Stability Augmentation System

[tacks]

Hey guys,

does somebody know, which type of helicopter was equipped with a 'SAS' first ?!?

[Lu Zuckerman]

I may be wrong on this but I believe it was the Apache.

:E :E

[C4]

First puma's had it..

[NickLappos]

tacks,
I'm not sure if it was a first (though I think it might be), but the SH-34J back in the mid 1950's was equipped with an automatic approach auto hover system. I note that Hamilton Standard had an electronic stability system in 1955, according to several web sites that describe the Hiller H-12 and FH-1100.

[PPRUNE FAN#1]

My father tells me that the Piasecki HUP-2 had SAS long before his squadron got the HSS (H-34).

[RDRickster]

Brantly developed, tested, and flew a light SAS in their B2B several decades ago. Needless to say, it never went into production. One of their current dealers in North Carolina is rebuilding / improving the same SAS in an attempt to make the B2B a SPIFR ship.

Jerry Toms (click to e-mail) ([email protected]) was one of their engineers back in the day, and he's the manager at East Carolina Helicopters (click for website) (http://www.eastcarolinahelicopters.com/). He can give you the specs and dates of testing. I don't have any other details, except to say that there is no doubting his engineering skills.

[NickLappos]

pprune fan#1 is right, here is a site that says the HUP-2 in the late 40's had a full asw autopilot! That is darn early, and just might qualify as the earliest "sas"

http://www.dvhaa.org/hup-2.html

"Early into production, an autopilot and dipping sonar were incorporated into the design, making the HUP the Navy's first Anti- Submarine Warfare helicopter. ASW technology was in it's infancy at the time, and in 1952 production shifted to non-ASW capable HUP-2's, or "Retrievers", as they were now nick named."

This site says it was a Sperry Autopilot, fitted to tame the tandem's very unstable characteristics:

http://www.helis.com/UpTo50s/h_h25.php

[SASless]

Nick Dear Chap:

Tandem rotor helicopters are not "unstable"....they just seem to be in a constant state of confusion as to which rotor head goes in front unless there is a referee of some sort. SAS....being a mechanical thing....and programed to "think"....does a very good job of mediating the feud whereas mere mortals soon grow weak and despondent after putting up with the divergent views. The
Chinook...particularly the "A" model with the sharp tail (vice the square tail of all other models)...was a particular delight to fly "SASless"....(all these years and I finally found a way to name drop!) As a fledgling Army Instructor Pilot....I in a very weak moment....snapped off the SAS on a transition pilot...immediately had my hat blow off from the 100 knot draft that developed as the old girl tried to swap ends ...the sound of the droop stops pounding themselves to death somehow awoke the new guy from his slumber.....as did my pushing the pedal to the stop and wishing it could go another foot or two. After pausing to get my heart started...and start breathing again.....I explained the concept of yaw control in helicopters to the Nimrod....and swore never ...never ....never do that again.:D

[Lu Zuckerman]

The HSS-1 and later the H-34 had an Automatic Stabilization System (ASE) that was based on the Lear auto pilot that was originally installed in the North American F-86. On the Navy version it had Barometric hold in that it would maintain a fixed altitude. For SONAR dipping it had hydrostatic sensor in the SONAR ball that would maintain a fixed depth for the SONAR ball. In heavy waves as the water pressure changed the helicopter would ride up and down with the waves. It also had a directional hold and it had the capability of maintaining a fixed attitude, which was in reference to a fixed cyclic position. It also had sensors that detected movement of the SONAR cable due to moving water current. These sensors would send a signal to the ASE and it in turn would move the servos to make the helicopter move with the current keeping the SONAR below the helicopter. In essence it was an autopilot but it had no SAS/SCAS capabilities. If as Nick said it had auto hover capability I don’t know, as this inclusion would have been made long after I left the program.

On the Apache the normal control inputs by the pilot into the servos was by mechanical push-pull tubes into the mixing unit and then into a servo pilot valve that moved in relation to a fixed servo valve spool. If the pilot moved his controls too quickly LVDTs attached to his controls would send a signal monitored by the control section of the air data computer. If the control movement were sufficient enough to cause heavy stresses in the airframe this signal would be processed and sent to the SCAS servo, which in actuality is the spool on the servo. The spool would move in relation to the pilot valve and in effect moderate the pilots input so the end effect was a smooth input and not causing overstress of the airframe.

If for any reason any control lane became jammed the pilot would force the control until he broke a shear pin. In doing this, two micro switches would be enabled causing the mechanical input to the effected servo to be locked out. Then, any movement of the controls would send a corresponding signal from the LVDTs through the air data computer and then to the SCAS servo valve moving the spool in relation to the fixed pilot valve resulting in the correct movement of the servo. This is a SCAS. Many commercial and military aircraft have similar control systems. I believe the concept was developed by Bertea.

I do not believe the other systems described are the same.

:E :E

[heedm]

Tough one to dig up, but with the high workload in a non-augmented tandem, it seems reasonable that those would be the designers that first had a reason to pursue augmented helicopter flight.

Bit of research and I found that the HUP prototype first developed in 1948 flew with a Sperry Autopilot to develop the HUP2 without the large rear stabilizers. I couldn't find the date on that test, but the paper, "Piasecki Test Autopilot System" was released some time in 1951. In June 1951 Meyers, Donald N. and Vanderlip, Edward G. published “Helicopter Stability via Automatic Control,” in Aero Digest, vol. 62, no. 6.
____________

SASless the SAS control switch in the H46 I flew was identical and very near the windshield wiper knob. One IP would occassionally play the uncooperative FO. Flying in moderate rain, I asked him to turn on the wipers, instead he turned off the SAS. Definitely recommend doing this only to experienced pilots, I could handle the SAS Off well enough, but learned a lesson in supervision.
____________

Of course, the horror stories of non-augmented flight in a tandem mostly apply to new pilots. Transit, IF flight, rescue sequences, etc are all possible albeit with a very high workload (Cooper-Harper of 8 or 9).

[tacks]

dear gents,

thank you for your replies.
I'm quite amazed that a heli was that early SAS-equipped !!!
My personal guess was the SA 340 Gazelle (developed in the late 60's), but this seems to be a bit out of range.

Tacks.

[Lu Zuckerman]

If by definition you are trying to determine what helicopter was first with some sort of stabilization then it was an HO3S1-G in the US Coast Guard around 1949 or possibly earlier. What they did was attach an airfoil to the swashplate, which stabilized the swashplate in any position the pilot set it in. In the configuration of that HO3S the flight controls had jackscrews which had some degree of reversibility which allowed feedback to the cyclic. The airfoil helped to dampen the feedback forces by stabilizing the swashplate.

:E :E

[Helipolarbear]

My father tells me that the Piasecki HUP-2 had SAS long before his squadron got the HSS (H-34).

Pprune Fan #1 gets my vote. The 'Piasaki' Banana had the first real SAS system in heli's. Lu Zukerman: You are correct, the SCAS on the AH-64 is different than SAS. The wind excursions, yaw excursions etc are effected differently, and not just from gyro inputs. A distinguishment of modern SAS can be found on the level of Airspeed Data inputs and sensitivity. B430 has A/S data input. B222 does not have effective input below approx 60KIAS. If you have total SAS failure, regardless of Heli type, shake the stick in very small movements in the effected axis...and nobody in the back will notice!!!!!:p

[Shawn Coyle]

Slightly off topic, but I just flew an AFCS fitted to a R-44. Quite nice, took about 3 minutes to get used to, and transformed the machine.
More in the article in Helicopter World coming soon.

[Helipolarbear]

Sounds like an expensive addition to an R-44....WHY??
Should be an interesting article!;)

[chuckolamofola]

Anyone remember the old IFR Bell 212's, they had SAS in them. You could always tell the IFR birds by the big dorsal fin on top of the cockpit roof. I understand that Bell later allowed the operators to remove this fin. I don't think these were coupled auto pilots but only stability systems. They may have been designed in the sixties or even earlier as I first worked with them in the late seventies. I also may be remembering the name wrong it could have been SCAS as I think about it.

Chuck

[John Eacott]

Chuck,

Yes, the 212 had/has SCAS, + AFCS. The dorsal fin was a PITA for pre flights, getting nicely in the way, and was (IIRC) an FAA requirement. We had one in the Brent Field, the other three 212's were all CAA certified without the fin.

Out of the four 212's we had, one had the AFSC release on the cyclic in a different position to the other three. Needless to say, that was the one that gave me grief one dark miserable night off Sumburgh, so when I "trim released" for a panic turn for home (after the float bottle head exploded) I knocked out the lot and slightly compounded my problem :rolleyes:

Funny how I don't miss the North Sea ;)

[teeteringhead]

Depends how you define terms, I suppoe the question implies ELECTRONIC SAS ... arguably the Bell stabilizer bar was a Stability Augmentation System on the classic teetering head.

Certainly if the dampers failed, it got so darned stable it would only reluctantly move out of a hover IIRC!!

[Shawn Coyle]

Price is obviously one of the interesting points. Suffice to say that the price is commensurate with the aircraft type - and probably low enough to make it attractive even for the crowd that flies the R-44.
I'm not going to quote a price now, as it's not finalized, and the FAA is making strange noises for certification of same.