Approach angles
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question about approach angles
normal approach is 10 degrees..
steep is 15 degrees..
shallow is 5 degrees..
right??
when doing a steep approach in an r22, you level at 300ft agl until steep approach angle is reached - ie spot just above console. this looks more like a 30-40 degree angle to me. not 15 degrees.
likewise a normal approach looks greater than 10 degrees
can anyone explain this?
steep is 15 degrees..
shallow is 5 degrees..
right??
when doing a steep approach in an r22, you level at 300ft agl until steep approach angle is reached - ie spot just above console. this looks more like a 30-40 degree angle to me. not 15 degrees.
likewise a normal approach looks greater than 10 degrees
can anyone explain this?
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Per the FAA:
Shallow - less than 8 degrees
Normal - 8 to 12 degrees
Steep - more than 12 degrees (with 15 degrees being the recommended maximum)
As far as what it looks like, remember that the "spot on the windscreen" technique only works to identify the place where you start your descent. As you decelerate, the aircraft attitude changes (more nose-high), so the spot will "move down" even though the angle remains the same.
Shallow - less than 8 degrees
Normal - 8 to 12 degrees
Steep - more than 12 degrees (with 15 degrees being the recommended maximum)
As far as what it looks like, remember that the "spot on the windscreen" technique only works to identify the place where you start your descent. As you decelerate, the aircraft attitude changes (more nose-high), so the spot will "move down" even though the angle remains the same.
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Fling is right on, the normal deceleration that we continuously perform during an approach requires about 2 to 3 degrees nose up, which makes the approach look steeper. Each degree nose up from normal causes about 1/2 knot per second deceleration.
The limiter to steepness is forward speed. If you are faster, the steepest approach you can make becomes more shallow, because the helo will only descend at a given amount to stay above autorotation. If you slow to 35 or less, the autorotation boundary is very far below your flight condition, so you can descend in full control at angles up to about 20 degrees. If you want to be steep and safe, be steep and slow.
No, Vortex Ring State is not possible in steep approaches, within normal reason (anything is possible for the truly ungifted pilot.)
The limiter to steepness is forward speed. If you are faster, the steepest approach you can make becomes more shallow, because the helo will only descend at a given amount to stay above autorotation. If you slow to 35 or less, the autorotation boundary is very far below your flight condition, so you can descend in full control at angles up to about 20 degrees. If you want to be steep and safe, be steep and slow.
No, Vortex Ring State is not possible in steep approaches, within normal reason (anything is possible for the truly ungifted pilot.)
Spot on the screen works very well from entry into descent until about 150 ft agl and about 250m away from landing zone. Only really need to decelerate when you are getting that close. Bear in mind this works very well for a 300 when your approach speed is 40 kt ground speed, imagine the R22 would be about the same.
Vortex ring is possible if you have a very steep approach in no wind with slow slow fwd speed( less than 20 kts) high rate of descent ( 500ft plus) and then take an armful of power. As Nick said for the truly ungifted - I think stupid would be better than ungifted, Nick is being too kind.
Vortex ring is possible if you have a very steep approach in no wind with slow slow fwd speed( less than 20 kts) high rate of descent ( 500ft plus) and then take an armful of power. As Nick said for the truly ungifted - I think stupid would be better than ungifted, Nick is being too kind.
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From the cockpit the angles always seem steeper than they actually are.
If want to do the math to determine your approach angle use your GPS to determine distance back (in feet if your altimeter reads in feet) for the start of your "steep approach" and record your altitude.
use the following formula : (ALt/dis) which will give you slope percentage. Then take the INV TAN of the slope and voila decent angle .
i.e. 200 feet alt and 1520 feet (1/4 NM) back from the spot=
200/1520=.13157 (13% slope)
the INV TAN(ARC Tangent) of .13157 =7.49 degrees.
Therefore a continuous approach angle from 1/4 NM and 200 feet = a 7.5 degree approach angle to touch down.
If want to do the math to determine your approach angle use your GPS to determine distance back (in feet if your altimeter reads in feet) for the start of your "steep approach" and record your altitude.
use the following formula : (ALt/dis) which will give you slope percentage. Then take the INV TAN of the slope and voila decent angle .
i.e. 200 feet alt and 1520 feet (1/4 NM) back from the spot=
200/1520=.13157 (13% slope)
the INV TAN(ARC Tangent) of .13157 =7.49 degrees.
Therefore a continuous approach angle from 1/4 NM and 200 feet = a 7.5 degree approach angle to touch down.
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In an attempt to win a argument (with my chief instructor at the time) I developed a spreadsheet where you can input a groundspeed, and a rate of descent and it will tell you the angle you're moving down.
If the math is right a constant 30kts groundspeed with a 500'/min r.o.d. should yield a 9.46 deg. angle, keeping 30 kts., and increasing r.o.d to 800'/min should give a 15 deg. angle. (Interestingly, 1700'/min at 60 kts groundspeed gives a an angle if 15.8, so a typical r22 auto should demonstrate a textbook steep approach angle)
Of course we don't fly approaches at these constant conditions, but you could set up a steady state descent holding these numbers to demonstrate an angle to a student.
The best solution if you really wanted to fly and visualize precision glideslopes would be to build an alignment of elements visual glideslopt as mentioned in 2-1-2 e. in the AIM
You could make it adjustable to demonstrate different angles!
I think students should be taught to fly apporaches with a lot of variation, i.e. slow and shallow, fast and shallow, slow and steep, etc.. as this develops a great feel for the ship which can then make flying a "normal" approach a no brainer.
If the math is right a constant 30kts groundspeed with a 500'/min r.o.d. should yield a 9.46 deg. angle, keeping 30 kts., and increasing r.o.d to 800'/min should give a 15 deg. angle. (Interestingly, 1700'/min at 60 kts groundspeed gives a an angle if 15.8, so a typical r22 auto should demonstrate a textbook steep approach angle)
Of course we don't fly approaches at these constant conditions, but you could set up a steady state descent holding these numbers to demonstrate an angle to a student.
The best solution if you really wanted to fly and visualize precision glideslopes would be to build an alignment of elements visual glideslopt as mentioned in 2-1-2 e. in the AIM
You could make it adjustable to demonstrate different angles!
I think students should be taught to fly apporaches with a lot of variation, i.e. slow and shallow, fast and shallow, slow and steep, etc.. as this develops a great feel for the ship which can then make flying a "normal" approach a no brainer.
Perhaps to convince unbelievers, you could try getting your students to sit in their normal seating position and see where 45 degrees from the horizontal is.
To do this, sit in the seat, stick your arm out level in front of you, then straight down beside you, and then point to the position that's half way between the two. For me, it's a couple of inches in front of my feet.
Then look at where the top of the instrument panel is with reference to the horizon; it won't be too far down. The angle between your eyes and the horizon is basically horizontal, so you can judge angles between your eyes and aim points on the ground with reference to that.
Then adding in the illusory 'steepening' effect that is brought in by the decelerative attitudes you get into while approaching (can be quite exciting on a dark night), and the whole picture should make more sense.
To do this, sit in the seat, stick your arm out level in front of you, then straight down beside you, and then point to the position that's half way between the two. For me, it's a couple of inches in front of my feet.
Then look at where the top of the instrument panel is with reference to the horizon; it won't be too far down. The angle between your eyes and the horizon is basically horizontal, so you can judge angles between your eyes and aim points on the ground with reference to that.
Then adding in the illusory 'steepening' effect that is brought in by the decelerative attitudes you get into while approaching (can be quite exciting on a dark night), and the whole picture should make more sense.
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Mr Lappos and Vortex ring again....who do you believe ? My current instructor swears by Nick's beliefs so much, that VR is not even considered in steep approach training. Is it something that is over emphasised to trainees ? Hopefully, i'll never find out.
Confused but aware, TFS.
Confused but aware, TFS.
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As an (extremely) low-timer, I always thought the standard approach angle was like in a Cessna, 3 degrees or so. Hitting the spot was like trying to widdle through a letter box from the other side of the road. I would have preferred to start with something much steeper, as though jumping off a wall - much easier to judge where you'll end up.
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Arm out the Window
I like your attempt to answer thecontroller's question. It is probably a human misperception, even without descelerations.
For me it does not only happen in a heli, but also when being on mountain slopes: it always looks a lot steeper than it is.
d3
For me it does not only happen in a heli, but also when being on mountain slopes: it always looks a lot steeper than it is.
d3
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TFS,
The issue with VRS is that the name is often applied to all those many more accidents where the power is simply not enough to both hover the aircraft where the pilot desires, and stop its descent prior to the hover. That temporary burst of energy needed on a normal steep, fast approach is often 10 or 15% more than that needed to perform a still hover. When a pilot makes a poor approach, drops through, droops the rotor, and whacks the ground, he says "Vortex Ring" and we all nod knowingly. The helicopter got the poor chap. If he spins around at the bottom (that extra 15% torque, remember?) we call it "LTE!"
I do try to keep our folly in the properly labeled boxes in the hope that when it is all said, we all at least know WHAT caused the accident, as a slight first step to actually not having one.
As a little refresher - you cannot experience vortex ring state in any helicopter at less than about 1000 feet per minute vertical descent, and at more than about 8 knots forward speed.
The issue with VRS is that the name is often applied to all those many more accidents where the power is simply not enough to both hover the aircraft where the pilot desires, and stop its descent prior to the hover. That temporary burst of energy needed on a normal steep, fast approach is often 10 or 15% more than that needed to perform a still hover. When a pilot makes a poor approach, drops through, droops the rotor, and whacks the ground, he says "Vortex Ring" and we all nod knowingly. The helicopter got the poor chap. If he spins around at the bottom (that extra 15% torque, remember?) we call it "LTE!"
I do try to keep our folly in the properly labeled boxes in the hope that when it is all said, we all at least know WHAT caused the accident, as a slight first step to actually not having one.
As a little refresher - you cannot experience vortex ring state in any helicopter at less than about 1000 feet per minute vertical descent, and at more than about 8 knots forward speed.
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The Robinson training regime at the two centres I have used preaches limits of not exceeding 300 fpm when IAS is below 30kts.
Is this just making sure we are massively within the envelope, or to keep us clear of incipient state?
BW
Is this just making sure we are massively within the envelope, or to keep us clear of incipient state?
BW
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bladewashout,
Remember the joke about the little boy who blew a small horn every minute. When asked why, he said "It keeps the elephants away." When told there were no elephants within 100 miles, he said, "See, it works!"
To make an approach and at the bottom be much less than 300 fpm is good pilotage, and likely to produce a very satisfactory approach. I used to tell students that at 100 feet they better be at 300fpm or less, or I would start yelling, even in a three engined monster with 13,000 horsepower. Nothing to do with VRS, it is because it keeps the elephants away.
Regarding descending vertically, if you are in a helo with barely the power to hover IGE, who wants to try and hover OGE? You will fall like a rock, hit the ground and say "VRS!" and we will all nod sagely. Meanwhile, US Army attack helicopters fly profiles where they hover OGE to shoot over a ridgeline, bob back down, straight down, at 300 to 500 fpm, stop quickly in space and move laterally to the next fire point. I guess VRS is against Army regs, or perhaps these helos have 10% power margin while HOGE.
I even saw a poster above who was worried about pulling in power while at low speed in a descent, as if the power pull would CAUSE the VRS! The misunderstanding about the low speed portion of our envelope is aweful, and the old guides and sage advice from practical but (forgive me) slightly misinformed instructors does not help.
There are great reasons not to descend vertically in underpowered helos, but they are not VRS. Follow the advice about 300 fpm, as a limited case where underpowered helos must be babied, just don't take the aerodynamics to the bank. In a helo with enough power, that vertical region is a whole new degree of freedom. Ask photo chase pilots, folks who tend power lines, those who fly NOE for a living.
VRS is:
Caused when you descend vertically fast enough to start catching up with your downwash.
Never experienced at less than 50 to 75% of your downwash speed
Not at all likely to occur in any helo at 300 fpm
Often confused with "over pitching" or "hovering without proper power"
Grossly misunderstood by almost every old line instructor and training guide
Harder to experience at high altitude or high gross weight
Very very seldom the cause of any helo accident (see "over pitching" for the real reason, in most cases.
One of the best ways to kick off a good thread on pprune!
Regarding listening to your flight instructor, please remember your Mother told you to bundle up, so you don't catch a cold. She was off base (viruses do not care how cold you are!), but the advice was sound, and the intention was excellent!
Remember the joke about the little boy who blew a small horn every minute. When asked why, he said "It keeps the elephants away." When told there were no elephants within 100 miles, he said, "See, it works!"
To make an approach and at the bottom be much less than 300 fpm is good pilotage, and likely to produce a very satisfactory approach. I used to tell students that at 100 feet they better be at 300fpm or less, or I would start yelling, even in a three engined monster with 13,000 horsepower. Nothing to do with VRS, it is because it keeps the elephants away.
Regarding descending vertically, if you are in a helo with barely the power to hover IGE, who wants to try and hover OGE? You will fall like a rock, hit the ground and say "VRS!" and we will all nod sagely. Meanwhile, US Army attack helicopters fly profiles where they hover OGE to shoot over a ridgeline, bob back down, straight down, at 300 to 500 fpm, stop quickly in space and move laterally to the next fire point. I guess VRS is against Army regs, or perhaps these helos have 10% power margin while HOGE.
I even saw a poster above who was worried about pulling in power while at low speed in a descent, as if the power pull would CAUSE the VRS! The misunderstanding about the low speed portion of our envelope is aweful, and the old guides and sage advice from practical but (forgive me) slightly misinformed instructors does not help.
There are great reasons not to descend vertically in underpowered helos, but they are not VRS. Follow the advice about 300 fpm, as a limited case where underpowered helos must be babied, just don't take the aerodynamics to the bank. In a helo with enough power, that vertical region is a whole new degree of freedom. Ask photo chase pilots, folks who tend power lines, those who fly NOE for a living.
VRS is:
Caused when you descend vertically fast enough to start catching up with your downwash.
Never experienced at less than 50 to 75% of your downwash speed
Not at all likely to occur in any helo at 300 fpm
Often confused with "over pitching" or "hovering without proper power"
Grossly misunderstood by almost every old line instructor and training guide
Harder to experience at high altitude or high gross weight
Very very seldom the cause of any helo accident (see "over pitching" for the real reason, in most cases.
One of the best ways to kick off a good thread on pprune!
Regarding listening to your flight instructor, please remember your Mother told you to bundle up, so you don't catch a cold. She was off base (viruses do not care how cold you are!), but the advice was sound, and the intention was excellent!
Last edited by NickLappos; 10th Nov 2005 at 15:46.
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Nick Lappos - please, please, please write a book!
It might help put to bed all the myths we get taught as helicopter neophytes! It's very frustrating and confusing to read /be taught/told one thing and then read from yourself that it's just not the case!
Please?
It might help put to bed all the myths we get taught as helicopter neophytes! It's very frustrating and confusing to read /be taught/told one thing and then read from yourself that it's just not the case!
Please?
Not sure how steep the angle needs to be for a normal approach in the UK, however in Canada using the flight instructor manual a normal approach is between 6 and 8 degrees anything steeper is a steep approach anything less is a shallow approach.
To work out your angle of approach draw two lines on an A4 (8 by 11) sheet of paper at 6 and 8 degrees from the corner up then when flying hold the sheet level look down the lines and you have your approach angle for a normal approach , you will see from this even if the instructor guide for the Jaa(caa) says ten degrees most of you will have been doing steep approaches as normal approaches.
Vortex ring state: aircraft descending into its own down wash
High rate of descent: greater than 3/500feet per min
Low air speed: below translational lift
Power applied: more than 20/30% power applied
If you don't have all three factors no VRS
Recovery Get airspeed altitude permiting reduce collective setting
Or autorotate
Hope this helps
To work out your angle of approach draw two lines on an A4 (8 by 11) sheet of paper at 6 and 8 degrees from the corner up then when flying hold the sheet level look down the lines and you have your approach angle for a normal approach , you will see from this even if the instructor guide for the Jaa(caa) says ten degrees most of you will have been doing steep approaches as normal approaches.
Vortex ring state: aircraft descending into its own down wash
High rate of descent: greater than 3/500feet per min
Low air speed: below translational lift
Power applied: more than 20/30% power applied
If you don't have all three factors no VRS
Recovery Get airspeed altitude permiting reduce collective setting
Or autorotate
Hope this helps
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The psychological angle
I am interested in tc's original question.
If I can restate it:
He and his students experience an illusion on approach. The approach angles appear 2-3 times larger than they actually are. What is the basis of this illusion?
The explanation about nose-up attitude due to decelleration only accounts for a few degrees. In any case tc appears to be trying to rule out that factor by supposing a level attitude prior to picking out the landing point.
So I also experience this illusion, but don't have an explanation. It looks like a human factors question to me. Maybe there is a psychological basis for it.
If I can restate it:
He and his students experience an illusion on approach. The approach angles appear 2-3 times larger than they actually are. What is the basis of this illusion?
The explanation about nose-up attitude due to decelleration only accounts for a few degrees. In any case tc appears to be trying to rule out that factor by supposing a level attitude prior to picking out the landing point.
So I also experience this illusion, but don't have an explanation. It looks like a human factors question to me. Maybe there is a psychological basis for it.
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WHK4,
Who says the poor judgements of untrained people are worth debating? What training or experience does the student have in telling 12 degrees from 16 anywhere, let alone in a cockpit? Why the mystery and need for "human factors" explanations for people who have no experience and no basis for it? This does not take away their need for info, nor our wish to help.
Let me restate their question as I see it: I have no earthly idea how to tell the angle of approach, any more than I can guess the weight of a prize bull or the height of a far tree. Can someone give me some tips?
In that case, I see lots of good thoughts on this thread.
Who says the poor judgements of untrained people are worth debating? What training or experience does the student have in telling 12 degrees from 16 anywhere, let alone in a cockpit? Why the mystery and need for "human factors" explanations for people who have no experience and no basis for it? This does not take away their need for info, nor our wish to help.
Let me restate their question as I see it: I have no earthly idea how to tell the angle of approach, any more than I can guess the weight of a prize bull or the height of a far tree. Can someone give me some tips?
In that case, I see lots of good thoughts on this thread.
A couple of factors that probably contribute to the over-estimation of approach angles would be:
1. The fact that our eyes don't actually end up at the aim point spot on the ground - in the hover with the mast over the spot, our eyes are some distance above and in front of it, which would contribute to an 'overshoot' illusion, especially on short final.
2. A true appreciation of where we're going on an approach takes a while to build up; i.e. we look out the front at the aim point, imagine a direct line between us and the point, and over period of time (a few seconds, say) assess how we are travelling with respect to that line (over- or undershooting, or right on).
Just a quick look out the front, especially with a high nose attitude, will probably give an inaccurate mind-picture of how the approach is going.
1. The fact that our eyes don't actually end up at the aim point spot on the ground - in the hover with the mast over the spot, our eyes are some distance above and in front of it, which would contribute to an 'overshoot' illusion, especially on short final.
2. A true appreciation of where we're going on an approach takes a while to build up; i.e. we look out the front at the aim point, imagine a direct line between us and the point, and over period of time (a few seconds, say) assess how we are travelling with respect to that line (over- or undershooting, or right on).
Just a quick look out the front, especially with a high nose attitude, will probably give an inaccurate mind-picture of how the approach is going.
N. Lappos about VRS:
There is something that troubles me about statements like this and in fact all that we "know" about VRS/SWP: That Canadian RAF Sea King at the airshow in upstate NY some years back.
If you can find the whole clip, you'll see the big Sikorsky hovering around up at 100 feet or so (it's hard to tell) in an OGE hover. It is nice and stable, and the cameraman is easily able to "track" the ship without a lot of jerky camera movements. The ship does a sort of sliding-pedal-turn without losing much altitude (again, hard to tell), when all of a sudden the bottom falls out and it starts descending vertically, blades coning like the proverbial ballerina, collective obviously up under two armpits, until it smashes into the ground like a ton of bricks, landing gear fails and it rolls over. (Most of the internet video clips I've seen only show the last few seconds of the flight as it is already in...whatever flight regime is causing the downward cable-snapped elevator ride.)
Now to this observer, it does not *look* like the ship was in a big vertical descent before The Event. In fact, just the opposite, it looks like the crew was being pretty cautious and slow. They didn't seem to be all that heavy, so available power shouldn't have been a problem. But "something" happened, and I'd sure like to know what. Engine failure?
Not at all likely to occur in any helo at 300 fpm
If you can find the whole clip, you'll see the big Sikorsky hovering around up at 100 feet or so (it's hard to tell) in an OGE hover. It is nice and stable, and the cameraman is easily able to "track" the ship without a lot of jerky camera movements. The ship does a sort of sliding-pedal-turn without losing much altitude (again, hard to tell), when all of a sudden the bottom falls out and it starts descending vertically, blades coning like the proverbial ballerina, collective obviously up under two armpits, until it smashes into the ground like a ton of bricks, landing gear fails and it rolls over. (Most of the internet video clips I've seen only show the last few seconds of the flight as it is already in...whatever flight regime is causing the downward cable-snapped elevator ride.)
Now to this observer, it does not *look* like the ship was in a big vertical descent before The Event. In fact, just the opposite, it looks like the crew was being pretty cautious and slow. They didn't seem to be all that heavy, so available power shouldn't have been a problem. But "something" happened, and I'd sure like to know what. Engine failure?