TR malfunctions for beginners - a refresher lesson!
Several decades ago in Borneo,I had a tail-rotor blade depart,followed by the other one and the t/r gearbox.The day had started with a troop lift to various LZs,and whilst landing to refuel,someone pointed out `something` under the aircraft,Ilifted off and moved away,revealing a large pool of oil on the ground,so parked,shutdown and inspected it.It was a broken transfer oil connection between the engine and reduction g/box. Short story ,called `home` ,who sent a standby aircraft and groundcrew ,who whipped out the engine/gbox and replaced the bit,whilst the other crew finished my task.A/C ground -run,so we set off as a pair to RTB,,with a couple of the mechs downstairs with an access panel removed to check if it was all OK at the back of the g/box.As we climbed,I checked down in the cabin to get a `thumbs-up `(no intercom) from the lads,when there was an almighty `Bang`,the aircraft yawed hard right,and pitched nose down.Pedalling produced no response,and the stick was on the back stop,to prevent it pitching further.I thought I had collided with the other aircraft,as I couldn`t see it,and had gone into autorotation instinctively about 800ft, looked for a place to land,as I had no idea of further damage,thinking I had collided,and put out a couple of `Maydays`,just in hope..As we were over a mix of primary and secondary jungle,I saw what appeared to be a small clearing,and continued a right spiral towards it,closed the HP cock,and flared as much as I could,finding that the area was actually a `small` hillock,or pimple,and then EOL`d at zero speed,but finding we were on about 10-15 deg slope.The mechs were OK,strapped in,and the only other damage was a burst tyre from a tree stump ,that was stopping the a/c from rolling off...Shortly after,the other aircraft appeared,and winched us out.The Board of Inquiry offered the local Headman,and villagers money for any bits they could find,and the blades and g/box were recovered a week later.It was found to be a fatigue crack in the threads of the blade spindle that had caused it,but it had taken some time to propagate.
Throughout the incident,I had poor roll control,probably due to a lowish speed 50-60 kts,and limited cyclic f/aft,but that may have improved as the mechs `down below` went aft to strap in.I don`t recall any yaw on touchdown,probably because the undercarriage was caught in the secondary ground foliage.
The aircraft was lifted out,and repaired at base,and the following day one of the other pilots gave me a USAF Flight Safety magazine, with an article about `How to handle t/rotor failures in the H-34!
There`s a pic or three on P15 of `Rotorheads around..Cockpit views`,#294...
Throughout the incident,I had poor roll control,probably due to a lowish speed 50-60 kts,and limited cyclic f/aft,but that may have improved as the mechs `down below` went aft to strap in.I don`t recall any yaw on touchdown,probably because the undercarriage was caught in the secondary ground foliage.
The aircraft was lifted out,and repaired at base,and the following day one of the other pilots gave me a USAF Flight Safety magazine, with an article about `How to handle t/rotor failures in the H-34!
There`s a pic or three on P15 of `Rotorheads around..Cockpit views`,#294...
Thread Starter
Jelly: I thin k it's horses for courses. The Gazelle TR take off is simply another cog running from the planetary gear in the MGB simples.
In this type of a/c, when the engine stops for any reason including hi speed shaft failure - you enter auto and the MGB drives the TR. Simples.
In the 206/350, during auto the MGB drives a reduction GB which in turn drives the TR.. which in itself is 'awkward' and unnecessary BUT THEN you have to have the engine running AS WELL to drive the FPT to drive the reduction GB to drive the TR....in case you experience a hi spd shaft failure?????
Where in the design team @ Aerospatiale did they have a shift of ideas about single engine drive train layout...just out of curiosity. For better or worse
In this type of a/c, when the engine stops for any reason including hi speed shaft failure - you enter auto and the MGB drives the TR. Simples.
In the 206/350, during auto the MGB drives a reduction GB which in turn drives the TR.. which in itself is 'awkward' and unnecessary BUT THEN you have to have the engine running AS WELL to drive the FPT to drive the reduction GB to drive the TR....in case you experience a hi spd shaft failure?????
Where in the design team @ Aerospatiale did they have a shift of ideas about single engine drive train layout...just out of curiosity. For better or worse
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If the MGB input driveshaft/high speed shaft fails, it can not drive the tail as the only shaft between it and the engine has failed and thus no relation between MGB and tail speeds. MGB no longer driven and tail will go with the free turbine due its connection.
Thread Starter
That's just what I said VP
That's the problem I see with 350/206 drive train layout: you need to keep your engine running to drive the TR during a hi spd shaft failure. In all other singles you don't.
That's the problem I see with 350/206 drive train layout: you need to keep your engine running to drive the TR during a hi spd shaft failure. In all other singles you don't.
Now as I see it....in the situation you are describing.....if you shut the engine down....you don't really need the tail rotor as you are going to be in autorotation. Granted it would be nice to have the tail rotor working....but in an autorotative landing...it isn't absolutely necessary as in a power on landing.
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Exactly! If the MGB is powerd the airframe wants to go opposite direction to the MR direction. If MGB is not powered the frame wants to go with the MR. There lies the trick with the 350 as the TR is countering a non existingnforce if the MGB is not powered and pushing the tail where it wants to go with the MR if say the MGB input shaft failed. Only way to stop is to take eng to grnd or shutdown as no use to MR?
Thread Starter
SAS and VP.
TRE makes sense if during auto/eol you want to turn, say 180 degrees into wind. Without TRE you have to rely on side slip to get it round the corner and we all know that takes time and height. With TRE at hand you simply apply pedal during the turn to hasten the change in direction. You may want to dodge obstacles during auto, how do you do that comfortably during auto with no TR? It could be achieved but at the expense of a marked increase in height loss.
At the bottom of an auto/eol when you flare, the Nr goes up...so what would happen to the nose of the a/c if you didnt have a TR? It would put you in a yaw offset situation which would probably make it harder to cross control to land.
All in all it still strikes me as odd that designs like this exist when the other far simpler designs don't rely on the engine having to be kept running if the hi spd shaft fails.
PS: The designers obviously beleive there is a need to drive the TR when a hi spd shaft fails because they advise you to keep the engine running during this malfunction. So presumably my argument that you always need a TR running to assist flight is true?
[Yes - I know a/c survive without TR's, we've seen examples recently. But from a design perspective, AS350's and some others have designed in the need to keep your FPT running during a hi spd shaft failure????
C'mon u 2 ...you can do better
TRE makes sense if during auto/eol you want to turn, say 180 degrees into wind. Without TRE you have to rely on side slip to get it round the corner and we all know that takes time and height. With TRE at hand you simply apply pedal during the turn to hasten the change in direction. You may want to dodge obstacles during auto, how do you do that comfortably during auto with no TR? It could be achieved but at the expense of a marked increase in height loss.
At the bottom of an auto/eol when you flare, the Nr goes up...so what would happen to the nose of the a/c if you didnt have a TR? It would put you in a yaw offset situation which would probably make it harder to cross control to land.
All in all it still strikes me as odd that designs like this exist when the other far simpler designs don't rely on the engine having to be kept running if the hi spd shaft fails.
PS: The designers obviously beleive there is a need to drive the TR when a hi spd shaft fails because they advise you to keep the engine running during this malfunction. So presumably my argument that you always need a TR running to assist flight is true?
[Yes - I know a/c survive without TR's, we've seen examples recently. But from a design perspective, AS350's and some others have designed in the need to keep your FPT running during a hi spd shaft failure????
C'mon u 2 ...you can do better
TC,
You are mixing up the argument. The question was about what happens if the engine is not driving the Tail Rotor following the other failure.
My response was to say that if the engine was no longer running....then there would be no Torque to counter act as it would be with the engine running.
Yes, maneuvering without a tail rotor is awkward and yes....at the bottom when you decelerate the nose of the aircraft is going to want to move to one side but that can be minimized by applying a bit of Collective.
Yes....if the engine is running....leave it running on the 350 and 206....but that was not the question as I recall.
Tail Rotor failures are not the bugger bear some folks make them out to be.....but that is due to way too many folks having no real certain grasp of how their aircraft responds in unusual circumstances like tail rotor failures.
The tendency these days is to discuss over a cup of Tea and not get out and do the drills that used to be normal fare. Our growing tendency to be "Risk Adverse" is not necessarily a good thing in all regards.
I remember being told of a conversation by the owner of a company I worked for as a TRE/IRE.....which stemmed from his seeing one of his BO-105's spinning around a fair old rate....as it passed by the office window that overlooked our practice area. As he spilled his Tea thinking something was seriously amiss.....he make a query to the Chief Pilot along the lines of "What the Hell is going on!" or other mild words to that effect. The CP never looked up and said....."Sasless is discussing Torque Control with Hose Nose." (Hose Nose was the Pilot's Nickname.).
I did have the benefit of US Army training back during a period of time where we got lots of practice in Tail Rotor failures and EOL's....as upon graduation from Flight School we were almost assured to need those skills in our first operational assignment. I lucked out and wound up in Chinooks where we did not even discuss Tail Rotor failures for simple reasons.
On all of my check rides under the UK system.....not once did we do a Tail Rotor failure drill....and when asked if there was anything I would like to do at the end of a check.....not one TRE ever took me up on a request to do some Tail Rotor Drills.
That kind of situation does not lend itself to building any Monkey Skills that would be very useful in coping with a real Tail Rotor Failure.
You are mixing up the argument. The question was about what happens if the engine is not driving the Tail Rotor following the other failure.
My response was to say that if the engine was no longer running....then there would be no Torque to counter act as it would be with the engine running.
Yes, maneuvering without a tail rotor is awkward and yes....at the bottom when you decelerate the nose of the aircraft is going to want to move to one side but that can be minimized by applying a bit of Collective.
Yes....if the engine is running....leave it running on the 350 and 206....but that was not the question as I recall.
Tail Rotor failures are not the bugger bear some folks make them out to be.....but that is due to way too many folks having no real certain grasp of how their aircraft responds in unusual circumstances like tail rotor failures.
The tendency these days is to discuss over a cup of Tea and not get out and do the drills that used to be normal fare. Our growing tendency to be "Risk Adverse" is not necessarily a good thing in all regards.
I remember being told of a conversation by the owner of a company I worked for as a TRE/IRE.....which stemmed from his seeing one of his BO-105's spinning around a fair old rate....as it passed by the office window that overlooked our practice area. As he spilled his Tea thinking something was seriously amiss.....he make a query to the Chief Pilot along the lines of "What the Hell is going on!" or other mild words to that effect. The CP never looked up and said....."Sasless is discussing Torque Control with Hose Nose." (Hose Nose was the Pilot's Nickname.).
I did have the benefit of US Army training back during a period of time where we got lots of practice in Tail Rotor failures and EOL's....as upon graduation from Flight School we were almost assured to need those skills in our first operational assignment. I lucked out and wound up in Chinooks where we did not even discuss Tail Rotor failures for simple reasons.
On all of my check rides under the UK system.....not once did we do a Tail Rotor failure drill....and when asked if there was anything I would like to do at the end of a check.....not one TRE ever took me up on a request to do some Tail Rotor Drills.
That kind of situation does not lend itself to building any Monkey Skills that would be very useful in coping with a real Tail Rotor Failure.
Thread Starter
Concur wholeheartedly SASless. Hence the reason for my opening post, to stimulate activity in the ab initio world.
But without training and practice, it will continue to haunt pilots as a sinister malfunction.
But without training and practice, it will continue to haunt pilots as a sinister malfunction.
When teaching in the Huey....one exercise I liked to do was to put the Governor in Manual....and have the Pilot fly a full circuit using the Throttle to control the Nr....then on the second circuit apply a bit of Left Pedal and have the Pilot remove feet from pedals and use the throttle to control yaw as we flew the full length of the runway at a slow airspeed and about 2-3 feet off the runway. Usually, by the time we got to the end....the Monkey Skill was in place. On the next circuit....quite a bit of left pedal was applied and we did the same drill but slowed the aircraft to the slowest speed the nose would stay centered.....until we determined the slowest speed we could use even if it was a steady hover. The final trip round the pattern was to set up for the same scenario....but this time I asked the Pilot to let the nose go all the way across.....accelerate till the nose swung back over....and repeated that drill as many times as possible before reaching the end of the runway.
That demonstrated to the Pilot the kind of control you might have in a real failure.
Demonstrations are not the real thing.....just as Simulators are good but not the real thing. What you are teaching is the Concepts so the Pilot is better equipped to deal with a real situation.
That demonstrated to the Pilot the kind of control you might have in a real failure.
Demonstrations are not the real thing.....just as Simulators are good but not the real thing. What you are teaching is the Concepts so the Pilot is better equipped to deal with a real situation.
RVDT, thanks for posting the engine schematic. I note that it has a "Muff Coupling" which sounds a lot better to me than a Thomas Coupling.
Sorry TC - it is what it is!
Sorry TC - it is what it is!
Thread Starter
Have another go Krypton. See if you can contain yourself and say something constructive to help all the ab initio's out there who clicked on this thread to only to read your musings. Well done. 
Sasless - in your EOL with no TR, what happens as you decay the Nr to cushion the landing?
I think Mr Newton would argue that the action of slowing down the rotor will cause a reaction by rotating the fuselage in the opposite direction.
I don't recall many EOLS (and I have done a few) where I didn't need the TR to keep straight during the landing.
I think Mr Newton would argue that the action of slowing down the rotor will cause a reaction by rotating the fuselage in the opposite direction.
I don't recall many EOLS (and I have done a few) where I didn't need the TR to keep straight during the landing.
Crab,
As you rightly state....there will be a yawing movement but that can be minimized somewhat by application of Collective ( a quick pulse), then as the aircraft touches down any other yawing will have to be followed by cyclic as the aircraft comes to a stop.
The point is even with no Tail Rotor Control by use of the Tail Rotor Pedals.....one does retain some control by application of Collective (if no engine power) and use of Collective and/or Throttle if the engine is running.
If you do not have a usable Tail Rotor....you will have to live with the fact the nose may not remain pointed in the direction of travel. The key is to have as slow a ground speed as possible....and follow what yaw you have with cyclic to keep the aircraft upright.
As you rightly state....there will be a yawing movement but that can be minimized somewhat by application of Collective ( a quick pulse), then as the aircraft touches down any other yawing will have to be followed by cyclic as the aircraft comes to a stop.
The point is even with no Tail Rotor Control by use of the Tail Rotor Pedals.....one does retain some control by application of Collective (if no engine power) and use of Collective and/or Throttle if the engine is running.
If you do not have a usable Tail Rotor....you will have to live with the fact the nose may not remain pointed in the direction of travel. The key is to have as slow a ground speed as possible....and follow what yaw you have with cyclic to keep the aircraft upright.
And therein lies the problem of a 'one size fits all' piece of advice.
In a light helicopter, achieving a zero speed touchdown for an EOL, whilst not being simple, is a reasonable expectation, especially if there is a bit of wind to help you.
In a larger helo, this becomes progressively more difficult and a run on (at some speed) is inevitable - usually because the amount of nose up required to wash off all the speed will, in all probability, smack the tail into the ground and rather aggravate the situation, or leave you quite high with decaying Nr. Whilst this (putting the tail in) might be a desirable technique when conducting the EOL to water (or perhaps into the tops of trees), in normal circumstances it is more likely to prejudice the outcome of the EOL than assist it.
This is where lots of lateral cyclic and friction from the skids or differential braking on the wheels will probably help.
In a light helicopter, achieving a zero speed touchdown for an EOL, whilst not being simple, is a reasonable expectation, especially if there is a bit of wind to help you.
In a larger helo, this becomes progressively more difficult and a run on (at some speed) is inevitable - usually because the amount of nose up required to wash off all the speed will, in all probability, smack the tail into the ground and rather aggravate the situation, or leave you quite high with decaying Nr. Whilst this (putting the tail in) might be a desirable technique when conducting the EOL to water (or perhaps into the tops of trees), in normal circumstances it is more likely to prejudice the outcome of the EOL than assist it.
This is where lots of lateral cyclic and friction from the skids or differential braking on the wheels will probably help.
In a larger helo, this becomes progressively more difficult and a run on (at some speed) is inevitable - usually because the amount of nose up required to wash off all the speed will, in all probability, smack the tail into the ground and rather aggravate the situation, or leave you quite high with decaying Nr.
Do you consider a Chinook to be a "larger" Helo?
Why is a Run On landing inevitable?
By "inevitable"...you mean to say every single time no matter the conditions?
Do you consider a Chinook to be a "larger" Helo?
Why is a Run On landing inevitable?
By "inevitable"...you mean to say every single time no matter the conditions?
When did a Chinook grow a tail rotor??????? Keep with the program Sas - this is a TR thread.
no, you might be operating with a very strong wind, you might be the best pilot in the world or you might just be really lucky - but for the most part, an EOL in a bigger helo (not a chinook or anything else without a TR) with a TR failure will result in a landing with some forward speed.
There, is that specific enough?
By "inevitable"...you mean to say every single time no matter the conditions?
There, is that specific enough?
What is the smallest "bigger" helicopter you have in mind? Where do you draw the limit between smaller and bigger? Do you account for the difference in rotor system inertia dynamics when you draw that line?
When it comes to the Chinook....it does very much have a Tail Rotor....one that is as big as the forward rotor....but EOL landings were part of the syllabus.
Since you added the "bigger" helicopter discussion.....and the Sea King is what you are considering a "bigger" helicopter as that is what you fly....I can only assume you are providing commentary about your personal experience in the Sea King.
When it comes to the Chinook....it does very much have a Tail Rotor....one that is as big as the forward rotor....but EOL landings were part of the syllabus.
Since you added the "bigger" helicopter discussion.....and the Sea King is what you are considering a "bigger" helicopter as that is what you fly....I can only assume you are providing commentary about your personal experience in the Sea King.
Last edited by SASless; 3rd Mar 2013 at 13:39.
Thread Starter
SAS I regard the EC135 as a suitable a/c for a running landing. don't confuse readers with tandem or other non tail rotor a/c. it's bad enough holding it together so far!
crab: you'll have your hands full with some of the conversations here
crab: you'll have your hands full with some of the conversations here
Crab was talking about Zero Ground speed EOL's and opined that "Bigger" helicopters could not do them without ground run. I was seeking his definition of "Bigger" so as to see if I had flown one of his "Bigger" aircraft.
As I have said before.....Wokka's and Tail Rotor Failures don't take much discussion.
As I have said before.....Wokka's and Tail Rotor Failures don't take much discussion.