# Tag Info

79

The reason was to give the bombs the place close to the center of gravity. Wing sweep (for high cruise Mach numbers) in combination with a high aspect ratio of the wing (for low induced drag) made it impossible to place the landing gear in the wing, so it had to be integrated into the fuselage. The main landing gear normally needs to be close to the center ...

54

Adding to the excellent Peter's answer who explained why for this particular model the wheels are placed far behind the centre of gravity (CG), I would like to clarify why this makes impossible to rotate at take off. A standard aircraft takes off right after the rotation, increasing the angle of attack and the lift. Before and while performing the rotation ...

36

This is called stall hysteresis. You have two different situations and the flow reacts differently in each of them. When increasing the AOA The flow is attached to the wing and the boundary layer is resisting the adverse pressure gradient as much as possible. At some point the flow detach from your profile and you have stalled let's say at 18°. At this point ...

34

As far as I can tell, NASA has never given a straight-forward answer to this question. The theoretical stall AoA is likely in the 33-40° range (see reason for that guess below). However, at operational airspeeds, the orbiter becomes aerodynamically unstable at a lower angle of attack than the stall angle. Therefore, the stall angle never mattered for shuttle ...

24

From what I have studied at my instrumentation course, it rotates and reads the angle between the current position and the reference position. You then have several (3-4) of them around the fuselage because a roll maneuver (for example) will alter the measurements asymmetrically and in this way you can compensate for this effect.

20

An AOA vane (like what you have shown) works by aligning itself with the local airflow, like an arrow. The angle to some reference line (normally aircraft fuselage horizontal) is then measured with a potentiometer/RVDT/etc. This is the local angle of attack. Often the local angle of attack is converted to aircraft angle of attack through a calibration ...

20

Would installing the AOA vane (or, in general, sensor) at the wing root be more accurate than installing it near the nose? No, it wouldn't. In fact, it may be slightly worse due to the larger upwash at the wing leading edge and the vane protrusion may even negatively interfere with the wing aerodynamics. Traditionally, AOA measurements are used for stall ...

18

It's possible to land by touching the tail first, but this is undesirable as it puts a lot of stress on the tail, so it's not trained for and there are no circumstances where you would do this deliberately. There are two common methods of landing a tail-dragger: a three-point landing (where the tail and mainwheels touch together) and a wheel landing (where ...

16

Many aircraft do include them, because it's very useful. For example a modern 737: A Garmin G1000 (one of the more common General Aviation glass cockpits): Specifically the part that looks a bit like this And a more traditional analog/mechanical gauge: The problem is that usually when someone stalls, it's because they've made a mistake - not because ...

16

Your stall speed decreases because the $C_{L_{MAX}}$ of the wing increases with flaps deflected. Deploying flaps increases wing camber and increases both $C_L$ and $C_D$ at the same AoA and airspeed. Depending on the type of flap, the critical AoA actually reduces: the airfoil with simple flaps deflected stalls at a lower AoA than without flaps. Slats ...

16

The driving variable here is airspeed, not pitch attitude per se. Your airplane naturally goes faster when you put the stick forward and decrease the wing's angle-of-attack, and this changes the prop rpm. Your pitch input is changing the wing's angle-of-attack which leads to an airspeed change. Even with the engine switched off, the aircraft would fly (...

16

I think this has been at least hinted at in other answers, but, just to put it succinctly, the diagrams aren't actually intended to show the airflow as always being parallel to the horizon. The airstream is just shown flowing along the horizontal axis of the graph because it's convenient to illustrate it that way. There is no implication intended in the ...

15

Updated answer based on F-16 specifics. The top arrow shows the nose position—pitch angle, in the F-16 it is based on the Gun Cross (Boresight Cross), which also indicates the fuselage reference line. The middle arrow shows the position of the flight path marker (FPM, also known as FPV), it shows where the aircraft is going. The vertical distance (angle) ...

15

Most modern military aircraft HUDs have two primary methods of displaying the velocity vector (or flight path vector) relative to the pitch ladder. Uncaged Mode When the HUD is operating in uncaged mode, the velocity vector remains fixed between the pitch ladder and, instead, the pitch ladder slews around the HUD. It is important to note that even though ...

14

Slightly off-topic, but I recently came across the "side string" which gives a direct reading of AoA. Every gilder pilot is familiar with the yaw string, but in two years of learning to fly gliders, I'd never heard anyone mention the side string. Now, in the ultralight / open-cockpit world they use a single piece of yarn mounted on a stick, which acts as a ...

14

No, it is not possible to place the sensors inside the aircraft, because the angle-of attack sensors need exposure to the surrounding air, in order to measure, as you mention yourself, "relative motion between the aircraft and the surrounding air".

14

Prop blades from side view at two RPMs Vector diagrams help with visualizing prop blades. Above the vertical vector lines are two RPMs, the horizontal vector lines are the forward velocity (the same for both), and the connecting orange vector lines are the resultant airflows. Note the AOA for the same blade pitch and how it is affected by the airflow at the ...

13

The Boeing 737 MAX has 2 AoA sensors. However, MCAS only takes input from 1 AoA sensor at a time. Sources: The black box flight recorder data for Lion Air JT610 shows the data from 2 AoA sensors, labeled "Left" and "Right". Also, if you look at the nose of the 737 MAX, you will see a left and right AoA vane. (The sensors with the red tags are pitot tubes)...

12

Control authority is a function of the local dynamic pressure (the product of air density and speed squared), geometry (the product of control surface area and lever arm), local angle of attack $\alpha$, the angle of deflection $\eta$ and the relative flap chord. Generally, the control surface works fairly linearly in a range between $-15° < \eta < 15°$...

12

if a single angle of attack sensor fails No. An A320 has three AoA sensors. If one reports a different value to the other two, the avionics will ignore values from that AoA sensor and use the values from the other two. If two of the three fail and report consistent values - the avionics will believe the third is the odd-one out and unreliable. If those ...

12

I found several patents that resemble the L-1011's, dating back to at least the 50s. One such patent remarks that there are two main types, the vane, and the rotating pneumatic tube (also comes in conical shape). The advantages of the latter when compared to the vane-type are: [B]etter balancing characteristics, lower air friction, greater sensitivity, ...

11

Climbing further while cruising is saving fuel, not wasting it. First, every airplane has an optimum angle of attack for most economical cruise. If it loses mass (due to fuel consumed), it needs to adjust either its altitude or its speed to keep that angle of attack. The goal is to keep dynamic pressure, the product of air density and the square of airspeed,...

11

Obviously, drag should be smallest for symmetrical airfoils at zero angle of attack. However, most airfoils have camber, and then the lowest drag is at positive lift coefficients in case of positive camber. Where that point is exactly depends on many parameters; in case of laminar airfoils even local imperfections can have a noticeable effect. Generally, ...

10

Yes, it does vary slightly due to viscous effects. In inviscid flow, the flow speed would not affect the lift coefficient - angle of attack relation. However, increasing the flow speed will result in a thinner boundary layer and a slightly different shape of the airfoil - boundary layer combination as "seen" by the outer flow. This influence is captured by ...

10

I just finished reading this article and couldn't understand why in 3 minutes and 30 seconds even though there was no reliable speed data, pilot could not level the plane? If you look at this video by the French accident investigation bureau (BEA) you can see what happened. The problem started when the speed indicators failed temporarily because of ...

10

First, let's assume that all lift is created by the wing, and that the plane is flying in ideal conditions, where fuel flow per distance flown is minimal. This point is given by $$c_L = \sqrt{\frac{1-n_v}{3+n_v}\cdot c_{D0} \cdot \pi \cdot AR \cdot \epsilon}$$ Please see this post for more background on this formula. Nomenclature: $c_L \:\:\:$ lift ...

10

The flaps mostly increase the camber, which increases the Cl (albeit, with greater drag). In quite a few cases (especially low-end GA aircraft) the flaps have little or no effect on the wing's surface area (the flaps are just a section of the trailing edge that swings downward on a hinge). Even in those that do slide the flaps back on a track, the change ...

10

Yes, through the Reynolds number The Reynolds Number is a function of airspeed and is used to predict the transition from laminar to turbuluent flow: $${Re} = \frac{\rho v L}{\mu} = \frac{v L}{\nu}$$ The critical angle of attack is affected by the separation of the boundary layer, which, in turn, depends on the laminar or turbulent qualities of said ...

10

A symmetric airfoil will generate no lift at no angle of attack, and negative lift at a negative angle of attack. However, cambered airfoils are curved such that they will generate lift at small negative angles of attack.

10

An INS gives your speed & orientation in space, but without reference to what the airmass that you're flying in is doing. The Pitot tube and AOA sensors give speed and pitch orientation in relation to the local airmass, only. An indicated airspeed of 60 knots, measured by the Pitot tube, may correspond to a stationary aircraft pointed into 60 knots of ...

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