# Questions tagged [drag]

Aerodynamic drag is the fluid drag force that acts on any moving solid body in the direction of the fluid freestream flow. Part of the drag is the direct consequence of the wing generating lift.

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### How to calculate lift and drag of commerical aircraft in different phases of flight?

What is the best way to mathematically calculate values of lift and drag forces, in different phases of flight: takeoff, climb, cruise, descent, and approach? Edit: I have the idea of calculating the ...
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### Why XFOIL predicts a lower drag coefficient at higher Re?

A well known idea is that for aerodynamic/streamlined bodies the friction drag is larger than pressure drag. Hence, a laminar boundary layer is preferable (only looking at minimal drag, no other ...
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### Has there ever been a VTOL aircraft thruster that generated lift through the use of a drag force?

I have been recently thinking about a conceptual VTOL aircraft thruster that should generate lift through the use of a drag force and I am very curious to know if such a thruster has ever been built ...
1 vote
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### Extrapolating Oswald Efficiency Factor from CL^2 vs CD Graph

I have plotted this CL^2 vs CD graph for a glide test performed in a flight simulator. I want to find the Oswald Efficiency Factor, e from it and I assume I can do that from its gradient. With a wing ...
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### Can induced drag be negative?

For an aircraft in straight and level flight, lift-induced drag is the horizontal component of the force perpendicular to the wing chord. Positively cambered aerofoils generate lift starting at small ...
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1 vote
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### What's the relationship between mach number and drag force on an airplane?

From what i've read drag coefficient at mach 1 is several times (up to 10x) the drag coefficient below drag divergence mach number. It drops as the mach number increases. It's easy to find plots ...
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### Why does lift decrease and drag increase when approaching the stall condition?

This is an ECQB-PPL question specifically asking what happens before the stall. I do understand that after the critical angle has been reached, the airfoil is no longer generating lift (so obviously ...
1 vote
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### Is it possible for the lift force unit vector to be equal to the weight force unit vector?

I know that the drag force is parallel to the direction of flow, thus equal to the unit vector of velocity. But if you consider a vehicle, when its angle of attack is below the velocity vector from a ...
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### Help with calculate forces from pressure distribution

V=50m/s deltaPg= -981 Pa deltaPd=490,5 Pa c=1m r.com/PCshZ.png Above is calculate Fz with integrals and with average pressure. Why F3 is calculate from 0 to C/2 if pressure distribution is drawn at ...
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### How can PreciseFlight speedbrakes double the drag while being so small?

Look at this photo of some PreciseFlight© speed brakes: On the website it is claimed that these little red plates can double drag and descent rates. I cannot believe that. Can this be true, and if ...
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### How to calculate drag of a flat rectangular surface at given area, air density, airspeed and angle of attack?

I'm a complete noob in aerodynamics, and I'm trying to calculate the drag of a rectangular flat area, given the air pressure / density, area, angle of attack and airspeed. I've read this question, but ...
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### How much drag is actually caused by open cowl flaps?

I am modelling the Cessna 210 for FlightGear, which has cowl flaps. I want the model to be as realistic as possible, and so, I want to know: how much drag do cowl flaps produce ? I could not find any ...
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### Why is the CG assumed to be between the CP and the tail?

While discussing stability (Longitudinal, Lateral, Directional), invariably, all texts assume CG to be between CP and tail. Ex: Look at the specific image in wikipedia https://en.wikipedia.org/wiki/...
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### Does $C_d$ change with speed? [closed]

In aircraft drag calculations, drag D is computed as $D = C_D \cdot \frac{1}{2} \rho V^2 \cdot S$, with $C_D$ a dimensionless factor determined by the "streamline shape" of the measured ...
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### How does a forward lifting surface affect ideal lift distribution of a main wing?

In Peter K's answer to this elliptical wing with lowest drag question the minimum induced drag lift distribution for a wing is described as one with a constant downwash angle across its span. When a ...
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### Do all Fuselage sections have same performances?

The Burnelli machines had an airfoil shaped fuselage; some indicate near 10% of lift in a 21 century airliner comes from fuselage; 'Flying Wing' concept is old, and still attracts many; bottom of ...
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### How can my CD0 estimation be improved?

In this question (link) @PeterKämpf asked me to give a basis for my results. I will share my method for estimation here to see if you guys agree it is correct and how I can improve on it. Note that I ...
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### How does the drag coefficient behave at transonic and supersonic speeds for swept wing aircraft?

I was reading about wave drag and Concorde recently and found some contradictory information relating to drag. For example Wikipedia says: Afterburner was added to Concorde for take-off to cope with ...
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### Does form drag require skin drag?

Theoretically, if there was sphere with zero skin drag, would that make form drag nonexistent? If fluid could flow around symetric object whose shape doesnt generate any lift without any skin friction,...
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### Why does NASA say $v^2$ is velocity squared rather than speed squared?

Lift and drag forces scale as the square of the relative flow speed, $v$. But speed is the magnitude of the velocity vector; that is, speed is the square root of the sum of the squared velocity ...
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### How do I calculate induced drag? [closed]

How would I go about solving this problem? An aircraft has 6000lbs of total lift and a downwash angle of 6 degrees. Remember that the total lift vector is tilted aft by HALF the downwash angle. What ...
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### Are the lift / drag coefficients considered dimensionless?

Since the lift coefficient, $C_L$, and the drag coefficient, $C_D$, are obtained by rescaling the full lift and drag by $$\frac12 \rho A v^2$$ does that mean they're dimensionless numbers? It's ...
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### Do high wings aircraft create an additional vortex in the middle?

At the same time, the air on the upper surface has a tendency to flow in toward the fuselage and off the trailing edge. This air current forms a similar vortex at the inboard portion of the trailing ...
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### Why does stalling increase drag?

I understand (I think) why lift reduces in a stall. What I don't understand is why drag increases. I can see that the ratio of drag to lift would increase, but I'm not sure I understand the mechanism ...
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### Exam question on upwash and downwash, follow-up to earlier post

I asked before about the difference between wingtip and delta wing leading-edge vortices and got a really comprehensive, concise answer, although one that I think contradicts what I've learnt ...
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### Formula for comparing drag on planes flying at different speeds at different altitudes. Ex: Mach .80 at 40,000 ft, vs Mach 5 at 100,000 ft

I am interested in getting a sense of how much extra energy is needed to overcome drag at different speeds and altitudes. For example, for me a baseline would the drag on an airplane flying something ...
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### What is the relationship between aspect ratio and lift-dependent drag? [duplicate]

It has been a long held view that aspect ratio of the wing has a significant role to play in the lift-dependent drag. However, mixed opinions have been expressed on the importance of aspect ratio in ...
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### Coefficient of Parasitic Drag - What is the Preferred Basis of Measurement?

In attempting to determine the coefficient of Parasitic (Zero Lift) Drag - the cD0 - for various aircraft, I have discovered that there appear to be several ways this number is represented: by ...
1 vote
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### Drag estimation of Xfoil and Vortex Lattice Method?

I have been working on building a software to estimate lift and drag properties of a fixed wing being tested at a wind tunnel. The setup is a low AR wing with NACA0012 profile and 0.3m chord, with 0.4 ...
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### What would be the Sref i.e. Reference Wing Area for Drag Build Up Calculation in case of a box wing design?

Would Sref be sum of areas of both, the front and the back wing? or just one wing? Assuming both the wings have equal areas (image below) Details - So, I am calculating drag using the component drag ...
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### Would large, low aspect ratio fan/propeller blades be more efficient? Why not?

With reference to this answer We read in the above that accelerating a larger mass of air by a smaller amount is (theoretically) more efficient. This is an advantage of a larger propeller than is ...
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### What exactly happens to kinetic energy in the turbulent layer on an aerofoil?

Sources I've read contains contradicting information. As far as I know, when the laminar airflow breaks up, it becomes a thicker and draggy layer, causing a layer of what essentially is slowed air; ...
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