User avatar
EvrenErdem
Topic Author
Posts: 39
Joined: Fri Oct 28, 2016 9:00 am

Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 1:56 pm

First of all, Hello everyone from Turkey, this is my first topic and I have an interesting question. I searched about it but I couldn't find a nice answer.
So here is the question;
Although all aircrafts have two components of each things, such as 2 wings, 2 ailerons, two engines, two pilots, two hydraulic systems etc., why is there only one rudder / rudder surface?
(it is also an interview question)
My most logical answer for this question is due to aerodynamic design. However I'd like hear your answers.
Thank you.
 
StereoTechque
Posts: 89
Joined: Sat Nov 28, 2015 7:24 am

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 2:34 pm

It all depends on what mission your aircraft is designed for. The aircraft requires rudder for maneuvering around the vertical axis. These days aircraft design is all about compromise between fuel efficiency, thrust, Pax load etc. They are designed to have as less Components as possible. So if one rudder does the job of yawing, you don't need another one.
There are also aircrafts having two rudders - AN 225.
P. S. Modern Airliner wing is considered as a single wing.
Priortise..Revise and Improvise..
 
frmrCapCadet
Posts: 1235
Joined: Thu May 29, 2008 8:24 pm

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 2:58 pm

We think of wings as having two ailerons, but actually a modern wing is a complex system having innumerable moving parts. Like a bird wing it can change shapes and flight characteristics to match specific flight needs.

The P38 has a twin rudder. It had an unusually long turbo super charger, and designers realized extending the two of them just a little would support the rear part of the plane. https://en.wikipedia.org/wiki/Lockheed_P-38_Lightning This was an odd precursor of the often heard adage that to build a plane you take on engine first, and see how much plane you can build around it. This is opposed to the Wright brothers insight that controlling the flight was the first problem to solve.
Last edited by frmrCapCadet on Thu Mar 16, 2017 3:04 pm, edited 1 time in total.
Buffet: the airline business...has eaten up capital...like..no other (business)
 
GalaxyFlyer
Posts: 46
Joined: Fri Jan 01, 2016 4:44 am

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 3:00 pm

Two wings gets you nothing when one comes off! Besides most large aircraft actually have either two rudders or several means to power the rudder(s), usually from two or three hydraulic systems. Merhaba.
 
113312
Posts: 628
Joined: Sat Apr 16, 2005 9:09 am

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 4:15 pm

Unlike a ship, the rudder does not "turn" the aircraft. Some personalities, who comment on aviation as "experts" on TV often convey the notion that a rudder turns an aircraft. The rudder is used to offset unwanted yaw motion due to such factors as asymmetric thrust and aileron design or gust upsets. It is also used to align the aircraft with the runway during crosswind operations. You could have two, three or more rudder surfaces as some aircraft designs have but additional surfaces can increase weight and control complexity. A rudder size, area, and deflection angles are designed to produce the necessary degree of control, on that axis, under all flight envelope extremes.
 
rmilstre
Posts: 13
Joined: Mon Sep 12, 2016 11:42 pm

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 5:57 pm

Ideally, since a rudder (and the fin/vertical stabilizer) controls yaw moments and the horizontal stabilizer controls pitch moments, you'd want a (smaller) rudder/fin/stabilizer on the top of the fuselage and an equivalent one on the bottom.

But that's gonna make your tailstrike problems essentially insurmountable. So, the engineering compromise is to "live with" just one on the top, making it sufficiently large to safely do the job.

-R
 
mmo
Posts: 970
Joined: Thu Apr 18, 2013 3:04 pm

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 6:46 pm

Just to be technically, the 747 family does have 2 rudders. There is the upper and lower rudder......
If we weren't all crazy we'd all go insane!
 
KLDC10
Posts: 369
Joined: Tue Jun 14, 2016 8:15 pm

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 6:52 pm

mmo wrote:
Just to be technically, the 747 family does have 2 rudders. There is the upper and lower rudder......


And the Lockheed Constellation had three ;)
DC9/MD90/MD11/F70/BAE146/Q400/737/738/739/752/772/A320/A332/A333/E190
 
User avatar
EvrenErdem
Topic Author
Posts: 39
Joined: Fri Oct 28, 2016 9:00 am

Re: Why Is There Only One Rudder in an Aircraft?

Thu Mar 16, 2017 7:48 pm

Thank you for your answers, I am here and reading your answers. It's like a brainstorm for me and also I learn new things, thanks again.
As I mentioned on my first message, it is an interview question and an interesting one for an interview.
so if you have any more answers or any brainstorm ideas, I'd like to continue hearing...
 
User avatar
Starlionblue
Posts: 17442
Joined: Fri Feb 27, 2004 9:54 pm

Re: Why Is There Only One Rudder in an Aircraft?

Fri Mar 17, 2017 1:04 am

Most widebodies have two rudders for redundancy.

As mentioned above, the aerodynamic ideal might be a cruciform tailplane, which is impractical for other reasons.

KLDC10 wrote:
mmo wrote:
Just to be technically, the 747 family does have 2 rudders. There is the upper and lower rudder......


And the Lockheed Constellation had three ;)


StereoTechque wrote:
There are also aircrafts having two rudders - AN 225.
.



Not the best aerodynamic solution in either case. The Connie allegedly had three smaller fins as opposed to a large one so it would fit in existing hangars. The An-225 has two fins because when it carried Buran the orbiter would mask a central rudder. An-225's daddy the An-124 only has one fin.

Compromises as ever.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
WIederling
Posts: 3089
Joined: Sun Sep 13, 2015 2:15 pm

Re: Why Is There Only One Rudder in an Aircraft?

Fri Mar 17, 2017 10:32 pm

Starlionblue wrote:
Compromises as ever.


The Belugas get endplates for more directional stability.

A380 has a segmented rudder.
Murphy is an optimist
 
User avatar
7BOEING7
Posts: 2471
Joined: Fri Oct 12, 2012 5:28 pm

Re: Why Is There Only One Rudder in an Aircraft?

Sat Mar 18, 2017 12:49 am

Starlionblue wrote:
Most widebodies have two rudders for redundancy.



The 747 has two rudders (upper& lower) but the 767, 777 and 787 only have one. In both cases the systems supporting the rudder(s) are redundant.
 
User avatar
Starlionblue
Posts: 17442
Joined: Fri Feb 27, 2004 9:54 pm

Re: Why Is There Only One Rudder in an Aircraft?

Sat Mar 18, 2017 1:11 am

7BOEING7 wrote:
Starlionblue wrote:
Most widebodies have two rudders for redundancy.



The 747 has two rudders (upper& lower) but the 767, 777 and 787 only have one. In both cases the systems supporting the rudder(s) are redundant.


I can't believe I wrote most widebodies have two rudders. I was thinking of redundant actuation... Brainfart...

To add to the list, the 330/340 has one rudder. However it has triple redundant actuation..
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
QuarkFly
Posts: 93
Joined: Mon Aug 15, 2016 4:20 pm

Re: Why Is There Only One Rudder in an Aircraft?

Sat Mar 18, 2017 3:00 am

Just in case it has not been clarified already...More than one rudder is not necessary because aircraft can fly without the rudder (in most cases) since the ailerons can turn the aircraft without the rudder. The rudder is used primarily to keep the nose pointed in the direction of the turn only and in an emergency the pilot can fly without a rudder. Thus, a second rudder is not necessary for redundancy...there are always some exceptions.
Always take the Red Eye if possible
 
User avatar
tb727
Posts: 1861
Joined: Thu Jun 30, 2005 1:40 pm

Re: Why Is There Only One Rudder in an Aircraft?

Sun Mar 19, 2017 12:01 am

The 727 had an upper and lower rudder as well. The engine driven pumps ran the lower and the upper was by the electric pumps as well as the standby hydraulic pump. The rudders were also double hinged to increase effectiveness. Dutch roll was a big deal with this airplane so the rudder is very important and the way to make it redundant was to split and power them the way they did.
Too lazy to work, too scared to steal!
 
mxaxai
Posts: 89
Joined: Sat Jun 18, 2016 7:29 am

Re: Why Is There Only One Rudder in an Aircraft?

Sun Mar 19, 2017 11:35 am

A single rudder induces some torque on the fuselage, though. That may or may not have been the reason for the japanese J7W https://en.wikipedia.org/wiki/Kyushu_J7W had an unusual rudder configuration both above and below the wing. Other flying objects for whom takeoff and landing are not a concern have a cruciform tailplane, like the X-15 https://en.wikipedia.org/wiki/North_American_X-15 or many missiles.
 
benbeny
Posts: 115
Joined: Thu Nov 03, 2016 1:44 pm

Re: Why Is There Only One Rudder in an Aircraft?

Mon Mar 20, 2017 3:24 am

Actually, every rudder induces torque to airframe part it sits. You cannot turn airplane with rudder without torque exerted from the rudder.
 
User avatar
77west
Posts: 667
Joined: Sat Jun 13, 2009 11:52 am

Re: Why Is There Only One Rudder in an Aircraft?

Mon Mar 20, 2017 4:28 am

tb727 wrote:
The 727 had an upper and lower rudder as well. The engine driven pumps ran the lower and the upper was by the electric pumps as well as the standby hydraulic pump. The rudders were also double hinged to increase effectiveness. Dutch roll was a big deal with this airplane so the rudder is very important and the way to make it redundant was to split and power them the way they did.


I believe the lower part of the 777 rudder is triple-hinged (or at least double hinged) as well.
77West - AW109S - BE90 - JS31 - B1900 - Q300 - ATR72 - DC9-30 - MD80 - B733 - A320 - B738 - A300-B4 - B773 - B77W
 
WIederling
Posts: 3089
Joined: Sun Sep 13, 2015 2:15 pm

Re: Why Is There Only One Rudder in an Aircraft?

Mon Mar 20, 2017 10:32 am

benbeny wrote:
Actually, every rudder induces torque to airframe part it sits. You cannot turn airplane with rudder without torque exerted from the rudder.


My guess is that the OP was thinking about introducing some roll torque (longitudinal axis) into the plane while the primary purpose is torque around the vertical axis.

Do 335 had a cruciform tail with the lower part and rear propeller being emergency detachable.
Murphy is an optimist
 
User avatar
EvrenErdem
Topic Author
Posts: 39
Joined: Fri Oct 28, 2016 9:00 am

Re: Why Is There Only One Rudder in an Aircraft?

Mon Mar 20, 2017 7:09 pm

So, as I understand from your messages, if I say that everything is related to aerodynamic and also design, it won't be wrong, I guess.????
Connie has 3 rudders bcs it didn't fit into hangar.
An-225 has 2 rudders bcs it carries space shuttle.
Some military jets have 2 rudders bcs they need fast movement.
etc.
However, even though there is only one vertical stabilazer, so one rudder, there are always more than one system to control the rudder.
And Although it is not a vital part and an aircraft can fly without it, it is neccessary having a rudder surface to control the aircraft yaw movement easily.
So to have a comfortable travel with a passenger aircraft, the rudder is a crucial part.

By the way, one more time, thank you for your answers.
 
User avatar
Starlionblue
Posts: 17442
Joined: Fri Feb 27, 2004 9:54 pm

Re: Why Is There Only One Rudder in an Aircraft?

Tue Mar 21, 2017 1:01 am

EvrenErdem wrote:
So, as I understand from your messages, if I say that everything is related to aerodynamic and also design, it won't be wrong, I guess.????
Connie has 3 rudders bcs it didn't fit into hangar.
An-225 has 2 rudders bcs it carries space shuttle.
Some military jets have 2 rudders bcs they need fast movement.
etc.
However, even though there is only one vertical stabilazer, so one rudder, there are always more than one system to control the rudder.
And Although it is not a vital part and an aircraft can fly without it, it is neccessary having a rudder surface to control the aircraft yaw movement easily.
So to have a comfortable travel with a passenger aircraft, the rudder is a crucial part.

By the way, one more time, thank you for your answers.


Pretty much.

I'll add that in addition to the maneuverability bit, some military aircraft also have two fins due to to height restrictions, particularly carrier based aircraft like the F-14 and F/A-18. The first F-14 concepts had a single fin like the F-111.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Bostrom
Posts: 64
Joined: Tue Feb 02, 2016 7:11 pm

Re: Why Is There Only One Rudder in an Aircraft?

Tue Mar 21, 2017 10:01 pm

Starlionblue wrote:

Pretty much.

I'll add that in addition to the maneuverability bit, some military aircraft also have two fins due to to height restrictions, particularly carrier based aircraft like the F-14 and F/A-18. The first F-14 concepts had a single fin like the F-111.


A problem that also could be solved in another way. http://modellbygge.ifokus.se/u2/7081b56 ... /image.jpg
 
User avatar
Starlionblue
Posts: 17442
Joined: Fri Feb 27, 2004 9:54 pm

Re: Why Is There Only One Rudder in an Aircraft?

Wed Mar 22, 2017 12:44 am

Bostrom wrote:
Starlionblue wrote:

Pretty much.

I'll add that in addition to the maneuverability bit, some military aircraft also have two fins due to to height restrictions, particularly carrier based aircraft like the F-14 and F/A-18. The first F-14 concepts had a single fin like the F-111.


A problem that also could be solved in another way. http://modellbygge.ifokus.se/u2/7081b56 ... /image.jpg


Quite right. And carrier based aircraft use that method as well. It adds weight and complexity, though. But then again so do double tails. Image
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
benbeny
Posts: 115
Joined: Thu Nov 03, 2016 1:44 pm

Re: Why Is There Only One Rudder in an Aircraft?

Fri Mar 24, 2017 9:46 am

as usual, everything comes to a tradeoff. will people buy a plane with shorter height but heavier structure, or will people buy taller plane with better aerodynamics efficiency?
anyway, boeing chose solved the hangar height problem of stratocruiser by making complex and heavy folding mechanism instead of triple tail of constellation, maybe because they think that folding mechanism was worth the effort

Who is online

Users browsing this forum: Balerit, MarkusB, Starlionblue and 4 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos