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Why Does A380 Have Only One Vert Stablizer?  
User currently offlineBOACVC10 From United States of America, joined Jul 2006, 614 posts, RR: 0
Posted (5 years 8 months 3 weeks 1 day ago) and read 11467 times:

Hello, I looked at the cutaway of the A380 recently which can be seen here, and was thinking of the structural penalty in that design for having that humongous vertical stablizer (the Tail) at the rear of the aircraft. Obviously there is a lot of supporting material there, but could it have been replaced with a simpler support structure if the aircraft was twin-tailed (like the AN-225) or three-tailed (like the Connie) ?


If their were two vertical stablizers, could the rear fuselage be enlarged somewhat and allow more seating/crew rest arrangements, do you think ?


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BOACVC10


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37 replies: All unread, showing first 25:
 
User currently offlineWingedMigrator From United States of America, joined Oct 2005, 2214 posts, RR: 56
Reply 1, posted (5 years 8 months 3 weeks 1 day ago) and read 11449 times:

I think you are looking at two design compromises.

The twin tail on the An-225 was there to accommodate the Russian space shuttle, riding piggy back

The triple tail on the Connie was (reportedly) to fit inside low hangars.

I doubt that either of these solutions is more structurally efficient than a single vertical stab, since the stab root must bear moments from both the vertical and horizontal surfaces... and the bigger loads (on the vertical stabilizer) are cantilevered out to the end of the H stab. Not good.

Quoting BOACVC10 (Thread starter):
If their were two vertical stablizers, could the rear fuselage be enlarged somewhat and allow more seating/crew rest arrangements, do you think ?

The A380 isn't big enough?


User currently offlineBOACVC10 From United States of America, joined Jul 2006, 614 posts, RR: 0
Reply 2, posted (5 years 8 months 3 weeks 14 hours ago) and read 11288 times:

Quoting WingedMigrator (Reply 1):

The twin tail on the An-225 was there to accommodate the Russian space shuttle, riding piggy back

I thought the Buran was smaller than the shuttle by a bit, so why would they need to remove the vertical stablizer, when the NASA Shuttle Carrier Aircraft kept the original Vert. Stablizer.

If anything, I would have thought the laminar air flow around the Orbiter when atop the Shuttle Carrier Aircraft would have rendered the airflow around the principal Vertical Stablizer, and consequently, they would have removed it without penalty, and used only the outboard stabilizers.


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[Edited 2009-01-13 07:42:22]


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User currently offlineOly720man From United Kingdom, joined May 2004, 6757 posts, RR: 11
Reply 3, posted (5 years 8 months 3 weeks 12 hours ago) and read 11230 times:



Quoting BOACVC10 (Reply 2):
they would have removed it without penalty, and used only the outboard stabilizers.

The Shuttle B747 still has to fly about without the Shuttle on its back. The smaller surfaces on the elevators are nowhere big enough for control of the B747 and they have no rudder. The additional surfaces are there to compensate for any loss in lateral control caused by the presence of the Shuttle.



wheat and dairy can screw up your brain
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (5 years 8 months 3 weeks 12 hours ago) and read 11218 times:



Quoting BOACVC10 (Reply 2):
I thought the Buran was smaller than the shuttle by a bit, so why would they need to remove the vertical stablizer, when the NASA Shuttle Carrier Aircraft kept the original Vert. Stablizer.

The AN-225 was purpose built to carry the shuttle. Since they started with that in mind, I can see why they just ditched the central vertical stab and went with two outboard ones with rudders.

The 747 was modified from the existing 747, which already had a central vertical stab. Augmenting the yaw stability with the fixed horizontal stabilizer extensions looks like a much simpler mod than removing the vertical tail entirely and designing a whole new rudder system.

Tom.


User currently offlineBOACVC10 From United States of America, joined Jul 2006, 614 posts, RR: 0
Reply 5, posted (5 years 8 months 3 weeks 12 hours ago) and read 11197 times:



Quoting Oly720man (Reply 3):
The Shuttle B747 still has to fly about without the Shuttle on its back. The smaller surfaces on the elevators are nowhere big enough for control of the B747 and they have no rudder.

the AN-225 Mriya regularly flies without their Buran on the back, and it is larger than the 747 Shuttle Carrier Aircraft. Yes, the supplementary vertical stablizers are quite small on the SCA.



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User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 6, posted (5 years 8 months 3 weeks 11 hours ago) and read 11191 times:



Quoting BOACVC10 (Reply 5):
the AN-225 Mriya regularly flies without their Buran on the back

It now always flies without the Buran on its back as the Buran is no longer in design use



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3527 posts, RR: 67
Reply 7, posted (5 years 8 months 3 weeks 8 hours ago) and read 11074 times:



Quoting Tdscanuck (Reply 4):
Quoting BOACVC10 (Reply 2):
I thought the Buran was smaller than the shuttle by a bit, so why would they need to remove the vertical stablizer, when the NASA Shuttle Carrier Aircraft kept the original Vert. Stablizer.

The AN-225 was purpose built to carry the shuttle. Since they started with that in mind, I can see why they just ditched the central vertical stab and went with two outboard ones with rudders.

Plus the Shuttle wake makes the 747 vertical buffet, leading to restrictions in cruise speed.

The buffet with the Shuttle aft body fairing is bad enough, but when flights were made with the fairing removed for Shuttle glide tests, flight times were limited to insure the vertical did not fail from fatigue.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineDocLightning From United States of America, joined Nov 2005, 19794 posts, RR: 59
Reply 8, posted (5 years 8 months 3 weeks 7 hours ago) and read 11016 times:



Quoting EMBQA (Reply 6):

It now always flies without the Buran on its back as the Buran is no longer in design use

In fact, the Buran was destroyed when its hangar collapsed on top of it.


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 9, posted (5 years 8 months 3 weeks 2 hours ago) and read 10900 times:



Quoting DocLightning (Reply 8):
In fact, the Buran was destroyed when its hangar collapsed on top of it.

Was there only one built.Any link to the story?
regds
MEL.



Think of the brighter side!
User currently offlineFlypig687 From United States of America, joined Jul 2007, 56 posts, RR: 0
Reply 10, posted (5 years 8 months 3 weeks 2 hours ago) and read 10897 times:

to get back to the root of the conversation, one reason Airbus may have gone with the single vertical stab is since the double and triple tail a/c look kinda tacky where the single tail looks very good. Since the moments and aerodynamic benefits are very similar between the different aesthetics may of come into play.

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17054 posts, RR: 67
Reply 11, posted (5 years 8 months 3 weeks 1 hour ago) and read 10894 times:

As I understand it, a single tail is always the lightest and simplest solution. The only reasons for multiple tails are:
- Redundancy for aircraft that may get shot at. For example F-15, MiG-29, Su-27.
- Maximum height restrictions in hangars. For example Connie.
- Airflow issues. For example An-225.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineWingedMigrator From United States of America, joined Oct 2005, 2214 posts, RR: 56
Reply 12, posted (5 years 8 months 3 weeks 1 hour ago) and read 10893 times:



Quoting Flypig687 (Reply 10):
Since the moments and aerodynamic benefits are very similar

They aren't! That's the whole point. See reply 1. Aesthetics have very little role in airliner configuration. Form follows function.


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3527 posts, RR: 67
Reply 13, posted (5 years 8 months 2 weeks 6 days 22 hours ago) and read 10823 times:



Quoting Starlionblue (Reply 11):
The only reasons for multiple tails are:
- Redundancy for aircraft that may get shot at. For example F-15, MiG-29, Su-27.
- Maximum height restrictions in hangars. For example Connie.
- Airflow issues. For example An-225.

There is at least one other reason:

Shorter span verticals reduce some the stability problems that result from Yaw-Roll coupling.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (5 years 8 months 2 weeks 6 days 21 hours ago) and read 10800 times:



Quoting OldAeroGuy (Reply 13):
There is at least one other reason:

Shorter span verticals reduce some the stability problems that result from Yaw-Roll coupling.

And one more...twin tails allow you to cant the tails, which reduces radar reflection back to the radar and can improve stealth. Tilting the vertical stab isn't really an option when you only have one.

Tom.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17054 posts, RR: 67
Reply 15, posted (5 years 8 months 2 weeks 6 days 18 hours ago) and read 10744 times:

Ok so that's five reasons, none of which have any relevance for the 380 except the yaw-roll coupling thing mentioned by OldAeroGuy. And I'm guessing a good yaw damper is cheaper than twin tails.  Wink


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBuyantUkhaa From Mongolia, joined May 2004, 2900 posts, RR: 3
Reply 16, posted (5 years 8 months 2 weeks 6 days 18 hours ago) and read 10737 times:



Quoting HAWK21M (Reply 9):
Was there only one built.Any link to the story?

There were several.

List of built copies: http://en.wikipedia.org/wiki/Buran_program (you never know with this source, but anyway)

Pics of the collapse:

http://www.buran.ru/images/jpg/bbur89.jpg

http://www.buran.ru/images/jpg/bbur90.jpg



I scratch my head, therefore I am.
User currently offlinePtrjong From Netherlands, joined Mar 2005, 3944 posts, RR: 18
Reply 17, posted (5 years 8 months 2 weeks 6 days 14 hours ago) and read 10623 times:

A single tailfin as appied on the overwhelming majority of aircraft is obviously the simplest solution. The A380's scale makes no difference in principle.

So the proper question is, why did so many aircraft in the WW II era have twin tailfins? For the nosewheel designs, I guess hangar height clearance may have been a reason. But there's also many tailwheelers with twin tailfins like the Beech 18 and Lockheed 12/14. Where is the structural or aerodynamic advantage?

Quoting BOACVC10 (Thread starter):
vertical stablizer (the Tail)

Strictly speaking, the tail is the rear end of an aircraft.

Quoting BOACVC10 (Thread starter):
twin-tailed


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User currently offlineBOACVC10 From United States of America, joined Jul 2006, 614 posts, RR: 0
Reply 18, posted (5 years 8 months 2 weeks 6 days 13 hours ago) and read 10586 times:



Quoting Ptrjong (Reply 17):
So the proper question is, why did so many aircraft in the WW II era have twin tailfins? For the nosewheel designs, I guess hangar height clearance may have been a reason. But there's also many tailwheelers with twin tailfins like the Beech 18 and Lockheed 12/14. Where is the structural or aerodynamic advantage?

Perhaps they were concerned about metal fatigue, and the possibility that one of the tails may uncouple in mid-flight ?

BOACVC10



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User currently offlineFlypig687 From United States of America, joined Jul 2007, 56 posts, RR: 0
Reply 19, posted (5 years 8 months 2 weeks 6 days 13 hours ago) and read 10561 times:

Quoting WingedMigrator (Reply 12):
They aren't! That's the whole point. See reply 1. Aesthetics have very little role in airliner configuration. Form follows function.

I looked back at the first reply and from the way I read it you agree with me. Since the weight/structure of a single and multiple vert stab will be probably in the same realm therefore the moments on the hub will be the similar.

As far as aerodynamics are concerned, from what I understand yaw/roll moments are more dependent on total area and span of the vert. stabalizer. The individual stabs in a multi-stab configuration will by no means have the same area and span as a single fin, however the combined area and span will, i would imagine, need to be similar to the single fin configuration to achieve similar performance, therefore aerodynamics would be similar.

Quoting OldAeroGuy (Reply 13):
Shorter span verticals reduce some the stability problems that result from Yaw-Roll coupling.

would the smaller individual span matter with the combined area and span most likely similar if not greater than a single configuration?

Your reasons for the multiple fins a) carry Russian space shuttle b) fit in hangar, are not concerns for A380 and say nothing about what I said. The aerodynamic need for the An-225 twin tail is due to the big structure usually placed on top which would block the flow to a single tail configuration; not something the A380 deals with.

Also ugly things usually don't fly as well as pretty things, from what I have been told.

If you think I am mistaken please correct me.

[Edited 2009-01-14 08:29:47]

User currently offlineOly720man From United Kingdom, joined May 2004, 6757 posts, RR: 11
Reply 20, posted (5 years 8 months 2 weeks 6 days 12 hours ago) and read 10511 times:



Quoting Ptrjong (Reply 17):
aerodynamic advantage?

One comment I've read is that with the fins in the propwash they are more effective than a single larger central fin, especially at low airspeed.



wheat and dairy can screw up your brain
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3527 posts, RR: 67
Reply 21, posted (5 years 8 months 2 weeks 6 days 7 hours ago) and read 10340 times:



Quoting Ptrjong (Reply 17):
So the proper question is, why did so many aircraft in the WW II era have twin tailfins?

On the bombers, it allowed the dorsal turret to engage better a fighter coming in from 6 o'clock high.

On the twin boom P38 (and others of that configuration) where else would you put the verticals?

Quoting Flypig687 (Reply 19):
Quoting OldAeroGuy (Reply 13):
Shorter span verticals reduce some the stability problems that result from Yaw-Roll coupling.

would the smaller individual span matter with the combined area and span most likely similar if not greater than a single configuration?

One aspect of roll-yaw coupling is that when the airplane rolls at a high rate, like a fighter, the induced angle of attack on the vertical causes it to produce a side force. This force causes the airplane to yaw into the turn and damps the roll rate.

If you replace a single vertical with two smaller verticals of half the area each and the same planform, the smaller verticals will have half the span. For the same side force, the twin verticals will have approximately half the roll damping of the single vertical since their center of pressure will be about half as far vertically from the airplane c.g. To have the same side force on single and twin verticals, the roll rate has to be higher to begin with on the twin vertical fighter since vertical tail sectional angle of attack is a function of roll rate and local span. At a constant roll rate, the single vertical will have a higher loading since it is seeing a higher overall angle of attack by virtue of its higher span.

This is one of the reasons you see twin verticals on many fighters.

There are other roll-yaw coupling effects, but discussing dynamic effects on this forum is a bit difficult.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineBhill From United States of America, joined Sep 2001, 980 posts, RR: 0
Reply 22, posted (5 years 8 months 1 week 4 days 2 hours ago) and read 9576 times:

It will..as soon as the ESA builds a shuttle for the 380 to carry it...or the Beluga monster..after Airbus designs and sell us the next replacement for AF1.


Carpe Pices
User currently offlineKalvado From United States of America, joined Feb 2006, 491 posts, RR: 0
Reply 23, posted (5 years 8 months 1 week 4 days 1 hour ago) and read 9573 times:

As far as I remember, A380's vertical stabilizer height was one of big issues with FAA. What was the outcome of that story?

User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 24, posted (5 years 8 months 1 week 3 days 22 hours ago) and read 9525 times:

Unless the A380 is used to carry something on it,which would affect the relative airflow to the vertical stablizer.There seems no reason for an alteration to the VS.
regds
MEL.



Think of the brighter side!
25 Post contains links and images Ptrjong : OK, but that should still hold true for modern props, if not jets, so why did twin fins disappear then? Could it be that they improved engine-out per
26 OldAeroGuy : Not in the six o'clock position. A fighter coming in at 4 or 8 o'clock has a more difficult time scoring hits and isn't as great a threat.
27 Kalvado : As far as I remember, there was something about A380 vertical stab reaching high enough to interfere with a late go-around. Something along the lines
28 OldAeroGuy : Not my quote. Try Ptrjong. Takeoff obstacle clearance is bsed on the lower extremities, not the upper ones. I can't think of a single reason why the
29 Kalvado : Sorry, my bad.. we're talking about go-around of any aircraft, flying over A380 blocking runway. Apparently lowest point of aircraft going around mus
30 Ptrjong : Makes sense, thanks. Peter
31 HAWK21M : Wow.What height clearence is that? regds MEL.
32 Ptrjong : 22 metres, so a 747 can pass but an A380 cannot. It's not a major taxiway, though. Peter
33 HAWK21M : I guess they did not foree a A380 at the time of construction. regds MEL.
34 Iwok : I think otherwise. If the twin V stabs intersect the H stab in the middle of each V stab, then there is no moment on either of the V stabs, which wou
35 WingedMigrator : That would be wonderful, if only the runway had a couple of notches to accommodate the V stabs as the aircraft rotates
36 Tdscanuck : There's still a moment. Structurally, you've just got four cantilever V stabs (two up and two down) that are shorter. So the moment is smaller, but y
37 Iwok : Heh heh. Real world use add all sorts of complexities. I guess that's why planes with twin V stabs have a raised tail.. Correct you are. If there wer
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