Peter, so your current installation does the turn anticipation by the fact that the GPS will activate the next leg before raching the waypoint.
Yes.
I thought that was normal 
The only problem is that if you have a mechanical HSI, you have to turn the course pointer yourself. There are mechanical HSIs with a motor-driven CP but not in the GA scene. I used to have a KI525 and, as Emir, says, you can “play with it” by turning the CP at just the right time or the right rate, to get the intercept just right.
Now you either are very quick in a manual system turning the needle of the HSI or you have an EHSI which does the job for you. Is that right?
Yes, although turning the CP manually is not exactly difficult. I flew with that for 9 years.
One of the basic issues with “automatic turning” is that you don’t necessarily get an advance notification of when it is going to start the turn. So you have to sit there and watch it very carefully (dedicating 100% of your attention to watching it) and if it doesn’t commence the turn, you say “what the **** is it doing now” (the standard Airbus phrase ) and very quickly sort it out. Probably, by setting the heading bug and pressing HDG before things get too far out of hand
Everybody has that “is it going to do it…?” issue when intercepting an ILS localiser (with an autopilot) but with any sort of automatic GPS turning you have that situation at every turn.
The only problem is that if you have a mechanical HSI, you have to turn the course pointer yourself. There are mechanical HSIs with a motor-driven CP but not in the GA scene. I used to have a KI525 and, as Emir, says, you can “play with it” by turning the CP at just the right time or the right rate, to get the intercept just right.
Not exactly, although under many conditions you can come close. The problem is that winds, GS and actual track are not taken into account. For roll steering, it constantly adjusts in real time the bank angle as needed to obtain the new course joining. For a WAAS GPS there are 5 position updates per second. The KLN94 has 1 update per second. There are limits such as the roll steering can’t command a turn rate greater than the maximum for the autopilot. For example most HBK autopilots have a 25 degree bank limit whereas the Stec autopilots have a 90% of standard rate limit. Overshoot will occur if these limits are exceeded. If they are not, then the bank angle is adjusted as needed around the turn. This kind of action does not occur on a CDI based turn where the course pointer is adjusted to the new course as it will use more of a fixed bank angle until the roll out is being commanded. This means you get inconsistent results trying to use turn anticipation with the HSI course pointer technique and very reliable, hands free results with roll steering.
Timothy wrote:
And having SBAS also enables smooth roll steering (whether a/p, f/d or hand flown).
You don’t need SBAS for roll steering. Or do you mean that the GTN boxes can do roll steering while the GNS boxes can’t?
You don’t need a W box to get roll steering.
I can’t type much on the phone though.
The value of roll steering depends.
Yes, you can get roll steering on non-SBAS boxes, but it is much smoother and more accurate on SBAS boxes.
Both GNSWs and GTNs can feed (as far as I can make out, equally) smooth roll steering.
GTN will provide Visual approaches to grass runways, provided they are in the AIP.
ESKC does not seem to be in the Swedish AIP?
I am guess that that is also why it can’t be a VNAV target, if there isn’t a verified elevation, but you can always use sea level and add the elevation.
Can someone explain from a technical perspective the difference between an AP performing with roll steering and without it?
How can one sense if his AP is configured to use roll steering without looking at the wiring diagram? From what I’ve heard, it behaves the same, and you can only sense the difference when flying a ‘curved’ path.
Doesn’t the AP fly the plane using ailerons control in both cases? Will the non roll steering one overshoot the turns in a ‘snaking’ pattern, or how becomes one ‘smoother’ than other?
Thanks!
GPSS steering is great. The plane behaves as it should without much pilot input, it will fly a whole flightplan without telling you to change OBS settings e.t.c. It also anticipates turns, can use fly over waypoints e.t.c in procedures and fly holdings and other stuff provided by the GNS box.
Once you have had it, you won’t want to fly without it.
The 60-2 will most probably need the S-Tec GPSS converter installed to use this feature off a 530/430W box, or you can install an Aspen which has it’s own converter. My 55x has it native and it works very well indeed.
Once you have had it, you won’t want to do without it. I certainly don’t.
AlexTB20 wrote:
Can someone explain from a technical perspective the difference between an AP performing with roll steering and without it?
Roll steering is an output from an FMS/GPS system that defines a precise bank angle for the autopilot to intercept and track a course. It does not depend on a CDI deflection, but rather the desired track, actual track, ground speed etc. The FMS/GPS generates the bank angle needed to fly the course or procedure. Modern autopilots have a roll steering input, but most legacy autopilots do not. So the KFC 225 and the Stec 55X have a roll steering input, but the KFC200, KFC150 Century III, Stec 60-2, Stec 50, Stec 30 do not. The legacy autopilots can be connected to a roll steering adapter that converts the bank angle into a command input accepted by these autopilots. What is accepted by the legacy autopilots is the heading bug signal that is used to guide the autopilot in heading mode. The heading bug signal is referred to as heading error and is normally generated by the DG or HSI anytime the heading and heading bug differ. Some clever engineers at Stec recognized that the heading error signal generated a voltage proportional to the error and that the heading mode autopilot computer would introduce a bank in proportion to the signal. So if the heading error is 5 degrees, the computer would introduce a 5 degree bank to correct the heading back to where the heading bug is located. A 10 degree error would introduce a 10 degree bank, and so on up to the bank angle or rate limit of the autopilot. Stec came up with a converter that converts a bank angle into a heading error and inserted a switch between the autopilot and one of the two sources for the heading error signal, either the DG/HSI or the GPS/Converter that was driven by the roll steering output. That is why on most legacy autopilots, you set the autopilot into heading mode when you wish to use GPSS or roll steering.
This is what will get you going with GPSS on a 60-2 AP:
As you are asking about replacing your EHSI with something more modern you can actually kill this problem by getting an Aspen. The Aspen has the same functionality inbuilt. All you do is fly the AP in HDG mode all the time you want GPSS and select GPSS on the Aspen.
Operationally, what is the difference between having roll steering and not?
I recommend a search with the term
“roll steering” AND kln94
and one thread is here
The benefit is negligible unless you want the autopilot to fly arcs, holding patterns, etc. I would certainly not spend 4 or 5 figures on it.
And LPV depends on where you fly; if you fly out of the UK then all airports you fly to need Immigration (called “Customs” in standard international terminology, though not the same thing) and unless you fly a lot to particular airports and in bad weather you will find they have an ILS anyway. At least, that is what I continue to find, and all the time I continue to find it, I won’t be spending the money
