Helicopter pitch change when orbiting around a fixed point??
an aircraft flies at a constant power setting, straight and level in calm wind, airspeed = groundspeed = lets say 100kts.
Suddenly, the wind pick ups to a 40kt headwind.
Does the airspeed increase momentarily? Of course it does. The inertia of the aircraft will keep it moving at 100kts groundspeed and a higher airspeed will be observed for a moment (how high depends on how quickly the wind picked up), until the aircraft has slowed down to 60kts groundspeed, 100kts airspeed again.
For the same reason, you WILL see a momentarily increase of airspeed when turning into the wind and a decrease when turning downwind. It's not just perception, it works whether you look out the window or not.
If the inertia of the aircraft did not make a difference, why would the airspeed indicator jump all over the place when flying through turbulence?
Suddenly, the wind pick ups to a 40kt headwind.
Does the airspeed increase momentarily? Of course it does. The inertia of the aircraft will keep it moving at 100kts groundspeed and a higher airspeed will be observed for a moment (how high depends on how quickly the wind picked up), until the aircraft has slowed down to 60kts groundspeed, 100kts airspeed again.
For the same reason, you WILL see a momentarily increase of airspeed when turning into the wind and a decrease when turning downwind. It's not just perception, it works whether you look out the window or not.
If the inertia of the aircraft did not make a difference, why would the airspeed indicator jump all over the place when flying through turbulence?
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FOOL proof
Terrifying that self declared 'test pilots' don't seem to understand the basics of their craft.
They have been able to ply their trade with out understanding:
Relative velocity.
Conservation of enery.
L2Driver and B540 and lelebbel urgently need to rethink their understanding of the dynamics of flight.
A circle flown in the air at a constant airspeed (80kts) , above cloud with say a 70kt wind, is just a constant speed circle in the air!
Unless the aircraft can 'see' the ground it doesn't know it has to get faster or slower over the ground - it does not need 'extra energy' on the 'downwind leg' it's airspeed is unchanged. Its speed is unchanged just a constant 80kts.
The kinetic energy is Relative to the medium against which the force will be applied ! (amazingly) So the 'useful' kinetic energy to a pilot is a function of Airspeed NOT groundspeed.
You can't use the 70kts plus 80kts - 150kts of ground referenced kinetic energy (in the above example) to do a bigger pullup than the 80-70 = 10 kts ground speed kinetic energy when flying at 80 kts in the 'other' direction. It is 80kts both ways.. same pullup - same flight characteristics (just different ground result - if you can detect the ground position)
MIGHTY GEM said it more elegantly - but nobody listened !
Now pilots (who don't understand that) might get confused -
They have been able to ply their trade with out understanding:
Relative velocity.
Conservation of enery.
L2Driver and B540 and lelebbel urgently need to rethink their understanding of the dynamics of flight.
A circle flown in the air at a constant airspeed (80kts) , above cloud with say a 70kt wind, is just a constant speed circle in the air!
Unless the aircraft can 'see' the ground it doesn't know it has to get faster or slower over the ground - it does not need 'extra energy' on the 'downwind leg' it's airspeed is unchanged. Its speed is unchanged just a constant 80kts.
The kinetic energy is Relative to the medium against which the force will be applied ! (amazingly) So the 'useful' kinetic energy to a pilot is a function of Airspeed NOT groundspeed.
You can't use the 70kts plus 80kts - 150kts of ground referenced kinetic energy (in the above example) to do a bigger pullup than the 80-70 = 10 kts ground speed kinetic energy when flying at 80 kts in the 'other' direction. It is 80kts both ways.. same pullup - same flight characteristics (just different ground result - if you can detect the ground position)
MIGHTY GEM said it more elegantly - but nobody listened !
Now pilots (who don't understand that) might get confused -
Last edited by AnFI; 17th Jun 2009 at 23:54. Reason: spling
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If you are walking along a pavement at say 1mph, your legs will move at a certain speed to achieve 1mph. Now if that is a moving pavement at say 4mph & your legs still move at 1mph, then you are going at 5mph one way or 3mph the other way, depending in which direction you are facing. The speed of the pavement does not effect the speed of your legs & I think the same could be applied to flying by replacing the pavement with air.
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nubb of the matter?
Nigel ...
they've got that - I think.
but they're trying to say that you'll have to put in some more effort to do 1 mph to 'accelerate' in the 5mph direction and will need less effort when turning to walk at 1mph in the 3mph direction on the moving walkway....
that is the dangerous idea - eh?
they've got that - I think.
but they're trying to say that you'll have to put in some more effort to do 1 mph to 'accelerate' in the 5mph direction and will need less effort when turning to walk at 1mph in the 3mph direction on the moving walkway....
that is the dangerous idea - eh?
Last edited by AnFI; 18th Jun 2009 at 00:33. Reason: shpelink
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actually if you're walking along at 1 mph on a 5 mph moving sidewalk and then step off or come to the end of that 5 mph sidewalk those 1 mph legs had better get stepping or you get a good example of what inertia is. Imagine an aircraft at a 5ft stationary hover, with a 25kt wind. The wind suddenly stops. What happens to the aircraft. Does it remain at 25 KIAS? Does it instantly accelerate to 25 KIAS? What it does is hit the ground, because power applied is less than power required. With enough altitude it would accelerate to 25 kts but at a 5ft hover, the time required is more than the time available. Low level maneuvering at relatively low airspeeds with wind speed or gusts that are significant require the techniques mentioned if you want to use the aircraft more than once. That much I'm sure of. Enjoyed the discussion, you guys stay safe.
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Different point
B540
Yup that's true - but a different thing. If the 'wind' changes then you recieve or lose energy. but if you run circles inside a cruise ship - you cant tell which way the ship is travelling - no kinetic energy difference (relative to the ship)
Surprisingly
Autorotation downwind is, in energy terms, more useful - since the wind sheer 'adds energy' - from the reduced tail wind (equivalent to increased headwind)
WHO WAS GIVING THE LECTURE referred to AT THE BEGGINING OF THE POST - was it military?
Yup that's true - but a different thing. If the 'wind' changes then you recieve or lose energy. but if you run circles inside a cruise ship - you cant tell which way the ship is travelling - no kinetic energy difference (relative to the ship)
Surprisingly
Autorotation downwind is, in energy terms, more useful - since the wind sheer 'adds energy' - from the reduced tail wind (equivalent to increased headwind)
WHO WAS GIVING THE LECTURE referred to AT THE BEGGINING OF THE POST - was it military?
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Terrifying that self declared 'test pilots' don't seem to understand the basics of their craft.
You can't use the 70kts plus 80kts - 150kts of ground referenced kinetic energy (in the above example) to do a bigger pullup than the 80-70 = 10 kts ground speed kinetic energy when flying at 80 kts in the 'other' direction. It is 80kts both ways.. same pullup - same flight characteristics (just different ground result - if you can detect the ground position)
Please read the G-TIGH accident report again. In appendix F, FDR readout, you can see that the IAS went from ca 73 KIAS to about zero at the same time the helicopter turned out of the wind into a downwind heading. Now, why did the speed drop?? because of low altitude and below clouds? It happened because the helicopter had mass and it tends to stay at the same GS. So going from a headwind condition to a downwind one, they lost IAS. When IAS drops below Vy, which in a S.Puma is about 70 KIAS the power required will increase. During this accident the power stayed at 14-15 degrees of collective pitch, which normally will keep the S. Puma flying nicely, but not at very low airspeeds.
This is called being behind the power curve and it applies to all aircraft. Less speed = more power required. If you are in this state, and speed is decreased even very little, the aircraft will not revert to the speed it had before unless you add power. It will decelerate, this has killed people numerous times.
I have the utmost respect for the UK AAIB, and they got it right.
(i)The handling pilot's failure to recognize the rapidly changing relationship between airspeed and groundspeed which is a fundamental problem associated with turning downwind in significant wind speeds
Last edited by L2driver; 18th Jun 2009 at 07:42. Reason: added some text
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How about this scenario.
I am in a closed stationary train and flying a model helicopter around a smooth circle. Nothing complex yet and the power is constant.
I stop the flying. The train accelerates to 100mph. Once it is steady at this speed in a straight line I start to fly my helicopter again.
Surely the power and smoothness of orbit in these two cases is the same despite the helicpter flying downwind (or even backwards) relative to the Earth.
Is this not akin to flying compass swings in a strong wind that L2 describes.
Why does one exhibit varying power and the other not ?
As I said initially, I am not saying that anybody is wrong here, I am just trying to understand where the difference comes in.
Thanks
TB
I am in a closed stationary train and flying a model helicopter around a smooth circle. Nothing complex yet and the power is constant.
I stop the flying. The train accelerates to 100mph. Once it is steady at this speed in a straight line I start to fly my helicopter again.
Surely the power and smoothness of orbit in these two cases is the same despite the helicpter flying downwind (or even backwards) relative to the Earth.
Is this not akin to flying compass swings in a strong wind that L2 describes.
Why does one exhibit varying power and the other not ?
As I said initially, I am not saying that anybody is wrong here, I am just trying to understand where the difference comes in.
Thanks
TB
I have to say that when I teach 30 degree turns the following happens everytimein a 300. Set 20" mp,60 kts, roll into the turn, by about 45 degrees into turn nose will start to drop. Add .5" mp the nose will come back to 60 kt attitude and the ac will go round and round in circles at a constant height and speed all day. Tried this in loads of different conditions always the same so seems to show that wind does not make a difference
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Can't help it...
Train scenario: As long as the helicopter model is kept inside the cabin -yes the model helicopter will behave exactly the same stationary or at speed as it is not exposed to the relative wind on the outside. Same as a fly in an airliner at Mach 0.82. There is no acceleration except that the model or fly do in relation to the environment. Same as us all living on Earth.
Hughes 300 scenario:
Yes you are correct as long you are on the "right side" of the power curve. The aircraft will correct itself back to the initial speed due to a "good" L/D ratio. Try this at 30 kts with 20 kts wind, and I think you will find it different
What is dangerous here is that some people don't understand the relationship between GS and IAS and energy required. Most posters have elected to ignore the dynamics of slow speed flight, i.e. flight at speeds below best L/D. At higher speeds, the aircraft takes care of itself. At lower speeds, it does not unless you are on 4 axis autopilot.
Energy in aircraft is either altitude or engine power (and you might add your current speed, but that is temporary). If you are out of one of these , be very careful. If you are out of two or more, you should not be there in the first place.
Train scenario: As long as the helicopter model is kept inside the cabin -yes the model helicopter will behave exactly the same stationary or at speed as it is not exposed to the relative wind on the outside. Same as a fly in an airliner at Mach 0.82. There is no acceleration except that the model or fly do in relation to the environment. Same as us all living on Earth.
Hughes 300 scenario:
Yes you are correct as long you are on the "right side" of the power curve. The aircraft will correct itself back to the initial speed due to a "good" L/D ratio. Try this at 30 kts with 20 kts wind, and I think you will find it different
What is dangerous here is that some people don't understand the relationship between GS and IAS and energy required. Most posters have elected to ignore the dynamics of slow speed flight, i.e. flight at speeds below best L/D. At higher speeds, the aircraft takes care of itself. At lower speeds, it does not unless you are on 4 axis autopilot.
Energy in aircraft is either altitude or engine power (and you might add your current speed, but that is temporary). If you are out of one of these , be very careful. If you are out of two or more, you should not be there in the first place.
Last edited by L2driver; 18th Jun 2009 at 13:10. Reason: misprint
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I only fly model Helis so risk the wrath of proper pilots by posting here so apologies in advance .
I am talking about decent sized IC engined models with a full set of controls inc a govenor to keep constant head speed .
I often do walking speed manouvers out of ground effect but low enough to have the ground as a reference . In a flat calm pitch change is only really needed to maintain constant height if airspeed changes (no wind so airspeed =ground speed )
A breeze particularly if gusty needs contant and quick attention to pitch to maintain height and groundspeed particularly with slow turns .
I am talking about decent sized IC engined models with a full set of controls inc a govenor to keep constant head speed .
I often do walking speed manouvers out of ground effect but low enough to have the ground as a reference . In a flat calm pitch change is only really needed to maintain constant height if airspeed changes (no wind so airspeed =ground speed )
A breeze particularly if gusty needs contant and quick attention to pitch to maintain height and groundspeed particularly with slow turns .
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No need to apologize,- same dynamics.
Your model would climb and descend according to the wind because of the before mentioned power required curve.
However, if you made your model take off into a 15 kts wind, and then made an immediate 180 degree turn, I think you will find out what I mean.
Your model would climb and descend according to the wind because of the before mentioned power required curve.
However, if you made your model take off into a 15 kts wind, and then made an immediate 180 degree turn, I think you will find out what I mean.
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HuntandFish, once again you are referencing to the ground.
L2driver, I'm trying to keep an open mind either way here, but I think you conceded to the opposition here
Surely if we take the parcel of air inside the train to be a free stream air flowing over the earth, then this is exactly how we fly everyday.
I also feel you mised a point made by the AAIB:
If the wind is gusting, and most wind is to some degree, then as we turn into/out of it, we will experience a change in airpeed, but no more than we would experience anyway in level flight. The only difference I can see is that we find it harder to judge/cope with due to the constantly changing relative direction.
L2driver, I'm trying to keep an open mind either way here, but I think you conceded to the opposition here
Train scenario: As long as the helicopter model is kept inside the cabin -yes the model helicopter will behave exactly the same stationary or at speed as it is not exposed to the relative wind on the outside. Same as a fly in an airliner at Mach 0.82
I also feel you mised a point made by the AAIB:
(ii)The Commander, who was the handling pilot at the time, shortly after takeoff inadvertantly allowed the airspeed and then the height to decrease whilst turning away from a strong gusting wind
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L2driver
If I take of with 15kt head wind and hold constant postion hover I need to drop the nose a bit as I have a 15kt forward airspeed .
Turn 180 and quick corrections neccessary to hold as I have changed airspeed tp-15kts .
Is that what you mean .
If I take of with 15kt head wind and hold constant postion hover I need to drop the nose a bit as I have a 15kt forward airspeed .
Turn 180 and quick corrections neccessary to hold as I have changed airspeed tp-15kts .
Is that what you mean .
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Why is the model heli in the train or the bug in the aircraft any different to a real heli that is well OGE doing a constant 60 degree bank turn (and hence spiralling down wind when looked at relative to the ground) ? None of them are 'feeling' the ground in any different way as they are all moving in an orderly manner relative to the airmass.
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HuntandFish
Not really
Unless you let the airspeed build up nicely and make a gentle turn out of the wind with sufficient power on, I think that you will find the entire exercise very expensive.
Unless you let the airspeed build up nicely and make a gentle turn out of the wind with sufficient power on, I think that you will find the entire exercise very expensive.
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This "model" scenario is all related to the pilot on the ground. Obviously with the pilot on the ground, the pilot will use a given power for flight into wind and will most likely notice the model fall out of translational lift on the downwind turn, so will instinctively add power to prevent this. So therefore the model pilot will be constantly modifying power to maintain level flight with reference to the ground, because that is the only reference he has.
The full size helicopter pilot flying a constant airspeed turn without reference to the ground will not require a power change just because he is going downwind, there is no (relative) downwind.
The full size helicopter pilot flying a constant airspeed turn without reference to the ground will not require a power change just because he is going downwind, there is no (relative) downwind.
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I am sorry that I have to remind you all, but this thread started with: Helicopter pitch change when orbiting around a fixed point??
And to Chopjock: why don't you show some respect to people that were killed in the G-TIGH accident. According to you the AAIB is completely wrong.
Read the report for God's sake
And the previous posts too!
I am seriously worried about the lack of basic physics knowledge and airmanship a lot of posters show on this forum. We are supposed to be the Professional Pilots Rumour Network, not the idiot commentators we find in the media elsewhere.
And to Chopjock: why don't you show some respect to people that were killed in the G-TIGH accident. According to you the AAIB is completely wrong.
Read the report for God's sake
And the previous posts too!I am seriously worried about the lack of basic physics knowledge and airmanship a lot of posters show on this forum. We are supposed to be the Professional Pilots Rumour Network, not the idiot commentators we find in the media elsewhere.
Last edited by L2driver; 18th Jun 2009 at 09:55. Reason: Added text
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NF stable
You are quite correct in most of what you say.
However:
When the handling pilot allowed the airspeed and then the height to decrease whilst turning away from a strong gusting wind it means he did not increase the power to a sufficient level.
And this is the crux of the matter gusts or not, they did not have (use) the energy they needed to keep flying.
You are quite correct in most of what you say.
However:
The Commander, who was the handling pilot at the time, shortly after takeoff inadvertantly allowed the airspeed and then the height to decrease whilst turning away from a strong gusting wind
And this is the crux of the matter gusts or not, they did not have (use) the energy they needed to keep flying.
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L2, when you do compass swings, are these orbits relative to a fixed point or just constant rate turns ? I understood from your earlier post that they were the latter and that you said that these required constant changes in power.
Have I misunderstood ?
If they are constant rate turns then please can you explain why they need power changes as I am still stuck on this point as I see it as the same as the model in the train as there is no reference to the fixed ground.
Thanks
Have I misunderstood ?
If they are constant rate turns then please can you explain why they need power changes as I am still stuck on this point as I see it as the same as the model in the train as there is no reference to the fixed ground.
Thanks