The brake steer comparison is an interesting one. Maybe a little challenge then, to ponder over during next coffee break:

Say you have a skid steer tracked vehicle. The steering is controlled by two levers in front of you, left for left right for right. The question is would you expect to pull or push the levers to apply that steer brake?

The question is not loaded, and there are no right answers. I'm just trying to apply the control system out of context - that way there are no preconceptions. :ok:

Mart

Grav,
As kids, we learned to use left foot push for a right turn on the "Flexible Flyer" sled. Carts are set that way sometimes also.
When I moved on to gliders my brain had to relearn, and that is harder than when you are young.
Ultralights often have reversed controls, with the simple cart type nosewheel.
The stick is reversed on weight shift ultralights as well!

Slowrotor, thanks for your thoughts.

Being a dumb engineer i'm lucky that i can usually picture a simplified model of a system in my head. It's quite a powerful technique for learning new things quickly, and to be honest i would be astonished if any heli pilot didn't use similar tricks - particularly from the detailed level of technical knowledge that appears on this forum.

There are two lines of reasoning when the control gets more complicated, as clearly it does in a helicopter. Either the machine should only be controlled by those able to grasp the (at times) the more subtle details of the dynamics involved, or the machine should be designed so that there is no control complexity. Being a design engineer i frequently find myself having to ask the question what is the driver (or pilot in my interest of choice) expecting from this control system. This applies equally to hydraulics, electronics or mechanical systems.

It is with this in mind that i am interested in thoughts about pedal direction. Truthfully, it is an unfair question to pose on a forum intended for aviation professionals, since the natural reaction will be "i figured it ok". :ok:

Mart

There are several things being discussed here.
To keep things straight - a SAS system (like the UK military Gazelle Mk2 and 3) will have a short term heading hold below a certain airspeed (in this case 40 knots). It is pretty simple - when you don't move the pedals, it holds heading reasonably well for a while. When you move the pedals, two small 'switches' open - one for pedal movement, and one for yaw rate. The pedal movement switch stays open as long as the pedals are moving - when the pedals stop, the switch will close a couple of seconds later. When that switch closes, the yaw rate switch waits till the yaw rate drops below 2° per second, and then it closes. The logic is that the pilot isn't moving the pedals, and the yaw rate is pretty low, he must want to hold this heading. It will damp out yaw rates, and try to hold a steady heading, but will enventually drift off heading.
But it won't work above 40 KIAS and it won't hold heading forever with just the simple yaw series actuator.
If you can understand this system, most of the rest are easy to understand.
Above 40 to 60 KIAS, most systems will revert to turn co-ordination (not the Gazelle).
A huge help in controlling a helicopter, and should be considered for every light machine.
I hear that Chelton is coming out with a system for the R-22 and Bell 206 that is pretty nifty.

Slowrotor, i'll have to reconsider pedal direction at some point in the future. Last post developed into a bit of a rant, but not specifically aimed. :ok:

Shawn, I'll keep an eye out for that Chelton system. Interesting that the Gazelle system does not try to modify pedal input.

Mart

Graviman:
When the pedals aren't being moved, the SAS will make small adjustments to try to maintain the heading. Uses a series actuator, which doesn't feed back to the cockpit controls.
Like everything else, you need to know how to use it, and have someone demonstrate how it works.

Shawn,
Is it not a little misleading to say that SAS tries to maintain heading? Surely the Yaw SAS (as with SAS in the other axes) is simply correcting short period divergence? This has the consequence of appearing to maintain heading, but is a secondary, rather than a primary, effect. True heading hold (and the reason the Gazelle would not have turn coordination) requires an outer loop AFCS function which requires parallel trim actuators (which do move the controls).

Not teaching Shawn to suck eggs (He's forgotten more than I'll evevr know about AFCS systems!) but trying to keep the discussion pure for those less familiar with SAS etc.

212man:
You are correct- all it does is damp out rates, and tries to return to the original heading.
True heading hold classically needs a large authority actuator, but I think if you could look at the Apache AFCS, you'd find it does everything, including hover position hold, with only a series actuator, so an open mind is always necessary.

Wow: could make for some interesting actuator runaway conditions!

From my experience in a BK117 (with a SAS in Pitch/Roll and Yaw), a SeaHawk and SeaKing (with full AFCS) , a SAS will only dampen the divergence and the yaw will definitely not hold its heading (it could be me but the darn thing always wants to go left). The AFCS aircraft will hold its heading even from takeoff (SeaHawk much better that the older SeaKing) and have a heading hold in flight.
The SAS yaw takes all the twichiness out of the tail in the hover - quite remarkable when we switch it out for training.
On the other thread with regards to which pedal push to turn, didn't the Commanche do some trials with a side controller that, in addition to pitch and roll, it had a twist function to take care of the yaw?

The B206 in FS9 is a game, not a sim. The B206 in FSX is a joke. If you want a realistic helicopter in FS9, purchase the Dodosim Advanced 206. It is THE only heli for FS that models VRS, rotor droop, accurate autos, LTE, and torque properly (or at all in the case of VRS, rotor droop, and LTE).

If you want some real heli flying in the sim go over to http://hovercontrol.com and register in the forums. You will find a wealth of knowledge, and a great community.

Sunnywa, this is the spirit in which i ask about pedal direction. I accept that most pilots adapt very quickly to "left means left", possibly after those famous words "I have" ;) . What i am really trying to establish is whether Igor Sikorsky was right to reconsider pedal direction from an intuitive ergonomic perspective. Perhaps handle bar yaw control would only be right with a handle bar and foot pedals, then again rear steer is also quite a strong cue.

Shawn, does yaw suffer from a short period oscillation by itself? If the problem was dutch roll wouldn't cyclic SAS series actuator sort this out, as well as hover stability?

Mart

Mart,
a SAS will sort out 'dutch roll' using yaw and roll damping. The EC-155 only has a secondary SAS for this very reason. The initial intent was simply to certify it with the AP (which also has a SAS function imbedded, obviously) but the certifying authorities were unhappy that in the event of an AP failure in some phases flight (high power climb) the divergent dutch roll mode would be problematic. There is therefore a secondary SAS, activated with a cyclic buton, for the case of an AP failure. It only operates in roll and yaw: pitch remains undamped, but is naturally so stable it is not a problem.

You should avoid confusing the type of actuators used: a SAS uses series actuators, which are high speed limited authority. Parallel actuators are low speed high authority, and are used for attitude retention and outer loop functions.

Heading hold
 

We did try years ago to adapt a heading hold in the 76A+ (Phase 2, SAS only) by using just the yaw series actuator. We flew with a variable gain box and thought we had it working a couple of times, but each time we froze the gain and put in a fixed gain box it didn't work....We never did get back to the drawing board!

Thanks 212man - this forum teaches me a lot!

Mart

And it's not just an AFCS or SAS function. The Westland Lynx has a Collective/Yaw interlink which is a mechanical coupling in the controls that applies a proportional amount of yaw dependent on how much collective is applied. It's apparent effect to the pilot is to re-centre the yaw datum and counter the torque input. Very elegant and effective design for a bunch of tin-bashers.

"Two's in", does that system work well in all flight conditions? I would imagine it to be slightly under effective in hover, but over effective in cruise - due to vertical stabiliser effectiveness with airspeed.

Mart