Super Job of Flying after a mechanical failure
Thread Starter
Super Job of Flying after a mechanical failure
Rumour has it that a Bell 205A++ operated by Aerowest Helicopters on contract to the US Forest Service had a tail rotor pitch change link fail as the pilot was lifting away from a dip site while carrying a water bucket on fire fighting work.
The aircraft is supposed to have spun approximately eight full revolutions before the pilot could achieve enough airspeed to stream line the aircraft and fly to a safe landing area.
Upon reaching the safe landing area, the pilot performed an autorotation and set the aircraft down without any damage. (Beyond his nerves and laundry!)
If true...."Hand Salute!" Well done Sir.
The aircraft is supposed to have spun approximately eight full revolutions before the pilot could achieve enough airspeed to stream line the aircraft and fly to a safe landing area.
Upon reaching the safe landing area, the pilot performed an autorotation and set the aircraft down without any damage. (Beyond his nerves and laundry!)
If true...."Hand Salute!" Well done Sir.
Join Date: May 2000
Location: Darkest Wiltshire
Posts: 124
Likes: 0
Received 0 Likes
on
0 Posts
Hmmm. Not sure about this. If just one t/r pcl failed there would have been serious vibration as the 'uncontrolled' blade went to 'full left' (because that's what happens) and any pilot input to reduce or control the resulting yaw would increase the vibes to the point that the t/r lost interest and came off.
IMHO that is.
On the other hand, if it did happen, and said driver did get away with it... way to go!
Taff
IMHO that is.
On the other hand, if it did happen, and said driver did get away with it... way to go!
Taff
Join Date: Jan 2006
Location: uk
Posts: 29
Likes: 0
Received 0 Likes
on
0 Posts
isn't a tail rotor a symetrical aerofoil? -Why wouldn't the blade adopt a neutral pitch angle if pitch control was lost?
Hats off to the lad if he managed to get it on the floor safe though
Hats off to the lad if he managed to get it on the floor safe though
I agree with Toohey29 - i'd have thought that if you lost a TR pitch link the blade would want to go flat pitch (i guess it depends on the design) - which would be the same as almost full right pedal - so you'd have to match it with the other one (with pedals) to stop the vibration. Then with enough altitude you can roll off throttle to stop the spin, get some airspeed and either bring back some power to carry on or continue the auto.
If the blade had gone full left (i assume he meant full pitch meaning nose left)as the other guy said, the TR would still have been providing thrust and there woudn't have been much rotation.
If the blade had gone full left (i assume he meant full pitch meaning nose left)as the other guy said, the TR would still have been providing thrust and there woudn't have been much rotation.
Around 1983 one Dave Moran, ex-AAC, had the same malfunction just as he was positioning a 205A to pick up an underslung load at Saiq in Oman (6300 ft amsl, temp at that time of year around 20 degrees). I gather he rolled the throttle shut and landed right next to the USL on the other side from the Jebel VOR who was waiting to hook-up. Don't know how many rotations the aircraft made, but the aircraft landed level and was completely undamaged. Top bit of flying.
It gave me pause for thought, as only the day before I'd been flying the same aircraft for the artillery cadets at Izki. Usual stuff - load the aircraft up full, quick circuit to make sure they're all happy then off at low level (SOAF version) across the bundu to give them their moneysworth. If that same malfunction had occurred just a few flying-hours earlier, would anyone have bothered to look for the pitch-change link in the wreckage or would it have just gone down as yet another low-flying-pilot-cocks-it-up-bigtime? It didn't stop me from operating at low altitude, but I spent a great deal more attention going through the "what-ifs" when doing so...
It gave me pause for thought, as only the day before I'd been flying the same aircraft for the artillery cadets at Izki. Usual stuff - load the aircraft up full, quick circuit to make sure they're all happy then off at low level (SOAF version) across the bundu to give them their moneysworth. If that same malfunction had occurred just a few flying-hours earlier, would anyone have bothered to look for the pitch-change link in the wreckage or would it have just gone down as yet another low-flying-pilot-cocks-it-up-bigtime? It didn't stop me from operating at low altitude, but I spent a great deal more attention going through the "what-ifs" when doing so...
You would think that a rotating aerofoil like a tail rotor blade would streamline when left to its own devices, but there are other factors at play, eg:
- centrifugal twisting moment (CTM) vs. aerodynamic twisting moment (ATM) - see a fixed wing aerodynamics book for this
- position of hinge point with respect to centre of pressure
- other rotating bits attached to it, eg 'chinese weights' on the AS350
- weight distribution on the blade and grip - construction, various nuts, bolts, screws, laminations etc.
- centrifugal twisting moment (CTM) vs. aerodynamic twisting moment (ATM) - see a fixed wing aerodynamics book for this
- position of hinge point with respect to centre of pressure
- other rotating bits attached to it, eg 'chinese weights' on the AS350
- weight distribution on the blade and grip - construction, various nuts, bolts, screws, laminations etc.
Join Date: Jan 2006
Location: uk
Posts: 29
Likes: 0
Received 0 Likes
on
0 Posts
CTM would cause the blade to fly to a neutral position as the couple of the moments about the feathering axis will twist the blade towards a reduced or finer blade pitch setting, hence the need for balance weights in some main rotor designs to aid the pilot and counter CTM.
With regard to the hinge / centre of pressure normally the hinge will line up with or be in front of the centre of pressure to minimise torsional loads (the only picture i could find shows this to be the case on the 205).
What we really need is a person who's flown / broken / taken one apart to know the real answer......Sasless have you done any of the afore mentioned?
With regard to the hinge / centre of pressure normally the hinge will line up with or be in front of the centre of pressure to minimise torsional loads (the only picture i could find shows this to be the case on the 205).
What we really need is a person who's flown / broken / taken one apart to know the real answer......Sasless have you done any of the afore mentioned?
Join Date: May 2000
Location: Darkest Wiltshire
Posts: 124
Likes: 0
Received 0 Likes
on
0 Posts
Theoretically at least, you would think that CTM would cause the t/r to 'fine out' or go to a neutral pitch setting and on some aircraft this may be the case. My experience of later model 205's and the 212 in this situation is that if t/r control is lost, the blades will go to maximum pitch (or the full left pedal position on the 205/212).
In this case, where control is lost on one blade, the loss of t/r track (with one blade at max pitch and the other where-ever the pilot puts it) would result in significant levels of vibration and in a very short space of time, the loss of the t/r assy or possibly the t/r g/box. Not good either way.
The only way for the pilot to reduce the vibration would be to apply full left pedal and an armful of collective to fly away. He'd have to be a very brave chap to do this and the initial reaction I think would have been to close the throttle and dump it as described by T&B. If he did go down the flyaway route he could then attempt a run-on landing by gradually rolling off the throttle. Bristow in Duri, Indonesia used to practice this after a series of t/r control chain lock-ups on the 205's before they were modified to push/pull rods.
Taff
In this case, where control is lost on one blade, the loss of t/r track (with one blade at max pitch and the other where-ever the pilot puts it) would result in significant levels of vibration and in a very short space of time, the loss of the t/r assy or possibly the t/r g/box. Not good either way.
The only way for the pilot to reduce the vibration would be to apply full left pedal and an armful of collective to fly away. He'd have to be a very brave chap to do this and the initial reaction I think would have been to close the throttle and dump it as described by T&B. If he did go down the flyaway route he could then attempt a run-on landing by gradually rolling off the throttle. Bristow in Duri, Indonesia used to practice this after a series of t/r control chain lock-ups on the 205's before they were modified to push/pull rods.
Taff
Join Date: Sep 2003
Location: Region 5 / Region 4 / and sometimes Region 8?
Posts: 83
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Taff Missed
<snip>
The only way for the pilot to reduce the vibration would be to apply full left pedal and an armful of collective to fly away. He'd have to be a very brave chap to do this and the initial reaction I think would have been to close the throttle and dump it as described by T&B. If he did go down the flyaway route he could then attempt a run-on landing by gradually rolling off the throttle.
<snip>
The only way for the pilot to reduce the vibration would be to apply full left pedal and an armful of collective to fly away. He'd have to be a very brave chap to do this and the initial reaction I think would have been to close the throttle and dump it as described by T&B. If he did go down the flyaway route he could then attempt a run-on landing by gradually rolling off the throttle.
<snip>
While doing bucket work on the Navajo Mountain fire, about half way through the fuel cycle the ship had a tail rotor pitch change link failure. As the pilot was coming into the dip site and the bucket just got into the water the pilot felt a quick buzz in the pedals and the helicopter started to rotate to the right. The pilot released the water, added full left pedal, and got forward flight. The helicopter spun several times, the pilot released the line and bucket and still spun a few more times before regaining forward flight. After getting forward flight the pilot picked a safe landing site next to the lake and did a run on landing. The helicopter slid approx. 15 feet in soft sand before it came to rest without further damage. The manager and mechanic flew out and made all the arrangements with maintenance folks.
Thread Starter
I always included a similar maneuver on all single rotor helicopter conversion (transition) courses I taught. It was not taught as a pitch link failure per se, but rather as a yaw control failure similar to a boot full of either right or left pedal just prior to/just after leaving a hover.
The teaching point was more about effect of throttle and/or collective than "simulating" recovery from a particular kind of failure. It worked to get a pilot to think about what was going on rather than merely reacting out of some deeply instilled robotic response. It also worked to relieve the fear of tail rotor failures as the pilot had some experience practicing torque control without using pedals.
My experience of being in either high hovers OGE or being over very hostile terrain where immediate landings were not always the choice thus necessitating dealing with a spinning aircraft became more probable than being in a position to simply land is what got me to doing these exercises.
Congratulations to the pilot....he shows what one can do when you really "know" your aircraft and how it responds to control movements. I sure hope his boss bought him a very big steak dinner and several pints for that!
The teaching point was more about effect of throttle and/or collective than "simulating" recovery from a particular kind of failure. It worked to get a pilot to think about what was going on rather than merely reacting out of some deeply instilled robotic response. It also worked to relieve the fear of tail rotor failures as the pilot had some experience practicing torque control without using pedals.
My experience of being in either high hovers OGE or being over very hostile terrain where immediate landings were not always the choice thus necessitating dealing with a spinning aircraft became more probable than being in a position to simply land is what got me to doing these exercises.
Congratulations to the pilot....he shows what one can do when you really "know" your aircraft and how it responds to control movements. I sure hope his boss bought him a very big steak dinner and several pints for that!
