon. Taking off from a platform and climbing out at BROC (74 knots) turning downwind had absolutly no impact on aircraft performance. However there is an extremely strong and powerful VISUAL impact as the groundspeed goes from 14 knots to 134 knots. This is where pilots (my opinion only) run into trouble as they perceive the reduced climb gradient on the downwind as a loss of climb performance and naturally pull back on the stick to restore the perceived performance required. More attention to what the dials are saying negates the very powerful visual influence. As helo pilots we are a very visual lot in that we take our cues from what the terrain about us is doing rather than what the gauges may be saying (VSI, airspeed). What helo pilot has not been caught out and finding him/her self landing with the wind, however slight, up the tail.
The accident reports are replete with people who on turning downwind find the collective up under the arm pit and the aircraft still descending. Why? Because they've allowed the airspeed to zero out at some point during the turn due to them taking their cues from ground motion.
Used to see new guys occasionaly fall afoul of this powerful visual stimuli in another way as well. Enter the downwind with 60 knots of wind and decelerate the aircraft to zero airspeed prior to commencing the turn to base/final because they are taking their cues from outside the cockpit. On one occassion I unfortunately let the situation in a 76 deteriorate to the point where we just had enough height to make a recovery.
The accident reports are replete with people who on turning downwind find the collective up under the arm pit and the aircraft still descending. Why? Because they've allowed the airspeed to zero out at some point during the turn due to them taking their cues from ground motion.
Used to see new guys occasionaly fall afoul of this powerful visual stimuli in another way as well. Enter the downwind with 60 knots of wind and decelerate the aircraft to zero airspeed prior to commencing the turn to base/final because they are taking their cues from outside the cockpit. On one occassion I unfortunately let the situation in a 76 deteriorate to the point where we just had enough height to make a recovery.
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There seems to be an edict which resulted in at least one so far unanswered question during this thread.
That it is folly to roll these types too quickly to starboard.
Why is this so? is this a northern hemisphere and direction of blade rotation, bit of jungle talk?
As sasless has pointed out,
1) A/C rolling too quickly,
2) excercise aft cyclic, and top pedal ~ all the way ho-say ~ quick time. 3) Extra drag onto the M/R and clean air for the T/R should drag it upright. ~ as long as airspeed is available.
I think the running out of airspeed situation is a bit far fetched in this clip, after all the machine was getting along at quite a clip when it impacted.
However, deliberately pushing students into the downwind scenaio that Dennis K describes is standard practice around here. After all, if they are gullible it ambushes them into the dreaded VR envelope. ha ha . Descend, into wind, next time please!
Descending ~ downwind ~ decelerating
is just like
drinking ~ driving ~ death,
suit yourself, but not on my AOC thankyou.
The clip may illustrate that it once again illustrates the fallacy of coupling a non critical component, ~ the camera ~ however cheap~ into a seemingly safe operation.
That it is folly to roll these types too quickly to starboard.
Why is this so? is this a northern hemisphere and direction of blade rotation, bit of jungle talk?
As sasless has pointed out,
1) A/C rolling too quickly,
2) excercise aft cyclic, and top pedal ~ all the way ho-say ~ quick time. 3) Extra drag onto the M/R and clean air for the T/R should drag it upright. ~ as long as airspeed is available.
I think the running out of airspeed situation is a bit far fetched in this clip, after all the machine was getting along at quite a clip when it impacted.
However, deliberately pushing students into the downwind scenaio that Dennis K describes is standard practice around here. After all, if they are gullible it ambushes them into the dreaded VR envelope. ha ha . Descend, into wind, next time please!
Descending ~ downwind ~ decelerating
is just like
drinking ~ driving ~ death,
suit yourself, but not on my AOC thankyou.
The clip may illustrate that it once again illustrates the fallacy of coupling a non critical component, ~ the camera ~ however cheap~ into a seemingly safe operation.
Top points out my assumption of having forward airspeed when I talk of recovering by means of maximum use of left pedal. The discussion so far suggests that was not the case at hand or at best minimal forward speed.
The accident report stated the aircraft rolled to a bank angle of 98 degrees. I wonder at what point they measured that and if it was immediately before impact or a bit before that.
As I view the video, I notice the aircraft rolling but also a distinct tuck of the nose with a rotation about the mast (or are my tired old eyes deceiving me?). I wonder at what point recovery was impossible if an application of full left pedal was made? Would the nose have rotated to the right considering the angle of bank and lack of significant forward airspeed?
Or....was the rotation of the nose an attempt to gain airspeed such as in a torque turn but done at too low an altitude?
It would seem natural to me had I been caught in that situation, I would have been trying to level the aircraft with full left and moderate aft cyclic at a minimum and possibly full aft cyclic if I realized I was at or approaching the cyclic stops. I could even imagine a reduction in cyclic if I had hit the cyclic stops. The full application of left pedal would have been the last thing I would have done unless I had hit the cyclic stops.
Am I correct in assuming all that would be appropriate until the pitch angle of the aircraft started dropping below level? After the nose drops, it makes recovery at very low altitude very unlikely?
The accident report stated the aircraft rolled to a bank angle of 98 degrees. I wonder at what point they measured that and if it was immediately before impact or a bit before that.
As I view the video, I notice the aircraft rolling but also a distinct tuck of the nose with a rotation about the mast (or are my tired old eyes deceiving me?). I wonder at what point recovery was impossible if an application of full left pedal was made? Would the nose have rotated to the right considering the angle of bank and lack of significant forward airspeed?
Or....was the rotation of the nose an attempt to gain airspeed such as in a torque turn but done at too low an altitude?
It would seem natural to me had I been caught in that situation, I would have been trying to level the aircraft with full left and moderate aft cyclic at a minimum and possibly full aft cyclic if I realized I was at or approaching the cyclic stops. I could even imagine a reduction in cyclic if I had hit the cyclic stops. The full application of left pedal would have been the last thing I would have done unless I had hit the cyclic stops.
Am I correct in assuming all that would be appropriate until the pitch angle of the aircraft started dropping below level? After the nose drops, it makes recovery at very low altitude very unlikely?
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B 105 Handling
Thanks guys for all the viewpoints, notes and handling experiences being put forward ... if nothing else, it has certainly exercised my brain for a while.
I feel that the major point that emerges from the Hoffman accident, is that with the quoted 98 degree banking angle, any vertical thrust from the M/R could only accelerate the machine further into its steep descent.
My standard display sequence does include a loop, but when I was first shown the manoeuvre in the 1970s, by a former world champion, he made it 1000% clear that at the highest point, the collective lever must be fully down and with a minimum 'gate' speed well above translation lift if the manoeuvre is to be continued. If not and with adequate height, it is a simple manoeuvre to 'duck out.'
I do understand that there is a body of opinion out here that absolutely disagrees with any helicopter display manoeuvres. Having flown a little over 1200 public displays in half a dozen types over thirty years, I mildly take the opposite view - that with the right training and proper understanding, display flying should stay as an exciting part of our industry and used to demonstrate the capabilities of the helicopter ... but having said that, I'm always listening to the other guys who take the reverse view.
Safe flying to all,
Dennis K
I feel that the major point that emerges from the Hoffman accident, is that with the quoted 98 degree banking angle, any vertical thrust from the M/R could only accelerate the machine further into its steep descent.
My standard display sequence does include a loop, but when I was first shown the manoeuvre in the 1970s, by a former world champion, he made it 1000% clear that at the highest point, the collective lever must be fully down and with a minimum 'gate' speed well above translation lift if the manoeuvre is to be continued. If not and with adequate height, it is a simple manoeuvre to 'duck out.'
I do understand that there is a body of opinion out here that absolutely disagrees with any helicopter display manoeuvres. Having flown a little over 1200 public displays in half a dozen types over thirty years, I mildly take the opposite view - that with the right training and proper understanding, display flying should stay as an exciting part of our industry and used to demonstrate the capabilities of the helicopter ... but having said that, I'm always listening to the other guys who take the reverse view.
Safe flying to all,
Dennis K
Svenestron:
You're not a pilot, are you Sven? Wait, don't answer that. It's obvious. If you were a pilot, you'd know that even the best of us screw up sometimes. It's a sad fact, but there have been many times in my life have I heard of a particular aircraft accident and thought, "How could that have happened to HIM?!" But eh- it does. And it doesn't mean Hoffman was a bad person or a bad pilot. But he certainly wasn't a "victim" of some wierd and capricious cosmic sneeze. That may sound cold but it's not. He merely messed up and it cost him his life. Yes, it's tragic, but we pilots understand it.
I wonder how many times he had rehearsed that specific little demonstration for those particular cameras? Or, had he done something similar so many times before that he just went ahead and "winged" it (or parts of it)? In such a routine, everything must be thought-out well in advance. As a Bolkow pilot, I cannot imagine how that maneuver could have worked out any differently, given his entry speed and the "radical-ness" of it. I'm sure he knew at the top of that diagonal-loop-roll-RTT-whatever that it was all wrong. He should have been *much* higher.
We who have flown a while have all been there. We put ourselves in a position where our heart is suddenly jammed up in our throats and we go, "Oh, no..." Sometimes we pull off a miracle and squeak out of it. And sometimes we crash and it gets discussed ad nauseum on internet discussion boards such as this.
As Dennis says, if nothing else Ziggy's accident has generated exactly that sort of thoughtful discussion. It all gets stored in the back of my mind, ready to be recalled and used perhaps (but hopefully not) the very next time my hands touch the controls.
Not knowing exactly what went through Siegfried’s mind at the time, I prefer to believe he was in no way “caught out there” due to any lack of judgment or planning, but was rather the victim of one of history’s most “inopportune sneezes..”
I wonder how many times he had rehearsed that specific little demonstration for those particular cameras? Or, had he done something similar so many times before that he just went ahead and "winged" it (or parts of it)? In such a routine, everything must be thought-out well in advance. As a Bolkow pilot, I cannot imagine how that maneuver could have worked out any differently, given his entry speed and the "radical-ness" of it. I'm sure he knew at the top of that diagonal-loop-roll-RTT-whatever that it was all wrong. He should have been *much* higher.
We who have flown a while have all been there. We put ourselves in a position where our heart is suddenly jammed up in our throats and we go, "Oh, no..." Sometimes we pull off a miracle and squeak out of it. And sometimes we crash and it gets discussed ad nauseum on internet discussion boards such as this.
As Dennis says, if nothing else Ziggy's accident has generated exactly that sort of thoughtful discussion. It all gets stored in the back of my mind, ready to be recalled and used perhaps (but hopefully not) the very next time my hands touch the controls.
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I think what Dennis and Shawn are saying is that, as you turn downwind from into wind - if you allow the airspeed to decay you can lose translational lift and it is reference the ground only by the fact that it is beneath you and without enough height, as you sink, you can crash into it. It isn't so much a fixed point beneath you, just a loss of altitude with a loss of effective lift...
If turning from upwind to downwind is no problem and does not affect the aerodynamics and the helicopters performance, then we should all be ok with taking off downwind.... or what....
cmon people lets not try to make a simple thing and stir it into some complex physics crap.
Did Newton ever performe in a helicopter or test fly them? Don't think so
I think Dennis and Shawn know one or maybe even two things about helicopter aerodynamics so you should be ok with theirs explanations
Clever stuff!! So if it where like that would it be danger to make steep right in northern hemispere but left in the southern
and ok at the equator
So does all french helicopters rotate in the right way in the south but wrong way in the north
omg this is getting worse...
This right turn problem is most likely desing related then again I don't know but "loss of translational lift" is there for sure and it will bite you in the ass....
and btw guy's isn't Nick just too busy building new Bell's to show up with good explanation
cmon people lets not try to make a simple thing and stir it into some complex physics crap.
Did Newton ever performe in a helicopter or test fly them? Don't think so
I think Dennis and Shawn know one or maybe even two things about helicopter aerodynamics so you should be ok with theirs explanations
There seems to be an edict which resulted in at least one so far unanswered question during this thread.
That it is folly to roll these types too quickly to starboard.
Why is this so? is this a northern hemisphere and direction of blade rotation, bit of jungle talk?
That it is folly to roll these types too quickly to starboard.
Why is this so? is this a northern hemisphere and direction of blade rotation, bit of jungle talk?
and ok at the equatorSo does all french helicopters rotate in the right way in the south but wrong way in the north
omg this is getting worse...This right turn problem is most likely desing related then again I don't know but "loss of translational lift" is there for sure and it will bite you in the ass....
and btw guy's isn't Nick just too busy building new Bell's to show up with good explanation
Last edited by rotorrookie; 9th Apr 2008 at 01:36.
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If turning from upwind to downwind is no problem and does not affect the aerodynamics and the helicopters performance, then we should all be ok with taking off downwind
The first is takeoff from hover. While hovering downwind(or in any wind), the main rotor has increased efficiency especially dramatic above ETL. To takeoff downwind, you actually initially decrease the relative wind on the rotor and pass through a moment of zero wind on your way to gaining airspeed. (this calls for more power required)
Second is if the engine quits on takeoff, you will hit the ground with more relative GROUND speed.
Third and not as understood by most, climbing downwind (though a gradient which is often the case) actually continually saps energy from the helicopter and actual rate of climb as measured on the VSI will be less. As soon as you pass through the gradient (often most dramatic surface through 300 or 400 feet)your rate of climb will be identical upwind or downwind.
Plain fact is the helicopter knows no downwind or upwind. It only knows airspeed. No offence intended, but I am having a hard time believing that some of you guys who are professionals believe this downwind "voodoo". It is only in reference to the ground that the wind matters....not including gusts, gradients and wind sheer in this discussion for simplification.
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when you climb out and turn downwind, does the rate of climb stay constant? What angle of bank are you using?
Try this ..fly straight and level at or below BROC turn downwind with 60°bank keep your airspeed and look at the performance of your aircraft. I bet that you have to bring the nose down to keep the airspeed where it was at the beginning. Is that a visual problem
To those still having trouble coming to grips, perhaps an illustration or two. A ram air parachute requires airspeed to remain inflated, and its BAD, BAD news should it deflate. Any problems turning up wind down wind? Absolutely none, and nothing can turn quicker than one of those babies. They are certainly affected by changes in airspeed due to gusts and care has to be taken in such conditions because they will collapse – as a BA 747 Captain found recently (lost his life).
You are in a jet at FL370 flying at 450 knots. You take a walk to the back and return to the front. Notice any difference to when you might do the same with the aircraft parked at the gate? Think of the jet as being the body of air in which you are flying and yourself as the aircraft flying in that body of air. Does the fact the body of air (jet) is moving at 450 knots influence the movement of anything (you) moving within that body? Plain as mud?
If turning from upwind to downwind is no problem and does not affect the aerodynamics and the helicopters performance, then we should all be ok with taking off downwind
Join Date: Mar 2008
Location: England... what's left of it...
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A ram air parachute requires airspeed to remain inflated, and its BAD, BAD news should it deflate. Any problems turning up wind down wind? Absolutely none, and nothing can turn quicker than one of those babies. They are certainly affected by changes in airspeed due to gusts and care has to be taken in such conditions because they will collapse
There won't be problems provided there is some airspeed as you say, and there usually is from below due to descending. Try an instant 180 "level" turn to downwind at 90 degree bank with a parachute and see what happens.... same effect as the gusts you mention: negative airspeed.
Join Date: Aug 2003
Location: Sale, Australia
Age: 80
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Try an instant 180 "level" turn to downwind at 90 degree bank with a parachute