Descending with IAS-ALT

[vmilner]

Hello,

I am really enjoying the sim, it's unbelievable how realistic the SR22TN is -- thank you!

For my emergency practice, I tried yesterday an engine-out descent. In a real plane, I set the IAS to 88 kts, which is my best glide speed, ALT to 0, and the autopilot pitches for that airspeed. When I did it in the sim, DFC-90 kept flying straight (instead of pitching up) until the AS eventually got down to 88, at which point it started lowering the nose to maintain that indicated airspeed. So it behaved as if it will only *lower* the nose but not raise it in order to maintain the desired IAS. Is that by design?

Attached is the picture when I am in a descent from 2000 at IAS=100kts and the AP wouldn't raise the nose to slow down to 88kts.

Thanks,

Valery

 

[Coop]

That behavior is typical with most autopilots, though I can't confirm that is exact DFC90 behavior. If someone has evidence to the contrary, I'd definitely take a look.

[Dukemd]

This is from my DFC90 manual.  I think when you set the ALT to “0” the autopilot is also trying to capture that altitude.  When I am flying my SR22 (which is always over the mountains here in Northern CA and Southern OR, I am constantly thinking about what I would do in a loss of engine power.  My process would be:

1. Sync the HDG bug on my PFD by pressing the lower right knob.

2. Set my DFC90 to HDG.  IAS and use the dedicated IAS knob to set 88.  

3.  Make sure AP is pushed.  

Now I am flying straight at an IAS of 88.  I would expect my plane to briefly gain some altitude to go from 120 to 88.  Engine out, 120 to 88 will happen fast.  The DFC90 will now “sacrifice altitude to maintain IAS of 88.”

I can now use my heading bug to fly (glide) to a safe are for a CAPS pull if I can not get an in air engine restart.  

R