Diamond 20, T- Tail, fuel tanks on fuselage

[Dreamlinerwannabe]

I have flown a couple of hours of a DA20... And I am still figuring it out why does it have T-tail, and fuel tanks of fuselage instead of on the wings.


Wikipedia and folks from airliners.net are saying T-tail has advantages of:

1."T-tail will give you better rudder authority at very high AOA and stalls so as to prevent a spin."

Why?

2."A longer tail arm to reduce trim drag"
How?

3. "Lets the airplane have better longitudinal pitch characteristics in high speed flight as the tail is above the wing wake. "
How and Why?

There were no further explanations at all after just these single sentences....

Also, is it both airliners and light aircraft with T-tail can suffer from deep stall?

Why don't the Austrian put the fuel tanks on the wings? Now put it on the fuselage instead?

Thank you very much!

[FlyingStone]

2."A longer tail arm to reduce trim drag"
How?

The longer the tail arm, the lower downforce the tail has to produce to negate the moment effect of wings lift around CG. Lower lift/downforce on tail = lower drag.

Why don't the Austrian put the fuel tanks on the wings? Now put it on the fuselage instead?

Given that the fuel capacity is not so large and this is primarily trainer where baggage capacity is not needed that much, fuselage tank is a good choice. Besides, wings aren't thick as in other spamcans (C172 etc.), so the tanks would have to be pretty wide. And of course, single tank fuel system is more simple - no need for a fuel selector, all you need is a fuel shutoff valve.

3. "Lets the airplane have better longitudinal pitch characteristics in high speed flight as the tail is above the wing wake. "
How and Why?

DA20's tail with its relatively low height is in the prop wash anyway, but I think the remarks were meant for a jet aircraft with T-tail.

[Dash8driver1312]

Answering point 1, a low tail plane will mask the rudder, so you have no useful airflow over the rudder. A T tail leaves the rudder in clear(er) airflow, but also can result in putting the tail plane into the disturbed air coming off the wing. That will depend upon the design and airflow characteristics of each aircraft type.

[Dash8driver1312]

(I'd also recommend looking a little deeper than wiki for answers, it is a decent starting point but a genuine listed and published text on aerodynamics would be far more useful to you!)

[flyboyike]

I, too, have a couple of hours in a DA20 (for spin training), and yet was never concerned about any of the above issues. It's enough to think the engineers knew what they were doing.

[Dreamlinerwannabe]

May I ask what do you mean by "low tail plane would mask the rudder"?

Thanks for all the response, it really helped a lot!