Autorotation
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Autorotation
I've got some questions about autorotations. Is it true a helicopter can keep his RRPM in the green with 0 speed? It sounds logical to me, but I can't find any reference on it. Secondly I saw a movie of a (low speed) no flare autorotation in a Jet Ranger (http://www.youtube.com/watch?v=CJGvm...related&search=). Is this a know manoeuvre? What are your thoughts on it?
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Yes. You can autorotate at any airspeed. It looks to me like there is plenty of speed there - it just looks slow because of the steep descent angle. A zero airspeed auto to the ground would be over a lot quicker, and you'd need perfect timing to not get hurt.
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not a helo pilot but plan to be one and own a bell-222 once earn enough with airlines 
as i understand it, to keep the rotors turning, you need forward velocity....you can keep the rpm in the green, but then you`ll be falling like a rock
as i understand it, to keep the rotors turning, you need forward velocity....you can keep the rpm in the green, but then you`ll be falling like a rock
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Zero air speed or zero ground speed autos are no problem if you practise, just like any other tricky manoevre. Basically if you start at a steady 40 kts into a 20 kt wind & run on at 20 kts, you would be surprised how easy it is to gradually reduce your airspeed to achieve zero ground speed. You also should start with a light machine & slowly build up weight. Of all the dozens of pilots I've trained to do this, not one has had a problem, in fact they had more problems judging when to flare & level off.
For a Constant Attitude EOL - ie there is no flare - we used to teach that you wait until the green turns into grass (between 20 and 30' agl) and make a short, sharp check up with the lever to begin to reduce the RoD, then cushion the touchdown using the rest of the Nr. It is technique that works well in a reasonably high inertia rotor system but not something I would like to try in a robbie.
I did fly with a colleague (RN) at Shawbury who delighted in checking your bottle by leaving all the lever movement until about 6 inches from the ground and then pulling to 16 degrees of pitch in about half a second. The aircraft just shuddered a bit and plopped onto the ground quite gently but it wasn't a technique you could afford to get wrong
JFR where are you?
Denlopviper - make sure you pay attention in groundschool - it is the rate or air movement through the rotors that produces the autorotative force to keep the blades turning - you can autorotate and any speed from zero to Vmax and the only thing that will change is the RoD. Most helicopters have an optimum auto speed between 50 and 70 knots where RoD will be least - above and below that speed the RoD will be higher.
I did fly with a colleague (RN) at Shawbury who delighted in checking your bottle by leaving all the lever movement until about 6 inches from the ground and then pulling to 16 degrees of pitch in about half a second. The aircraft just shuddered a bit and plopped onto the ground quite gently but it wasn't a technique you could afford to get wrong
JFR where are you?Denlopviper - make sure you pay attention in groundschool - it is the rate or air movement through the rotors that produces the autorotative force to keep the blades turning - you can autorotate and any speed from zero to Vmax and the only thing that will change is the RoD. Most helicopters have an optimum auto speed between 50 and 70 knots where RoD will be least - above and below that speed the RoD will be higher.
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Constant Attitude Autos
We teach 40knots autos inthe R44 which are an absolute delight !!! if you get it spot on you can touch down almost without feeling it, with a little bit of flare at about 20ish feet to reduce spead you can almost bring it to a hover
I've also used a 40 knot auto in a 206 on low skids worked a treat
I've also used a 40 knot auto in a 206 on low skids worked a treat
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Whenever I went up in R22, R44 or 206 I nearly always during the flight did a practice Auto and power recovery, I only actually went onto the ground whilst in my training time or if I had a much more experienced second pilot with me( dont ask me why) but I found that wind strength/speed was the governing input to ground speed , forward speed meant very little once I had picked the spot for my final theoretical act, A pilot called Geoff Day showed me well how to make S turns whilst under auto's situation and this helped a lot in being able to pick out and stay with a good landing spot without allowing the wind to compromise the final act of landing without power
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The zero airspeed autorotation is, as mentioned earlier, quite possible, and a very useful tool for getting rid of unwanted height if you're trying to get to a specific spot.
One of the myths about this is that it generates a very high rate of descent - I've seen mention of over 4,000fpm - this would be enough to make most people not want to get close to zero airspeed.
My experience in the Bell 206 series is that if a 60 KIAS auto produces 1500 - 1600 fpm, the zero airspeed auto will produce in the vicinity of 1800-2000fpm rate of descent.
And using Microsoft Flight Sim for 'training' will give completely the wrong impression - when you go to zero airspeed, the rotor stops - not the same as real life at all!
One of the myths about this is that it generates a very high rate of descent - I've seen mention of over 4,000fpm - this would be enough to make most people not want to get close to zero airspeed.
My experience in the Bell 206 series is that if a 60 KIAS auto produces 1500 - 1600 fpm, the zero airspeed auto will produce in the vicinity of 1800-2000fpm rate of descent.
And using Microsoft Flight Sim for 'training' will give completely the wrong impression - when you go to zero airspeed, the rotor stops - not the same as real life at all!
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Autos
It was Geoff Day that taught me the constant attitude auto in the R44, at 40 knots. The first time when Geoff was doing the demo I suffered a little bit from ground rush but once used to it, it was a doddle.
Every morning Geoff would arrive at Sandtoft with a constant attitude auto to the helo parking area.
Every morning Geoff would arrive at Sandtoft with a constant attitude auto to the helo parking area.
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Originally Posted by Shawn Coyle
My experience in the Bell 206 series is that if a 60 KIAS auto produces 1500 - 1600 fpm, the zero airspeed auto will produce in the vicinity of 1800-2000fpm rate of descent.
Last edited by Graviman; 9th Dec 2007 at 09:51. Reason: Misused the word "flare" when meant "raise collective for landing". Thanks lelebebbel..
no flare - why would you flare at zero airspeed. you just raise at the right moment like in a hover auto.
It works in a R44*, so I would believe it could work in a 206, too.
*i've had this demonstrated to me at the RHC factory. R44 from a 1000agl hover to 0 with no forward airspeed. according to the instructor, you only get away with it if the ship is light. Don't try this at home..
It works in a R44*, so I would believe it could work in a 206, too.
*i've had this demonstrated to me at the RHC factory. R44 from a 1000agl hover to 0 with no forward airspeed. according to the instructor, you only get away with it if the ship is light. Don't try this at home..
No, Crab is correct. You may be referring to transient effects during cyclic input, perhaps?
The words 'Factors A, B & C in autorotation' popped unbidden into my head on reading the last few posts - at least a few things must have stuck over the years.
Haven't thought to look back over that stuff for a good while, but looking back at the aerody books shows a few factors in play when increasing forward speed from zero in autorotation and comparing rates of descent.
As my aerody manual would have you believe, factors A and B relate to disc tilt and act to increase rate of descent as speed is increased, whereas factor C is about the disc flying into undisturbed air and acts to decrease rate of descent.
As published in flight manuals, and as we know from experience, there are best (lowest ROD) speeds for autorotation, so what Crab says sounds right to me.
Haven't thought to look back over that stuff for a good while, but looking back at the aerody books shows a few factors in play when increasing forward speed from zero in autorotation and comparing rates of descent.
As my aerody manual would have you believe, factors A and B relate to disc tilt and act to increase rate of descent as speed is increased, whereas factor C is about the disc flying into undisturbed air and acts to decrease rate of descent.
As published in flight manuals, and as we know from experience, there are best (lowest ROD) speeds for autorotation, so what Crab says sounds right to me.
I almost mentioned A,B and C in my first post but decided not to complicate the explanation for denlopviper.
A.agincourt - I am afraid it is you who are not quite right old boy - Factor A is the disc tilt which does reduce the inflow angle - so does factor B which is the increase in the horizontal airflow BUT!!!! Factor C saves the day as the air is effectively moving faster up into the disc compared to the air that was being slowed by the disc. Factor C is essentially an increase in RoD flow which increases the inflow angle again. Therefore no loss of autorotative force and no reduction in Nr.
Graviman - flare effect is gained by changing the angle of the induced flow into the disc, reducing its magnitude and thereby generating an increase in AoA and rotor thrust. At zero speed in auto, all the RoD flow is coming straight up at the rotor and any cyclic change will reduce the RoD flow and reduce rotor thrust, thereby increasing the RoD itself - not what you want to do for an EOL. Read fewer textbooks and go flying more
A.agincourt - I am afraid it is you who are not quite right old boy - Factor A is the disc tilt which does reduce the inflow angle - so does factor B which is the increase in the horizontal airflow BUT!!!! Factor C saves the day as the air is effectively moving faster up into the disc compared to the air that was being slowed by the disc. Factor C is essentially an increase in RoD flow which increases the inflow angle again. Therefore no loss of autorotative force and no reduction in Nr.
Graviman - flare effect is gained by changing the angle of the induced flow into the disc, reducing its magnitude and thereby generating an increase in AoA and rotor thrust. At zero speed in auto, all the RoD flow is coming straight up at the rotor and any cyclic change will reduce the RoD flow and reduce rotor thrust, thereby increasing the RoD itself - not what you want to do for an EOL. Read fewer textbooks and go flying more
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Hi Mr Agincourt
In part your right;
1) As you push the cyclic forward, you reduce the angle at which the air flows into the rotor disc, this will reduce RRPM.
2) However as forward airspeed increase's the air will flow into the rotor disc quicker, this will increase RRPM.
A cyclic flare will produce the opposite effects.
In part your right;
1) As you push the cyclic forward, you reduce the angle at which the air flows into the rotor disc, this will reduce RRPM.
2) However as forward airspeed increase's the air will flow into the rotor disc quicker, this will increase RRPM.
A cyclic flare will produce the opposite effects.
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Heliski,
Could have been the same Geoff Day, I meet him about 1998ish at EGNH and he did a few of my yearly checks, plus showed me quite a few very safe but easy moves for getting down quick QUICK.
Regards
Peter R-B
Vfrpilotpb
Could have been the same Geoff Day, I meet him about 1998ish at EGNH and he did a few of my yearly checks, plus showed me quite a few very safe but easy moves for getting down quick QUICK.
Regards
Peter R-B
Vfrpilotpb
A.agincourt - the transient effect of moving the cyclic which can temporarily reduce Nr is because you are unloading the disc causing a reduction in 'G'.
Application of positive G increases Nr, application of negative (eg less than 1)G reduces Nr but only temporarily.
Yes it is easily demonstrated but it only lasts while you have the reduction in G. This has absolutely nothing to do with the migration of the driving section of the blade which happens when you raise or lower the lever.
According to your theory, if you start at 60 kts in auto and then increase to range speed (say 90 kts) in auto you will see a permanent decrease in NR which just ain't the case.
Application of positive G increases Nr, application of negative (eg less than 1)G reduces Nr but only temporarily.
Yes it is easily demonstrated but it only lasts while you have the reduction in G. This has absolutely nothing to do with the migration of the driving section of the blade which happens when you raise or lower the lever.
According to your theory, if you start at 60 kts in auto and then increase to range speed (say 90 kts) in auto you will see a permanent decrease in NR which just ain't the case.
A.agincourt - I presume that last page of bo**ocks is an attempt to mask your misunderstanding of this question. You can try and wind me up as much as you like but you may confuse guys who actually want to understand P of F.