ukoverlander
Topic Author
Posts: 389
Joined: Thu May 13, 2010 10:57 pm

T Tails On Commercial Turboprops

Sun Apr 14, 2013 9:13 am

I'm hoping somebody can answer what may well turn out to be a fairly simple question. In the modern jet age we seem to have seen the almost complete disappearance of T tails from new aircraft design. On the other hand leading turboprop manufacturers continue to incorporate the T tail design into some of the most successful TP designs used throughout the world such as the Q400 and the ATR. I do realize there are other TP manufacturers who don't utilize the T tail.

I understand the risk a T-tail may present in terms of a possible 'deep stall' and clearly in the past jet aircraft manufacturers have utilized it in the design on aircraft such as the 727, MD 80 series, etc. I just wondered if there was more recent thinking in commercial aircraft design that considers the T-tail a better option specifically for turbo props? If anyone can shed light on this I'd appreciate your thoughts.
 
mauriceb
Posts: 2150
Joined: Tue Aug 10, 2004 2:50 am

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 9:36 am

Goodmorning,

The main thing that turboprops still use T-tails is because of a number of reasons, well just my view on it:

-Lot's of props work from small airports in remote area's with lots of mountains, which require a steep glide-path. A t-tail gives u a better pitch momentum making it easier to control the descent ratio on approach. Also props are less fast most of the times, for wich u need to compensate the lack of lift with a longer arm from youre center of gravity to maintain in good control.
-T-tail's stay, mostly, clear of the downwash created by the wings. Certainly at lower speeds when the induced drag increases, this could really be disturbing for both pilots and pax, as the vibration's can be heavy, and eventually dammaging for the plane. U can imagine that smaller planes are more sensetive for those vibrations.

Correct me if i'm wrong!
 
starrymarkb
Posts: 285
Joined: Thu Apr 28, 2011 9:19 pm

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 10:09 am

Would the propwash be a factor? it would be more turbulent then jetwash because of the fewer blades
 
MEA-707
Posts: 3736
Joined: Mon Nov 15, 1999 4:51 am

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 10:40 am

The down wash from the wings and exhaust fumes are definitely a factor.
Most turboprops have high wings and these would interfere somewhat with lower stabilizers.
Think of DHC-8/ Q-400, ATR and Dornier 328.
There are some high wing props with low stabilizers, like the F-27/F-50, An-24 and Hercules. The engine exhausts are pointed downward and the stabilizers are still relatively high on the fuselage and maybe they are like what MauriceB describes less smooth in slow speeds.
nobody has ever died from hard work, but why take the risk?
 
mauriceb
Posts: 2150
Joined: Tue Aug 10, 2004 2:50 am

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 11:15 am

Quoting starrymarkb (Reply 2):
Would the propwash be a factor? it would be more turbulent then jetwash because of the fewer blades

Certainly!

Imagine that propblades are basically small wings, creating horizontal lift (thrust), which creates induced drag. Although less that the wings, since induced drag increases as the speed goes down and the angle of attack is high. Blades do always have a high speed, even at lower rpm settings.. + that when approaching a field, the AOA is less due to the lower forward speed. (most if not all modern props have constant speed props, adjusting the pitch is being controlled by the FADEC)

Once more, Principles of flight isn't really my thing, but i can imagine it has to do with something like this.
 
cornutt
Posts: 333
Joined: Sun Jan 20, 2013 6:57 am

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 4:37 pm

Doesn't the Q400 share its airframe with one of the CRJ models? That would definitely be a factor, since the CRJs have tail-mounted engines.

If memory serves, the EMB-120, which had a T-tail, derived from Xingu RJ project, which also had tail-mounted engines.
 
Kaiarahi
Posts: 1807
Joined: Tue Jul 07, 2009 6:55 pm

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 4:53 pm

The same topic is already being discussed here: Are T - Tails Condemned To Extinction? (by Gonzalo Apr 4 2013 in Tech Ops)
Empty vessels make the most noise.
 
Arrow
Posts: 2325
Joined: Wed Jun 19, 2002 7:44 am

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 5:49 pm

Quoting cornutt (Reply 5):
Doesn't the Q400 share its airframe with one of the CRJ models? That would definitely be a factor, since the CRJs have tail-mounted engines.

In a word -- no. The Dash 8 fuselage long predates the CRJ, and I don't think they did much to it when the Q400 was developed (other than stretch it). The CRJ came from the Challenger, and AFAIK Bombardier did not own deHavilland when the original Dash 8 was developed. I wonder if there's any Dash 8 commonality with the Dash 7 though.

I suspect you are thinking of the Embraer ERJ which shared the fuselage with the Brasilia?
Never let the facts get in the way of a good story.
 
bohica
Posts: 2414
Joined: Tue Feb 10, 2004 3:21 pm

RE: T Tails On Commercial Turboprops

Sun Apr 14, 2013 7:31 pm

One of the reasons turboprops like the Dash-8 and ATR have T-tails is because of "ramp rash." Having a T-tail keeps the horizontal stabilizer above the ground equipment, reducing chances of inadvertant damage.
 
robsaw
Posts: 431
Joined: Sun Dec 28, 2008 7:14 am

RE: T Tails On Commercial Turboprops

Mon Apr 15, 2013 6:13 am

The high-wing that would align with a low horizontal stabilizer pretty much mandates a T-tail regardless of any other benefits. The aerodynamic interference of the wing and prop-wash make any other choice non-optimal.

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