Downwind turn Myth
11-22-2010, 03:20 PM
#51
RE: Downwind turn Myth
ORIGINAL: rjbob
The only thing to change will be the track over the ground.
In the example you gave, if the plane wouldn't stall in still air, it won't stall in the 30 knot headwind.
You should be able to find a video of a pylon race in the wind somewhere.
ORIGINAL: hugger-4641
I've said this before but I'll say it again: If Highhorse would like to prove his theory once and for all as it applies to RC flight, we need to see a video of him flying a Cessna 150 at 55knts, 50 ft AGL, into a 30knt headwind, then make a 180 degree course change at say 50% bank and 50% up elevator input. If his theory is correct, there will be no ''real'' effect, the plane will not know the difference in wind direction or speed, and he should be fine.
(Please don't try this for real by the way.
)
I've said this before but I'll say it again: If Highhorse would like to prove his theory once and for all as it applies to RC flight, we need to see a video of him flying a Cessna 150 at 55knts, 50 ft AGL, into a 30knt headwind, then make a 180 degree course change at say 50% bank and 50% up elevator input. If his theory is correct, there will be no ''real'' effect, the plane will not know the difference in wind direction or speed, and he should be fine.
(Please don't try this for real by the way.
)
In the example you gave, if the plane wouldn't stall in still air, it won't stall in the 30 knot headwind.
You should be able to find a video of a pylon race in the wind somewhere.
But yes, I have done the equivalent of that and more.
Dude, I assure you that I do not have an axe to grind with you on any personal level. I am telling u for ur own good tho, that your challenge simply makes you look foolish and demonstrates a complete lack of knowledge on the topic.
Don't believe me, I don't care. I'm telling you the facts, and they are verifiable elsewhere.
I can lead u to water, but I can't make you drink.
11-22-2010, 03:24 PM
#52
RE: Downwind turn Myth
Imagine the sheer quivering ecstacy we'd feel now if you had actually DONE few thousand loops in a Pitts, Suk, or whatever. Especially if you'd made round loops (scoring 10/10) in front of certified judges, starting from both downwind and upwind entries, while engaged in national competitions !!
Then you'd actually have experience on your side in addition to your superior logic and intellect.
Then you'd actually have experience on your side in addition to your superior logic and intellect.
11-22-2010, 03:29 PM
#53
RE: Downwind turn Myth
ORIGINAL: Pete737
May I ask you highhorse, since I have never flown a full scale plane solo.
While flying along , does you IAS react to gusts of wind? Will the instrument measure I change? I cannot imagine it would not...
Pete
May I ask you highhorse, since I have never flown a full scale plane solo.
While flying along , does you IAS react to gusts of wind? Will the instrument measure I change? I cannot imagine it would not...
Pete
Yes, I am a professional aviator with 35 years and something over 11,000 hours of experience. Several type ratings. Former aerobatic competitor and airshow performer (Pitts and Sukhoi). Currently a Captain, A-300.
Yes, gusts are quite readily felt and observed on the a/s indicator. Gusts which are strong enuff (windshear) are quite deadly and all of us in the industry train extensively for that condition as well.
I'm at a loss as to why you asked, tho, cus absolutely nothing in the previous discussion has anything to do with gusts at all. I was, in fact, quite specific when I said "steady state winds".
Thanks for playing.
11-22-2010, 03:41 PM
#54
RE: Downwind turn Myth
ORIGINAL: siclick33
Haha that's funny. Thanks for brightening up my evening. Highhorse by name......................................
Imagine the sheer quivering ecstacy we'd feel now if you had actually DONE few thousand loops in a Pitts, Suk, or whatever. Especially if you'd made round loops (scoring 10/10) in front of certified judges, starting from both downwind and upwind entries, while engaged in national competitions !!
Then you'd actually have experience on your side in addition to your superior logic and intellect.
Then you'd actually have experience on your side in addition to your superior logic and intellect.
When you can't make a logical, relevant point and multiple posters are adding verifiable references and scientific facts which counter your circular reasoning, you have only one move left in a pathetic attempt to save face, and that is to veer into left field with a completely irrelevant comment.
Disagree with me all day, matters not to ME, but u are digging urself into a deeper and deeper hole in your defense of a MYTH which has been thoroughly and completely debunked over and over and over again..........
LMAO
DON'T BELIEVE ME !!!! PLEASE !!!! Just GO DO THE RESEARCH on your own. Or don't.
11-22-2010, 03:45 PM
#55
RE: Downwind turn Myth
Have you actually read my posts?
I'm not disagreeing with you about the myth and I'm quite happy with the depth of my hole thankyou. Can you please post some more of your qualifications for me?
Thanks.
I'm not disagreeing with you about the myth and I'm quite happy with the depth of my hole thankyou. Can you please post some more of your qualifications for me?
Thanks.
11-22-2010, 03:59 PM
#56
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RE: Downwind turn Myth
Try a simple test. Get on a bicycle and ride it with a 10 mph wind at your back. You will notice at a certain speed you will feel no wind in your face. That is what happens with an airplane there is a point where there is not enough wind flowing over the wings to generate lift. It usually happens when you are flying at or near stall speed and the tail wind suddenly climbs. There was a major airline crash in Dallas years ago where they determined that contributed to it I think.
11-22-2010, 04:11 PM
#57
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RE: Downwind turn Myth
Highhorse is right, of course, but it's good to be reminded (as in post 42) that an RC pilot standing on the ground may assume from the added ground speed when flying downwind that the plane has enough airspeed to be able to make a sharp turn safely, when it doesn't. Furthermore, when turning onto the base leg and again on final, the urge to make a turn that looks good from the ground combined with the fact that the plane's high downwind ground speed necessitates a sharper-than-normal turn to make that turn look good can lead to a stall. So the "downwind turn" is a myth if you believe wrong things about airspeed changing according to wind direction, but it's real when you take into account the RC pilot's tendency to make mistakes and to take ground speed too seriously. Even full-scale pilots can make mistakes like this, though as they have airspeed indicators they have less excuse than we do.
11-22-2010, 04:15 PM
#59
RE: Downwind turn Myth
ORIGINAL: H.Dale
Try a simple test. Get on a bicycle and ride it with a 10 mph wind at your back. You will notice at a certain speed you will feel no wind in your face. That is what happens with an airplane there is a point where there is not enough wind flowing over the wings to generate lift. It usually happens when you are flying at or near stall speed and the tail wind suddenly climbs. There was a major airline crash in Dallas years ago where they determined that contributed to it I think.
Try a simple test. Get on a bicycle and ride it with a 10 mph wind at your back. You will notice at a certain speed you will feel no wind in your face. That is what happens with an airplane there is a point where there is not enough wind flowing over the wings to generate lift. It usually happens when you are flying at or near stall speed and the tail wind suddenly climbs. There was a major airline crash in Dallas years ago where they determined that contributed to it I think.
But the two examples u give are not related to each other or to the case at hand.
The bike is in contact with the ground. Not suspended in the moving air stream.
The Dallas (Delta L-1011) was a case of windshear, not a steady state wind. Apples and oranges.
11-22-2010, 04:23 PM
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RE: Downwind turn Myth
Highhorse....you say 'steady state' and by that if you also mean inertial effects are not to be considered, then, of course, your arguments are correct. But that's kinda disingenuous.
Because, in the real world, planes/models have mass, and therefore are subject to the laws of physics ...i.e., they cannot accelerate at an infinite rate to immediately match changing conditions....whether gusts or a turn from (say) downwind to upwind. There will be an effect, however small, as the plane/model does, indeed, require some time to 'catch up' to that sea of air around it. That effect may be undetectable during slow turns/maneuvers....perhaps your 'steady state'. But a fast transition (e.g., from upwind to downwind) will produce a loss in altitude (all else being same), as the model must lose lift in not being capable of accelerating instantly to maintain a same relative AS.
I.e., maneuvers (accelerations) even in steady wind conditions do produce an effect. Simple physics, and demonstrable all the time at the field, esp w/ high inertia (heavy) models. And nothing to do w/ AS vs GS, etc.
Ray
Because, in the real world, planes/models have mass, and therefore are subject to the laws of physics ...i.e., they cannot accelerate at an infinite rate to immediately match changing conditions....whether gusts or a turn from (say) downwind to upwind. There will be an effect, however small, as the plane/model does, indeed, require some time to 'catch up' to that sea of air around it. That effect may be undetectable during slow turns/maneuvers....perhaps your 'steady state'. But a fast transition (e.g., from upwind to downwind) will produce a loss in altitude (all else being same), as the model must lose lift in not being capable of accelerating instantly to maintain a same relative AS.
I.e., maneuvers (accelerations) even in steady wind conditions do produce an effect. Simple physics, and demonstrable all the time at the field, esp w/ high inertia (heavy) models. And nothing to do w/ AS vs GS, etc.
Ray
11-22-2010, 04:37 PM
#61
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RE: Downwind turn Myth
No comments about udders please
Here's another good figure showing G relative to stall and airspeed. If you enter a loop downwind you will need much more speed to overcome the G forces and keep enough air speed over the wing.
Here's another good figure showing G relative to stall and airspeed. If you enter a loop downwind you will need much more speed to overcome the G forces and keep enough air speed over the wing.
11-22-2010, 04:46 PM
#62
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RE: Downwind turn Myth
For you doubters with full scale experience, try this experiment:
Get an instructor and a Cessna 150 and go flying on a steady 20kt. windy day. (Approximate substitutions allowed.)
Climb up to a safe altitude and put on a hood.
Crank it over into a 60 degree bank at 70 kt. and hold everything nice and stable.
As long as you keep the hood on, you will neither feel nor sense anything other than a steady 2g force on your butt.
Get an instructor and a Cessna 150 and go flying on a steady 20kt. windy day. (Approximate substitutions allowed.)
Climb up to a safe altitude and put on a hood.
Crank it over into a 60 degree bank at 70 kt. and hold everything nice and stable.
As long as you keep the hood on, you will neither feel nor sense anything other than a steady 2g force on your butt.
11-22-2010, 04:48 PM
#63
RE: Downwind turn Myth
Heres another test :
Get yourself a fullsize helicopter such as a Robinson or Bell 47.
Bring it to the hover into a 20 or 30 knot wind, groundspeed zero, IAS will be the value of the headwind. .
Pedal it around 180 degrees in 2 or 3 seconds or so so you are now pointing downwind.
IF your airspeed was to remain constant at the 20 or 30 knots the groundspeed would, in 2 or 3 seconds need to increase to 40 or 60 knots (20 or 30 knot tailwind plus the airspeed you had in the hover ) in the time it took, 2 to 3 seconds, to yaw 180 degrees !
It doesn't happen, (not many sports cars can accelerate from 0k to 60k in 2 or 3 seconds !) Airspeed falls, then increases as as the chopper accelerates which suggests that the downwind turn is not totally a myth !
Anyone care to try this for real ?
(caution, you may run out of lateral, wind on the beam, and aft cyclic with the tailwind, with unfortunate results ! !)
Now if you do a progressive co-ordinated turn the turn rate is much slower so that the effect is hardly noticeable, if at all.
By all means shoot me down but please prove it, (and explain how a low powered helicopter can suddenly accelerate like a dingbat !) but we were cautioned about turning downwind at low speed and low height in helicopters on the RAF rotary course. !
Regards, David Gladwin.
Get yourself a fullsize helicopter such as a Robinson or Bell 47.
Bring it to the hover into a 20 or 30 knot wind, groundspeed zero, IAS will be the value of the headwind. .
Pedal it around 180 degrees in 2 or 3 seconds or so so you are now pointing downwind.
IF your airspeed was to remain constant at the 20 or 30 knots the groundspeed would, in 2 or 3 seconds need to increase to 40 or 60 knots (20 or 30 knot tailwind plus the airspeed you had in the hover ) in the time it took, 2 to 3 seconds, to yaw 180 degrees !
It doesn't happen, (not many sports cars can accelerate from 0k to 60k in 2 or 3 seconds !) Airspeed falls, then increases as as the chopper accelerates which suggests that the downwind turn is not totally a myth !
Anyone care to try this for real ?
(caution, you may run out of lateral, wind on the beam, and aft cyclic with the tailwind, with unfortunate results ! !)
Now if you do a progressive co-ordinated turn the turn rate is much slower so that the effect is hardly noticeable, if at all.
By all means shoot me down but please prove it, (and explain how a low powered helicopter can suddenly accelerate like a dingbat !) but we were cautioned about turning downwind at low speed and low height in helicopters on the RAF rotary course. !
Regards, David Gladwin.
11-22-2010, 04:51 PM
#64
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RE: Downwind turn Myth
Downwind turns:
I cannot, will not, and simply must not take it any more !!!!!!!!!!!!!
Please, just kill me now and get me out of my misery!!!!!
Arggggggggghhhh!!!!
littlera
I cannot, will not, and simply must not take it any more !!!!!!!!!!!!!
Please, just kill me now and get me out of my misery!!!!!
Arggggggggghhhh!!!!
littlera
11-22-2010, 04:52 PM
#65
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RE: Downwind turn Myth
For you doubters with full scale experience, try this experiment:
Get an instructor and a Cessna 150 and go flying on a steady 20kt. windy day. (Approximate substitutions allowed.)
Climb up to a safe altitude and put on a hood.
Crank it over into a 60 degree bank at 70 kt. and hold everything nice and stable.
As long as you keep the hood on, you will neither feel nor sense anything other than a steady 2g force on your butt.
Get an instructor and a Cessna 150 and go flying on a steady 20kt. windy day. (Approximate substitutions allowed.)
Climb up to a safe altitude and put on a hood.
Crank it over into a 60 degree bank at 70 kt. and hold everything nice and stable.
As long as you keep the hood on, you will neither feel nor sense anything other than a steady 2g force on your butt.
11-22-2010, 04:52 PM
#66
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RE: Downwind turn Myth
I'm not sure why the analogy of a bicycle being on the ground makes a difference. If an airplane requires 30 mph of wind flowing over the wings to keep it in the air and an abrupt tail wind causes that to drop below 30 then how does it stay in the air? The wind shear in the L-1011 crash was just that, an abrupt change in wind speed from what I remember.
11-22-2010, 05:02 PM
#67
RE: Downwind turn Myth
The plane experiances 2G's of force in a turn, it increases the stall speed or minimum airspead from this G force. But it has noting to do with the down wind effect. High horse is completely correct and others are on a bad tangent that makes them look silly.
11-22-2010, 05:07 PM
#68
RE: Downwind turn Myth
ORIGINAL: 67Jag
Highhorse....you say 'steady state' and by that if you also mean inertial effects are not to be considered, then, of course, your arguments are correct. But that's kinda disingenuous.
Because, in the real world, planes/models have mass, and therefore are subject to the laws of physics ...i.e., they cannot accelerate at an infinite rate to immediately match changing conditions....whether gusts or a turn from (say) downwind to upwind. There will be an effect, however small, as the plane/model does, indeed, require some time to 'catch up' to that sea of air around it. That effect may be undetectable during slow turns/maneuvers....perhaps your 'steady state'. But a fast transition (e.g., from upwind to downwind) will produce a loss in altitude (all else being same), as the model must lose lift in not being capable of accelerating instantly to maintain a same relative AS.
I.e., maneuvers (accelerations) even in steady wind conditions do produce an effect. Simple physics, and demonstrable all the time at the field, esp w/ high inertia (heavy) models. And nothing to do w/ AS vs GS, etc.
Ray
Highhorse....you say 'steady state' and by that if you also mean inertial effects are not to be considered, then, of course, your arguments are correct. But that's kinda disingenuous.
Because, in the real world, planes/models have mass, and therefore are subject to the laws of physics ...i.e., they cannot accelerate at an infinite rate to immediately match changing conditions....whether gusts or a turn from (say) downwind to upwind. There will be an effect, however small, as the plane/model does, indeed, require some time to 'catch up' to that sea of air around it. That effect may be undetectable during slow turns/maneuvers....perhaps your 'steady state'. But a fast transition (e.g., from upwind to downwind) will produce a loss in altitude (all else being same), as the model must lose lift in not being capable of accelerating instantly to maintain a same relative AS.
I.e., maneuvers (accelerations) even in steady wind conditions do produce an effect. Simple physics, and demonstrable all the time at the field, esp w/ high inertia (heavy) models. And nothing to do w/ AS vs GS, etc.
Ray
I have made, in the real world, two consecutive 360 degree turns from a 150kt headwnind thru the reversal to a 150 degree tailwind and back into a headwind again.
These "300 knot speed reversals" were done at a weight in excess of 300,000 pounds and while flying only 30 kts above the stall speed. Once established in the turn (and the extra induced drag had been compensated for) , the airspeed and power settings never varied by more than 5 knots or a few percent, respectively. Furthermore, the turns were completed in far less time than the a/c is physically capable of recuperating and then shedding 150 "lost" and then "re-aquired" knots.
I've also played these games at 1600 pounds with zero and even negative airspeeds. I've repeatedly and at low level (airshows) bet my life on these facts of physics as I pushed negative to level inverted flight from a vertical downline, deadstick mind you, and buffeting on the edge of a stall the entire time. There was never a shred of difference when transitioning from upwind to downwind.
When squeezing these last ounces of performance from an airplane day after day, one feels every nuance. After a while the airplane becomes more familiar than your car.
This isn't abstract book sh*t fellas, although the books bear this out too
11-22-2010, 05:07 PM
#69
RE: Downwind turn Myth
As long as you keep the hood on, you will neither feel nor sense anything other than a steady 2g force on your butt.
11-22-2010, 05:10 PM
#70
RE: Downwind turn Myth
When I saw the title of the thread I was sure it would provoke a lot of discussian, I was right
This has been 'dicussed' since the early days of aviation, I would have to say I agree with highhorse, he is largely correct.
In theory we can hover a helicopter in a 120 knot wind, or fly forward at 120knots in still air,the point being the helicopter would not know, and as David said as long asthere is no sudden changes of direction all will bewell, and of course with fixed wing,the aircraft does not know it is turning downwind, or up wind for that matter.
This has been 'dicussed' since the early days of aviation, I would have to say I agree with highhorse, he is largely correct.
In theory we can hover a helicopter in a 120 knot wind, or fly forward at 120knots in still air,the point being the helicopter would not know, and as David said as long asthere is no sudden changes of direction all will bewell, and of course with fixed wing,the aircraft does not know it is turning downwind, or up wind for that matter.
11-22-2010, 05:13 PM
#71
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RE: Downwind turn Myth
ORIGINAL: David Gladwin
Heres another test :
Get yourself a fullsize helicopter such as a Robinson or Bell 47.
Bring it to the hover into a 20 or 30 knot wind, groundspeed zero, IAS will be the value of the headwind. .
Pedal it around 180 degrees in 2 or 3 seconds or so so you are now pointing downwind.
IF your airspeed was to remain constant at the 20 or 30 knots the groundspeed would, in 2 or 3 seconds need to increase to 40 or 60 knots (20 or 30 knot tailwind plus the airspeed you had in the hover ) in the time it took, 2 to 3 seconds, to yaw 180 degrees !
It doesn't happen, (not many sports cars can accelerate from 0k to 60k in 2 or 3 seconds !) Airspeed falls, then increases as as the chopper accelerates which suggests that the downwind turn is not totally a myth !
Anyone care to try this for real ?
(caution, you may run out of lateral, wind on the beam, and aft cyclic with the tailwind, with unfortunate results ! !)
Now if you do a progressive co-ordinated turn the turn rate is much slower so that the effect is hardly noticeable, if at all.
By all means shoot me down but please prove it, (and explain how a low powered helicopter can suddenly accelerate like a dingbat !) but we were cautioned about turning downwind at low speed and low height in helicopters on the RAF rotary course. !
Regards, David Gladwin.
Heres another test :
Get yourself a fullsize helicopter such as a Robinson or Bell 47.
Bring it to the hover into a 20 or 30 knot wind, groundspeed zero, IAS will be the value of the headwind. .
Pedal it around 180 degrees in 2 or 3 seconds or so so you are now pointing downwind.
IF your airspeed was to remain constant at the 20 or 30 knots the groundspeed would, in 2 or 3 seconds need to increase to 40 or 60 knots (20 or 30 knot tailwind plus the airspeed you had in the hover ) in the time it took, 2 to 3 seconds, to yaw 180 degrees !
It doesn't happen, (not many sports cars can accelerate from 0k to 60k in 2 or 3 seconds !) Airspeed falls, then increases as as the chopper accelerates which suggests that the downwind turn is not totally a myth !
Anyone care to try this for real ?
(caution, you may run out of lateral, wind on the beam, and aft cyclic with the tailwind, with unfortunate results ! !)
Now if you do a progressive co-ordinated turn the turn rate is much slower so that the effect is hardly noticeable, if at all.
By all means shoot me down but please prove it, (and explain how a low powered helicopter can suddenly accelerate like a dingbat !) but we were cautioned about turning downwind at low speed and low height in helicopters on the RAF rotary course. !
Regards, David Gladwin.
I'm no helicopter jockey, but why don't YOU try your same experiment except with NO wind:
You're cruising along at 30 knots.
Now you "Pedal it around 180 degrees in 2 or 3 seconds or so...".
I doubt that the results would be much different than if you attempted the same maneuver as per your example with a 30 kt. headwind.
Let us know how it goes!
11-22-2010, 05:23 PM
#72
RE: Downwind turn Myth
ORIGINAL: rcjets_63
Yes, how aggressively the turn is made does have an effect. A high ''G'' turn will produce a higher amount of drag and the airplane will lose AIRSPEED.
The ''basic principal of physics'' you mention is Newton's First Law which is ''Every body remains in a state of rest or uniform motion (constant velocity) unless it is acted upon by an external unbalanced force.''
If you are flying straight and level at a a constant airspeed then lift = gravity and thrust=drag. When you start to turn, you bank and pull back on the stick (to maintain altitude). This increases your ANGLE OF ATTACK which increased the amount of lift AND drag the wings develop. The increase in drag (the outside unbalanced force) will result in a decrease in airspeed (assuming that you don't increase your throttle setting).
Nope, you realized a 40kt change in GROUND SPEED not AIRSPEED.
Incidentally, airspeed has no effect on lift coefficient. The coefficient of lift is a dimensionless number associated with a particular shape of an aerofoil. Lift coefficient varies with angle of attack. Lift coefficient is used in the lift equation which calculates the lift force generated by a wing using this particular cross section flying at a given airspeed and air density.
Regards,
Jim
ORIGINAL: Erik R
Depending on how aggressively the course reversal is made,the relative wind,and resultant coefficient of lift can change. The basic principal of physics,that an object in motion,stays in motion,relative to the stored energy,which varies as a function of mass x velocity,is a player.
Depending on how aggressively the course reversal is made,the relative wind,and resultant coefficient of lift can change. The basic principal of physics,that an object in motion,stays in motion,relative to the stored energy,which varies as a function of mass x velocity,is a player.
The ''basic principal of physics'' you mention is Newton's First Law which is ''Every body remains in a state of rest or uniform motion (constant velocity) unless it is acted upon by an external unbalanced force.''
If you are flying straight and level at a a constant airspeed then lift = gravity and thrust=drag. When you start to turn, you bank and pull back on the stick (to maintain altitude). This increases your ANGLE OF ATTACK which increased the amount of lift AND drag the wings develop. The increase in drag (the outside unbalanced force) will result in a decrease in airspeed (assuming that you don't increase your throttle setting).
ORIGINAL: Erik R
In simple terms,think of a 3D airplaneflying into a 20kt headwind,and doing a a 3D type push/pull over of 180 degrees.At completion it is now in a 20 kt tailwind.It used thrust/lift to overcome the physics principal described earlier,yet realized a 40 kt loss of airspeed,with a corresponding loss in coefficient of lift.
In simple terms,think of a 3D airplaneflying into a 20kt headwind,and doing a a 3D type push/pull over of 180 degrees.At completion it is now in a 20 kt tailwind.It used thrust/lift to overcome the physics principal described earlier,yet realized a 40 kt loss of airspeed,with a corresponding loss in coefficient of lift.
Incidentally, airspeed has no effect on lift coefficient. The coefficient of lift is a dimensionless number associated with a particular shape of an aerofoil. Lift coefficient varies with angle of attack. Lift coefficient is used in the lift equation which calculates the lift force generated by a wing using this particular cross section flying at a given airspeed and air density.
Regards,
Jim
I am very familiar with what coefficient of lift,angle of attack,and relative wind are..If you notice in my earlier post,I referred relative wind,and I stated that an airplane can stall at any airspeed or attitude.If you want to nitpick,your last statement is technically incorrect,but nitpicking was not my intention.
My point was,in the real world,with our rc models,with their ability to pull extreme g's,and other maneuverabilty characteristics that far exceed the capability of any full scale aircraft,and more so any human being strapped to that aircraft,the downwind issue described has a greater chance of coming into play.The mass vector of the airframe,and by default the wing,and it's corresponding angle of attack,are not necessarily "drifting" in the sea of air,still or 100kts of wind.In most cases highhorse is correct,but not all.
Erik
11-22-2010, 05:24 PM
#73
RE: Downwind turn Myth
Bring it to the hover into a 20 or 30 knot wind, groundspeed zero, IAS will be the value of the headwind. .
Pedal it around 180 degrees in 2 or 3 seconds or so so you are now pointing downwind.
IF your airspeed was to remain constant at the 20 or 30 knots the groundspeed would, in 2 or 3 seconds need to increase to 40 or 60 knots (20 or 30 knot tailwind plus the airspeed you had in the hover ) in the time it took, 2 to 3 seconds, to yaw 180 degrees !
Pedal it around 180 degrees in 2 or 3 seconds or so so you are now pointing downwind.
IF your airspeed was to remain constant at the 20 or 30 knots the groundspeed would, in 2 or 3 seconds need to increase to 40 or 60 knots (20 or 30 knot tailwind plus the airspeed you had in the hover ) in the time it took, 2 to 3 seconds, to yaw 180 degrees !
11-22-2010, 05:24 PM
#74
RE: Downwind turn Myth
ORIGINAL: H.Dale
I'm not sure why the analogy of a bicycle being on the ground makes a difference. If an airplane requires 30 mph of wind flowing over the wings to keep it in the air and an abrupt tail wind causes that to drop below 30 then how does it stay in the air? The wind shear in the L-1011 crash was just that, an abrupt change in wind speed from what I remember.
I'm not sure why the analogy of a bicycle being on the ground makes a difference. If an airplane requires 30 mph of wind flowing over the wings to keep it in the air and an abrupt tail wind causes that to drop below 30 then how does it stay in the air? The wind shear in the L-1011 crash was just that, an abrupt change in wind speed from what I remember.
I know that it's counter-intuitive, but it just doesn't.
In the case of the L-1011, wind basically exploded behind the plane faster than the co-pilot could react. (It was survivable had he reacted sooner and smarter. After the crash, that became an industry case study so that we could all learn from others' sacrifices, and many of us trained in sims loaded with the data from their flight recorder)
Flying circles in a steady state wind is to swimming circles in a flowing river, as flying in a windshear is to swimming circles in a still river next to the dam as it bursts.
In the former you will feel nothing, in the latter ur gonna swallow some water !
11-22-2010, 05:40 PM
#75
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Join Date: Sep 2003
Location: Napa,
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RE: Downwind turn Myth
Some 20-plus years ago I attended an airshow at the Arcata California airport. It was an unusual severe clear day and there was a steady wind off the sea of about 15 to 20 knots on the ground. There was a near stock Piper J-3 Cub (full span, 90 hp, seaplane prop) that did a "low and slow" type aerobatic routine. On his loops into the wind it looked like he almost stopped on his entry, and then rapidly picked up speed as he swooped back over the top . Then he did a downwind loop. It appeared that he didn't even change his direction of travel - but that he simply tumbled end over end as he rapidly flew across air show center. As you can imagine, the crowd loved it!