Dutch Roll effect despite SAS engaged?

[pewbeef]

Was out free flying a bit and took the Hog to around angels 34 and engaged the altitude hold autopilot. Didn't take long until I noticed a typical Dutch Roll effect that rather quickly got out of hand and eventually made the autopilot disengage. I had both SAS systems and EAC enabled (don't know if EAC has input on the Dutch Roll prevention though).

 

Can it be that the SAS inputs are off at those extreme altitudes, or what can it be?:huh:

[MTFDarkEagle]

What was your IAS at altitude?

[KaspeR32]

I'd take a guess his Pitot heat wasn't on and his IAS said he was going faster than he actually was?

 

Or his IAS was correct and he was just going too slow anyway.

[pewbeef]

You might be on to something there guys...Think my IAS was around 130-150 knots, but I probably hadn't enabled pitot heating...did a foul start from the taxiway, and I normally enable pitot heat right before takeoff when rolling onto the runway, so I might have forgotten that!

 

Wrong IAS input would maybe lead to faulty automatic control parameters and thus failure of the Dutch Roll prevention...maybe?

[Flamin_Squirrel]

You might be on to something there guys...Think my IAS was around 130-150 knots

 

That's a bit on the low side.

[pewbeef]

That's a bit on the low side.

 

You mean in general or for the Yaw SAS to work properly? Flying at those heights will make your IAS slow however.

 

As I mentioned before, if pitot heating is not enabled, that might lead to erroneous speed indications, right?

[Kid18120]

As I mentioned before, if pitot heating is not enabled, that might lead to erroneous speed indications, right?

 

Correct.

[Hamblue]

Pito heaters off will do it