# Tag Info

8

Static stall is what we typically think of, when we think of stall. Slowly increasing AOA and then loss of lift as the flow separates. But pitch rate (rate of increase of AOA) has an impact too. At high pitch rates, the wing can go beyond normal stall AOA and still provide significant lift, but for just a short period of time. After that, the bottom falls ...

7

The answer is deeply rooted in the theory of compressible fluid dynamics, so for a fully satisfactory take on the matter you might want to refer to a textbook on that topic (such as Thompson or Shapiro). I will try to give a qualitative explanation. For our discussion here, let's consider a shockwave as the way to abruptly slow down a supersonic flow and ...

7

Beta lines are either linear or parabolic shaped lines that are conveniently placed and spaced between the surge line and the choke line of the compressor (or fan) characteristic (also known as compressor/fan map). Such lines are also found in the turbine characteristics maps. Basically, the Beta lines create a new axis system that prevent a solver from ...

6

What you are describing is a characteristic of fluid dynamics known as eddies. As different portions of the fluid flow faster than others, the friction and surface adhesion between the two layers cause swirling of the fluid and reversal of the current, creating a turbulent flow region. It is this same principle that holds a ping pong ball stationary in a ...

5

Tripping the boundary layer refers to the action of artificially transitioning a laminar boundary layer into a turbulent one. It can happen intentionally (via turbulator) or unintentionally (via imperfect aero-smoothness, such as rivets, bolts, counter-sinks). At the point of boundary layer tripping, the surface protrusion destabilizes the laminar boundary ...

5

No. These are very different things. The shear centre (SC) is a purely mechanical (structural) feature of the wing design. It is a point along the chord such that application of force - no matter what force - causes the wing only to bend but not twist. Unlike the aerodynamic centre (AC) and centre of pressure (CP), it makes no sense to talk about a single ...

4

Rectangular wings can get away without washout because that planform tends to have favourable root to tip stall progression as a characteristic of the rectangular shape. The stall strips aren't really to change the root to tip stall behaviour as a substitute for washout; their job is to generate a local flow separation, just prior to the natural stall, who'...

4

The airfoil always starts with a laminar boundary layer; at some point on the airfoil surface, the boundary layer may transition to turbulent. In a uniform free-stream, two modes of transitions dominate: Natural transition Forced transition a. Natural transition Natural transition is the transition mechanism that we typically associate with Reynolds ...

3

This is due to the Coandă effect. https://www.britannica.com/technology/fluidics#ref129652 In the 1930s Henri Coandă, a Romanian scientist, described what is now known as the Coandă effect, a major contribution to fluidic technology. He observed that as a free jet emerges from a jet nozzle the stream will tend to follow a nearby curved or inclined surface. ...

3

Excellent application inverted on the drag racer, which brings home the point perfectly. If you have enough excess thrust, devices like these can dramaticly increase Coefficient of Lift, but at the cost if loss of lift efficiency, or lower lift to drag ratio. In the case of the dragster, more propulsion efficiency is lost if tires break loose from the ...

3

The subtitle of the video states: This video shows a high-fidelity CFD simulation of flow control applied to realistic wing profiles using PHASTA and ParaView Catalyst. Work done by Michel Rasquin from Argonne and Ken Jansen from UC Boulder. Realistic wing profiles sounds like: we're actually looking at a wing in a vertical orientation - or in a ...

3

The illustrations under the time-invariant, inviscid, irrotational and incompressible (potential) description is a bit misleading, in my opinion. In the real world, assuming the airfoil starts from rest (no flow field) and you start accelerating it to some airspeed, viscosity should start generating vorticity as soon as airspeed becomes non-zero. Therefore, ...

3

Absolutely you can use a fabric for covering and airframe. I used to build large scale R/C aircraft much like they used to build real world aircraft. I used fine silk to cover the wings, elevator, tail, and fuselage. I used epoxy to adhere it to the wooden airframe and then later apply some kind of lacquer, which serves to shrink and pull tight the silk and ...

3

First, let me explain the context of your question: It is about a concept for a future airliner: Boeing Blended-Wing-Body Model 450-1U, taken from NASA/CR-2006-214534. In the artist impression above the engines are podded and sit on struts in order to achieve a uniform flow field at the intake face. However, the strut and nacelle surface area will ...

2

6 degrees of washout means the angle of incidence is 6 degrees lower at the tip than the wing root, causing the wing root to stall first. Leading edge slats serve the same function, especially in combination with trailing edge flaps near the roots. Whether these strips would replace washout is debatable, trying to "save" an approach by pulling hard on the ...

2

This is a fascinating topic, and it really boils down to the mechanics of lift. Physically, upwash and downwash are generated as the air accelerates/decelerates and curves around the LE of the wing. At the wingtips, higher pressure air curves upward and generate the vortices we are familiar with. In fact, there are vortices generated at the trailing edge of ...

2

Both are different ways to express the boundary layer thickness in a deterministic way. The boundary layer according to wikipedia: a boundary layer is an important concept and refers to the layer of fluid in the immediate vicinity of a bounding surface where the effects of viscosity are significant. Since there can be debate about what significant ...

2

These may be regional terms, I have not heard of static vs dynamic stall, I am a pilot in the USA. Airplane flight (heavier than air, lifted mainly by reaction of wings not engine thrust.) is inherently dynamic and so a stall must be as well. I assume the question is actually asking about a typical low speed stall compared to an accelerated stall? An ...

2

As far as I can tell, there are two general approaches: Solid body dynamic simulation with lots of experimental coefficients. Most of the aerodynamic effects are simply summed for the whole aircraft, though the more advanced simulators need to calculate the wheel position and wing and fuselage flexing to get proper reactions mainly at landing. But it is ...

2

This is a very good question, as it shows some of the misunderstandings regarding "tailless" aircraft. With deltas, one can consider them as blended wing/tails. The function of a horizontal tail surface is pitch control. The back of a delta is certainly large enough to do this. So much so, that now one can design a forward canard to go with it. This ...

2

14 CFR Part 60 regulates what constitutes a Flight Simulator Training Device (FSTD) for a particular aircraft model. FSTD is divided into two broad categories: Full Flight Simulators (FFS) and Flight Training Devices (FTD). A big difference between the two categories is FFS requires having motion cues, whereas motion cue is optional on FTD. Furthermore, the ...

2

I think it is erroneous to say that lift is solely produced just because of the Bernoulli's or Newton's law. Sixty Symbols(A youtube channel) explains the best how a wing actually produces lift. Instead of explaining I thought this video might help you more than my explanation. And also look at "Incorrect Lift theory" by ...

2

TL;DR Speed does not produce low pressure, increasing it does! Bernoulli's equation says that for a fluid flow, in absence of elements doing work on the stream or having work done on them by the stream¹, $p + \frac12\rho v^2$ stays constant². But it does not tell us what constant. You can have flows with any combination of $p$ and $v$, and all will still ...

2

You need to think in 3D. A vortex will induce a flow speed everywhere. That is the point 𝑃 lies in the plane containing the flow induced by the vortex at 𝑂 Why would you think that vorticity induces a speed only in one plane? You start from the wrong presupposition. Now consider the rings around the vortex filament in your first drawing. All around those ...

2

On a flat plate the thickness of the boundary layer grows along the flow path without a tendency to separate. Therefore, thickness alone is not the culprit. However, when the pressure gradient in flow direction becomes positive (increasing pressure), the flow will slow down and thickness grows much faster than in non-decelerating flow. Now separation happens ...

2

Turbulent boundary layer is thicker than laminar boundary layer as rightly pointed out, for any given distance travelled by fluid over a surface. However, thickness is not directly related to separation. The separation results when the fluid doesn't have enough energy (read momentum) to counter an adverse pressure gradient (typically a divergent section). ...

1

Even though this isn’t strictly an aviation question, it does involve aerodynamic principles. To put it simply, the diffuser’s main purpose is to gradualize the transition from rapidly flowing air under the car’s body as it transitions back to the speed of the ambient air behind the car. There is a high pressure zone in front of the car from air particles ...

1

In the video with the flat plate, the flow is much faster on the side closest to the other plate, and so the pressure is lower than the other side of the plate, which is exposed to atmospheric pressure. That attraction of the plates that you see is due to the pressure difference between the near-side (suction) and the far-side (ambient). To generate ...

1

The ping-pong ball is floating due to the Coandă effect and Bernoulli principle. I edited your picture to explain what I think is going on with the flat plate. For the suction effect of formula one vehicles however, they employ Bernoulli and other principles, the diffuser, and until the 1980s, suction skirts coupled with the venturi effect. Please refer to ...

1

The Reynolds number is the ratio of a characteristic velocity and a characteristic dimension (never mind the viscosity for now). The key is the choice of the characteristic quantities. So, the onset of turbulence around Re=2300, what you often find in fluid dynamics textbooks, applies only to pipe flow, with the pipe diameter used as characteristic length ...

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