Questions tagged [aerodynamics]

Aerodynamics is the study of how air moves and interacts with solid objects. It is an essential part of aircraft design.

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How do wings generate lift?

Just the basic question that every aviation enthusiast must be curious about: exactly how does a wing generate lift?
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27 votes
1 answer
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Is there any equation to bind velocity, thrust and power?

I am designing a remote controlled airship. I will tune it so that the lift given by Archimedes' Principle will exactly balance the weight of all the structure. It will be propelled by brushless ...
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23 votes
8 answers
23k views

Does lift equal weight in a climb?

This subject keeps coming up in the discussions and questions such as this one, which asks if lift equals weight in level flight. Good answers there, pointing out that upwards force has many sources. ...
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57 votes
5 answers
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Is a winglet better than an equal span extension?

Is there indisputable evidence that a winglet improves performance over an equal span extension? Please note: I am only interested in L/D improvements. Winglets do improve roll performance, that is ...
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50 votes
8 answers
13k views

How complete is our understanding of lift?

I'm currently studying for my PPL and one of the accepted textbooks contains the following disclaimer at the end of the Principles of Flight section on lift: It is important to note that the forgoing ...
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36 votes
8 answers
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How does stall depend on angle of attack but not speed?

Everyone says that the angle of attack is what determines a stall, not the speed. I understand the theory and understand that it is separation of the airflow that matters for stalling. However, I don’...
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12 votes
2 answers
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How is the induced drag calculated for a wing with elliptical planform?

How is the induced drag calculated for a wing with elliptical planform ? Is this wing shape the most efficient ?
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26 votes
5 answers
10k views

How does an aircraft tailplane work?

How does an aircraft tailplane keep the aircraft stable, and prevent it from tipping over? Also, how does the lift generated by a tailplane compare to that generated by the wing?
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52 votes
11 answers
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Why do airplanes lift up their nose to climb?

Is it right that basically an airplane just needs to accelerate to climb? Greater velocity of an airplane leads to greater lift - and since its weight remains constant (or even decreases) - a greater ...
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9 votes
1 answer
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What is the aerodynamic centre and how does it relate to the pitching moment?

Okay so I have been trying to get my head around the Aerodynamic centre and the Pitching moment. Wikipedia really isn't helping much but from what I can gather the Pitching moment is a force caused by ...
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68 votes
3 answers
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Are we at peak speed efficiency for jet airliners at Mach 0.85?

The cruising speed of large jet airliners has not increased in the past four decades. The 747 cruised at Mach 0.85 and the new Dreamliner 787 also cruises at Mach 0.85 even though it was designed 40 ...
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19 votes
3 answers
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Why do some military aircraft use variable-sweep wings?

There are a couple of American military aircraft (the retired F-14 and the B-1 come to mind immediately), that have variable swept wings. I know that they keep the wings full out (roughly ...
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29 votes
2 answers
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What is vortex lift?

In a recent question I asked, I was given an answer by Peter Kämpf and he described something about lift being created by a vortex used on delta wings and the Bird of Prey wing. How exactly does ...
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3 answers
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What is compressibility drag?

I don't mean wave drag here. What is compressibility drag, which is understood to be a form of miscellaneous drag?
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43 votes
5 answers
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What is a 'deep stall' and how can pilots recover from it?

West Caribbean Airways Flight 708 which crashed in 2005, fell victim when their plane encountered a deep-stall. From my understanding, only certain planes can 'deep-stall' How can pilots recover ...
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13 votes
2 answers
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What is the method to calculate a finite wing's lift from its sectional airfoil shape?

I am struggling to get my head around a concept that I believe should be fairly simple to understand. Lift versus drag and AoA data of many airfoils are freely available, for instance the NACA 4-...
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11 votes
3 answers
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Does the downwash created by induced drag increase or decrease lift?

According to the theory I know, lift is produced by accelerating air downwards at the trailing edge (downwash). Hence, as downwash increases so does lift. Induced drag is due to vortices at the wing ...
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15 votes
2 answers
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What is the reason for the poor low-speed characteristics of sweptback wings?

I know there are advantages of swept-back wings delaying shock-wave allowing a aircraft to fly faster. However, what are the disadvantages. I know one of them is that they have very poor low speed ...
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12 votes
1 answer
14k views

What is the relation between an airplane's altitude and the drag it is experiencing?

The Reynolds-Number $Re$ is defined as $Re = \frac{c \cdot L \cdot \rho}{\mu} = \frac{c \cdot L}{\nu}$, with the velocity $c~\left[ \frac{m}{s} \right]$, the reference length $L~\left[ m \right]$, ...
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20 votes
3 answers
28k views

Why and when to use flaps?

On a commercial airliner, what is the purpose of the flaps? I understand that depending on which direction they move in, they can be used to decrease airspeed, but I don't know when flaps are used. ...
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41 votes
8 answers
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Why would a glider have water ballast? If it is trying to stay aloft without an engine, wouldn't it be better to be as light as possible?

So I was looking at the description of a ASW 27 B glider and ran across this statement: Two water tanks in the wing plus a further 35 liter tank in the fuselage enable the ASW 27 B to carry more ...
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21 votes
2 answers
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What does it mean for a plane to be aerodynamically stable?

I've heard that most planes (excepting fighter jets) are "aerodynamically stable." What does that mean? Let's say you're cursing around in a Cessna 172 without autopilot, and you take your hands off ...
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31 votes
2 answers
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What is the difference between centre of pressure, aerodynamic centre and neutral point?

I have just started learning some aerospace concepts, and I am not able to understand the difference between the three terms centre of pressure, aerodynamic centre and neutral point. What are their ...
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14 votes
2 answers
5k views

Why is the coefficient of drag for straight wings at supersonic speeds lower than for swept wings?

Why is the coefficient of drag of a straight wing lower than the coefficient of drag of a swept back wing at higher supersonic speeds (above, say, Mach 2)?
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22 votes
4 answers
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How does a flying wing keep from going into a flat spin when maneuvering?

How do flying wings, like the B-2 Stealth bomber, actually keep themselves from yawing out of control without a vertical stabilizer? For the record, I assume this has to be a simple mechanics process....
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9 votes
3 answers
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Is induced drag essentially nothing more than a specific type of form drag?

If I were standing outside on a windy day holding a flat rectangular object such as a food tray up in the wind, orthogonal to the direction of flow, the drag created would be classified, mostly, as ...
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14 votes
1 answer
3k views

Why does the wing root of the A330 have a pronounced twist?

just wondering what the purpose of the pronounced twist on the Airbus A330 wing root is, I've noticed this on the 380 as well.
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36 votes
9 answers
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Why does An-225 have anhedral wings though it is a cargo aircraft?

What are the rationale behind this anhedral high mounted wing configuration? Is that usual for very large carge aircraft?
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26 votes
7 answers
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Why are adjustable area jet engine nozzles mostly limited to military use?

It seems that only jet engines with afterburners use adjustable area nozzles (this means adjusting the area of the nozzle but not necessarily the direction). This includes most fighter jets, as well ...
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18 votes
3 answers
18k views

Why are high-wing aircraft more stable?

A high-wing aircraft is considered to be more stable in a side-slip because of the pendulum effect. How does the pendulum effect increase stability in high wing aircraft? This question is about high-...
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40 votes
9 answers
88k views

What are the pros and cons of high-wing compared to low-wing design?

What are the advantages and disadvantages of a high-wing vs. low-wing aircraft design? When might one prefer one to the other? Is the answer the same for large and small aircraft?
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16 votes
1 answer
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What are the merits of an inlet cone/spike/centerbody vs. a 2D inlet?

And which is better for a scramjet? Is a 2D inlet basically a "2D cone"? Similar to how an aerospike engine is made "2D" in the linear aerospike? What's inside the cone/spike? Or is it just hollow?
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14 votes
2 answers
11k views

What is the "area rule"?

The "area rule" states that the supersonic drag on an aircraft is related to the total area on part of the aircraft. What is the exact definition of the rule? Why does this happen?
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22 votes
3 answers
6k views

Why is the use of tail-down force so common?

Why is the use of tail-down force so prevalent in aircraft design? Why not use canards to avoid induced drag?
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8 votes
1 answer
12k views

How does Reynolds Number affect skin friction drag?

I'm an aerospace engineering student, and I'm worried about efficiency as it relates to high and low Reynolds numbers. I don't understand which is more helpful for a aircraft. On a website I read ...
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116 votes
9 answers
27k views

Is there a maximum possible size for an airplane?

Is there any theoretical or practical limit to the maximum number of passengers - and therefore size - one can build an airplane for?
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21 votes
2 answers
73k views

What are the different wing planforms? What are each's advantages? Where are they commonly used?

I remember reading that there are four common wing planforms: Rectangular Eliptical Tapered Sweptback I'm sure there are more. What are the different types of planform out there? Each must have its ...
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27 votes
3 answers
24k views

What's P-Factor and why does it occur?

Whenever I hear anyone talking about P-Factor, (whether it be single-engine left turning tendencies or multi-engine loss of directional control scenarios), someone always brings up the fact that the ...
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23 votes
2 answers
4k views

Is a golf ball surface a good idea for wings or fuselage?

I searched for an infamous golf ball question on this site but did not find any, so I guess it's time for one. Would a dimpled surface like a golf ball somehow improve the aerodynamics of an airplane?...
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7 votes
2 answers
785 views

'Gravitational' power vs. engine power

A glider gets the power it needs to fly from the decrease of gravitational potential energy associated to the descent. My question is: for the same weight $W$, airspeed $V$, and a prop efficiency of ...
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53 votes
4 answers
22k views

Why are the F/A-18 rudders deflected in opposing directions during takeoff?

Looking at some videos and photos of F/A-18 Hornets and Super Hornets taking off from carriers and from airfields, I recognised that the left rudder is pointing right, and the right rudder pointing ...
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48 votes
2 answers
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Why/when is the blunt nose better?

Most large aircraft and some fighters have blunt, rounded nose cone. OTOH many fighters (that don't use the nose for air intake) and notably the two supersonic airliners (Concorde, TU-144) have the ...
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15 votes
3 answers
12k views

Why do low wing aircraft have higher dihedral than high wing aircraft?

I have noticed and read in books that low wing aircraft have higher dihedral than high wing aircraft. Dihedral is design feature for lateral stability so should be needed for both designs. So why is ...
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9 votes
3 answers
28k views

How can I calculate maximum rate of climb?

By what way and with which variables could you determine a plane's maximum rate of climb per time? If I'm not mistaken, I'm looking for VY.
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18 votes
2 answers
8k views

Why do some airplanes have vertical strakes?

A lot of different aircraft have vertical or near-vertical fins below the empennage, or above the empennage and attached to the front of the vertical stabilizer. What purpose do these devices serve?
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17 votes
4 answers
32k views

What is the performance of a flat plate wing?

By flat plate I mean this: Source: Physics.SE Low performance indeed, but how much low? How would: The angle of attack, The speed range, The turn capability, The fuel consumption, Or other ...
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26 votes
8 answers
4k views

Is there an aerofoil that gives reasonably good lift for both air flow directions: forward and backward?

Could an aerofoil be designed to give reasonably good lift for both flow directions? I was motivated by this related question on Aviation SE: Can a plane fly backward if its propeller is in reverse? ...
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8 votes
5 answers
82k views

How to calculate angular velocity and radius of a turn?

How can I calculate with known tangents of different angles and by rules of thumb? Which formulae should I use for fps and NM?
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20 votes
6 answers
18k views

Do box-wings suffer from induced drag the same way as normal wings?

Most wings suffer from induced drag due to a pressure difference above and below the wing causing air to sneak around the tip, forming a vortex. There are various methods to minimize these effects, ...
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10 votes
2 answers
7k views

Why does the vortex created by wing affects its own angle of attack?

According to potential flow theory, we know that the lift generated by the wings is due to the vortex it creates. In case of a 3D finite wing, there is also a span wise flow due to tip leakage from ...
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