Setting autopilot altitude

[Bob Edge]

Hi all,

I have run into a problem with my autopilot project.

The autopilot altitude setting (offset 07D4) seems to be acting in a very strange way. It should be meters X 65536. So to send feet this should be; value to send = (alt in feet / 3.048) X 65536

In FS9 the value sent is close to what you want, usually just a few feet or even inches from the altitude I intended. Not a huge problem, but still anoying. In FSX no matter what value I send the alt sets to zero. Even if I read the value from FSX then send back exactly the same data it is set to zero feet.

Anyone know what I'm doing wrong?

Regards

Bob.

[Pete Dowson]

The autopilot altitude setting (offset 07D4) seems to be acting in a very strange way. It should be meters X 65536. So to send feet this should be; value to send = (alt in feet / 3.048) X 65536

There are 3.28084 feet in a metre, not 3.048. And it would be more accurate when arriving at an integer to multiply by 65536 before dividing by 3.28084.

In FS9 the value sent is close to what you want, usually just a few feet or even inches from the altitude I intended. Not a huge problem, but still anoying.

0.2 in 3.2 is 6% error.

In FSX no matter what value I send the alt sets to zero. Even if I read the value from FSX then send back exactly the same data it is set to zero feet.

FSX and FS9 work in the same way in this area. Do some logging -- Monitor 07D4 on the right side, as type SIF32, to "normal log", and enable IPC write logging on the left side.

Regards

Pete