Sikorsky S-76: Ask Nick Lappos
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A quick Google search turned up the following, which provide rather brief overviews, but may be of some help:
http://www.faa.gov/ATPUBS/AIM/Chap10/aim1001.html
http://www.freepatentsonline.com/7108232.html
AFAIK there is nothing on the Sikorsky site. It's rather sparse.
http://www.faa.gov/ATPUBS/AIM/Chap10/aim1001.html
http://www.freepatentsonline.com/7108232.html
AFAIK there is nothing on the Sikorsky site. It's rather sparse.
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Mart,
The Sikorsky web site has a pretty detailed 22 page brochure that is written by the technical marketing people, and is very accurate, but it does not have system descriptions. The Flight Safety training manual or part 2 of the flight manual have good descriptions of the systems. I searched on eBay but didn't find any. Perhaps a ppruner would let you copy his/hers.
The Sikorsky web site has a pretty detailed 22 page brochure that is written by the technical marketing people, and is very accurate, but it does not have system descriptions. The Flight Safety training manual or part 2 of the flight manual have good descriptions of the systems. I searched on eBay but didn't find any. Perhaps a ppruner would let you copy his/hers.
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Gomer, thanks. Patents give a pretty good idea of what system would look like.
Nick, downloaded brochure - i'm in the wrong business!
Am i right in understanding that this system gives virtually hands off hover stability, wih the trim-switch providing hands off airspeed stability?
Mart
Nick, downloaded brochure - i'm in the wrong business!
Am i right in understanding that this system gives virtually hands off hover stability, wih the trim-switch providing hands off airspeed stability?
Mart
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Mart,
The current S76 stability system is a Honeywell SPZ7600 with a few Sikorsky enhancements. It has basic stability, attitude hold, airspeed hold, rate of climb hold, nav tracking and (with the SAR kit) auto approach, hover hold and rear crewman hover position trim. These capabilities are found in many of the top of the line helos these days, frankly.
There is an older system on many A's and B's that is a basic stability system (so-called SAS II). It does not nav track nor does it do automatic pproaches, but its flight handling and stability is mighty fine.
The current S76 stability system is a Honeywell SPZ7600 with a few Sikorsky enhancements. It has basic stability, attitude hold, airspeed hold, rate of climb hold, nav tracking and (with the SAR kit) auto approach, hover hold and rear crewman hover position trim. These capabilities are found in many of the top of the line helos these days, frankly.
There is an older system on many A's and B's that is a basic stability system (so-called SAS II). It does not nav track nor does it do automatic pproaches, but its flight handling and stability is mighty fine.
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Thanks Nick, i'll do some reading up:
SAE Tech Paper on Honeywell SPZ 7600
My head is still reeling from that Nr control system patent...
Mart
SAE Tech Paper on Honeywell SPZ 7600
My head is still reeling from that Nr control system patent...
Mart
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Brett Eddy was one of the design engineers on the system, I flew with him back in 1982 or so when Sikorsky and Sperry teamed up on the EFIS/DFCS. He and his coworkers are great guys!
Still, I recommend that you find an S-76 pilot who would lend you his FSI training book, you could Kinko's it and have a great resource.
Still, I recommend that you find an S-76 pilot who would lend you his FSI training book, you could Kinko's it and have a great resource.
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T/R driveshaft Failure
Hi Nick...
Just finished my annual C+ refresher training at FSI in Palm Beach... A tailrotor driveshaft failure in the Sim is a fairly violent maneuver with no option except immediate autorotation with one engine off and other at idle (for a gen)... the RFM seems to imply that flight may be possible with such a failure ("...autorotate if necessary to control yaw")... The Sim instructor told us there is no way you can fly with a T/R failure... it is a Sim thing
My question.... during 76 development was this failure actually flight tested or is it computed mathematically?
Just finished my annual C+ refresher training at FSI in Palm Beach... A tailrotor driveshaft failure in the Sim is a fairly violent maneuver with no option except immediate autorotation with one engine off and other at idle (for a gen)... the RFM seems to imply that flight may be possible with such a failure ("...autorotate if necessary to control yaw")... The Sim instructor told us there is no way you can fly with a T/R failure... it is a Sim thing
My question.... during 76 development was this failure actually flight tested or is it computed mathematically?
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Flap,
What was the initial airspeed and GW just before the failure? Sounds like low speed and high weight.
IMHO the yaw will be very bad, and down collective is the only cure. Remember, there is no difference between down collective zero torque and autorotation, as far as an anti-torque failure is concerned. Cutting throttles is cleanup work, frankly. It is the down collective and the zero torque that does the work.
I wrote those words that you quote, and the intent is that under some circumstances, you could stabilize in a down collective descent at zero torque, and then if you were feeling frisky, you could sneak in some torque to see if the yaw could be controlled with bank. It is possible at lighter gross weights that you could steady out at 1000 fpm powered descent, and stretch your glide out considerably.
The sim sounds right, the older A sim allowed one to fly out of a tr failure in a hover - pure fiction, I think.
All my comments are based on work with the Sikorsky research simulator (a vastly more valid thing than any training simulator - but still a simulator. The day someone proposes that we blow off the TR as a test, you will see TP's flying with guns strapped to their sides!
What was the initial airspeed and GW just before the failure? Sounds like low speed and high weight.
IMHO the yaw will be very bad, and down collective is the only cure. Remember, there is no difference between down collective zero torque and autorotation, as far as an anti-torque failure is concerned. Cutting throttles is cleanup work, frankly. It is the down collective and the zero torque that does the work.
I wrote those words that you quote, and the intent is that under some circumstances, you could stabilize in a down collective descent at zero torque, and then if you were feeling frisky, you could sneak in some torque to see if the yaw could be controlled with bank. It is possible at lighter gross weights that you could steady out at 1000 fpm powered descent, and stretch your glide out considerably.
The sim sounds right, the older A sim allowed one to fly out of a tr failure in a hover - pure fiction, I think.
All my comments are based on work with the Sikorsky research simulator (a vastly more valid thing than any training simulator - but still a simulator. The day someone proposes that we blow off the TR as a test, you will see TP's flying with guns strapped to their sides!
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S76C++ RFM info
Hey all:
In continuing my analysis for a replacement to the 76A, I am looking for the RFM supp for Cat A Ops for the C++. Also, looking for HOGE charts for same.
any help would be greatly appreciated.
Wde
In continuing my analysis for a replacement to the 76A, I am looking for the RFM supp for Cat A Ops for the C++. Also, looking for HOGE charts for same.
any help would be greatly appreciated.
Wde
S76 ground taxying, old age and stress
I noticed that the S76, when ground taxiied, appears to have a castoring nose wheel, not controlled by the feet pedals. Am I right in assuming that this means the aircraft, when ground taxiing, turns by the tail rotor 'pushing' the tail in the opposite way to the way in which you wish to turn, and in doing so, wouldn't it create a considerable stress on the tail? I would have thought that the forces involved to push a 76 tail hard enough to get the nose to change direction, over a period of time ie 20years plus of use, would lead to stress of the tail. Can anyone tell me how correct my thinking is on this one? Any known defects/cracks in S76 tails in the past?
Thank you.
Thank you.
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You are correct about how it works, but I regularly fly aircraft more than 20 years old, and have not seen nor heard of any cracks. Moving a weight that is on wheels is really very easy, and it doesn't take that much force to turn an S76, plus the tailboom is pretty beefy, at least in comparison to many other medium helicopters. The tail rotor exerts a lot of force just preventing spins in a hover, regardless of the model, and turning while taxiing isn't a big deal.
Avoid imitations
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Although it's not unusual to have a castoring nosewheel on helicopters, there certainly IS a history of tail pylon cracking on some S-76s.
I know of one UK based aircraft that came very close indeed to complete structural failure of the pylon, far too close for comfort.
There is a strengthening mod available, also a scheme to fit the pylon with inspection panels.
I know of one UK based aircraft that came very close indeed to complete structural failure of the pylon, far too close for comfort.
There is a strengthening mod available, also a scheme to fit the pylon with inspection panels.
Turns on a circle tho
I dont know yet any helicopter on wheels without castoring nose or tailwheel. The steering is always? done with tailrotorthrust supported with differential brakingaction on the mainwheels.
The 76 nosewheel also castors through 360 degrees, and the only limitation is on retracting the gear when the nosewheel is pointing backwards.
Much better than the A109 with its restrictive nosewheel turning limits.
Much better than the A109 with its restrictive nosewheel turning limits.
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The forces on the tail cone on the ground are peanuts, it typically takes just 50 to 100 pounds of thrust to turn the S76, and the tail rotor can develop over 600 pounds. The tail cone's highest stress maneuver is the "yaw kick" maneuver, which is imposed on the design by FAA regulations. It is an assumed full throw of the pedals at Vne, and not a pretty picture. Do not even think about doing one!
Airframes are usually designed to extreme maneuver loads like that one, or crash loads that involve up to 20 G's. Therefore, taxi loads are just peanuts.
BTW the cracks some S76s have exerienced on the vertical pylon are due to long term tail rotor balance issues, because the loads are low but the frequency is high (about 50 Hz) so that many cycles build up over time.
Airframes are usually designed to extreme maneuver loads like that one, or crash loads that involve up to 20 G's. Therefore, taxi loads are just peanuts.
BTW the cracks some S76s have exerienced on the vertical pylon are due to long term tail rotor balance issues, because the loads are low but the frequency is high (about 50 Hz) so that many cycles build up over time.
Nick
I could not beleive what I read from you on the "yaw kick". Is this actually done in air or just computer simulated? Sounds like this is when TP is earning their money!
What about mast moment during this maneouver?
CB
I could not beleive what I read from you on the "yaw kick". Is this actually done in air or just computer simulated? Sounds like this is when TP is earning their money!
What about mast moment during this maneouver?
CB