14 votes

Why does this curved wind tunnel rotate?

While superficially similar, this curved windtunnel solves a very different problem from a straight windtunnel. A straight windtunnel is used to study steady flight without needing a very long ...
Sanchises's user avatar
  • 13.3k
9 votes

Why does this curved wind tunnel rotate?

Here you'll find his paper about the wind tunnel. Apparently the rotation has been introduced in order to compensate for the Coriolis effect.
sophit's user avatar
  • 11.9k
9 votes

Why does turbulence over a wing make drag?

Short answer: turbulent flow causes vigorous mixing of the flow nearest the wing with flow further away from the wing. this tends to share the energy imparted from the wing to the airflow nearest the ...
niels nielsen's user avatar
6 votes

Why does this curved wind tunnel rotate?

Key point from another related answer: A stationary curved windtunnel would not be the same, because now the air mass needs to curve. This introduces very different phenomena. Perhaps easiest to ...
quiet flyer's user avatar
  • 22.6k
5 votes

Why does turbulence over a wing make drag?

Stop thinking about the direction of the velocity as a force pushing on a wing. Velocity is not a force. Stop it, you're making yourself confused. Turbulence has different meanings. Normal people (...
Rob McDonald's user avatar
  • 11.4k
4 votes

Why does induced downwash vary across a wing in a sideslip?

This effect is really only substantial for swept wings. Here is the lift distribution on an un-swept rectangular wing at 10deg AoA at 0 and 10 deg Beta. Notice the general slight reduction in lift - ...
Rob McDonald's user avatar
  • 11.4k
4 votes

What happens to tip vortices in a sideslip?

The following quote is from "Oblique Flying Wings: An Introduction and White Paper" from Desktop Aeronautics, Inc., available at https://www.desktop.aero/library/ofwwhitepaper.pdf. 2.2.2 ...
quiet flyer's user avatar
  • 22.6k
3 votes

Conundrum about designing a glider relating to coefficient of lift

To start with, you can ignore changes due to compressibility (Mach number) and viscosity (Reynolds number). Your aircraft will have a drag polar approximately of the form: $C_D=C_{D,0}+K\,{C_L}^2$ You ...
Rob McDonald's user avatar
  • 11.4k
3 votes

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

You seem to have such a grasp on this question that it seems impossible that you don't actually understand. I'd really like to understand what is missing between what you know and what you're trying ...
Rob McDonald's user avatar
  • 11.4k
3 votes

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? If the object making noise is far enough, then you always hear it after it has passed, no matter ...
sophit's user avatar
  • 11.9k
3 votes

How are shockwaves able to refract?

The quote you cite does not say refraction. It says rarefaction. Refraction (of light) is when light bends because it transitions from one material to another -- say air to water. I do not think ...
Rob McDonald's user avatar
  • 11.4k
3 votes
Accepted

How is the pressure constant across the boundary layer but density isn't?

Because the pressure is constant across the boundary layer. If the pressure at the wall was higher, it would do something strange -- such as push the streamlines away from the wall. The pressure at ...
Rob McDonald's user avatar
  • 11.4k
3 votes

Why does this curved wind tunnel rotate?

An automobile with front steering pivots on its rear wheels. This may cause a significant amount of side lift in front from a change in the relative wind, making it more difficult for the tires to ...
Robert DiGiovanni's user avatar
3 votes

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 No, you don't. Lift is determined by camber and angle of attack. Both don't change with thickness, so ...
Peter Kämpf's user avatar
3 votes

How I determine numerically the pitch rate of an aircraft?

You need to do a static maneuverability analysis. This involves knowing the size of the control surfaces, calculating their effectiveness (which is not easy), some knowledge of the moments of inertia ...
Rob McDonald's user avatar
  • 11.4k
3 votes

Pitch of a glider with altitude

The angle of the velocity vector relative to the ground reference frame is the flightpath angle, or the climb angle. Typically a $\theta$ or $\gamma$ depending on which reference you use. The angle ...
Rob McDonald's user avatar
  • 11.4k
3 votes

Pitch of a glider with altitude

"Pitch" can be confusing in aviation because we have "pitch to the horizon" and "pitch control" with the elevator. For purposes of clarity let's separate "pitch"...
Robert DiGiovanni's user avatar
2 votes
Accepted

What way does induced downwash make a wing roll?

Downwash is not a force. It is a small increment in the velocity vector. Downwash can change the local angle of attack -- which can change the lift -- which is a force. However, A wing has a rolling ...
Rob McDonald's user avatar
  • 11.4k
2 votes
Accepted

Wouldn't the induced downwash "pull" the wing of a plane down?

NO. First, this is a 2D image and represents a 2D flow. There are no tip vortices (trailing vortices) in a 2D flow. Instead, it is all about the bound vortex (at the quarter chord). Notice the ...
Rob McDonald's user avatar
  • 11.4k
2 votes

Elevator / horizontal tail effectiveness at high speeds?

lift force from the tail and lift increases quadratically with airspeed Correct That means that the faster jet will have a turning moment 11 times stronger than the slower plane? No, because the ...
sophit's user avatar
  • 11.9k
2 votes

Why does turbulence over a wing make drag?

Let's slightly change your concept and reframe your thinking, if that is ok. Think of drag as the wing dragging air in the direction of flight. Now think of the process by which that would happen. ...
Thomas Perry's user avatar
  • 1,255
2 votes
Accepted

Flow separation in inviscid flow

Euler CFD solutions are subject to something called artificial (or numerical) viscosity. How much you have depends on whether your method is odd or even order -- dictating whether a diffusive or ...
Rob McDonald's user avatar
  • 11.4k
2 votes

How to maximize L/D ratio by design in a high altitude glider?

Will a glider automatically adjust to the most optimum angle of attack for the given speed? Yes. Actually, it will adjust to the only possible angle of attack at a given speed. Within limits: If ...
Peter Kämpf's user avatar
2 votes

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. This is true only till around 12% thickness, afterward the $C_{l_{max}}$ decreases with increasing ...
sophit's user avatar
  • 11.9k
1 vote

Which is more efficient, thickening an airfoil or adding a bottom-surface curve?

Adding thickness doesn't add lift. Don't cite Bernoulli's principle and Newton's 3rd law as causal in an aerodynamics discussion -- everything is far more complex and nuanced than that. You can't add ...
Rob McDonald's user avatar
  • 11.4k
1 vote

Conundrum about designing a glider relating to coefficient of lift

However, something that does change the coefficient of lift is the AoA, which is determined from Reynolds number. The AoA is determined solely by the relative angle between the lifting surface and ...
sophit's user avatar
  • 11.9k
1 vote

What happens to a shockwave when it goes through different temp/density air?

Higher temperature does not make the air more compressible. Think of the air in layers. Assume zero wind -- all the layers of air are still. The thing that is moving (through still air) is the object ...
Rob McDonald's user avatar
  • 11.4k
1 vote

How to maximize L/D ratio by design in a high altitude glider?

Let's keep it subsonic to help avoid significant changes in Lift/Drag ratio. Take heart, this 1322 lb aircraft flew to 96,000 feet under power with an indicated airspeed of around 20 knots. Using the ...
Robert DiGiovanni's user avatar
1 vote

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

if you change the shape of the nose of the aircraft ... It seems that is what NASA is doing here. So now one is reducing shock wave amplitude (how loud it is), not the shape of the cone, which ...
Robert DiGiovanni's user avatar
1 vote

Flow separation in inviscid flow

This is a well known phenomenon, a Kármán vortex street. Wikipedia explains it adequately. I won't quote that entire article, though, daring for now to post a link-only answer.
Camille Goudeseune's user avatar

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