# Tag Info

## Hot answers tagged flight-mechanics

52

What you observed is probably a Gulfstream production test flight, either an initial or a snag clearance flight, or possibly a Customer Acceptance from Savannah Air Center, which is a completion center across the ramp from Gulfstream. It could be possibly an experimental test flight if Gulfstream runs experimental flying from Savannah (I think they have a ...

38

Yes it can. The steady-heading sideslip (SHSS) maneuver is used in flight testing to demonstrate static lateral/directional stability (similar maneuvers exist as sideslip approach in crosswind, or stabilized control with one-engine-inoperative at low speed). In this maneuver, rudder is applied to hold a sideslip, which generates an opposing side force and ...

25

The fact that it's near Savannah and tracking within a confined airspace, I'm fairly certain this is a flight test being carried out by Gulfstream.

25

Static stability means that a deviation from a trimmed state produces forces which return the system to this trimmed state. If these forces produce an overshoot which increases over time, such that the system oscillates around this trim point with increasing amplitude, the system is dynamically unstable. The long period oscillation (phygoid) of gliders is ...

24

This approach of using an engine is called pulse and glide. It generally works because each engine has an optimal power setting at which it converts fuel into power most efficiently. If the most efficient power is higher than is required, something should be done to accumulate and later use the excess energy. Raising the vehicle up looks like a solution, ...

18

If an aircraft is statically stable, it will always return to equilibrium after a disturbance. But what happens after can either show instability or stability. This is where the dynamic stability comes in. You can think of an aircraft at equilibrium at a particular speed, altitude and angle of attack and it is suddenly faced with a disturbance which changes ...

17

Yes, it's entirely possible. You can use the rudder to oppose the turn induced by the roll, and thus fly straight. However, doing so means that your nose is pointed off at an angle from your direction of flight, so this dramatically increases drag. In fact, this is a common technique (at least among general aviation pilots) for losing altitude without ...

16

There are multiple configurations which are possible with tail or canard, which based on their locations and whether they produce lift or down-force, results in a stable or unstable aircraft (taking the aircraft center of gravity into account). The figures below show some of the possible configurations. Source: f-16.net In the most general case, there is ...

16

Here is one thing that WILL save fuel-- where possible-- such as when flying VFR. Note that this strategy only applies within the layer where thermal convection or orographic uplift are significant, not at higher altitudes where the air is generally not rising or sinking to any significant degree (apart from wave lift in which case the strategy will still ...

15

But assume, there comes a wind gust, and the angle of attack will increase. This causes the center of pressure to move forward in front of my gravity location. So the aircraft will become instable because the angle of attack will further increase (nose up). The only thing the pilot could do is to use the elevator to trim in pitch. This is not accurate. Are ...

12

Of course, just put the center of gravity back to its rear limit and fly slowly. Then all of them will produce positive lift on their tails. Stability is not produced by a downforce at the tail. The newest book I read which claimed this was from 1911 (I happened to read the 1913 edition). Stability is produced by making the lift per area of the forward ...

12

I think you misunderstand how it works, and how you would respond to changes in wind. Increases in airspeed impact all flight surfaces, including the elevator, so a change in airspeed due to a gust isn't going to create large changes in pitch. There will be some change, however typically the changes in pitch would balance out with the fluctuations. It's rare ...

11

what is causing the "corners" that we see at the following points? Compressibility. Close to Mach 1 the lift curve slope increases according to the Prandtl-Glauert rule with the factor $\frac{1}{\sqrt{1-Ma^2}}$. Since the X-axis shows indicated speed, the Mach 1 point moves left with increasing altitude. Technically, those corners should also be ...

10

A tandem wing airplane has two sets of wings, each providing upward lift. One is near the front of the plane, one is near the back, and the center of gravity is between them. (source: nurflugel.com) The Rutan Quickie is one such plane: (souce: wikimedia) This design is actually fairly old; it even predates (successful) heavier-than-air flight, as it was ...

10

The standard equation applies to any coordinated level turn (so that the G felt is "straight down" to an occupant of the aircraft, in an aircraft frame of reference). Matters not how it's all achieved - flaps, high-lift devices, helo rotor, thrust vectoring, whatever... a coordinated level turn at "this" bank will take "this" ...

9

This is commonly known as the Speed Stability, not to be confused with speed stability in the sense of static longitudinal stability. I think there's some common confusion with this phenomenon. The first part of this answer addresses the OP's question; the second part clarifies a common confusion. 1. Main Answer In level flight (i.e. zero vertical rate), ...

9

This makes sense and is approximately what happens if you reduce thrust during trimmed straight and level flight. The aircraft will go though a series of damped oscillations, called 'phugoid' until it finds its new equilibrium state. The new state will be the original airspeed, but now in a constant descent.

8

With thrust vectoring you no longer turn (as in: the wing creates the force that accelerates you in the desired direction) but you do post-stall maneuvering. Next, you need to distinguish between highest instantaneous turn rate (trading altitude for higher rate) and continuous turn rate (which is limited by the available thrust in most cases). Turn rate ...

7

Both are right in their own ways. First the basics: Power is thrust times speed and is constant over speed for variable-pitch propeller-powered piston aircraft. Therefore, propeller thrust is proportional to speed inversed. The minimum power required coincides with the point of maximum excess power since it needs the lowest power setting for trimmed flight. ...

7

You are very perceptive to note that for a given angle-of-attack, a return to the exact airspeed that allowed level (horizontal) flight would indeed imply a return to level (horizontal) flight. But that's not what we expect to happen when we reduce the power. Hopefully this answer will help you to understand why not. When you elevator trim to fly ...

7

Here are two questions back at you. Can a plane turn, with banking? Yes, of course it can, the normal way using the ailerons to tilt the airplane and thus change the angle of lift. You already know all about that. Can a plane turn, without banking? Yes, it can; by using the rudder to do the turning it can pull off a “flat turn” as it were. OK... are you ...

7

It is the same thing that makes you slide sideways in your seat going around a corner in your car. Or the same thing that would cause you to slide sideways the other way if you were driving straight ahead on a side hill. Don't overthink it... the ball simply responds to the same forces you feel. ADDENDUM: “I agree the comparisons are spot on if you are only ...

7

Don't overthink it too much. Simplify in your mind. Trim is used to pre-set hands-off angle of attack. Static stability forces will focus on regaining the trimmed angle of attack if the plane is displaced from its trim state. Since pilots use airspeed as a proxy for angle of attack, trim sets hands-off airspeed, as far as the pilot is concerned. The best ...

6

In simple mechanical stick linkages, is there crosstalk between the aileron and the elevator movement? In almost all cases, there is no intentional-- or discernable-- mechanical coupling between aileron deflection and elevator deflection. However in the Schleicher Ka-6 sailplane, the mechanical linkage is designed to raise both ailerons a little bit, ...

6

I would second what John K said, it’s most likely a GAC factory flight test or demonstration flight. Also with the airplane identified as GLF6 and, most likely going be the call sign “Gulf Test six” would pretty much confirm that suspicion. You will also see similar flights down to Brunswick Golden Isles airport (KBQK), as Gulfstream does a lot of flight ...

6

Can planes bank without turning Yes, a plane may fly in a banked attitude without turning. But when the plane is tilted to the left or right relative to Earth's surface and gravity, shouldn't it be "pushed" to the left or right? Yes, whenever a plane is banked and the wing is generating lift, the lift vector has a horizontal component that tends ...

6

The sum of all work done on the airplane must be zero in a glide. That is, the work done by gravity must equal the work done by drag. Note also that lift equals the force of gravity in equilibrium Work is force times distance. If gravity is X times larger than drag, this means that the distance in vertical direction must be X times smaller than in the ...

6

I'm going to answer with the caveat that I don't have as deep of an understanding of this as I would like, and someone smarter than me may be able to correct or expound on my response. Best Glide is a purely aerodynamic concept. There is no powerplant involved, so you're simply converting potential energy (altitude) into forward motion, at a rate and L/D ...

6

Lots of good information in answers posted so far but I think it is also useful to point out that with no static stability (in the pitch axis), the aircraft wouldn't be trimmable. With positive static stability (in the pitch axis), you can trim for a given airspeed, and if you then pull the stick aft, you'll feel an increasing forward pressure on the stick, ...

6

The main purpose of the tail surface is to prevent the pitch instability of the wing from affecting the whole aeroplane. This is why it is often called the horizontal stabilizer. In the simplest case, the stabilizer exerts no lift force when the plane is in trim. If the nose lifts, the tail AoA increases and it starts to generate lift. The design is arranged ...

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