T-Tail design advantages?

[bobbysamd]

Seminole T-tails

I, too, remember showing my Seminole students the shaking T-tail. It was a standard part of training. Now that I think about, we discussed t-tails quite a bit during training. When I was teaching multi, the PTS did not require full stalls.

 

[jetdriven]

you should do a full stall in a traumahawk. The t-taip bangs and pops quite loudly, it also oscillated in a twisting motion, the horizontal stab would oscillate up to 5-10 degrees. Interestingly enough a tomahawk hasnt lost a tail i know of doing stalls. the crappy spin characteristics are moslty due to the airfoil design, the NACA GA(W)-1 airfoil.

 

[airnik]

Caveman,

This is all second-hand information, as the final report isn't out yet, but from what I understand when you pull the yoke out in the Tomahawk, you somewhat have to pull the yoke down first, then push the yoke in, to break the stall (and secondary stall if one has developed from the yoke being "stuck"). I'm not sure myself, as I have no time in that a/c. But I noticed it a little bit even in the Arrow IV. Anyways, I think the NTSB is looking into this more.

 

[avbug]

The primary advantage to the T-tail design (and the cruciform design) is a greater elevator moment and an expanded CG range.

A t-tail configuration in some cases removes the horizontal stab from airlfow interference of the wing, though not completely.

The t-tail is disadvantaged in being unable to provide an induced download from downwash from the wing.

T-tails typically suffer from deep-stall considerations separate from swept wing or other issues; the most obvious being a blanketing effect on the horizontal stab by the main airfoil (wing) during the stall, and a loss of pitching authority. Additionally, as the t-tail doesn't rely on a download from the main airfoil during normal operations, the introduction of download during high angle of attack operations may drive the stall deeper, or make it unrecoverable. The learjet is a good case in point.

Someone had mentioned the C-130; while I'd disagree that it's antiquated (it's the longest production run of any aircraft ever built, and is still being built), there was no need for a t-tail. That airplane has a different susceptability, which is the fin stall; a type of aerodynamic rudder reversal at high angles of attack on the rudder; high sideslip angles. Elevator authority is never a problem, the airplane has good stall characertistics, and it has a very large CG range. It also utilizes airflow fromthe inboard engines, and a download in most cases on the vertical stab.

On most light aircraft, the T-tail is entirely cosmetic. On several airplanes, the tail was moved higher to boost sales, not for reasons of aerodynamic purity.

The t-tail does tend to enhance spin entry and recovery authority. In many cases, greater rudder authority exists due to lack of interference by the horizontal stab. In designs with neutral inertia, this is important. In wing loaded aircraft, the elevator is the primary recovery instrument from a spin, and the placement of the elevator atop the tail enhances this in some designs, and can be detrimental in others. (On fuselage loaded aircraft, of course, the aileron is the primary spin recovery control, and the placement of the horizontal stab is of little consequence).

T-tails tend to require increased armature and rigging to effect control. The frequent use of jackscrew assemblies, additional bellcranks, runs of control rod or cable, etc, leave more vulnerability in the system, increase weight, and require heavier materials to retain strength with the additional arm and moment imposed by loads atop the vertical stab.

In some cases, t-tails were put there because there was simply no other place to put them. The 0V-10 is such an example. (although that design is a cross-tail, rather than a t, but is still mounted high on the vertical stabs).

Finally, you must look at the needs of each design on an individual basis. There is no blanket rule for the use of the t-tail. There are a great many variables, and each design is unique. It is impossible to state that the t-tail is good or bad; one must stick to a particular design to make such observations. In many cases, the use of the t-tail may be the best compromise for that particular design. Remember that any aircraft design is nothing more than a series of interrelated factors, and compromises. Many times, features of a design are not used because they are the best feature of a superior feature, but a good compromise.

Then again, it's hard to pay for a compromise unless it sells. Often the design features do nothing more than sell the airplane. Such is the case with a lot of T-tails.

 

[A Squared]

>>>>it's(the c-130) the longest production run of any aircraft ever built, and is still being built.

Actually, the Beechcraft Bonanza and the Antonov AN-2 started production well before the C-130 (1947, for both designs, if memory serves me correctly) and the Bonanza I know is still being produced. I'm less sure of the AN-2, but they were still being built a few years ago.

Regards

 

[avbug]

How about longest continuous production run?

Longest continuous production run with one factory paint scheme? (now offered in at least two).

How about the longest continuous production run with a minimum of six guys at any one given time on the airframe assembly line, all named Ed?

I can't malign the AN-2, much as I'd like to do so. I may be flying one around to airshows and other such places, soon.

How about longest continuous production airplane that the tail doesn't fall off of with regularity?

How about the longest continuous production airplane not regularly purchased by people with far more dollars than sense (though it would be a great mission, one never hears the herc intentionally referred-to as a "lawyer killer.").

How about this; line up the various airplanes that have been in production the longest, end to end. See which line is the longest.

Is anybody else bored to tears?

 

[freddriver]

AVBUG, sorry if you took offense to my C-130 comment. I love that plane (especially since my dad was a loadmaster on it during Farmgate).
As far as T-tail deep stall, even the C-5 has this problem. I've given it a shot in the sim a few times and its entirely possible to lose complete elevator authority due to the wing masking clean air during a deep stall.

 

[avbug]

No offense it all. The herc has a face only a mother could love, but it was a worker. I started to lose my affinity for it when the wings started coming off.

I promise not to make any jokes about the C-5 flying nose low over corn fields...

 

[FSIGRAD]

Wow! Great posts! A lot of very good information and a lot of points I never would of considered. I was able to put together a solid brief on T-tail design just from this thread. (However, my head is still buried in Aerodynamics for Naval Aviators trying to figure out what the heck is neutral interia?)

Thanks again!

 

[avbug]

The mathmatical formula for spin recovery is Ix (moment of inertia in roll), multiplied by Iy (the moment of inertia in pitch, divided by M (mass) times b2 (wing span squared).

This formula is used to predict spin recovery behavior. If the formula produces a value within plus or 50 points of zero, the aircraft is said to have neutral inertia, generally speaking. The Cessna 150, Citabria, etc, fit into this category. Typical spin recovery input will depend on rudder, followed by elevators at neutral or slightly forward. Aileron is generally not used due to ineffectiveness, or counterproductivity in the recovery.

 

[Pink Panther]

A test pilot for the Fokker 100 showed me once a video about what happend if you stall a Fokker-100 (T-Tail). Since the elevator is indeed ineffective if it becomes in the wash of the stalled wing.

They knew this could happen and so the installed 6 little rockets, three on each side of de back of the fuselage. To recover from the stall incase the elevetor became ineffective.

They had cameras in the flap mechanism boxes, so you could see exactly what happend, and indeed when they couldn't recover they activated the rockets and in no time the plane was from a stall position in an 90 degree pitch down position. Very spectacular.

This happend in a test flight, so I guess the found some other solutions to recover from a stall.


I know the Pilatus PC-12 has a T-tail so it's easier to load and unload the plane withe a forklift!