# Questions tagged [horizontal-stabilizer]

Questions about the surfaces that typically extend out from the left and right sides of an aircraft's tail, providing longitudinal stability and a place to mount the elevators.

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

Many aircraft - particularly large commercial airliners - have both an all-moving tailplane (horizontal stabiliser) and elevators. (They also have a small third moving element on the trailing edge of ...
1k views

### Is setting elevator to certain angle equal to trimming the horizontal stabilizer?

(I was trying to understand the longitudinal stability of aircraft and how it is related to elevator) If I pull the stick back by, say 2 inches, will it have the same affect as trimming the ...
97 views

### Does the yoke move when trimming a THS like it does when using elevator trim?

I would like a clarification from the operational point of view: Both the THS and elevator trim tab is used to remove pilot pressure on the yoke / stick. On the elevator trim similar to the C-172 the ...
4k views

### Why should the centre of mass be ahead of the centre of pressure?

Why is the centre of mass located ahead of the centre of pressure? And what would happen if centre of mass would be too close or too far away from the centre of pressure?
114 views

### Do horizontal stabiliser force direction change with CG variation for a given aircraft? [duplicate]

I am wondering about the direction in which horizontal stabilizer provide force. I know that it can provide either upforce or downforce. But I am wondering whether is it determined for a particular ...
143 views

### When was the first THS (Trimmable horizontal stabilizer) used and on what aircraft?

When was the first THS (Trimmable horizontal stabilizer) used and on what aircraft? Has any UL or GA trimmable stabilizer?
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### What is hinge moment?

What is hinge moment? Why in the process of calculating it we must calculate the coefficient of hinge in 2D? Why the distribution of airfoil thickness at 90%, 95%, and 99% of the line should be ...
2k views

After having encountered this meme too often for comfort, I ask myself today in order to have the possibility to explain the issue in detail.
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### Do horizontal stabilizers on airliners have varying angle of incidence in the span-wise direction (washout or negative twist)?

Reading this question and answers, I was wondering if modern airliners with cruciform tail have some noticalbe washout or negative twist along the horizontal stabilizer's span. During cruise, if wing'...
2k views

### Are there cases where a double horizontal stabilizer is useful?

I was watching Agents of Shield recently, and in it the team fly a plane that's claimed to be a modified C-17 Globemaster. It has two extra engines, rotary turrets, and, according to the wiki, a pair ...
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### What is the angle of attack of horizontal stabilizer?

It 'appears' that in most flights the horizontal stabilizer is set for positive angle of attack. So does this produce an 'up force' (lifting force) on tail thus making the aircraft nose-heavy? Or ...
51 views

### Can aerodynamic forces move the stabilizer by itself? [duplicate]

So if a plane is accelerating with nose down trim, and the electric trim motors are turned off by the crew, can the aerodynamic forces move the stabilizer and make the situation worse?
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### Did the First Officer of Ethiopian Flight 302 trim in the wrong direction? [closed]

Looking at the accident report of Ethiopian Airlines Flight 302, it says the cut out switches were used. But the manual trim moved from 2.3-2.1? My reasoning for asking this is because the timeframe ...
306 views

### Why is the angle of the horizontal stabilizer marked on the fuselage?

Why are the angles displayed on the fuselage? I understand having markings with depth on the hull of boats, but I don't understand the use case on a plane. Photo of the root of the trimmable ...
149 views

### Do aircraft fitted with both a trimmable horizontal stabilizer and a trim tab exist?

This question is restricted to trim on the pitch axis. Both trim tab and THS (trimmable horizontal stabiliser, a whole moving horizontal stabilizer whose movements are used as trim) are used to trim ...
342 views

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

Here is what I read about the X-15 spaceplane: The X-15 had a thick wedge tail to enable it to fly in a steady manner at hypersonic speeds.[14] This produced a significant amount of drag at lower ...
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### How much does the horizontal stabilizer on a 737 move for one unit of trim?

Inspired by this question, what exactly is the meaning of a stab trim unit? Is it exactly one degree of stabilizer movement? The 737 NG FCOMv2 (9.20.9 Flight Controls - System Description) only lists ...
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### What are the checklist items for a runaway stab trim on a B737 MAX 8 and MAX 9?

This is a follow up question to this question. This question is not directly related to the MCAS system in the new B737 MAX aircraft, instead, my question is about the checklist for a runaway stab ...
392 views

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

The Maneuvering Characteristics Augmentation System (MCAS), found, in two slightly-different variants, on the 737 MAX and KC-46, provides nose-down pitch inputs in certain very-high-angle-of-attack ...
79 views

### Why is the horizontal stabilizer of the Lazair swept back? [duplicate]

Why is the horizontal stabilizer of the Lazair swept back? I understand the hinged elevators are perpendicular to the fuselage, but the horizontal stabilizer is actually swept back.
399 views

### Documentation about “drag stabilized flying wings using non-reflex airfoils”?

What provides lift is the wing, but it is unstable without one stabilizer. Flying wings airfoils, or reflex airfoils, carry their stabilizer inside them, through a reversed camber of the trailing ...
137 views

### What airfoil is used for the horizontal stabilizer of a 737? Is it inverted?

I cannot find the airfoil of the Boeing 737 horizontal stabilizer or any typical tail airfoil of a civilian aircraft.
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### How the stabilizer cutout switch functionality has changed from Boeing 737 NG to 737 MAX?

The Boeing 737 NG has stabilizer trim cutout switches marked as MAIN ELECT (left) and AUTOPILOT (right). Turning off the right switch disables automatic stabilizer trim in autopilot mode and automatic ...
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### What are the maximum possible stabilizer and elevator deflections for the A320?

For research purposes I would like to know the maximum deflection angles (in both positive and negative direction) of the A320-200's stabilizer and elevator. I am trying to analyse what flight ...
365 views

### Why does not the lift produced by main wings create pitch moment?

Pitch moment is created by lift created by the horizontal stabilizers via the elevators. But then main wings also create lift, why does not this lift enough to create pitch moment?
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### What kind of horizontal stabilizer does a Boeing 737 have?

Does this plane have fixed horizontal stabilizers and elevators or has it been fixed with stabilators instead?
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### Why are cambered airfoils used for horizontal stabilizers in some designs?

From what I know, usually NACA9/12 or similar symmetrical airfoils are used for the tail. Still some aircrafts use highly cambered airfoils for elevators. What are some advantages and disadvantages ...
296 views

### Why does the Comet's horizontal stabilizer have so much dihedral?

The Comet's horizontal tail has a noticeably extreme amount of dihedral compared to that of, say, a 707: (Image by MilborneOne at Wikimedia Commons.) Note how the Comet's tail has about twice as ...
79 views

### Does the canard config have radically different controls than classic config?

Classic configuration is something like the A320: wings in the middle, horizontal stabilizers at the tail. Canard configuration is something like the Beechcraft Starship: wings at the back and ...
326 views

### Why donāt airliners use stabilizer movement to assist with large pitch control inputs?

Most large airliners not only have elevators for pitch control, but also moveable horizontal stabilizers. The elevators are used for primary pitch control, with the stabilizers being used to trim the ...
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### Why can't the 737 MAX's horizontal stabilizer autotrim be cut out by control yoke inputs?

According to this article, a horizontal stabilizer runaway on the 737 MAX, unlike with all other 737s, cannot be countered with yoke inputs: Older 737s had another way of addressing certain problems ...
201 views

### Is there a general approach for designing a Trimmable Horizontal Stabilizer?

What is the general design flow when designing a Trimmable Horizontal Stabilizer (THS) and the attached elevator? I assume you would dimension the max. positive/negative deflections of the THS to ...
634 views

### Why do the stabiliser trim wheels not move exactly in sync?

I've watched a few videos about the Boeing 737, and in particular because it's a bit of a current topic, about the stabiliser wheels in the cockpit. On some of these videos, which are often in ...
710 views

### Do horizontal stabilisers provide any lift?

Do jumbo and smaller airliners' horizontal stabilizers provide any lift? Apart from maintaining the aircraft's angle of attack, can they perform the dual function that includes adding some lift as ...
4k views

### Why does the DC-10's horizontal stabilizer have such a pronounced dihedral?

If you look at this picture, you'll see that the horizontal stabilizer has a very pronounced dihedral in comparison to the wings. Could somebody explain in a simple way why? I understand that a ...
600 views

### Why the Antonov AN-225 has negative dihedral wings combined with a positive dihedral horizontal stabilizer?

I know the reason why it has negative dihedral wings, but I do not really know why it is combined with a positive dihedral horizontal stabilzer, which are the benefits this configuration provides?
659 views

### Why aren't there any jets with horizontal-stabilizer-mounted engines?

Looking at the spectrum of where jet aircraft put their engines, there are examples of almost every place that could conceivably used to carry a jet engine: slung under the wings buried inside the ...
221 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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### How do the vortices affect the flow of the horizontal stabilizer upon leaving the wing?

Other than the downwash effect, what other factors that affect the flow to the horizontal stabilizer? such as Dynamic Pressure? Air Flow Disturbance?
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### Does the wake from horizontal stabilizers merge with the wing wake?

There is already a long series of questions about the downwash and tip vortexes with nice images, but I'm going to add another one... Large airliners (A380, B747-8) have horizontal stabilizers ...
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### Does the A320 Trimmable Horizontal Stabilizer automatically reset after landing?

Does the A320's Trimmable Horizontal Stabilizer (THS) automatically reset after landing? If so, is there any condition where it doesn't? And what about the rudder trim? I'm asking because I'm ...
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### What is the horizontal stabilizer failure procedure?

During the final flight of Alaska Airlines Flight 261: The CVR transcript reveals the pilots' continuous attempts for the duration of the dive to regain control of the aircraft. At one point, ...
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### Why did Concorde not have horizontal stabilizers?

The Concorde did not have horizontal stabilizers or elevators. As a result, the pilots have to move fuel around the aircraft to trim it up or down, as sluggish and hazardous move. Why did the design ...
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### Is trimming for constant speed equal to trimming for constant angle of attack?

My understanding of trim: When you say you have trimmed an aircraft for a constant speed, say 100 mph, you are actually trimming the horizontal stabilizer so that there are no forces on stick (or tail ...
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### Why would a stretch variant need a larger horizontal stabilizer?

Update and accept reason The reason for asking why would as opposed to why does is I was not aware of any previous [jetliner] stretch requiring a larger horizontal stabilizer. For example, all the DC-...
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### What is the sweep angle of the Boeing 787's horizontal stabilizers?

What is the sweep angle of the horizontal stabilizers on a Boeing 787 Dreamliner? Does it have to be equal to that of the wings, and how is it determined?
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### Why do tailplanes provide down force, if not for longitudinal static stability?

We can see that most conventional aircraft have their horizontal tail surfaces arranged to provide a down force. This question asks if that is required for static longitudinal stability, and the ...
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### Do airliners perform a dive maneuver to reduce altitude [duplicate]

DO airliners, jumbos included, like the Airbus A380 and Boeing 747 routinely perform dive (nose down) maneuvers to descend or do they rather reduce speed and descend with the nose up? If not, why not?