Hot answers tagged

37

The control surfaces of airliners are not connected to the pilots' control via cables; they are operated by a hydraulic pump. When the engines are shut down, there is no hydraulic pressure in the pipes, and the control surface is free to move. The rudder is moved from the center position by wind. If you observe the gates, you should note that all airplanes ...


31

It is the Auxiliary Power Unit (APU) inlet door. Image from Boeing Aero Magazine


29

Two reasons: T-tail design is often imposed on designs with twin engines mounted at the aft fuselage. This means they have a small moment arm in the yaw direction, the vertical tail is dimensioned to compensate for engine failure. The further away form centreline the engine is mounted, the higher the yawing moment that the remaining engine exerts upon ...


25

What is better and easier for small-scale models is not necessarily better for larger aircraft. First, you can't say that the fixed part "does nothing". The tail is primarily a stabiliser; without it, a normal airplane will not fly at all. Only then it is a control surface, which allows it to fly well and how you want it. Consequently, the size of the tail ...


21

Excerpt from McDonnell Douglas MD-11 by Arthur A C Steffen: The remaining eight aircraft were delivered bare-metal with a corrosion protection coating, except for the rudder which has to be painted prior to being installed and balanced, and was completed in the full livery in the carrier's modern paint facilities. The above text is in reference to KLM's ...


20

Most of the initial aircraft made by Wright brothers had the twin horizontal stabilizer setting. However, the elevators in these cases were set in the front, rather than back, as is the norm now. By Wright brothers - OhioLINK Digital Media Center, Public Domain, Link Quite a few of the early aircraft had a 'box' like configuration, notably the Santos-...


19

The double decker horizontal tail was a popular choice for large biplanes, even into the 1930s. Below is a picture of the Zeppelin Staaken R VI giant airplane and below it a Handley-Page H.P.42 passenger aircraft from 1931. Zeppelin Staaken R VI over Leipzig (picture source) Handley-Page HP42 passenger aircraft (picture source) As with the wing, a braced ...


18

As was said in the comments above, it is the support structure for the engine as seen in this drawing:


16

Tailless means no horizontal tail, but a vertical tail is still allowed. Examples are the Convair F-102 or Convair B-58. Convair B-58 Hustler (picture source) Compare this to a flying wing: Here even the vertical tail is left off. Since a classic delta would have too little lever arm for yaw control, this requires a higher aspect ratio wing. An example is ...


16

That is almost certainly a navigation antenna. From the E190 AOM (Airplane Operations Manual): You can see the VOR2/LOC2 antenna rather more clearly in this photo: (The VOR1/LOC1 and VOR3 antennae are embedded within the tailfin.) Similar nav antennae are used on many smaller aircraft such as (more modern) light aircraft, utility aircraft, business ...


16

There are two features that you may be referring to. A) Is an antenna that is shaped to provide low drag. Not all F16 have this. B) The true dorsal "fin": increases structural strength decreases drag by providing a fillet for the vertical stabilizer, improves stability about the vertical axis, and specifically in the case of the f16 (when ...


15

It is a seal- to prevent entry of air into the stabilizer mounting area. For aircraft with trimmable horizontal stabilizers (THS), there is an opening to the rear of the aft bulkhead to allow for the movement of the THS. It can be seen in the following image for Boeing 787. Boeing 787 aft fuselage structure; image from aero-news.net Now, as the opening ...


15

(Source) The comments and answers already say it's for noise reduction. What's more intriguing is the how: The blades are not coplanar (image). The tail-rotor of the Apache rotates clockwise (video) when viewed from the port side. The nearest blades (nearest plane) to the viewer are the leading blades of each group. A group is two close blades regardless ...


14

I have no experience on Boeing or Airbus airplanes but the most likely cause would be gust locks installed on the aircraft. Some aircraft, like a C-172, have a pin that locks the aileron and elevator in place. Other airplanes have an externally mounted device locking the rudder in place. http://www.weekendcfii.com/photos/c172preflt/C172_gust_lock.jpg ...


14

You are missing the weight force. The wing should stall first because then it will produce less lift and the weight will make the aircraft pitch down. In attached flow, the lift from wing and tail is balanced such that the combined resulting force is acting exactly at the longitudinal position of the center of gravity. If the wing stalls, the balance of ...


13

It comes down to a matter of philosophy. Or, if you are less generous, it’s a matter of fashion. Note that the Russian equivalent to the C-141, the Il-76, uses a T-tail, too, while the An-124 uses a conventional tail. T-tails were in fashion in the early jet age. They were widespread, first in fighters and later in transport aircraft, too, because they: ...


12

Two characteristics drive vertical tail size in airliners: Critical engine out: Here the tail needs to compensate the yawing moment of the live engine on one wing. Yaw damping: This is aided by a yaw damper, but enough damping must remain for the case of a failed damper. Especially the dutch roll eigenmode is driving tail size. On the other hand the tail ...


12

Complicated is a matter of opinion and I wont address that specifically since its somewhat subjective. But the core of the question is "why did the L-1049E have 3 tails" which is a legitimate question for this site. The design was to allow the aircraft to fit in hangars of the time A sleek fuselage, something like an elongated fish with smooth curves, ...


11

Raymer gives the following answer: The 'T-Tail' is also widely used. A T-tail is inherently heavier than a conventional tail because the vertical tail must be strengthened to support the horizontal tail, but the T -tail provides compensating advantages in many cases. Due to end-plate effect, the T -tail allows a smaller vertical tail. The T ...


9

Controllability and redundancy. Airliners are certified according CFR 14 Part 25, which specifies that upon engine fail the aircraft must still be able to fly and climb: it must have more than one engine. After an engine has failed, the rudder must be deflected in order to compensate for the asymmetric thrust of the remaining engine. With a V-tail, this ...


9

The four parts you're referring to contain the actuation mechanism for the rudder, similar to the wing pods that contain the flap actuation mechanism. The reason they are not arranged symmetrically is that the rudder has two sections (you can see the 'cut' in the middle in your image)- apparently to provide redundancy and improve safety. So,each section has ...


9

High wing military aircraft (c141 and c5 both are) use T tails for multiple reasons. to prevent rocks and debris from damaging the tail when landing off airport to keep tails out of the engine thrust line (which are higher than on a low wing aircraft) during cruise where vibration may cause fatigue a T tail can be smaller (lighter with less drag) as the ...


8

There is quite a famous example of this! but other than the Wright Flyer, I don't know of any. My layman conjecture as to why this is not more common is that the tail only needs to be large enough to counteract the moment that CG exerts relative to the center of pressure of the wing. Large tail surfaces can balance large torque loads, but that is ...


7

Image source The tail rotor of the Apache consists of two 2-bladed teetering rotors, referred to as scissor rotors. This unusual configuration was first implemented by Hughes Helicopters in the late 1960s for reducing the noise of the OH-6 helicopter. The OH-6 had a single twin blade teetering tail rotor, which Hughes wanted to rotate slower for reducing ...


7

Doesn't this make it more difficult to control during flight as the surface is way smaller? Design Rudder authority becomes most important (arguably) when one wing-mounted engine fails or is shut down. To combat this on the DC10 The rudder takes up a large proportion of the area of the fin The rudder has dual articulation - there are two vertical hinges....


7

A propeller accelerates the air flowing through it in order to create thrust. This acceleration is highest at low speed. The acceleration will increase the dynamic pressure at the tail if it is in the slipstream. A higher dynamic pressure will cause a proportionally higher aerodynamic force. A H-tail will, therefore, only be in the slipstream if two engines ...


7

For a small RC plane that travels at slow speeds your design would work great. However these type of designs have structural limitations. For an all movable vertical and horizontal stabilizer setup all the forces exerted on the control surfaces would be transferred to a movable bearing. This would be a single point of failure if the bearing were to fail. ...


6

No, not at all - there are at least two Delta Wing aircraft that feature a conventional tail, and they are the Gloster Javelin and the Mig 21 https://en.wikipedia.org/wiki/Gloster_Javelin https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-21 (Courtesy of http://airheadsfly.com/) In addition (and I believe this is within the spirit of what you've asked) ...


6

When the aircraft is parked there's no hydraulic pressure, which means that the rudder will be deflected by external forces, ie wind. The ailerons and elevators might get deflected by the wind or their own weight as well.


Only top voted, non community-wiki answers of a minimum length are eligible