Maximum range airspeed in autorotation
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Better be careful no misconceptions stat to creep in here.
airframe attitude to me is airspeed, at any power setting, anyone care to disagree?
the '47 is about the only lightie that has a movable horizontal stab, and in fact the G5's came out stock standard without them.
minimum power speed in the '47 is around 39 to 41 knots, max range in the auto i always used 60 knots. I never put a clock on it to see whether i stayed up longer at the lower airspeed but that is very academic when the sight picture is vastly different.
same in an R22, try the picture at minimum power airspeed of 52 knots and a much better range speed of 65knots.
RRPM well down also for max range.
most important thing to remember in an auto, there is only one power source, you better believe it. (excessive energy use from high RRPM or turning will only result in a higher ROD)
second most important thing, when practising sight pictures, never but never keep watching it with the needles joined as you will be transmitting power (however little) and the picture will not be real. try it an see.
third most important, when you do the unexpected throttle chop, do it in a safe area in case the donk stops when you do. (all to do with a little orifice which might not have been put in!)
and the Shawn Coyle theory, bang on. and not just for the reason of teaching how to do an EOL
airframe attitude to me is airspeed, at any power setting, anyone care to disagree?
the '47 is about the only lightie that has a movable horizontal stab, and in fact the G5's came out stock standard without them.
minimum power speed in the '47 is around 39 to 41 knots, max range in the auto i always used 60 knots. I never put a clock on it to see whether i stayed up longer at the lower airspeed but that is very academic when the sight picture is vastly different.
same in an R22, try the picture at minimum power airspeed of 52 knots and a much better range speed of 65knots.
RRPM well down also for max range.
most important thing to remember in an auto, there is only one power source, you better believe it. (excessive energy use from high RRPM or turning will only result in a higher ROD)
second most important thing, when practising sight pictures, never but never keep watching it with the needles joined as you will be transmitting power (however little) and the picture will not be real. try it an see.
third most important, when you do the unexpected throttle chop, do it in a safe area in case the donk stops when you do. (all to do with a little orifice which might not have been put in!)
and the Shawn Coyle theory, bang on. and not just for the reason of teaching how to do an EOL
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The math is very simple. If you divide forward speed (distance/time) by vertical speed (height/time) you end up with Distance per unit height.
Take airspeed in Knots (nm/hr), divide by 60 and you get Nm/min. Divide by the vertical speed (feet of descent/min) and you get Nautical miles of glide / foot of descent.
60 knots/60 = 1 Nm/min.
1.0 Nm/min/1200 feet per minute = .00083 Nm/ft or .83 Nm/1000 ft
Just do this for a spread of speeds, perhaps 4, and you can look for the speed that gives you the most Nm per 1000 feet. Use your flight instruments, they are quite accurate enough. Two auto descents with a clip board and a pencil, and you have the figures for your machine.
Take airspeed in Knots (nm/hr), divide by 60 and you get Nm/min. Divide by the vertical speed (feet of descent/min) and you get Nautical miles of glide / foot of descent.
60 knots/60 = 1 Nm/min.
1.0 Nm/min/1200 feet per minute = .00083 Nm/ft or .83 Nm/1000 ft
Just do this for a spread of speeds, perhaps 4, and you can look for the speed that gives you the most Nm per 1000 feet. Use your flight instruments, they are quite accurate enough. Two auto descents with a clip board and a pencil, and you have the figures for your machine.
Last edited by ramen noodles; 25th May 2009 at 21:18.
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Bell 427:
You're exactly on the money, like the Flight Manual says. But that's only valid for a no-wind situation.
And sadly, given that you might have put the engineless helicopter into a particular spot, there is no one airspeed that is going to do that for you in all situations. You need to know a lot more than just the 'best glide' or minimum rate of descent airspeed - and that knowing can only be obtained from some experience and practice.
You're exactly on the money, like the Flight Manual says. But that's only valid for a no-wind situation.
And sadly, given that you might have put the engineless helicopter into a particular spot, there is no one airspeed that is going to do that for you in all situations. You need to know a lot more than just the 'best glide' or minimum rate of descent airspeed - and that knowing can only be obtained from some experience and practice.
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Isn't there a blue line on Bell 206 ASIs? And doesn't it prescribe an Autorotation speed limit? Seems to remember there might be a problem maintaining RRPM above this speed. Memory dims with time, so could be wrong!
G
G
As Shawn says, the only way to sort this out for yourself is practice - all the maths in the world won't save you when the donk stops if you don't have an idea about what picture you are looking for out of the front window.
From about 2000' into wind, note a marker on the ground (fence, road, field boundary etc) and do your normal entry to auto as you get overhead the marker.
Once established in auto at the normal speed, look for a feature on the ground ahead that is staying in the same place in the windscreen (like a collision course with a constant relative bearing) - this is the place you will hit the ground if you do nothing and is therefore an achievable landing point (you might get a bit further if you fly the EOL nicely but don't bank on it).
If you can't continue to an EOL or power recovery in the hover, note where you are at 500' and see how far you have travelled from your entry point.
Now do the same thing again but at different speeds - make sure you still do a normal entry to auto - going straight for range speed is kidding yourself that you will react quickly enough to an engine failure - chances are you will need lots of flare to recover the Nr.
If you fly this exercise accurately and repeat it on different days with different wind strengths, you will build a knowledge of the performance of your helicopter which will allow you to make a pretty good assessment of where you can go in auto.
Then, once you are confident that you know your machine, fly around and pick areas, enter auto and see if you can make them (again normal entry so you get a true picture).
Those that have been taught advanced autos and PFLs might well recognise the sortie profile. If the landing point is moving up the windscreen you are undershooting it and will land short - if it is moving down the windscreen you are overshooting it and will land long (this is better since you can always lose height but seldom gain it!).
As you increase your speed in auto, you have more energy to dissipate in the EOL and if you haven't practised one from 90 kts you will probably overshoot the intended landing area so this is another aspect to consider - once you are confident of making your intended LS (ie it is starting to move down the windscreen) then bring back the speed to normal auto where you will have done most of your EOLs from and reassess.
You really need to have all this stuff well sorted before you start worrying about reducing Nr and doing 120kt autos in 100kt winds
A good point was made earlier about using a little bit of lever in the flare of the EOL to contain the Nr and make the flare more effective - this is a particularly useful technique in helos with lively Nr as it saves winding it off the clock. I just add a squeeze (not a handful) as I start the flare and remove it once the flare effect has dissipated so as to conserve Nr for the cushioning phase.
TeT - airframe attitude isn't airspeed in many aircraft - you don't need a moveable stabiliser, it just develops more downward force as the speed increases and tries to level the fuselage - otherwise you would end up hanging forward in your straps at 100 kts.
From about 2000' into wind, note a marker on the ground (fence, road, field boundary etc) and do your normal entry to auto as you get overhead the marker.
Once established in auto at the normal speed, look for a feature on the ground ahead that is staying in the same place in the windscreen (like a collision course with a constant relative bearing) - this is the place you will hit the ground if you do nothing and is therefore an achievable landing point (you might get a bit further if you fly the EOL nicely but don't bank on it).
If you can't continue to an EOL or power recovery in the hover, note where you are at 500' and see how far you have travelled from your entry point.
Now do the same thing again but at different speeds - make sure you still do a normal entry to auto - going straight for range speed is kidding yourself that you will react quickly enough to an engine failure - chances are you will need lots of flare to recover the Nr.
If you fly this exercise accurately and repeat it on different days with different wind strengths, you will build a knowledge of the performance of your helicopter which will allow you to make a pretty good assessment of where you can go in auto.
Then, once you are confident that you know your machine, fly around and pick areas, enter auto and see if you can make them (again normal entry so you get a true picture).
Those that have been taught advanced autos and PFLs might well recognise the sortie profile. If the landing point is moving up the windscreen you are undershooting it and will land short - if it is moving down the windscreen you are overshooting it and will land long (this is better since you can always lose height but seldom gain it!).
As you increase your speed in auto, you have more energy to dissipate in the EOL and if you haven't practised one from 90 kts you will probably overshoot the intended landing area so this is another aspect to consider - once you are confident of making your intended LS (ie it is starting to move down the windscreen) then bring back the speed to normal auto where you will have done most of your EOLs from and reassess.
You really need to have all this stuff well sorted before you start worrying about reducing Nr and doing 120kt autos in 100kt winds
A good point was made earlier about using a little bit of lever in the flare of the EOL to contain the Nr and make the flare more effective - this is a particularly useful technique in helos with lively Nr as it saves winding it off the clock. I just add a squeeze (not a handful) as I start the flare and remove it once the flare effect has dissipated so as to conserve Nr for the cushioning phase.
TeT - airframe attitude isn't airspeed in many aircraft - you don't need a moveable stabiliser, it just develops more downward force as the speed increases and tries to level the fuselage - otherwise you would end up hanging forward in your straps at 100 kts.
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I see this thread is meandering towards an accurate conclusion... I was about to make an inaccurate contribution myself but after a consultation with Wagtendonk's 1st Ed 1996, p103 i've 'remembered' that IAS for range does change with wind speed (see p103 for power-on examples on graph, p145 for power-off but it has no wind variations). Endurance doesn't, btw.
I think the main factor in wind is planning. Firstly, which sites are reachable from a given point and secondly a) flare w.r.t to reduced wind speed (sheer) near surface and b) flare w.r.t. IAS vs GS for landing.
If you've practised in different conditions and you're mentally making a note of conditions at the start of each flight you're more likely to make the right decision if the unfortunate event occurs which necessitates the 'making like a glider' routine.
I think the main factor in wind is planning. Firstly, which sites are reachable from a given point and secondly a) flare w.r.t to reduced wind speed (sheer) near surface and b) flare w.r.t. IAS vs GS for landing.
If you've practised in different conditions and you're mentally making a note of conditions at the start of each flight you're more likely to make the right decision if the unfortunate event occurs which necessitates the 'making like a glider' routine.
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do tell, the horizin sits at the same positon on the windscreen for many models?? very , verrry interesting.
I must fly one, one day
airframe attitude isn't airspeed in many aircraft
I must fly one, one day
TeT - not exactly the same but the range of attitude change with speed is markedly reduced by the horizontal stab.
You may have a helicopter that has less than a 2 or 3 degree pitch attitude range across a 120kt speed range. Try flying speeds in 10 kt increments accurately just using attitude.
If you fly a helo with a small horizontal stab (R22) for example you will see a bigger range of attitude with speed but grown-up helicopters tend to be a bit more refined.
The whole point of my comment was that disc attitude is a poor guide to best auto speed and whilst showing it to a student may help them understand why best auto speed is what it is, it doesn't help much when flying autos since the ASI is the more accurate guide.
You may have a helicopter that has less than a 2 or 3 degree pitch attitude range across a 120kt speed range. Try flying speeds in 10 kt increments accurately just using attitude.
If you fly a helo with a small horizontal stab (R22) for example you will see a bigger range of attitude with speed but grown-up helicopters tend to be a bit more refined.
The whole point of my comment was that disc attitude is a poor guide to best auto speed and whilst showing it to a student may help them understand why best auto speed is what it is, it doesn't help much when flying autos since the ASI is the more accurate guide.
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Who's going to look at the disk when the engine really fails? For that matter, who should be looking at the ASI when in the midst of a real engine failure trying to get to a safe spot to land??
the only 'instrument' in the aircraft that doesn't lie is the window- you should be looking outside!
the only 'instrument' in the aircraft that doesn't lie is the window- you should be looking outside!
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To that point, at 407 school at Bell back in January, Kevin Brandt covered my airspeed indicator for the entire session of emergencies. That reinforced where you need to be looking to make your spot in an auto .... and it isn't inside.
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The whole point of my comment was that disc attitude is a poor guide to best auto speed and whilst showing it to a student may help them understand why best auto speed is what it is, it doesn't help much when flying autos since the ASI is the more accurate guide.
The only time I refer in training to the disc is when doing confined area take offs.
attitude to me is only the airframe attitude to the horizon, and the slave's attitude to the bartender!
The only other time that I look at the disc is when I am checking that is still in track. Mind you that's a fairly regular thing with me.
looking at the disc when going into auto is a totally backward step, away from the "picture." time - waste- potential for trouble- etc.
