Questions tagged [stability]

The physics of maintaining a specific state in the dynamic system of aircraft flight.

Filter by
Sorted by
Tagged with
1 vote
3 answers
537 views

Is C.G. of wing itself in line with hang point (hang glider)?

Where is c.g. of hang glider wing,at hang point ,in front or behind hang point? Is control bar "neutral" when glider is at rest and there is no wind or flip backward or forward? At 0:45 ...
0 votes
0 answers
70 views

After designing an autopilot, how does it affect aircraft modes?

Let's say an autopilot will be designed for the longitudinal axis. A pitch attitude hold will be made with a sas in the inner loop and a pid in the outer loop. How does this system change the phugoid ...
3 votes
1 answer
171 views

Is the AOA on the horizontal stabilizer positive?

I am making a flight sim and would like some help. If I am correct, the angle of attack on the horizontal stabilizer should look something like this: aoa(Hstab) = aoa(Wing) - downwash + Hstab ...
3 votes
1 answer
207 views

What are the effects of a corrugated surface on spanwise flow deviation, for a swept back flying wing?

Considering a Ju-52 wing in some hypothetical swept back flying wing configuration using the same strucural design as the Ju-52. What would be the effects of that corrugated skin, regarding spanwise ...
8 votes
1 answer
4k views

Is there an aerodynamic reason for airship fins to be at the tail?

I've read this interesting Stack Exchange question about why airships have fins: Why do blimps have fins? Which has me wondering why the fins are almost always located in the tail section. After some ...
0 votes
1 answer
209 views

Does pilot need to increase thrust when gust hit him at landing and where is axis of rotation?

Let's say a plane is flying above a runway in straight line, and gust of wind hits the plane from side. Do pilot need increase thrust to stay above runway and where is axis of rotation ? It often said ...
6 votes
7 answers
1k views

Why do most commercial aircraft have the Center of Gravity before the Aerodynamic Center?

I've looked at the other questions concerning this topic, such as: How does an aircraft tailplane work? Does static longitudinal stability require download on the tail? But I'm still confused about ...
1 vote
0 answers
193 views

What can cause an unstable phugoid mode?

For clarity, I am wondering about how aircraft design can lead to the phugoid poles becoming complex with a positive real part, so an oscillation with increasing amplitudes. My understanding of the ...
0 votes
3 answers
138 views

Simultaneous yaw damping and sideslip control of aircraft with rudder?

Yaw damping is achieved by using the rudder to generate a yawing moment that opposes any yawing motion. Also, rudder is used to correct sideslip by applying a rudder input in the opposite direction of ...
4 votes
1 answer
137 views

Confusion about center-of-lift vs center-of-gravity [duplicate]

As usually depicted, in a small aircraft (maybe larger commercial ones too), the lift due to the main wing (excluding the elevator) is depicted as on average aft of the center of gravity, with the ...
1 vote
3 answers
881 views

How attitude, speed, and altitude vary when increasing pitch?

I have been struggling with the following question for a while, would greatly appreciate some help and explanation why. Scenario: I'm cruising in my Cessna- cruise attitude 2300 RPM trimmed for 95. ...
9 votes
1 answer
221 views

Did the dog-tooth notches in the wing of the F-8 Crusader really have anything to do with "yaw stability"?

What was the real function of the "dog-tooth" notches in the leading edge of the wing of the Vought F8U crusader? Wikipedia says:1 Vought's design team... produced... a relatively ...
1 vote
2 answers
2k views

What is rotor damping and how does it affect helicopter stability?

What do we mean by rotor damping (in terms of helicopters)? How is it affected by air density? How does helicopter stability depend on rotor damping?
1 vote
0 answers
33 views

How does distance between wings of a biplane affect its horizontal stabilizer design?

When for instance pitching down, a biplane's upper wing has higher airspeed than lower wing, therefore higher drag that should dampen the pitching down rate. How significant is this, if it is, ...
4 votes
2 answers
260 views

How does conical camber decrease roll due to sideslip?

I was reading Ray Whitford's Design for Air combat and came upon a passage that said that on the SR-71 conical camber "gives a useful reduction in the otherwise very high rolling moment due to ...
4 votes
3 answers
1k views

Does dihedral improve roll stability in gusty conditions?

Against roll instability, should I add more dihedral/a high wing? I'm trying to build an RC plane that can handle windy conditions. For that I want extraordinary aerodynamic stability. For ...
6 votes
2 answers
2k views

Is there a formula to calculate how big a ventral fin should be?

I've been doing some research into vertical stabilizer designs for a university assignment and have come across ventral fins. I've found a fair bit of information on why they're fitted but can't find ...
9 votes
2 answers
1k views

What is purpose of engine pylon airfoils on the Hondajet HA-420?

The engine pylons on the Hondajet are aerodynamically shaped so as to provide a lift force laterally and outwardly. Engine pylon as viewed from rear Engine pylon as viewed from front Are these for ...
0 votes
0 answers
185 views

Why might a canard aircraft suddenly pitch down from a level flight?

I have a canard aircraft which has pitch stability issues that I'm trying to troubleshoot. The aircraft has a characteristic tendency to depart level flight in sudden dive/ or generate a massive nose-...
0 votes
0 answers
644 views

How to calculate Cm0 and Cmac,wb for an RC plane?

I am currently going through all of my stability and control calculations and am a bit confused on how to find $C_{m_{ac,wb}}$. The only things I'm finding online is that they are given through ...
0 votes
0 answers
83 views

Should the planform area inside the fuselage be considered for a stability calculation?

I am using lower order tools (xflr) for calculation of neutral point and CG location.I can think of modelling the wing in three ways wing with section inside the fuse missing wing with section ...
8 votes
4 answers
3k views

Does "pendulum effect" apply to hang gliders or any aircraft?

In discussion of aircraft roll stability in FAA paragraph on dihedral effect and in keel effect and in Why are high wing aircraft more stable the question of pendulum effect arises. This is usually ...
17 votes
4 answers
5k views

Why does the Airbus A320 series seem to rock left and right in level flight?

I have noticed on all Airbus of the A320 series that I have flown as a passenger (which includes the 319, the 320 and the 321), that whilst in level flight, the aircraft has always a longitudinal axis ...
6 votes
6 answers
5k views

Without wind, would a plane go straight if the pilot let go of the controls?

If you let go of the steering wheel of a (properly maintained) car, it will typically go in a straight or nearly straight line. Would a powered airplane in no-wind conditions do the same thing?
4 votes
1 answer
1k views

How is an aircraft designed to be longitudinally stable?

How do aircraft designers ensure that a specific aircraft is longitudinally stable? Are there any different considerations for subsonic and transonic aircraft?
1 vote
1 answer
418 views

Estimating Moment Coefficient about Aerodynamic Center for wing-body combination

Are there any references or analytical methods to estimate the moment coefficient about the aerodynamic center, C_M,ac for a given wing-body combination? Even something rough would be useful such as &...
8 votes
3 answers
5k views

When leaving ground effect, why is there a nose-up change in moment?

The Airplane Flight Handbook states: The aircraft leaving ground effect will Require an increase in AOA to maintain the same CL Experience an increase in induced drag and thrust required ...
1 vote
1 answer
348 views

Why do most canards have swept wings?

So most canards have swept back wings. Now I have been told that it is that way to ensure yaw stability (for example in a crosswind) - not sure though. But then I look at the new Lilium jet, which is ...
1 vote
2 answers
210 views

What happens when you put significant weight on the tail of a commercial airplane?

I'm curious what happens if you put some extra weight in the back of the airplane (let's say a small GE turbine or something). I'm new to Stability and Control side of things and curious how the new ...
1 vote
3 answers
205 views

Can the flap on one wing be used to reduce a left turning tendency?

I fly a single engine Jabiru UL45 and it has a tendency to turn left during straight and level flight. Is it possible, in order to reduce a "Heavy Wing" to slightly increase the degree of ...
7 votes
4 answers
3k views

Why do tailplanes provide down force, if not for longitudinal static stability?

We can see that most conventional aircraft have their horizontal tail surfaces arranged to provide a down force. This question asks if that is required for static longitudinal stability, and the ...
8 votes
3 answers
640 views

Is a glider on a winch directionally stable?

Let's say I were to fly a glider with the stick and rudder exactly centered laterally, while making the appropriate pitch inputs, during a winch launch. Would the glider remain wings level throughout ...
6 votes
4 answers
1k views

How does a tailplane provide downforce if it has the same AoA as the main wing?

If an airplane is traveling through a uniform environment and its main wing is parallel to its horizontal stabilizer, how does its tailplane generate downforce? Only explanation I can think of is ...
3 votes
2 answers
407 views

Are there any relationship between lateral and directional stability?

Directional stability is affected by the side areas such as the vertical stabilizers and lateral stability is affected by dihedrals. Is there any relationship between lateral and directional stability ...
2 votes
1 answer
239 views

General Rule for Calculating Center of Gravity of any Aircraft Configuration

I'm looking for method(s) to determine the CG of any fixed wing aircraft for it to be reasonably stable. I only know for conventional aircraft, placing the CG between 1/4th and 1/3rd of MAC behind MAC ...
13 votes
2 answers
2k views

Longitudinal stability of airships: How is the critical speed defined?

Airships are unstable in pitch above a certain speed, called the critical speed. What causes the instability, how does it manifest itself for the pilot, and how is the critical speed defined and ...
0 votes
1 answer
184 views

Control surface deflection during takeoff

What is a reasonable (or typical) control surface deflections required for takeoff? I would like to know two ball park values if possible elevator deflection for conventional transport aircraft ...
5 votes
4 answers
1k views

Why does static directional stability decrease with altitude?

At constant CAS, high altitude means lower air density and therefore higher TAS: this decreases the aerodynamic damping during a rotation. For this reason, I cannot understand why directional ...
2 votes
1 answer
313 views

The Effect of Pitching Moment on Aircraft Stability

I'm designing a small RC plane and I'm currently at the first iteration of airfoil selection. I have converged to Clark-Y, NACA-2412, NACA-2415, and S-8036. In comparing the four, I noticed that all ...
2 votes
3 answers
335 views

Are there any aircraft where wing, horizontal empennage and optionally canards produce positive lift?

Planes are more stable if the center of mass is ahead of the center of lift. But this means that the tail must provide downforce to keep the nose up, which is inefficient. Are there any designs where ...
3 votes
1 answer
142 views

Angle of Attack influence on Adverse Yaw

we are analyzing an aircraft's lateral-directional control characteristics with self-made code. We have observed that the aileron's influence on the body axis yaw moment is quite sensitive to the ...
0 votes
1 answer
275 views

What is the location of the CG on the T-38?

Is the Northrop T-38 Talon's CG forward or aft of the center of lift (like the F-16)?
3 votes
1 answer
856 views

Why is the CG assumed to be between the CP and the tail?

While discussing stability (Longitudinal, Lateral, Directional), invariably, all texts assume CG to be between CP and tail. Ex: Look at the specific image in wikipedia https://en.wikipedia.org/wiki/...
5 votes
3 answers
781 views

How to correct the design of an aircraft that is not speed-stable during approach?

I was just wondering if an aircraft is found to NOT be speed stable during the approach flight phase, what might a designer be able to do to stabilize the aircraft without adversely impacting its ...
10 votes
1 answer
476 views

What does it mean exactly when an aircraft is "35% unstable"? (aircraft stability factor)

CNN's Grumman X-29: The impossible fighter jet with inverted wings contains several interesting photos, and says: It was unflyable -- literally -- without a digital flight computer on board, which ...
1 vote
0 answers
131 views

How do boxwing and tandem airplanes balance moment

I want to build a hydrofoil like this picture: I discovered that you can pump it with a leg motion and moving the center of mass. Like this: I discovered xflr5 and ...
0 votes
2 answers
531 views

How can I calculate the tail area required to achieve longitudinal static stability?

I've got a longitudinal stability question. I've not attempted this question yet as I didn't know where to start from, also my lecturer hasn't explained static stability to us clearly and I needed a ...
3 votes
4 answers
3k views

Do high-wingers have dihedral?

I know that high wingers have an inherent dihedral effect. Are there any examples of high wing aircrafts with a dihedral? If so, what is the reason behind it?
2 votes
1 answer
177 views

What are the stability criteria of helicopters?

In airplanes, longitudinal stability is maintained if centre of lift lies aft of center of gravity. Like in the airplane shown in the figure below, do helicopters also have stability criteria? They ...
5 votes
5 answers
8k views

How does the angle of attack vary in turns?

I read somewhere that when the aircraft banks to turn, its angle of attack increases.Since angle of attack is the angle between the relative wind and chord line, how does turning increase it? Is it ...

1
2 3 4 5