How to change autopilot increment/decrement reference ?

[antuanas]

Is it possible to change fsx default aircraft autopilot altitude increment/decrement reference value throught FSUIPC ? As You know default reference value is 100 ft and i need 10 ft sometimes in some situations.

To do this directly changing variables in fsx it seems mission impossible. What about using FSUIPC ? If it is possible, help me please cause i'm not strong in using and programming FSUIPC.

[Pete Dowson]

Is it possible to change fsx default aircraft autopilot altitude increment/decrement reference value throught FSUIPC ? As You know default reference value is 100 ft and i need 10 ft sometimes in some situations.

To do this directly changing variables in fsx it seems mission impossible. What about using FSUIPC ? If it is possible, help me please cause i'm not strong in using and programming FSUIPC.

The autopilot altitude in FS is actually encoded in 1/65536ths of a meter. However, I don't know of any FS aircraft which can set or use any altitude in any accuracy other than 100's of feet.

Here's a Lua plug-in which will increment or decrement the internal FS altitude by any amount you like in feet:

alt = ipc.readSD(0x7d4) * 3.28084 / 65536
alt = alt + ipcPARAM
ipc.writeSD(0x7d4, alt * 65536 / 3.28084)

Save this in the FS Modules folder, as say "incalt.lua", then, after "reloading" keys or buttons to get FSUIPC to re-catalogue the plugins, simply assign keypresses or buttons to "lua incalt" with the parameter set to the increment (eg 10 or -10) and experiment with it. I think you'll find it does increment or decrement the internal value, but it doesn't affect anything until suddenly FS rounds it up or down to the next multiple of 100 feet.

When you think that the accuracy of the altitude setting is only to, at best, 1 hPA of setting on the altimeter adjustment, assuming you can know the actual sea level pressure at your exact position all the time, and a difference of 1 hPA represents around 30 feet, there's little point in trying to fly an altitude to any accuracy like 10 feet in any case. Even 50 is a doubtful ambition. 100 seems eminently reasonable and normal.

Regards

Pete

[antuanas]

Hi there,

The results after many experiments are negative. For example, if i set parameter to 10, then altitude reference value increases by 100 ft. after pressing assigned key tree times..Experiments with other parameters gave no results - reference value changes nevertheless only by 100 ft. only depending what parameter was choosen and then according to that parameter how many times was pressed assigned key. Also try to find and use other offset but nothing happens...Maybe i want changes which cannot be achieved.

Despite that, thanks for help Pete.

[Pete Dowson]

The results after many experiments are negative. For example, if i set parameter to 10, then altitude reference value increases by 100 ft. after pressing assigned key tree times..Experiments with other parameters gave no results - reference value changes nevertheless only by 100 ft. only

I think if you used a parameter of 200 it would increase by 200. It is simply that the minimum increment or decrement it actually uses is 100.

depending what parameter was choosen and then according to that parameter how many times was pressed assigned key. Also try to find and use other offset but nothing happens.

Is this with FSX or FS9, or some other simulator? With FSX all changes go through SimConnect in any case, so it makes no difference -- and FSUIPC only supplies one offset in any case to adjust the A/P altitude.

Note that the actual value in FS may well be changing -- I don't know whether the A/P will fly according to that precise altitude setting or not, though. It may only be the value fed back to the gauges which is kept to multiples of 100. I doubt it though.

..Maybe i want changes which cannot be achieved.

As I said in the first place, I don't think an altitude set to within 10 feet has any meaning in any case. It simply is not possible to set the altimeter more accurately than 1 hPA which means it could be 15 feet out either way in the first place, and that's assuming you do actually know the QNH all the time at your position and you constantly check and keep it correct.. And in fact the precise QNH at any point is also not determinable in reality -- all you can get is reports from nearby weather stations, usually delayed. A possible variation therefore, in my opinion, of at least 50 feet is likely, making 100 foot increments eminently sensible.

So why do you want to achieve something not even possible in reality? What's the point?

Regards

Pete

[antuanas]

I think if you used a parameter of 200 it would increase by 200. It is simply that the minimum increment or decrement it actually uses is 100.

Yuo are right. I can set any parameter above 100 ft - 200, 300 and so on - and it will work. Altitude reference value will increment/decrement by that value. And i can do it without lua script - simply use 'Ap Alt Var Inc' control or use 'Ap Alt Var Dec' if i need decreasing. With setting parameters above 100 ft everything woks perfectly. And this is with FSX.

So why do you want to achieve something not even possible in reality? What's the point?

The point was to make smooth refuel from tanker (with fixed drogue) using autopilot. But it can be done only if aircraft autopilot have more precise and accurate altitude reference value - what i was seeking for.

Maybe it seems a little funny at first...But i'm not seeking to feel reality when playing FSX. For me - it is only the game..Hope You understand what i want to say :)

[Pete Dowson]

The point was to make smooth refuel from tanker (with fixed drogue) using autopilot. But it can be done only if aircraft autopilot have more precise and accurate altitude reference value - what i was seeking for.

You want an altitude hold which is stable, then. It doesn't have to be a specific altitude, surely, just one holding steady enough once you've got into the right position to receive the nozzle?

Regards

Pete