Questions tagged [trim]

Trim tabs are small surfaces connected to the trailing edge of a larger control surface on a boat or aircraft, used to control the trim of the controls, i.e. to counteract hydro- or aerodynamic forces and stabilise the boat or aircraft in a particular desired attitude without the need for the operator to constantly apply a control force. This is done by adjusting the angle of the tab relative to the larger surface.

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1answer
1k views

How do A320 pilots trim?

So, I am very familiar with the 737NG, and there is a trim switch on the yoke for vertical trim. However, I can't seem to locate this trim switch in the A320. Is there a trim switch on the joystick in ...
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4answers
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Does “trimmed for current speed” mean that the plane will do whatever to maintain the current airspeed?

If I understand right, when you are trimmed for current speed, let’s say 290 KTAS, does that mean if airspeed increases to 295, the plane will pitch up to slow it back down? And vice versa for the ...
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3answers
108 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 ...
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1answer
155 views

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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1answer
120 views

Is fuel in trim tank usable?

Some aircraft (A380, Concorde,...) are equipped with a trim tank in the tail. Transferring fuel from or to this tank help controlling the CG. This feature can only be achieved if there is fuel to ...
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1answer
253 views

Did the pilots 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? At the speed the crews eventually hit, can it be said ...
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What is the white pattern on trim wheel for?

On a A320, there are white patterns spread regularly on the trim wheel (highlighted on the right of the picture). First I though it was to have visual feedback about THS (trimable horizontal plane) ...
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1answer
229 views

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 ...
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How does the A350 variable camber system decrease drag?

Just curious how the A350 reduces drag/fuel burn by extending the flaps ever so slightly during cruise. Everything I've read about extending flaps says that extending them pushes the centre of ...
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5answers
279 views

Why does instability in pitch lower trim drag for an aircraft with a tail?

I have a hard time figuring out why a longitudinally unstable aircraft has a lower trim drag. This seems to be a thing especially in fighter aircraft, so does it have to do anything with supersonic ...
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1answer
802 views

When was the Speed Trim System implemented on the Boeing 737?

The Speed Trim System (STS) is a speed stability augmentation system designed to improve flight characteristics during operations with a low gross weight, aft center of gravity and high thrust when ...
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1answer
660 views

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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2answers
584 views

What is the THS deflection speed?

Let's restrict this question to best sellers airliners (A320 and B737). On this aircrafts, the THS is used for pitch trim. The speed requirements may not be has intense as for elevator as it control ...
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2answers
669 views

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 ...
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1answer
798 views

What is the trim wheel behavior on the A320 family?

The Trim Wheel in the A320s usually is moving by itself, representing the current stabilizer position (or rather command). Before takeoff I believe it is set by hand to set the takeoff trim. During ...
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436 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 ...
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538 views

What does 'in-trim speed' mean with respect to Boeing 737 mis-trimming correction?

This question was prompted by discussions of the recent Boeing 737 MAX crashes, but it is not specifically about that variant. In Boeing's 737 NG Flight Crew Training Manual, in Chapter 8 (Non-Normal ...
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1answer
559 views

Why does the 737 auto-land trim up at around 400 feet RA?

From the 737NG FCOM: 400 Feet Radio Altitude The stabilizer is automatically trimmed an additional amount nose up. If the A/Ps subsequently disengage, forward control column force may be ...
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When is aileron trim used?

There is an aileron trimmer in some Boeings. When and why should it be used? P.S. I'm not a pilot, can you answer with less smart words?
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What does “out of trim” mean?

Our flight was delayed from takeoff because the captain reported it to be "out of trim". What does this mean?
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0answers
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What are stick position stability and stick force stability?

What are stick position stability and stick force stability? What are the difference between them? How will changing trim of an aircraft affect them?
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2answers
565 views

What happens aerodynamically when we trim an aircraft?

I'm trying to understand stability & control. Please correct me if I'm mistaken. An aircraft will have longitudinal stability if the aerodynamic center (AC) is behind the center of gravity (CG). ...
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1answer
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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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1answer
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Why don't the A380 and A350 have trim wheels?

(wikimedia.org) A350 thrust levers without the flanking trim wheels. Why don't the Airbus A380 and A350 have trim wheels? On the other fly-by-wire Airbus aircraft the trim wheels are there for ...
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Why do many light aircraft have a trim tab on one side of the elevator only?

Most light GA aircraft, like this C172, have pitch trim tabs on one side of the elevator only. Why not on both? Doesn't the asymmetry add inefficiency in the form of a slight rolling moment?
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Differenciate- the motion of “Nose-up trim” and “Nose-down trim” [closed]

I wanted to understand a part in ‘Take Off” where the study starts to explain “… the airspeed for best rate of Climb.” I am a little confused about the (how to) of pushing the wheel forward to relieve ...
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1answer
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Do I need a trim tab system on my twin tail?

I plan on building a single engine H-tail aircraft with retractable landing gear, removable wings for transportation, and either split flaps or plain. My only problem is, do I need a trim tab system ...
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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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Does static longitudinal stability require download on the tail?

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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2answers
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What exactly is trim? [duplicate]

Although I have a rough idea of what it is... In my mind from growing up watching hundreds of hours of Seconds from Disaster / Air Crash Investigation, trimming an aircraft is turning a dial that ...
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1answer
531 views

Do helicopters have automatic tail rotor compensation for anti-spin?

Helicopter pilots need to push on the pedals constantly to compensate for the main rotor torque, so that the helicopter does not start an unintended spin. But it would be annoying to indefinetly put ...
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1answer
266 views

When was trim on airplanes used for the first time?

I would like to know when trim control was set for the first time on airplanes.. thank you!
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1answer
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What does “redatum” means?

I was doing a question about a fully hydraulic elevator and it's position in relation to the trimmable horizontal stabiliser and the explanation of the answer contained the word "redatum". What does ...
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How to trim in level flight when speed increases?

What is required to happen to control surfaces and trim tabs to remain trimmed in straight and level flight, as speed increases? (for a GA propelled aircraft) My manual tells me that the elevator ...
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4answers
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Is a monobloc variable incidence wing viable (updated)?

Could this be a viable way to control roll on an aerobatic airplane, using some sort of tab to control a monobloc variable incidence wing? Both wings are mechanically linked together in order to only ...
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1answer
843 views

Why does automatic trim exist only in the pitch axis?

Why does automatic trim exist only in the pitch axis? For example, a flight computer can hold the current pitch automatically when engine thrust is applied. Why automatic trim not lies in roll and ...
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1answer
473 views

What was the Trim Problem on the Brabazon's First Flight?

In this video, starting at 18:15, the copilot on the Bristol Brabazon's first flight recounts that the aircraft became airborne a little sooner than its pilots expected, and that despite the captain ...
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How do pilots adjust trim on the B777, where the control forces are simulated?

I know that pilots of small airplanes (e.g. Cessna 172) use force to trim, i.e. they hold the required attitude using the yoke, then trim the aircraft until no force is required to hold the yoke in ...
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1answer
558 views

How much do aileron on a commercial airliner move for manoeuvring and trim?

I recently flew on an MD88 and had a good view of the aircraft's wing from my seat (read: I sat right next to the toilet). During the flight I noticed a couple odd things about the ailerons on the ...
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8answers
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Why are airliners not inherently “speed stable”?

In a light aircraft, once the pilot has trimmed for a speed, the power controls the pitch (climb/descent rate). I don't know the technical name for this stability, so I chose "speed stable" for now. ...
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What exactly is a variable incidence tailplane?

I've been reading about it regarding trim changes and such, but I don't exactly know what a VIT is? Can someone explain that to me?
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Is it possible to land a commercial aircraft with an elevator trim stuck at a high degree?

I know this is not practical (considering there is normally not much use to use up to 30 degrees of elevator trim), but if you were on a Boeing 777 or 737, or similar, and the elevator trim was set ...
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How is a horizontal stabilizer attached to the fuselage and works as a trimmable Horizontal Tail as well?

I am trying to figure out how does the horizontal stab attached itself to the plane and moves up and down? Is the HS attached by the rear spar and to the fuselage?
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1answer
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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 ...
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2answers
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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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1answer
378 views

Are elevator trim tabs required for an aircraft equipped with movable horizontal stabilizer?

The Bombardier C-Series aircraft has a movable horizontal stabilizer. It also has Trim Up/Down (discrete) switches in the cockpit. Is the aircraft also equipped with trim tabs? If so, when pilot ...
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1answer
143 views

Does being out of trim affect drag?

If the aircraft is not trimmed correctly and either the pilot or autopilot is having to use constant pressure on the elevator does this increase drag?
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1answer
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What is an out-of-trim condition and how is it detected?

I am reviewing autopilot requirements which mention that whenever an aircraft's altitude changes as a result of air disturbance or an out of trim condition, the inertial sensors will detect this ...
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1answer
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How does pilot know when to trim when flying an aircraft that have fly by wire flight control computer [duplicate]

My understanding of trim (on non fly by wire aircrafts) is that when the pilot feels force on his column or side stick, he trims the aircraft (either up/down) until the forces on the stick or yoke are ...
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1answer
280 views

How does an elevator offload function works in fly by wire flight control systems? [duplicate]

In some fly by wire systems I found that there is no trim in the traditional sense. I believe it is because the forces that pilot feels on the stick are artificial. I was told that those fly by wire ...