Skip to main content
25 votes
Accepted

How is metal fatigue detected in an aircraft?

How do the engineers, maintenance team, etc know if an aircraft has metal fatigue? First of all, is not an "aircraft" that has fatigue, but a component. To the naked eye, there is no way to detect ...
Federico's user avatar
  • 32.6k
16 votes
Accepted

Why does the DC-9-80/MD-80 have this cusp in its fuselage?

It's not a stress concentrator; it's just the opposite. What you're missing is that the floor itself at the pinched part forms a tension bridge that allows a more or less 'ovalized' circle while ...
John K's user avatar
  • 132k
14 votes

How is metal fatigue detected in an aircraft?

Engineers have a variety of ways to detect metal fatigue in aircraft: Visual inspection: sometimes cracks are visible to the naked eye, or can be seen under magnification Auditory inspection: ...
GdD's user avatar
  • 54k
12 votes
Accepted

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

The problem isn't the relief of stress from dumping of loads. If it was, you would have the same failures happening because of the act of landing, where the wing goes from being heavily loaded to ...
John K's user avatar
  • 132k
12 votes
Accepted

Why was the B-52's wet wing more susceptible to fatigue than its dry wing, and not less?

Earlier B-52s did not carry all their fuel in the fuselage. They also carried their fuel in the wings using rubber bladder-type wing tanks. The new B52G “wet wing” was a weight savings measure which ...
Mike Sowsun's user avatar
  • 37.8k
8 votes
Accepted

What is the life limit due to metal fatigue in large bombers?

Metal fatigue and fatigue corrosion are and have been a problem since the type's introduction. They always fatigue and corrode, they always undergo expensive repairs due to corrosion. DIEGME ...
Therac's user avatar
  • 27.4k
7 votes
Accepted

Do large non-pressurized metal planes have a maximum fatigue cycle?

Yes they do, and here is why. Airplanes are made mostly of aluminum rather than steel. It is possible to design a steel part in such a way that it will never succumb to fatigue failure (crack ...
niels nielsen's user avatar
7 votes

Why was the B-52's wet wing more susceptible to fatigue than its dry wing, and not less?

The decrease in fatigue is not a property that's automatically conferred to the plane by the introduction of wet wing - it's a product of smart design. Usually the decision to use a wet wing is made ...
Danila Smirnov's user avatar
6 votes

Why does the DC-9-80/MD-80 have this cusp in its fuselage?

To add to John's answer, why did they do it? To make more room in the passenger area. It is important to remember that, opposite a submarine, pressure is higher on the inside of the aircraft in ...
Robert DiGiovanni's user avatar
5 votes

Do large non-pressurized metal planes have a maximum fatigue cycle?

When you subject aluminum to cyclic loadings, there is a relationship of cycles it takes to crack/ vs material thickness, or structural meat you might say. If the structure is sufficiently meaty, the ...
John K's user avatar
  • 132k
5 votes

What is the fatigue life of a fuselage based on?

Most (large) aircraft life times are measured in cycles. "Aircraft lifespan is established by the manufacturer," explains the Federal Aviation Administration's John Petrakis, "and is usually ...
Dave's user avatar
  • 101k
5 votes

Why does the DC-9-80/MD-80 have this cusp in its fuselage?

This is called the "double bubble". The 737 has a similar but less pronounced design. Both aircraft had a primary requirement to seat a specific number of passengers in each row: 5 in the DC-9 and ...
bscottid's user avatar
4 votes
Accepted

Why weren’t the Comet’s overhead ADF windows roundified along with its passenger windows?

It wasn't the square-ish windows (they still had round corners, just not as rounded as modern square windows). They knew square windows were less than ideal stress wise and built the frame structure ...
John K's user avatar
  • 132k
4 votes
Accepted

Why don’t double-bubble fuselages cause severe fatigue problems?

Because the effects you describe are too small to place enough bending stress on critical locations to be a significant problem, and to the extent that is a problem, you simply add extra meat as ...
John K's user avatar
  • 132k
4 votes

Why don’t double-bubble fuselages cause severe fatigue problems?

How and why isn’t this a problem in practice? The answer is in the question: in practice. There will always be stresses in the construction, including bending stresses. The double bubble just has ...
Koyovis's user avatar
  • 61.8k
3 votes

What is the life limit due to metal fatigue in large bombers?

Back in the day the BUF (correct acronym for "D" model) airframe usage was calculated using variable aspects of actual flight that were outside the assumptions that the engineers used to ...
figmo's user avatar
  • 31
3 votes

How is metal fatigue detected in an aircraft?

Some metal fatigue can be spotted visually as an visible crack or as a collection of tiny cracks that can give the metal a 'frosty' look but most is done via non-visual non destructive testing ...
AndyW's user avatar
  • 1,171
3 votes

Why does the DC-9-80/MD-80 have this cusp in its fuselage?

The answer is soap bubbles: They are filled with slightly higher pressure air, and when they're attached to each other, they have a planar "reinforcement-like" part between them. (see the picture) ...
Nyos's user avatar
  • 131
2 votes

Did the cusp in the Boeing 377/C-97/KC-97’s fuselage structure cause fatigue problems?

You can actually see the same effect happening with soap bubbles when they touch and form a flat film connecting them. You can actually still see this type of fuselage in use in the Boeing 717 (...
Oliver Coran Giesaitis Stow's user avatar
2 votes

What are the characteristics of the F-16 airframe lifetime?

It is difficult to estimate how long a particular airframe might last. Also, different aircraft might last different amounts of time for esoteric reasons. For example, mercury amalgamates with ...
Tyler Durden's user avatar
  • 13.3k
2 votes

What is the life limit due to metal fatigue in large bombers?

Lifetime limit depends on the design and on usage. Many aircraft have a lifetime limit given in cycles (i.e. number of takeoffs and subsequent pressurization cycles). For the B-52, flight hours are ...
Hobbes's user avatar
  • 10.2k
1 vote
Accepted

How much of an effect do structural overloads have on an airframe's safe fatigue life?

Airplane structures are designed to take a certain number of extreme conditions during their life which are defined based on statistical analyses of past flights. For example a manufacturer can design ...
sophit's user avatar
  • 13k
1 vote

What is the life limit due to metal fatigue in large bombers?

With some combination of regular Non Destructive Test inspections, patches and reinforcements, and in some critical areas replacement of primary structural fittings, panels and skins, and you can run ...
John K's user avatar
  • 132k
1 vote

What are the characteristics of the F-16 airframe lifetime?

All military aircraft have airframe time limits, and they are mostly related to fatigue. It should be easy to figure out what portions of the airframe are stressed the most -- think of what sticks out ...
Juan Jimenez's user avatar
1 vote

Is In-Seat Rest used regularly where it is legal, and is it restricted by airline SOPs?

Too complex for me to give a specific answer, and this answer is assuming only airline transport not private flights or business charters. Duty time limits are different for every country and may ...
Max Power's user avatar
  • 2,604
1 vote

What is the fatigue life of a fuselage based on?

The safe/fatigue life of a structure is the number of events during which there is a low probability that the strength will degrade below its design ultimate value due to fatigue cracking. The events ...
Talonhawk's user avatar
  • 346
1 vote
Accepted

Did the cusp in the Boeing 377/C-97/KC-97’s fuselage structure cause fatigue problems?

It is not the stress concentrating type of sharp corner. That is the natural shape that allows the parts to be in a nice smooth tension at lowest energy. If you made an elastic rubber balloon with a ...
Max Power's user avatar
  • 2,604
1 vote

Do large non-pressurized metal planes have a maximum fatigue cycle?

Older planes like the DC3 undergo 100 hour and/or annual inspections when used for hire just like other planes, and Airworthiness Directives for maintenance issues are sent out to the fleet as things ...
CrossRoads's user avatar
  • 8,795
1 vote

What are the fatigue regulations in the US and Australia for military transport helicopters/rotorcraft?

The US Federal Aviation Administration does not regulate aircraft owned and operated by the military services. I suspect that is the same situation with Australia's CASA. Parameters for aircraft ...
Juan Jimenez's user avatar
1 vote

How is metal fatigue detected in an aircraft?

The pilot listens and notify the technicians that the plane is giving out strange noises. And now seriously: For each plane type there are cards which parts need to be replaced or inspected after ...
gusto2's user avatar
  • 273

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