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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11
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3answers
312 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
187 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 ...
2
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1answer
118 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 ...
3
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1answer
224 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
105 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
491 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 ...
5
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1answer
448 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
317 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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2answers
248 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 ...
4
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1answer
447 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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3answers
729 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?
13
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3answers
2k 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?
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0answers
164 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?
4
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2answers
435 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
816 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
2k 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
4k 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
1k 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
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1answer
59 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 ...
4
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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 ...
8
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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.
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2answers
10k 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
489 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
198 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
387 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". What does ...
6
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2answers
718 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 ...
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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 ...
3
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1answer
714 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
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1answer
446 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
5k 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 ...
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1answer
511 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
4k 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?
11
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2answers
2k views

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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3answers
2k views

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?
4
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1answer
741 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 ...
14
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2answers
1k views

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 ...
6
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1answer
355 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 ...
9
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1answer
135 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?
4
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1answer
3k views

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
989 views

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 ...
0
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1answer
244 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 ...
15
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3answers
4k views

Why don't we use elevator trim as the primary flight control?

One thing you're repeatedly told as a student pilot is to fly with the stick (or yoke), not the trimmer. To select a new pitch attitude, fly to it with the stick, wait for the aircraft to settle, and ...
13
votes
1answer
2k views

What is the relation between trim setting and constant airspeed?

I'm having an argument regarding elevator trim. According to a book my friend showed me, trim is for constant airspeed. So, let's say we are flying level at 100 kts with 2300 RPM and it's trimmed. My ...
3
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2answers
1k views

How is an aircraft with a stabilator trimmed?

Many supersonic fighters have a stabilator to control pitch. My question arises when I cannot see any trim-tab on the stabilisator (e.g. on the F-16 or on the F-22). Other means to trim an aircraft ...
4
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1answer
5k views

How does auto-trim work on fly-by-wire aircraft?

As I understand, you trim to reduce the effort needed to maintain the stick in the right position. Thus, you may reach steady flight before moving the trimming wheel. In fly-by-wire aircraft (to fix ...
8
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1answer
3k views

What is the working principle of trim tabs on the elevators?

Trim tabs are used on the tail's horizontal elevators to adjust its neutral position. What is the working principle behind this? How does this affect the sensitivity (the feel) of the pitch to the ...
10
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2answers
9k views

How does trim work on an A320?

In the very interesting answer from Jan Hudec to a question about the various flight control computers on Airbus planes, two different means to trim the aircraft are mentioned: The stabiliser and the ...
7
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1answer
3k views

What is trimming the fuel tank?

In a recent news of a Airbus A400M crash, it has the following line - ...
7
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1answer
1k views

Can the design for neutral stability reduce trim drag?

If one were to design an aircraft to have neutral longitudinal stability would this reduce the required horizontal stabiliser surface and hence trim drag?