Backwards auto-rotation?
Thread Starter
Joined: Jul 2006
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From: Brisbane
Backwards auto-rotation?
I thought I'd get a few experienced suggestions about the use of a backwards auto-rotation in an aerodynamic sense.
With a normal auto you have to flare the helicopter to build up a pocket of air that you can ride the way down. I was surpised that while being shown a backwards auto that the flare was extended to the point where you were actually going backwards until the site picture you wanted came into view.
Is it me, or would this extended flare dissipate the pocket of air that should be kept under the rotors? Has anyone else had experience with this type of auto?
With a normal auto you have to flare the helicopter to build up a pocket of air that you can ride the way down. I was surpised that while being shown a backwards auto that the flare was extended to the point where you were actually going backwards until the site picture you wanted came into view.
Is it me, or would this extended flare dissipate the pocket of air that should be kept under the rotors? Has anyone else had experience with this type of auto?
Joined: Apr 2000
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From: EGDC
The only problem with a zero airspeed/negative groundspeed auto is that you need to have enough height to convert back to a normal auto before you carry out the EoL. When you do the recovery, note how long it takes the RoD to get back to normal after you have achieved your normal auto speed.
Riding a pocket of air...........hahahahahahahahahahahahah.......good one
Is that from 'My first Book of Helicopters'?
Riding a pocket of air...........hahahahahahahahahahahahah.......good one
Is that from 'My first Book of Helicopters'?
Joined: Aug 2004
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From: Earth
Any truth to a story I heard?
I was told that the British Military used to practise EOL's to the ground with zero forward airspeed in the Bell 47.
So if its true how was it done? Just cut the power at 1000, nose up to zero attitude and drop, then pull the collective up to your armpit at about 15 feet?
Like I said someone told me so it's worth checking it out on PPrune.
I was told that the British Military used to practise EOL's to the ground with zero forward airspeed in the Bell 47.
So if its true how was it done? Just cut the power at 1000, nose up to zero attitude and drop, then pull the collective up to your armpit at about 15 feet?
Like I said someone told me so it's worth checking it out on PPrune.
Joined: Sep 2002
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From: Great South East, tired and retired
Hey, Eagle 86, you probably remember the zero-speed autos in the Hueys done by 9Sqn? Or did the pussycats in 5 not do them? The famous Tedley and Spida taught them thus:
Pull the nose up to wash off all speed, then select hover attitude. You now have something less than 30 kt, but the needle wasn't all that accurate at low speed and vertical motion.
Aim point / impact point was between your toes in the chin bubble. Float down, continue through normal flare height. When your backside took a bite from the cushion, you did a mini-flare, took a big bite of the collective, levelled out, causing a big "WHOCK! wok. w..o..k.." and the machine seemed to leap forward to land at a walking pace. Took some judgment, but you could put it on a tennis court without having to finesse the flare from 60 kt or 99 kt if you were going for range.
And Tedley thought up the Broomstick Approach. Drill a hole beneath the collective, insert a broomstick under the lever, projecting below the skids. Make your auto flat at zero speed. No flare. Whatever your descent rate, when the broomstick hit the ground, it pushed the collective up at the appropriate rate.
Still an untested theory.
Pull the nose up to wash off all speed, then select hover attitude. You now have something less than 30 kt, but the needle wasn't all that accurate at low speed and vertical motion.
Aim point / impact point was between your toes in the chin bubble. Float down, continue through normal flare height. When your backside took a bite from the cushion, you did a mini-flare, took a big bite of the collective, levelled out, causing a big "WHOCK! wok. w..o..k.." and the machine seemed to leap forward to land at a walking pace. Took some judgment, but you could put it on a tennis court without having to finesse the flare from 60 kt or 99 kt if you were going for range.
And Tedley thought up the Broomstick Approach. Drill a hole beneath the collective, insert a broomstick under the lever, projecting below the skids. Make your auto flat at zero speed. No flare. Whatever your descent rate, when the broomstick hit the ground, it pushed the collective up at the appropriate rate.
Still an untested theory.
Combine Operations
Joined: May 2005
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From: U.K.
No, definitely not, Heliringer. Loads of engine-off landings, but with normal autorotation. I don't remember zero-speed landings as being part of the course. Low speed, yes. With a strong enough head-wind, of course, it shouldn't be all that difficult, especially in a Bell 47.
Joined: Mar 2005
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From: Europe
We did practice zero speed autos in the Bell 47, and they were very easy to do. I had to do one for real at night in an area covered by trees.
There was nothing magic about it, enter auto as normal and when near the ground, make a bigger flare than normal level the skids and land on. There was so much inertia in the blades it was almost like a landing from the hover.
There was nothing magic about it, enter auto as normal and when near the ground, make a bigger flare than normal level the skids and land on. There was so much inertia in the blades it was almost like a landing from the hover.
Joined: Aug 2000
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From: SW England
During a 2 FTS visit to Frosinone, I was shown a backwards-180 auto in a 47. Still finished with a nudge forwards to achieve +ve airspeed for the touchdown, though. It was difficult to see all that was going on for the smoke from the other pilot's Meerschaum (sp?), though.
Joined: Nov 2001
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From: Norfolk
This thread has been raised before. Whether or not it can be done depends on the ASI errors in autorotation on that particular type. Some types do actually underread in auto, leading to the notion that a safe EOL can be performed from aspparently very low airspeed. when in fact you are effectively doing a Constant Attitude technique. Unfortunately on a significant number of types (including the R22), the ASI badly overreads in auto and safe EOL,s need at least 40 kt for a constant attitude touchdown. To illustrate the trap; the Bell 47 G2's were quite benign at low IAS's whereas the G4 model with a different pitot/static set up were liable to skids round the ears if you attempted a constant attitude from 30 kt or less. Worse, the actual extent of the error depends on whether you come at the final speed from above it or below it.
The only safe advice is to limit autos to vertical relative to the ground and lower the nose to recover to normal auto by 600' AGL. this will work for all types. Yes you can go backwards over the ground in strong winds; the problem is that you will not know if you have inadvertently got backwards airspeed on. If so, the recovery to forwards auto can take a looooong time and the brown bits start to look very close.
The only safe advice is to limit autos to vertical relative to the ground and lower the nose to recover to normal auto by 600' AGL. this will work for all types. Yes you can go backwards over the ground in strong winds; the problem is that you will not know if you have inadvertently got backwards airspeed on. If so, the recovery to forwards auto can take a looooong time and the brown bits start to look very close.
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From: St Pierre et Miquelon
Bat-Off
Building up pockets of air
Here's what you said last September:
Maybe you need to order the above and go back to learn a few basic principles
Building up pockets of air
Here's what you said last September:
Maybe it requires some determination, and I admire the people who stick with it, but 60-100 hours taking that long to learn and grasp basic principles? Correct me if I'm wrong, but I think that is past the point when things come naturally.
Helo pilots have to be the ones that learn, think and act quickly for money and safety reasons.
Helo pilots have to be the ones that learn, think and act quickly for money and safety reasons.
Maybe you need to order the above and go back to learn a few basic principles
Joined: Jul 2005
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From: North
Yep we did. Used to enter from 3* feet and have a go at every technique for auto's on the way down. The best was to just cant the nose about 40 degreees from the wind, reduce fwd speed to whatever you felt like, and see how far you could let it blow you downwind before recovery. It's a technique I continued using and other types later on instead of attempting a 360/180.
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From: uk
Bat-Off may I suggest like the others that you put down the glass of Champagne and the little Budgie book and trot off to a competant flight instructor to learn some helicopterisms.
The Agusta A119 has an IAS in auto of 80 kts which following some rigorous testing turned out to be 65 kts actual airspeed, so what you see on the ASI is all that you have and have to use it. B47 autos were taught by the Army Air Corps at Middle Wallop as Flare Auto, Constant Attitude, Zero Speed and Hover Auto. The Constant Attitude was taught to be used at night as the landing light was fixed and as soon as the ground was seen in the landing light the collective was raised to cushion the landing giving a minimal run on.
The Agusta A119 has an IAS in auto of 80 kts which following some rigorous testing turned out to be 65 kts actual airspeed, so what you see on the ASI is all that you have and have to use it. B47 autos were taught by the Army Air Corps at Middle Wallop as Flare Auto, Constant Attitude, Zero Speed and Hover Auto. The Constant Attitude was taught to be used at night as the landing light was fixed and as soon as the ground was seen in the landing light the collective was raised to cushion the landing giving a minimal run on.
Thread Starter
Joined: Jul 2006
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From: Brisbane
God, some of you guys are pathetic! You’re all adults’ right? Correct me in a mature manner then! anjouan, did finding that info make your penis grow?!?
I was after the aerodynamic principles that are present when you will be repeatedly extend that flare at the start of an auto to build RRPM. To the point of being zero airspeed is there an excessive coning angle experienced?
I was after the aerodynamic principles that are present when you will be repeatedly extend that flare at the start of an auto to build RRPM. To the point of being zero airspeed is there an excessive coning angle experienced?
Joined: Sep 2002
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From: Great South East, tired and retired
Ermmm... Bat-Off, coning angle is a compromise between lift being generated and the RRPM. Low revs, blades cone up. High revs, blades flatten out.
If the revs are zooming off the clock from a flare, you sure as heck won't have a problem with coning angle. And in a zero-speed auto, you aren't extending the flare to gain revs, you are flaring to wash off speed and to stay over the top of a chosen spot.
If the revs are zooming off the clock from a flare, you sure as heck won't have a problem with coning angle. And in a zero-speed auto, you aren't extending the flare to gain revs, you are flaring to wash off speed and to stay over the top of a chosen spot.
Joined: Apr 2000
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From: EGDC
Batoff - try looking past page 2 in your book........
If you want proper information try asking proper questions. Yes we have had a laugh at your expense but we are still nice enough to answer your question if you phrase it in a way we understand.
I think you want to know what happens to the Nr when you keep the flare on during the entry to a zero speed autorotation. Flare effect increases the Nr but for a given nose up attitude is more effective at high speed than low. Practically speaking that means that if you select 15 degrees nose up at 90 kts as you enter auto, then initially the Nr will want to rise very quickly but as the speed decays you will have to keep moving the cyclic back to maintain 15 degrees nose up (overcoming flap forward) and the Nr will be less lively. You will only get excessive coning if you allow the Nr to rise, therefore containing it with a small amount of collective will prevent this (remember to lower it again once the risk of overspeeding the Nr is over, probably by the time the speed has reduced to below 40 kts or so.)
If you want proper information try asking proper questions. Yes we have had a laugh at your expense but we are still nice enough to answer your question if you phrase it in a way we understand.
I think you want to know what happens to the Nr when you keep the flare on during the entry to a zero speed autorotation. Flare effect increases the Nr but for a given nose up attitude is more effective at high speed than low. Practically speaking that means that if you select 15 degrees nose up at 90 kts as you enter auto, then initially the Nr will want to rise very quickly but as the speed decays you will have to keep moving the cyclic back to maintain 15 degrees nose up (overcoming flap forward) and the Nr will be less lively. You will only get excessive coning if you allow the Nr to rise, therefore containing it with a small amount of collective will prevent this (remember to lower it again once the risk of overspeeding the Nr is over, probably by the time the speed has reduced to below 40 kts or so.)
Joined: Feb 2004
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From: St Pierre et Miquelon
Bat-Off,
The only pathetic thing here is you with your almost-total knowledge of even the basics of helicopter principles of flight. I just hope you're not a helicopter pilot. Crab has been very kind, unlike me, but that's because I'm having a bad week and I'm fed up with stupid questions which aren't even asked in understandable English
The only pathetic thing here is you with your almost-total knowledge of even the basics of helicopter principles of flight. I just hope you're not a helicopter pilot. Crab has been very kind, unlike me, but that's because I'm having a bad week and I'm fed up with stupid questions which aren't even asked in understandable English
Joined: Apr 2003
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From: USA
Wow! You guys are rough on the guy!!
I have done backwards autos in the old H-13, Bell 47 and had a blast doing them. Takes a little work on the pedals, and you have to be intuitive about the airspeed, because there isn't any indication of same. But the autos work out just fine! I would never do them in a less forgiving helo (read that as any other helo) because the Bell 47 is a very very sweet machine in the auto.
I have done backwards autos in the old H-13, Bell 47 and had a blast doing them. Takes a little work on the pedals, and you have to be intuitive about the airspeed, because there isn't any indication of same. But the autos work out just fine! I would never do them in a less forgiving helo (read that as any other helo) because the Bell 47 is a very very sweet machine in the auto.
Joined: Aug 2001
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From: Cornwall
Pill-Box Pleasures
My chum Gazza used to demo putting the 47 (engine off) on to the roof of a 10x8 concrete pillbox on the edge of Fairoaks airfield. Junglies always were a bit funny in the head........... me, I could manage the target square but then us 'Pingers' were always a little more circumspect!!. Wasn't the G5A a wonderful toy!!
G
G
Joined: Jan 2004
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From: South Wales
Practiced this manoeuvre a few times when I was an instructor. An excellent way to demonstrate this movement of the air pocket effect is to enter the autorotation at the nominal speed, enabling the air pocket to develop below the aircraft. Begin pitching the nose up to bleed off the speed at a rate that allows the differential pressure to secure the air pocket below the A/C at a perpendicular angle. When zero speed is accomplished, the air pocket has now had time to anchor itself below the body as well as several “pockettes” being formed, at the latter stage, below the horizontal stabilisers. Due to the zero airspeed, the wind then blows these pocki’s to the rear of the foresaid surfaces allowing the aircraft to sit in what is essentially an inverted parachute effect. Company policy was then to engage the rotor brake allowing Nr to drop to around 10% to further emphasis this phenomenon as well as demonstrating aerodynamic forces play no role in this manoeuvre. On successful completion of the demonstration, Nr was then increased to 100% whilst maintaining zero airspeed at a ROD of approximately 4000 fpm. Introduction of pitch on the blades then induces the essential vortex ring, which is necessary for the displacement of the air pockets and enabling a safe and gentle set down.
Hope this clears that up!
Hope this clears that up!