# Thread: help with sim rate 8 and up

1. ## help with sim rate 8 and up

At sim rate 16 above 20,000 feet the plain starts rocking up and down!
Anybody with some help please!

2. Originally Posted by zoltna67
At sim rate 16 above 20,000 feet the plain starts rocking up and down!
Anybody with some help please!
How many knots per hour are the winds?

3. Regardless of windspeed or cloud conditions, that much time acceleration will always cause instability.

As an example, say that the autopilot looks at the vertical speed 10x a second, and adjusts appropriately to stay at a set altitude. If you move through an area of turbulence where the vertical air movement changes strength every 1.6 seconds, the autopilot has 16 cycles to correct for the movement. If you speed the sim up to 16x, the autopilot is still scanning at 10 scans per second, but you're now moving through those air pockets every .16 of a second, so every time the autopilot looks at the vertical speed of the aircraft and the altitude, the two variables are different. The autopilot will still attempt to correct, but it has no time to do so, therefore the error gets worse and worse the longer you leave the sim at 16x time acceleration.

Another way of looking at it is that if, say, you are running your sim at 32fps, if you see a tiny change, you can correct for it. If, however, you are running at 16x, those "slight" changes happen 16x as fast, so you react 16x as slowly. You'll end up with 16x the error that you would have if you were running it at 1x and might as well be flying at 2fps - by the time you've seen the change and tried to correct for it, it's too late and you're making the wrong correction.

Basically, there's no way you will ever keep a flight model stable at that speed. Even a microscopic trimming error or a tiny area of turbulence will throw you miles out of balance.

Ian P.

##### Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

#### Members who have read this thread: 0

There are no members to list at the moment.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•

Avsim - Flightsim - SimFlight - Simviation - iflyonline - CFS IP - Quarter Moon Saloon - Com-Central