New answers tagged

1

the question is not is there or is there not any lateral force component. It is whether or not the lateral force components all cancel, as in the topmost image you posted, where the lift vector is collinear with the resultant of the aircraft's weight and the centrifugal force.


0

Dynamic pressure is $$ q = ½\varrho v^2 $$ where $q$ is dynamic pressure, $\varrho$ is density and $v$ is velocity. The important bit here is that it is proportional to density and since density and pressure are closely related and pressure decreases with altitude, so does density For the intuition of particles hitting the surface, note that pressure is ...


2

Think of it this way. Your airspeed indicator is not directly measuring the distance traveled of any object, aircraft nor air molecules, over time. Your airspeed indicator is a pressure sensitive device that measures ram air pressure (dynamic pressure) versus static pressure. It converts that measurement into a meaningful value of airspeed. That ram air ...


4

Air pressure reduces with altitude, so while an individual molecule is striking the the aircraft at 100kt, there are fewer of them. This means there is less pressure placed on whatever surface is being struck. The difference in indicated speed is simply one of a physical limitation with the air speed indicator - air speed indicators rely on dynamic pressure/...


0

No, that thinking is incorrect. The air involved in lift creation is roughly the amount that flows through a disk with a diameter equalling wing span, and your distributed propulsion concept will involve a far smaller amount of air.


0

Flapping, the vertical up/down movement of the blades, is not directly controlled. What a pilot controls is the blade feathering or pitch angle. Increasing feathering / pitch generally increases the aerodynamic forces on the blades, which changes the flapping. Unless the rotor and blade are infinitely rigid, which would cause other problems, flapping will ...


4

The Abdullah's answer is correct to it's level of approximation, but I'd like to expand on why the pressure is reduced on the leeward side. As the air encounters the leading edge, it is pushed out of the way. Due to first law of motion, it would like to continue moving outward from the wing and avoid the area just above the wing. But besides inertia, air ...


0

One of the reasons for this is too cause the wing to stall differently or at a different rate at different parts of the wing. In other words the angle of attack near the tip of the wing will be lower than the angle of attack near the root. This will cause the wing near the body of the plane to reach the critical angle of attack and stall before the wing ...


-2

From a layman’s point of view: As far as lift generation, it is more precise to say that the lower static pressure generated perpendicular to the chord line of the wing is created by an increase in velocity of the air molecules instead of saying that the acceleration is created by the lower pressure. The acceleration of air molecules is greatest on the side (...


2

Air accelerates over the upper side. The reason is simple: As the wing - or anything else in air - moves, it creates high pressure at the front and low pressure at the back. The air flowing around the wing gets sucked into this low pressure region, and the suction accelerates it. (It will slow down again at the end of the low pressure zone) But the ...


0

The A320 wing is a complex design with no clear mention of chord or angle of incidence, as it is not topical to the operation of the aircraft. The wing is swept back, has variable symmetry from root to tip , as some say twisted. This info is not shared by Airbus.


1

You can use the Lifting Line Theory to first calculate the downwash at each spanwise station, which are then converted to the induced AOA ($\alpha_i$). The sectional moment coefficient and lift coefficient are: $$c_m = c_{m_0}+c_{m_\alpha}(\alpha-\alpha_i)$$ $$c_l=c_{l_0}+a(\alpha-\alpha_i)$$ To get the total moment of a straight tapered wing (about the root ...


1

Shed vortices from unsteady flow over an airfoil result in decrease and phase lag in lift. Ref: https://www.researchgate.net/figure/Vortex-shedding-from-an-airfoil-oscillating-in-pure-heave-2_fig2_251006855 Using thin airfoil theory in incompressible flow, the lift coefficient for an airfoil undergoing cyclical pitching and/or heaving can be expressed as (...


2

I worked at Mooney for 11years, 6 as the Director of Engineering after Roy Lopresti left the company. Art Mooney asked Al to design the wood spars so he could build them on a flat table. This resulted in t iconic and characteristic "Mark" of the M20 Type.


0

The CP of the wing will, for most airplanes, still lie aft of the CG which is usually required to be longitudinally stable. Peter was addressing the whole airplane. The CP of the airplane as a whole (Lift, Weight, Drag, Thrust), will need to lie exactly in the CG or a moment will exist and rotation will take place. Peter chose to use the CP of the wing and ...


2

the lift generation mechanisms of these two wing designs are quite different. Insects use completely flat wings to great advantage. They generate both thrust and lift by shedding vortices in a flight regime in which the wing is operated right at the threshold of flow separation. Dragonflies operate there, and can accelerate from zero to 10 meters/second in ...


-1

In their first version Smith and Gamberoni concluded from a series of experimental results that an N-factor of 9 very well correlated the experiments. Their value for N=9 is in fact very close to the mean value of 7.8 and 10 as concluded by van Ingen. (...) If the value N = 9 is assumed to be universally valid, we can “predict” transition for a new case by ...


1

The droplet shaped airfoil has multiple advantages. It provides space for storing stiffening structures. The flat plate foil is very thin, so would need to be quite heavy to maintain stiffness, as stiffness is proportional to the square of the thickness. It provides space for storing fuel. This is important to reduce weight on modern cantilever aircraft. ...


1

No. MiG-21 (any modification) didn't need it and didn't have it. With its low-aspect-ratio delta wing and most mass concentrated in the centre, it was agile enough with standard ailerons. The elevator had a single hydraulic booster driving both halves of the stabiliser. Differential stabiliser was used on MiG-21's successor, MiG-23. That one had no ailerons ...


4

Not really. First, the 'legal' reason: the flight manual doesn't offer this method. So you are not supposed to do it. Second, there is a technical reason: MiG-21 had so called 'floating flaps' (as they call it), which are held down only by hydraulic pressure. The pressure is set such that the air dynamic pressure would retract the flaps as the airspeed rises ...


1

Are you sure you're calculating all these forces in the correct axis? Weight is always straight down toward the Earth, but the other three forces rotate with the plane as shown in your diagram. If the nose of the plane is pointed straight down, then the force of thrust points directly down and thus is added to gravity. Drag will point straight up, and lift ...


-3

Congratulations, you have just discovered... Vbg! First, remember vertical lift opposes weight, and this will be the $cosine$ of your lift vector (which is correctly drawn). As your speed increases, your plane will depart from its line of flight (which is descending). With a glider, the wing is now not only supporting weight, it also has a horizontal ...


3

Watch the pitch equilibrium better. Normally, when an airplane picks up speed in a dive, the lift coefficient drops. This will shift the balance of moments (lift and weight times their moment arms) such that the aircraft returns to its old speed (after several oscillations). Unless you show us the full mathematical model, it is hard to say where you went ...


1

As the helicopters speed increases the angle of attack on the retreating blade will continue to increase. Due to the rotational velocity increasing along the length of the blade, the angle of attack will be greatest at the end. It is this area as the speed increases combined with the blade flapping down which will stall. ('Berp' blades (looks like a paddle ...


2

For the same reason aircraft have $V_{S}$ — you don't want to get into stalled condition, because while recovery is possible, it is difficult and far from certain. Due to the gyroscopic effect, the rotor blades reach the lowest point 90° behind the point of minimum lift. As the helicopter accelerates, the lift would decrease on the retreating side, which ...


3

Flow separation and turbulent transition are completely different phenomena. Flow separation is driven by an adverse pressure gradient in the flow direction. On the top surface of a lifting surface, the flow has to decelerate and return to farfield pressure as it approaches the trailing edge of the surface. So there is an adverse pressure gradient near the ...


0

For these kind of jobs VLM is nice tool or there exist some improved version of xfoil. CFD will be too advanced i think. You are in correct path


3

I would recommend the use of Aeolus ASP for aerodynamic shape optimisation. Edit: I am not associated with the software in any way. I had found its shape optimisation features useful for an assignment at my university.


1

You won't be measuring any static pressures because facing the transducers into the sense direction produces dynamic positive pressure which is not subject to temperature compensation or air density corrections at altitude. A Vertical Speed Indicator works by taking static pressure and a calibrated leak inside the instrument to show your climb rate. You can'...


7

Think of the boundary layer as a multi-lane highway with rubber cars which can bump into each other. This highway has a sticky curb on one side and the cars are a bit sticky themselves, so cars near that curb get the slower the nearer they are. In one case the cars stay in their lanes and the rightmost lane, right next to the curb, (sorry, you Australians, ...


15

At what point does one say "oh, this flow has changed from turbulence to separation" At the point where the flow reverses direction. Flow separation. The bold curve is the surface/wing. Yes, that can happen. Both turbulent and laminar flow can separate. Turbulent flow is in fact less likely to separate than laminar flow. This is why aircraft ...


0

Ultimately, CFD (Computational Fluid Dynamics), i.e. computer simulation of the airflow and its effects on the wing, will do the job. Many such programs are available, including free ones.


4

The graphs in the OP show fairly typical results that one would expect from linear analyses (e.g. VLM). 1. Lift In the linear range, the lifting surface's lift coefficient ($C_L$) can be expressed as: $$C_L = a_0 \alpha + a_1 \delta$$ where $a_0=\frac{\partial{C_L}}{\partial{\alpha}}$ is the lift curve slope and $a_1=\frac{\partial{C_L}}{\partial{\delta}...


3

It is true that an aerofoil and a fast car both have streamlined and cambered profiles. A wing in flight generates a high-pressure wave beneath it, which helps support the plane. This wave travels down to the ground and reflects off it. Normally the reflection trails well behind the plane, but very low down it can impact the wing and boost lift. This is ...


1

the wing on a plane is designed to generate lift while flying in the open air. It happens to generate less drag when flying ~ten feet off the ground, because a "bubble" of air gets squeezed between the bottom of the wing and the surface of the ground and this helps support the wing. this is called "ground effect" for airplanes. you want a fast car to stay ...


3

venturi effect occurs until the venturi is so extreme that the flow is "choked" and the venturi effect ceases to operate and you just have an air cushion? Is that the answer? No. Neither answer to your linked question talks about venturi effect at all! In the aircraft case the wing is still far enough above the ground there there is no significant venturi ...


1

The Doak VZ-4 twin ducted propulsor flew in 1958, the Bell X-22 took that up to four in 1966. So yes, people have been thinking about it for over half a century. Analogously to any tailless aircraft, the side-by-side twin is sensitive to CG in vertical mode and trim must be closely maintained. Although not ducted, the Boeing V-22 Osprey convertiplane suffers ...


1

No. Slow-moving also means low mass flow. In order to re-energize the boundary layer, the air has to move fast, meaning high mass flow. Also, speed means reduced pressure, so the stagnation pressure is not sufficient to produce that desired high-energy flow. Also, contamination (bugs, ice) accretes close to the stagnation point. Ideally, in order to remove ...


3

Maybe I'm missing something obvious to you, but why do you think there's zero circulation? Take the simplest case of an infinitely thin 2D flat plate in linearized supersonic flow. The solution in the perturbed velocity potential ($\hat{\phi}$) is: $$\hat{\phi}= \begin{cases} 0 & x\pm\beta z<0 \\ \frac{1}{\beta}\alpha(x-\beta z) & 0\...


2

Tail volume is a measure for the ability of the tail to compensate for the destabilizing pitch moment created by the wing in case of the horizontal tail and for adverse yaw in case of the vertical tail. This pitch moment is proportional to the square of the wing chord (one factor comes from the area, the second from the lever arm), so if you compare two ...


-1

Do biplanes need bigger tail coeefficients than monoplanes (of equal wing area)? Here's where building free flight models and testing them in cross wind conditions is very helpful. As a designer, it is important to consider wing and tail functionality. Many "tailless" designs, such as deltas, have adequate stability without a separate and distinctive "...


1

The lift over a wing comes from an imbalance of pressure above and below the wing. The higher the pressure, the more force is imparted to the wing. Thus, by generating a higher pressure on the bottom of the wing then on the top, a net upward force is created which offsets the pull of gravity on the airplane. The greater the pressure differential, the more ...


2

Of course not. Thin Airfoil Theory produces a beautiful result that relates the zero-AOA lift to the mean camber of the airfoil, as well as the lift slope vs AOA of any thin airfoil is $2\pi$. But that's assuming: Airfoil is asymptotically thin: such that the mean camber line represents the flow path Camber is close to the chord: such that the vortex sheet ...


1

In the inertial frame of the free airstream, the pressure force causes the particle to accelerate inwards. Centrifugal and centripetal forces do not play a direct role; there is no space station wall for centrifugal force to be exerted on, nor to exert a reactive centripetal force. The pressure force acts in the role of the centripetal force shown in the ...


0

can you write your answer? Air flow striking the wing is deflected either up or down as the wing literally slices through the air. This can be looked at as either the air hitting the wing (wind tunnel) or the wing hitting the air (actual flight). Relatively, between air and wing, the effects are the same. The bottom airflow is rather mundane, slowing and ...


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