Turn rate on autopilot

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AKar
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Re: Turn rate on autopilot

Post by AKar »

Yes indeed - at least around here the most common PMA pump is Rapco's. The wear indicator port (into which you stick an included measuring stick or a caliper if you've lost it) is a neat feature, but I wouldn't turn them backwards any more than necessary. There is/was some manufacturer who made pumps which I think could even be installed regardless of the drive direction, I don't remember which it was.

-Esa

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Nick - A2A
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Re: Turn rate on autopilot

Post by Nick - A2A »

Stratocruiser2 wrote:Thanks Nick! That video plus the STEC manual have allowed me to get to grips with the Comanche (and Cherokee) autopilots and I had a couple of short but very enjoyable flights in both today. I agree with Esa that this autopilot, although pretty vintage technology (like me!) is a pleasure to use once you get the hang of it and it means that you actually have do do something every so often during a flight rather than just sitting watching it or going off to do something else.

My thanks to all who helped me with this query,
Bill
Glad to hear you're enjoying the S-TEC Bill! :) As Esa says though, it's actually a good bit more modern than the Comanche itself. (Not sure which year the S-TEC System 30 first made an appearance... :?: ) However, standard in top-of-the-range late 50s/early 60s PA-24s fitted with "AutoFlite" would be the proprietary "Piper Autocontrol" and "Altimatic Pilot" as shown below...

Image

I guess there aren't too many instrument panels left in today's Comanches which still resemble the one pictured above. :)

Cheers,
Nick
A2A Simulations Inc.

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AKar
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Re: Turn rate on autopilot

Post by AKar »

How to correctly and easily track GPS with S-TEC 30

A quick 'beginner's tip' on how to track GPS with S-TEC 30. I'll get into the in-depth tutorials later on. It may be of interest to check out some more 'in-depth' writings about the autopilot I wrote earlier in here and here. The S-TEC 30 simulation is truly an A2A gem on its own.

Let us start from a situation where you've manually (or in a heading select - doesn't matter) flown the airplane on the track and successfully engaged the TRK mode. Lots of folks figure it is a hands-free mode like the NAV mode in many default, and default-derived GA autopilots in the FSX. Fortunately, it isn't.

So, without further to do, let us jump into this arbitrary situation:

Image

I'm sorry about all the airspace borders cluttering the view - I'll avoid France in the future! :mrgreen: Anyways, note that I'm tracking towards FJR with GPS driving the NAV needle. Note the turn to the right after the waypoint. Most folks soon find out that the autopilot will not track properly through the turns like this. Why? Well, basically because it
  • a) does not know our desired track;
    b) does not know our current heading; and
    c) it does not have any built-in routine to intercept any track or to correct any larger off-track displacement.
The above list of doesn'ts is not a collection of necessities for a useful autopilot, but some pilot input and situational awareness is needed to substitute them. Apparently, many folks just disconnect the autopilot for the turn, intercept the new track manually and then re-engage it. I've seen that suggested every now and then. Nothing wrong in that, but it is not necessary either.

So, using a bit of common sense, and the features of the autopilot, do the following.

First, find out your next track, that is, your track after the turn. If you use GTN-series 3rd party GPS units, a one way is to go back from the map screen to the main menu, select the flight plan and find the next waypoint after the turn. In this case, that is Saint Tropez VOR, and the course will be 099°:

Image

With long flight plans, you could as well check out many tracks coming up and write them down already! If you printed out your flight plan, and was still following that, you'd have these on there.

Then, rotate your heading bug to your next track. (You could turn the course indicator as well right away when tracking GPS, for it affects nothing when doing GPS, but not when tracking VOR of course! Therefore I keep the course selection at my current one to avoid blunders if I were tracking a VOR - consistency is generally a good idea!)

Image

You can do this whenever you've got time, with S-TEC 30 the offset heading bug doesn't affect the navigation in any way. Actually, even the HSI's compass card's heading doesn't - try this out: track a segment with GPS or track a VOR and throw the HSI well off the heading manually, and see how autopilot does not react in any way. I leave it to homework to figure out why.

So, you're now set up like this:

Image

You're:
  • - flying the current track, indicated by course needle;
    - having the heading bug on the next track.
Now it's only eyes on the GPS when approaching the waypoint! The unit will display a countdown when it calculates that you should turn - it does not work precisely with S-TEC's turn rate, but it is a good starting point! When it's time to turn, cycle through the modes to HD, or heading select. The autopilot will turn to the heading bug, and roll out rather nicely to the next track. With a bit of practice, you can fine tune your technique to switch the mode a bit in advance or late of what the GPS calculates. Also, you can turn the heading bug a bit off the next track to take into account any wind correction you're estimating. After the turn just establish yourself over the track and re-select the TRK mode.

Has tracking the magenta line ever been so fun? :)

To summarize, when approaching a turn in the flight plan:
  • - rotate the heading bug to next desired track ± any desired wind correction;
    - check that the compass card on the HSI is properly aligned ("D"-key to cheat);
    - wait until GPS commands the turn ± your own estimate;
    - select HD mode and the plane will turn approximately on to your next track;
    - establish yourself in HD and select TRK again. Rotate the course needle to your new track when you wish - note that if you were tracking VOR, you'd need to do this before selecting the TRK mode of course - preferably immediately after commencing the turn!
Quite of a common sense!

Just remember also that you need to intercept the tracks - be them VOR or GPS ones - in ST or HD modes or in manual flight. It is important to understand why. Review the list above, of what the autopilot does not know.

If I created an arbitrary GPS route segment, crossing ahead of me, and wanted to intercept that, the TRK mode won't do! Here I was flying heading 099° or so, tracking the heading bug. I created a route segment from MARRI waypoint to some arbitrary location so that the track would be 350°, as indicated by the course needle, and the segment would be ahead of me. Selection of TRK mode, in hopes it would intercept the track is foolish, and results in this:

Image

Note the airplane is turning the wrong way, I would think, if I didn't know what it was doing! Surely it would feel like a bug if I was all used to arcade autopilots in FSX.

But no, note the HSI deviation indicator is actually displaced to the right (relative to the course). That's the only thing the AP sees! It sees a deviation to the right, and it turns there. As I never cross the segment in this case, the deviation will remain to the right, and the airplane - logically! - will end up flying in circles, like so:

Image

The red one is my track and the yellow line is the approximation of the course segment I created. During the second turn I disconnected the TRK mode and flew away - intentionally overshooting a bit to not accidentally disturb my circles.

Note that if I did cross the course segment, the turn would change over to the left - but it would be all but useless to intercept the track! That needs to be done by the pilot.

-Esa

KPWoodsong
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Re: Turn rate on autopilot

Post by KPWoodsong »

Is there a way to map the STEC autopilot mode/turn button to the keyboard or joystick keys?
Cessna C172
Piper Comanche 250
Piper J3 Cub
T6 Texan

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Nick - A2A
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Re: Turn rate on autopilot

Post by Nick - A2A »

KPWoodsong wrote:Is there a way to map the STEC autopilot mode/turn button to the keyboard or joystick keys?
Hello KP,

Yes, you can assign a button or key to the MODE button using the Comanche Input Configurator, which is available from the Windows Start Menu → A2A Simulations group. Using the same tool you can also assign a hardware axis (should you have a spare one) to turn this knob.

Hope this helps,
Nick

KPWoodsong
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Joined: 11 Mar 2018, 18:20

Re: Turn rate on autopilot

Post by KPWoodsong »

It did, thank you.


KP
Cessna C172
Piper Comanche 250
Piper J3 Cub
T6 Texan

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Nick - A2A
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Re: Turn rate on autopilot

Post by Nick - A2A »

You're welcome KP.

Nick

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