Helicopter pitch change when orbiting around a fixed point??
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They are constant bank angle turns. The requirement in addition making the bank constant is also to keep the IAS constant at 100 KIAS.
You just fly figure 8's and maintain these conditions until the aircraft system tell you it has the data it needs. Very much like advanced compass system in boats these days.
And again, the L2 has mass, that needs to be accelerated to keep the same IAS going into downwind. See post 27 in this thread
You just fly figure 8's and maintain these conditions until the aircraft system tell you it has the data it needs. Very much like advanced compass system in boats these days.
And again, the L2 has mass, that needs to be accelerated to keep the same IAS going into downwind. See post 27 in this thread
That is one of the big mysteries of flying and has confused quite a lot of people.
Let's take a trusty old C150 and practice turns around a point as required for a checkride. Normaly there is some wind therefore I have to correct for it every moment of the 360° turn. I start into the wind and do my first 90°. The wind is pushing me toward the point on the ground and I have to BANK a bit less than in a no wind condition ... and so on all the way round. Now, what does change when I fly like this? Airspeed? No, because I don't change the power setting and I do not climb or decend (apart from a bit less speed while having a higher bank angle, but that does not really matter). Groundspeed changes? Yes. Do I care? No. Groundspeed has nothing to do with the aerodynamics of my plane or helicopter.
When I do a rec for a landing spot, I should do a circle around it. Is there any difference then in a plank? No. I just bank more or less depending where the wind is pushing me, but I do not change airspeed if I do not climb or descend or change the power setting. Therefore you can not crash due to loss of airspeed while doing normal circles around a point, because the airspeed does not change when you do it correctly, only the bank angle.
Now, if you fly on a extremly windy day, you probably have to hurry turning while going downwind to keep the point on the ground in sight and bank angles will come close to aerobatic limits, but airspeed would still not change a bit.
... an now something completely different ... hopefully.
Let's take a trusty old C150 and practice turns around a point as required for a checkride. Normaly there is some wind therefore I have to correct for it every moment of the 360° turn. I start into the wind and do my first 90°. The wind is pushing me toward the point on the ground and I have to BANK a bit less than in a no wind condition ... and so on all the way round. Now, what does change when I fly like this? Airspeed? No, because I don't change the power setting and I do not climb or decend (apart from a bit less speed while having a higher bank angle, but that does not really matter). Groundspeed changes? Yes. Do I care? No. Groundspeed has nothing to do with the aerodynamics of my plane or helicopter.
When I do a rec for a landing spot, I should do a circle around it. Is there any difference then in a plank? No. I just bank more or less depending where the wind is pushing me, but I do not change airspeed if I do not climb or descend or change the power setting. Therefore you can not crash due to loss of airspeed while doing normal circles around a point, because the airspeed does not change when you do it correctly, only the bank angle.
Now, if you fly on a extremly windy day, you probably have to hurry turning while going downwind to keep the point on the ground in sight and bank angles will come close to aerobatic limits, but airspeed would still not change a bit.
... an now something completely different ... hopefully.
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Originally Posted by L2driver
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!
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!
Sorry, L2. Your theoretical knowledge is far superior to mine(as is most peoples, it has to be said 
).
Anyway, I've just landed. We've got a bit of a breeze up here tonight, and at 1000' it's 30 knots. You're right, of course, altitude has nothing to do with it: it just gets you out of the turbulence zone, and as we are on the coast, 1000' is fine.
So, S&L, 65 kts, 1000'. Trim into a 10 deg banked turn. Now, as you know, the nose is going to climb or drop slightly, depending which way the turn is. Trim adjusted slightly for that, and hands off.
No IAS or ALT holds, just the trim, and around she goes. Speed stays the same plus or minus 2 or 3 knots. Did the same at 80kts with 20 deg of bank. Nothing different.
Now, I spend alot of my time going around in circles, so this is not a strange occurrence.
).Anyway, I've just landed. We've got a bit of a breeze up here tonight, and at 1000' it's 30 knots. You're right, of course, altitude has nothing to do with it: it just gets you out of the turbulence zone, and as we are on the coast, 1000' is fine.
So, S&L, 65 kts, 1000'. Trim into a 10 deg banked turn. Now, as you know, the nose is going to climb or drop slightly, depending which way the turn is. Trim adjusted slightly for that, and hands off.
Yeah - trim it up, use IAS hold plus ALT hold
Now, I spend alot of my time going around in circles, so this is not a strange occurrence.
Also, I was a bit puzzled about your comment on gliders:
As a glider pilot you would know that they are not speed brakes, but are used to control rate of descent and are used in all landings, whether a tight spot or not, and not as a result of bad planning.
Of course
they have speed-brakes, but that is for bad planners and landings in tight spots.
they have speed-brakes, but that is for bad planners and landings in tight spots.
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L2 I'll give you the benefit of the doubt.
You keep making good points that everyone accepts about ground speed illusions, being on the wrong side of the power curve, and the energy impact of windshear (gusts). But then you exhibit this confusion about acceleration.
This acceleration that you feel the helicopter has to undergo when turning downwind is relative to what ? Early on you seemed to think it was relative to 'mother gravity', and hopefully I skewered that when I said that the gravity vector is not going to change over these distances, it'll still be straight down. Now from the quote above you seem to imply that the acceleration has to be relative to the air, but why ? Especially if you accept the model helicopter in the train scenario.
Your airmanship views concerning the downwind turn are smack on the button, but your physics is a bit rusty.
And again, the L2 has mass, that needs to be accelerated to keep the same IAS going into downwind. See post 27 in this thread
This acceleration that you feel the helicopter has to undergo when turning downwind is relative to what ? Early on you seemed to think it was relative to 'mother gravity', and hopefully I skewered that when I said that the gravity vector is not going to change over these distances, it'll still be straight down. Now from the quote above you seem to imply that the acceleration has to be relative to the air, but why ? Especially if you accept the model helicopter in the train scenario.
Your airmanship views concerning the downwind turn are smack on the button, but your physics is a bit rusty.
Last edited by puntosaurus; 19th Jun 2009 at 05:47.
I've been resisting this one, but my strength ran out... actually I think both sides are right, subject to the appropriate context.
Of course the aircraft does have inertia relative to the ground. So if the wind changes instanteously, there will be a change in IAS for the time it takes the (new) force of the wind to effect an acceleration. It would take more tedious math than I can be bothered with to work out how long it would take, but based on what it's like hovering or doing pedal turns in a gusty wind, I'd say not long - a second or two max.
In a steady wind and a normal banked turn (heli or fixed), the time it takes to change direction is significantly greater than this wind acceleration time, so it has no noticeable effect. Otoh the visual effect of the changing ground speed can be very striking, especially at lower speeds typical of a heli. The first time I flew a heli in the pattern with a 30 knot wind at 1000', I found it very noticeable and it took a conscious effort to focus on the airspeed indicator and not the ground. (Much less of an issue in even a small plane at 80 knots than in a heli at 60). That is what (so they say) causes problems for low-time fixed wing pilots - they see the ground suddenly rushing by and they reduce power or pull on the yoke, and stall.
Gusts are a different matter. A sudden gust or wind-shear can turn 60 knots into nothing in a fraction of a second. Airliners have fallen out of the sky because of this on several occasions (higher absolute speeds of course, but 727s don't hover very well anyway) - although their extra mass and much smaller ratio of effective frontal area to mass probably makes it a lot worse for them than an R22 or a 152.
If you were OGE at 1000' and had a sudden 60 knot wind change (i.e. 30 knots N turns to 30 knots S), I guess you'd feel it but you'd have time to add collective and unless you were watching the altimeter like a hawk it probably wouldn't be big shock. Same thing at 30 feet or 3 feet and it could indeed spoil your whole day. (I confess I didn't read the G-TIGH report so I don't know what their altitiude was).
My 2c, off to bed now...
n5296s
Of course the aircraft does have inertia relative to the ground. So if the wind changes instanteously, there will be a change in IAS for the time it takes the (new) force of the wind to effect an acceleration. It would take more tedious math than I can be bothered with to work out how long it would take, but based on what it's like hovering or doing pedal turns in a gusty wind, I'd say not long - a second or two max.
In a steady wind and a normal banked turn (heli or fixed), the time it takes to change direction is significantly greater than this wind acceleration time, so it has no noticeable effect. Otoh the visual effect of the changing ground speed can be very striking, especially at lower speeds typical of a heli. The first time I flew a heli in the pattern with a 30 knot wind at 1000', I found it very noticeable and it took a conscious effort to focus on the airspeed indicator and not the ground. (Much less of an issue in even a small plane at 80 knots than in a heli at 60). That is what (so they say) causes problems for low-time fixed wing pilots - they see the ground suddenly rushing by and they reduce power or pull on the yoke, and stall.
Gusts are a different matter. A sudden gust or wind-shear can turn 60 knots into nothing in a fraction of a second. Airliners have fallen out of the sky because of this on several occasions (higher absolute speeds of course, but 727s don't hover very well anyway) - although their extra mass and much smaller ratio of effective frontal area to mass probably makes it a lot worse for them than an R22 or a 152.
If you were OGE at 1000' and had a sudden 60 knot wind change (i.e. 30 knots N turns to 30 knots S), I guess you'd feel it but you'd have time to add collective and unless you were watching the altimeter like a hawk it probably wouldn't be big shock. Same thing at 30 feet or 3 feet and it could indeed spoil your whole day. (I confess I didn't read the G-TIGH report so I don't know what their altitiude was).
My 2c, off to bed now...
n5296s
RVDT -thanks for that link. The article it leads to is in my view a very clear and correct description of the whole issue.
I have spent the last couple of days trying to frame my response to L2's mish-mash of truths, half-truths, and downright misunderstanding of the situation described, but the above article answers all the issues.
I particularly take issue with his interpretation of the TIGH accident report, and as for
"I am seriously worried about the lack of basic physics knowledge 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."
All I can think is pot....kettle......black........
(Please note I have deleted airmanship from the above quote, as I am not questioning that, only the physics aspect)
I have spent the last couple of days trying to frame my response to L2's mish-mash of truths, half-truths, and downright misunderstanding of the situation described, but the above article answers all the issues.
I particularly take issue with his interpretation of the TIGH accident report, and as for
"I am seriously worried about the lack of basic physics knowledge 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."
All I can think is pot....kettle......black........
(Please note I have deleted airmanship from the above quote, as I am not questioning that, only the physics aspect)
I particularly take issue with his interpretation of the TIGH accident report
Oh, the irony, as L2driver smugly declares:
after such mumbo jumbo nonsense as:
With such awful knowledge of basic physics and sailplane operation, his mocking taunt
of another contributor is laughable.
His claim to be "a pilot, test pilot and an accident investigator too." is worrying. "Actually the Air Force and then my company declared me a 'test pilot'. I have the papers to prove it."!!!!
More worrying is the way he uses this forum to belittle others whose knowledge of the physics of flight is far greater than his.
But most worrying of all is that other more impressionable readers might well fall for his arguments, and believe the same nonsense that he clearly believes and spouts as fact.
As for expecting others to buy him a beer for the quality of his teaching -pah! It really is about time that 'idiot commentators' and their bunkum physics misunderstandings are 'brought down to earth with a bump'.
Never mind L2driver - I'm sure the big expensive Breitling still impresses everyone even if your physics doesn't.
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
Sorry - Mass is a term used in the JAR-OPS/EU-OPS these days. Please substitute mass with weight which is relative to gravity for people to understand....
sailplanes are no different from other aircraft... I'll let you in on a secret: I have flown them too. Of course they have speed-brakes, but that is for bad planners and landings in tight spots....
sailplanes are no different from other aircraft... I'll let you in on a secret: I have flown them too. Of course they have speed-brakes, but that is for bad planners and landings in tight spots....
where did you go to school??.
His claim to be "a pilot, test pilot and an accident investigator too." is worrying. "Actually the Air Force and then my company declared me a 'test pilot'. I have the papers to prove it."!!!!
More worrying is the way he uses this forum to belittle others whose knowledge of the physics of flight is far greater than his.
But most worrying of all is that other more impressionable readers might well fall for his arguments, and believe the same nonsense that he clearly believes and spouts as fact.
As for expecting others to buy him a beer for the quality of his teaching -pah! It really is about time that 'idiot commentators' and their bunkum physics misunderstandings are 'brought down to earth with a bump'.
Never mind L2driver - I'm sure the big expensive Breitling still impresses everyone even if your physics doesn't.
Last edited by pilotmike; 21st Jun 2009 at 09:54. Reason: to add that L2driver wears a Breitling watch - so he must know what he's talking about...
Good one, n5296s. I think you've explained it nicely.
Steadily moving airmass which the aircraft turns with respect to, no appreciable change in IAS in the turn.
Rapid changes (ie gusts, shear), or pilot reacting to slip/skid illusions or trying to maintain position with respect to a ground feature, then we get IAS changes.
Steadily moving airmass which the aircraft turns with respect to, no appreciable change in IAS in the turn.
Rapid changes (ie gusts, shear), or pilot reacting to slip/skid illusions or trying to maintain position with respect to a ground feature, then we get IAS changes.
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l2driver, self praise is never a good recommendation. you prove that adage many times in your posts.
having a beer with you even if you paid, i would imagine, would be one of the most boring things a person could do. let me know what pub you drink at so i can avoid it at any cost.
pompous, arrogant and demeaning to your peers probably made you quite the outcast at school and a target for practical jokes.
i can't agree with you even if you are right and i don't think you are.
post some where else please mr "test pilot" and leave us to our ignorance.
gg
having a beer with you even if you paid, i would imagine, would be one of the most boring things a person could do. let me know what pub you drink at so i can avoid it at any cost.
pompous, arrogant and demeaning to your peers probably made you quite the outcast at school and a target for practical jokes.
i can't agree with you even if you are right and i don't think you are.
post some where else please mr "test pilot" and leave us to our ignorance.
gg
For some further reading on the effect of wind on instantaneous airspeed in the case of a turning aircraft (the aircraft having inertial mass - 'inertial' for emphasis, mass would suffice of course) have a look at Dynamic Soaring.
This is a technique of imparting energy to an aircraft (or bird) by utilising the differing wind speed in different envionments and by manoeuvering the aircraft between the environments. Apparently this is the method that albatrosses use to cover 1000s of miles across the oceans without significant effort. In the latter case the variation of wind speed in the troughs and crests of waves is utilised.
The speed record for radio control model gliders using this technique near mountain ridges is apparently 392mph, so the effect can be seen to be not small. This is *sustained* flight - as long as the wind blows. Yes really!!!!! From an on-line video of 370mph I estimated that the model was pulling 35g - I am not 100% on the integrity of the video or my calculations.
There seems some interest in Dynamic Soaring within the full sized glider community.
Dynamic Soaring links
YouTube - Great sounds of formation DSing at Jones Pass
YouTube - New Dynamic Soaring World Record -- 392mph
Dynamic soaring - Wikipedia, the free encyclopedia
ESA Experimental Soaring Assn
http://www.esoaring.com/albatros_presentation_esa.pdf
YouTube - Dynamic Soaring (DS) on 50ft Dam in Tennessee...
-- dam in Tennessee
-- DS at 1:51-2:35 and 4:42-5:10 the rest is slope soaring I guess.
The last link is from an on board video showing DS utilising the different wind speeds above and in the lee of a dam.
I'll redo the links in a mangled form if they disappear.
Little explanation -ette, sort of thinking out loud.
It might perhaps be thought of as picking up energy from the wind at high altitude and then recovering position in the lower wind speed at low altitude in the lee of a wave or hill. Rinse and repeat. [I just made this para up so it might be crap since I do not really follow what is going on here.] Quite how this turns into 392mph I have no idea. Ah yes, the airspeed of the aircraft downwind (300mph in a 30mph wind) is not relevant the aircraft *still* gets yet more energy out of the wind. I'm still not sure I follow myself.
This is a technique of imparting energy to an aircraft (or bird) by utilising the differing wind speed in different envionments and by manoeuvering the aircraft between the environments. Apparently this is the method that albatrosses use to cover 1000s of miles across the oceans without significant effort. In the latter case the variation of wind speed in the troughs and crests of waves is utilised.
The speed record for radio control model gliders using this technique near mountain ridges is apparently 392mph, so the effect can be seen to be not small. This is *sustained* flight - as long as the wind blows. Yes really!!!!! From an on-line video of 370mph I estimated that the model was pulling 35g - I am not 100% on the integrity of the video or my calculations.
There seems some interest in Dynamic Soaring within the full sized glider community.
Dynamic Soaring links
YouTube - Great sounds of formation DSing at Jones Pass
YouTube - New Dynamic Soaring World Record -- 392mph
Dynamic soaring - Wikipedia, the free encyclopedia
ESA Experimental Soaring Assn
http://www.esoaring.com/albatros_presentation_esa.pdf
YouTube - Dynamic Soaring (DS) on 50ft Dam in Tennessee...
-- dam in Tennessee
-- DS at 1:51-2:35 and 4:42-5:10 the rest is slope soaring I guess.
The last link is from an on board video showing DS utilising the different wind speeds above and in the lee of a dam.
I'll redo the links in a mangled form if they disappear.
Little explanation -ette, sort of thinking out loud.
It might perhaps be thought of as picking up energy from the wind at high altitude and then recovering position in the lower wind speed at low altitude in the lee of a wave or hill. Rinse and repeat. [I just made this para up so it might be crap since I do not really follow what is going on here.] Quite how this turns into 392mph I have no idea. Ah yes, the airspeed of the aircraft downwind (300mph in a 30mph wind) is not relevant the aircraft *still* gets yet more energy out of the wind. I'm still not sure I follow myself.
Last edited by jimjim1; 22nd Jun 2009 at 12:29.
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Priciples of flight
Here's a different idea to explain this then..... At normal cruise speeds, the effect that we are discussing is minimal, due to the relative speed of 100 kts cruise vs 20-30kt wind. Now lets decel the helo down to 40kts for the reccie as in the original question, and a 30kt HEAD wind. (Example a Frog Helicopter with head turning Clockwise when viewed from above)
Advancing side of the disc is at a speed of Rotational velocity + 30kts (max at the 9 o'clock position), causing FlapBack (Disc High) in the 12 o'clock, and the Inflow axis will cause a 2 o'clock disc high position. If the wind is turbulent or the turn is tight (low A/s therefore tight Radius of Turn) As the helo is turned at a low speed, the Inflow Axis will be close to the 11-5 o'clock position across the disc = half past 2o'clock disc high, therefore initially the helo will be rotating the fuselage into the disc high region - meaning to stop the helo decelerating, the cyclic needs to be tilted forward - just as in overcoming flapback. If this does not happen quickly enough, the helo will decelerate - in the example towards 30 kt and the danger of Vortex ring...........
Now, did anyone follow that???
As a continuation, Why does a helicopter in the hover next to a hill experiencing updrafting air, not get into Vortex Ring?? Hover = Low airspeed, Updrafting air = Rate of Descent Flow, = Hover = Power applied.
Advancing side of the disc is at a speed of Rotational velocity + 30kts (max at the 9 o'clock position), causing FlapBack (Disc High) in the 12 o'clock, and the Inflow axis will cause a 2 o'clock disc high position. If the wind is turbulent or the turn is tight (low A/s therefore tight Radius of Turn) As the helo is turned at a low speed, the Inflow Axis will be close to the 11-5 o'clock position across the disc = half past 2o'clock disc high, therefore initially the helo will be rotating the fuselage into the disc high region - meaning to stop the helo decelerating, the cyclic needs to be tilted forward - just as in overcoming flapback. If this does not happen quickly enough, the helo will decelerate - in the example towards 30 kt and the danger of Vortex ring...........
Now, did anyone follow that???
As a continuation, Why does a helicopter in the hover next to a hill experiencing updrafting air, not get into Vortex Ring?? Hover = Low airspeed, Updrafting air = Rate of Descent Flow, = Hover = Power applied.
Why does a helicopter in the hover next to a hill experiencing updrafting air, not get into Vortex Ring??
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Advancing side of the disc is at a speed of Rotational velocity + 30kts
