Questions tagged [aircraft-structures]

For structural engineering questions about airframes and the mechanical structures aboard aircraft

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53
votes
8answers
28k views

Why are fuel tanks located in wings?

Passenger aircraft have fuel tanks in the wings. Why? What are the advantages and disadvantages of this location ? examples of disadvantages I would suspect: added weight increases the structural ...
27
votes
4answers
6k views

Why are empty pylons weighed down?

(airplane-pictures.net) Airbus A330 no engine option. Why are empty pylons weighed down? The plausible answer is to maintain the correct center of gravity. But why not just load ballast pallets in ...
20
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2answers
4k views

Why do T- tail airplanes have a shorter vertical stabilizer?

Airplanes with a T-tail design have a shorter vertical stabilizer than the conventional design , what is the reason?
18
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2answers
2k views

How strong is aircraft-grade spruce?

I have been trying to find some real numbers on how strong a single solid piece of aircraft graded spruce wood timber is, but haven't had much luck and the numbers that I have found so far were either ...
16
votes
3answers
4k views

How come planes can endure more positive than negative g's? I.e. how come V-n diagrams are not symmetric?

In this question A380 reverse thrust on only half the engines some doubts were raised about the strength of structures in certain directions. Specifically, Peter Kämpf states: Aluminium and ...
16
votes
1answer
274 views

Are helicopters reinforced asymmetrically?

Helicopters are under a constant torque due to the action-and-reaction forces caused by the rotation of the rotor(s). In the tail rotor and tandem rotors configuration, the airframe is experiencing ...
15
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2answers
3k views

Why does the Pilatus PC-24 have such a large “Airplane Support”?

The PC-24 has, under the fuselage, a kind of huge support to hold the wings. If we compare with the Citation CJ4 or the Phenom 300, this difference is quite significant. Why??
14
votes
3answers
18k views

How are engines mounted onto wings?

I've heard that the engines on a commercial air transports are typically mounted with 2 or 3 bolts. Is this true? If so, how big are these bolts and what are they made of? I'm optimizing a bolted ...
14
votes
1answer
2k views

What are the tube shaped structures on the back of the fuselage of this 737?

A previous question asked what the little metal plates between the horizontal and vertical stabilizer were (they are vortex generators), however I am much more interested in what the gray tube shaped ...
13
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1answer
2k views

Are modern airliners still stressed-skin aircraft?

Can modern airliners still be seen as stressed-skin aircraft? i.e. is the skin, whether it be aluminium or composites, still an integral structural member of the airplane?
11
votes
5answers
10k views

Why do airliners have “pressure bulkheads”?

Image source: FAA What part of the fuselage aft of the bulkhead would leak pressure? Or is it just there to reduce stresses? How does a DC-9/MD-80/90 incorporate aft bulkheads when there's a ...
10
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3answers
3k views

Could winds of up to 150 km/h impact the structural loads on a Boeing 777?

From 15 October 2016, AI 173 from Delhi to San Francisco started flying over Pacific. Jet streams over Pacific helped Air India in reducing the flight time by 2 hours, despite increasing the travel ...
10
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3answers
3k views

What is the purpose of a wing Yehudi? [duplicate]

Apart from covering the landing gear leg, the Yehudi also increases the wing root cord which allows the build height for the root to increase for the same wing relative thickness. This is useful as ...
9
votes
2answers
2k views

What is the function of the leading edge strip?

I understand the function of every wing part labelled above except the leading edge strip,what is its use in a fabric wing and will the wing function normally without it,if removed?
9
votes
1answer
4k views

How do GFRP and CFRP compare?

I have seen that aircraft mostly use CFRP (carbon fiber reinforced polymer) in large composition. But in some places like the leading edge of the wing, fin, and radome, GFRP (glass-fiber reinforced ...
9
votes
2answers
741 views

What could cause the Boeing “Pickle Fork” issues?

The Boeing 737-NG has been in the news recently regarding cracks discovered in the "pickle fork" assembly which transfers loads from the wings to the body of the aircraft. The "pickle fork" was ...
9
votes
2answers
2k views

Are lockwires still preferred over self-locking nuts and other ways of bolted joints` safety?

I've watched some of the lockwiring videos and if I understood it right then there are two most widely used ways of ensuring that a bolted joint does not get loose: Lockwire Self-locking nuts ...
8
votes
4answers
1k views

Why do cargo aircraft still have floors?

Even with dedicated cargo aircraft built as cargo aircraft (rather than converted from a passenger-carrying configuration), the cabin is virtually always still divided into an upper and a lower lobe (...
8
votes
1answer
435 views

How do weapon pylons attach to a fighter's wings?

How do weapon pylons attach to a fighter's wings? I'm particularly interested in the inner structure.
8
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2answers
383 views

What is the aerodynamic purpose of an Acorn?

This is an IL-62. On the tail of the aircraft, there is a large cone, protruding out of the vertical and horizontal stabilizer which is called acorn. I am trying to figure out what is the aerodynamic ...
8
votes
2answers
4k views

How do you choose engine placement for under wings engines?

I'd like to know how you choose the location of the engines under the wings, in the case of a 4-engines aircraft with low wings (and therefore with engines under the wings). Concerning the ...
8
votes
2answers
1k views

What is the name for the Mitsubishi A6M Zero's one-piece wing/fuselage?

The Wikipedia article on Mitsubishi A6M Zero fighter cites an article from Life magazine published on Nov 4, 1942: The Zero's fuselage and wings were constructed in one piece, unlike the American ...
7
votes
1answer
3k views

How are folding wings managed?

There exist several aircraft - especially carrier-based ones - that have folding wings, to save space. How is this structure strong, taking into account the considerable amount of force on the hinge-...
7
votes
1answer
306 views

Stress on wing/fuselage-joint of aerial water tanker aircraft - and possible mitigating measures

Following the unfortunate crash of a C-130 aerial water tanker aircraft in Australia, a friend brought to my attention a 2002 C-130 tanker crash in the US. As can also be seen in this video, the wings ...
7
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3answers
3k views

Why are modern aircraft wings often pointed instead being more rectangular?

When viewed from the Z axis (above or below), why are modern aircraft wings often pointed as they get towards the wingtips instead of maintaining the same surface area for their entire length? This ...
6
votes
2answers
1k views

What material is used for the floor panels in the main cabin for Boeing 747-400?

Just conducting some research into materials used in construction for Boeing 747-400 and Douglas DC-3. I just found out that in a DC-3 the floor panels in the main cabin and companionway are of ...
6
votes
3answers
586 views

How can filling a tube with foam help prevent buckling?

How can filling the empennage (aluminium tube) with Styrofoam stiffen it to avoid buckling as seen in Whingding ultralight?
6
votes
2answers
2k views

How does the fuselage handle the different loads?

I have been trying to find out how the loads experienced by a fuselage are transferred between structural members (bulkheads, formers, frame assemblies, skin, longerons, stringers). I understand that ...
6
votes
7answers
12k views

What is the definition of load factor and how do you apply it?

I'm a little confused about the definition of the load factor, n, as the definitions I found seem to contradict its application in force and moment balance analysis of an aircraft structure. The ...
6
votes
1answer
749 views

On a large transport aircraft where exactly is the Forward pressure bulkhead?

Is the Forward pressure bulkhead in front of the pilots.. I.e when you lift the Radome for maintenance is that the Forward pressure bulkhead you can see? Some images or a diagram would be great.
6
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2answers
2k views

Can delamination be detected early?

When a composite structure is hit, the impact causes shockwaves which travel through the structure, and cause delamination. Delamination reduces the strength of the composite structure and may cause ...
6
votes
1answer
1k views

What is the average weight difference between composite and metal airliners?

Is there any rule of thumb for weight savings using composite materials. For example, is there an early model large airliner like the B747 or even B737 that later was modified with composite wings or ...
6
votes
1answer
317 views

Why does taxiing produce large lateral loads on the 747's engine pylons?

While reading through a bunch of old AARs recently, I found (in the context of a 1993 747 in-flight engine separation) this interesting tidbit: [...] Boeing engineers report that the modifications ...
5
votes
3answers
785 views

Why are these spec and serial numbers blank on a part's plate of a WWII US military plane?

These pictures are of a plate from WWII US military plane that crashed in the high mountains of central Japan. People living there say that after the war officials recovered the crash sites and some ...
5
votes
1answer
206 views

Does Active Thermal Imaging (NDI method) detect all types of structural faults in modern civil aircraft?

What are the weaknesses of Active thermal imaging in NDI of different composite materials used in aircraft structure ? How much time and effort does it take to complete a full structure inspection ...
5
votes
1answer
537 views

What physical tests are involved with verifying a wing spar is suitably constructed for a homebuilt aircraft, such as the piper cub kit from wicks?

During construction how is a spar tested to ensure it can adequately cope with bending and twisting forces of the completed structure, or is this performed after complete?
5
votes
1answer
180 views

What adds more weight to a twinjet? Tail-engines or wing-engines?

Let's say we have a large commercial jet, with exactly 2 engines, capable of holding at least 200 passengers. It could be a traditional jet like the Boeing 777, where both engines are in the wing. Or ...
5
votes
1answer
343 views

What's the name for the structure that helps stop the nose wheel in Boeing 747-400?

From my understanding the nose wheel of a Boeing 747 does not have brakes, and as such when it is retracted it is still spinning. However, there are two "plates" that make contact with the wheels and ...
5
votes
2answers
130 views

What is the function of cross bracing of interplane strut?

Pic 1 is the top and lower wing of a biplane called Bloop Ultralight,what is the function of the cross bracing between the interplane struts as seen in pic 1(I'm not talking about landing and flying ...
4
votes
2answers
1k views

Is it ever permissible to takeoff on an aircraft heavier than its MTOW?

I'm thinking in terms of the Concorde accident in 2000 having just read part of the report which states that they were in effect several tonnes heavier than they should of been factoring in the ...
4
votes
1answer
392 views

Why isn't aircraft structure inspection done by robots? Is there any known active research on the subject?

From my research I've found that (correct me if i am wrong): Structure inspection (in B,C and D Checks) including (visual, thermography, ultrasonic inspections) looking for structure damage of ...
4
votes
1answer
115 views

What is the difference between a wing station and wing buttock line?

Can someone explain (with images) what the difference between a Wing Station and Wing Buttock Line is, in terms of aircraft structures location identification? The text I'm reading states: W. STA ...
4
votes
3answers
422 views

Why are Vertical tails generally tapered?

I'm just intrigued to know why the vertical tail of a majority of aircraft is tapered? Is it due to aerodynamics, structural design or due to some instrumentation or multiple other reasons?
4
votes
1answer
790 views

How does wing bending relief of an a340 compared to an a330 allow it to carry 30t more fuel in a center section of nearly identical wings?

From this question this reference in ymb1's answer states that the a340 and a330 have nearly identical wings. Because of bending relief from the weight of its outboard engines, the bending moment ...
4
votes
1answer
900 views

Why does the aspect ratio of a wing become less important at supersonic speeds?

My understanding is that an increase in the aspect ratio (AR) of a supersonic wing won't increase the efficiency like it would for a subsonic wing. If the subsonic induced drag is: $C_{D_i} = (C_L^2)...
4
votes
1answer
140 views

What exactly are the “sealed” leading-edge slats in B737 short field performance aircraft?

"The 737 design enhancements allow operators to fly increased payload in and out of airports with runways less than 5,000 feet long. The design enhancements include a two-position tail skid that ...
4
votes
2answers
604 views

What is the effect of wingspan on wing stiffness?

In an article in aviationweek about flight testing the GE9X, this statement is made. To reduce aeroelastic interaction between the testbed and the big engine, GE has also stiffened the wing by ...
4
votes
1answer
87 views

What is pressurization influence (if any) on maximum G load an airliner can withstand?

Reading here about skin thickness of airliners I was wondering if, considering some pressurized airliner at cruise altitude, there are differences in maximum operational acceleration loading the ...
4
votes
1answer
484 views

Is it viable to put an engine at the rear of the plane like in this photo?

I saw this image on a NASA page talking about hybrids and I was wondering if the back-engine placemente is actually viable and if it is why hasn't been done yet?
4
votes
1answer
264 views

How are further structural failures prevented if an aft pressure bulkhead fails?

In a modern airliner, if the aft pressure bulkhead experiences a structural failure, what design features are incorporated into the empennage to prevent the empennage from being overpressurized (i.e. ...