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40 votes
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What are these holes in my Cessna 172, just in front of the elevator?

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 ...
J W's user avatar
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21 votes
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In this MD-11 stall test video, are we seeing the tail stalling first?

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 ...
John K's user avatar
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20 votes
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Is trimming for constant speed equal to trimming for constant angle of attack?

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 ...
Peter Kämpf's user avatar
20 votes
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Are there any known aircraft (experimental, otherwise) with non-fixed vertical/horizontal stabilizers?

The SR-71's rudders pivoted without any fixed leading edge, as shown: Source Source The T-38 (along with many other supersonic jets of its era) had a pivoting horizontal stabilizer with no fixed ...
Ralph J's user avatar
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19 votes
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Why does the F-16 have a fixed stabilizer section inboard of the stabilators?

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 ...
aeroalias's user avatar
  • 100k
17 votes
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Why are the leading edges on the Boeing 787 made from aluminum?

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 ...
fooot's user avatar
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17 votes

Why did Concorde not have horizontal stabilizers?

(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 ...
John K's user avatar
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15 votes
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What is the horizontal stabilizer failure procedure?

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 ...
Anilv's user avatar
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15 votes

Are there any known aircraft (experimental, otherwise) with non-fixed vertical/horizontal stabilizers?

Many aircraft use an all-moving horizontal tail—with or without an elevator. Fighter aircraft (F-15, F-22, F/A-18, etc.) often use an all-moving tail without elevators. This gives superb control ...
Rob McDonald's user avatar
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14 votes

Does static longitudinal stability require download on the tail?

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 ...
Peter Kämpf's user avatar
14 votes
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Does static longitudinal stability require download on the tail?

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 ...
Koyovis's user avatar
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13 votes

What kind of horizontal stabilizer does a Boeing 737 have?

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 ...
Bianfable's user avatar
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13 votes

Why do big modern airplanes not use a T-tail configuration for the horizontal stabilizer?

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 ...
Jpe61's user avatar
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12 votes
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Does the wake from horizontal stabilizers merge with the wing wake?

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 ...
Peter Kämpf's user avatar
12 votes

What are the checklist items for a runaway stab trim on a B737 MAX 8 and MAX 9?

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 "...
Mike Sowsun's user avatar
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12 votes

Why do most aircraft with variable incidence tailplane have the possibility to trim much more degrees for nose up than for nose down?

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 ...
Peter Kämpf's user avatar
12 votes

Are there any known aircraft (experimental, otherwise) with non-fixed vertical/horizontal stabilizers?

In the light aircraft world, plenty of designs use non fixed horizontal tails, called, "stabilators" or "all flying tails" when they first came out. With unpowered controls, you ...
John K's user avatar
  • 132k
11 votes

Is it possible to balance a tail heavy plane with a vertical prop on its tail?

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 ...
Peter Kämpf's user avatar
9 votes

Why would a stretch variant need a larger horizontal stabilizer?

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 ...
DeltaLima's user avatar
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8 votes
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What is the angle of attack of horizontal stabilizer?

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, ...
Peter Kämpf's user avatar
8 votes

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

Simple answer: To provide enough static stability and a wider center of gravity range. The lift on the tail will become negative if more stability is desired than what is achievable with no load on ...
Peter Kämpf's user avatar
8 votes
Accepted

Why would a stretch variant need a larger horizontal stabilizer?

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 ...
jwzumwalt's user avatar
  • 11.5k
8 votes

What is the horizontal stabilizer failure procedure?

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 ...
John K's user avatar
  • 132k
8 votes
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Do horizontal stabilisers provide any lift?

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 ...
Bronco6363's user avatar
8 votes

Why does the MCAS use the horizontal stabiliser rather than the elevators?

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 ...
Koyovis's user avatar
  • 61.8k
8 votes

Why is a blunt trailing edge a better stabilizer at hypersonic speeds?

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 ...
Peter Kämpf's user avatar
8 votes
Accepted

Why do many aircraft have both all-moving tailplanes and elevators?

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 ...
Jan Hudec's user avatar
  • 56.4k
8 votes
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How does a tailplane provide downforce if it has the same AoA as the main wing?

For a stable configuration the incidence of the wing is normally higher than that of the tail. Also, the wing has more camber, so its zero-lift angle of attack is lower. Even at the same incidence the ...
Peter Kämpf's user avatar
8 votes

Are there any known aircraft (experimental, otherwise) with non-fixed vertical/horizontal stabilizers?

I think fully-flying control surfaces are too common to merit a mention. Especially for supersonic airplanes they are de rigeur. But there is one design which had a variable-sweep control surface: The ...
Peter Kämpf's user avatar

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