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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1answer
95 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
168 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 ...
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1answer
123 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
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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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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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6answers
174 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 ...
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4answers
167 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
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 ...
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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
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 ...
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1answer
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 ...
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4answers
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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
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-...
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4answers
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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
538 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
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 ...
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1answer
101 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
289 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 ...
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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 : <...
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2answers
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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-...
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3answers
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 ...
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6answers
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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 ...
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1answer
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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 ...
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7answers
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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?
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1answer
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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 ...
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3answers
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 ...
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2answers
296 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-...
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0answers
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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 ...
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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 ...
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5answers
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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 ...
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2answers
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 ...
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1answer
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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 ...
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2answers
142 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 ...
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1answer
152 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 ...
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5answers
557 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?
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3answers
473 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 ...
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3answers
165 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 ...
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2answers
217 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 ...
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1answer
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 ...
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1answer
152 views

How are pitching and rolling moments transferred from rotor to the body?

When a rotorcraft pilot moves pushes on the cyclic control stick, the swashplate tilts so that angle of attack of the retreating blades increase and of the advancing blades decrease, which creates ...
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2answers
272 views

Forces in a slipping turn [duplicate]

I have trouble understanding why the ball (on the turn & slip indicator) falls into the turn e.g. drop to the left when aircraft is rolled left, when in an uncoordinated turn (slipping turn). What ...
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3answers
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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 ...
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6answers
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Forces “felt” by pilot, G-meter, inclinometer--are they the aerodynamic forces generated by the aircraft, or the sum of weight+centrifugal force?

Consider a pilot sitting at the CG of an aircraft, with instruments also located at the CG of the aircraft. (Feel free to consider other cases as a bonus, but the core of the question is aimed at ...
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4answers
1k views

What exactly happens when power is reduced in trimmed, straight and level flight?

I understand that trimming an aircraft at a particular airspeed e.g. 100kts will keep the aircraft flying at that airspeed (100kts) even if you were to e.g. Lower power. This is apparently ...
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1answer
122 views

Are there any helicopters with tail rotors where slip-skid ball may be centered even when fuselage is streamlined to the airflow in cruising flight?

In a related answer, I stated "The tail rotor of a helicopter also generates an aerodynamic sideforce. Again, just as with the twin-engine airplane with one failed engine, when the fuselage is ...
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4answers
255 views

When do the lift and drag vectors contribute a force component along a glider's path of travel as seen from the ground?

It is often said that the lift vector helps to propel a glider forwards. The lift vector has no component acting parallel to the glider's trajectory through the airmass, but in many cases the lift ...
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4answers
5k views

How do “tip jet” helicopters cancel the torque effect of the main rotor?

Some helicopters use "tip jet" on the rotor blades tips such as the McDonnell XH-20 Little Henry and Hiller YH-32 Hornet. How do they cancel the rotor torque (often canceled by the tail rotor)?