Re: T-tail

Date:         08 Sep 97 02:03:43 
From:         k_ish <kenish@ix.netcom.com>
Organization: Netcom
References:   1
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Steven.Nicolaou@zippo.com wrote:

> I read somewhere that T-tails have poorer handling at low speeds. Why
> is this? Also, what other disadvantages do T-Tails have compared to
> non-T-tail aircraft and what advantages (for that matter) do they have
> in order to be preferred to non-T-tails?

Airflow over the horizontal and elevator is augmented by propwash.  So
you have more elevator authority at low airspeeds with a conventional
tail, where a T-tail starts getting pretty "mushy".  Obviously this is
not the case with jets.

T-Tail advantages:
    Aft fuselage clear of structure, cabin can extend further aft.  I
speculate this is why many bizjets are T-tails.
    Allows rear-mounted engines which are less prone to FOD and makes
for a quieter cabin.  (Bizjets, again.)
    Tail is clear of rocks, slush, etc. thrown up from the tires (a DC-8
once crashed when a stone jammed the elevators).
    Tail is clear of damage from ground vehicles.
    Looks slick (I'm serious....the "jet look" was Piper's main
motivation for going to T-tails).

T-Tail disadvantages:
    Need stronger and heavier vertical fin structure.
    Vertical fin must be generally shorter and longer in chord than
aerodynamically optimum shape.
    Horizontal harder to inspect and service.
    On some aircraft, in a high-angle of attack, the wing can "shadow"
the elevator, and aircraft pitch cannot be changed to recover.  Results
in a nose-high pancake into the ground, called a "cold stall".  Not much
of a problem anymore; prevented by design, or by systems that push the
nose down before this mode can occur.
    Control cables harder to route.

No doubt others can think of more.

Ken Ishiguro