Tightest Radius Turn?
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Tightest Radius Turn?
I'm getting myself somewhat confused about exactly how to make the tightest possible 180 degree turn (in the horizontal plane) in a non aerobatic aircraft. While I do not ever intend to do any scud running (who would?), the question of reversing course in a valley exercises my imagination.
Now the texts will tell you that as your velocity increases, then at constant G the radius must increase as the square of the speed. So in theory, if I pull 2G in a level 60 degree banked turn, I need to be doing 1.414 (ie square root two) times Vs to generate the required lift. In say an Arrow, Vs = 60 knots indicated, so I should be doing a little above 85 knots to do the minimum radius turn possible at 2G. Anything over 85 knots is going to widen the turn more than necessary. When you read the Piper POH, well bugger me, the stall speed at 60 degrees bank is....85 knots.
Then you can do the exercise with flaps down, Vs = 55 and you get 77 knots...although the book says 75 is the stall speed.
So in both cases we are flying just below the critical angle.
However Mr. Robson's excellent book on basic beginners aerobatics has managed to both educate and perhaps slightly confuse me at the same time, and I wonder here if anyone can elucidate some of the mysteries.
1. He explains that at Vs in level flight, no turns are possible because there is no excess lift - which is so blindingly obvious, I wonder why it never entered my head before, and it explains why approach speeds are what they are.
2. He also explains that if I wish to pull 3.8G, the maximum allowable on my theoretical Arrow, then I have to be doing very close to twice Vs for obvious reasons. I can't use flaps as the limit is 103 knots and I assume that they are rated for 2G max extended anyway.
So my question is, which of these approaches, 3.8G at 120 KIAS, 2G at 85 KIAS or 2G at 77KIAS flaps extended to 40 deg. (plus a gust margin and a little bit extra) is going to produce the tightest turning radius?
Now the texts will tell you that as your velocity increases, then at constant G the radius must increase as the square of the speed. So in theory, if I pull 2G in a level 60 degree banked turn, I need to be doing 1.414 (ie square root two) times Vs to generate the required lift. In say an Arrow, Vs = 60 knots indicated, so I should be doing a little above 85 knots to do the minimum radius turn possible at 2G. Anything over 85 knots is going to widen the turn more than necessary. When you read the Piper POH, well bugger me, the stall speed at 60 degrees bank is....85 knots.
Then you can do the exercise with flaps down, Vs = 55 and you get 77 knots...although the book says 75 is the stall speed.
So in both cases we are flying just below the critical angle.
However Mr. Robson's excellent book on basic beginners aerobatics has managed to both educate and perhaps slightly confuse me at the same time, and I wonder here if anyone can elucidate some of the mysteries.
1. He explains that at Vs in level flight, no turns are possible because there is no excess lift - which is so blindingly obvious, I wonder why it never entered my head before, and it explains why approach speeds are what they are.
2. He also explains that if I wish to pull 3.8G, the maximum allowable on my theoretical Arrow, then I have to be doing very close to twice Vs for obvious reasons. I can't use flaps as the limit is 103 knots and I assume that they are rated for 2G max extended anyway.
So my question is, which of these approaches, 3.8G at 120 KIAS, 2G at 85 KIAS or 2G at 77KIAS flaps extended to 40 deg. (plus a gust margin and a little bit extra) is going to produce the tightest turning radius?
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Here you go Sunny. For homework I'll let you do the maths.
http://en.wikipedia.org/wiki/ROT
http://en.wikipedia.org/wiki/ROT
Why do you want to know?
If its just for the mental gymnastics - then skip this post. Its too long since I did all that stuff to be bothered with it now, but ........
..... if you genuinely want to know how to do a 180 to get out of IMC, then I would suggest that you focus on holding a Rate 1 turn on the T&B, but ......
...... if you want to know how to do a 180 in the least amount of sky, this is how I would do it -
roll into the turn and pull on 1st stage of flap as you speed washes off, and continue to increase bank and increase back pressure until you feel the start of buffet or until the stall warning starts - then adjust your angle of bank to stay just above the stall until you are ready to roll out.
Something you probably should practice!
Does a Max Rate turn = Min Radius turn?
Beggered if I know - but probably near enough.
I have done it only once in anger when I flew up a blind valley in NZ in a Traumahawk and realised the cloud covered mountains either side were closing in on me. Needed a change of undies afterwards but lived to fly another day. Others have been less fortunate.
Dr
If its just for the mental gymnastics - then skip this post. Its too long since I did all that stuff to be bothered with it now, but ........
..... if you genuinely want to know how to do a 180 to get out of IMC, then I would suggest that you focus on holding a Rate 1 turn on the T&B, but ......
...... if you want to know how to do a 180 in the least amount of sky, this is how I would do it -
roll into the turn and pull on 1st stage of flap as you speed washes off, and continue to increase bank and increase back pressure until you feel the start of buffet or until the stall warning starts - then adjust your angle of bank to stay just above the stall until you are ready to roll out.
Something you probably should practice!
Does a Max Rate turn = Min Radius turn?
Beggered if I know - but probably near enough.
I have done it only once in anger when I flew up a blind valley in NZ in a Traumahawk and realised the cloud covered mountains either side were closing in on me. Needed a change of undies afterwards but lived to fly another day. Others have been less fortunate.
Dr
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Sunfish
The only figure I have is radius of turn = V squared over 11.26 x TAN bank angle.
Mathmatically wouldn't have a clue how the various configs change that, but they probably do.
But at the end of the day. Is it really relevant cos if you have put yourself in that much sh1t, you probably won't have time to change your config any way.
PM
The only figure I have is radius of turn = V squared over 11.26 x TAN bank angle.
Mathmatically wouldn't have a clue how the various configs change that, but they probably do.
But at the end of the day. Is it really relevant cos if you have put yourself in that much sh1t, you probably won't have time to change your config any way.
PM
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It's the V-squared that'll kill ya...
Why use 60deg AOB? why fly it fast? You dont want to get out quick, just in minumum radius. Stick to a comfortable, safe Angle of Bank (even rate 1) and fly as slow as the a/c config will let you. The slow speed is what dramatically reduces the radius of the turn.
RB
RB
if I wish to pull 3.8G, the maximum allowable on my theoretical Arrow
Just rack it over and fly it on the point of the stall by feel!
Oh yes - and you can leave your feet flat on the floor too!
Dr
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Too many numbers and too much to think about if you're in the shiite and about to pancake onto a valley wall - do as FTDK says...turn hard, keep enough speed/use enough flap/power, to keep you above the stall.
Definitely something you should practice. If you need it one day, guarantee you'll not be focusing on formula's or flight manual details.
Not being a smart arse here, kudos to you for digging into the theory, however reality is sometimes a tad different. Just go and try it.
Definitely something you should practice. If you need it one day, guarantee you'll not be focusing on formula's or flight manual details.
Not being a smart arse here, kudos to you for digging into the theory, however reality is sometimes a tad different. Just go and try it.
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Dr & 'dicko' is right, keep it simple & just remember that stall speed increases the more AofB you pull on, that's the basics of it & that's all you ought need to recall when the spam hits the fan!. Lower the nose slightly in the tight turn if alt permits also. And finally the BEST advice I can offer here as well as everyone else DON'T get yrself in a position where it requires very tight turns in the first place ! If you need to figure out from all the boffins in here as to how you can achive the tightest possible turn then yr going to be too damn close to the valley wall anyway.
CW
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?????
Figure out what the theory says is best for your aircraft, then go out and practise it at altitude.
Remember the Hamilton Island accident. Too many of todays pilots have not done spin training.
It's also smart to stay on the downwind side of the valley, so you will be turning into wind.
I remember once, a long time ago, flying through the Haast pass in NZ under the cloud. Fortunately we did not have to turn around, as we took all the right valleys.
NZ (south Island)and PNG pilots will have intimate knowledge of these techniques.
(and lots of ozzies who will not admit it)
Remember the Hamilton Island accident. Too many of todays pilots have not done spin training.
It's also smart to stay on the downwind side of the valley, so you will be turning into wind.
I remember once, a long time ago, flying through the Haast pass in NZ under the cloud. Fortunately we did not have to turn around, as we took all the right valleys.
NZ (south Island)and PNG pilots will have intimate knowledge of these techniques.
(and lots of ozzies who will not admit it)
bushy
Correct. Smallest radious turn is achieved with full flap and as slow as you can go. Any technique that results in high g's being pulled will kill you in a tight enviroment.
NZ (south Island)and PNG pilots will have intimate knowledge of these techniques.
aaaaaaaaaaaaaahhhhhhhhhhhhhhh Sunfish, this is one of my favourite discussion topics over a cup of coffee or glass of red wine.
The rest of the question is whether you can descend or not?
Refer figure 11 at http://www.avweb.com/news/airman/182421-1.html For the Cessna 172, the tightest turn radius is at 100 kts CAS pulling 3.8g but descending at over 4000 fpm - gives a radius of 350 ft. Unfortunately the graph is provided only at an altitude of 12,000 ft (I've been down a canyon at 12,000 ft in a 172).
If you want to maintain height then you've got to fly slower - that same chart suggests 58 kts CAS but again that's at 12,000 ft. At lower altitudes the performance is better so a higher airspeed.
So my question is, which of these approaches, 3.8G at 120 KIAS, 2G at 85 KIAS or 2G at 77KIAS flaps extended to 40 deg. (plus a gust margin and a little bit extra) is going to produce the tightest turning radius?
Refer figure 11 at http://www.avweb.com/news/airman/182421-1.html For the Cessna 172, the tightest turn radius is at 100 kts CAS pulling 3.8g but descending at over 4000 fpm - gives a radius of 350 ft. Unfortunately the graph is provided only at an altitude of 12,000 ft (I've been down a canyon at 12,000 ft in a 172).
If you want to maintain height then you've got to fly slower - that same chart suggests 58 kts CAS but again that's at 12,000 ft. At lower altitudes the performance is better so a higher airspeed.
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From someone who has done them in anger, the practical tips above are worth noting. At least some flap (in the vast majority of acft) is very helpful - keeps the speed slower and usually gives you a much better margin over the stall. Secondly, telling you to suck eggs but you would be surprised how much speed can be washed off in these turns - especially in a loaded aircraft. Add power - probably more than what you would expect.
Know your aircraft and how it handles - especially at different weights. What's easy in a light aircraft can become very challenging in a loaded one.
When you are poking up a valley where you think you may need to turn around - ALWAYS fly on one side (downwind if possible).
As has been previously mentioned, if you can descend while turning - great - you don't have to load up as much - but watch the speed! If your speed races away you could find the radius increasing rapidly and you might be in trouble with your white arc also. If you are doing this in anger it could be harder than what you thought as you will have no proper horizon and your motor skills can become impaired with stress...
Wouldn't advise it but Smithy saved his hide in NZ doing a stall-turn to get out of a valley once...
Know your aircraft and how it handles - especially at different weights. What's easy in a light aircraft can become very challenging in a loaded one.
When you are poking up a valley where you think you may need to turn around - ALWAYS fly on one side (downwind if possible).
As has been previously mentioned, if you can descend while turning - great - you don't have to load up as much - but watch the speed! If your speed races away you could find the radius increasing rapidly and you might be in trouble with your white arc also. If you are doing this in anger it could be harder than what you thought as you will have no proper horizon and your motor skills can become impaired with stress...
Wouldn't advise it but Smithy saved his hide in NZ doing a stall-turn to get out of a valley once...
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Guys,
Take FTDK's advice and add full power (if you are saving your life, that is). Think about it - buffet threshhold, stall AoA, ability to gain a bit of height. You'll never find a knuck trying max rate/min radius without full chat+AB.
Gru
Take FTDK's advice and add full power (if you are saving your life, that is). Think about it - buffet threshhold, stall AoA, ability to gain a bit of height. You'll never find a knuck trying max rate/min radius without full chat+AB.
Gru
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Turn downwind initially until at about 30 deg to the side of the valley, when relatively close to the side turn into wind, slow lots of flap, at about 45 deg to the other side if you are certain you are going to make it around, rack it over (45 to 60 deg bank max) and continue the turn, lots of power, above the stall. Practice it first.
Turning into the wind for the reversal will make a huge difference, turning away (downwind) for the reversal kiss your @ss goodbye
Turning into the wind for the reversal will make a huge difference, turning away (downwind) for the reversal kiss your @ss goodbye