Use of AFCS in USL

[Shawn Coyle]

For those of you lucky enough to have some form of AFCS and who are involved in lifting Underslung Loads, I'm curious to know what level of stabilization you use. If you can turn off the force trim, do you turn it off while leaving SAS on, for example.
I'm looking for information for an upcoming vertical article... (no names will be used to protect the innocent/ guillty.)

[JohnDixson]

Some background on an aspect of your subject.

The CH-54 community had noticed that the AFCS could, sometimes, be de-stabilizing. Pilot out of the loop ( i.e., hands off the cyclic )

I think it was about the time the CH-54B arrived that two of our very sharp AFCS engineers conceived the idea of a dynamic AFCS " Load Stabilization and Precision Hover System. The Program Office proposed it to the Army and they funded the design and flight tests, all of which were quite successful. Loads that went unstable above 35-40 kts could now be flown to 80. May not sound like much, but now, one had an IFR capable machine with that load. Principle behind the load stabilization system was sensing cable angle at the Cargo hoist and timing the corrective signal. Precision hover was based on a ground contrast electronic signal. Remote control of the helicopter was provided thru a hand held model airplane type device, so that a ground controller could put the load exactly where he/she wanted it.

The Army decided not to incorporate, but lo and behold, when the Boeing HLH model was designed, the SA tested system was provided to Boeing ( The Army owned it, after all ).

As I recall, there had been one horror story from Vietnam about a night CH-54 sling load of a D-8. The weather was lousy and the load got to swinging. Attempts to pickle the load via the electrical hook release failed. The cable cutter charge did not fire. The Crewchief attempted to use his M-16 to break the cable as it swung ( shooting out the door of the " back porch ", as it was called. No joy there. Eventually the pilots got down close enough to land the load in a situation where the issue of whether they were flying the load or the load was flying them was open to argument. They rolled it up in the landing, but all survived.

One of the engineers, Don Fowler, may still be working at SA and you might try chasing him down.

Good luck in your endeavor,
John

[oleary]

Hi Shawn,

Well, that's a topic all right :ooh:

I have a bit experience night (uhhh, sort of) slinging in the Okie Arctic days and here is what we learned.

Sperry IFR Bell 212 with coupled FD. Heli 1&2 always on (obviously) and most of us would use HDG and ALT if the load was reasonably stable, FD off otherwise. Force trim off for takeoff and landing.

I should note that if the AIPs weren't kept fairly close to centre you could get what APPEARED to be a "partial hardover" (yeah, I know) with a swinging load. It wasn't of course, it was just the actuator reaching the limits of its authority. Many loads were dumped over this problem.

Sperry IFR Bell 212 without coupled FD. Heli 1&2 always on. Force trim off for takeoff and landing. Same note as above - just touch the force trim button momentarily to centre the AIPs and the problem goes away.

Bell IFR 212 - SCAS always on, use of AFCS seemed to be more personal preference. I found most loads could be better flown SCAS only. Force trim off for takeoff and landing.

S76 - AFCS always on. Force trim off for takeoff and landing.

S61 - AFCS always on. Force trim off for takeoff and landing.

I must say that night slinging in the Arctic for 8 years was one of the most enjoyable jobs I have ever done :)

Finally, I have flown with guys who like to daytime vertical ref with force trim on and some, like me, who prefer it off. Personal preference I reckon. AFCS always on, of course.

Cheers,
Jerry Cutler

[John Eacott]

Shawn,

Going back into ancient history, we used the Sea King for a lot of sling load in the early years: selling the machine to the world, as it were. Water purification plant material out to Lan Tau island (yes, what's now the airport) included an air portable bulldozer, Phantom Spey engines from Gan and the AFCS was just another piece of kit to be used when suitable. I even did a GCA IMC with a Mk46 torpedo underslung with the AFCS used as per normal feeding into the approach path. Maybe a current junglie could elaborate on what they do now: USL is part of their DNA ;)

S76 was fairly benign for USL, and we only had the early Sikorsky lashup but had no issue with engaging what we had to assist in the cruise.

Bell 212 much as oleary has described, but helitack work you are too active to need anything but SCAS. Firebombing is, after all, an extension of underslung load work.

Force trim is, as you said, a personal preference but sometimes it is an integral part of the kit and the coolie hat trim works overtime: sore thumb at the end of the day :hmm:

[Boudreaux Bob]

Helicopter Operators on the North Slope of Alaska did night IMC Underslung work for decades using 212/412's. The aircraft had both Sperry and Bell SCAS systems.

[oleary]

Helicopter Operators on the North Slope of Alaska did night IMC Underslung work for decades using 212/412's. The aircraft had both Sperry and Bell SCAS systems.


Yup, we did the same in the Beaufort Sea (just a bit to the east) for years as well using 212/61/76's. IFR slinging was not approved in Canada at the time so we just turned the landing lights out at 200 feet on the way up.

And any stories of people shooting S61 ILS approaches into Inuvik with slingloads are, ummmm, ... probably not true :oh:

[drmondo]

CH-146 (Bell 412CF) best practice was APs on (either SAS/ATT), FT on or off, but to press and hold FT release on initial pick-up and/or whenever the load started to oscillate in flight (press and hold FT release combined with a gentle turn usually did the trick).