Questions tagged [stability]

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

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How to calculate variation of Z force with elevator deflection (Zδe) in Nelson for pitching dynamics?

I have been trying to model the pitching dynamics of a General Aircraft (Nelson : Flight Stability and Control) but during the modelling, I find that I need to use the ...
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3answers
114 views

Does pumping fuel to each wingtip affect roll trim in a stabilized turn?

If an aircraft is stabilized in a constant-bank, constant rate turn with no sideslip, and then we pump 200 gallons of fuel from a fuselage tank to a tank on the tip of each wing, without changing the ...
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1answer
64 views

Helicopter tail horizontal stabilizer angle

In helicopters what factors decide the horizontal tail stabilizer angle? By angle I mean that in some helicopter they are -6 deg relative to tail boom while in some -3 deg. These angle were remain ...
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0answers
64 views

Does/Can combustion instabilities occur in SCRAM jet?

I was told that combustion occurs at Supersonic speeds in SCRAM jet. So acoustic disturbances/ pressure fluctuations can't travel into incoming jet stream. Does this avoids combustion instabilities in ...
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2answers
61 views

Why does instability in pitch lower trim drag for an aircraft with a tail?

I have a hard time figuring out why a longitudinally unstable aircraft has a lower trim drag. This seems to be a thing especially in fighter aircraft, so does it have to do anything with supersonic ...
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1answer
79 views

What causes 'wing rock' and how does it work?

Currently studying for a course on fighter aircraft. I came across the phenomenon of 'wing rock', which occurs at very high angles of attack, but I couldn't find any good sources that explain how this ...
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3answers
524 views

How does this RC helicopter keep itself upright?

I have this (cheap, beginner-level) RC helicopter: It has 3 controls: one for climbing and descending (collective throttle), one for yawing (differential throttle), and one for pitching (the tail ...
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2answers
79 views

Sensitivity of aircraft stability with respect to the CG location

I am working on the design of an aircraft (2 m long, wingspan = 3 m). The platform is longitudinally stable but it is very sensitive to the variation in CG location. For example, 1) CG_location = 100 ...
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1answer
143 views

Why was the Akron’s spy basket installation so remarkably unstable?

A spy basket (also known as a cloud car) is a type of airship appurtenance consisting of a streamlined one-(usually)-person gondola attached to its host airship by a long cable; to use it, the host ...
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2answers
109 views

Contribution of wing vertical location to roll stability

Recently, I was reading about the factors that contribute to roll stability of an aircraft and came across a point stating that the wing's vertical location (Distance of wing from CG) contributes to ...
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9answers
2k views

Is a vertical stabiliser needed for straight line flight in a glider?

My team is designing a glider and I am unsure about whether or not to include a vertical stabiliser. The task the glider must complete is to achieve the largest possible displacement in a straight ...
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1answer
151 views

Would knowing the exact weight that has been loaded on a commercial plane and it's distribution be useful? [duplicate]

There's been a bit in the media about weighing passengers in order to get more accurate take off weights for commercial planes. I'm guessing the delta between a heavy set of passengers and a light ...
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1answer
157 views

How does engine geometry affect flight stability?

News items around the recent aviation accidents involving Boing 737 MAX 8 aircraft suggest, that bigger engine diameter demanded for a different (longer) nacelle strut for proper ground clearance ...
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2answers
822 views

How does having a bigger engine placed slightly more forward and higher impact the plane in pitch?

I'm asking about general aerodynamics for under-wing twin-jets – I'm not after information/speculation on the Max 8 crashes/systems, but I mention the crash below because of what I see as an unclear (...
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1answer
231 views

What is the stability of a 777-like plane if the engines flameout and the autopilot disconnects and the pilots don't make any inputs?

According to Wikipedia: If no control inputs were made following flameout and the disengagement of autopilot, the aircraft would likely have entered a spiral dive and entered the ocean within 20 ...
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2answers
191 views

Are there any airplanes with the Centre of Gravity behind the Centre of Pressure? [duplicate]

We are used to seeing a forward CG in all airplanes, from a small Cessna to a large Boeing. I wonder whether any airplane with CG behind wing CP exists in production? Is it even possible? If so, what ...
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2answers
431 views

What prevents BFS from becoming unstable when pitching from horizontal to vertical?

In this video from (SpaceX's BFS landing) there is a point where the ship tilts from horizontal « belly first » terminal velocity freefall, to vertical « engine first » landing position. The graph ...
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How would a sudden change in weight affect a plane? [duplicate]

If I have a plane trimmed for perfect straight and level flight and then suddenly I removed some mass from the airplane (let’s ignore any momentums introduced by mass release) – how would the aircraft ...
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2answers
192 views

What would happen if the elevators were set to opposite angles?

For example left elevator angle = +30 deg, right elevator angle = -30 deg. Would these settings be able to induce a rolling moment on the aircraft? What would happen with the pitch?
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1answer
188 views

What is the source for the “rule” forbidding configuration changes below 200ft AGL?

I keep hearing from countless instructors, and even some DPE's, that in single engine aircraft, no configuration changes are allowed below 200AGL (i.e. flaps). Some have also stated that this is ...
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155 views

What are stick position stability and stick force stability?

What are stick position stability and stick force stability? What are the difference between them? How will changing trim of an aircraft affect them?
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5answers
569 views

Is the aircraft neutral point a function of the tail incidence angle?

While using XFLR v5 for a basic analysis I am facing this issue. For a fixed configuration I varied the tail incidence angle and XFLR is displaying a change in the Neutral point location. But as per ...
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1answer
279 views

Why is the delta wing naturally stable in pitch?

Any thoughts on why the delta wings are naturally more stable in pitch, so they don't require any tail surface? What's the physics behind this?
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2answers
402 views

What happens aerodynamically when we trim an aircraft?

I'm trying to understand stability & control. Please correct me if I'm mistaken. An aircraft will have longitudinal stability if the aerodynamic center (AC) is behind the center of gravity (CG). ...
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1answer
126 views

What is the location of AC for typical modern airplanes?

Some sources state that AC must be located behind CG, so that AC is stable. There is a source, which throughout the study of stability and control consider AC located ahead of CG and positive cambered ...
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1answer
344 views

Why do some Mach trimmers move the elevator?

A pop-up rod on a the FO's control column on a DC-9 that shows the Mach trim position. (YouTube) Regarding the title, I'm not sure if it's just some or all jetliners (I tried to research it). On the ...
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3answers
633 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?
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1answer
200 views

Is aerodynamic flutter speed dependent?

Is it possible for control surface flutter to occur at low Reynolds and low speed? If yes,why don't Ultralights have counter weights or tail sting mass to immune the control surfaces against flutter ...
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0answers
40 views

What happens to the neutral point of a fighter jet during supersonic flight? [duplicate]

I understand that for a fighter aircraft, it would have to be inherently unstable. To do this I believe that the neutral point needs to be aft of the cg. I was told that during supersonic flight this ...
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1answer
151 views

Is there a difference in stability between a tail downforce (cg ahead of ac) and a tail upforce (cg behind)?

So from what I understand, having a - 1.cg ahead of the neutral point(ac) with a tail downforce and 2.cg behind ac with a tail upforce are both stable configurations.(Please correct me if I'm ...
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4answers
560 views

Is this paragraph about the dihedral effect in the FAA's Glider Flying Handbook correct?

I've been reading the FAA's Glider Flying Handbook, 2013 (FAA-H-8083-13A). In chapter 3 ("Aerodynamics of Flight"), the book is discussing stability. On page 3-12, it states: Dihedral is the upward ...
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5answers
7k views

Why do most biplanes have their top wing slightly forward of the lower wing?

In most of the biplanes, the top wing is located a little forward of the lower wing. What is the use of this? Also, how does this affect stability of the aircraft.
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2answers
308 views

What is the airplane with the best flying characteristics? [closed]

I'm reading Stick and Rudder by Wolfgang Langewiesche, and in Chapter 7 titled, "What the Airplane Wants to Do" he discusses stability. In discussing it, he says that no plane yet built is completely "...
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73 views

Controlled stall,aileron or rudder input?

I know aileron input in a stall approach is not adviced, what if vortex generators are placed at the wingtip where the ailerons sit meaning there will still be aileron authority even at stall, at this ...
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1answer
201 views

At what angle of deflections do rudders become inefficient?

This article (picture) says rudders for ships can deflect 35° max,so at what aoa does an airplane rudder lose its efficiency,at what " angle of deflection " does it start to stall ?
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1answer
494 views

Can an aileron stall in-flight?

Horizontal stabilizers stall, so I was wondering, is it possible for an aileron to stall? If yes, at what angle of attack?
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1answer
187 views

Do elevators have cambered airfoils inverted or symmetrical airfoils

Do horizontal stabilizer of ga planes e.g cessna 172(or ultralights e.g lazair) have cambered airfoils inverted to provide the tail downward force or do they have symmetrical airfoils at negative aoi ...
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1answer
405 views

Where can I get a graph of lift coefficient against AOA for a symmetrical airfoil?

Where can I get get a graph lift coefficient against AOA for a symmetrical airfoil ? I am asking for a source or link to a graph or table of AOA against Cl of any symmetrical airfoil.
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1answer
314 views

What is decalage and how it affects airplane performance?

What is decalage in airplanes and how important is it in respect to airplane performance?
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145 views

Which kind of stability have the aerobatic aircraft?

im designing an aerobatic aircraft (similar to EXTRA 330SC) and i would like to know about the stability lateral and longitudinal, estatic and dynamic. I read somewhere that the aerobatic aircraft ...
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1answer
597 views

How does angle of incidence affect an aircraft's stability?

How does angle of incidence affect an aircraft's stability? I've tried searching the web for the simplest answer that makes sense but so far I've come up with nothing as yet. I know it sounds simple, ...
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2answers
445 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 ...
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1answer
621 views

Which moments are acting on a flying airplane?

I would like to ask some clarifying questions regarding the moments acting on a flying airplane. My understanding is that there are following force: Weight (pointing down and applied to the CG of ...
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1answer
128 views

How to carry out a CFD simulation for determining the stability derivatives of an aeroplane?

I want to create a 3D model of an aircraft to determine the stability derivatives by using a computational fluid dynamics (CFD) simulation. I tried to google for tutorials that explain how it is ...
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1answer
474 views

How to calculate the location of C.G. A.C. & N.P. in static longitudinal stability?

We are in the conceptual stage of design and, using Raymer & Nicolai as references, I am doing a rough calculation of "power off" neutral point (N.P.) to find the optimum c.g. and a.c. positions. ...
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4answers
972 views

Why don't single-engine jets suffer severe gyroscopic effects?

I was reading up on World War I fighter aircraft, and saw that rotary piston engines, which powered many of those planes, produced extreme gyroscopic effects due to the large, heavy chunk of metal ...
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2answers
148 views

Does ducting help to stabilise heavy lift drones?

I'm looking to build a UAV that is extremely stable. It doesn't have to be fast, it doesn't have to be agile, but it will have to carry up to 50lbs (agriculture focused UAV that has to operate for at ...
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1answer
450 views

Can the fly-by-wire system of a modern airliner handle an unstable condition?

According to this answer airliners/large passenger aircraft such as an A320 are designed such that they are longitudinally, statically stable under normal flying conditions. What if, for some reason, ...
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3answers
1k views

What are the relations between stability, controllability and maneuverability?

As preparation for my CFI checkride I have been trying to understand aerodynamics very well. One of the things I’m struggling with is stability If I have a stable aircraft, this means is less ...
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1answer
1k views

Why is deploying speed brakes not recommended with the flaps extended?

I read this in the normal procedures section of the A320 FCOM. Why is it so? When the speed brakes are deployed, extending the flaps beyond FLAPS 1 may induce a slight roll movement, and in calm ...