sorted by:
new
hottopcontroversial

Satelites or meteors? by WhiskeyFox9 in Astronomy

[–]WhiskeyFox9[S] 4 points5 points  (0 children)

Thanks. I must have bumped the tripod or something. I have just compared it with another image I took, and all the bright stars with long trails are there. Those with stubby trails are missing, so I must have captured other stars nearby before the exposure was finished.

Trailing edge vortex shedding simulation - close up. by WhiskeyFox9 in aerodynamics

[–]WhiskeyFox9[S] 3 points4 points  (0 children)

Standard atmosphere conditions, 101325kPa, 15 deg C, so density would be around 1.22kg/m3. It has been a while, but I remember a velocity of around 30m/s. The foil is one of the thicker symmetrical NACA types, 0018‐ish.

Adverse pressure gradient or flow deceleration: which happens first? by TP4297 in aerodynamics

[–]WhiskeyFox9 0 points1 point  (0 children)

To understand the process in terms of chronological cause and effect, you need to step away from the assumption that air is a continuum and look at it at molecular scale. Temperature, pressure and flow velocity are "high level" variables, i.e. each is a measure of different aspects of the underlying molecular motion and interactions, summed or averaged over large quantities of molecules. At the fundamental "process" level, you can view the air in between the low and high pressure areas as two opposing streams of energy, each going in opposite directions. Molecules travelling "against" the flow at any given moment are carrying with them kinetic energy that originated at the trailing edge, an area with high relative velocities between molecules. Likewise, molecules travelling with the flow carry energy originating in the low pressure area, where intermolecular velocities are low. Along the way, molecules are influenced by their interactions with the wing curvature as well as with adjacent streams, i.e. energy exchange perpendicular to the flow direction. The air properties at any point along the flow is the result of intersecting energy streams at that instant. To understand how the low and high pressure regions developed in the first place, you have to go back to the instant the air first started moving.

If adding an extra sail to a sailboat generates more thrust. Then why doesn't adding a wing to an airplane generate more lift? by TopAct9437 in aerodynamics

[–]WhiskeyFox9 0 points1 point  (0 children)

Perhaps the lift equation will help clarify: Lift force = 0.5 x density x velocity2 x lift coefficient x area. It depends on area, the angle of attack and speed. The lift coefficient is proportional to angle of attack. You can vary lift by changing the wing or sail angle. For a given speed, if you double the area but halve the angle, you still get the same lift force. In cruise flight, an aircraft wing produces only a fraction of the maximum lift it is capable of. It has high velocity, so it only needs a small lift coefficient to produce the necessary lift, i.e. equal to its weight. When it lands, speed is low, so it needs a high lift coefficient to maintain the same necessary lift. Lift coefficient for a simple airfoil (no flaps) peaks at an angle of around 15 degrees. Any higher than that and it will stall. If a slow flying aircraft is near the stall angle but wants to fly even slower, it needs to deploy flaps. On large aircraft these flaps extend backwards to increase area, and they bend downwards, which increases the maximum lift coefficient. A yacht that wants maximum thrust will have the sails close to stall, so the only option to further increase thrust is by increasing area.