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indigo duck
21st Nov 2006, 09:05
Bit of a curly one for you boffins out there ....

I am trying to find out the dihedral of the wing of an SA227 Metro III (or any metro type that has had the wing extension). The reason being ....

(perhaps there might be someone able to provide some assistance in working this out)

In a turn (or if it makes it easier, sideslip) at an angle of bank of say 30 degrees, what would be the average rate of flow with the crossfeed valve open? What rate would this increase to if the AOB was 60 degrees?


This relates to the metro accident (loss of control at altitude) over Stratford, NZ approx 18 months ago when the autopilot disconnected whilst trying to balance (crossfeed) fuel using a sideslip technique. I am curious as to at what point (i.e how many seconds/minutes) the fuel imbalance would lead to a loss of aileron effectiveness. (hence a loss of control and inability to use normal unusual attitude recovery techniques).

Kiwiguy
21st Nov 2006, 10:27
Wasn't the issue that the crew disconnected the autopilot and immediately lost control ?

I imagine once the aircraft was in trouble the gyroscopic effect made it pretty near impossible to recover.

indigo duck
21st Nov 2006, 22:30
Not entirely ... from the accident report they were crossfeeding (balancing fuel) with the autopilot on and manually applying rudder, which caused the yaw damper to disconnect - disconnecting the autopilot.

But this has already been discussed in other threads and I think the analysis has already been thrashed out.


What I am trying to find out is, at what point would there be an excessive imbalance that would make recovery from an unusual attitude such as this impossible (i.e no aileron control). I know there is a manufacturer's figure for maximum imbalance for takeoff and landing, but usually there is still some effectiveness in the ailerons.

Fltidl
22nd Nov 2006, 00:30
Dunno about the dihedral, but in a banked turn with the crossflow open it can move quite fast - faster still if cross controlled....60 degree bank angle: yikes!

Was possibly a factor in a crash here in the US.

Limit imbalance 500 lbs in the 14.5 and 400 if under 2,000 lbs total, or 200 if over 2,000 lb total in the 16.0.

Have heard a 1,000 imbalance being controllable, but tough. also heard the fuel vent lines can fail, causing uncommanded transfer.......

Just as well we have no autopilots in our birds!

hoggsnortrupert
22nd Nov 2006, 16:01
:ok: Bit of a curly one for you boffins out there ....
I am trying to find out the dihedral of the wing of an SA227 Metro III (or any metro type that has had the wing extension). The reason being ....
(perhaps there might be someone able to provide some assistance in working this out)
In a turn (or if it makes it easier, sideslip) at an angle of bank of say 30 degrees, what would be the average rate of flow with the crossfeed valve open? What rate would this increase to if the AOB was 60 degrees?
This relates to the metro accident (loss of control at altitude) over Stratford, NZ approx 18 months ago when the autopilot disconnected whilst trying to balance (crossfeed) fuel using a sideslip technique. I am curious as to at what point (i.e how many seconds/minutes) the fuel imbalance would lead to a loss of aileron effectiveness. (hence a loss of control and inability to use normal unusual attitude recovery techniques).
Q: Having read the report, do you think it sound?
Chr's
H/Snort

indigo duck
23rd Nov 2006, 01:31
H/Snort

Could be a bit of a mute point with some people I know, but I'm just exploring a theory .....

Macgyver
24th Nov 2006, 21:33
I fly a metro II, and according to the AFM, the dihedral is 5 degrees.

indigo duck
25th Nov 2006, 02:29
Thanks Macgyver.