Why do we Lose Airspeed in a Turn and What Causes This?
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Getting back to the original question, the following points are relevant -
(a) for a constant power setting at constant level, a heavier aircraft will fly slower than the lighter example
(b) in a balanced turn, the load factor increases in relation to angle of bank
(c) one can view increased load factor as being much the same as increased weight (mass, whatever)
(d) ergo, turn and you slow down
.. for most of us, this is the typical calculation basis for a first approximation effect of turn on performance.
The underlying cause, as stated elsewhere, above, is that we need a tad more lift .. needs a bit more pitch ... which results in a bit more drag ... equals slow down. For the instructor who posed the question, the preferred answer should lie with the increase in load factor.
(a) for a constant power setting at constant level, a heavier aircraft will fly slower than the lighter example
(b) in a balanced turn, the load factor increases in relation to angle of bank
(c) one can view increased load factor as being much the same as increased weight (mass, whatever)
(d) ergo, turn and you slow down
.. for most of us, this is the typical calculation basis for a first approximation effect of turn on performance.
The underlying cause, as stated elsewhere, above, is that we need a tad more lift .. needs a bit more pitch ... which results in a bit more drag ... equals slow down. For the instructor who posed the question, the preferred answer should lie with the increase in load factor.
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Deliverance, with regard to your example at post 21:
The KE of the ac is 0
The GPE of the ac is 0, considering its initial ht as the datum.
Zoom climb begins:
GPE increases with height.
Airspeed decays, increasingly negative groundspeed. KE increases.
KE if the wind reduced by increased aerodynamic drag in the pullup.
Energy conserved.
Your move.
Please explain why windshear affects airspeed, if the Earth frame of reference is irrelevant. Also consider that a turn in wind is effectively a varying headwind component with respect to the aircraft.
The KE of the ac is 0
The GPE of the ac is 0, considering its initial ht as the datum.
Zoom climb begins:
GPE increases with height.
Airspeed decays, increasingly negative groundspeed. KE increases.
KE if the wind reduced by increased aerodynamic drag in the pullup.
Energy conserved.
Your move.
Please explain why windshear affects airspeed, if the Earth frame of reference is irrelevant. Also consider that a turn in wind is effectively a varying headwind component with respect to the aircraft.
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OK final point, thank God, and I'm going to bed.
PBA and Deliv, you've hit the nail.
I suppose the turn in the hover is the ultimate example of an aggressive turn, possibly a Rate 10 turn. A turn in forward flight will be less rapid to varying degrees.
The pilot hasn't done anything. The aircraft has experienced a reduced airspeed. The aircraft has a tendancy to vary its airspeed because in varying headwind component, the Earth frame of reference is significant. Positive action from the pilot is required to maintain airspeed. In IMC, as mentioned earlier, the IAS is scanned and the pilot will conciously or subconciously increase the forward thrust slightly to nail the speed. Likewise in an E-3 doing a Rate 1 turn where the wind is 5% of the TAS, the effect will be negligable. In a slow aircraft, turning rapidly in a strong wind you WILL see in airspeed variation and you will have to adjust thrust to control it.
Goodnight
Helicopter in the hover with a 10 kt headwind... IAS 10kts
Turns 180 out, IAS -10 kts
voila a 20 kt decelleration.
Turns 180 out, IAS -10 kts
voila a 20 kt decelleration.
All that is happening is that he is changing his IAS to maintain a fixed ground speed!
Goodnight
How windshear affects IAS:
Imagine model plane flying steadily with zero groundspeed, 20 kt IAS in front of a fan.
Fan is suddenly turned off.
Model plane is suddenly at zero airspeed, will lose height rapidly and either crash or accelerate to a suitable airspeed to fly away before it hits the floor.
Not the same as the downwind turn in steady strong wind case - as succinctly described above, aircraft flies with reference to the air and, to the pilot in IMC, will feel the same if a constant IAS turn is flown no matter what the steady wind.
In visual low level manoueuvering, the visual slip/skid illusions fool us into thinking the airspeed changes are an effect of the wind.
Imagine model plane flying steadily with zero groundspeed, 20 kt IAS in front of a fan.
Fan is suddenly turned off.
Model plane is suddenly at zero airspeed, will lose height rapidly and either crash or accelerate to a suitable airspeed to fly away before it hits the floor.
Not the same as the downwind turn in steady strong wind case - as succinctly described above, aircraft flies with reference to the air and, to the pilot in IMC, will feel the same if a constant IAS turn is flown no matter what the steady wind.
In visual low level manoueuvering, the visual slip/skid illusions fool us into thinking the airspeed changes are an effect of the wind.
Mike,
What you're not understanding is that kinetic energy is relative.
I'll give you an example-
My cofee cup is sitting beside me. It's on a table. The table is on the floor which is attached to the Earth. The earth is spinning at 600mph and orbitting the sun at about 3000. The sun is orbiting the centre of the galaxy at about 100 000 mph, and the galaxy is receeding from the centre of the universe at a signifigant percentage of the speed of light.
My coffee cup has enough kinetic energy to destroy a fair sized city- better not drop it!!
Of course it's not a problem because the table and everthing around the cup is moving at the same rate, so RELATIVE to it's surroundings, the cup is stationary.
An aeroplane flys due to interaction with the air around it. Imagine a gold fish in a bowl on the back of a truck. Does the fact that the truck is moving at a constant rate make it hard for the goldfish to swim in the direction the truck is moving? No! he can happily swim in circles to his hearts content, not even aware that the truck is moving. In the same way, a turning aeroplane interacts with the "Bowl" of air around it, completely indedendent of the surface of the earth, moon, sun or horse head nebula!!
If the truck brakes, it's a different story- That's windshear, a sudden chane in velocity of the environment the aircraft is in at the time.
As I said- you're sitting in front of a computer- do a little research and find one authorititive confirmation of the "Down wind turn" and I'll eat my shorts!!!
What you're not understanding is that kinetic energy is relative.
I'll give you an example-
My cofee cup is sitting beside me. It's on a table. The table is on the floor which is attached to the Earth. The earth is spinning at 600mph and orbitting the sun at about 3000. The sun is orbiting the centre of the galaxy at about 100 000 mph, and the galaxy is receeding from the centre of the universe at a signifigant percentage of the speed of light.
My coffee cup has enough kinetic energy to destroy a fair sized city- better not drop it!!
Of course it's not a problem because the table and everthing around the cup is moving at the same rate, so RELATIVE to it's surroundings, the cup is stationary.
An aeroplane flys due to interaction with the air around it. Imagine a gold fish in a bowl on the back of a truck. Does the fact that the truck is moving at a constant rate make it hard for the goldfish to swim in the direction the truck is moving? No! he can happily swim in circles to his hearts content, not even aware that the truck is moving. In the same way, a turning aeroplane interacts with the "Bowl" of air around it, completely indedendent of the surface of the earth, moon, sun or horse head nebula!!
If the truck brakes, it's a different story- That's windshear, a sudden chane in velocity of the environment the aircraft is in at the time.
As I said- you're sitting in front of a computer- do a little research and find one authorititive confirmation of the "Down wind turn" and I'll eat my shorts!!!
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Here's a link.
http://www.pilotsweb.com/principle/load.htm
Would a way of looking at loss of lift in a turn be by seeing lift as a vertical component and a product, amongst other things, of horizontal wing surface area? If so, on a turn the horizontal wing surface area is reduced (ie the wing surface that can be 'seen' by a vertical force) and therefore the lift generated is also reduced. It will require an increase in angle of attack or forward speed to keep the amount of lift as it was.
(from an ignoramamus and it may show - I've got my tin hat ready!)
http://www.pilotsweb.com/principle/load.htm
Would a way of looking at loss of lift in a turn be by seeing lift as a vertical component and a product, amongst other things, of horizontal wing surface area? If so, on a turn the horizontal wing surface area is reduced (ie the wing surface that can be 'seen' by a vertical force) and therefore the lift generated is also reduced. It will require an increase in angle of attack or forward speed to keep the amount of lift as it was.
(from an ignoramamus and it may show - I've got my tin hat ready!)
The KE of the ac is 0
The GPE of the ac is 0, considering its initial ht as the datum.
Zoom climb begins:
The GPE of the ac is 0, considering its initial ht as the datum.
Zoom climb begins:
Could you please explain how a zoom climb begins if the initial KE is 0?
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This is becoming like the bl00dy conveyor belt, so I'll call it a day after this one.
Thank you Deliv. No, I am not mental. My comments are based on an A grade in Maths Mechanics A Level, 1st Class Honours in Aero Eng from one of the big 3 universities, RAF wings, the teaching received from a number of OCU/frontline instructors and experience.
Sarbloke. An object with zero groundspeed has zero KE wrt the Earth.
I actually said thrust. Whilst carrying out your selective radial scan, you carry out numerous tiny corrections, and when experienced will do so without a great deal of concious decision making. Under the circumstance I've described the pilot may have nibbled the throttle open without ever having conciously decided "I'm going to open the throttle".
When flying an approach, do you still make big concious power/attitude decisions like a first solo stude or do your inputs 'just happen', subconciously, like when riding a bike?
Yes correct about windshear. But are you (plural) trying to say that sometimes GS is relevant (above) and sometimes it isn't (turning)?
To quote John Farley, no less:
(Google 'downwind turn airspeed' and you'll find two ancient cached pprune pages. The above paragraph is from the thread begining 'among light aircraft pilots...')
How would you like your shorts cooked Deliv?
I reiterated that what I have described is a transient effect, negligible in normal circumstances, light winds and gentle turns but it exists.
Sarbloke. An object with zero groundspeed has zero KE wrt the Earth.
How can a pilot flying on instruments subconciously increase IAS
When flying an approach, do you still make big concious power/attitude decisions like a first solo stude or do your inputs 'just happen', subconciously, like when riding a bike?
How windshear affects IAS:
Imagine model plane flying steadily with zero groundspeed, 20 kt IAS in front of a fan.
Fan is suddenly turned off.
Model plane is suddenly at zero airspeed, will lose height rapidly and either crash or accelerate to a suitable airspeed to fly away before it hits the floor.
Not the same as the downwind turn in steady strong wind case - as succinctly described above, aircraft flies with reference to the air
Imagine model plane flying steadily with zero groundspeed, 20 kt IAS in front of a fan.
Fan is suddenly turned off.
Model plane is suddenly at zero airspeed, will lose height rapidly and either crash or accelerate to a suitable airspeed to fly away before it hits the floor.
Not the same as the downwind turn in steady strong wind case - as succinctly described above, aircraft flies with reference to the air
As I said- you're sitting in front of a computer- do a little research and find one authorititive confirmation of the "Down wind turn" and I'll eat my shorts!!!
On the other hand, if the air is not still, but moving at a steady speed over the ground, the aircraft will suffer a fluctuating ground speed after the “steady ” turn is established at “constant” airspeed. This ground speed (and its related kinetic energy) will be a minimum when flying into wind and a maximum when downwind.
This energy change and the problems it produces (thanks to inertia) is what is at the heart of the so-called downwind turn stall issue. I say so-called because this effect (while always having some transient effect on airspeed, related to the transient change in ground speed) will only cause a STALL in quite EXTREME CIRCUMSTANCES. Normally there will be no more than a minor reduction of height or a slight loss of airspeed (both usually so small that I recommend you don’t even think of wasting your time airborne by trying to measure them in real air, which is anything but steady)
This energy change and the problems it produces (thanks to inertia) is what is at the heart of the so-called downwind turn stall issue. I say so-called because this effect (while always having some transient effect on airspeed, related to the transient change in ground speed) will only cause a STALL in quite EXTREME CIRCUMSTANCES. Normally there will be no more than a minor reduction of height or a slight loss of airspeed (both usually so small that I recommend you don’t even think of wasting your time airborne by trying to measure them in real air, which is anything but steady)
How would you like your shorts cooked Deliv?
I reiterated that what I have described is a transient effect, negligible in normal circumstances, light winds and gentle turns but it exists.
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So by MO 's logic, maintaining a constant airspeed and altitude 45 deg banked turn would require continual changes of power throughout each 360 deg turned , these depending on the windspeed. 
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Thought I'd throw my lot in.
Constant vector, speed is proportional to thrust and drag.
Change the vector, angle of attack must change, drag must increase so speed declines therefore thrust must increase proportionally to maintain constant speed.
Or so I think,
Imagegear
Change the vector, angle of attack must change, drag must increase so speed declines therefore thrust must increase proportionally to maintain constant speed.
Or so I think,
Imagegear
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Looking at the starting post, the instructor in question would probably trash most of you for talking the exact scientific bullsh!te 
1st Newton's law: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Hence, to bring a craft into a turn from a straight flight requires action of force. The energy to generate that action of force must come from somewhere (energy is conserved), and that's from its kinetic energy of forward motion.
That being said, if you had a ball flying in a vacuum and wanted to change its direction of flight without touching it (external input=force added into system=unacceptable), you would have to slow the ball down. That exactly applies even to electrons orbiting around atomic core and any lift-drag and other bollox is totally irrelevant here.
1st Newton's law: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Hence, to bring a craft into a turn from a straight flight requires action of force. The energy to generate that action of force must come from somewhere (energy is conserved), and that's from its kinetic energy of forward motion.
That being said, if you had a ball flying in a vacuum and wanted to change its direction of flight without touching it (external input=force added into system=unacceptable), you would have to slow the ball down. That exactly applies even to electrons orbiting around atomic core and any lift-drag and other bollox is totally irrelevant here.
Hipper
Loss of lift in a turn ….?
On the contrary, lift increases substantially in a turn as it is this increase in lift that provides the centripetal force to enable the aircraft to change direction (vectored thrust aside).
Loss of lift in a turn ….?
On the contrary, lift increases substantially in a turn as it is this increase in lift that provides the centripetal force to enable the aircraft to change direction (vectored thrust aside).
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Speaking of scientific bullsh1t WRAITH, ideal circular motion is a constant energy motion. The centripetal force acting on the body acts radially towards the centre of the circle but there is no change of displacement in this direction and no radial velocity. Hence, no energy is expended by the radial force. The tangential speed is constant hence constant energy.
Hilife, I think what Hipper was trying to say, is that with an angle of bank, the vertical component of lift decreases. To maintain level flight, the total lift must be increased, by increasing alpha, to maintain a vertical component of lift equal and opposite to weight. The increase of lift and alpha, increases induced drag, and if thrust is not increased to match drag, airspeed will settle at a reduced value. I think this is the one point that we have all agreed on since post 2.
OUT.
Hilife, I think what Hipper was trying to say, is that with an angle of bank, the vertical component of lift decreases. To maintain level flight, the total lift must be increased, by increasing alpha, to maintain a vertical component of lift equal and opposite to weight. The increase of lift and alpha, increases induced drag, and if thrust is not increased to match drag, airspeed will settle at a reduced value. I think this is the one point that we have all agreed on since post 2.
OUT.
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"So by MO 's logic, maintaining a constant airspeed and altitude 45 deg banked turn would require continual changes of power throughout each 360 deg turned , these depending on the windspeed. "
Yup, and that's what kills his argument. MO can argue all he wants, but if his assumptions are incorrect (i.e. we are talking about a particular reference frame, he is mixing two) then no matter how great his logic and maths, it still isn't right.
It doesn't matter how many degrees you have of what patches you wear - the logical argument based upon correct assumptions is always going to triumph (thank goodness).
"Yup, and that's what kills his argument. MO can argue all he wants, but if his assumptions are incorrect (i.e. we are talking about a particular reference frame, he is mixing two) then no matter how great his logic and maths, it still isn't right.
It doesn't matter how many degrees you have of what patches you wear - the logical argument based upon correct assumptions is always going to triumph (thank goodness).
'Medium Turns' is usually the first exercise a student QFI learns to teach.
And with it comes the acronym KISS!
None of the grandiose 'energy concept' bolleaux is worth a rat's - it's utter boffinry and irrelevant. Ignore frictionless particles, kinematic viscosity and the time of day on Saturn's moons - and keep it simple!
Aircraft in turn requires more lift because only the vertical component of lift opposes weight. The increase in lift is achieved by increasing the angle of attack; this also increase drag. An increase in thrust is necessary to avoid deceleration.
As for 'downwind turns' and relativistic mechanics or whatever, if you really want to complicate matters and you remember that the angle of attack is the angle between the chord line and the relative airflow, if some external factor such as a vertical gust changes the relative airflow then angle of attack will also change as a result. Mention that during a medium turns brief to a trapper and the pen will start to make notes - followed by "Why's that, sir?".....
The illusory effect of wind on apparent speed is covered during low level intro - but only demonstrated if there is a significant wind during the air exercise.
I found that my Aero Eng degree was worth the square root of sod all when it came to teaching P of F - the CFS way was infinitely simpler and easier for all to understand....
And with it comes the acronym KISS!
None of the grandiose 'energy concept' bolleaux is worth a rat's - it's utter boffinry and irrelevant. Ignore frictionless particles, kinematic viscosity and the time of day on Saturn's moons - and keep it simple!
Aircraft in turn requires more lift because only the vertical component of lift opposes weight. The increase in lift is achieved by increasing the angle of attack; this also increase drag. An increase in thrust is necessary to avoid deceleration.
As for 'downwind turns' and relativistic mechanics or whatever, if you really want to complicate matters and you remember that the angle of attack is the angle between the chord line and the relative airflow, if some external factor such as a vertical gust changes the relative airflow then angle of attack will also change as a result. Mention that during a medium turns brief to a trapper and the pen will start to make notes - followed by "Why's that, sir?".....
The illusory effect of wind on apparent speed is covered during low level intro - but only demonstrated if there is a significant wind during the air exercise.
I found that my Aero Eng degree was worth the square root of sod all when it came to teaching P of F - the CFS way was infinitely simpler and easier for all to understand....
Ok Mike,
So if taking your datum where PE and KE is zero, where does the energy come from to zoom climb? In your example both PE and KE increase. The energy to do this must come from somewhere. If not, I'd patent your findings and make Bill Gates look like a pauper.
A turn in the hover is not an aggressive turn as you describe it. It is completely different mode of flight as the pilot is intentionally maintaining groundspeed. Airspeed is irrelevant in this case (subject to aircraft and power limitations). In the downwind turn being discussed the pilot is maintaing airspeed.
So if taking your datum where PE and KE is zero, where does the energy come from to zoom climb? In your example both PE and KE increase. The energy to do this must come from somewhere. If not, I'd patent your findings and make Bill Gates look like a pauper.
A turn in the hover is not an aggressive turn as you describe it. It is completely different mode of flight as the pilot is intentionally maintaining groundspeed. Airspeed is irrelevant in this case (subject to aircraft and power limitations). In the downwind turn being discussed the pilot is maintaing airspeed.
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Speaking of scientific bullsh1t WRAITH, ideal circular motion is a constant energy motion.
No energy is being expended because a balance exists between the central and the centrifugal force (force acts, but no displacement => no work done => no energy consumed), none of which we can dismiss from the consideration. Note that Newton explicitly mentions that unbalanced force is required to change the state. This is where energy is consumed in the ideal case. In reality though, aerodynamic aspects come into play, but as I understand it that's exactly what the instructor didn't want to hear.
EDIT: Although yeah, if you want to get into aerodynamics, Beagle is spot on.
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WRAITH,
That's where you suggested otherwise. That part of what you said is not correct. A force can exist without consuming energy, for example the centripetal force in circular motion. There is a centripetal acceleration but at constant zero radial velocity and no change of radial displacement.
SAR bloke, read again what I said. Drag doesn't just act on the aircraft, its equal and opposite effect acts on the air. That's why a slipstream exists behind lorries. KE is taken out of the air that is decelerated from '300 kts' to a lower value by drag, in the example.
If you're hovering into a 25 kt wind with, say 8 deg nose down and you yaw the helo down wind maintaining your 8deg nose down, yes eventually you will be flying at 25kts AS, 50kts GS (ignoring stoofing into the ground due to loss of translational lift), but it will take time to reach that equilibrium. During that time you are experiencing a transient reduced airspeed. Same deal to a lesser extent in forward flight.
Hence, to bring a craft into a turn from a straight flight requires action of force. The energy to generate that action of force must come from somewhere (energy is conserved), and that's from its kinetic energy of forward motion.
SAR bloke, read again what I said. Drag doesn't just act on the aircraft, its equal and opposite effect acts on the air. That's why a slipstream exists behind lorries. KE is taken out of the air that is decelerated from '300 kts' to a lower value by drag, in the example.
If you're hovering into a 25 kt wind with, say 8 deg nose down and you yaw the helo down wind maintaining your 8deg nose down, yes eventually you will be flying at 25kts AS, 50kts GS (ignoring stoofing into the ground due to loss of translational lift), but it will take time to reach that equilibrium. During that time you are experiencing a transient reduced airspeed. Same deal to a lesser extent in forward flight.