# Tag Info

27

Good question! There's a bit of a misconception: when the elevon moves up, it actually decreases lift. It pushes air up which pushes the wing down. This explains the roll behaviour, but how does decreasing the lift make the plane go up? The key here is that the lift is reduced only at the rear of the plane. In other words, the rear of the plane is pushed ...

24

You are absolutely right, a load factor of greater than 1 is impossible to avoid in a proper barrel roll. The barrel part of its name comes from the spiral path the aircraft needs to perform in order to add a centrifugal acceleration which is greater than gravitational acceleration at the top of the roll. This is the condition to ensure a still positive ...

17

It is easier if we look only at the forces experienced by the aircraft, and in an inertial frame of reference In this revised diagram, the vertical component of the lift balances the weight, which is vertical. There is a remaining horizontal component of the lift, and this causes the turning. "Centrifugal force" does not exist (and is not needed) in an ...

14

Source: Wikipedia. Origin of the theory Klaus Holighaus, one of the famous glider pilots of the 70s, and himself a glider designer at Schempp-Hirth, is at the origin of a controversy when he recommended not to turn with the ball centered, and especially when climbing in thermals. Mr Holighaus did see two problems with the perfectly coordinated turn: It ...

13

The problem of the picture you are looking at is that both the actual and the apparent forces are shown. The real force is the centripetal one (that in turn is only the horizontal component of the lift force), the centrifugal one does not exists, is only an "impression" of the centripetal one as seen by a person standing in the aircraft (a non inertial ...

13

From a deleted question: by @ffejrekaburb From an email from the author of the SeattleTimes article, Dominic Gates: The description of MCAS provided by Boeing for regulators (FAA and foreign) during certification, is this: MCAS “was added to address potential nose-up pitching moment at high angles of attack at high airspeeds outside the ...

10

The diagram is not a correct force diagram in the inertial frame of reference. In the inertial frame of reference, the horizontal force on the aircraft is unbalanced. This causes the aircraft to accelerate in the direction of the net horizontal force, perpendicular to the direction of flight, and this curves the path of the aircraft. The law of "equal and ...

9

Is this use of "straight and level" correct? What is the definition of straight and level, if any, regarding heading, attitude, speed, altitude? In the airplane flying handbook the FAA defines straight and level flight as Straight-and-level flight is flight in which heading and altitude are constantly maintained. My understanding and the ...

8

Two things are important here: It is about a glider, so no fuel is consumed, and the mass is constant over time. The angle of attack is constant. This means also that the lift and drag coefficients are constant. If the mass and the lift coefficient are constant, and we assume a constant load factor (implied by the gliding along its path description), the ...

8

First of all, in the diagram they show the force on each wing being the same. In a steady roll, i.e. when the roll rate is constant, the forces are the same. A non-zero moment causes angular acceleration, so when the aircraft is rolling with constant rate of roll, the moment must be zero, which means the lift on both wings have to be equal. That rules out ...

8

This is the heat distribution during reentry for the Orion capsule: So the leading edge is hotter than the trailing edge, even for very large angles of attack (almost perpendicular). I assume a disk would have a similar heating profile. So spinning the disk would move the edge of the disk from a high-heating area to a less hot area. This suggests ...

8

A somewhat simplified answer. When both elevons go up, they will push the back of the plane down. This makes the nose start to point upwards, or, as we say, the plane pitches up. This increases lift, and so the plane goes up. So the sequence really is: elevons up --> back end pushed down = pitch up --> increased lift --> increasing height. If one elevon ...

7

These are generally 3 different auto pilot modes. The first two are related to pitch and the third to heading/roll a nice overview can be found here Altitude Hold: Generally speaking setting an autopilot to altitude hold will cause the autopilot to maintain that altitude by varying the pitch of the aircraft. Depending on the system it may attempt to ...

7

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 reference of pitch is the horizontal. The reference of AoA is the direction of the relative wind.

6

Turn rate is referenced to earth axes, yaw rate to aircraft axes, hence the $cos\Phi$: If you turn at $\Phi$ = 0, your rate of turn is the yaw rate and the pitch rate is zero. If you turn at $\Phi$ = 90°, your yaw rate is zero and your pitch rate = rate of turn. In order to maintain a steady turn and not lose altitude the pilot does need to pull on the ...

6

I'll quote from Rod Machado's first ground school lesson: Straight flight means the airplane's nose remains pointed in one direction and the wings are parallel to the earth's horizon. Level flight means the airplane doesn't gain or lose altitude. (my emphasis) Therefore, there are three constraints for "straight and level" flight: Constant heading (...

6

You are correct. Suppose the headwind just 10 meters above you is 10 knots stronger then where you are now. Climbing the 10 meters will cost you some kinetic energy which is transformed to potential energy. Suppose you were flying 200 knots airspeed initially, you will end up with 198.1 knots airspeed if the transformation from kinetic to potential energy ...

5

There are many phenomena which can cause vibrations. Without knowing further details like the frequency, starting moment or the weather conditions on landing it is difficult say. Common causes are: Stall buffet/ self induced turbulence Normally when a plane lands it flies with low velocity and a high lift coefficient, near to stall. The flow detaches much ...

5

Constant angle of attack implies a constant CD and constant CL. The fact that the aircraft is a glider implies a constant mass. 'along its path' does not imply that the path angle is constant. In a phugoid motion, the flight path angle is oscillating and so are the speed and the load factor, but the AoA is constant (by approximation). We can assume ...

5

By approximations, I believe you mean the following (found in any major stability & control textbook and this MIT course note), where the $_0$ notation stands for undisturbed trim condition: Short-Period damping: $$\zeta_{sp}\approx-\frac{M_q}{2}\sqrt{-\frac{1}{V_0M_wI_{yy}}}$$ Short-Period frequency: \omega_{sp}\approx\sqrt{-\frac{V_0M_w}{I_{yy}}...

4

To answer what you wrote: $c_{n_q}$ is the yawing moment induced by a pitching motion. In a conventional, symmetric configuration this is zero for the airframe and has a small value for propeller aircraft, depending on the rotation direction of the propeller. If the tractor propeller is spinning clockwise (when seen by the pilot), a positive pitch motion $q$ ...

4

Straight and level is a kind of the broader steady flight. Steady flight is "a special case in flight dynamics where the aircraft's linear and angular velocity are constant in a body-fixed reference frame." As constant velocity means no acceleration, straight and level is maintaining altitude, heading, and speed. A plane on approach would qualify as a ...

4

Hang gliders weigh less than 100lbs and some can carry 200lbs. The FAI distance record is 475 miles and must have taken hours to accomplish. Note that the distance is measured as a point-to-point distance, not as actual ground track distance. Unpowered airplanes require lift to stay aloft and must circle in rising colums of air to gain altitude. The 475 ...

4

By the very definition, a free-flying object can only pivot around its CG. Using anything else as a pivot (e.g. Aerodynamic Center) involves a combination of momentum and translation (linear movement) of the CG and will quickly get you into mathematical problems once you start combining the forces acting on the object. Make no mistake, an object only ...

4

The equation is certainly oversimplified, hence the name 'short period': it only models short period pitch oscillations. In this model, there are only two states: pitch and pitch rate. Any other effect is thus neglected. A step response in an elevator would in the short term definitely lead to a nonzero pitch rate, as the model predicts. In reality, the ...

4

Rate of turn is easy to define: it is the rate at which the direction of aircraft motion changes with respect to the ground (rate of change of track). If the aircraft is not slipping and there is no change in wind, then it is equivalent to the rate of change of heading. Yaw rate, on the other hand, is slightly messier. Technically, yaw rate of the rate of ...

4

What you've proposed is a reference frame translation of the aircraft velocity, so instead of the velocity referenced to East, North, and Up (ENU), it's referenced to the direction the aircraft is pointing. That gives you components of aircraft velocity along the nose, across the wing, and towards the ground. (You can find more details on these conversions ...

3

Um..it's a bit of a counterintuitive and hard to visualise field of aeronautics. There are six degrees of freedom (if we assume that the aircraft is rigid) that need to be transformed from aircraft axes into earth axes. And since we're looking at aerodynamic stability, we need to consider wind axes to introduce disturbances: if the aircraft moves as an ...

3

If all equations are digitally computed multiple times per second, all variables are updated at every frame and the integration error is only one time-step old. Full Flight Simulators use four sets of quaternions to compute the state of the aircraft in earth reference frame. To illustrate how it is done in FFS flight dynamics, here is a partial set of the ...

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