Sikorsky S-76: Ask Nick Lappos
Join Date: Sep 2003
Location: THE MANGROVE SWAMPS (RETIRED)
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
Remember a simple rule: Training sims are designed to program YOU, they are NOT designed to replicate the real aircraft, in spite of pilot mythology otherwise.
Join Date: Jan 2001
Location: Brunei
Age: 62
Posts: 44
Likes: 0
Received 0 Likes
on
0 Posts
Mr Lappos
Let me firstly make an unequivocal statement: Pilots and organisations should not make up their own procedure, where there is already a laid-down procedure within the RFM/Ops manual/EOP NOP (which should have derived from RFM anyway). I hope this states my position clearly...
Where there seems to be a better way to bring an anomoly to a decent conclusion, that procedure should be considered by the manufacturer (aided by a little consultation with clients), and if deemed better, included as an amendment to the RFM. There is a responsiblity encumbent upon the manufacturer to continue improving thier product after point-of-sale. These are not 'fire and forgets'. The first stage of any such change will probably come from pilots, familiar with the aircraft, discussing things.
I do acknowledge that there is a danger that individuals will have a discussion with their 'inner Douglas Bader' and try things that are inappropriate, at inappropriate times... Not good
I also agree that the Sim is exactly that, Cyclic only autos that can be succesfully completed at WPB should not be attempted in real life! There is from necessity, a generic synthetic element to producing a computer generated fault, from something mechanically derived (good example being the aforementioned interaction of DECU/stepper/manual input/FMV within an esentially mechanical FMU).
If my original question is read, in conjunction with my rather lengthy notes here, I hope that you'll agree that I was asking the question of pilots, with the hope that someone from Sikorsky PLC, would contribute some developmental notes. As My Question poses: Has the manufacturer thought beyond the obvious? i.e. Is there a good reason why my observation is completely wrong?
Cheers
Doc
Where there seems to be a better way to bring an anomoly to a decent conclusion, that procedure should be considered by the manufacturer (aided by a little consultation with clients), and if deemed better, included as an amendment to the RFM. There is a responsiblity encumbent upon the manufacturer to continue improving thier product after point-of-sale. These are not 'fire and forgets'. The first stage of any such change will probably come from pilots, familiar with the aircraft, discussing things.
I do acknowledge that there is a danger that individuals will have a discussion with their 'inner Douglas Bader' and try things that are inappropriate, at inappropriate times... Not good
I also agree that the Sim is exactly that, Cyclic only autos that can be succesfully completed at WPB should not be attempted in real life! There is from necessity, a generic synthetic element to producing a computer generated fault, from something mechanically derived (good example being the aforementioned interaction of DECU/stepper/manual input/FMV within an esentially mechanical FMU).
If my original question is read, in conjunction with my rather lengthy notes here, I hope that you'll agree that I was asking the question of pilots, with the hope that someone from Sikorsky PLC, would contribute some developmental notes. As My Question poses: Has the manufacturer thought beyond the obvious? i.e. Is there a good reason why my observation is completely wrong?
Cheers
Doc
Join Date: Jan 2001
Location: Brunei
Age: 62
Posts: 44
Likes: 0
Received 0 Likes
on
0 Posts
Oh Well
Deary me, it seems I have killed the thread, just as it was getting interesting! I do think it a shame that no-one, with developmental knowledge, has a view.
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
We shouldn't kill threads, should we?
I do agree that all pilots should continue to look for better ways to do things. When I was the project pilot on the S76, we made several changes based on wise and well thought out customer pilot comments/opinions/complaints. For example, the concept of ganging the tail/Intermediate temps on one caution light and the chip on another was thought of by an Air Log pilot, and incorporated by the factory.
I think the operative thing here is to be sure all bright ideas are vetted by folks who are expert in knowing how to properly judge them. Pass on good ideas to the factory, or at least some entity that has the expertise to pass judgement (an STC holder for example). I must admit, the factory folks can be hard to communicate with, in that they are often quite busy.
Perhaps we really agree?
I do agree that all pilots should continue to look for better ways to do things. When I was the project pilot on the S76, we made several changes based on wise and well thought out customer pilot comments/opinions/complaints. For example, the concept of ganging the tail/Intermediate temps on one caution light and the chip on another was thought of by an Air Log pilot, and incorporated by the factory.
I think the operative thing here is to be sure all bright ideas are vetted by folks who are expert in knowing how to properly judge them. Pass on good ideas to the factory, or at least some entity that has the expertise to pass judgement (an STC holder for example). I must admit, the factory folks can be hard to communicate with, in that they are often quite busy.
Perhaps we really agree?
Join Date: Aug 2006
Location: paradise
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
Attn: Mr Nick Lappos
Dear Mr. Lappos,
Was wondering if you, or any other of our learned colleagues on this forum, could assist with a question regarding the S-76.
Primarily of interest is the Collective/Yaw coupling. Should any restriction be felt in the pedals (right pedal) whilst doing taxi turns to the right, with the collective firmly placed at flat pitch.
I recently noticed an aircraft that had the right pedal hitting the stop at approximately 1 inch fwd of the centered position during a tight taxi turn(Is that normal??).
The only way to alleviate this was to raise the collective during the turn.
Correct me if I'm wrong but is there some form of pedal stop in the right pedal.
Thank you
WTF.
Was wondering if you, or any other of our learned colleagues on this forum, could assist with a question regarding the S-76.
Primarily of interest is the Collective/Yaw coupling. Should any restriction be felt in the pedals (right pedal) whilst doing taxi turns to the right, with the collective firmly placed at flat pitch.
I recently noticed an aircraft that had the right pedal hitting the stop at approximately 1 inch fwd of the centered position during a tight taxi turn(Is that normal??).
The only way to alleviate this was to raise the collective during the turn.
Correct me if I'm wrong but is there some form of pedal stop in the right pedal.
Thank you
WTF.
Nick Lappos et al. please excuse me if I'm wrong here, or for jumping in early, but this is normal for the S76. If you attempt a tight right turn taxi off the chocks you're going to drive UP the collective through the interaction of the mixing unit. This happens at the point when the tail rotor hits its stop, and through the feedback interaction of the mixing unit. Hence explains the pedal resistance you noticed in the turn whilst trying to keep the collective down.
Try taxiing forward slowly before commencing a less upbrupt right turn and the collective won't drive up. Either that or turn left.
p.s. most who've seen an S76 collective mixing unit would first wonder how someone was so smart to work that all out.
Try taxiing forward slowly before commencing a less upbrupt right turn and the collective won't drive up. Either that or turn left.
p.s. most who've seen an S76 collective mixing unit would first wonder how someone was so smart to work that all out.
Last edited by gulliBell; 13th Aug 2006 at 12:43.
"most who've seen an S76 collective mixing unit would first wonder how someone was so smart to work that all out."
With slide rules and tables too!
With slide rules and tables too!
Join Date: Apr 2003
Location: 18 Degrees North
Posts: 699
Likes: 0
Received 0 Likes
on
0 Posts
well there is an urban legend that the bloke who designed the mixing unit for the S76 ended up in
(and I'm quoting now) "the nut house"
dont have any information as to the truth of this !
regards
CF
(and I'm quoting now) "the nut house"
dont have any information as to the truth of this !
regards
CF
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
WTF,
I think the symptom as you describe it is not quite right, it should take lots of right pedal before you hit the stop while taxiing at flat pitch, probably more than half the pedal travel, almost to the end. If the right pedal is only 1" from neutral while the stop is contacted, I would think the rigging is slightly off (or the pedals are biased). Where are the pedals at normal cruise, 145 knots or so?
The mixer in the 76 is an interesting bit of kit, it makes the workload lower in normal flight (all Sikorskys since the S-58/H-34 have the mixing) but the lack of any boost servo means the pilot sees the mixing, producing some interesting combinations of control interactions at times. The designer is certainly not in the nuthouse, he is retired now, and his son is a fine engineer for Sikorsky, to boot.
I think the symptom as you describe it is not quite right, it should take lots of right pedal before you hit the stop while taxiing at flat pitch, probably more than half the pedal travel, almost to the end. If the right pedal is only 1" from neutral while the stop is contacted, I would think the rigging is slightly off (or the pedals are biased). Where are the pedals at normal cruise, 145 knots or so?
The mixer in the 76 is an interesting bit of kit, it makes the workload lower in normal flight (all Sikorskys since the S-58/H-34 have the mixing) but the lack of any boost servo means the pilot sees the mixing, producing some interesting combinations of control interactions at times. The designer is certainly not in the nuthouse, he is retired now, and his son is a fine engineer for Sikorsky, to boot.
Join Date: Oct 2003
Location: Over here
Posts: 1,030
Likes: 0
Received 0 Likes
on
0 Posts
What happens on the stick jump test? When we do the flight controls/servos check during the start checklist, we move the pedals and collective separately, and any interaction there is a grounding condition, immediately. Our procedure is that any connection between the pedals and collective on this test means an immediate shutdown and no flight.
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
Gomer,
The stick jump test is performed for two reasons:
1) To see if the servos are mis-timed or misadjusted. This means that if the servos are not well synchronized, one might be fighting another, and so when one is turned off, the other will slightly jump, since it has a coorection input already in place.
2) The pedal/collective feedback -
(2A - one servo turned off) if one side of the yaw servo has a fault where it develops little force (blown seals, etc) it will not move easily while the rotor is turning at low rpm, so when you turn the good side off, this bad side will be harder to move, and the pilot's force on the pedals is more easily transmitted to the collective instead of the (higher force) yaw control system. In effect, the yaw force is "reflected back" from the mixer to the collective.
(2B - both servos on) if the yaw cable system has unusually high force (mis-aligned pullys, misrouted cable) then it will have fairly high frictional force, but might not be felt by the leg/foot when making a pedal check at low rpm. An easy way to detect such friction is to see if the pedal motions cause a motion of the collective, because the collective path "reflected" from the mixer is an easier path for the pedal force to go. Any significant motion of the collective while moving the pedals is a sign that the yaw control system needs to be looked at for the source of the extra friction.
Neither of these conditions happens spontaneously, they usually are the result of maintenance of the controls, so MTP's especially should understand the checks to help diagnose faults after maintenance.
The stick jump test is performed for two reasons:
1) To see if the servos are mis-timed or misadjusted. This means that if the servos are not well synchronized, one might be fighting another, and so when one is turned off, the other will slightly jump, since it has a coorection input already in place.
2) The pedal/collective feedback -
(2A - one servo turned off) if one side of the yaw servo has a fault where it develops little force (blown seals, etc) it will not move easily while the rotor is turning at low rpm, so when you turn the good side off, this bad side will be harder to move, and the pilot's force on the pedals is more easily transmitted to the collective instead of the (higher force) yaw control system. In effect, the yaw force is "reflected back" from the mixer to the collective.
(2B - both servos on) if the yaw cable system has unusually high force (mis-aligned pullys, misrouted cable) then it will have fairly high frictional force, but might not be felt by the leg/foot when making a pedal check at low rpm. An easy way to detect such friction is to see if the pedal motions cause a motion of the collective, because the collective path "reflected" from the mixer is an easier path for the pedal force to go. Any significant motion of the collective while moving the pedals is a sign that the yaw control system needs to be looked at for the source of the extra friction.
Neither of these conditions happens spontaneously, they usually are the result of maintenance of the controls, so MTP's especially should understand the checks to help diagnose faults after maintenance.
Join Date: Sep 2004
Location: Back of Beyond
Posts: 80
Likes: 0
Received 0 Likes
on
0 Posts
Nick,
Several times over the last few years we have had to replace pulley's that were discovered by the procedure you describe in 2b, checking for collective movement with pedal input.
In some cases the bearings in the pulley didn't feel that bad when we physically inspected them, but with the cables tensioned they were creating enough friction to show up on the pedal check.
A great check to give you advance warning of any yaw problems.
Regards.
Several times over the last few years we have had to replace pulley's that were discovered by the procedure you describe in 2b, checking for collective movement with pedal input.
In some cases the bearings in the pulley didn't feel that bad when we physically inspected them, but with the cables tensioned they were creating enough friction to show up on the pedal check.
A great check to give you advance warning of any yaw problems.
Regards.
Join Date: Jun 2006
Location: hot & wet
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
Sikorsky S76B model
I drive an A++ model that sits nose high in hover.... Was wondering if the B model suffers the same problem, as haven’t ever seen them with a nose high attitude....
Any B model drivers able to tell me if the B model has the same problem?? And if the boot mounted Aux tank contributes greatly to this problem??
Any info appreciated
Cheers
Sundance...
Any B model drivers able to tell me if the B model has the same problem?? And if the boot mounted Aux tank contributes greatly to this problem??
Any info appreciated
Cheers
Sundance...
Currently flying the B but have just done the C++ transition training at Flight Safety.
I believe all S76 hover nose high due to the built in tilt of the rotor mast and the high position of the tail rotor. This is so that it flys level at cruise speeds.
If my PoF serves me right the tail rotor and rotor head will align horizontally in the hover. The 76 is designed for the cruise so the tail is higher than the rotor head on the ground. Something like the Lynx, with is designed to be level in the hover, has the tail and rotor head aligned on the ground.
FNW
I believe all S76 hover nose high due to the built in tilt of the rotor mast and the high position of the tail rotor. This is so that it flys level at cruise speeds.
If my PoF serves me right the tail rotor and rotor head will align horizontally in the hover. The 76 is designed for the cruise so the tail is higher than the rotor head on the ground. Something like the Lynx, with is designed to be level in the hover, has the tail and rotor head aligned on the ground.
FNW
Those PT6 engines are heavy, and even moving two batteries into the nose doesn't help the rear cg problem much. This also limits the cruise speed, with so much cyclic used up just to get the attitude level and not much left to go forward. 
The early A's weren't too bad, although they had a bit of a nose up hover attitude, but the Arriel installation puts the engine mass nearly a foot further aft than the C30's. The engine bay cover also shifts the CG further aft: the early C30 engine bay cover was a one man operation, but the extra weight of the Arriel bay cover made it into a two man job to open/close.
The first A+ I flew was so tail heavy, we had to fill the nose flotation bag bays with lead weight to bring the CG into the approved range
The first A+ I flew was so tail heavy, we had to fill the nose flotation bag bays with lead weight to bring the CG into the approved range