40

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 ...


21

The entire tail is shaking (not just the horizontal stabilizer) not because it's stalling but because it is in the turbulent wake of the main wing. The tail is generating downforce as you can see from the up elevator. The main wing's nose down pitching moment increases when the center of pressure shifts aft at stall, as well as the change in the overall ...


20

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 ...


19

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) ...


16

(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 ...


14

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

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. ...


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 (...


13

A horizontal tail on top of vertical tail would require strong and heavy structures, which in turn is not good for economics of flight. The bigger the plane is, the more challenging the loads the tail has to handle are, so what might be a feasible solution on a regional jet might not work at all for a large jet. T-tails are an obvious choice when the ...


13

Here McDonnell Douglas does not use the roller-type seal. Their own method uses doors that pivot out of the stabilizer's way. From their patent: In your photo you can see the hinge line of the upper door (42) as well. Their method inherently doesn't fully cover the opening at large deflections, which is "permissible": While it is important that ...


12

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-...


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

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

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

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. ...


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.


11

The wide negative trim range is for operation with lowered flaps. Fowler flaps shift the center of lift backwards both by adding wing area at the trailing edge and by increasing camber. Both effects require more downforce on the tail to shift the sum of all lift forces such that it remains at the center of gravity.


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

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 ...


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

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 ...


Only top voted, non community-wiki answers of a minimum length are eligible