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1337Delta764
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Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 4:19 am

Sorry that I had to abbreviate the title.

Why hasn't Boeing made a T-tailed/rear engined aircraft since the 727? The 717 doesn't count as it was originally designed by McDonnell Douglas, and is a modernized DC-9.

The 757 was originally supposed to have a T-tail, but with wing-mounted engines. In the end, Boeing decided to go with a conventional tail.

The 7J7 was supposed to have both a T-tail and rear-mounted engines, but the propfan engines did not appeal to airlines.

While there are some who believe that the 737RS will use a T-tailed rear-engine design to accomadate the larger engines, most believe that Boeing will stick to an aircraft with wing-mounted engines and a conventional tail using a taller landing gear to accomodate the larger engines.

Does anyone have thoughts on this?
 
jamesbuk
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 4:26 am

It adds a hell of a lot of weight, you have to strengthen the vertical part of the tail, and i believe that the T-tails are more likely to tail stall. so all in all not economically viable

Rgds --James--
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futurecaptain
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 4:28 am

Easier to work on engines
Quieter cabin
Less structure needed in rear of a/c
Better CG placement
Deep stall characteristics of T-tail's

Just my  twocents 
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trintocan
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 6:02 am

Some might argue that the rear-mounted engines actually give a quieter cabin than wing-mounted ones although the rear cabin would be noisier. Then again, the limitations as described by others hold true, along with the fact that there is a practical limit to the size of the engines one can rear-mount as the centre of gravity and weight issues become significant. The V2500s of the MD90 are the largest ever rear-mounted engines.

The prop-fan engine project was eventually shelved because the engines suffered from excessive vibration - again requiring considerable structural support to overcome - and the improvements in efficiency were not as great as originally thought.

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Flyboy14295
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 6:10 am

I would also think that the sheer size of the tail for say, the 747, although i know that would never happen, would have to withstand so much on not that big of a support, I.E. the top of the tail. I don't think that the wings these days are actually visually connected. They just go into the body of the a/c and are connected internally. Correct me if I am wrong which i probably am.
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airfrnt
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 6:16 am

Quoting 1337Delta764 (Thread starter):

Why hasn't Boeing made a T-tailed/rear engined aircraft since the 727? The 717 doesn't count as it was originally designed by McDonnell Douglas, and is a modernized DC-9.

There are a few problems with it.

  • T-Tails have really bad problems with Deep Stall characteristics. A stalling plane basically has situations where the control surfaces can be in the "shadow" of the wing (ie, no Air flow over it) making a stall very difficult if not impossible to recover from.
  • Rear mounted engines are actually harder for maintainence.
  • Turbulence problems are different because of sharper and shorter wings.
 
ksupilot
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 6:25 am

They really seem to be a thing of the past. Even RJs are beginning to stray away from T-Tails, look at the E-Jets.
Even though T-Tails are usually more quiet, this is an issue that is disappearing in wing mounted engines as well as engines become more quiet. Therefore it doesn't make sense to go through all off the trouble of mounting the engines on the tail.
 
roseflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 8:15 am

Quoting Jamesbuk (Reply 1):
It adds a hell of a lot of weight, you have to strengthen the vertical part of the tail, and i believe that the T-tails are more likely to tail stall. so all in all not economically viable

Actually the T-tail is a more aerodynamic and efficient design. With the placement of the horizontal stabilizor and elevators farther back, they can be smaller. A T-tail produces less drag. That's a big advantage. It can overcome the extra weight associated with a stronger vertical stabalizor. However again the effectiveness of the rudder improves, so the stabalizor is shorter. It is the deep stall characteristics that really kills the T-tail.

Quoting Futurecaptain (Reply 2):
Quieter cabin

That's an advantage of rear mounted engines. Yes it is louder in the back, but those aren't the passengers that the airlines care about. The front of the cabin is quieter with rear mounted engines, which means the higher fare paying passengers get a better ride.
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wukka
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since

Fri Nov 10, 2006 11:14 am

An engineer working in any aspect of aircraft design that misspells stabilizer frightens me.
We can agree to disagree.
 
mpdpilot
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 11:26 am

Quoting Trintocan (Reply 3):
Then again, the limitations as described by others hold true, along with the fact that there is a practical limit to the size of the engines one can rear-mount as the centre of gravity and weight issues become significant.

if you look at the weight of a MD-90 and MD-88 they actually weight less per passenger than all of the airbuses and most of the boeings. also as long as the CG position isn't that important as long as it is under the wings. one last thing a rear center of CG is much better aerodynamically.

so I have wondering for a very long time why rear mounted engines aren't more popular.
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wukka
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 12:34 pm

Quoting MPDPilot (Reply 9):
also as long as the CG position isn't that important as long as it is under the wings. one last thing a rear center of CG is much better aerodynamically.

Huh? Please explain how the center of gravity is not important to flight, and how a "rear center of center of gravity" (you said it, not me) is much better aerodynamically, unless you want to fly loop-de-loops to your destination.

You can't change CG just because you want to avoid dealing with physics.

Weight and balance, dude.
We can agree to disagree.
 
roseflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 12:43 pm

Quoting Wukka (Reply 8):
An engineer working in any aspect of aircraft design that misspells stabilizer frightens me.

I'm not sure where you got the idea that engineers are supposed to be able to spell. I don't work on stabilizers, so I think it is acceptable not to be able to spell the word. I work on jet engines myself, but I know that spelling is not a forte of my colleagues, but some damn fine electrical generators are designed in the plant that I work at, so I think that is acceptable. It is amazing how many spelling errors there are on engineering designs and prints from back in the day before everything was done on computers. It's amazing we got to the moon.

Quoting MPDPilot (Reply 9):
also as long as the CG position isn't that important as long as it is under the wings. one last thing a rear center of CG is much better aerodynamically.

There is a very narrow range where the CG can safely be on any given plane. Weight and balance is crucial as to controling it. If you have a bigger center of gravity range, you are going to have to fight it in order to have it fall in line with the center of lift. That would mean bigger elevators and much less efficiency. A smaller CG range increases performance.

[Edited 2006-11-10 04:44:35]
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dz09
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 12:49 pm

Quoting Wukka (Reply 8):
An engineer working in any aspect of aircraft design that misspells stabilizer frightens me.

Engineers cannot spell because they usually think faster than they can write. Beware of people who can spell and have nice handwriting, they're usually not as sharp as their spelling. Thank god for spell check!
 
wukka
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 1:54 pm

Quoting RoseFlyer (Reply 11):
I'm not sure where you got the idea that engineers are supposed to be able to spell.



Quoting DZ09 (Reply 12):
Engineers cannot spell because they usually think faster than they can write.

Spelling is the "simple" part, right?

We all started out as little kids with English, Mathematics and whatnot. Spelling was in there somewhere. Somehow you found your way into higher education, which involves proving yourself through testing; the SATs and or the ACTs, as well as a nice interview with some college staff, mayhap. Spelling has followed you throughout your career, even if it doesn't matter to you.

Not to piss in your Wheaties, but an Engineer of any sort, including the ones that drive trains, should be paying attention to detail. Spelling is a detail, and you apparently think that it doesn't matter.

There's no doubt that you were of strong enough character to get yourself into school, as evidenced by your degree.

So when your drawring up you're plans for your engun, remembur that sometimes detale counts and the next time a fan blaid brakes off and peerces the hidrawlicks, you mite have missed a detale. Congradulations on colledge.

...and as for Engineers thinking faster than they can write? Perhaps. Applying their skills in the same fashion is nothing short of carelessness.
We can agree to disagree.
 
redflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 2:07 pm

For all those who say a major drawback to the T-tail is its deep stall characteristics, why in this day and age would anyone care about that? Are modern FBW systems (including those of Boeing) not programmed to prevent stalls? Even on slightly older aircraft you have stick shakers/pushers that prevent a stall or, at a minimum, give ample warning of an impending stall. When was the last time an airliner went into a deep stall that, had it been a T-tail, would not have been able to recover?

Also, regarding the issues with the CG, has anyone taken a gander at the Bombardier CRJ900? Doesn't seem to be a big deal with that airplane (although 2 out of the 4 flights I've been on required re-arranging everyone in the cabin in order to keep the plane within its CG limits).

Not trying to flame anyone's opinion or analysis here; just asking simple questions.

[Edited 2006-11-10 06:34:02]
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futurecaptain
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 2:17 pm

Quoting RedFlyer (Reply 14):

It is true, most modern airplanes have devices to prevent stalls in airliners. Nevertheless there are weather phonomena which may quickly induce a stall such as a microburst...but with one of those you are probably close to the ground and it wouldn't matter t-tail or not. Or perhaps on takeoff the pilot flying may pull back on the stick just a little too much. So yes, stalls are not common, but not unheard of.
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gigneil
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 2:24 pm

Quoting MPDPilot (Reply 9):

if you look at the weight of a MD-90 and MD-88 they actually weight less per passenger than all of the airbuses and most of the boeings.

And both are fractionally as capable, too...

NS
 
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 2:47 pm

IIRC the main reason for the t-tails was because the short/medium haul jets being produced then (727, Caravelle, DC-9, 1-11, 737) needed to get in and out of short runways and use terminals with limited facilities for servicing the aircraft, and rear engines with a t-tail was one way to make the wing as efficient as possible and keep the aircraft relatively low to the ground. The main exception was the 737, and even then the -100/-200 had the engines mounted directly to the wings to keep the aircraft low to the ground. Since these classic aircraft were designed, airports have improved to the point that the vast majority have full facilities for servicing modern jet aircraft. While I prefer the aesthetics of the t-tail (especially on the 727, DC-9, and VC-10) the t-tail will probably be limited to bizjets and the small end of the rj market (if it continues to exist).
 
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 3:10 pm

Quoting Wukka (Reply 13):
Not to piss in your Wheaties, but an Engineer of any sort, including the ones that drive trains, should be paying attention to detail. Spelling is a detail, and you apparently think that it doesn't matter.

And getting lost and stuck in such a trivial detail would make one lose sight of the bigger picture. An editor must perforce spell well, but I'm better reassured that the plane I'll be flying on was designed by someone who computes brilliantly! I'd much prefer that they're careless with their spelling rather than their design analysis. BTW, aren't these two skills supposedly controlled by different brain lobes?
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ksupilot
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 3:16 pm

Quoting Wukka (Reply 8):
An engineer working in any aspect of aircraft design that misspells stabilizer frightens me.

Who cares if they are the worst speller or the National Spelling Bee Champion, as long as they do their job right I'm happy.
 
TrijetsRMissed
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 3:35 pm

Quoting RedFlyer (Reply 14):
For all those who say a major drawback to the T-tail is its deep stall characteristics, why in this day and age would anyone care about that? Are modern FBW systems (including those of Boeing) not programmed to prevent stalls? Even on slightly older aircraft you have stick shakers/pushers that prevent a stall or, at a minimum, give ample warning of an impending stall. When was the last time an airliner went into a deep stall that, had it been a T-tail, would not have been able to recover?

As you said, stalls are very uncommon nowadays. The last uncontrollable dive involving a T-tail plane in the US was the Alaska Airlines MD-83 crash in 2000. This was a result of poor maintenance not a stall and why I will never fly that airline. They cut costs deliberately and forged inspections. It was a disaster waiting to happen.

Having said that, in general the MD-80 family has a far better safety record than the 737 or A320.
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Viscount724
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 6:36 pm

Rear engined, T-tail designs also significantly increase the aircraft's overall length in relation to the actual revenue-generating length of the passenger cabin, due to the proportion of the rear fuselage to which the engines are attached. Mounting the horizontal stabilizer at the top of the tail further increases the overall length.

The original 727-100 is 33 feet longer than the 737-200 but the passenger capacity at maximum seating density is virtually the same.

The 727-200 has almost identical maximum seating as the 737-800 and 737-900 but the 727-200 is 15 feet longer than even the 737-900.

It's often overlooked that the 727-200 is several inches longer than the longest 707-320, and only 2 feet shorter than the 757-200, and as has already been mentioned, wing-mounted engines make the engines and tail control surfaces more accessible during maintenance.

Aircraft with wing-mounted engines also take up less space at airports and in maintenance hangars.

[Edited 2006-11-10 10:39:07]
 
boeingfixer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since

Fri Nov 10, 2006 9:42 pm

Quoting Trintocan (Reply 3):
The V2500s of the MD90 are the largest ever rear-mounted engines.

Not true:

MD90 V2528D5 5250 lbs

Il62M D30KU 5882 lbs

L1011 RB211-524 9814 lbs

The largest ever rear-mounted engine is the RB211 on the L1011. The largest all tail mounted engines are the Soloviev D30KU on the Il62M.

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AirbusA6
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 10:01 pm

Quoting Trintocan (Reply 3):
The V2500s of the MD90 are the largest ever rear-mounted engines.

RR tested their initial RB211 on the back of a VC10, producing the ultimate 3 engined jet (2 Conways on one side, 1 RB211 on the other!). Maybe BAC should have reintroduced the VC10 as a twin!
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roseflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Fri Nov 10, 2006 10:58 pm

Quoting Wukka (Reply 13):
Somehow you found your way into higher education, which involves proving yourself through testing; the SATs and or the ACTs

The fact that the SAT is a multiple choice test shows the importance of spelling in getting in to college. (I'm just giving you a hard time because you gave me a hard time).

Quoting Wukka (Reply 13):
Not to piss in your Wheaties, but an Engineer of any sort, including the ones that drive trains, should be paying attention to detail. Spelling is a detail, and you apparently think that it doesn't matter.

I pay attention to detail at work. I am meticulous to make sure the work that I do is correct. Right now I spend my days redesigning the cores for the electrical generators found on many jets such as the F-16, 787, among other planes. When it comes to bonding the lamination surfaces with a steam oxide coating, I'm careful. No mistakes are acceptable. But when I'm at home on my couch. I don't give a **** about spelling.

Quoting Wukka (Reply 13):
So when your drawring up you're plans for your engun, remembur that sometimes detale counts and the next time a fan blaid brakes off and peerces the hidrawlicks, you mite have missed a detale. Congradulations on colledge.

Good one!

Quoting RedFlyer (Reply 14):
For all those who say a major drawback to the T-tail is its deep stall characteristics, why in this day and age would anyone care about that? Are modern FBW systems (including those of Boeing) not programmed to prevent stalls?

Stalls can occur in weather conditions. In todays world, planes land in conditions that they probably shouldn't be landing in. For example take the crashes of the last decade from planes flying in thunderstorms. What is worse is when planes fly near typhoons and get unexpected winds. When a plane is slow on approach in strong winds in stormy weather, stalls are more likely to occur and even the best FBW and computers can't protect from a microburst. Better stall characteristics can save lives.
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Revelation
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since

Fri Nov 10, 2006 11:42 pm

In addition to all of the above, my reading has taught me that manufacturers do not like the T-tail because it makes it harder to make follow-on models. To make a longer-range airplane, you need more thrust to lift the extra fuel, so you end up with heavier engines, thus a heavier tail, so you have to stetch the nose to keep the plane balanced, which means the fore fuselage has to be stronger, so it has to be heavier, which reduces range. The net effect is you can add in capacity but not much in range. This is one of the reasons we never saw a long range follow-on to the 717. If the engines are CG-mounted, the balancing issue is a non-issue, and you can choose to add larger engines and stretch to get more capacity (ala 777-300ER), or not stretch and get more range (ala 777-200LR).

As pointed out above, the T-tail allows a lot more freedom in wing design. The wing can be thinner, because it doesn't have to support the weight of the engine, and it can have more freedom in the shape, because the wing doesn't need to be designed with the pylons in mind. On the other hand, the engines oppose the tendency of the wing to twist.

Bottom line: the trend is clear: industry is moving away from the T-tail.

And do we really need to clutter up the board with arguments about spelling?
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Rj111
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 12:20 am

Quoting BoeingFixer (Reply 22):
The largest ever rear-mounted engine is the RB211 on the L1011. The largest all tail mounted engines are the Soloviev D30KU on the Il62M.

I believe the MD-11 just about swoops the largest (heaviest) tail mounted award at 9850lb (CF6-80C2D1).
 
redflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 12:22 am

Quoting RoseFlyer (Reply 24):
Stalls can occur in weather conditions. In todays world, planes land in conditions that they probably shouldn't be landing in. For example take the crashes of the last decade from planes flying in thunderstorms. What is worse is when planes fly near typhoons and get unexpected winds. When a plane is slow on approach in strong winds in stormy weather, stalls are more likely to occur and even the best FBW and computers can't protect from a microburst. Better stall characteristics can save lives.

Good explanation but it still seems a very insignificant reason (meaning a seldom occurring event) to avoid T-tail designs.

Quoting Revelation (Reply 25):
In addition to all of the above, my reading has taught me that manufacturers do not like the T-tail because it makes it harder to make follow-on models. To make a longer-range airplane, you need more thrust to lift the extra fuel, so you end up with heavier engines, thus a heavier tail, so you have to stetch the nose to keep the plane balanced, which means the fore fuselage has to be stronger, so it has to be heavier, which reduces range. The net effect is you can add in capacity but not much in range. This is one of the reasons we never saw a long range follow-on to the 717. If the engines are CG-mounted, the balancing issue is a non-issue, and you can choose to add larger engines and stretch to get more capacity (ala 777-300ER), or not stretch and get more range (ala 777-200LR).

Now THAT seems like the most valid explanation yet! Thanks.  Smile
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787engineer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since

Sat Nov 11, 2006 1:07 am

Quoting Revelation (Reply 25):

As pointed out above, the T-tail allows a lot more freedom in wing design. The wing can be thinner, because it doesn't have to support the weight of the engine, and it can have more freedom in the shape, because the wing doesn't need to be designed with the pylons in mind. On the other hand, the engines oppose the tendency of the wing to twist.

On a similar note, by having wing mounted engines it creates a more uniform spanwise wing loading which allows the wing to be somewhat lighter. It may not be as aerodynamic efficient, but there are always trade-offs. There's also the issue of moving the fuel from the tanks in the wing to the back of the plane.
 
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 1:13 am

An Engineer I know at Boeing explained to me that it also has to do with T-tail requirements in either Britain or in Europe as a whole, I forget which. Anyone else heard this?
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c680
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 1:48 am

There must be a size / weight cross over point for T-Tail vs. Non-T-Tail.

Why?

Every single aircraft ever designed to be a biz jet that I can think of has some form of rear engine and T or mid tail.

Care to explain that from an enginerring point of view?

Quoting Revelation (Reply 25):
In addition to all of the above, my reading has taught me that manufacturers do not like the T-tail because it makes it harder to make follow-on models. To make a longer-range airplane, you need more thrust to lift the extra fuel, so you end up with heavier engines, thus a heavier tail, so you have to stetch the nose to keep the plane balanced, which means the fore fuselage has to be stronger, so it has to be heavier, which reduces range. The net effect is you can add in capacity but not much in range. This is one of the reasons we never saw a long range follow-on to the 717. If the engines are CG-mounted, the balancing issue is a non-issue, and you can choose to add larger engines and stretch to get more capacity (ala 777-300ER), or not stretch and get more range (ala 777-200LR).

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roseflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 1:59 am

Quoting RedFlyer (Reply 27):
Good explanation but it still seems a very insignificant reason (meaning a seldom occurring event) to avoid T-tail designs.

If it saves one crash and a single life, then it is a signficant reason. I don't know of documented cases though were the deep stall characteristics of the T-tail caused a plane to crash when a conventional tail would not have.
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Ferret
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 2:18 am

Can I ask a silly question? (going to anyway)  Smile :

Aren't we confusing T-tail and rear-mounted engines? The two are mutually exclusive and having one does not necessarily mean you have to have the other. I recall that there were 747 studies that included T-Tail with wing-mounted engines. And the L1011 and DC10 both have rear mounted engines but not T-tails.

Another silly question, since I am on a roll....  Wink :

What about a mid mounted horizontal stabilizer? Call it a lowercase t-tail. Does this split the difference and create a good compromise of all other considerations and designs?
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redflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 2:24 am

Quoting RoseFlyer (Reply 31):
If it saves one crash and a single life, then it is a signficant reason. I don't know of documented cases though were the deep stall characteristics of the T-tail caused a plane to crash when a conventional tail would not have.

Hi RoseFlyer: I didn't mean to diminish the value of your point. I know as a private pilot that T-tails have an inherent weakness when it comes to stalls (One reason, among others, the Piper Tomahawk had the moniker "Traumahawk"?). The fact is, though, that there are a lot of things that could save lives. But where is the balance in the trade-off? For example, I think putting inert gas into fuel tanks would save more lives than any potential deep stalls resulting from a T-tail, but you don't see engineers moving away from past fuel system design. (Yes, I know there is movement in that direction lately.)

Best regards,

R
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c680
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 2:43 am

Quoting Ferret (Reply 32):
Aren't we confusing T-tail and rear-mounted engines?

A bit, yes. Look at the Beech King Air 200 for a wing mounted engine with a T-tail. King Airs were also produced with a low (normal) tail...

Quoting Ferret (Reply 32):
What about a mid mounted horizontal stabilizer? Call it a lowercase t-tail.

Like a Cessna 680 Citation Sovereign?

Look at the Cessna Citation V for an example of a "low" horizontal stab with rear engines...

but again, these are all biz planes....
My happy place is FL470 - what's yours?
 
ksupilot
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 2:44 am

Quoting C680 (Reply 30):

Every single aircraft ever designed to be a biz jet that I can think of has some form of rear engine and T or mid tail.

Some of this does have to do with the fact that biz jets are lower to the ground, and some do have engines that would not clear the ground if they were under the wing.
 
KPIE172
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 3:47 am

I know its been discussed in Tech/Ops a few times before but don't the devices at the rear of most T-tail aircraft (ie MD-80) that deploy during a stall help to negate some of the more deadly properties of the T-tail deep stall? The name escapes me as to what they're called... They're located just behind the engines close against the fuselage.
Blue side up!
 
boeingfixer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 3:56 am

Quoting RJ111 (Reply 26):
I believe the MD-11 just about swoops the largest (heaviest) tail mounted award at 9850lb (CF6-80C2D1).

Beat the RB211/L1011 out by 36 lbs but the Il62M still retains the prize for the heaviest ALL tail mounted engines.
Cheers, John YYC
 
roseflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 4:05 am

Quoting Ferret (Reply 32):
What about a mid mounted horizontal stabilizer? Call it a lowercase t-tail. Does this split the difference and create a good compromise of all other considerations and designs?

Look at the Caravelle if you want an example of this. It was the first jet with rear mounted engines and had a lowercase t tail.

Quoting RedFlyer (Reply 33):
, I think putting inert gas into fuel tanks would save more lives than any potential deep stalls resulting from a T-tail, but you don't see engineers moving away from past fuel system design. (Yes, I know there is movement in that direction lately.)

I'm not sure where you are going with that. There are going to be nitrogen generators on the 787 that fill the fuel tanks with Nitrogen as fuel is consumed to cut the risk of volatile vapors catching fire or causing an explosion.
If you have never designed an airplane part before, let the real designers do the work!
 
redflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 5:17 am

Quoting BoeingFixer (Reply 37):
I'm not sure where you are going with that. There are going to be nitrogen generators on the 787 that fill the fuel tanks with Nitrogen as fuel is consumed to cut the risk of volatile vapors catching fire or causing an explosion.

My point was that despite several instances of fuel tank explosions, the most infamous one being the TWA accident in 1996, there was very little movement until recently to inert fuel tanks. Certainly, more lives have been lost in fuel tank explosions in recent years than from deep, unrecoverable stalls.

Very few lives lost from fuel tank explosions = no changes to fuel systems (787 and future planes notwithstanding).

Even fewer lives lost from deep unrecoverable stalls = systemic avoidance of T-tail designs???

The point is, and the point I've been trying to make is, that I don't think a lack of T-tail/rear-mounted engine aircraft models is a result of bad stall characteristics. There are plenty of ways to overcome bad characteristics in different flight regimes through either mechanical devices (e.g., stall strips, stick pusher, etc.) or other means (FBW system restrictions).

I would think wing mounted engines pose their own set of bad characteristics, such as assymetrical thrust in an engine-out situation or being more prone to FOD or even an engine ground strike in x-wind landings. But you don't see manufacturers avoiding that kind of design because of bad characteristics.

So far, the most plausible explanation I've heard for a lack of rear engine/T-tail designs is Revelation's in reply #25. But that's just my opinion; I am not an engineer nor do I spend billions buying airplanes for an airline  Wink
A government big enough to take away a constitutionally guaranteed right is a government big enough to take away any guaranteed right. A government big enough to give you everything you need is a government big enough to take away everything you have.
 
TrijetsRMissed
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 5:44 am

Quoting Ferret (Reply 32):
Aren't we confusing T-tail and rear-mounted engines? The two are mutually exclusive and having one does not necessarily mean you have to have the other

I think you are confusing mutually exclusive with independent variables. To say the two are mutually exclusive means you can have one or the other, but not both. In almost all cases, T-tail aircraft have rear-mounted engines.
There's nothing quite like a trijet.
 
TrijetsRMissed
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 5:51 am

Quoting Revelation (Reply 25):
The net effect is you can add in capacity but not much in range. This is one of the reasons we never saw a long range follow-on to the 717.

The reason there is no larger long range version of the 717 is Boeing's takeover of McDonnell Douglas. The MD90-50 would have been the plane you are describing. One hundred seventy passengers, 2,800 NM range. Now if you are suggesting an aircraft with 777 range and size then you have a point.
There's nothing quite like a trijet.
 
roseflyer
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 6:02 am

Quoting RedFlyer (Reply 39):
So far, the most plausible explanation I've heard for a lack of rear engine/T-tail designs is Revelation's in reply #25. But that's just my opinion; I am not an engineer nor do I spend billions buying airplanes for an airline

I'm not really sure I Revelation's is the best. I think that is part of the reason to stay away from T-tails as it may be more difficult to stretch them and increase range, but the DC-9 was one of the most stretched airliners ever. The CRJ has been stretched twice and the CRJ to begin with is a commercial version of a stretched business jet.
If you have never designed an airplane part before, let the real designers do the work!
 
Ferret
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 7:28 am

Quoting TrijetsRMissed (Reply 40):
but not both. In almost all cases, T-tail aircraft have rear-mounted engines.

Fair enough, they're not MUTUALLY EXCLUSIVE. But you CAN have one without the other. Some examples of this noted by some of the other replies.
Murphy lives here.
 
TrijetsRMissed
Posts: 1983
Joined: Sun Oct 29, 2006 12:15 pm

RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sat Nov 11, 2006 8:39 am

Quoting Ferret (Reply 43):
Fair enough, they're not MUTUALLY EXCLUSIVE. But you CAN have one without the other. Some examples of this noted by some of the other replies.

That's true, most notably on the widebody aircraft. DC10/L1011
There's nothing quite like a trijet.
 
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Devilfish
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since

Sat Nov 11, 2006 7:55 pm

Quoting TrijetsRMissed (Reply 40):
In almost all cases, T-tail aircraft have rear-mounted engines.

And here's a very common exception.....

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twal1011727
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sun Nov 12, 2006 1:45 am

Quoting MPDPilot (Reply 9):
if you look at the weight of a MD-90 and MD-88 they actually weight less per passenger than all of the airbuses and most of the boeings. also as long as the CG position isn't that important as long as it is under the wings. one last thing a rear center of CG is much better aerodynamically.



Quoting Wukka (Reply 10):
Huh? Please explain how the center of gravity is not important to flight, and how a "rear center of center of gravity" (you said it, not me) is much better aerodynamically, unless you want to fly loop-de-loops to your destination.

The statement MPDPilot says is missing a very important part and that is as long as its within the limits designed into any aircraft (CG envelope.)

If the CG is towards the aft end of the cg envelope, the horz stab exerts less downward force to keep the nose up(tail mount stabs A/C only.)
Less L/D necessary.

Concerning the rest of his post, He needs to reword his statement to include "the CG envelope." If he did then his "CG location" statement would be semi correct.

KD
 
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ClassicLover
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sun Nov 12, 2006 3:26 am

Quoting AirbusA6 (Reply 23):
RR tested their initial RB211 on the back of a VC10, producing the ultimate 3 engined jet (2 Conways on one side, 1 RB211 on the other!). Maybe BAC should have reintroduced the VC10 as a twin!

... and the airframe of that particular VC10 was so distorted that it was scrapped for parts.

Yes indeed - why not have a t-tail without rear mounted engines if the t-tail is more efficient?
I do enjoy a spot of flying, especially when it's not in economy!
 
mpdpilot
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RE: Why No T-tail/rear Eng. Boeing Aircraft Since 727?

Sun Nov 12, 2006 3:29 pm

Quoting TWAL1011727 (Reply 46):
Concerning the rest of his post, He needs to reword his statement to include "the CG envelope." If he did then his "CG location" statement would be semi correct.

I am sorry I didn't make that clear. you did however get what I was trying to say. I have another question and that is: "semi correct" what do you mean?

after reading all these replies I still don't see a sound reason for the lack of rear mounted engines. there are reasons for both so one might think that there would have been some out there.
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