Vertical Stabilizers. Options

[airlinepilote]

Hi guys,

If got a question.
Its about the vertical stabilizers.
Why does some fighters have two of those and some have one?
Look at this: http://www.richard-seaman.com/Aircraft/Air...Afterburner.jpg
2 Vertical stabilizers.

And this: http://www.aeronautics.ru/lockheed/f-16_fa...lcon/f16-10.jpg
1 Vertical stabilizer.

Why is that?
And what are the differences about it?

[Archangel]

it usually has to do with the fact that most have 2 engines and loss of power will require more rudder control thus needing 2 v-stabs. now not all fall under that stipulation. take the f-35 for example, it has a single engine but has 2 fins. but 9 times out of 10 fighters with 2 engines will have 2 vertical stabs. it also plays a roll in turning ability and braking. some planes turn the rudders in opposite directions for added speed braking. If i forgot something then one of the jet drivers will fill the slot.

[USMCmech]

The F-14 has twin vertical stabs because of height requirements on the carrier's hanger bay.

If it had had only one, it would be too tall to fit.


Same story on the Connie. It's triple tail was designed to fit into TWAs maintence hanger in St Louis.


Two short vertical fins can sometimes be made lighter than one big one.

[Archangel]

but in the case of the f-16 it does just fine so the reasons behind each plane is to each its own. the f-35 does have very short fins though.

[airlinepilote]

Could 2 v-stabs have something with speed?
Cause if you look at the SR-71, it has 2 v-stabs.

[Corsair]

Could 2 v-stabs have something with speed?  
Cause if you look at the SR-71, it has 2 v-stabs.

The stabs on the Blackbird are canted inwards to reduce the radar return. I don't think speed was the main reason for angling them.

[VH-OJQ]

What about the B-2 ????

it got none!!!!!!

how do they turn / manuvour????




Amazing

UFO???

Beauty...

ok .. can somebody explain to me how this bird turns, etcetc - without Rudders???

[Corsair]

ok .. can somebody explain to me how this bird turns, etcetc - without Rudders???    :shock:  :shock:

You can do it on any plane.

You just bank the plane to one side with the ailerons, then pull on the stick or yoke. The plane will start pointing in the direction you have turned to. Sure the turn won't be coordinated, but whatever. When flying on the sim, I rarely use the rudder at all. It's a bad habit I learned from my joystick having less than satisfactory rudder capabilities.

Granted, most planes are much more stable with a vertical stabilizer, and so the B-2 needs a computerized fly-by-wire system that makes many small corrections in the control surfaces to keep the bird flying.

It wouldn't surprise me if the B-2 could deploy the outboard speed brakes/flaps in flight to give more yaw control.

[PC-6]

Granted, most planes are much more stable with a vertical stabilizer, and so the B-2 needs a computerized fly-by-wire system that makes many small corrections in the control surfaces to keep the bird flying.

A flying wing does not necessarily need a digital FBW to fly. The YB-49 was flying in 1947, well before FBW.

There is another thread going at the moment on this forum discussing trim tabs and the effect of the stabilizers. The flying wing does not have any empennage, so all the stability problems are solved in a different way. It can be very interesting...

Two links for some of you

http://www.desktopaero.com/appliedaero/con...n/tailless.html
http://www.nurflugel.com/Nurflugel/Horten_...ody_theory.html

[flyingcanuck]

Granted, most planes are much more stable with a vertical stabilizer, and so the B-2 needs a computerized fly-by-wire system that makes many small corrections in the control surfaces to keep the bird flying.

A flying wing does not necessarily need a digital FBW to fly. The YB-49 was flying in 1947, well before FBW.

There is another thread going at the moment on this forum discussing trim tabs and the effect of the stabilizers. The flying wing does not have any empennage, so all the stability problems are solved in a different way. It can be very interesting...

Two links for some of you

http://www.desktopaero.com/appliedaero/con...n/tailless.html http://www.nurflugel.com/Nurflugel/Horten_...ody_theory.html

The YB-49 has 4 small V-stabs though.

[AirRabbit]

Hey Guys:

Actually, it takes all of the control surfaces to “turn” the airplane. You put the airplane into a banked position with aileron and rudder (or some other form of yaw control – e.g., flight spoilers – and in most flight spoiler equipped airplanes, rudder input is not necessary to maintain coordinated flight through the turn) and deflect the elevator. Yes, I know you can input rudder alone, keeping the wings level and at constant altitude, and eventually the thrust and the deflected rudder surface will change your heading, but you have to prevent the airplane from doing what it wants to do (bank and pitch down) in order for this to work.

[VH-OJQ]

ok .. can somebody explain to me how this bird turns, etcetc - without Rudders???

You can do it on any plane.

You just bank the plane to one side with the ailerons, then pull on the stick or yoke. The plane will start pointing in the direction you have turned to. Sure the turn won't be coordinated, but whatever. When flying on the sim, I rarely use the rudder at all. It's a bad habit I learned from my joystick having less than satisfactory rudder capabilities.

Granted, most planes are much more stable with a vertical stabilizer, and so the B-2 needs a computerized fly-by-wire system that makes many small corrections in the control surfaces to keep the bird flying.

It wouldn't surprise me if the B-2 could deploy the outboard speed brakes/flaps in flight to give more yaw control.

i know that you dont have to use rudder, but when i fly, my instructor always says "keep the ball in the middle." (meaning so the plane wont 'slip' or 'drift' while turning.)

wouldnt that have the same effect on the B-2 ? you cant even "keep the ball in the middle" when theres no ball.. lols.

alright, heres another question. lets just say the planes landing in heavy crosswinds, alot of the pilots uses 'crab' technique, then they use RUDDER to staighten it just before touchdown.. now, how does the B-2 work without rudder(s). ? ? ? ? ? ?

[flyingcanuck]

alright, heres another question. lets just say the planes landing in heavy crosswinds, alot of the pilots uses 'crab' technique, then they use RUDDER to staighten it just before touchdown.. now, how does the B-2 work without rudder(s). ? ? ? ? ? ?

I can't remember if it was the B-2 that has this technology, or some other plane; but I think the landing gear actually rotates to line up with the runway.

[glnflwrs]

Simply put, an airplane turns when the pilot banks the aircraft. Some of the lift is then diverted sideways and it is this sideways lift that causes the plane to turn.

Rudder input is not required to turn the plane as any pilot is aware. CFI's are notorious for reminding students to "step on the ball" to coordinate the turns. But, the aircraft was turning without the rudder.


A helicopter is a machine who's only function is to shake itself to pieces.

[Corsair]

I can't remember if it was the B-2 that has this technology, or some other plane; but I think the landing gear actually rotates to line up with the runway.

I know the B-52 can.


Okay. "Stepping on the ball" means that you are using the rudder to 'coordinate' your turn. (The rudder points the nose of the plane into the turn so that the plane doesn't slide 'uphill' as you bank due to centrifugal forces.) Now, I'm not a pilot (yet) but it would seem to me that if you banked it hard enough, the gravitational forces causing the aircraft to 'slide' down would perfectly counteract the centrifugal forces causing the plane to 'slide' up. Thus, you would use gravity to coordinate your turn - without a rudder.

Ya think? Lemme know. :D

[yaarpanjabi]

The B-2 does have "rudder" but not in the traditional sense. There is nothing that sticks up/down (vertical) as most of you know. I believe the B-2 can yaw using differential drag. You see, the outboard control surfaces can split (like the rudder of the Space Shuttle) and can increase the drag dramatically, this allows the airplane to yaw (-< sort of like that). The FBW system is constantly changing the control surfaces to keep the aiplane in controlled condition. I don't think there has been a stable aircraft without the vertical surfaces that has NOT had a FBW system.

If you were to bank a rudderless aircraft, it would probably start to side slip and end up being uncontrollable, which is why you either need some sort of vertical surfaces so that the aircraft stays in positive control, or a FBW system which can use differential drag to generate yaw.

Hope it helped. (I read this a long time ago so there might be some missing bits that I don't remember).

[glnflwrs]

The Northrop XB-35 Flying Wing had no vertical control surfaces and was very stable once they perfected the eleflaperons. (Huh?)

Corsair was very much on track when he stated that gravity would coordinate the turn without a rudder. Once a bank angle and rate of turn is established the force of gravity is acting perpendicular to the lateral axis and the wing.

[glnflwrs]

From NASA's Glenn Flight Research website...

http://www.grc.nasa.gov/WWW/K-12/airplane/turns.html

A fundamental aircraft motion is a banking turn. This maneuver is used to change the aircraft heading. The turn is initiated by using the ailerons or spoilers to roll, or bank, the aircraft to one side. The lift of the wings of the aircraft is a vector quantity which is always directed perpendicular to the flight path and perpendicular to the wings generating the lift. As the aircraft is rolled, the lift vector is tilted in the direction of the roll. We can break the lift vector into two components. One component is vertical and opposed to the weight which is always directed towards the center of the earth. The other component is an unopposed side force which is in the direction of the roll, and perpendicular to the flight path.

As long as the aircraft is banked, the side force is a constant, unopposed force on the aircraft. The resulting motion of the center of gravity of the aircraft is a circular arc. When the wings are brought level by an opposing motion of the ailerons, the side force is eliminated and the aircraft continues to fly in a straight line along a new heading. Notice that the rudder is not used to turn the aircraft. The aircraft is turned through the action of the side component of the lift force. The rudder is used during the turn to coordinate the turn, i.e. to keep the nose of the aircraft pointed along the flight path. If the rudder is not used, one can encounter an adverse yaw in which the drag on the outer wing pulls the aircraft nose away from the flight path.

[AirRabbit]

I can't remember if it was the B-2 that has this technology, or some other plane; but I think the landing gear actually rotates to line up with the runway.

I know the B-52 can.

Yes, the B-52 could land "in a crab" with a pretty decent crosswind (I don't remember the amount - but it was up there) while the landing gear would be tracking straight down the runway. Watching them exercise that capability while taxiing out for takeoff was really weird!

...it would seem to me that if you banked it hard enough, the gravitational forces causing the aircraft to 'slide' down would perfectly counteract the centrifugal forces causing the plane to 'slide' up. Thus, you would use gravity to coordinate your turn - without a rudder. Ya think?

Actually, Corsair, it’s Lift that causes the turn. Excuse me, I don’t mean to “talk down” to you, but for anyone who might read this, the forces on a straight and level, un-accelerating airplane are all balanced. The force of Thrust is equal to and opposite of the force of Drag; and force of Lift is equal to and opposite of the force of Weight. [OK all of you physics majors, don’t jump on me for the terms…] If you bank the airplane, the forces become unbalanced. Because Lift works in a direction perpendicular to the wing surface (which has now been “tilted” because of the bank angle), and weight (gravity working on the mass) always acts down (toward the center of the earth), the vertical portion of the Lift (the vertical Lift vector) is no longer equal to, even though it is still opposite of, the weight, the airplane will start to descend. If there is no intent to turn the airplane (i.e., there is no rudder applied to maintain “coordinated” flight), this descent (in the form of a slip) will change the direction of the relative wind striking the leading edge of the downside wing and (if there is any dihedral) will increase the Lift on the downside wing more than on the Upside wing, and tend to roll the airplane back to level. Once regaining level flight (IF the airspeed has remained constant – and in the real world that would not have happened) the vertical portion of the Lift vector will return to its original value, and balance the weight – bringing the airplane back into “stable” flight.

However, if rudder IS applied to maintain “coordinated” flight, the small amount of the Lift being generated that is horizontal (toward the center of the turn) will change the airplane heading – turn the airplane. And, IF the pilot decides to keep the airplane at the same altitude, s/he will have to pull harder on the elevator – increasing the amount of Lift being generated, so that the vertical component of Lift will equal the vertical force of weight (i.e., maintaining level flight), s/he will also have increased the horizontal component of that increased Lift and the airplane will turn more quickly.

That is a very short way of explaining the very long reasoning behind why increasing “back-stick” pressure, resulting in increased Lift, turns the airplane. I hope this helps. And, again, forgive me if I sound like I'm talking "down" to anyone.

[Corsair]

Thanks for taking the time to write all that out, AirRabbit. You have indeed made it easier for others to understand the aerodynamics involved. Especially the vector component details - my professors would be proud!

So let's put it all together:

Viewed from behind:
1) Plane banks left (with enough elevator to keep it from losing altitude).
2) Lift vector now points diagonally up to the left. (Plane starts to turn.)
3) Gravity vector points down.
4) Centrifugal force vector points to the right.
5) If you sum up 3) and 4) the resulting vector points diagonally down to the right.
6) Now 2) and 5) are opposite to each other and the plane is coordinated without using the rudder (assuming that the bank was hard enough to cause enough of a loss of lift to give gravity an edge which is enough to keep the turn coordinated).

Granted, finding the perfect bank angle to allow this 'gravitational coordination' is kinda difficult. A rudder would make a lot more sense.
In fact.....
I've put probably 75+ hours into my aerobatic computer sim. Out of habit (and the lack of a nearby CFI) I taught myself this technique of using gravity to coordinate my turns. Looking back, I wouldn't be surprised if this technique is only viable in a plane equipped to handle high-G loading and high bank angles.
In fact.....
When I was flying recently in an AT-6 Texan (another cool story) I was directed to bank to the left. Guess what I did? Yeah. Out of habit, I threw the plane into a 45-degree bank and started to pull. The pilot in the back made it clear very quickly under no uncertain terms that that much bank was unnecessary and that the rudder was also to be used.

- All that to say that gravitational coordination may only be possible with high performance planes.....

A few more days and I'll be getting back into this stuff when college starts up again.