Questions tagged [aircraft-structures]

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

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Can the torsional strength of a wing be increased by adding more ribs?

I understand increasing the skin thickness is the best way to increase the strength in torsion, but if that is not an option will just adding more ribs work? In a composite wing skin, will adding a ...
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How is modal analysis useful in structural design of wings?

In this aviation stackexchange question - Spar-rib-stringer spacing and their thickness in relation to the wingskin thickness , OP mentions modal analysis in relation with stiffness. I would like to ...
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2 votes
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How deep do lift pins go inside the wing in gliders?

In the photograph below, how are the lift pins structurally attached to the ribs and how far does its support structure run inside? Does the discontinuity in the torsional flow in the wing skins pose ...
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In aircraft with single spar in each wing, are the spars at different chord locations?

In aircraft like the Pipistrel Virus, there's a single spar in each wing which is held with steel pins inside the fuselage. Are these spars offset along the chord line or are they bent at an angle for ...
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8 votes
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Why does the hardpoint mechanism on sweep wings produce a contact trace in front of the axis?

The basic structure and photos have already been explained on this site and on Wikipedia: How does a variable-sweep-wing aircraft keep wing-mounted payloads straight? Variable-sweep wing, Wikipedia ...
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4 votes
1 answer
244 views

How to estimate the ribs spacing?

I would like to know what is the general logic behind the choice of the rib spacing in the thin-walled load bearing structure of a straight or swept all-metal wing? Is it the global or local ...
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84 views

What happens to Lift and Drag on aircraft (and its components) when sideslip is increased gradually from 0 degrees to 90 degrees?

I possess an Aerospace Engineering background, and work as a Aerospace structural analyst at a local firm. A portion of my job is dedicated to determining the critical conditions that the aircraft and ...
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3 votes
1 answer
218 views

What is the difference between a tear strap and a doubler?

Is there a difference between a tear strap and a doubler? If I get it right, the tear strap reinforce the main structure locally and prevent the propagation of tears, while the doubler, well, it has ...
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3 answers
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Is Peter Sripol’s Mk4 ultralight design safe and/or practical? [closed]

I recently rewatched Peter Sripol’s Mk4 ultralight video Obviously, the aircraft flew, but I have several questions as a result. First and foremost, is a vinyl-covered ...
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How should I decide on the type of stringer to be used in an Aircraft's wing and fuselage?

I am trying to add stringers on the skins of an aircraft's wing as well as fuselage, for the same reason why they are present in most of the aircrafts i.e. to resist bending (and a possible buckling ...
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5 votes
2 answers
205 views

How is it possible that the design criteria for turbulence intensity has nearly doubled, but the manoeuvring load factor is the same?

https://www.law.cornell.edu/cfr/text/14/25.341 Here it says the turbulence intensity used for certification is 90 feet per second. Before, it was 50 feet per second, that section was added in 1981. So ...
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Is all the extra lift from flaps added upstream where the spars sit?

Flaps can significantly increase the lift for a wing, is all that extra lift added upstream where the spars sit? I ask this question because the flaps in airliners seem to be only connected by a few ...
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Can buckling of wing skin panels occur without external compressive loads?

State whether True or False: In general, the buckling of thin and slender structures occurs under applied axial compressive stresses. In the case of wing skin panels, they can fail in buckling even if ...
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2 answers
222 views

What is the structural impact on the wing if no fuel is stored in the wings and just in the fuselage?

What is the structural impact on the wing if no fuel is stored in the wings and just in the fuselage and how to counter possible advantages/disadvantages? Has this topic already been researched?
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In wing design, how is factor of safety related to G-limits?

What does factor of safety mean with regard to the maximum G force an aircraft is rated for? Does a rating of 3Gs mean the same as a safety factor of 3? Or is there some extra margin?
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How do I find the shear center of an unsymmetrical airfoil?

I'm quite a newbie of these systems and I am designing the wing box of a drone. I know where I want my shear centre. However, I have been trying to determine the shear centre of my idealized airfoil. ...
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Texts on aero-engine structures

I have been scouring the web for resources on aero-engine structures and structural design (preferably civil turbofans) but unfortunately it seems like they are hard to come by. I would like dedicated ...
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Why are Stratolaunch's engines so far forward?

Stratolaunch's engines hang from pylons, not under the wing, but entirely forward of the wing's leading edge. (Even farther forward than, say, the 747's.) What benefit does this have, to compensate ...
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231 views

Is there any advantage to having both wings integrated into a single wing unit, rather than being attached separately to the fuselage?

if I have a wing, which is split in the middle of it and attached at each side of the aircraft (like in any commercial aircraft today), I get a bending moment at the root of the wing. What if I have ...
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2 votes
2 answers
752 views

How does an outflow valve work mechanically?

Under Environmental control and oxygen systems chapter of Aircraft Maintenance and Repair book by M. Kroes, there's an topic of working of the outflow valve The diagram is of a valve that also works ...
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Why is the assumed Lift-to-Weight-Ratio for the limit drop test for heavy aircraft (FAR-25) higher than for small aircraft (FAR-23)?

The FAR-25.725 assumes a Lift-to-Weight-Ratio L/W = 1 for the landing gear drop test while the FAR-23.725 assumes only L/W=0.667. This factor affects the load inertia factor n which is also needed for ...
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8 votes
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What's the difference between multiple disc brake and segmented rotor brakes?

Going through FAA's aircraft maintenance manual I came across a topic under braking systems, which had two different types of brakes: multiple discs and segmented rotor disc brakes Looking at the ...
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9 votes
2 answers
282 views

What is dual mode adaptive landing gear system?

Referring to the NASA document Design and Development of the Blackbird: Challenges and Lessons Learned. On page 31, there's a mention of dual-mode adaptive landing gear, which is quoted below. ...
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2 answers
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What are different components of an engine pylon?

What are the different structural components that are inside the fairing of engine pylon and what are the functions of each part? The pylons for each aircraft are made of Ti-64 alloys, can they be ...
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32 votes
3 answers
15k views

Why are commercial aircraft windows typically oval instead of circular?

Pretty much what the title says. Surely a circular window would allow more window area while not compromising on strength? Some planes(Gulfstream jets) do have circular windows. Is there a reason for ...
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How does the B777 Side brace locking mechanism work?

The B767 has jury strut actuators and their working is pretty straight forward. They oppose the collapsible geometry of jury strut and lock them in the over centre locking position. But for B777 this ...
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1 answer
835 views

What materials form the structural elements of the Boeing 737?

What materials form the structural elements (leaving the spars, ribs etc) of the B737? It was tough to get any information on the kind of composites used on the 737 structure. Hoping to get some ...
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3 votes
4 answers
2k views

Why landing gears still need bungee springs?

While studying landing gear, I came across this term 'bungee spring' to which there was no definitive explanation in text with regards to its usage. So in the image, you can see for the jury strut/ ...
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1 vote
0 answers
54 views

Are the firewall and forward pressure bulkhead different components? [duplicate]

Suppose in a single engine aircraft, where the engine is located near the nose of the aircraft. If the cabin is pressurized, I know there will be a requirement of pressure bulkheads, both in the rear ...
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2 answers
221 views

Could abrupt flight controls input cause damage in these circumstances?

I went flying yesterday with a friend in my 1972 Grumman AA-5. She's a good copilot for someone who doesn't know much about flying. I showed her how you can pitch up and down, cause 0G, and float, ...
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159 views

When does an UAV need an internal structure?

I´ve seen some UAV models without internal structure (stringers, longerons and frame). I guess the drone´s shell is the frame itself. So what is the best approach to calculate the shell thickness to ...
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37 votes
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Why does the second floor of the Boeing 747 occupy only part of the plane?

Why does the second floor of the Boeing 747 occupy only part of the plane, while the second floor of the Airbus a380 occupies the entire space of the plane?
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1 vote
0 answers
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How do I reinforce a tubular spar that has been drilled vertically for an attachment bolt?

Previously posted a question about lift strut attachment to tubular wing spar with a bolt vertically through the spars. See drawing below. I tried using Bruhn's analysis book to formulate a a ...
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6 votes
1 answer
299 views

What's the wisdom of attaching an aircraft lift strut to a wing spar utilizing a single eye bolt vs the common two plate or strap method?

in the enclosed picture are three examples of types I'm speaking of. In the top picture, the lift struts are attached via a single eye bolt. The eye bolt is obviously vertical through the wingspar I ...
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10 votes
3 answers
5k views

What is the piece that covers the top part of tires?

I would like to know the name and the usefulness of this piece that covers the top of the tire of some planes, such as some Cessnas.
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5 votes
2 answers
2k views

How to calculate bending moments and shear forces on a wing?

I am trying to create a MATLAB script to plot the Bending Moment Diagram (BMD) and Shear Force Diagram (SFD) as a function of spanwise distance, x, along a wing from the wing root (x=0) to the wingtip ...
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17 votes
6 answers
7k views

Do aircraft have accelerometers?

Do modern aircraft employ accelerometers or other similar equipment to measure g-forces on the aircraft? I could imagine this being used as an inspection/service indicator, particularly after hard ...
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7 votes
1 answer
395 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 ...
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1 vote
1 answer
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How do the wings connect to the centre wing box?

First of all does the centre wing box form part of the fuselage as it's in the centre of the fuselage? Secondly how does the wing spars connect to this centre wing box to hold everything together?
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6 votes
1 answer
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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.
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6 votes
1 answer
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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 ...
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4 votes
1 answer
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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 ...
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6 votes
1 answer
751 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 ...
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9 votes
2 answers
938 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 ...
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Wing fuselage joint in small aeroplanes [duplicate]

I know that there are bolts to connect the centre wing boxes of the fuselage and wings in large aircraft, but what are the methods of connecting the wings and fuselage of small aeroplanes? I’m mostly ...
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8 votes
1 answer
2k 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.
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7 votes
1 answer
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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 ...
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15 votes
2 answers
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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??
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19 votes
2 answers
3k 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 ...
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6 votes
1 answer
237 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 ...
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