T Tail aircraft???

[MikeSF340]

What are some of the advantages and disadvantages of a T Tail in high speed jet aircraft? Seems wierd that some planes have one (727,MD80,CRJ, ERJ, ETC.) and some don't (777, 747, 757, ETC.) Thanks for the help.

Mike

 

[dav8or]

Think about where the engines are on those planes.

 

[MikeSF340]

Good point, but.......

Definitely a great point, but why was the aircraft designed like that? There has to be an aerodynamic reason for it. Thanks for all the replies.

Mike

 

[sqwkvfr]

Handling characteristics in a thrust vs. no thrust situation would be more constant.

It'd be more difficult to control an aircraft if it's jet/turbopropwash were blasting across the horizontal components of it's empennage.

 

[minitour]

Okay, I have no clue if I'm even talking about the right concept here so just ignore me if I'm way off base:

If you had engines on the wings and a T-Tail aircraft (KingAir 350 comes to mind) wouldn't you have less elevator authority than say an aircraft with wing mounted engines (KingAir 90, 737, 777) and no T-Tail?

Again...I could be way off base, but I'm guessing that the airflow from the props/jets over the horizontal stabilizer/elevator would give you more control rather than less?

-mini

 

[avbug]

Minitour,

The placement of the engines below the wings or on the wings really makes little difference, especially when considering a T-tail configuration. One reason, a big one, that the T-tail came about is sex appeal; it looked classier, and that's why you see it on a lot of smaller airplanes.

Placing the tail high above the airframe puts it in relatively undisturbed air from the powerplants and airframe. It also provides a greater aerodynamic range, with a greater moment potential against the center of lift, and center of gravity. It tends to permit, generally speaking, a wider CG range for a given design than a tail placed lower, and it means that the inboard sections of the horizontal stab are less affected by the aerodynamic influence of the empennage.

A t-tail puts the horizontal stab, spar,and associated mechanisms away from the engines, and allows for a thinner back end, with a reduced cross section. This is frequently reduced adjacent to the engine pods with aft mounted engines in an area rule configuration (empennage gets thinner, or concave, adjacent to the engine nacelles) to reduce interference drag.

A horizontal stabilizer that's out of the prop wash and out of the jet blast means less potential for damage to the stab, and less drastic changes in pitch trim with changes in power.

 

[dougal28]

I believe another reason for t-tails is to avoid some of the problems of Mach Tuck. As an aircraft reaches speeds close to Mach 1, some of the air that passes over the wing is actually traveling at speeds greater than mach 1. The shock waves disrupt the air and making the horizontal stab/elevator ineffective. By placing the elevator higher up and out of the disturbed air from the wing, it maintains effective control.

 

[dougal28]

I have got to sign out from other peoples login as well.

 

[mattpilot]

YOu can find a lot of information about T-tail on this forum if you do a search. But to summarize it, everything in designing an airplane is a tradeoff. Everything has advantages and disadvantages. Ask the engineers of the aircraft why they choose that particular configuration. To get a detailed answer, use the search function.

 

[mar]

Load it up

One of my former instructors was a retired Douglas engineer from the Long Beach plant. He told me that he was never fond of the T-tail design simply because of the load it imparts on the vertical stabilizer.

Obviously you'd need a pretty beefy vert. stab. with a T-tail compared to the empennage mounted horiz. stab.

For what's it worth...