1977 Bell 212
 

I delivered a friends 1977 Bell 212 the other day and was checking out the SCAS system. My previous time had been in a USMC UH-1N where we had both RadAlt and Baro Alt hold and AFCS.

In the helicopter in question I noticed the SCAS did its expected job of stabilizing the flight characteristics while above 40 kts. When I switched each channel to ATTD I did not notice any difference, nor would it would it hold a heading, pitch or yaw. The console panel had no effect either. The system checked out on the ground according to checklist procedures. Any thoughts?

Are you sure you operated it right?
Sorry for asking-but sometimes it´s just "finger troubles"…

The system had a "1 or 2" flight director mode-for each pilot?

Was it operating in the right mode (e.g. "2" if you were flying from the right seat)?

The ATT itself doesn´t do much-it just "freezes" the stick, and is supposed to maintain the aircraft attitude….only the operating modes (ALT, VS, IAS, HDG…..) will do the "work"….

Was it a Bell AFCS which gives you attd hold but there is no alt hold , heading hold or nav function.
Basically a glorified SAS but most useful for IFR.
Or was it a Sperry system? There was a "full Sperry" which had all the bells and whistles and the "1/2 Sperry" which was basically equal to the Bell AFCS.

There are some 212s which had a Sperry panel with all kind of options alt, hdg, nav ect but none worked and the placard that said they did not had long ago disappeared.

Long time ago but I am sure someone will be along with knowledge and truth directly.

Is this the one you´re talking about that has the two "wheels" on the panel as well?

The one "wheel" for adjusting pitch, the other one for bank?

The name gives you a big hint:

SCAS = Stability Control Augmentation System. It is NOT an autopilot, all it does is give some extra stability to allow 2-pilot IFR. One to fly (with a bit of electronic help) and one to monitor the instruments.

Yes, I selected "Pilot" (did not have #1/#2 option) flight director. SCAS checked thru the "No Go" checklist, green lights when engaged and flew as advertised, but when each ATTD channel was engaged there was no change in flight characteristics and no associated control of the axis. I am thinking the system could be corrupted (inop) but wanted to check with regular users.

Yes, it is the basic Bell AFCS with pitch and roll wheels and a yaw dial. While I realize it is not an auto pilot I was surprised it would not "hold" the cyclic in a static position. Let go of the cyclic it slowly fell off center (roll right, pitched down). Checked the wheels on the panel, no difference. Also the coolie hat on the cyclic provided no difference in axis control.

Did you have the force trim switched on?

That was exactly my thought as well the moment i read this…

:D

Adding Friction to the Cyclic is also a "Must". On the Sperry system there is a preset minimum Friction.

A question....in ATT Mode....did the two trim wheels get a reaction when moved back and forth? Did the Turn Knob....push and turn....left and right...get a reaction?

When the system is operating correctly in ATT mode...you can "fly" the machine with those control "Wheels" and Turn Knob.

Force Trim must be on as I recall.....and Trim Release not depressed.

The Attitude Reference can be re-set by means of the Force Trim Release and moving the Cyclic to the desired position....and re-engaging the Force Trim by letting go of the Force Trim Release Button.

As indicated by others....the SCAS will "hold" a selected Attitude with minor adjustments being made with the two Trim Wheels and Turns being made by use of the Turn Knob. Major changes in Attitude Reference requires the use of the Cyclic and Force Trim Release.

OK, now we getting somewhere. In the cockpit there was an abbreviated checklist and prior to take off two items that surprised me: SCAS-On, Force Trim-Off. Earlier in checklist it had Cyclic Friction-Off.

Now reviewing the AFM checklist does have Force Trim On prior to take off but nothing addressing Cyclic Trim to be set to any amount of friction.

So for normal ops: Force Trim-On and a medium amount of Cyclic Friction. On the cyclic I have both a Force Trim button and an AFCS release button (the same thing as Control Wheel Steering on fixed wing?), push, reset attitude, release and it will hold new attitude?

You got it!

Friction dampens any PIO from vibrations and other movements of the aircraft. Force Trim-ON sets an Attitude Datum until you over ride it by depressing the Force Trim Button and moving the cyclic. Set the Cyclic position you want, let go of the Stick Button and let the SCAS do the work.

Make your minor adjustments using the Pitch and Roll Trim Wheels.

Turns can be made by pushing and Turning the Turn Knob.

In SAS mode the SCAS will only "stabilize" the aircraft but not "Hold" an Attitude.

Outstanding, thanks to BB and the others on this thread. A/C will not vome out of annual until late August, will let you know.

Try this Download.


http://www.aavnc-school.com/ftd/rftb...fr-fm-1-03.pdf

This is good as a reference but of course your Aircraft should have the most up to date RFM with all the pertinent Supplements and Updates.

As you read down through the Checklist Items you will see where it states FORCE TRIM-ON and Cover Down.

It also states Cyclic Friction-As Desired (Add just enough that you can feel a small bit of resistance to movement)

Later on it takes you through the Functional Check of the SCAS.

"Boudreaux Bob voted #1 resaon for misspent company time" :ok:

Thanks a lot for that upload Bob, made a very good reading during uhmm, extended lunch break. Although I - as a newbie (Hu269 only) - did not get the effective difference between AFCS and SCAS in flight. From reading the preflight checks they seem to be "either or". :suspect:
The wording regarding AFCS while on the ground insinuates that AFCS is an mathematically integrating closed loop, slightly adding control input as long as the AFCS-perceived "desired attitude/bank" is not reached, hence the risk of it maneuvering the controls to their respective stop when active while on the ground. That sounds like automatically held attitude to me.:8

I'd like to find out what pure SCAS mode (AFCS off) is doing for the pilot.
You don't happen to have a Bell AFCS/SCAS training manual/behind the scenes documentation you could upload :E

TIA
P.

For an autopilot to work, the force trim has to be ON, or else the A/P has no "grip" on the cyclic. It would be trying to make inputs, but without force trim, there is no connection to the stick.

Cyclic friction makes it harder for the A/P to move the stick, so I always set the cyclic friction OFF.

For any AFCS (in the broader sense of the word), to work, the Force Trim must be on, or the actuator will move the cyclic in the cockpit instead of the mechanics downstream to the rotor head.
I've never had any difficulty flying with force trim on all the time even in OH-58A/C or Bell 212. Wish the Jet ranger had it as basic kit, and we'd avoid a lot of later problems adapting to more complex machines.

Quite! See my SNS EC-155 comments...

OK, have been off the grid for a couple of weeks since I brought the 212 down from Sandpoint.
First, Bob thanks for the link to the Manual. The full Bell checklist is better than my NATOPS.
Second, while I understand Force Trim-On in flight mode, it makes implicit sense and I did not understand why FC-OFF was in the checklist, I have to ask why do you want some light cyclic friction... doesn't that just make AFCS work harder? Or is the AFCS working "behind" the cyclic?
Third, I understand there is no collective friction in this setup, but in flat pitch to hover the collective movement is "sticky", it is difficult to make a slow smooth pull. Is that normal for this configuration?
Fourth, any scoop or tricks to filling the port aux fuel tank faster than slow gravity feed?

Thanks for the assist. Richard

Light friction is always a matter of choice to suit flying FT off, whatever the machine. The AFCS is doing just as you say, working 'behind' the cyclic to move the jacks. It doesn't move the cyclic.


No: I'd suggest that either the collective friction is on too tight or the collective control run needs some maintenance. When you say "there is no collective friction in this setup" have you inadvertently forgotten the normal collective friction further down the stick from the twist grips?


The port aux tank is effectively waiting for the fuel to work its way across from the stbd filler point. Unless you can find a bit of sloping ground to raise the stbd side, or even use the ground handling wheel on the stbd side, it will be a slow fill. Don't forget to open the interconnect ;)