Gonzalo
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Are T - Tails Condemned To Extinction?

Thu Apr 04, 2013 11:14 pm

The number of large aircraft with T - tail design is low, all of them are old designs ( Mad Dogs, Tupolevs, BAe ), and the fleets of this models are very few ( I can think of some large fleets of MD's in North America, but all of them aging rapidly and being phased out in most cases ). The T Tail is not part of all the latest designs for large aircraft from Boeing, Airbus, Embraer, CSeries, Sukhoi SSJ....
Is the "extinction" of the T - Tail sentenced by the industry ?
Or are any hope for this design with little known / undeveloped projects ?


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PlymSpotter
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Are T - Tails Condemned To Extinction?

Thu Apr 04, 2013 11:45 pm

Quoting Gonzalo (Thread starter):
Or are any hope for this design with little known / undeveloped projects ?

All the ATR models, the Q400/Successor and the An-140/An-148 come to mind at once. Plus a large number of smaller projects in the pipeline.


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eaglewarrior
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Are T - Tails Condemned To Extinction?

Thu Apr 04, 2013 11:52 pm

A lot of the business jets (Gulfstream, Bombardier's Global aircraft for instance) and some of the regionals like the CRJs have T tails. But in terms of the large jets, I don't think they the manufacturers are going to use them anymore. However I could be proven wrong.
 
Gonzalo
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 12:10 am

Quoting PlymSpotter (Reply 1):
Quoting eaglewarrior (Reply 2):

Yes, but maybe I should be more clear about " Large Aircraft". For me this "title" starts at 90 seats, like a CRJ9 ( 90 seats )or an Airbus 318 (100 seats ) more or less... that leaves almost all the turboprops, and the smaller CRJ and E-Jets out.

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prebennorholm
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 12:29 am

T-tails are for planes with tail mounted engines. Boeing made one, the 727, some fifty years ago. Airbus never did.

And for smaller planes where the horizontal tail might otherwise be in the way for service vehicles.

The ATR is sitting very low, and most have passenger door in the back. A low tail might be so low that tall passengers might run their head into the tail when boarding/deboarding when it is dark, rain, snow or worse.

A main reason for having the door in the back is to avoid pax running into the propeller.
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Yflyer
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 12:53 am

Quoting prebennorholm (Reply 4):
T-tails are for planes with tail mounted engines. Boeing made one, the 727, some fifty years ago.

And if I understand correctly the main reason for tail mounted engines on planes like the 727 and DC-9 was to allow for shorter landing gear so the plane would be easier to service at smaller airports. While that might have been a problem in the 1960s nowadays any airport that sees planes that size regularly would surely have jet bridges or airstairs available, as well as baggage belts, etc. So there's no good reason to put tail mounted engines on a plane that size anymore, and therefore no good reason for a T-tail.

They'll likely be relegated to RJs, turboprops, and bizjets in the civilian world. With smaller RJs on the way out we might not even see them there for much longer.
 
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Starlionblue
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 5:49 am

Quoting Yflyer (Reply 5):
And if I understand correctly the main reason for tail mounted engines on planes like the 727 and DC-9 was to allow for shorter landing gear so the plane would be easier to service at smaller airports.

That was one of the main reasons. There was also:
- Less risk of FOD ingestion, but the days of larger airliners on gravel strips are numbered.
- Clean wing design without engine nacelles.


The 757 design had a t-tail for a while. Don't know why it was considered.

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HAWK21M
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 11:09 am

Quoting Starlionblue (Reply 6):
The 757 design had a t-tail for a while. Don't know why it was considered.

I read someplace that it was supposed to be modelled on the B727......
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Starlionblue
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 11:55 am

Quoting HAWK21M (Reply 7):
Quoting Starlionblue (Reply 6):
The 757 design had a t-tail for a while. Don't know why it was considered.

I read someplace that it was supposed to be modelled on the B727......

Makes sense. However since they were developing the 767 at the same time and there is little aerodynamic or structural point in a t-tail on an aircraft with underwing engines, I fail to see the logic. The one aerodynamic point I can see is that a t-tail with a swept fin gives a longer arm for the elevator and stabilizer.
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masi1157
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 2:35 pm

If (or when?) the CROR (counter rotating open rotor) engines ever will be used on larger pax aircraft, they will most surely be tail-mounted. And then you will have loads of T-tails flying around.


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Starlionblue
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 2:49 pm

Quoting masi1157 (Reply 9):

If (or when?) the CROR (counter rotating open rotor) engines ever will be used on larger pax aircraft, they will most surely be tail-mounted. And then you will have loads of T-tails flying around.

Good point. Unless they make the Kermit Cruiser of course. 
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KPWMSpotter
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Are T - Tails Condemned To Extinction?

Fri Apr 05, 2013 4:40 pm

T-Tails are inherently more aerodynamically efficient than conventional tails. A conventional tails sits directly in the down wash from the wing. The down wash from the wing creates an effective angle of attack relative to the horizontal stabilizer, forcing the stabilizer to either have a greater surface area or move to greater deflections to produce the required pitching moments. A T-Tail sits above the majority of the down wash and can act in free-stream air.

Typically a T-Tail horizontal stabilizer can be sized smaller (ie lighter) than a conventional horizontal tail thanks to higher aerodynamic efficiency. Unfortunately, mounting the horizontal stabilizer atop the vertical stabilizer tends to reduce the speed at which the assembly will succumb to flutter. The reduced flutter speed can be corrected by installing reinforcements to stiffen the vertical stabilizer, negating most of the weight savings from the smaller horizontal tail.

The aerodynamic and structural benefits and problems that come with a T-Tail usually cancel each other out. Most modern T-Tails are installed due to other operational concerns. For biz-jets and aircraft like the CRJ, the T-Tail is necessary to get the stabilizer out of the jet blast from rear mounted engines. For aircraft like the ATR and Q400, the tail is removed from the prop-wash. For large cargo aircraft like the C-5 or C-17, the tail is mounted high to allow for the installation of a rear cargo ramp and to prevent ground vehicles from inadvertently running into the low tail while loading.

The T-Tail is hardly dead, but it's heyday has certainly passed. When designers were working on the Piper Tomahawk or T-Tailed Lance they knew full well of the aerodynamic benefits, but did not fully understand the costs of the structural stiffening required. These days, designers will tend to choose the most conventional design unless other operational concerns drive them to something like a T-Tail.
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Goldenshield
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RE: Are T - Tails Condemned To Extinction?

Sat Apr 06, 2013 12:13 pm

Quoting KPWMSpotter (Reply 11):
hese days, designers will tend to choose the most conventional design unless other operational concerns drive them to something like a T-Tail.

Although there have been several design trends over the past few century, the trend currently in glider design is to have a T-tail, which minimizes the chance of FOD, handling damage, and easy assembly/disassembly for putting into a trailer.
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nomadd22
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RE: Are T - Tails Condemned To Extinction?

Sat Apr 06, 2013 5:07 pm

Quoting KPWMSpotter (Reply 11):
T-Tails are inherently more aerodynamically efficient than conventional tails. A conventional tails sits directly in the down wash from the wing. The down wash from the wing creates an effective angle of attack relative to the horizontal stabilizer, forcing the stabilizer to either have a greater surface area or move to greater deflections to produce the required pitching moments. A T-Tail sits above the majority of the down wash and can act in free-stream air.

Efficiency mainly matters in cruise. And since most plane fly with negative lift on the horizontal stabilizer, that downwash can be an advantage.
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DocLightning
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RE: Are T - Tails Condemned To Extinction?

Sat Apr 06, 2013 7:46 pm

For now, all engines are still ducted turbofans and it appears as if they will continue to be for the forseeable future because they avoid several engineering problems that occur as part of other arrangements, like UDFs.

The only advantage to a T-tail is that if the engines are mounted high, it keeps the tailplane out of the way of the jetwash. T-tails have multiple disadvantages, such as increased total aircraft length, increased weight, and issues with recovery from deep stalls.

For a ducted turbofan, the most efficient place to mount the engines is on the wings for a number of reasons. For even small airliners (70+ seats), all services will be to airports where a jetramp or at least some airstairs will be available. Thus, the fuselage can be serviced easily even though the engines do eat up some height. The 737 right now requires airstairs and a belt loader, and these are available at almost any airport with enough commercial service to receive at least one 100+ passenger aircraft a day.

For very small jet aircraft, like bizjets, they may be operating in and out of airfields without airstairs or any means of servicing the fuselage, and so in their case there are advantages to rear-mounting the engines (less FOD risk on semi-prepared fields, too). Thus, T-tails will remain for those.
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TrijetsRMissed
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RE: Are T - Tails Condemned To Extinction?

Sat Apr 06, 2013 8:33 pm

It's highly unlikely we'll see another T-tail at the mainline level. The reality is Airbus and Boeing have proven conventional designs, which will remain their calling card. Each has shown their unwillingness to sway from the A320/737 designs, let alone a clean sheet T-tail. New entrants seem to be piggy backing off of this technology as well.

Unfortunately, the inevitable extinction of T-tails (and tri-jets, for that matter) was sealed when Boeing acquired McDonnell Douglas. MDC was dedicated to both designs until the end, and at least for the T-tail, would have continued on for another generation. Sadly for airliner spotters, the Executives decided to cash-in with the acquisition, and the rest is history.

Quoting DocLightning (Reply 14):
The only advantage to a T-tail is that if the engines are mounted high, it keeps the tailplane out of the way of the jetwash. T-tails have multiple disadvantages, such as increased total aircraft length, increased weight, and issues with recovery from deep stalls.

Not true, Doc. The height of the engines is not the only advantage. Others, such as the aerodynamic advantages, have been detailed above. Any viable training program makes the deep stall phenomenon inconsequential.

Secondly, increased length is not inherently a bad thing. When MDC stretched the MD-90 to accommodate the larger engines, it provided additional capacity. According to a reliable source of mine, DL earns greater profitability on it's MD-90 when compared to the A320. The operating costs favor the MD-90 slightly, and the revenue potential is also higher with capacity for 12 additional seats.

Lastly, increased weight is also a false generalization. The fact is 717's OEW is approx 20,000 lbs lighter than the A319...and the 717 is 13 ft longer...
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DocLightning
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RE: Are T - Tails Condemned To Extinction?

Sun Apr 07, 2013 6:11 am

Quoting TrijetsRMissed (Reply 15):
Secondly, increased length is not inherently a bad thing. When MDC stretched the MD-90 to accommodate the larger engines, it provided additional capacity. According to a reliable source of mine, DL earns greater profitability on it's MD-90 when compared to the A320. The operating costs favor the MD-90 slightly, and the revenue potential is also higher with capacity for 12 additional seats.

Lastly, increased weight is also a false generalization. The fact is 717's OEW is approx 20,000 lbs lighter than the A319...and the 717 is 13 ft longer...

When you are designing an aircraft, it helps if all total linear dimensions are as small as possible. Length is one of them. In certain situations, a few extra meters of overall length won't make much difference. But there are some tight clearances in which length is the limiting factor. As the DESIGNER of an aircraft, rather than the operator, total length is a significant value.
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CRJ900
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RE: Are T - Tails Condemned To Extinction?

Sun Apr 07, 2013 10:16 pm

As long as Delta is around, T-tails will not be extinct, with growing fleets of B717 and MD90 plus the latest top-up order for 40+30 x CRJ900  

T-tails are lovely aircraft, love watching them take off.
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Viscount724
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RE: Are T - Tails Condemned To Extinction?

Sun Apr 07, 2013 10:31 pm

Quoting TrijetsRMissed (Reply 15):
Lastly, increased weight is also a false generalization. The fact is 717's OEW is approx 20,000 lbs lighter than the A319...and the 717 is 13 ft longer...

Almost all the difference in overall length is due to the 717's T-tail configuration. There's less than a 2 ft. (20 inches) difference in the fuselage length, and the overall length of the A319 is the same as the fuselage length.

If not mistaken a higher percentage of the A319's fuselage length is also usable for seating/galleys/lavatories etc. That's always been an issue for rear-engined aircraft due to the portion of the the rear fuselage required for the engines.
 
TrijetsRMissed
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RE: Are T - Tails Condemned To Extinction?

Mon Apr 08, 2013 2:32 am

Quoting DocLightning (Reply 16):
As the DESIGNER of an aircraft, rather than the operator, total length is a significant value.

Considering aircraft are designed for operations, I don't see how this counters the actual data I provided in response to your claim. Is this a factor as why to A/B designers are unlikely to start with a clean sheet T-tail? Probably. Does it substantiate an implied inferior performance for operations. Not at all. My point is, arguments that are not absolute, should not be used as a blanket generalization.

For example, the MD-82 has about the same rate of fuel burn as a 733, but can carry an additional 40 pax due to it's length. This is why AA dumped the AirCal frames rather quickly, all the while taking NB deliveries of F100s...

Quoting Viscount724 (Reply 18):
That's always been an issue for rear-engined aircraft due to the portion of the the rear fuselage required for the engines.

It's true conventional tail aircraft have more usable fuselage length. But again, if it does not significantly hinder performance, weight, costs, etc - the actual quantitative data, then it not a critical issue. It goes back to my statement on absolutes. We can see a trend and spin it based on assumptions, but the real factual data needs to corroborate those claims.

Just like Doc's point, is this a factor as to why Airbus and Boeing will continue with conventional tail designs? Yes. Is it an accurate blanket statement on why T-tail designs are inferior and thus no longer produced? Absolutely not. See MD-82/733 comparison.
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thegeek
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RE: Are T - Tails Condemned To Extinction?

Mon Apr 08, 2013 3:54 am

How about a low wing, T-tail design with engines mounted above the wing. Is there any chance of that appearing ever? Seems to reduce the pitching moment caused by thrust with below wing mounted engines.
 
LH707330
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RE: Are T - Tails Condemned To Extinction?

Mon Apr 08, 2013 5:42 am

Quoting TrijetsRMissed (Reply 15):
Unfortunately, the inevitable extinction of T-tails (and tri-jets, for that matter) was sealed when Boeing acquired McDonnell Douglas. MDC was dedicated to both designs until the end, and at least for the T-tail, would have continued on for another generation.

Given that the MD-11 and MD-90 were warmed-over versions of their predecessors, I wouldn't say McDac was particularly "dedicated."

Quoting thegeek (Reply 20):
How about a low wing, T-tail design with engines mounted above the wing. Is there any chance of that appearing ever? Seems to reduce the pitching moment caused by thrust with below wing mounted engines.

Maintenance nightmare. The thrust moment is minor compared to the hassle (and damage risk) associated with overwing engines.
 
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Scooter01
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RE: Are T - Tails Condemned To Extinction?

Mon Apr 08, 2013 7:03 am

Quoting thegeek (Reply 20):
How about a low wing, T-tail design with engines mounted above the wing. Is there any chance of that appearing ever?

This one comes to mind:

View Large View Medium
Click here for bigger photo!

Photo © Mike Paschal



Here's another one:

View Large View Medium
Click here for bigger photo!

Photo © Leif Giesecke


Although not a T-tail, it was very fondly spoken about by a former Cimber cabincrew member in regards to cabin-noise, and people-comfort etc.

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Starlionblue
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RE: Are T - Tails Condemned To Extinction?

Mon Apr 08, 2013 7:14 am

Overwing engines are problematic. The one advantage is ground clearance. The pitching moment is not a big issue AFAIK.

With overwing engines you don't get wing twisting relief from under/forward engines and you don't get noise blanketing from the wing. You also make service more difficult.

Quoting Scooter01 (Reply 22):
lthough not a T-tail, it was very fondly spoken about by a former Cimber cabincrew member in regards to cabin-noise, and people-comfort etc.

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TrijetsRMissed
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RE: Are T - Tails Condemned To Extinction?

Mon Apr 08, 2013 8:24 pm

Quoting LH707330 (Reply 21):

Given that the MD-11 and MD-90 were warmed-over versions of their predecessors, I wouldn't say McDac was particularly "dedicated."

That's typical a.net non-sense. One can say the NEO and MAX are "warmed-over versions" as well. Does that mean Airbus and Boeing are not dedicated to these designs?

As someone who worked as a third party overlay with MDC in the '80s and '90s, they had certainly put all their eggs in the T-tail basket, for their narrow-body families. If the C-level didn't sellout and MDC held steady in third place, we would not be having this discussion.
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LH707330
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RE: Are T - Tails Condemned To Extinction?

Tue Apr 09, 2013 5:27 am

Quoting TrijetsRMissed (Reply 24):
That's typical a.net non-sense. One can say the NEO and MAX are "warmed-over versions" as well. Does that mean Airbus and Boeing are not dedicated to these designs?

One could say the NEO and MAX are warmed over, but they are still the same size as the CEO/NG. The MD-11 and MD-90 had small wings inherited from earlier designs that made them less competitive.
 
TrijetsRMissed
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RE: Are T - Tails Condemned To Extinction?

Tue Apr 09, 2013 6:11 am

Quoting LH707330 (Reply 25):
The MD-11 and MD-90 had small wings inherited from earlier designs that made them less competitive.

That is true. But that doesn't diminish the said "dedication" which you are questioning. I can tell you there were no alternative designs in LGB and the future of the company rested on the MD-90 and MD-95 in August, 1997. Like I said before, MDC engineers went all-in with the T-tail design, an in essence produced a 60 year run, (provided MD-90s and 717s operate into the 2020s as expected). You can spin the outcome of those decisions any way you want, but that's aside from the point. If the same basic design produces a 60 year run isn't dedication, then I don't know what is.
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