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My assumption is that there are plastics lighter and stronger than the materials used to build planes. That is not a correct assumption. Typical 3D printer plastics have a best-case tensile strength of 45-50 MPa. Aluminum 7075, a common aerospace alloy, has a tensile strength of 500-570 MPa. After dividing by specific gravity, that's at a 1:4-1:5 ratio ...


75

Whenever you see titanium being used on aircraft, look for heat sources. The metallic alternative aluminum is usually lighter and much cheaper. In most commercial aircraft the APU (Auxiliary Power Unit) is in the tail, behind the rear pressure bulkhead and the empennage. (modified from aerospaceweb.org) The APU is a small turbine and its exhaust gases are ...


46

How The Jet Engine Works: Inside the typical commercial jet engine, the fuel burns in the combustion chamber at up to 2000 degrees Celsius. The temperature at which metals in this part of the engine start to melt is 1300 degrees Celsius, so advanced cooling techniques must be used. You can read more about some of those cooling mechanisms in How are ...


42

Short answer Fan: Aluminum, titanium, or stainless steel Compressor: Nickel-, cobalt-, or iron-based alloys. Additive are aluminum and/or titanium, chromium, as well as rare earth elements like yttrium. Combustion chamber: Superalloys with refractory metals such as tungsten, molybdenum, niobium, tantalum. Ceramics and ceramic-metal mixes. Turbine: Nickel-...


33

Let's take ABS, which is an extremely common plastic used for 3D Printing. At a typical flight altitude, the exterior air temperature will be in the order of -51°C/-60°F. The lowest rated temperature for ABS is -20°C. I hope you can see why this alone might be a problem. Wikipedia also says that ABS and PLA, which is the other major 3D printing plastic, ...


33

My recollection of the Modulus of Rupture is about 6000 psi for aircraft graded sitka, based on the maximum allowed grain runout, and a maximum of around 10000 for straight grain. But you should be able to find everything you need in the old Forest Products Laboratory study at this google search link. The key weakness in spruce (and wood in general) used ...


29

To avoid overheating, the usual trick is to select the right material: The Concorde used a special aluminium alloy, called Hiduminium, which had higher strength at elevated temperatures and allowed the Concorde to cruise at Mach 2.02. Aluminium melts at 660°C. The MiG-25 used stainless steel instead of aluminium to make its top speed of Mach 3.1 possible (...


20

You are right, on first sight it is actually surprising that aluminium prevailed. It comes with some disadvantages: Crack growth must come first in this list. With only a small cyclic load, cracks in aluminium will relentlessly grow. This requires frequent checks and has caused many accidents. Fortunately for aluminium, this fact was only discovered after ...


20

There is actually quite a lot of information on the subject in the Braeunig web site Basics of Space Flight. To give the salient points: Liquid-fueled rocket engines Both the nozzle and the combustion chamber itself need to be cooled. Although most of the thermal energy produced is ejected with the exhaust, some of it will indeed push hardware temperatures ...


19

Ideally, fiber composites are bonded and connected by a scarf joint. The scarf ratio is determined by the ratio of fiber tensile strength and the shear strength of the resin. If your fiber takes 3000 N/mm², the resin transmits 20 N/mm² and the fiber content is 60%, the ratio is 1:90, so a 1 mm thick composite layer would need to be joined over a length of 90 ...


19

Peter's answer to another question has a nice chart that shows internal jet engine temperatures: You can see that the temperatures are highest by a fairly large factor in the combustion chamber. This means that only the combustion chamber needs to be able to withstand those temperatures. To save weight and often use less expensive and less exotic ...


17

Disadvantages of wing sweep Lift curve slope is reduced by the cosine of the quarter chord sweep angle. This means more angle of attack for takeoff, which requires a longer take-off run and a longer landing gear to avoid a tail strike on rotation. If you rotate the airplane, the tips of backward swept wings come down when the aircraft rotates for take-off. ...


16

They're made of alloy steels that have ultra-high strength, high fracture toughness, excellent fatigue resistance, and high resistance to stress corrosion cracking. Based on one of the manufacturers—QuesTek—the steel's grade is AMS 6516. The 6xxx grade is a chromium-vanadium steel: Chromium-vanadium steel refers to steel alloys incorporating carbon, ...


14

There are probably many factors in choosing aluminum vs. composites. A big one is bird strikes. The leading edges are at the highest risk for this. Metal tends to absorb the impact better while retaining its strength, while composites would tend to delaminate and become much weaker. Resistance to in-flight hail must also be considered. (Source Left, Right) ...


13

Polymethyl methacrylate (Plexiglas) The material was developed in 1928 in several different laboratories by many chemists. Historically, PMMA was an important improvement in the design of aircraft windows, making possible such iconic designs as the bombardier's transparent nose compartment in the Boeing B-17 Flying Fortress. From early on Plexiglas ...


13

There's a few things going on here. You assume plastics are stronger and lighter than the metals and composites used for aircraft manufacture today. Therac's answer counters this assumption (spoiler: plastics are much weaker and less stiff), but there's a subtlety. In many applications, 3D printed plastics can be made stronger or stiffer for the same weight,...


12

Wing sweep improves the performance by delaying the shock waves and accompanying aerodynamic drag rise caused by fluid compressibility at high (near sonic) speeds. However, there are some disadvantages associated with the wing sweep like: Wing sweep reduces the slope of the lift curve and the maximum lift coefficient of the wing. This means that the swept ...


12

Both the MiG-25 and MiG-31 designs had engines that would overheat and be damaged an anything past Mach 2.83, so both planes were limited by this. Typical speeds were closer to Mach 2.5 to extend the life of the planes. The highest aerodynamic heating occurs at the leading edges. It's possible that the MiG designs used titanium in these areas but opted for ...


12

The landing gears are manufactured by Messier-Dowty, a Safran group company. According to their site, Safran Landing Systems is responsible for the design, development, qualification testing, manufacture and support of the main landing gear for the A350-900 aircraft. Also, Safran Landing Systems also provides wheel and carbon brakes for the A350, as ...


11

On Sunday 4 October 1992, El Al Flight 1862 crashed into a suburb of Amsterdam after the right inboard engine separated from the wing and took part of the wing and the right outboard engine with it. The separation was caused by fatigue fracture of the fuse-pins that connect the engine to the aircraft. The engines of the Boeing 747-200 are joined to the ...


11

The Boeing 787 is special due to its high count of composite parts. When aluminium comes in contact with graphite fiber, contact corrosion will damage the aluminium whereas titanium will be unaffected due to its higher position in the electrochemical series. 15% of the initial 787s empty weight consists of titanium, a fraction much higher than in other ...


9

(Own work via boeing.com) Overlayed scaled drawings. Above you see similar sized planes with the same 3-class seating (± 1 seat). The newer-more-composite 787 is 16 tonnes heavier, yet delivers up to 20% fuel saving (route dependent). 3.4 of the 16 tonnes are the newer and bigger engines. And the rest is primarily bigger wings (which can be built bigger ...


9

As other answers mention, the strength of molded or printed plastics is an order of magnitude lower than that of typical aerospace metals. But also the stiffness is much lower. Compare Al 7075, which Therac's answer mentions, with Stratasys' certified Ultem 9085 thermoplastic. The aluminium has an elastic modulus around 70 GPa, while the Ultem's elastic ...


8

I'd like to answer with a focus on the SR-71, since I happen to have a book that gives details on its design. Ben Rich was the lead of the propulsion and thermodynamics group for the SR-71, and Kelly Johnson's successor as head of the Skunkworks for later programs. In the "Faster Than a Speeding Bullet" chapter of his memoir Skunkworks (pg 203 in the first ...


8

There are two big factors at play here: scale and throughput. First, automation is very good at repetitive tasks. The Wolfsburg plant produces over 800,000 cars per year. It's taken 25 years to make almost 600 Typhoons. That means yearly production is different by four orders of magnitude. It's a lot easier to justify the cost of buying, installing, and ...


7

First, the hot section is not the nozzle, but the combustor and the high-pressure turbine. Second, 650°C is nothing for modern high-temperature alloys like Inconel. The top gas temperature in a modern jet turbine is more like 1500°C, and the turbine blades tolerate temperatures of around 1200°C. For military turbines and the temperature in the combustor, ...


7

The first aircraft to have any sort of protection for the pilots had windshields made of glass, which offered some protection against propwash and wind. These were flat glass panes, which were later replaced with laminated glass. The first aircraft to have anything similar to the modern canopies were the Royal Aircraft Factory SE4 and SE5, which had ...


7

There are multiple ways to avoid overheating. The simplest method is to use a high temperature material- like Titanium in SR-71 or steel alloy in Mig-25; in Concorde, a special aluminum alloy (AU2GN) was used. In case of other aircraft, steel or Ti is used in stagnation points (like wing leading edges), while the other exposed surfaces are made out of other ...


7

On light aircraft, acrylic windshields have been the norm. On higher speed aircraft, glass and laminates are used, particularly with heated windshields. The laminates may use polyvinyl butyral (PVB) is tough and ductile which enhances mechanical properties and impedes shattering of glass layers and the transmission of cracks from one layer to another. ...


7

Titanium. Only the hottest portions of the fuselage (the chines) were cooled, using the fuel as a coolant. As far as I'm aware, there was no treatment to make the material stronger with age.


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