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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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10answers
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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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5answers
7k views

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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1answer
7k views

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 ...
42
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9answers
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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 ...
28
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7answers
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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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9answers
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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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2answers
3k views

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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1answer
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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 ...
12
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2answers
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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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3answers
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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 ...
18
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3answers
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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 ...
21
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5answers
7k 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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4answers
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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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4answers
4k views

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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3answers
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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 ...
27
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2answers
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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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7answers
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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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2answers
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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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2answers
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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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9answers
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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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1answer
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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?
14
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2answers
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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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2answers
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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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3answers
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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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7answers
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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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9answers
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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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8answers
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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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3answers
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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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1answer
5k 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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2answers
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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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2answers
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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 ...
27
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2answers
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How can a helicopter be designed without a tail rotor?

How will the main rotor torque be balanced if a helicopter doesn't have a tail rotor?
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3answers
8k 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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2answers
8k views

What is the typical temperature of an airliner's hull during flight?

Some high-speed military aircraft like the SR-71 had real heating problems, but airliners also travel almost at the speed of sound, use most of their fuel to make up for frictional losses, so I would ...
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2answers
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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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2answers
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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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2answers
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How can the zero-lift drag coefficient (parasitic drag) be calculated?

Consider a 3-D wing made from an arbitrary airfoil, say a NACA0012 airfoil. The wing has a trapezoidal shape, with a fixed span, root chord, and tip chord. Also, assume that the wing loading is known ...
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6answers
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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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1answer
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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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2answers
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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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9answers
15k 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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3answers
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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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5answers
6k views

Would connecting propeller blades with a continuous ring reduce induced drag?

Turbine engines are covered, which of course is to contain the process (just like a super/turbocharged engine is as soon as the air enters the intake). But it got me thinking, doesn't this also reduce ...
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4answers
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How do conventional and T-tails differ?

What design considerations go into the decision between conventional tails and T-tails? Functionally the horizontal stabilizer/stabilator are the same in both cases, providing negative lift, the ...
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2answers
2k 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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3answers
15k 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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3answers
2k views

Why do airfoil's trailing edges point downward?

The trailing edge of and airfoil is mostly pointing downward. Is there any reason for that? Down wash increases drag and down wash is due to the direction of air pointing down. If the trailing edge is ...
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4answers
12k 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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4answers
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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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2answers
28k views

Why are there no longer any biplanes?

Is there an aerodynamic reason why the concept of biplane or triplane has been completely abandoned? Practically all planes were biplanes in WW1, and in WW2 practically none were developed.