boacvc10
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Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 5:03 am

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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WingedMigrator
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 5:34 am

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?
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 3:41 pm

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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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 5:05 pm



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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 5:15 pm



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.
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 5:40 pm



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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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 5:49 pm



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
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OldAeroGuy
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 9:15 pm



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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Jan 13, 2009 10:30 pm



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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 3:31 am



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?
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 3:41 am

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.
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 3:45 am

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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 3:50 am



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.
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 7:10 am



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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 8:09 am



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.
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 10:54 am

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
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 11:08 am



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
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 2:47 pm

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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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 3:56 pm



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 ?

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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 4:25 pm

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]
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 5:34 pm



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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Wed Jan 14, 2009 10:11 pm



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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 3:34 am

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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 3:54 am

As far as I remember, A380's vertical stabilizer height was one of big issues with FAA. What was the outcome of that story?
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 7:24 am

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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 12:08 pm



Quoting Oly720man (Reply 20):
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.

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 performance, modern engines being much more reliable?

Quoting OldAeroGuy (Reply 21):
On the bombers, it allowed the dorsal turret to engage better a fighter coming in from 6 o'clock high.

I'd think that the area blocked for the gunner by twin fins is much larger than with a single fin, where you have only the frontal area.

Quoting OldAeroGuy (Reply 21):
On the twin boom P38 (and others of that configuration) where else would you put the verticals?

Of course. I was only pointing out that the use of the word 'tail' was a bit off.

Quoting Kalvado (Reply 23):
As far as I remember, A380's vertical stabilizer height was one of big issues with FAA.

Why? Because of structures like this?

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OldAeroGuy
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 3:56 pm



Quoting Ptrjong (Reply 25):
Quoting OldAeroGuy (Reply 21):
On the bombers, it allowed the dorsal turret to engage better a fighter coming in from 6 o'clock high.

I'd think that the area blocked for the gunner by twin fins is much larger than with a single fin, where you have only the frontal area.

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.
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 5:06 pm



Quoting OldAeroGuy (Reply 26):
Quoting Kalvado (Reply 23):
As far as I remember, A380's vertical stabilizer height was one of big issues with FAA.

Why? Because of structures like this?

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 of plane going around unable to clear 60 ft obstacle with enough clearance.
I don't remember details, but I believe that was discussed over here - still I cannot find the thread.
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 6:23 pm



Quoting Kalvado (Reply 27):
Quoting OldAeroGuy (Reply 26):
Quoting Kalvado (Reply 23):
As far as I remember, A380's vertical stabilizer height was one of big issues with FAA.

Why? Because of structures like this?

Not my quote. Try Ptrjong.

Quoting Kalvado (Reply 27):
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 of plane going around unable to clear 60 ft obstacle with enough clearance.

Takeoff obstacle clearance is bsed on the lower extremities, not the upper ones.

I can't think of a single reason why the FAA (or EASA) would have any issue with a vertical tail having too great a span.
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kalvado
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 6:44 pm



Quoting OldAeroGuy (Reply 28):
Not my quote. Try Ptrjong.

Sorry, my bad..

Quoting OldAeroGuy (Reply 28):
Takeoff obstacle clearance is bsed on the lower extremities, not the upper ones.

we're talking about go-around of any aircraft, flying over A380 blocking runway.
Apparently lowest point of aircraft going around must be above highest point of whatever is on a runway - 15 feet difference between 380 and 747 may become critical issue.
 
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ptrjong
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RE: Why Does A380 Have Only One Vert Stablizer?

Sat Jan 24, 2009 10:29 pm



Quoting OldAeroGuy (Reply 26):
A fighter coming in at 4 or 8 o'clock has a more difficult time scoring hits and isn't as great a threat.

Makes sense, thanks.

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RE: Why Does A380 Have Only One Vert Stablizer?

Sun Jan 25, 2009 12:22 am



Quoting Ptrjong (Reply 25):
Why? Because of structures like this?

Wow.What height clearence is that?
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ptrjong
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RE: Why Does A380 Have Only One Vert Stablizer?

Mon Feb 02, 2009 8:11 pm



Quoting HAWK21M (Reply 31):
Wow.What height clearence is that?

22 metres, so a 747 can pass but an A380 cannot. It's not a major taxiway, though.

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RE: Why Does A380 Have Only One Vert Stablizer?

Mon Feb 02, 2009 8:54 pm



Quoting Ptrjong (Reply 32):
22 metres, so a 747 can pass but an A380 cannot. It's not a major taxiway, though.

I guess they did not foree a A380 at the time of construction.  Smile
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iwok
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Feb 03, 2009 4:56 am



Quoting WingedMigrator (Reply 1):
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

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 would make them much lighter than a simply supported single V stab. The H stabs would not have any additional load on them along the weakest axis:

A V stab has a tremendous moment on it, necessitating the need for a very strong root: simply supported structures need to be the beefiest.

Hence the middle supported twin V stab should be lighter.

Quoting Starlionblue (Reply 11):
As I understand it, a single tail is always the lightest and simplest solution. The only reasons for multiple tails are:

I'm not sure from a simply statics point of view: however dynamics and yaw/roll/AOA combinations might do somethings funky to the actual loads.

Quoting Ptrjong (Reply 17):
But there's also many tailwheelers with twin tailfins like the Beech 18 and Lockheed 12/14. Where is the structural or aerodynamic advantage?

I believe structurally its better, but probably more complex and definitely in order to ensure safety each V stab might have to be over designed in case of one failing thus rendering any weight savings negligible.

I have no idea whatsoever on the aerodynamics....

Quoting Flypig687 (Reply 19):
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.

Moments have nothing to do with the weight or structure, but everything to do with unsupported length.

A bridge with only one end fixed will have huge moments at the ends. A bridge supported in the middle, much less and the stresses much lower.

Aerodymanics must have something to do with this: or cost?

iwok
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Feb 03, 2009 6:42 am



Quoting Iwok (Reply 34):
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

That would be wonderful, if only the runway had a couple of notches to accommodate the V stabs as the aircraft rotates Big grin
 
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Feb 03, 2009 6:52 am



Quoting Iwok (Reply 34):
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 would make them much lighter than a simply supported single V stab.

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 you've got four times as many joints. You could model the V stab as a plate stuck to the end of the H stab, but the stresses end up working out the same because you've got a distributed aero load over the V stab that's reacted at a single point where it attaches to the H stab (basically, a sideways coat hanger).

Tom.
 
iwok
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RE: Why Does A380 Have Only One Vert Stablizer?

Tue Feb 03, 2009 4:29 pm



Quoting WingedMigrator (Reply 35):
That would be wonderful, if only the runway had a couple of notches to accommodate the V stabs as the aircraft rotates

Heh heh. Real world use add all sorts of complexities. I guess that's why planes with twin V stabs have a raised tail..

Quoting Tdscanuck (Reply 36):
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 you've got four times as many joints. You could model the V stab as a plate stuck to the end of the H stab, but the stresses end up working out the same because you've got a distributed aero load over the V stab that's reacted at a single point where it attaches to the H stab (basically, a sideways coat hanger).

Correct you are. If there were two stabs, each supported in the middle, we'd see something like this.

Each V stab is half the height of a single V stab.

Since they're supported in the middle. The bending moment would be applied on half the hieght (which is already half the height of the single V stab ===> therefore the moments are 1/4 what you'd see on a single V stab = large weight savings + increased complexity.

Regardless, the 380 would be super sexy with twin V stabs.  Silly

-iwok

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