The Blind Leading The Stupid!

[sharkbait]

MAG SEAL and JETBOX Speak truth.
Not The old Servo Transparency Boogie Man again. :wacko:
If you get ST then you are at the G limit of the machine as explained in the RFM.
The Twinstar ( dual Hyd Sys ) has a limit light for this purpose.
The controls do not lock, the machine does not pitch up or down, roll, pitch, yaw, swap ends, do a loop, enter a spin or explode.
Relax the back pressure on the cyclic ( If you gotta release FWD pressure you are inverted or doing an outside loop and have just done or are doing something seriously wrong ). Perhaps a reduction in collective and a new plan is in order.
If you experience ST while the ground is in close proximity and is rushing towards you at an inordinate speed you have a huge problem. The a/c should remain controllable a you reef on the cyclic to precude an uncontrolled airframe/earth interface. You will feel feedback and need to muscle through it but the controls will work as intended. The engineers and the Stud Duck will not be kind when you confess to your sins but - hey you deserve it.
The above is meant to be humorous and I hope it will be taken that way.

The MNR, I assume, are getting advice from their Aviation Dept. and if it is made a contractual requirement they are the guys paying the bill.
Oil Companies overseas are always demanding extra equipment and their auditors go through the a/c with a fine tooth comb. At the moment, for example, we are carrying a regular ELT, a sonic locator, a water activated ELT, an EPIRB ( worn on the PFs belt) and a portable emergecy VHF. Not to mention the stuff in the 2 rafts. I think the don't trust us to come home at night.
The old dogs will remember when the Iron Ore Company in Sept Isles required the changing of the Pins and fittings in the 206 head at very frequent intervals ( was it 500 hrs?) after a tragic accident when an a/c lost a blade on the QNS+L railway contract.

I sincerely hope that they will find out what is causing the Astar problems but I don't think it is servo transparency.
Jeez this is a long post - sorry take so long and say so little useful. ( bored in the Persian Gulf ) B)

 

[407 Driver]

JetBox, I have to challenge you on your last post Re: Servo transparency....

You wrote ....I have no sympathy whatsoever for anyone that ends up in servo transparancy. The only time servo transparancy is an issue is when the pilot is exceeding the design limitations of the A/C. You'll never experience that phenomenon as long as you fly by the book and if you decide to hot dog or fool around, then don't complain that it's a design weakness.

I have encountered servo transparency in a 350B. I guarantee you that I was not hot-dogging, nor flying outside the design limits...unless that design limit precludes making a 15 degree banked LH turn around a fire at 80 Kts, 4500' +30 C.

It happens, and when you least expect it to !

 

[Blackmac]

Ethopia, doing a fast let down from 8,000 ft to land in Dira Dawa in a super 500C causes the cyclic to move forward rapidly when hitting hot desert air.

Maybe I was getting ST without hydraulics.

The only time I actually got ST (besides yul)was in a Gazelle, in a dive, drop the collective and pull back on the cyclic and pray, it worked.

Cheers Don

 

[T-rex]

JetBox,

You seem to have alot of answers, RE 500 blades falling off due to over grossing the disk. Get with the program! Maybe read up on Torque Events! MD never expected these machines nor designed the blades to do this manevore up to 200 times per hour! Now we have an idea why this is happening. This cracking of the MR blades is happening to operators who have excellent maintenace and piloting programs!
As per ST in an Astar, see what the hydraulics are like in turbulant winds in them there hills we call the Rockies! No stunting around there!

 

[jetbox]

Sorry boys but the only time I've been in an Astar and we encountered Servo Transpanrancy was when the driver was hot-doging or when they induced it on purpose to demonstrate it during training. If it happens during normal flying conditions, you should probably have the maintenance department fill out an S.D.R. and report the incident to Transport Canada.
T-Rex, those cracking blades owned by these "excellent operators" as you say, how long have they been in that company's fleet and can you be sure that every lift put on those blades since they left the factory was within the A/C's gross weight? (I'm not talkin about torque limits, there's a big difference!) Can you garantee that every pilot that flew that bird before you never over grossed it?
Have you ever seen the reaction on the flying staff when an operator anounces they're going to install tell tale boxes on their ships? You'd be surprised to see how many faces turn red and how many smiles disappear!!!!!!
You might fly by the book and every guy that flies with you might say they do but I'll bet you some of them are lying.
Just something to think about before putting the blame solely on poor design!


P.S. Correct me if I'm wrong Blackmac but you can't get servo transpanrancy if there are no servos on the helicopter!

 

[skullcap]

What a nice bunch of flatlanders goin off about the wetards getting into servo tranparency and not causing accidents.

Have been in SERVO TRANSPARENCY many times(about once a month in the rockies) and not stunting. A thing called turbulence and high altitude and high gross weight(not exceeding a dam thing thankyou). Not a big deal until terra firma( the ####) is coming up too fast as when it did kill a friend of mine and 4 others thank you.

Has less to do with disc loading and more with lock number of blades, is why B model blades more susceptable to it than 355 blades(have only been in once with those blades).


The controls do lock, only way out is to reduce disc load, lower collective/reduce turn.

No black magic or voodoo, just a crappy underdesigned hyd system in a great helicopter.

sc

 

[Nomex]

Don't want to start another Astar Hyd discussion, but I also had a ST, this winter on a B2 at 7500ASL, 500AGL, -6c, 60kts, descending left hand turn, got hit with a downdraft. After tapping a bit of down collective it came out without difficulty, after about 2 secs. No high G turn (less than 15 degrees) no hot-dogging. Just density altitude and turbulence.

Engineers checked everything out after and nothing amiss.

Key here I would say is to realize it will happen in the Astar, even during apparently normal flight ops and to recognize it and know what to do. There are other hyd malfunctions that will cause reactions that may be confused with ST such as the cyclic stiffening up (friction cup) or one servo jamming (slider/pilot valve).

 

[pitchlink]

Hey guys,

You can add me to the list of experiencing ST while within all limits. I've only experienced it once and it was when I was at altitude in a BA and in very turbulent conditions and I wasn't hot doggin!!! I was hovering out of ground effect trying to locate and chase a mother and her cub away from a group of jug hounds when I was hit by a gust. A combination of the gust that brought on the result passing and a reduction in collective cured me of the problem. It only lasted 1 or 2 seconds but it was long enough for me even though I had a relatively flat disk at the time. It's a great helicopter but I agree hydraulics capable of overcoming all possible loads doesn't seem like to much to ask!

I don't think an SDR is required for something the RFM describes as smooth and presenting no danger.

Regards,
pl

 

[jetbox]

I think I probably owe you fellas an apology, my past experiences obviously differ greatly than yours 🙁
No offense taken I hope. 🙄

 

[VERTICAL REF]

In a straight and level descent off the eastern slopes - yes full blown servo transparency! And this boy don't cowboy!!! <_<


Skully,

SERVO TRANSPARENCY has everything to do with DISC loading! 😉 You even said it yourself in the next line down!

 

[CTD]

I've only seen it once. It was in very heavy turbulence in a D model towing a snowmobile, and lasted the usual couple seconds.

It's surprising that I didn't get into it more, given the types of flying I've done with the D, B, BA, B2 and TwinStar. Towing bird in the rocks made for some pretty serious disc-loading events, very agressive applications of collective, and several hundred hammerhead turns all day to get back on 50 or 100 metre spacing. Never saw it.

I agree the system could be better, but I also have a feeling that the awsome governor and rock-solid Np/Nr performance of the 350 series makes us do things with them that we wouldn't try with other machines. I can't imaging doing some of the bird runs I did with an L.

Any thoughts?

 

[MagSeal]

can anyone quickly tell me the definition of Servo transparency (i'm too lazy today to find it myself)

I'm just wondering if everyone is on the same page with it, or whether certain conditions might 'feel' like it, when in reality it may be something different.

 

[recirqe]

Me too,
80 % of gross weight levelling out from a descent at 135 KTS at 5000'.Lower collective reduce severity of maneuvre. Grabs your attention though.

 

[sharkbait]

Being a glutton for punishment I will take a shot at it. :wacko:
Seeing as the Astar has a low pressure hydraulic system you can get yourself in a situation where the disc loading overpowers the hydraulics.
Basicaly the forces down from the rotor system equal the force the servos can send up to the rotor system so you start to feel feedback forces in the cyclic - not unlike hydraulics off in a jetranger for example. ( or flying a 47 G if you want to really wallow in the past.)
The RFM ( as I recall ) tells you you have reached the G limit of the a/c.
We used to demonstrate this by initiating a steep turn an then slowly tighting up the turn ( at a prudent altitude ) when feedback was felt we would hold it long enough to show that even though feedback was felt the controls still worked albiet with muscle power needed to move the controls. A reduction in the turn returned the rotor disc to below its max load and as you did so the feedback disappeared.
I would assume that if you tightened the turn and further loaded up the disc the feedback forces would increase a "G" increased.
In Discussion before I briefed that not unlike a spiral in a fixed wing the easiest way to recover was to reduce power, roll the wings to level and recover from any dive.
The demonstration was enough to alert pilots of the scenario and we never got any feedback from the field about any problems. Then again we were eastern flatlanders not used to mountain turbulance and stuff.
I do not recommend anyone trying this without a training pilot and the permisssion of the Chief pilot. Test pilots we ain't.
When the company I worked for was purchased by another company they did not demonstrate this scenario ( in fact did not know what the heck I was babbling about but thought it was a bad thing ) so I never taught it again.
Worst case would be High gross weight, high power, high turn rate.
As stated before the twinstar having a dual hyd. system this would not happen so there was a LIMIT light on the caution panel to tell you you had arrived at the "G" or discloading limit.
All this was on AS350D models so the B, B2 ect may be more susceptable (SP?)to this given higher gross wieghts and, I believe the same pressure Hyd. System. Never flew a B2 or anything so can not say.
If you get into this situation while trying to avoid terrain then you have put yourself in a bad place by having to pull to the G limit of any a/c.
Clear as mud???? :huh:
Perhaps someone with a 350 RFM can quote the actual applicable section or give a more scientific explanation.
Gentlemen you may fire at will.

 

[MagSeal]

I kind of knew the cause an effect of it. But didn't really know if there was a layman term for it. I guess the max "G" loading gives me a better understanding.

I had posted awhile back about the output force of these servo's and I think 184dNm is a pretty good output, nothing to be frowned upon. And to be using three of them for collective action seems like a bonus. Something as simple as the geometry of links and levers could give you the mechanical advantage to never have the problem.

In the end though, I guess no idiot light can beat the whole aircraft giving you a signal that you've approached the limit.

Now how do we connect in the Tq and TOT?