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At least incomplete LM, in theory a deep stall in a T tail light airplane is possible. Ultimately it would depend on CoG and the momentum of the airplane
When flying at a very high AOA with a low airspeed and an aft CG, the T-tail aircraft may be susceptible to a deep stall. In a deep stall, the airflow over the horizontal tail is blanketed by the disturbed airflow from the wings and fuselage. In these circumstances, elevator or stabilator control could be diminished, making it difficult to recover from the stall. It should be noted that an aft CG is often a contributing factor in these incidents, since similar recovery problems are also found with conventional tail aircraft with an aft CG.
My understanding of the deep stall was as the a/c is sinking the relative airflow now comes more from below the wing meaning you can have angles of attack of around 20 degrees with 0 degrees pitch angle. This is then exacerbated by the nose up moment from the centre of pressure moving forward.
The T-tail can make the deep stall impossible to recover from due to tail blanking, where the wash from the wing also disturbs airflow over the tailplane. This would make pitch inputs difficult/impossible.
Anyone please feel free to correct me if my understanding of this is incorrect.
Mounting the tailplane high puts it in an area of low downwash gradient making the tailplane a more effective stabiliser and a more aft cg is possible. This also leads to the tail generally having a more positive loading and thereby reducing trim drag
The T-tail raises the tailplane out of the fuselage drag-hole which can reduce your tailplane effective aspect ratio by 20% or more.
Very messy loading and structural design. Tailplane more difficult to clear snow off and access for maintenance and checking. Tilting of the principle axes of inertia giving rise to coupling issues in roll.
Last edited by Plastic Bonsai; 27th Dec 2012 at 11:49.
A T-tail does not cause deep stall, although it may well aggravate it when it happens.
The deep stall is caused by tip stall on a swept wing, which causes the lift centre to move inboard and forward.
Absolutely correct. B2N2, I don't find the definition above incomplete. I agree that that FAA figures give a different perspective, but in my opinion they are depicting a slight different scenario, where the wing is NOT actually stalled even if close to. By design, in the real stall (with weight and balance within certified limits of course) the nose should drop forward so giving better authority to the elevators while in the real deep stall that doesn't happen, because the CG keeps moving forward to a point that the recovery is virtually impossible. Anyway, imho, i think that the same term "deep stall" is used to define 2 different situations.
When it comes to military transport aircraft a T tail means you dont have to spend time worrying about parachute static lines fouling the elevator (as you have to for the Hercules). Also I had to smile when I saw the size of the tailplane design grow on the A400M after we had supplied Airbus with data on the cg transients of a heavy drop.
By design, in the real stall (with weight and balance within certified limits of course) the nose should drop forward
Most medium to high wing loading T-tail airplanes will do this only with the help of a stick pusher and/or ventral fins, an additional complexity to take into account when selecting a T-tail. This pitching moment sign reversal with fully deflected elevator normally takes place in the post stall regime though, that's why it is also called deep stall.
Anyway, imho, i think that the same term "deep stall" is used to define 2 different situations.
Last edited by Machdiamond; 14th Jan 2013 at 18:05.
T tail advantage: If the aircraft is a flying boat, it keeps the tail out of the water.
Disadvantages: Much more difficult to inspect for frost/snow/ice, and clean if required. More complex elevator and trim control systems, and, Depending upon aircraft type and configuration, a high tail might be out of the prop wash, which reduces pitch control on the ground (less able for soft field takeoffs).
engines at the tail means they are slightly more protected
Generally yes, though more vulnerable to snow and ice from the top of the fuselage being ingested.