T-Tail Deepstall
 

Hello everyone

Could a T-Tail straight wing aircraft like many of todays turboprop suffer from deep-stall or is that something thats exclusive for the t-tail and swept wing aircraft?

Theoretically, even a conventional tail can suffer from a deep stall, it's a matter of angle of attack being high enough.

Dash8-Q400 has a stick pusher to prevent deep stall.

The Dash 8 may have it but if the crew dont understand it you get the awful Colgan crash , was it in Buffalo NY some years ago. A dash 8 t just fell out of the sky in a flat attitude killing all on board and several on ground . A graphic illustration that its not just jets or swept wings that can suffer this problem

Stick pushers are generally on TPs because of their tendency for getting into a spin at the stall

pax britanica

That was largely because the captain flying held the stick back against the pusher all the way down to the ground. It was an unfortunate accident where if they had just sat back and done absolutely nothing for a bit they would have been fine. The stick shaker activated early because the anti ice was turned on and the captain induced the pusher by heaving back on the stick. Pure piloting muppetry.

The Dash 8 300 also has a pusher but the smaller 200 and 100 don’t.

"​The National Transportation Safety Board determines that the probable cause of this accident was the captain's inappropriate response to the activation of the stick shaker, which led to an aerodynamic stall from which the airplane did not recover." - From the Colgan Air crash Flight 3407

The NTSB findings suggest that inappropriate response to stick shaker was the cause for the crash which could have been avoided if the pilot reduced the AoA, a Deep stall would be impossible (or almost impossible) for the pilot to recover from, so its reasonable to believe that the DASH8 suffered a normal stall and not a deep stall.

#2, it’s not the magnitude of AoA which is the problem, it is if the control surface used for stall recovery (tail/elevator) is masked by the wing downwash and thus less effective.

#3 - #5, perhaps the main reason for having a stick push is that the aircraft’s natural stall warning or stall characteristics do not meet the certification requirements - particularly pitch down.
I do not recall that spin prevention specifically was considered. The aircraft will not spin unless stalled, stick push minimises the duration of a stall or avoids altogether.

Straight wing vs swept should not be an issue, the dominant factor is the inability to effect a nosedown pitching moment.

Both the BAe146 and HS125, relatively straight wing, were predicted to suffer deep stall based on wind tunnel testing. Both aircraft had stick pushers, but flight testing did not discover any deep stall situation.

Didn't Lear introduce those big ventral fins to prevent a stall forming on the Lear 55 etc.

The ventral fins are generally for longitudinal stability at high alpha.

Immediately after that accident I quoted the Coogan website which referenced the welcome of Dash 8 to their fleet. I commented on the likelihood of pilot knowledge/training being the cause on here and got slated for doing so.......

We can't change the past, but we can just keep learning.

Handling the Big Jets explains why turboprop have a spin tendency at the stall. In fact, DP Davies got into a spin while stall testing a Brittania

See the sticky thread at the top of the Tech Log forum for a link to some great podcasts of a detailed interview with Davies about test flying a large variety of airliners for the CAA. His tells the story of spinning the Brittania, scary stuff, and some great stories about dealing with various manufactures when things didn't go to plan.

https://www.pprune.org/tech-log/6029...ml#post9985073