Questions tagged [flight-dynamics]

Flight dynamics is the study of the physics driving the performance, stability, and control of aircraft. It is concerned with how forces acting on the aircraft influence its speed, altitude and attitude with respect to time.

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0answers
90 views

Can I just differentiate my Euler rates to get the angular rates?

There is this matrix: $${W_{\eta}}=\begin{bmatrix} -\sin(\theta) & 0 & 1 \\ \cos(\theta) \sin(\phi) & \cos(\phi) & 0 \\ \cos(\theta) \cos(\phi) & -\sin(\phi) & 0 \end{bmatrix}$...
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In a banked turn, why does the center of gravity, rather than the center of lift, follow the path of a circular arc?

I'm a post-solo student pilot who sometimes gets hung up on fundamental points of aerodynamics. "As long as the aircraft is banked, the side force is a constant, unopposed force on the aircraft. ...
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When pitching, how do planes establish a pitch rate which corresponds to the centripetal acceleration?

Coordinated flight requires that the yaw rate and the centripetal acceleration correspond. In other words, for a given $a_{centripetal} = v^2/r = \omega ^2 r$ this means that the yaw rate must equal $\...
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1answer
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Are the gyroscopic precession and P-factor of a pusher propeller in opposite directions?

according to this picture the P factor cuases airplane to yaw to the right but if pilot wants to pitch up , then p factor and gyroscopic precession acts on airplane at the same time but in opposite ...
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1answer
101 views

How do you quantify rudder effectiveness as a function of bank angle?

I'm currently reviewing just for fun aircraft dynamics based on OEI (one engine inoperative) scenarios. After reading that "lower pedal forces at higher bank angles" are required, it got me ...
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How should I understand aircraft rotation conventions (euler angles)? [duplicate]

I'm reading the manual for an IMU and it claims it reports out the vehicle's (aircraft's) heading, pitch, and roll, and I'm trying to get a feel for what these things mean. It seems to me that the ...
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1answer
73 views

Equations for Computing Temperature and Air Density Ratios at Different Altitudes

When computing aircraft performance at different altitudes, two useful variables are the air density ratio (dr) and temperature (T). Using a ratio is helpful because you can recompute values, such as ...
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189 views

Can yaw develop a spiral dive?

I'm wondering if the 'prolonged' effect of using yaw causes a spiral dive. I understand that a spiral dive is caused by an excessive angle of bank, but can it also be created by an excessive amount of ...
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Which way to turn to return to runway for downwind landing-- into crosswind or with crosswind?

The scenario-- you are taking off with a significant headwind component but also a significant crosswind component. You experience a power loss (or perhaps a tow rope break in a glider). You judge ...
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1answer
324 views

What is the difference between equilibrium and steady flight?

If I'm flying a regular Cessna 172 and its perfectly trimmed and flying in circles holding the same altitude, is the aircraft in equilibrium? Or steady flight? (The definition of equilibrium flight ...
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How to calculate Longitudinal dynamic stability derivative for a wing? Mq and Mα

How to calculate Moment due to rate of change in pitch(Mq) and Moment due to rate of change in AOA(Mα) manually and How to extract from CFD software? Consider a fighter aircraft is in Case 1- Cruise ...
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Is the total upwards vertical force (lift included) greater than the weight in a steady climb?

Related to questions on forces in a climb: if any aircraft is climbing with a constant velocity, is the total upwards vertical force (lift included) greater than the weight?
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Calculating angle of attack during bank

I'm programming a flight dynamics simulation and am running into issues with calculating the angle of attack during banked flight. I know what I'm doing wrong, but I'm not sure what I should be doing ...
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1answer
456 views

Is thrust larger than weight in a vertical climb?

Image source Very much related to the many questions and great answers to lift and weight in a climb - if an F-16 climbs vertically at a constant speed, is thrust greater than weight?
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In large transport aircraft, is the amount of elevator travel that is physically possible ever a limiting factor in turning performance?

In large transport aircraft, do we ever encounter the situation where we are unable to maintain a given, low airspeed while banked and turning, because we "run out of elevator travel" (...
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Is lift less in a steeper descent than in a shallower descent, and if so, by how much?

Is lift less in a steeper descent than in a shallower descent, and if so, by how much? For example, if we change our ratio of horizontal distance travelled to vertical distance travelled (through the ...
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1answer
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Can a normally poorly handling airframe with high moments of inertia actually have superior flight dynamics under autonomous control? [closed]

I’m not a pilot but know a thing or two about flight dynamics. As you know there are currently quite a few aircraft under development designed for low-and-slow and (eventually) autonomous flight. ...
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Is a trimmed flight not always an unstable system?

As soon as I am flying in trimmed flight condition, my pitching moment around the center of gravity becomes zero. So my center of pressure has to be located in the center of gravity, so that there is ...
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2answers
258 views

What happens if an aircraft is only stable at higher angles of attack?

Does anybody know what will happen to an aircraft, if it is stable (in longitude) for let's say: -8° > angle of attack > 8° ? So for angle of attack 4° the aircraft is not stable (centre of ...
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In this F-104 V-n diagram, why does the stall speed (in terms of IAS) decrease with altitude in some parts of the flight envelope?

(This question has been edited to reflect a change in perspective: based on answers to the related question What is causing these "corners" on this F-104 V-n diagram?, I now believe that the ...
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1answer
99 views

With flight dynamic equations, how do I return to positive alpha if alpha is always negative with negative w?

I'm coding a flight dynamics simulation, but my simulation runs into a problem with negative angles of attack. Once alpha is negative, it is impossible to get back to a state where the plane is ...
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5answers
364 views

What causes the ball to not be centered in a slip/skid?

I've reviewed quite a few questions on this forum including Forces in a slipping turn is-this-vector-diagram-of-the-forces-at-play-in-turning-flight-correct what-does-the-balance-ball-actually-...
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2answers
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Can a slow small plane, flying at a few meters above the ground, drop to the ground if the headwind abruptly stops? [duplicate]

Why do I ask this question? Because Wilbur Wright sent a letter to Georges Spratt (an aviation enthusiast he personally knew) saying that his plane, Flyer II, once in flight, accelerated easily to 45 ...
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2answers
234 views

Can a plane with a thrust-to-weight ratio less than one fly vertically and perform loops?

In the game Battlefield 1 you can fly a Sopwith Camel vertically and perform different kinds of aerobatic maneuvers like loops. According to its specifications, its thrust-to-weight ratio should be ...
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1answer
100 views

Relationship between Load-Factor AND Gliding Ratio

I am wondering about the g-load and its relation to the so called gliding ratio. I read this really good contribution here on this forum: Does lift equal weight in a climb? So the g load factor is ...
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2answers
999 views

What is the effect of thrust vectoring effect on the rate of turn?

I just got a question after reading my old Principles of Flight book. The equation for the rate of turn is $\textrm{ROT} = 1,091 \cdot \frac{\tan(\phi)}{V}$, with $\phi$ denoting bank angle and $V$ ...
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1answer
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Is there any formula that directly relate density to altitude for a wide range of altitude?

I am working on a code to simulate a vehicle trajectory based on forces act on it in different altitudes, I need a formula that gives density in an altitude range between 0 and 40 km to obtain lift ...
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1answer
1k views

The relation between Euler-angle rate and body-axis rates?

A paper about quadcopter dynamics and control shows the relation between Euler-angle rate and body-axis rates as: Q1: why are there $R_{v2}^{b}(\dot{\phi})$, $R_{v1}^{v2}(\dot{\theta})$, and $R_{v}^{...
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3answers
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Why do most aircraft with variable incidence tailplane have the possibility to trim much more degrees for nose up than for nose down?

Probably the question will be a little bit confusing but I'll try my best to make it clear. Due the position of the CP with respect of the AC, symmetrical airfoils don't produce pitching moments, but ...
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1answer
201 views

What happens when the eigenvalues of the longitudinal A matrix in dynamic stability analysis, are NOT two sets of complex conjugate pairs?

The complex conjugate pairs of eigenvalues of the longitudinal A matrix characterize phugoid and short period dynamic responses, this information is well established. My question is - what happens ...
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4answers
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What is the influence of yaw on P-factor?

From William Kershner's “The Advanced Pilot’s Flight Manual”- page 2-17, P-Factor: If the airplane is yawed, the P-factor effect is encountered. A left yaw would mean a slight nose down tendency and ...
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2answers
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Why do airplanes start descending when we initiate a left turn?

Today I watched a video about the Fly-by-Wire (FBW) system (see below) and at 3:20 there is a left turn initiated in a Cessna 152. Then it is shown that with a left turn (only by ailerons), in ...
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2answers
202 views

How should I attach an aircraft model in a wind tunnel when testing wind gust/yaw stability?

Where should I attach the rod to the aircraft model when simulating wind gust /weather vane effect in wind tunnel testing? At the center of gravity, behind the CG, in front of the CG...?
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2answers
149 views

How does an aircraft designer increase dynamic stability?

This question explains that an aircraft can be statically stable (it will seek to return to equilibrium) but dynamically unstable (the amplitude of the oscillations increase) if there isn't enough ...
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4answers
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What does it mean when an aircraft is statically stable but dynamically unstable?

I am reading this book: "Flight Stability and Automatic Control", second edition, Dr. Robert C. Nelson. In the chapter 2, page 42, the author wrote: Note that the vehicle can be statically ...
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7answers
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Is the elevator really an 'angle of attack control' as described in Stick and Rudder?

I've been reading Wolfgang Langewiesche's book Stick and Rudder and am a little confused about the definition of the elevator as the "Angle of Attack Control" or rather, the idea that each ...
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4answers
333 views

Is the turning motion of a banked airplane caused by true centripetal force?

Virtually every explanation I have read of the aerodynamics of a turning airplane ascribe the turning motion simply to centripetal force, without further comment. I'm hoping someone can check my ...
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2answers
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Why is airflow forced to be speed up on the upper surface of an aerofoil? [duplicate]

As the title says: Why is airflow compelled to flow further over the upper surface of an aerofoil? I understand because it has a larger distance to travel, but why can't the airflow travel at the same ...
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6answers
585 views

Why can't you have sail-powered airplanes?

So, sailing boats take the kinetic energy of a crosswind and turn it into thrust by using their sails as lifting surfaces, and the discussion I had in the comment section of this question made me ...
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2answers
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What is the purpose of downthrust?

Many light general aviation aircraft-- and perhaps many other aircraft as well-- are designed with some of amount of downthrust in the engine mounting, relative to the centerline of the fuselage. ...
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3answers
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Is "excess thrust" possible in a steady state vector diagram?

Being recently very much sold on the lift-weight-thrust closed triangle (with weight forming the hypotenuse) model for climbing flight, I proceeded to put the logic through its paces (validation) and ...
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1answer
154 views

What does "pitch plus power equals performance" really mean?

It is often said in aviation circles that "pitch plus power equals performance". A. What is it supposed to mean? B. Is it always true? C. If it isn't always true, why is it a useful concept ...
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4answers
415 views

Are there any situations where having high lift but low lift to drag ratio would be beneficial?

From my understanding, high lift to drag ratio could make an aircraft efficient during cruising conditions. This is when the aircraft is in equilibrium, lift is equal to weight, and thrust is equal to ...
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2answers
270 views

Can we show through simple geometry rather than formulae or graphs that the best glide ratio occurs at the maximum ratio of Lift to Drag?

For an unpowered glider, can we show through simple geometry involving force vector diagrams, rather than mathematical formulae or graphs, that the best still-air glide ratio is achieved at the angle-...
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4answers
959 views

How can L/D Max be both Best Glide speed and Max Range speed?

According to the book "Aerodynamics for Naval Aviators", best glide speed AND max range speed for propeller aircraft both occur at L/D max. This is a little confusing because in an A36 ...
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6answers
612 views

How can speed and power be made independent in an airplane? [closed]

I heard a piece of information many years ago, and the more I think about it, the less it makes sense. It was like: When airplanes what to raise altitude, they do not increase speed, but they ...
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1answer
135 views

What is the difference between a spin and an uncontrolled roll in an high speed dive?

A comment I had on another (now deleted) question states that Air china 006 didn't spin. For me it was a spin (unwanted roll due to asymmetrical stall). The comment states it was "it was a slow ...
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1answer
173 views

Is the mach number of an aircraft measured with respect to stagnation speed of sound?

I was reading chapter 8 of JD Anderson Aerodynamics when I came across something I find weird. I found out that there are different types of Mach number, based on what the speed of sound was taken as. ...
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3answers
739 views

Why is the L/D ratio numerically equal to the glide ratio?

*L/D is ratio of two forces, lift and drag. *Glide ratio is ratio of two distances. Can you explain mathematically how they end up numerically equal and are they always equal?
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4answers
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Can hang glider hover straight into wind and keep same position? [duplicate]

Isnt resultant force allways pointing slighlty backward at every wing,so why hang glider is not push downwind by the wind? From theory that cant be possible,so does wind somehow coming at him at ...