New answers tagged

4

Below is a cross section of the skin between the passenger windows of a Boeing 747-100 (N602US). It's 2 layers, each layer is ~.075" thick. This is the first iteration of the 747 (50 years ago) so might be different on later series as they improved the design and reduced weight. Source: own work


0

Using a delta wing for a glider would not be ideal because delta wings have a lower Coefficient of lift as well as a lower aspect ratio. However you can find wing span by using the formula in the link attached: https://www.grc.nasa.gov/www/k-12/airplane/geom.html AR=s^2/A when you use this formula you can get a idea on how well it would glide. For example ...


3

It's not just for the looks. The A350 is the first Airbus ever to feature curved cocpit windows to reduce drag, and according to Airbus, the black "mask" contributes to ease of maintenance and harmonization of the thermal condition of the windows: "The perfectly curved shape of the nose helps the air flow hug the surface, in the least turbulent manner, ...


1

There are three approaches to this need. First, you could build what amounts to a tandem wing. If you check the CoG location for a Rutan Quickie or its many derivatives, I'm pretty sure you'll find it's between the front (lower) and rear (upper) wings. Likewise, a Flying Flea (aka Pou de Ciel) has the CoG much further aft, relative to the forward/upper ...


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They certainly do. My airplane is built 100% out of 3d- printed plastic. It's really handy. Everything is easily replaceable. Crashes are no longer any concern. I've saved a template of my cranium too, just in case it might someday be need to be replaced.


3

If they have to pilot it manually, without training or guidance, a passenger has about as much chance to land an airliner as the airliner has to just happen to land on its own as it runs out of fuel. At least there will be less of it to burn. It's not a ground vehicle, you can't wing it, and the runway is tiny compared to the sky. Talkdown landings are a ...


0

Aluminum and titanium are used in aircraft because they are light weight materials that are strong and durable like steel, however they are non-ferrous unlike steel meaning no rust. The two metals are usually composited with another material such as carbon, composites are known for being stronger than using one base material because it will alter the ...


3

I've boldfaced the parts of this abstract that answer the question. Abstract: Ever since the advent of fiber reinforced polymer materials in the field of Aerospace, Metal-FRP stacks started to gain importance due to their superior fatigue performance, phenomenal low weight and good specific strength. However the machining, specially drilling these multi ...


1

The F-16 is unstable at low speeds, and stable at higher Mach numbers. It has a flight control computer though, which stabilizes the aircraft using the feedback from pitch rate (so from the view of the pilot an F-16 acts similarly as a stable aircraft). This applies to both positive and negative attitude disturbances, so for both + and - G loads perceived by ...


3

Robin makes a lot of great points, but since we are talking on a purely hypothetical case lets have fun and take it to supersonic speeds. Let's assume that somehow batteries have the required energy density to be used to run some sort of low-bypass electric turbofan to propel our aircraft to high speeds where the neutral point of the aircraft starts ...


9

There are a few electric aircraft now, and because batteries hold far less energy than fuel, they're low-performance and short-range compared to normal aircraft. If we imagine that at some point in the future we'll have batteries that can match fuel, the answer would be: Only slightly. Back in the 60's and 70's, airliners regularly carried a flight ...


1

Pre WW2 French Aircraft had the throttle reversed - i.e. Moving the throttle rearwards INCREASED engine power, and moving the throttle forwards DECREASED engine power. American Curtiss H-75 Hawks exported to France had the modifications made on re-assembly in France - something for any American company test-pilot in France to remember....


2

John K.s answer applies to lithium batteries. They're quite convenient in many ways, but they clearly don't work for this application. Fuel cells on the other hand are more reasonable. A fuel cell produces electricity from fuel, such as hydrogen or ethanol. As such, it doesn't have the weight penalties of batteries. Additionally, this mostly solves the ...


7

The top wing is always the most efficient, as the lower ones suffer reduced lift due to interference from the air flowing beneath the one above. Ailerons will therefore be most effective on the top wing. If they do the job OK then there is no need for any more. Reasons for adding more below include: The upper set are likely to be (or found to be) inadequate....


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A random guess without any supporting information. (please edit or delete if this turns out to be inaccurate) I would guess the logistics of manufacturing. It could the space needed for handling the aircraft in and/or out of manufacturing buildings. The B-2 program was wildly expensive due to the large number of new technologies involved. So I guess it was ...


6

Well, to use the same airframe, you'd basically have to find a way to replace the fuel volume in the wings with battery volume, and batteries are somewhere around 15-20% of the power density of fuel, as the answers in this ASE post lay out pretty well. So if you had an electric fan that made the required thrust, and somehow figured out how to replace all ...


8

Aspect ratio. Look at your two images: both wings offer the same wingspan, but the former requires a lot more wing area for it. Wing area is weight. More wingspan for less wing area means better fuel efficiency and thus better range. Poor aspect ratio, leading to excess induced drag, is a major disadvantage of delta wings. Much of modern stealth design is ...


3

Yes you simply fly with the pressurization system set to a mode that holds the outflow valve open so the air conditioning air being pumped in can't "inflate" the cabin; it all just goes overboard. Most transport aircraft have a specific QRH procedure for "unpressurized flight", which among other things, limits the maximum altitude to 10000 ft, the altitude ...


1

If you have zero sideslip, then the moment coefficients will be similar between the two configurations. The only difference would come from difference in drag and its effect on moments, which would be small. If you have non-zero sideslip, then the roll moment coefficients will be different due to dihedral effect.


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For a first approximation, the coefficients will be similar enough, but not exactly identical. As you correctly point out the moment arms will be the same, but the interference effects of the wing-fuselage joint may not. That is to say, your assumption that the lift distribution will remain unchanged will likely not hold out in reality. The stability ...


0

Remember that when you are analysing stability, you are interested in the derivatives by the parameter in question, not in the absolute magnitude. In longitudinal motion, you are mostly interested in how the balance changes when AoA changes. It is understood that in static motion, the absolute moment will be trimmed out (normally by tail) - otherwise it ...


3

So let’s assume the aircraft has a $C_{m_a}$ curve as you show. When you start to pull up you will feel nose down force on the yoke because of negative pitching moment. As you further increase the pull, the force required should increase also. However in your picture at some point the negative pitching moment $C_m$ decreases (in magnitude), still negative ...


4

There are several factors to consider, and depending on your preferences there is not one ideal size and place for a canard. For a first rough concept look at similar designs and use the same canard volume. That is the product of canard area and the distance between its and the wing's neutral points, relative to the aircraft's reference parameters. $$V_{...


0

This diagram is from the book Design for Flying by David Thurston and might be of use.


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Some fatigue related issues that are not directly tied to departures and arrivals, like wing bending from gust loads, but may be randomly continuous throughout the flight, need an hour limit. Taking it to a comical extreme, if the airplane flew for 3 years straight without ever landing because it had a new pixie dust powered engine, it would have close to ...


2

Aerodynamic Centre (AC) is particularly handy when we analyse the dynamics, that is, changes. For instance, changes due to disturbances: stability. First thing, for analysis, we split all forces into forces acting where we want plus moments caused by the fact that these forces actually act somewhere else. And then when we write our balance equation, we need ...


1

An airplane achieves steady flight at a given airspeed only if the total pitching moment about its CG is zero. This is achieved with a particular fixed tail angle/elevator angle/canard angle. If the AOA corresponding to the total lift at this airspeed is 0 AOA, then so be it. It's just that for typical airplanes at operational speeds (away from $V_{FE}$ for ...


2

The first certified stable aeroplane flew in 1910 at (and without) the hands of J W Dunne. It was also the first tailless swept plane to fly, sort of a biplane flying wing except that everything was piled in between the wings so not a true flying wing. Contemporaries Handley Page and Igo Etrich were obliged to add tails to their more bird-like attempts. ...


0

It's because anhedral wings remove one of the biggest disadvantages of dihedral wings - maneuverability. Although dihedral wings give roll stability by pushing up on the wing which is lowered while banking, it also means that whenever the pilot is rolling to one particular direction, the wings have a tendency to oppose that by rolling the aircraft to the ...


0

To fly, a wing must maintain its angle of attack within a certain range. If the AOA is too low, the wing produces no lift. If the AOA is too high, air moving over the top cannot follow the wing's contour, separates, and causes a reduction in lift (aerodynamic stall). Designs that employ passive stability to maintain an appropriate AOA will make the aircraft ...


4

The problem which this gap is solving has to do with boundary layer air as @ymb1 suggested but performance is not the only complication. Boundary layer is not only slower, in some regimes of flight it can become highly turbulent compared to the air that is offset from the aircraft's surface and is freely ingested by the aircraft's intakes. Mixing the two ...


1

If you're talking about flex thrust, then NO - it is not at all a problem. It is basically a FAKE temperature which the pilots provide the FADEC with so that the FADEC purposely reduces the amount of thrust generated by the engine. This can improve engine lift by reducing wear. But remember, PILOT'S ARE NOT SUPPOSED TO USE FLEX THRUST DURING ROUGH WEATHER. ...


1

No it's not dangerous. Flex thrust simply exploits all of the runway available, taking advantage of any length that is surplus to the minimum required at max thrust, to allow takeoff with less than maximum thrust to save wear and tear and fuel (wear and tear is a big deal taking off in a sandy/dusty environment and use of flex has a significant effect on ...


6

For one reason or another, the main gear was made longer that originally planned and it was decided to avoid the cost and weight also extending the nose gear to match. The nose down angle while rolling along the ground is no big deal one way or the other, except for looking bad and disconcerting passengers who wonder why the plane is tilted forward. Lots ...


4

Boeing B-52G Stratofortress In the design of the B-52G, considerable attention was paid to reducing the structural weight. Different materials were used in the construction of the airframe, and the wing structure was extensively redesigned. The most visible difference was a vertical tail which was reduced in size. The height was reduced from 48 feet 3 ...


3

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 also increased the fuel capacity over the bladder-type in-wing tanks. The metal fatigue of the new wing was due to a poor structural design which was supposed ...


1

Your general formulation seems fine. Two things to point out: If you choose to sample only half the wing, then you cannot utilize the relation: $C_L=A_1\pi A$. You would have to do the integration: $C_L=\frac{2}{V_\infty S}\int^{b/2}_{-b/2}{\Gamma(y)dy}$. That being said, maybe you can simplify the expression and get a closed-form result? Haven't tried ...


3

The tail only looks backward when people can usually see it: in the pattern, parked, or flying formation with a photographer in a slower aircraft. Rather than using trim tabs to push control surfaces out of alignment (which adds drag), the entire empennage pivots for pitch trim adjustments. To trim the nose up at low speed, the leading edge of the horizontal ...


1

Why wouldn't an airline choose the MD-90, which was more efficient? Airliners are usually retired because the airframe reaches the end of its useful life, not because the engines are "obsolete." Towards the end of an airliner's production run, the manufacturing process has been optimized and the cost to the manufacturer is lowest. They are willing to give ...


0

It sure can; in fact, they are equivalent (with an offset of 1G). In the body frame, the vertical equation of motion is: $$Z+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$ Accelerometers can't measure inertial or gravitational forces, so vertical acceleration as measured is $N_z=Z/m$.


1

I'd guess that they wanted to avoid an acute angle between the lower part of the vertical stabiliser and the horizontal - not for structural reasons but to limit interference drag. They could have made the top piece vertical and just kicked out the bottom part, but then the rudder would have to have been made in two parts (or the hinge wouldn't have worked!)...


4

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 during the initial design of a plane, and the support structure of the wing is built accordingly, so that it can take the dynamic strains that occur upon ...


5

I'm fairly sure (but have no sources to confirm) that the reasons are purely structural. The vertical stabilisers are simply set at a right angle to the horizontal one. This is just the easiest thing to do, and it also provides better clearance with deflected lower rudders. The aerodynamic consequences of this (for such small angles) are pretty minor. Now ...


2

Yes it's because of dispersion. With wing mounted guns you normally "harmonize" them to converge at a point, say 300 yards or 600 yards to have a sweet spot where most of the projectiles are passing through a small area to maximize the fire concentration. But at ranges closer and farther, the streams of projectiles are more dispersed and their effects are ...


28

No. It doesn't have an APU — it has two of them. They are located close to the main landing gears. From An-225 Mriya is the world’s largest aircraft (English version): Auxiliary power plant consisting of two TA-12 turbofans installed in the left and right chassis fairings provides independent power to all systems and starts the engines. I think "...


1

Also define obsolete. The 737, one of the (if not The) most successful airliner in the world was designed about the same time (1960s) and it shows no sign of seeing its production being stopped. About narrow body = obsolete, I think you will find members of the CRJ (four-across seating [1]) and ERJ families that are not only are narrowbodies but look very ...


3

Not necessarily if the aircraft flies slowly so forces stay small. But it is better to have balanced control surfaces. Now imagine that you fly through a vertical gust and the aircraft pitches up, then down. Since it rotates around its center of gravity, the tail will make the largest excursions from a straight line. Now imagine the elevator has no mass ...


4

Flutter is an energy storage and release phenomenon. Surface moves, applies a load to the fixed surface it's attached to, fixed surface bends under the load, stores some of the energy like a spring, then releases it in moving back to its original position, and some of this released energy is transferred to the moving surface attached to it, which is also ...


5

The MD80 was not obsolete at the time of its first flight and the decade thereafter. The market situation for 150 pax aeroplanes around 1980: Boeing B727-200: first flight 1967. Three JT8D-7/9/11 engines. MD-80: first flight 1979. Two JT8D-200 engines. The first generation of JT8D had a bypass ratio of 0.7, the JT8D-200 engines had an increased bypass ...


2

Regarding the aspect of obsolence: in contemporary personal land transport, the Otto engine is, by pretty much all means, obsolete. There are very few cases in which the Otto engine outperforms an all-electric drivetrain, but these cases hardly make up more than 10% of the field. Yet... The Otto engine prevails. Why? The infrastructure is there. The ...


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