# 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 I determine numerically the pitch rate of an aircraft?

I have done aerodynamic analysis on a UAV. Is it possible to calculate pitch rate and yaw rate of my UAV depending on design parameters? (I have aerodynamic analysis of the wing, CL, CD, MAC, W, etc.)
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### Which is more efficient, thickening an airfoil or adding a bottom-surface curve?

So if you were to take a standard airfoil and increase the thickness, you’d increase the lift (Bernoulli’s principle), but it would also increase the drag. Now imagine you have the same airfoil, but ...
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### Conundrum about designing a glider relating to coefficient of lift

I'm designing a high-altitude glider. Just to clarify a few points before my question: The glider will weigh close to 200 grams. It will be using the A18 airfoil. The glider is dropped from 80,000 ...
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### What happens to a shockwave when it goes through different temp/density air?

Specifically I am asking what happens to a shock as it travels through different density air. This answer's comments has some good information about it. As said in the linked answer, a shock will bend ...
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### How to maximize L/D ratio by design in a high altitude glider? [closed]

EDIT: Some initial confusion with TAS and IAS confused me, I now understand this better, thanks for everyone who helped. I'm designing a high-altitude glider, and I'm wondering how the angle of attack ...
222 views

### Why can you only hear an aircraft after the shockwave passes?

Why do you only hear engines and other noise from a jet going supersonic after the plane has passed? A lot of resources use this picture to illustrate : This is cool and all, but say you changed the ...
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1 vote
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### Intersecting Boundary Layers in XFLR5

I am analyzing an airfoil called RevE-HC. While doing a type-1 analysis, I encountered that the BL is intersecting towards the trailing edge. The panels are refined and the geometry is also smooth. ...
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1 vote
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### How are shockwaves able to refract?

How are shockwaves able to refract? As said in this, When two shock waves collide, they interact with each other and produce complex patterns of compression, rarefaction, and reflection. The ...
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### Flow separation in inviscid flow

I watched this video about CFD ( ) where flow was assumed to be incompressible and inviscid, but how can vorticies occur behind the ball at the start of the video, shouldn'...
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### Why does turbulence over a wing make drag?

Drag is the result of air ‘pushing’ the opposite direction of flight, if you want to think of it that way. The skin friction drag is made from the air trying to pull the wing opposite of the flight ...
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### What should be decalage angle for high lift to drag ratio biplane glider?

Assuming hypothetical biplane variant of a modern conventional glider, wingspan of 8m, 1m separation between the wings, no stagger, no struts, what should be the decalage between the wings assuming ...
1 vote
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### Wouldn't the induced downwash "pull" the wing of a plane down?

I asked a similar question on this recently, (here), and the answer said this: Downwash is not a force. It is a small increment in the velocity vector. Downwash can change the local angle of attack --...
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### Elevator / horizontal tail effectiveness at high speeds?

Take for example a jet fighter, when at low speeds vs high speeds, airspeed will differ a lot. As the turning moment is due to the lift force from the tail and lift increases quadratically with ...
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### VTOL Propeller Sizing and Executing a transition from VTOL to Forward Flight mission profile

Hi I am an engineering student, currently in the process of designing a compound UAV drone capable of both vertical and forward flight. I've made significant progress, having completed initial gross ...
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### How is the pressure constant across the boundary layer but density isn't?

In $P=ρRT$, ρ is density, R is the gas constant, and T is the temperature in Kelvin. In the boundary layer, the temperature and density varies, so why doesn't the pressure? If you have a slip line in ...
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### Why does this curved wind tunnel rotate?

Why does this curved wind tunnel rotate, why is it not just curved? A curved wind tunnel has a radial pressure gradient, but this pressure gradient doesn't exist in a real turn, so how do you get ...
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### What way does induced downwash make a wing roll?

Say you have a wing, no sweep or anything to simplify things. One side of it, let's just say the left, magically doesn't have a tip vortex, therefore no induced downwash from the tip vortex. Would the ...
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### Why does induced downwash vary across a wing in a sideslip?

in this excellent answer, it states this : A well-known effect of wing sweep is the variation of induced downwash along the span from the trailing wake that produces an additional lift distribution ...
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### What happens to tip vortices in a sideslip?

Say you're in a right sideslip. What happens to tip vortices? I'm fairly sure that it would just reduce the strength of the vortex (for the left wing), because there is a force trying to keep the high ...
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### Is it recommended to forward slip an aircraft wth a v-tail?

Is it recommended to forward slip an aircraft wth a v-tail just above stall speed at a maximum angle of attack? A forward slip requires crossed controls, eg. Full right rudder and full left aileron ...
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### How do tip vortices make downwash? [duplicate]

As seen in this picture, the tip vortices are said to make downwash. Why is that? I’m also not sure why that’d tilt the lift vector backwards, but that might require a separate question. Link to the ...
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### What causes the vapor cone when an aircraft is traveling at M ≤ 1? [duplicate]

What causes the vapor cone of an aircraft going M ≤ 1? I know that the vapor is from the air expanding, but why is it in the cone shape? What shock system forms it into that shape?
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### Why is the wave drag of a straight wing less than that of a swept back wing?

According to NASA's claims, when the swept back wing is inside the shock cone and the shock is not attached to the leading edge of the wing(subsonic leading edge), the wave drag of the swept wing is ...
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### Why don't shockwaves expand rearwards when they expand out?

Why don't shockwaves expand rearward when they expand out? In this for some reason really big picture, you can see the shocks expanding out past the actual plane. Why don't they also expand rearward? ...
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### Why are supercritical airfoils not used in GA aircraft?

Why are supercritical airfoils not used in GA aircraft? The 787 is assumed to use a supercritical airfoil, so why don't GA aircraft use them? My guess is that they're harder to manufacture, and a lot ...
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### Is the math behind my approach to design a propeller right?

I'm trying to design a fixed pitch propeller of diameter 1.8 m flying at 10000 ft going at forward velocity(85 m/s). What I've done is take a series of airfoils (from root to tip), found the ...
1 vote
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### How does a shear layer make vortices?

How does a shear layer make vortices? If you have 2 streams of air that are moving at different speeds or opposite directions right beside each other, how would that make a vortex? What causes the ...
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### How can I cross verify my propeller thrust? [duplicate]

I'm simulating a propeller in Ansys and im getting a thrust of 2000N. The forward speed is 85m/s and 240.25 rad/s angular velocity and the diameter of the propeller is 1.8m. Since I'm not able to find ...
1 vote
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### What causes this vortex pattern on the slip line of a shockwave?

What are these little vortex patterns from on the slip line of these shocks? At first I thought it was vortex shedding, but it looks a tiny bit different to me (than vortex shedding). You can see the ...
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### What causes the oscillation in vortex shedding?

When studying this video, I was wondering what actually causes the oscillation? Any source online that I found said that it was from oscillating low pressure zones, but what causes that?
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### How do thicker airfoils give better stall characteristics?

Why do thicker airfoils have better stall characteristics? They make more lift, but I don’t see any reason for them to have better stall characteristics. Also, I heard a rounded airfoil nose will help ...
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### Why does the wing drop prior to a spin?

In the process of understanding the aerodynamics of spins, I'm having a hard time understanding why one wing drops. I understand that the for spins to occur, a stall + a yaw must occur. I also ...
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### Max Range Relationship to Altitude for Propeller-Driven Aircraft

Chapter 11 of the PHAK states, "If a change in altitude causes identical changes in speed and power required, the proportion of speed to power required would be unchanged. The fact implies that ...
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### Is the ideal airfoil concave on the underside?

Virtually all airplane wings are convex on both the top and at least part of the bottom. But thus convexity on the bottom creates suction which reduces lift. I can only think of two reasons to have it:...
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### Minimum sink speed and maximum endurance speed

For a given airplane, are the minimum sink speed and maximum endurance speed the same? Thankyou
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### What happens when 2 air streams, one going faster but the same direction, are beside each other?

Inspired by this video, what happens when 2 air streams beside each other going the same direction, but one going faster, interact? Do they make turbulence and or vortices as said in the video? I’m ...
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### Is it better to fly faster or slower through turbulent air?

If you had to pass through turbulent air, and your only goal was to give the smoothest ride possible to your passengers, would you push that throttle or would you reduce the throttle, or would it be ...
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### What does air becoming compressible change? [duplicate]

You always hear that around Mach 0.3, air technically becomes compressible. What actually changes when this happens, in subsonic and supersonic flow? Does it affect the formation of shocks?
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### What are the differences between an oblique wing and a swing wing? [duplicate]

How they differ from each other. How do they work. What is the structural differences. How do they help in reaching mach speeds and get better fuel efficiency. How does they both perform with max ...
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### Does adding twist to wing always decrease induced drag and what are its effect on parasite drag? [duplicate]

I am doing an assignment and one question was the effect of twist on drag. The first two options are increased induced drag and decreased induced drag respectively. The third option is increased ...
1 vote
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### Do slats and leading edge devices increase lift at a constant AoA and airspeed?

I've seen mixed sources on this subject. Some say leading edge devices allow the wing to obtain a higher AoA, and others say it flat out increases lift. For me, the latter makes most sense, because ...
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### Are oblique shocks formed at the leading edge-top surface of a wing?

Do oblique shocks form on the leading upper surface of a wing? I know bow shocks are formed there, but is that the same thing as I’m talking about? Oblique shocks would have to form there because the ...
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### How much of the Virgin GlobalFlyer's L/D is due to laminar flow?

Despite travelling much faster than the Voyager, it has a significantly higher L/D. The latter seems to have two features that disrupt laminate flow, that are absent in the former. Namely the canards ...
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### Drag breakdown of a typical civil airplane wing

How much of the drag produced by a typical GA/airliner/cargo plane's wing at cruise is induced, frictional, and pressure drag?
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### why stabilator has a lower travel limit for down movements?

Within the POH of my aircraft, in a part titled "Control Surfaces Travel Limits", the manufacturer states: Stabilator: Up 18° --- Down 3° Why stabilator has a lower travel limit for ...
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### When an oblique shock forms, what happens to the normal shock that helped it form?

What happens to the normal shock that helped the oblique shock form, in the first shock of a lambda shock? Oblique shock waves form because : "An oblique shock wave is a shock wave that, unlike a ...
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### Computing the eigenvalues of the longitudinal dynamics _analytically_: is there a method to simplify the task, or must it be brute force?

I understand how to go about finding the eigenvalues and eigenvectors in principle, in order to distinguish the phugoid modes, but the first exercise in Lavretsky & Wise tells to compute those ...
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### How do canards reduce the X-59's sonic boom?

X-59 As of 2017, the ground noise was expected to be around 60 dB(A), about 1/1000 as loud as current supersonic aircraft. This was to be achieved by using a long, narrow airframe and canards to keep ...
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### What determines the angle at which a shock will form?

What determines the angle that a shock will form? If you look at a lambda shock, you’ll see it isn’t straight up, but with an angle (both the front and rear part of the lambda shock). The second ...
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