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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8
votes
1answer
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 ...
3
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4answers
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?
3
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1answer
90 views

Why are the A300/310’s electric pitch trim switches inhibited with the autopilot engaged?

The A300/A310, like most other aircraft (except for some small general-aviation aircraft), has an adjustable-incidence-angle horizontal stabiliser, which is used to trim the aircraft in pitch (for ...
4
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4answers
1k views

What exactly happens when power is reduced in trimmed, straight and level flight?

I understand that trimming an aircraft at a particular airspeed e.g. 100kts will keep the aircraft flying at that airspeed (100kts) even if you were to e.g. Lower power. This is apparently ...
19
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3answers
5k views

Why does Boeing use a trim wheel in the 737 and not their other products?

Why does Boeing use a trim wheel in the 737 and not any other products? Is the trimmed state for the 737 just more important than in the 777? Or even 747? It gives the impression that a secondary ...
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0answers
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?
2
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1answer
88 views

Why are Category II ILS approaches prohibited in an E-Jet with inoperative pitch trim?

Part of the Pitch Trim Runaway checklist for the E-Jet family states that Category II ILS approaches are prohibited if neither pitch trim channel is available: If both pitch trim channels are failed: ...
2
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2answers
73 views

What is the Dimension of Equilibrium Space in Longitudinal Space?

Full untrimmed Flight Dynamics model of an Airplane is separated into two separate systems: Longitudinal and Lateral. When the untrimmed model in Longitudinal direction, which is six dimensional, is ...
3
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1answer
336 views

Why were trim tabs invented?

I understand the need for a trimming mechanism, but why use a secondary control surface placed on top of the first, when you could just adjust the resting position of the aileron/elevator/rudder ...
3
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2answers
2k 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 ...
7
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4answers
363 views

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 ...
5
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3answers
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 ...
2
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1answer
310 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 ...
3
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1answer
189 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 ...
1
vote
1answer
321 views

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 ...
17
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2answers
3k views

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) ...
3
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1answer
393 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 ...
11
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3answers
1k views

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 ...
2
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5answers
397 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 ...
5
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1answer
2k 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 ...
5
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1answer
1k 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 ...
2
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2answers
1k 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 ...
4
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2answers
927 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 problems ...
5
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1answer
1k 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 ...
5
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2answers
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 ...
2
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2answers
778 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 ...
6
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1answer
786 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 required to ...
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3answers
2k views

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?
14
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3answers
3k views

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?
3
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1answer
431 views

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
742 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). ...
5
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1answer
1k views

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 ...
6
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1answer
4k views

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 ...
18
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3answers
6k views

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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2answers
2k views

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 ...
1
vote
1answer
61 views

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 ...
5
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3answers
2k views

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 ...
11
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3answers
2k views

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.
6
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2answers
14k views

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 ...
0
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1answer
620 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 ...
5
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1answer
293 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!
3
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1answer
509 views

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". ...
6
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2answers
916 views

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 ...
9
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4answers
1k views

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 ...
5
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1answer
1k 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 ...
10
votes
1answer
493 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 ...
6
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3answers
7k views

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 ...
1
vote
1answer
618 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 ...
10
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8answers
2k views

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. ...
5
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2answers
5k views

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?