Today's ridiculous question regarding the Lynx.

[Hedge36]

The downward cant of the tailboom: what's that all about? I've searched around on and off for years now and have yet to find an explanation for the design.

Supposition? Forward flight attitude places the stab in a more neutral position - but it seems as though a fixed AOA for the stab itself would take care of that.

Someone clue me in, please.

[spinwing]

Mmmmm ...

SIMPLE ......

So that the tail boom does NOT get the chop (so to speak) during extreme aircraft attitude changes ......

i.e Main Rotor clearance



:}

[Hedge36]

That was another theory I'd tossed around. Got a reference?

[spinwing]

Mmmmm ....

..... Got a reference? ....

Nah .... but if you wrote to or contacted the ETPS I'm sure they would be able to give you chapter and verse ....

Cheers ...

[Hedge36]

Damn. I'm a design geek, so such things interest me.

[Phoinix]

Maybe fuselage drag (as a whole) has something to do with it as lynx has very little forward tilt of the main rotor, so to prevent the tail sticking up in the air - a downward cant.

[BoeingMEL]

..by an old Middle Wallop QFI that it kept airflow from the TR away (as far as possible) from MR downwash... also that it eased TR inspection/maintenance..

certainly credible but just his opinion. Cheers bm.

[ptflyer]

As mentioned earlier it is probably to make sure the blades don't strike the tail. The Lynx has a semi-rigid rotor so the ammount of blade flapping is limited but the aircraft also has a very compact main gearbox, in terms of height, and a short rotor mast.

[spinwing]

Mmmmm ...

Like the Bolkow 105 ... the Lynx has a 'Rigid' rotor ... and as said above a short mast ...

In fwd flight the T/R is clear of the rotor airflow by being above the downwash.

And apart from inflight Aero's etc .....


Rotor clearance problems can arise with touchdown autorotations (like with the blo cow) it is possible to chop the tail because of blade flex at low Nr especially if it is kicked up by an over 'positive' touchdown.


:ok:

[Blind Bob]

Main rotor blade clearance is the answer. The Lynx collective range goes into negative pitch, primarily to 'push' the aircraft down onto the deck during shipboard operations in rough seas. It stops it being thrown off before the groundcrew have secured it.

I flew Army mk 7s and 9s and after an engine or governer change, torque matching was done on the ground in negative pitch. The RRPM was plotted against torque for each engine to obtain the best FTG matching. Pushing 100% torque with the lever down reverses the coning angle somewhat. The introduction of the BERP blades with their paddles and greater washout even more so.

Also, the Lynx and the Bo105 both have semi-rigid heads. They both have rotation around the pitch change bearings and as such have tie-bars fitted. the only 'rigid' head I am aware of is the EC135. It has the blades bolted directly onto the rotor mast. No hinges and no bearings! The best design yet.:D

[spinwing]

Mmmmmm ..

....Also, the Lynx and the Bo105 both have semi-rigid heads. ...


Blind Bob ... could be semantics but I disagree and so do others ...



"Rigid Rotor ... This system allows the blade freedom to feather only .... etc"

(Principles of Helicopter Flight 2nd Ed. W.J Wagtendonk Chap.6 P.45)

And the Bolkow105 and Bk117 certainly have Rigid Heads with only feathering axis freedom .... NO Lead or Lag hinging.


;)

[RVDT]

The 135 is not rigid, it is just (nearly) bearingless.

[Phoinix]

Why is 135 head not rigid? It is bearingless yes, but rigid, no?

[widgeon]

Aircraft in Detail - Helicopter Rotorhead Image Gallery Index (http://www.b-domke.de/AviationImages/Rotorhead.html)

The best site I have found for rotorhead pictures.
EC135 is described as hingless bearingless , did not know that Comanche had Bo108 rotor head .

[Blind Bob]

Further to my last........................

Agusta Westland Lynx manual states it has a semi-rigid main rotor system.

Eurocopter Bo105 and Bk117 training manuals both state semi-rigid rotor system with rigid hub.

The EC135 doesn't have a rotor head as such, it has a rotor hub shaft, to which the blades are attached. All flapping, dragging and pitch change movement is done in the blade spar. It is described as hingeless and bearingless. The only bearings on the mast assembly are on the rotating pitch control rods to the blade cuffs and in the swashplate.

NB. The EC135 was a Bo108 until the French got involved and replaced the conventional 2 blade tail rotor with their 'Fenestron'.

[Dave B]

This goes back much further than the Lynx. Look at pictures of the original Sikorsky S55, and you will see it has a straight tail boom. Now look at the Westland built version, the Whirlwind, and you will see it has a bent down tail boom. We were told it was for main rotor blade clearance.

[Data-Lynx]

Too True. One of the Flight Safety images shown to us sprogs, before we left Hillers and got to clamber up the side of the beast, was a very impressive example of blade sail downwards, way below the normal droop shown in the back of this pic.

http://www.royalnavy.mod.uk/upload/img_400/HU_098404.jpg

[widgeon]

DL are you referring to LH blade on # 14 ? , where those last 3 at full RPM ( not sure if any one in that pic is still reading PPrune )

[Data-Lynx]

14 and 15 right at the back are both rotors stopped. I moved onto the Wessex HU5 from the Whirlwind and you had to be wary of gusts, especially on board in the final stages of applying the rotor brake.

As for age, have faith. I know of at least one Sea Fury pilot and active silver surfer on the Internet.

[RLHDLW]

I think the original definition of "rigidity" referred to the presence or absence of hinges.

Fully articulated = flap and lead/lag hinges
Semi-rigid (semi-articluated) = flap hinge(s) only (UH-1, R-22)
Rigid = no hinges

The use of these terms became somewhat ambiguous with the advent of flexible blade elements and/or elastomeric bearings.

A rigid rotor may be hingeless, but still have bearings, e.g. Bo105 and Lynx for blade feathering.
A hingeless and bearingless rotor, e.g. EC135, may not be "rigid" at all, as the blade root is is highly flexible in bending (for flapping) and torsion (for feathering)
To add even more confusion, there are quite a lot of fully articluated rotors that have no hinges. Here, the function of hinges (elimination bending moments between the blade and the rotor head) is taken over by elastomeric bearings.

BTW, manufacturer's manuals are not fully reliable, neither is my website :)

Burkhard,
www.b-domke.de/AviationImages/Rotorhead.html (http://www.b-domke.de/AviationImages/Rotorhead.html)

[Yonez]

another slant to the original question - Lynx designed to be at optimum attitude during cruise, ie 5 degrees nose down. In this attitude engines(reason why it smokes so much during start & shutdown) & tail are level, so maybe its just old fashioned aerodynamics.

[Phoinix]

RLHDLW, thank you for your effort shown in your website. I'm surprised that the heli industrie, being all engeneers and scientists, more or less uses commercial names for their rotor head design even in the manuals, adding to the confusion in the rotor head basics.

[widgeon]

In the announcement today on the Lynx upgrade the picture showed a lynx with wheels , while the article talked of the Army . Do the army lynx not have skid gear still ?.

BBC News - Lynx helicopters upgraded for Afghanistan use (http://news.bbc.co.uk/2/hi/uk_news/8589135.stm)

Lynx helicopters upgraded for Afghanistan use


http://newsimg.bbc.co.uk/media/images/47541000/jpg/_47541460_000026512-1.jpg Lynx helicopters carry a crew of three and up to five passengers

An extra 10 Lynx helicopters are set to be upgraded and used in Afghanistan to support front-line troops, according to the Ministry of Defence.
The aircraft will get more powerful engines, increased firepower and advanced instrumentation.
It comes under a £41.8m contract with AgustaWestland, in Yeovil, Somerset.
Another 12 of the Army Air Corps Lynx, based at Dishforth, North Yorkshire, are now being upgraded with the first deploying to Afghanistan next month.
The helicopter, which carries a crew of three, as well as up to five passengers, will be used to protect convoys, move troops and carry out reconnaissance missions.
The Lynx has been used by British forces in Afghanistan since 2006, however until now the helicopters have only been able to fly during winter months.
Defence Equipment Minister Quentin Davies said the "improved version" of the Lynx helicopter "will greatly benefit our troops in Afghanistan".
He added: "The enhancements will allow it to perform in the extremes of climate and geography that characterise that theatre of operations."

[gsa]

Do the army lynx not have skid gear still

Yes, but the Mk9s they use have wheels.

[RotaryWingB2]

In the announcement today on the Lynx upgrade the picture showed a lynx with wheels , while the article talked of the Army . Do the army lynx not have skid gear still ?.

The picture shown isn't even a 'new' Mk9A Lynx, it's the original Mk9.

The army operate all three flavours now, Mk7s, Mk9s and the Mk9As.

[HEDP]

The Lynx AH9 when introduced had a greater MAUM than its predecesor the Lynx AH7.

The rationale explained at the time was the Lynx AH7 skided undercarriage was the limiting factor on the aircraft AUM, the rest of the airframe was capable of greater AUM.

The introduction of the Lynx AH9 incorporated significant reinforcement of the airframe to take the wheeled undercarriage and therefore the airframe could carry the extra AUM.

Ironically a MK7 with no TOW equipment or roof sight has a greater payload than the MK9 when all the reinforcing of the airframe is taken into account in the basic weight.

HEDP

[widgeon]

Thanks I have been out of the loop ( pun intended ) for some time now.

[jonwilly]

The original Lynx had an almost direct copy of the Tailboom fitted to the Scout/Wasp. External Stringers and all.
However I was assured that La Frog wanted an input and they redesigned the tailboom along Gazelle lines, tho of course without the Fenestron, a pity.
Two Lynx with the original tailboom existed in Aircraft Engineering Training Wing in Middle Wallop early 80's.
The tail assembly was prone to vibration and doubler plates where added around tail rotor gearbox area. Many problems happened with securing 'rivets' Joe bolts and many where replaced.
The vibration moved down to intermediate geabox area and then forward to Tailboom/Main fuselage attachment point, 72 ? bolts.
In early 1990 trebble six (Damian to the ground crew) was found to have a 6 inch vertical crack in the center fuselage skin, about 6 inches forward of the attachment point.
A Navy team form MARTSU came out inspected and Gobsmacked had cab shipped back to UK for repair.

john

[floatsarmed]

41.8 Million Pounds for an engine upgrade for 10 aircraft.

What a bargain? :eek:

No wonder the pommie economy is stuffed.

Maybe it's time to buy some Agusta Westland shares?:}

[dipperm0]

About Lynx vibrations, I remind myself flying at approx 120 Kts and being unable to read accurately the speed due to severe vivrations during the early years of 1980.

In front of such vibrations leading to cracks around the intermediate gear box, the French navy decided to create a track and balance team dedicated to the lynx. Using equipments such as Shadwick, Rotortuner and so on, that team succed in a very short period in a important reduction of vibrations both from the tail rotor and the main one.

This achivement makes me feel that the aircraft concept is not in fault. The vibrations and subsequent cracks came due to an lack of knowledge from the maintenance team. When they got the knowledge, the phenomenon went away.

DO

[jonwilly]

Memory says much of the tail rotor vibs came from the blade extension arms not having the same amount of 'Grease' in them, the wieght difference causing the vibration.
First IA on recieving reports of TR vibs was to purge all four extension arms and normally this would cure the vib.

"The vibrations and subsequent cracks came due to an lack of knowledge from the maintenance team. When they got the knowledge, the phenomenon went away."
Please believe me it was a painful process
The early 80's where the days of the 3 Sqn Regiment, newly set up and down to be the rapid anti tank attack force if Ivan came.
The bare faced lies that where told by the engineering side to Make aircraft 'S' would even embarrass me.
We found that when doing MR vib check that if pilot placed aircraft in a very shallow dive, then head vibs where much lower and the cab would pass the test.
Not honest but until late 80's no one had the solution to the dreaded 4 R vib, that Lynx developed after say 300 flying hrs.
The lies and Sh1t told to get around that one, from both Engineering and Flying side where legendary as any honest person involved at first line can tell.

john

[MightyGem]

Thanks JW. You've just destroyed all the faith I used to have in the Reems. :eek:

[jonwilly]

Morning Dave
Not News, all old stuff.
Sqn OCs and the CO where all screaming for 'S' cabs for the major exercises to prove the new CinC BAOR concept of Lynx Strike Force, pilot himself memory says.
Everyone knew what was going on. Well the REME hireriky did when not back stabbing each other.
All results from Vib runs had to go back to 71 Wksp 300 mtrs next door. The system could take weeks to make the delivery by which time one was deployed and for operational reasons Vib runs got ER Deferred /Forgotten until return to base.
The vertical crack in 666 was something No one I knew, had ever seen and that includes my short meeting with the Experts (and they where) in airframe repair from MARTSU, they thought they had been called out by the muppets.

john
Look after the Rozzers.

[CyclicRick]

As regards to the tailboom all I remember is it being covered in bloody oil from the engines resulting in " The endurance of the aircraft may not be due to fuel"
Someone came along one day and stuffed a block on top of the head which brought the vibration down a bit, I remember seeing one fitted to a Lynx in Detmold.

[diginagain]

Someone came along one day and stuffed a block on top of the head which brought the vibration down a bit, I remember seeing one fitted to a Lynx in Detmold. Main Rotor Head Vibration Absorber - aka 'the bonk'.

Just reading this thread is making my knees buzz.

[nodrama]

The link is a short video of the 1st test flight of the AW159. Interestingly, unless it is just fitted for prototype vibe analysis, this 'new' Lynx has a Bonk fitted too.
If the final version has a Bonk fitted.....that's all your theories about poor tracking & balance procedures out of the window.

Aviation Video: AgustaWestland AW-159 "Lynx Wildcat " | Patrick's Aviation (http://www.patricksaviation.com/videos/Radetzky/4510/)

[[email protected]]

I was never convinced by the 'bonk' on the Lynx because it was only optimised for one Nr and one stage of flight (cruise flight IIRC) which was not much use for hovering where the vibration was often worse because of the higher pitch settings. The bonks were leftovers from the appalling WG30 or so it was rumoured.

All AW manufactured helos vibrate and leak, why should the Wildcat be any different?

The undercarriage on the new wonderlynx doesn't look very dust-landing friendly - I won't be surprised when the first one is rolled over on an operational landing - not the first aircraft with a high C of G and a narrow undercarriage to suffer this problem - dynamic rollover anyone?

[HEDP]

John,

If nothing else the rear oleo's in the clip look as if they would snap in any sort of zero/zero landing let alone dust!

Is it just me or does there appear to be a moderate degree of overcontrolling going on or perhaps more relevantly FCS hunting?

HEDP

[dipperm0]

The main undercarriage on the clips looks to have the same width as the old one version and I never heard of dynamic rollover with that undercarriage. In other hand, very impresive crash control capabilities for night landing on small rolling deck.

[Two's in]

THAT'S HOW ACQUISITION WORKS # 27:

When the relevant authorities became sufficiently engaged with the Lynx vibration and tailboom cracking problems in the late 80's, they paid for a Design Authority investigation by WHL. After a lengthy investigation, the underlying reason for the unpredicted vibration and cracking problems was traced back to the fitment of the TOW Booms and equipment that were introduced under a mod to provide the ATGW capability, shortly after introduction to service. So the very DA that designed, implemented, and fitted the TOW mod to the Lynx was able to point at it 10 years down the road and subsequently lay the responsibility for all the vibration problems squarely at its door, because it was an MoD requirement to fit TOW. Nice work if you can get it....

[diginagain]

The oleos on the Mk9 gave the appearance of being an extremely robustly engineered item - almost a throwback to the standards of the 1950's. As I pointed out to one of Westland's top neddies during a factory visit when we collected some of the first, they bear an uncanny resemblance to Whirlwind oleos................

[jonwilly]

Twos In
I am not looking for an argument so I will trust what you say on the Tow Fit causing Much of the vibration.
I never fitted a "bonk' but memory says that when fitted you had to 'Strike it Hard' with you fist to assist setting up the first reading , hence the Bonk name.
I stand to be corrected on that.
The Curse of Lynx from early on was the 4 R Vib.
We, 9 Regt shared a hanger with 4 Regt who where the first unit in BAOR to be equipped with the Lynx.
Our new cabs where up and running and the Mechs from 4 Regt, where consistently busy trying to sort out the 4 R which had come from nowhere.
Much ribbing and friendly rivalry as we shared same Seniors Mess.
I cannot remember the figure of Flying Hrs when the 4 R appeared but will suggest 300 Hrs a Honest estimate.
Memory says we did our First Lynx Op Banner tour before we started to have 4 R problems.
The cab would be OK pass the electronic monitored Vib runs, Then Bang pilot would come in an complain about a 4 R from nowhere.
4 Regt where already up to their necks in this matter and could offer little serious advice.
The arguments in the maintenance side soon got nasty.
One side said 4 R so must be something that affects All 4 Mr Blades.
However expireance from the men at 4 SUGGESTED that by checking the complete system from Collective to Head you often found a worn linkage and by replace this you reduced or even brought the Vibs in limits.
The Falklands had finished and Lynx deployed down there, taking a unbelievable amount of stores out of the system, That is another story.
4 & 9 amalgamated to form a new 4 Regt with 3 line Sqns.
Blood letting then occurred in Maintenance organization which split the unit down the middle.
The other Regts in BAOR had similar problems on 4 R but someone else will have to make there contribution.
I could never get rid of the 4 R and I will suggest neither could anyone I knew UNLESS they managed to Change, The Main Rotor Gearbox and with all the items in the Falklands supply chain MRGB changes where few and far between.
Start of 86 I went to NI and saw out the 4 1/2 years I had left there.
Same problem but higher priority and availability for spares, especially after Lynx where withdrawn from Falklands and in NI, MRGB where change overnight. Cab in by 18.00 and back 'S' for 08.00 following morning, weather permitting airtest.
I was not involved in the solution but to the best of my knowledge,
SOMEONE at 71 Workshops in German finally put all the reports together and notice that the 4 R only developed over a certain number of Flying Hrs. About lets say 300 Hrs.
Further investigation I assume with Wastelands, led to the discovery that a large diameter spacer in the MRGB was 'Wearing' and then permitting vertical movement.
Replacement of this 'Spacer' cured the Vib.
In NI the OC Wksp arraigned with an engineering company down in Belfast to machine a new spacer to correct dimension after it had been determined on a strip down. This took place overnight and the 18.00 in 08.00 out procedure was accepted policy.
I was not involved in the matter having other duties at the time so all Hearsay, but I understand correct.
john
I have been told by a Little bird that the Lynx supplied to a friendly Mid East power now suffer the dreaded 4 R at 300 + Hrs.

[nodrama]

Nobody yet has mentioned the fact that between the MK1 and the MK7, Westlands reversed the direction of rotation of the tail rotor...supposedly to reduce vibration also.

Redesigned TRGB's, Bonks, lots of doubler plates, critical shimming of MGB/ MRH (and not all Lynx carry TOW).....sounds like a lot of expensive and unnecessary work if all Westlands had to do was educate the customer in how to track & balance the aircraft properly......in other words, poor maintenance practices wasn't the problem with the Lynx vibes and cracking.

[jonwilly]

Short & Sweet Nodrama and oh so true.
It was known from early on that a MRGB change solved the 4 R vib .
Very expensive way of curing a vibration problem and there where no spare MGRBs.
A great deal of :ugh:took place and it still grips with me to this day.
john

[Two's in]

Jon,

To be more specific, WHL claimed this was the cause of the vibration and hence were apparently not responsible for the cost of its subsequent fix - as you and I probably know, there were a myriad of reasons why the Lynx vibrated the way it did, and initially a lack of correct knowledge by the REME was undoubtedly a factor when this first became a maintenance problem. Whoever cracked the problem of correctly "shimmed" MRGBs deserved more than he probably got, when you think of the cost of all those endless track and vibe runs it saved.

[nodrama]

Changing the subject slightly...

Anybody out there know if they still use the red/white/blue lynx at Empire Test Pilot School (ETPS), Boscombe Down (can't remember reg).

If not, anyone know what happened to it?

[jonwilly]

" WHL claimed this was the cause of the vibration"
Two's in
I never knew that Westlands had said this.
In my minds eye they had to know this.
Do you have a fair estimate when this 'Gem' of knowledge was passed on to the shop floor, or Aircraft Branch.
Senior folk had their career ruined by the 4 R saga.
Toward the end of my time at 4 Regt we got a new WO 1, ASM, posted in.
We had been Cpls together many years before. He said to words to the efect that on recieving his Brief for the Job from Senior Aircraft Engineer BAOR, he was told there where only 3 ASM jobs of consequence in BAOR, they being the 3 Anti Tank jobs, eyes from the highest level where watching.

john
"and initially a lack of correct knowledge by the REME was undoubtedly a factor when this first became a maintenance problem."

I'll go to my grave knowing that to be true.

[nodrama]

It depends on how you look at “lack of correct knowledge”. Since I’ve left the Army I’ve seen numerous problems with civvi helicopter types that, in my opinion, should have been highlighted and sorted by the manufacturer long before they became an expensive and commercially embarrassing (for the operator) problem. I’ve come to realise that manufacturers don’t admit their design mistakes in a hurry, especially if they’re not life threatening…they’ve got too much to lose in the way of money and reputation. In my mind, that’s what happened with the 4R saga you refer too….the REME were left to struggle on blindly with no guidance and the top level Brass just wanted to see results. “Don’t give me problems, just give me answers!” springs to mind…..it all gets political and scapegoats get their heads chopped to protect the big-boys.