# Tag Info

## Hot answers tagged flight-dynamics

32

This is a basic physics question, involving Newton's third law of motion (For every action, there is an equal and opposite reaction.) When a centrally mounted engine applies force to turn the rotor, the equal and opposite reaction creates torque on the fuselage. With a tip jet, the force is applied by the jet shooting its exhaust perpendicular to the blade,...

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 ...

16

There are multiple configurations which are possible with tail or canard, which based on their locations and whether they produce lift or down-force, results in a stable or unstable aircraft (taking the aircraft center of gravity into account). The figures below show some of the possible configurations. Source: f-16.net In the most general case, there is ...

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 ...

12

Of course, just put the center of gravity back to its rear limit and fly slowly. Then all of them will produce positive lift on their tails. Stability is not produced by a downforce at the tail. The newest book I read which claimed this was from 1911 (I happened to read the 1913 edition). Stability is produced by making the lift per area of the forward ...

11

Think of the aircraft engine as one isolated system and the rotor as another isolated system. In its simplest terms, torque is the force required to move mass in a circular motion. Torque is caused by the engine providing power to the rotor shaft which moves the mass of the blades. The torque is the interaction of the stationary engine trying to move the ...

10

A tandem wing airplane has two sets of wings, each providing upward lift. One is near the front of the plane, one is near the back, and the center of gravity is between them. (source: nurflugel.com) The Rutan Quickie is one such plane: (souce: wikimedia) This design is actually fairly old; it even predates (successful) heavier-than-air flight, as it was ...

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 ...

9

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

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

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 ...

8

Think of 2 scenarios: in one you are holding a rocket shaped projectile that is inert and you throw this projectile using your arm. In the second scenario you hold a real rocket, which is then launched. In the first scenario you throw the projectile, and you have to counter the twisting motion of your arm because your arm is imparting a force. In the ...

7

Just to avoid some confusion that I feel in your question: It doesn't! That is, it doesn't happen by itself. The pilot or autopilot must actively pitch up (and possibly do other adjustments, e.g. increase thrust). Without active control, the angle of attack will stay about the same (initially), and the airplane will start descending if it enters a turn, ...

7

Angle of attack is not equal to pitch angle. Yes you can decompose weight into a forward and a perpendicular component - to airstream! Or you can draw lift relative to airstream. In this drawing, pitch angle is zero and AoA = 6 deg. Lift now has a forward component relative to gravity.

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

If at zero airspeed and zero absolute altitude this were to happen, then yes the aircraft would stall and be incapable of flying. Then again, at this point, it would not matter, AS THE AIRPLANE IS ALREADY ON THE GROUND IN THIS STATE. In all seriousness, though, the airplane would not slow and stall unless you attempted to remain at a constant altitude. In ...

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 ...

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 ...

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

The aircraft turns to change its speed vector. The absolute value of the vector stays the same, but its direction is changed. A force is needed to change the direction of movement of any mass, and the wing is used to provide this force in addition to the lift force. This is why lift is increased in a turn. For turning, the aircraft needs to add a force in ...

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