# Tag Info

37

Lift is (among other things) a function of the airspeed and the angle of attack of the wing. Hence, if you reduce your speed, you have to compensate the associated lift loss by increasing the angle of attack...

22

In order to maintain level flight, an airplane must generate lift equivalent to its weight. The lift generated by a wing diminishes rapidly as the airspeed decreases. To compensate, the angle of attack must be increased to maintain the necessary lift. This can be done until the the critical angle of attack is reached, at which point things get exciting.

18

Your scepticism is justified. The critical angle of attack (cAoA) can grow as well as shrink with increasing airspeed. Growth is generally due to a higher Reynolds number while a reduction in the cAoA with increasing speed is a transsonic effect, so it depends on the flight Mach number. In one peculiar case this already stated to happen at Mach 0.3, far ...

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 ...

10

The answer depends on two factors - aircraft speed, and pitch rate. There are virtually infinite combinations of these two variables, but let's consider four for the sake of discussion: Low speed, slow pitch rate - Done in a controlled manner, a fighter with a better than 1:1 thrust to weight ratio can rotate smoothly to vertical without exceeding stalling ...

9

It’s a STC head up display angle of attack kit. In addition to an angle of attack sensor being installed on the exterior of the aircraft, this device provides eye-level display of an angle of attack indicator. They’re becoming increasingly popular in general aviation airplanes and provides an additional sense of angle of attack, especially during low speed ...

8

This is an Angle Of Attack indicator, specifically Alpha Systems’ Eagle Above Dash HUD Kit:

7

It's a great step that you know about the acronym AOA while still not understanding well how it works! That's nice; but anyway, try to exercise the answers here using your hand as a wing through the wind when someone (ELSE, lol) drives for you. You'll notice that in order to keep you hand flying at slower speeds, you'll have to increase the angle. This is ...

5

Back to the basics: with credit to @jamesqf for the comment about soft/rough field takeoff ... "get weight off the wheels as soon as possible". With a cross-wind take off, we leave weight on the wheels as much as possible, then rotate. "Since you can't crab before becoming airborne" Rudder and ailerons become effective as speed ...

5

The 787 was not designed to perform such a maneuver. Any jet airliner could do this. What you need for such a steep climb is a good thrust to weight ratio (or enough excess speed to bleed off during the maneuver). A passenger twin-jet is designed such that it can still climb with at least 2.4% climb gradient after a single engine failure during a takeoff at ...

4

The 787 (and other commercial aircraft) are built to carry large loads, whether lots of cargo, or lots of passengers and bags. So, when empty, their performance is much better. If it can do a normal takeoff when full, then it can do a rocket-like takeoff when empty. The near vertical takeoff is, indirectly, a demonstration of how much power it has when ...

4

When you adjust a constant speed propeller to a higher rpm, this will be done by making the propeller blade AoA smaller. Contrary to your question though, manifold pressure and power output will not remain constant unless you adjust the throttle. Neither will your airspeed, not surprisingly. Exact effect will depend on the engine, but basically power is ...

4

As explained in various posts on StackExchange, at the end of the day the one thing that matters for lift is that air gets persuaded to move downwards (say, with velocity $v_\text{down}$). The downwards-acceleration of an air pocket of mass $m$ as it passes the wing corresponds to a momentum change of $m\cdot v_\text{down}$, and the same and opposite ...

4

Simply using the generic drag equation will get you within the ballpark required for FlightGear. $$D = C_D \cdot \frac{1}{2} \rho V^2 \cdot A$$ with $C_D$ the flat plate drag coefficient and A being a reference area of your cowl flaps. The data for the correct Reynolds number is best used, with $$Re = \frac{\rho V \bar{c}}{\mu}$$ with $\bar{c}$ = mean ...

3

Yes One way to gain greater understanding is to go to airfoil tools and observe the lift vs AoA of your favorite airfoil (try the Clark Y for starters) and you will see that Reynolds number effects generally occur across several orders of magnitude, well outside the speed envelope of your aircraft. A bit like saying from 0 to Vne would be a few centimeters ...

3

The lift a wing generates is directly proportional to the density of the air the square of the airspeed the Angle of Attack (AOA) (more or less linearly) (until it stalls) In non-accelerated flight, where the lift is roughly equal to the weight of the plane, the product V2AOA will be a constant, or AOA will be proportional to 1/V2. As the plane flies ...

3

In order to maintain level flight, the aircraft must push air downwards to create a force that supports the aircraft in the air. Lets consider a period of one second of time: An aircraft going fast slices through a large amount of air, and only needs to push that air down a bit. An aircraft going slow slices through a small amount of air, and needs to push ...

3

Wolfgang Langewiesche is right to appropriate order of approximation. For every elevator position a statically stable airplane settles to a specific equilibrium angle of attack. That's how static stability works. Airplane is statically stable if and only if increasing angle of attack causes higher increase in coefficient of lift on the aft airfoil (tail for ...

3

Stick and Rudder also states on page 5 that we normally teach "theory of building the airplane rather than of flying it." Take the Lift Formula, and let's put it into terms the pilot can control in flight. Lift = coefficient of lift x 1/2 air density x true velocity squared x wing area. When we teach this in ground school, we instantly see the eyes ...

3

The question mentions Speed and Orientation which are broad terms that could include: Group1: (Air Data sensor + computation) IAS - Indicated Air Speed CAS - Calibrated Air Speed EAS - EquivalentAir Speed. TAS - True Air Speed AoA - Angle of Attack (HDG(M) - Magnetic Heading)^^ Group2a : (Inertial/Rate sensor + computation) GS - Ground Speed HDG(T) - ...

2

The A320 is fitted with an air data inertial reference system (ADIRS) made of 3 ADIRUs. ADIRU 1 data (altitude, speed, etc) are shown on Capt side, ADIRU 2 on F/O side. ADIRU 3 can be selected manually. Each ADIRU contains an air data reference (ADR) and an inertial reference (IR). Each ADR receives the AoA value from a separate AoA probe. The AoA value is ...

2

You must use the same quantities for both speeds. Usually, this will be TAS. As you see, you are going to use a ratio of speeds: w/u. This ratio must be dimensionless, and furthermore, the quantities must be "compatible". For such purposes, you can't meaningfully divide IAS by TAS (or CAS), or, say, altitude by flight level, even though they are ...

2

An 'appreciable amount of lift' is subjective, but with thanks to @RobertDiGiovanni's answer above, I was able to work out some example values, shown below. (I used the link to airfoiltools.com to get CL data to approximately solve the lift equation for a B737 - exact type not specified - at various speeds during the ground roll). At an assumed constant (...

2

I think your problem is in part, that you assume that $w$ is positive if your aircraft is ascending. The opposite is the case. The aircraft coordinate system is defined as a right-handed system with the z-axis pointing downward. This means a positive $w$ indicates that your aircraft is descending. Therefore, if your plane keeps a constant velocity $u$, the ...

2

Your wrote: a value which, according to the report, would not have been altered by the aircraft's rapidly-increasing AOA The report did not say that (but I can see how that confusion can arise). It said the 1) flap retraction and 2) increasing g load -- would not alter the AOA trip point of 13.5 -- no mention of rapidly-increasing AOA: the flaps had ...

2

The answer to the title question is no, sideslip angle and drift angle are not the same thing. (in this figure, or any other...) What the diagram shows is drift angle, and drift angle only. If you are moving through a uniform airmass that is itself moving relative to the ground, your path across the ground (ground track, or course) will be affected by the ...

2

The question should really read, "how the pitch must change along the length to keep lift distribution reasonably constant while respecting stall considerations" or something like that. Rotor blades twist nose down going outboard, like propellers but with less twist, to account for the higher velocity toward the tip, so that the slower moving root ...

2

An examination of a typical flight envelope may leave one wondering about exceeding G limits, rather than stalling. A zoom climb typically starts by gaining as much kinetic energy as possible (speed) before turning sharply skyward. As excess drag would result in a lower, slower climb, stalls would be strictly avoided. At high speeds one would pull the stick ...

1

It seems to me that the crux of the misunderstanding in your question is here: If I then add power and climb (while holding the same attitude) If you hold the elevator in a fixed position and add power, the airplane will pitch up relative to the ground, to the extent needed to preserve the original angle of attack relative to the airplane's motion through ...

1

There is a contradiction built into the question. You write: Consider a certain elevator position for straight and level flight at cruise rpm. If I then add power and climb (while holding the same attitude) isn't it true the Angle of Attack will increase because the relative wind is now coming from in front and above the plane? If this is true, then how ...

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