# Tag Info

39

Those are called "Lightening Holes". The name refers to the weight reduction brought about by removing part of the material—lightening—and should not be confused with anything to do with electrical discharge—lightning. From the FAA's AMT Airframe Handbook, in Chapter 4, page 4-82: Lightening holes are cut in rib sections, fuselage frames, and other ...

18

The F-16 has an all moving tail plane all right. What you are referring to as the 'fixed part' is actually the fuselage portion which houses the air brakes. It can be seen clearly in the following photograph. Belgian AF stabilizer; image from designer.home.xs4all.nl

17

There are probably many factors in choosing aluminum vs. composites. A big one is bird strikes. The leading edges are at the highest risk for this. Metal tends to absorb the impact better while retaining its strength, while composites would tend to delaminate and become much weaker. Resistance to in-flight hail must also be considered. (Source Left, Right) ...

17

Short answer: Yes Generally you are right. You are trimming the aircraft for a point on its polar, and that point is reached at a specific angle of attack. You say yourself we should neglect secondary effects like the propeller blast, and under this condition you are right. Trimming means to set the distribution of lift between wing and tail surface, and ...

15

(Source: concordesst.com) It does have elevators in the form of elevons at the trailing edge. A delta is effectively a tailless flying wing with a really long chord. Like any flying wing, pitch stability is achieved by down force generated at the local trailing edge by a control surface that does the same job as a regular elevator/stab, by applying down ...

15

This would fall under catastrophic failure and theres not much that can be done. You may as well ask what will happen if a wing falls off. but.. UA232 Sioux City. The #2 engine (in tail) blew up and took out the hydraulic lines rendering all tail control surfaces (horizontal and vertical) inoperative. The crew found they could regain limited control of the ...

13

In a general sense, there are multiple reasons for the horizontal stabilizer to have dihedral/anhedral. To clear the tail from the downwash/propwash. A good example is the Cessna 425, which was developed from the Cessna 421. The 421 had a straight horizontal stabilizer. However, with the addition of dihedral, the tail is kept out of the propwash, improving ...

13

A Boeing 737 has a movable horizontal stabilizer for pitch trim with elevators for pitch control (also known as a THS – Trimmable Horizontal Stabilizer). This is true for all 737 variants, including the MAX. Note: The term stabilator is typically used when the entire tail is rotated for pitch control, like e.g. on a Piper Cherokee. The following image (...

12

Yes, when viewed from far enough away. Close up, both will have their own developing wake. The boundary layer leaving wing and tail will leave a speed discontinuity, and the downward moving wing wake will be complemented by a tail wake, which will slow down this downward movement directly behind the tail, and increase it left and right of the central tail ...

12

Most airliners with low horizontal tail surfaces have dihedral on them, for two reasons: To lift the horizontal surface above the wing wake. To lift the swept tail above the ground, so it will not be damaged in a tail strike. Note that the tail is roughly horizontal at the tail strike attitude to have enough clearance for full down elevator deflection. ...

12

No, static longitudinal stability does not necessarily imply a download on the tail. Static longitudinal stability requires that the Centre of Gravity is in front of the Centre of Lift, indicated as n.p.$_{fixed}$ in the drawing. Only then will an increase in Angle of Attack d$\alpha$ result in an opposing pitching moment: if d$\alpha$ > 0 then $dC_N$ > 0, ...

11

The main aerodynamic purpose of the horizontal stab (or certain canards) is to provide longitudinal stability. If the rear wing with the 5th and 6th engine flies "up," like the main wing, then it will counteract the longitudinal stability of the horizontal stabilizer. If the rear wing flies down, like the h-stab, then it is just extraneous, since the h-...

11

Tryin' to cheat the laws of stability, aren't we? In both videos it is evident that the plane is unstable in pitch. Adding a lifting prop will not change this, because changes in the angle of attack will not affect this prop's lift force much. Stability is achieved by shifting the center of gravity forward, so that changes in the angle of attack will ...

11

Here is a screenshot of a B737 Max 8 Runaway Stabilizer Checklist. There might be some small variations in the checklist when comparing each individual airline. Additionally, here is the Boeing "Uncommanded Nose Down Stabilizer Trim" bulletin that was issued to all B737 Max 8 operators after the Lion Air crash.

10

For the impatient reader: The answer is no. Let me explain it in detail. For this, it is helpful to simplify things as much as possible and then add the complications step by step so I can explain what each changes. The simplest layout uses a symmetric airfoil for both wing and tail and arranges both in the same plane and without a difference in incidence. ...

9

When the fuselage is stretched, the arm of the horizontal stabiliser is increased, and hence it's effectiveness increases linearly with the fuselage length. However, because the mass is distributed further away from the centre of gravity, the pitch moment of inertia increases too. If the fuselage would be modelled as a uniform rod, the moment of inertia ...

8

Of course it creates a pitching moment! Now we need to define around which reference point this moment should be measured. If the reference point is the center of gravity, it is even equally strong as the pitching moment of the elevator, it only has the opposite direction. If you use the aerodynamic center as the reference point, the moment will be less ...

8

The primary reason is probably because a larger tail increases the CG range. It does not make sense to stretch an aircraft without increasing the CG range. calculating tail volume Often the horz stab is used for the extra fuel capacity needed for stretch models (i.e MD11 and B747). "...the tail fuel tank will provide added range and improve the aircraft’s ...

8

Yes it is done regularly on recurrent sim training, but not to full travel because it is normally treated as a control system fault that can be stopped before it becomes totally uncontrollable, and the Alaska Airlines incident was a mechanical failure of the acme threads on the screw jack where the stab was free to tilt up as far as it could go and they were ...

8

The horizontal stabilizer provides lift, but usually in the negative direction. Could one provide positive lift? The answer depends on cg location. Forward CG, the answer is no. Aft CG, the answer is yes but only if the CG was aft of the center of lift. In other words, the more forward the CG is compared to the center of lift, the more downforce the tail ...

8

MCAS uses stabiliser input to retain full elevator authority in both directions for pilot input. MCAS is set up as an Inner Loop autopilot: it controls behaviour around the CoG of the aeroplane without displacing the cockpit flying controls. For aeroplane pitch control there are indeed two options: the stabiliser and the elevator. If the elevator is chosen ...

8

A converging shape at hypersonic speed in a low-pressure medium will produce close to vacuum pressure on its surfaces (hypersonic shielding). A small sideslip angle will only result in a very small pressure difference between both sides. Contrast this with a diverging shape which produces higher than ambient pressure on both sides. In hypersonic flow this ...

8

Moving each part has different effect on drag: Moving just the elevator increases camber, producing large force which is useful for manoeuvring, but it also produces more drag. Moving the whole stabilizer, keeping the camber low, produces less drag for the same force, which is good for cruise efficiency. That's why the elevator is used for control and the ...

7

You are right, the horizontal tail of a conventional airplane appears to have a higher incidence, but the actual angle of attack is smaller than that of the wing. The wing, flying ahead of the tail, produces downwash, so the flow at the tail location has a distinct downward component. The downwash angle can be calculated from the lift coefficient and the ...

7

As per the A320 flight manual (§127.20 p3), the maximum permitted total pitch alteration in normal law depends upon speed, aircraft mass, CoG, and other factors: Pitch Attitude Limitation: Pitch attitude is limited to: 30º nose up in conf 0 to 3 (progressively reduced to 25º at low speed) 25º nose up in conf FULL (progressively reduced to 20º at low speed) ...

7

When I was type rated in the CRJ200 with hydraulic controls and a THS, directly coming from light aircraft, the differences in technique are significant and it was definitely something new to learn. With a THS, column neutral is always the same spot. This means trimming to a speed is not a case of moving the control to location X and trim until it stays at ...

6

Yes, both are equal for small angle changes. Exceptions do apply, especially in transsonic flow. Both changing the stabilizer incidence and the elevator deflection will change the lift distribution between wing and tail surfaces and will trim the aircraft for a different angle of attack. Changing the incidence gives the empennage a new angle of attack while ...

6

Is the aircraft also equipped with trim tabs? From the images available online (this is a youtube screenshot, click it to see the larger version), no. And see point 3 on why I was not expecting any different. If an aircraft has both trim tabs and movable stabilizer I do not see the need of such a solution, a trimmable stabilizer is already ...

6

Because the safe situation is: a gravitational moment nose down, trimmed with an aerodynamic moment nose up. In all flight conditions. The critical situation is not cruise, but the conditions at low speed. At TO and landing the Angle of Attack is high: a nose up attitude, commanded by a downward tail force. Velocity is low, so the large force is achieved ...

6

As the manual shows, the Concorde's trim was conventional (and not by fuel transfer) and that the control surfaces shifted the neutral position as would be expected (here's a schematic). Moving the fuel around is not managed by the pilots, rather the flight engineer. It's a long-term process that has to do mainly with the lift force shifting aft as the plane ...

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