Helicopter pitch change when orbiting around a fixed point??
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jellycopter is right, on the conveyor belt, there is a small but real difference due to the fact that the air is in the terminal/floor/walls frame, and so airspeed does change. That is a fine point, and small inconsistency in my "thought experiment." Good catch.
In the airborne turn, the speed is always constant, as is the power and the altitude. In fact, one can trim the helicopter in a strong wind to a constant bank, and turn all day long without adjusting pitch or power in any way. The only way you can tell which way the wind is blowing is by reference to some nav instrument tied to the ground - there is no change to the aircraft's power attitude or altitude due to the wind.
BUT one point must be made. If the pilot is making a constant radius turn about a ground reference point (like circling in a tight downwind/base turn about a rig on short final approach) then the turn from upwind to cross wind to downwind would require a vast increase in bank angle to keep the radius of the turn constant as the groundspeed increased. In other words, the pilot must tighten up the turn to make the radius constant as the ground speed increases, and this increased bank needs lots of power, which a loaded helo will not have. At constant bank angle/load factor, the radius of turn gets bigger with the square of the velocity, so a 60 knot (airspeed) helo with a 30 knot wind will need THREE times the load factor to make the radius upwind (30 knot groundspeed) match the radius downwind (90 knot groundspeed). Close to the ground, the helo cannot give up altitude to fuel the load factor, so the speed is sacrificed with back stick, but it is a tricky maneuver, often done with an offshore poor horizon and weak altitude cues from a moving sea. The result can be a botched turn, big descent, and oops, sea contact.
The cure? Make the approach a bigger one, extend and make gentle turns, pay off radius for load factor so that it takes 2 min longer but you end up with a longer, more controlled final approach into the wind from a healthy distance (1/2 mile?)
Don't be fooled by the fact that you can do a sweet pylon turn in a VFR practice environment - at sea, with a poor horizon, squirming sea and few altitude cues, in dusk or misty conditions, the sudden realization that you have built a 2.5 G. 2000 fpm descent while at 60 degrees of bank and a full load WILL lead to a very tight situation - sometimes a nasty splash.
This has LITTLE to do with 1/2MVsquared, and all that downwind energy stuff. It has to do with the load factor/radius of turn/ground speed relationship that is described here. Note that for a 30 mph turn of 250 feet, it takes 15 degrees of bank. For that same 250 foot radius at 90 mph, it takes about 2.5 G (beyond the performance limits of most loaded helicopters). Disregard the modeler's comments about scale speed - the chart is useful anyway.
In the airborne turn, the speed is always constant, as is the power and the altitude. In fact, one can trim the helicopter in a strong wind to a constant bank, and turn all day long without adjusting pitch or power in any way. The only way you can tell which way the wind is blowing is by reference to some nav instrument tied to the ground - there is no change to the aircraft's power attitude or altitude due to the wind.
BUT one point must be made. If the pilot is making a constant radius turn about a ground reference point (like circling in a tight downwind/base turn about a rig on short final approach) then the turn from upwind to cross wind to downwind would require a vast increase in bank angle to keep the radius of the turn constant as the groundspeed increased. In other words, the pilot must tighten up the turn to make the radius constant as the ground speed increases, and this increased bank needs lots of power, which a loaded helo will not have. At constant bank angle/load factor, the radius of turn gets bigger with the square of the velocity, so a 60 knot (airspeed) helo with a 30 knot wind will need THREE times the load factor to make the radius upwind (30 knot groundspeed) match the radius downwind (90 knot groundspeed). Close to the ground, the helo cannot give up altitude to fuel the load factor, so the speed is sacrificed with back stick, but it is a tricky maneuver, often done with an offshore poor horizon and weak altitude cues from a moving sea. The result can be a botched turn, big descent, and oops, sea contact.
The cure? Make the approach a bigger one, extend and make gentle turns, pay off radius for load factor so that it takes 2 min longer but you end up with a longer, more controlled final approach into the wind from a healthy distance (1/2 mile?)
Don't be fooled by the fact that you can do a sweet pylon turn in a VFR practice environment - at sea, with a poor horizon, squirming sea and few altitude cues, in dusk or misty conditions, the sudden realization that you have built a 2.5 G. 2000 fpm descent while at 60 degrees of bank and a full load WILL lead to a very tight situation - sometimes a nasty splash.
This has LITTLE to do with 1/2MVsquared, and all that downwind energy stuff. It has to do with the load factor/radius of turn/ground speed relationship that is described here. Note that for a 30 mph turn of 250 feet, it takes 15 degrees of bank. For that same 250 foot radius at 90 mph, it takes about 2.5 G (beyond the performance limits of most loaded helicopters). Disregard the modeler's comments about scale speed - the chart is useful anyway.
Such a reduction in airspeed is the likely outcome of turning away from a substantial headwind whilst visually maintaining a constant groundspeed.
You really are completely muddled in your thinking, and the scary thing is that you are trying to teach others who might be fooled into believing your nonsense.
212man politely points out that you are digging yourself deeper and deeper. My advice would be to listen carefully him, and stop trying to impress us all with your flying theories and certificates.
People have so far been rather patient and polite in telling you that you have it wrong, but now you really are making yourself look silly. The outpouring of ridicule is beginning:
Would be surprised if L2driver was capable of driving a mk II cortina!
I don't flash a big Breitling, it is in my safe. I even keep my Test pilot and USC Safety Certificates in a drawer. I do not need to brag about this
To have you trying to teach us that somehow WE'RE all wrong because we disagree with you was irritating.
Being chastised for our "lack of basic physics knowledge" was particularly hard to take, coming as it did from you.
When you mockingly called us the "idiot commentators" for disagreeing with you, you were really starting to annoy, and it made you look very stupid.
And yet still you're here trying to give everyone a lesson in downwind turns, making yourself look more stupid by the minute.
Your continued lessons on flying, given your obvious lack of basic knowledge are very hard to take, and are becoming rather tiresome. Listen to Nick Lappos, and learn from the excellent article whose link was posted earlier. There are none so blind as those who refuse to listen!
Remember, 2 ears, 1 mouth. Use them in that proportion. Stop with trying to impress us all and giving us all flying lessons. Start to listen and learn from those who actually know what they are talking about.
I would strongly recommend taking Wee Willy Winky's advice, which neatly translates to:
You're trying to teach dolphins to swim.
EITHER LEARN OR LEAVE, OR THE THIRD OPTION: PREPARE TO BE FLOGGED!
Last edited by pilotmike; 28th Jun 2009 at 18:29.
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L2driver, there are a lot of knowledgeable people on this forum, most of them it seems, also have a lot of patience.
For each of the replies that you see addressed to you on this topic there are probably another 50 people sitting there shaking their head at your comments and your obvious lack of understanding. Until now I was one of them.
I would advise that you get some one on one tuition (from an engineer or scientist) on the principles involved in this discussion and eat some humble pie.
Oh and if I were you, I would send those certificates back to where you got them from and explain that you are not worthy. Not because of the mistakes that you have made in your explainations per se, but because you just continue to spout the same s$#t and don't open your mind up to the fact that you might just be wrong.
For each of the replies that you see addressed to you on this topic there are probably another 50 people sitting there shaking their head at your comments and your obvious lack of understanding. Until now I was one of them.
I would advise that you get some one on one tuition (from an engineer or scientist) on the principles involved in this discussion and eat some humble pie.
Oh and if I were you, I would send those certificates back to where you got them from and explain that you are not worthy. Not because of the mistakes that you have made in your explainations per se, but because you just continue to spout the same s$#t and don't open your mind up to the fact that you might just be wrong.
the beater,
sorry if my post resulted in your headbanging. In my defence, I'd say I was trying to add weight to the argument that the position L2 is adopting is nonsense, in an attempt to prevent more gullible people from believing him - and the instructor that was lecturing the originator of this thread!
Ok....
My thoughts are that you are correct with your stance and should politely ignore your instructor's lecture. He is using misunderstood school boy physics to confuse himself, you and many others. 
sorry if my post resulted in your headbanging. In my defence, I'd say I was trying to add weight to the argument that the position L2 is adopting is nonsense, in an attempt to prevent more gullible people from believing him - and the instructor that was lecturing the originator of this thread!
Can someone please explain to me just what relevance the last two posts have towards the original question?
I thought that it involved maintaining a constant AIR SPEED.
The above refers to posts 77 & 78
I thought that it involved maintaining a constant AIR SPEED.
The above refers to posts 77 & 78
RTFQ, ATFQ
What are people's thoughts on this?
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Oh dear! Talk about how to lose friends and alienate people!
You see, 212man, I actually agree with you. The problem was that as I wrote my reply, you posted yours, so my reply mentioning the previous two posts didn't make sense. Hence the editing of my post.
I hope that no-one posts whilst I'm writing this, or we could be locked in a loop forever!
You see, 212man, I actually agree with you. The problem was that as I wrote my reply, you posted yours, so my reply mentioning the previous two posts didn't make sense. Hence the editing of my post.
I hope that no-one posts whilst I'm writing this, or we could be locked in a loop forever!
You couldn't make this up!
I posted a link that explained the issues for all to understand. Many thanks to the chap in SA.
Nick Lappos also had to wade in and explain it in very clear terms as he is so good at.
For all you Naysayers and Hellfire and Brimstoners - Wikipedia is your best friend - read - weep!
Moderator - please shoot this thing. It is in the public domain and it is embarrasssing!
Rant over because I think I just noticed that the sky is falling! (with hopefully subsequent result)
I posted a link that explained the issues for all to understand. Many thanks to the chap in SA.
Nick Lappos also had to wade in and explain it in very clear terms as he is so good at.
For all you Naysayers and Hellfire and Brimstoners - Wikipedia is your best friend - read - weep!
Moderator - please shoot this thing. It is in the public domain and it is embarrasssing!
It is difficult to soar like an eagle when you are surrounded by fr@#kin TURKEYS!
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Having finally found time to read this thread (I've been meaning to ever since it popped up) I thought I'd add my 10 cents....
The perils of the low IAS, downwind maneuvers are well documented and hopefully all pilots flying out there are aware of the implications, if not perhaps a refresher flight with a instructor (and sufficient height agl) would be a wise investment.
VRS in a hover in a updraught, possible but unlikely as your power in use is probably considerably lower than in a normal hover (your in a updraught!), however if you start to sink a bit and decide to pull pitch......
To answer the initial post: if flying a constant radius turn around a ground feature at a constant IAS on a nil wind day there will be no requirement for pitch change. Throw in some wind but fly at a constant IAS and pitch change will be needed as the angle of bank required to maintain the 'K' radius of the turn changes, otherwise the a/c will climb and descend as the associated load factor changes.
A question I have always pondered is where in the orbit is the demand for Bank Angle (and thus pitch/power) greatest??
Conventional Principle of Flight would mandate this be in the downwind position due to the squared function of velocity in the Load Factor equation as discussed by Nick Lappos in post #84. However when flying a constant radius turn at say 60 kts IAS in a 20 kts wind the greatest angle of bank appears to be somewhat after the downwind position during the turn to crosswind? is this another illusion or due to the combination of high groundspeed (admittedly decreasing at this point in the turn but still higher than the IAS) and the drift caused by the (increasing) cross wind component...??
Any takers?
The perils of the low IAS, downwind maneuvers are well documented and hopefully all pilots flying out there are aware of the implications, if not perhaps a refresher flight with a instructor (and sufficient height agl) would be a wise investment.
VRS in a hover in a updraught, possible but unlikely as your power in use is probably considerably lower than in a normal hover (your in a updraught!), however if you start to sink a bit and decide to pull pitch......
To answer the initial post: if flying a constant radius turn around a ground feature at a constant IAS on a nil wind day there will be no requirement for pitch change. Throw in some wind but fly at a constant IAS and pitch change will be needed as the angle of bank required to maintain the 'K' radius of the turn changes, otherwise the a/c will climb and descend as the associated load factor changes.
A question I have always pondered is where in the orbit is the demand for Bank Angle (and thus pitch/power) greatest??
Conventional Principle of Flight would mandate this be in the downwind position due to the squared function of velocity in the Load Factor equation as discussed by Nick Lappos in post #84. However when flying a constant radius turn at say 60 kts IAS in a 20 kts wind the greatest angle of bank appears to be somewhat after the downwind position during the turn to crosswind? is this another illusion or due to the combination of high groundspeed (admittedly decreasing at this point in the turn but still higher than the IAS) and the drift caused by the (increasing) cross wind component...??
Any takers?
A question I have always pondered is where in the orbit is the demand for Bank Angle (and thus pitch/power) greatest??
2fly - I am with you on this one and I believe it to be crosswind (after the turn downwind) since you have maximum drift and must therefore have max AoB to negate it.
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Thank you all for your time and effort in answering my question. I can see this is a hot topic, and didn't mean for everyone to fall out with each other!
As for InTGreen's comments on the flapback effects, titled "Principles of flight", are you suggesting that this only happens on the first turn downwind, or as I continue turning would I get more and more nose down pitch, even as I come back into wind?
This would put the aircraft out of limits (15 degrees nose down) very quickly.
From my limited experience, this is not the case.
As for InTGreen's comments on the flapback effects, titled "Principles of flight", are you suggesting that this only happens on the first turn downwind, or as I continue turning would I get more and more nose down pitch, even as I come back into wind?
This would put the aircraft out of limits (15 degrees nose down) very quickly.
From my limited experience, this is not the case.
Alchef - your original question revisited an old chestnut that has been debated at length in many crewrooms and several tiomes on pprune in different forums.
Hopefully, Nick has put to bed once and for all the myth of needing more power in a constant AoB /IAS turn as you go downwind.
The potential pitfalls of turning downwind and maintaining constant groundspeed have been extensively covered and this is the area that catches out the unwary helicopter pilot, especially in the mountains when visual refernces can already be confusing due to the terrain.
I have taught lots of mountain flying and although I took flak for my suggestion about pushing then pulling - it works and has helped lots of students of all levels to improve their mountain techniques.
Hopefully, Nick has put to bed once and for all the myth of needing more power in a constant AoB /IAS turn as you go downwind.
The potential pitfalls of turning downwind and maintaining constant groundspeed have been extensively covered and this is the area that catches out the unwary helicopter pilot, especially in the mountains when visual refernces can already be confusing due to the terrain.
I have taught lots of mountain flying and although I took flak for my suggestion about pushing then pulling - it works and has helped lots of students of all levels to improve their mountain techniques.
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To attain a constant radius turn in wind (at a constant airspeed) the most bank angle is required in the middle of the downwind leg, that is when the wind is directly behind as this is when the ground speed is the greatest and you therefore need the greatest accelerating force towards the centre of the circle to attain the same radius.
If the maximum banking is timed incorrectly, by that I mean banking a little too late in the turn, it appears as though the greatest bank angle is required in the crosswind. This is however only a consequence of not banking enough during the downwind leg.
This is something that definately works in practice as the theory suggests it should.
If the maximum banking is timed incorrectly, by that I mean banking a little too late in the turn, it appears as though the greatest bank angle is required in the crosswind. This is however only a consequence of not banking enough during the downwind leg.
This is something that definately works in practice as the theory suggests it should.
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That graph of Nick's above is quite clever, and you can use it to prove this point. If you hold a pencil against a fixed radious of turn and then tilt it to simulate different groundspeeds, you can see the angle of bank changing in the turn, and the angle of bank is indeed greatest when the groundspeed is highest.
A few people have dabbled on this thread with trying to look at secondary aerodynamic issues when rolling into a turn. I'm quite interested in that, although I suspect the answers are complex and maybe type specific also. I have a firm belief that the R44 pitches up on rolling into the turn, and then pitches down as the turn develops. In all my experiments I've tried as hard as possible to move the cyclic purely laterally, but of course I can't rule out user error !
Anyone care to confirm, counter, or attempt to explain ?
A few people have dabbled on this thread with trying to look at secondary aerodynamic issues when rolling into a turn. I'm quite interested in that, although I suspect the answers are complex and maybe type specific also. I have a firm belief that the R44 pitches up on rolling into the turn, and then pitches down as the turn develops. In all my experiments I've tried as hard as possible to move the cyclic purely laterally, but of course I can't rule out user error !
Anyone care to confirm, counter, or attempt to explain ?
