What would you do!! (MD Explorer)

[tbc]

The scenario is:

In-flight, MD Explorer, directional (yaw) control cable separates = pedals no longer controlling drum, thruster drum rotates fully right :eek:

What would you do?

[teej5536]

Probably swing my legs around the back of my head, and give my cheeks a kiss goodbye! :}

[Pandalet]

Assuming you could make a reasonable stab at what had happened, presumably going straight into auto and maintaining a reasonable forward speed would mitigate the lack of yaw control?

I guess you'd then execute a fastish run-on landing.

Alternately, you could keep the engines going (keeping power down as much as possible), while maintaining forward speed, relying on the vertical stabiliser to keep you more or less straight. Still leaves the problem of landing, though.

[Thud_and_Blunder]

What would I do, tbc? What I normally do - leave that contract and go and fly something else, somewhere else before anything nasty happens! Then wait for some b1oody TRE to come out and give me my first frange on type!

Seriously, if you can't think of anything then I shouldn't think there's much hope for us mere mortals.

[mfriskel]

tbc,
Why does the rotating cone rotate fully open right? Except for autorotation, rapid decelerations and maybe VSCS hardover (never heard of one happening) your thruster doesn't go much more right than neutral. I could see getting stuck right in an aggressive decel and banging the tail on the ground.

The first thing I would do is put my pedals to a minimum fan pitch setting, approximately 1 inch right pedal forward. This will minimize the effect of the thruster, relative to the opening position. It will also give airflow to operate the slots which will help develop the COANDA effect, once / if you get the forward speed minimized depending on your approach technique.
Remember- if the thruster is open to the right, left or right pedal application will give you increased nose right yaw.

Following the flight manual emergency procedure loss of thrust or fixed thruster neutral to right will give you an option of landing with near zero groundspeed. This may take a couple approaches depending on conditions, but the NOTAR system / VSCS system does give you some good leeway to practice before you commit to a landing. You may try with SAS on, SAS off and also VSCS off- all will have an effect on the outcome of the maneuver depending on the conditions. Remember- if you turn the VSCS off and then find you need to do a go-around- you have to get them turned back on as you increase power. Also do not turn them off until you have started your descent on your approach angle.

You an talk all day about this, but knowing the systems that effect anti-tq will help you understand this. If you haven't been taught the techniques for aggressive deceleration (getting the machine to a hard, smooth landing area with minimum forward speed) and then getting the machine on the ground from a low hover, with a yaw rate building- I would recommend going to the factory and seeing it and practicing in their aircraft.
Mark

[FloaterNorthWest]

Ahhh tbc, Jedi Master, you are sent to test us! My ten pence worth (lets see if I was listening to you!)

Are we talking about the cable/rod aft of the diverter plate letting go and the control quadrant in the cone giving you a full cone right condition but still have control of the fan? If we are then it will depend on what stage of flight you are in when it goes on what you will feel.

Before I start, I will just say that all of this will depend on aircraft all up mass (heavier more torque reaction), wind strength (weathercocking/TL) and density altitude (as pushing air) at the time of failure.

It is going to be a balancing act of torque reaction + thruster vs coanda + VSCS at various speeds to give you directional control.

http://i189.photobucket.com/albums/z29/rich902cove/Thrustertoright.jpg
I will just add that talking about turning off the VSCS is a red herring. The VSCS on the 902 has no direct pilot input and is controlled by the magic boxes under their own control laws. They tell the fins what to do to aid directional control and stability, so best let them get on with it and let it help you and not disable it's assistance.

If we look at the division of control authority v speed

http://i189.photobucket.com/albums/z29/rich902cove/NOTARControlauthority.jpg

"TL = Translational Lift"

In the hover, into wind. As the thruster has only 30% authority the aircraft may start to yaw right but a combination of increasing the coanda with the pedal (natural action) and weathercocking will keep you straight or the yaw rate will be low enough to touchdown. A quartering wind from the left will assist to keep straight.

About 80kts as the thruster has no effect you aren't going to notice anything.

The interesting area will be as speed decreases below 80kts when the fins are losing authority, the thruster is taking more of the control authority and the coanda is yet to kick in.

As speed reduces further the fins become ineffective, the thruster is taking more of the control and the coanda effect is yet to kick in. This is when the aircraft may yaw right. I don't think the aircarft will yaw violently as the thruster doesn't have the power to move those slabs of fins through the weathercocking effect. As speed reduces below TL the coanda will have more say and counter act offset thruster and give you the situation in the hover.

So what would I do? Firstly at a safe height with a quartering wind from the left I would bleed the speed off and see how bad the yaw gets and see if it straightens itself below TL. You can always fly out of it and recover above 80kts and try again.

Once happy it is all controllable I set up to a clear area with a large hard surface and a quartering wind from the left and give it a go. Probably aiming to come to a higher than normal hover and then descend vertically.

I would also make sure someone is there to video it for YouTube!!

I await your comments Master!

FNW

[doublesix]

Bloody hell Rich you should know what to do. Ask the nice observer next to you;)

[FloaterNorthWest]

Doublesix,

Sadly I know longer have the pleasure of flying with an observer, just miserable passengers who don't appreciate what you do for them....................hang on!!!!

FNW

[skadi]

Is that question based on the latest accident with the Police 902 in Hannover/Germany?

http://www.pprune.org/forums/showthread.php?t=300309

They had a yawcontrolmalfunction, tried some approches and made at last a high speed running landing ( approx. 80-90kts )

skadi

[FloaterNorthWest]

Would have thought so looking at latest SB.

http://www.mdhelicopters.com/publications/pdf/900storage/service_bulletins/sb900106.pdf

FNW

[Peter-RB]

Never flown one but if this happened when I was theoretically flying I would shut power down keeping as fast a forward speed as possible controlling yaw(if any with throttle) and aim to run on at about 50 to 60ish knts,

Could be total boll**ks what I have just said but the speed would decay as you slowly closed the throttle and the forward speed ( would need to be checked whilst panicing) should be slowly reduced to try and stop any big yaw...

And hope I could walk after everything went quiet!!


Peter R-B

Vfrpilotpb:ooh:

[MightyGem]

Nice one tbc. You always did ask a good question. And I could never answer them.:(

[tbc]

A few more thoughts for those that wish to continue:

MightyGem - you can do better than that mate!

Peter RB - see where you are coming from but unfortunately this is an Explorer!!

FNW - you learnt well - obviously had a good teacher!! Drum is uncontrolled by the pilot, NOTAR fan is still under control of the pilot. You obviously didn't listen to the brief on the VSCS did you? What about the Yaw Trim switch that nobody remembers or in fact uses? Also think back to the jammed right pedal drill - we only used about 1" (actual) right pedal if you recall and remember how the aircraft reacted!! Now imagine the drum (pedal) is now full right!! I would like to witness your efforts at coming to a hover and descending vertically!! I think that technique was tried some years ago in the Japanese (I think) accident. Good use of colour by the way.

mfriskel - the short sharp answer to your initial query is - because it can and in my hypothetical scenario it did - if the drum is not under positive pilot control it could be free to find its own position - with 200 mph wind blowing out of it, it needs just a slight bias in its position and I suggest it would be blown fully open and stay there. I will reserve making comment on the RFM and its drills for NOTAR failures on the grounds that this is family show!!

T & B - Ah the frange - good memories. As someone who some people think is a close relative of mine once said (albeit many times) "I have a cunning plan".


Pandalet - again I see where you are coming from but again the is an Explorer. Enterring into auto when you have no air coming out of the drum (NOTAR drive shaft failure) OR you cannot control the drum via your yaw pedals is NOT GOOD!

Teej5536 - top of the class - best answer so far.

:ok:

[mfriskel]

tbc,
Send me a pm with your comments on the RFM procedure as it is currently written
Cheers
Mark

[FloaterNorthWest]

tbc,

I bet the bobbies love those long winter night shifts with you.

Understand what you are saying about the 1" right pedal but in that scenario we are controlling the fan and producing an additional force to the thruster. Was the Japanese accident a thruster failure or a total system jam?

I take it from the little I can gather "outside the loop" that possibly the tailboom extension modification is causing a failure of the rotating cone control rod? Hence the German crash.

Yaw trim switch on the collective. Is that the one that can change heading via yaw below 50kts or am I mixing my aircraft?

I still think the basic theory works but as we know in the world of PoF not anything is as it seems. Some of my instruction must have been flawed and I didn't spot it :}

FNW

[Creaser]

In a 60 knot run-on landing what is the best surface for passenger survival?

Concrete Asphalt or in the UK typically sodden grass?




Creaser

[teej5536]

Teej5536 - top of the class - best answer so far.

Top of the class? Thank you! But something tells me that in this scenario you're probably not going to want a smart a:mad:e, that fancies himself a comedian, in the RHS... Just a hunch!
:)

[Peter-RB]

Creaser,

Being in the Uk I would always plump for sodden grass, at least if you Farked it up it would be a mite softer than concrete, long low run in and hope/perform a greaser.:eek:

Peter R-B
Vfrpilotpb

[md 600 driver]

i would want to do it on the hard concrete at mesa with mfriskel that way i may have a chance [but not near aidrians chains]

[Senior Pilot]

In a 60 knot run-on landing what is the best surface for passenger survival?

Concrete Asphalt or in the UK typically sodden grass?

If you use grass, the chance of hitting a bump, or tipping forward on the skids, or sinking into a soft patch, is way higher than on a paved surface. Runway/taxiway for me, thanks :ok:

[tbc]

FNW - IIRC and surmising what little was made available about the crash, the crash occurred because a NOTAR fan blade torsion strap let go, this probably slowed the fan momentarily which shocked the NOTAR fan which caused the NOTAR drive shaft to shear just aft of the rotor brake. This meant the NOTAR system had failed (but he could still move the thruster, but there was nothing coming out of it). And again IIRC the broken drive shaft then smacked into the main fuel line for the No 2 engine which sheared it at the decking quick release self sealing couple - so he lost his No 2 engine as well.

I recall he carried out a slow speed/hover check at height and lost is and spiralled in to a crash.

Yes the Yaw Trim switch does allow pilot input to the VSCS - below 50 kts the aircraft yaws, above 50 kts it 'kicks' the ball. However I gave you a blind alley as it made no obvious change to the basic condition.

Some of my instruction must have been flawed - tut tut!! That is not what BJ said on the day!!

Regarding landing on hard or soft surfaces - IMCO go hard everytime and keep it hard if you can!! Soft has been proven to be asking for rollovers - the Hannover crash appears to have been caused when the aircraft unfortunately ran off the runway into the grass verge and rolled over. I believe the Knaus Explorer crash a few weeks earlier also rolled on grass.

Anyway - having just spent some time playing with a simulated right pedal jammed forward in-flight, I can confirm that the Yaw Trim had no impact on the problem. You must keep the IAS above 90 kts plus (if not more) to feel as if I had some control - and that was into a 36 kt wind!!

As regards trying to get it down - well thats another story:uhoh:

[Sulley]

tbc ever considered playing around with the vscs switches ?

if you have airspeed the indicators will be hard over to the left (tail of the fin position) when you start lowering the lever they exit stage right and are then of less use keeping the nose left. How far right they go is my point because if you turn off the vscs the fins go to mid point on the indicator scale. So if they go past this point wouldn't it be better to turn them off for the last bit if the crash ? and at least have them doing something ?

[tbc]

Sulley - remember that the role of the VSCS is to 'schedule' to an optimum position as determined by the CLP etc. to drive the nose left in order to assist in overcoming torque reaction. Switching them off takes away a 'friend' in this instance I would suggest. You also cannot disable the VSCS right fin unless you disable the SAS, so you are making things possibly worse and not better.

Not convinced switching them off causes them to go to neutral - the indicator might but I'm not convinced the fins do.

[Thud_and_Blunder]

Just to add my 2-penn'orth to the "hard vs soft" surface debate, if you have the choice between a runway and a taxiway, where the former has centreline lighting while the latter is unlit, then go for the taxiway. I've lost the photos of a 135 I ran-on in the Middle East; a chamfered 2 cm-tall runway light completely sheared one skid mount. We also found that the friction coefficients were very different - on the (very smooth) runway the aircraft carried on for over a hundred meters after a 25-kt touchdown, while on the taxiway it would stop 3-4 times more quickly.

[Peter-RB]

With all the experience you guys have I have now read and learned a little more and IF in future the need arises I will use CONCRETE and Taxiways at that.

Thank you all for the lessons you have learned,... and shared!

Whilst talking of experience, if any of you ever need to land in a ploughed field with skids, always land across the furrows(the lines) with wheels try never to land in a ploughed field! reason being the furrows of turned over soil hide voids that can be up to 24" or 2ft or 60 Cms deep going across will settle evenly with skids whichever way with wheels you sink!
Peter R-B:ok: