# 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.

109 questions
Filter by
Sorted by
Tagged with
99 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 ...
90 views

### 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 ...
169 views

### 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 ...
125 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...?
4k views

### 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 ...
121 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 ...
175 views

### 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 ...
168 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 ...
144 views

### In a full-rudder sideslip in a Schweizer 2-22 or 2-33 glider, is the descent rate higher at 50 mph airspeed than at 60 mph airspeed?

Is it really true that in a full-rudder sideslip in a Schweizer 2-22 or 2-33 glider, the descent rate is higher at 50 mph airspeed than at 60 mph airspeed? Likewise, is it really true that in a full-...
67 views

### 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 ...
442 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 ...
133 views

### 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. ...
150 views

### 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 ...
479 views

### What is physics explanation for minimum sink rate airspeed?

I did some research on Minimum Sink Rate, and saw much information defining it, (such as it is the speed at which the aircraft will remain in the air for the longest time, etc.) and how it is ...
240 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 ...
6k views

### Is excess lift or excess power needed for a climb?

As answered in this question, aircraft need excess power - not excess lift - to climb. This is plausible when the aircraft's thrust vector has a vertical component (its nose and engine points upwards),...
113 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 ...
17k views

### Does lift equal weight in a climb?

This subject keeps coming up in the discussions and questions such as this one, which asks if lift equals weight in level flight. Good answers there, pointing out that upwards force has many sources. ...
1k views

### Descending on a given glide slope (e.g. ILS) at a given airspeed— is the size of the lift vector different in headwind versus tailwind?

We had a discussion with friend and we were talking about if the airplane is on approach and the one is landing with tailwind and the other one is landing with headwind, so both have the same value of ...
664 views

### 'Gravitational' power vs. engine power

A glider gets the power it needs to fly from the decrease of gravitational potential energy associated to the descent. My question is: for the same weight $W$, airspeed $V$, and a prop efficiency of ...
300 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?
271 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 ...
229 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-...
544 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 ...
114 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 ...
102 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. ...
3k views

### 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 ...
35 views

### Coefficients outputs by DATCOM

I'm trying to understand the outputs given by the DATCOM method. For example I have this formula for pitching moment coefficient : DATCOM give me these coefficients related to the pitching moment : <...
138 views

### What is airflow direction in turn?

Let imagine that we put wind indicator on rotating merry-go-around. Will wind indicator stay prepedicular to the radius of circle,showing tangetinal airflow velocity? (Wind indicator has equal mass ...
5k views

### Can gliding your plane save fuel?

Aimed towards lighter piston planes including a powered glider, if a pilot wants to extend a plane's range unconventionally, could flying like a glider by climbing and then gliding down or would ...
85 views

### what is the actual force causes this issue according to IAS that shows normal descend speed?

When we have tail wind during approach , with respect of Aerodynamic forces that effect on airplane , the whole part of fuselage move forward due to tailwind, also we have about 70kts IAS (in general ...
4k views

### Plane that always flies into the wind?

Suppose that you dropped an uncontrolled, dummy glider into the air. You want it to always face into the wind by design. Would it be possible? If so, what would such a plane look like?
82 views

### Why does a steady-state non-zero body yaw and/ or roll rate induce side force?

An answer on ASE states The presence of steady-state non-zero body yaw and roll rate induces side force ($C_{y_p}$ and $C_{y_r}$). What is a non-mathematical explanation of why this is so? Is it ...
299 views

### What are the forces present in a coordinated turn?

During straight and level flight, coordinated flight is assumed when there is no net lateral force (no slip or no skid). But this concept totally breaks down when it comes to turning, in a co-...
165 views

### Why does a banked aircraft create sideslip?

Below is an excerpt from Raymer (Aircraft Design) where he explains the dihedral effect. He states that a banked aircraft (due to say a roll disturbance) will have a sideslip which leads to a ...
6k views

### Can a plane bank without turning?

Can planes bank without turning, and if so, how is it possible? A plane's wing is designed to naturally create lift; the explanation for that is that the greater speed of the air moving over the wing ...
56 views

### How long can an aerobatic (or any) plane fly “on its side”? [duplicate]

This recent question Can a plane bank without turning? asked if a plane can sustain some amount of roll in straight flight, sure they can. Consider an aerobatic plane (perhaps a Pitts?). As far as I'm ...
2k views

### How do handling characteristics depend on flying with a full vs. an empty tank?

Modern aircraft are capable of carrying a lot of fuel to achieve extra-long range; we're at a point where nearly every pair of destinations can be reached non-stop. Carrying so much fuel imposes ...
242 views

### When a paraglider pilot applies brake on one side and maintains the brake pressure, why does the roll rate eventually come to zero?

I recently started to study paragliding and I am confused about the rolling movement created when a brake is maintained. I was reading this answer How do paraglider controls work? and I am not clear ...
161 views

### Helicopter Basics: How does lead-lag of blades actually help in compensating for increase/decrease in speed due to flapping?

I understand the following - Due to dissymmetry of lift, flapping up and down occurs. Since angular momentum has to be conserved, the speed of blade increases/decreases during flapping up/down ...
394 views

### What is Neil Armstrong teaching in this image?

It seems to me that in this image Neil Armstrong is teaching something related with aerodynamics forces (lift, drag...), but I don't know exactly what is that "Triangle" that He drew (It doesn't seem ...
571 views

### How does retracting flaps help extend the glide of an aircraft?

As per the video from Smithsonian channel BA flight 38's captain retracted the flaps of the Boeing 777 by 5 degrees to extend glide, to travel further. Why?
72 views

### How are coefficients of equation of sideslip angle in the paper “A general Solution to the Aircraft Trim Problem” calculated?

I am sure many of you guys must have read the paper, "A General solution to the Aircraft Trim Problem" by Marco, Duke and Bernt. I am working with the turning of the Aircraft and I am not able to ...
143 views

### Do horizontal stabiliser force direction change with CG variation for a given aircraft? [duplicate]

I am wondering about the direction in which horizontal stabilizer provide force. I know that it can provide either upforce or downforce. But I am wondering whether is it determined for a particular ...
479 views

### Do adding high thrust in plane prevents it from stalling?

I am convinced that fighter jets (every flying object) do stall. So from quora, Why don't fighter jets stall? But most of the fighters have thrust:Weight ratio > 1 which means that they are not ...
669 views

### What is missing from these diagrams of the forces in slips and skids?

See these images that are widely reproduced in many different on-line ground school materials. A) Is the magnitude of the wing's lift vector illustrated correctly in each of the three cases? Should ...
168 views

### How does vertical stabilisation work?

I know that similar questions are available all over the internet, including this website. However, none of the answers make full sense to me. I'm looking for simple answer (explain-like-I-am-5 type ...
225 views

### Why did the Wright brothers take steps to increase the amount of vertical surface area forward of the CG on some of their aircraft?

Why did the Wright brothers take steps to increase the amount of vertical surface area in front of the CG on some of their aircraft? Could this have actually improved the flight characteristics in ...