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.
88
questions
4
votes
3
answers
646
views
Why does elevator trim hold a given airspeed? [duplicate]
I'm trying to understand a principle described in the book Stick and Rudder by Wolfgang Langewiesche between angle of attack and airspeed in relation to the elevator trim. He states that as angle of ...
- 297
2
votes
1
answer
228
views
Do the trim wheels on the Boeing 737NG move by themselves during the takeoff roll?
After the stab trim is set before take off, will it move by itself during the take off roll? If yes, why? Where can I find the reference?
- 21
5
votes
3
answers
1k
views
Could a trim system conceivably manipulate only primary surfaces?
Most airplanes' trim systems manipulate a tab associated with a primary surface. For example, a pitch trim tab (secondary surface) is attached to the elevators (primary surface) and will change the ...
- 1,657
5
votes
2
answers
880
views
Do aircraft have backup systems to trim when they don't have trim wheels?
What happens if the motor that trims the elevator of an airplane fails and there are no trim wheels in the cockpit (like in the Boeing 747). Is there a backup system or hidden trim wheels?
- 153
0
votes
2
answers
1k
views
Could the pilots really not trim manually to overcome MCAS, as shown in the Netflix Downfall documentary?
In the recent Netflix documentary, a claim is made that once MCAS activated, after several activations, the pilots physically could not trim the aircraft due to the speed and pitch.
Is this true? I ...
- 11.8k
4
votes
2
answers
294
views
Can I assume that aoa on horizontal stabilizers correspond to aoa of the main wing?
I am in the process of designing a small wing (Re ~ 50-100k) and am wondering if given (a) the Cm on the main wing is relatively small at low aoas, (b) the horizontal stabilizer will produce lift as ...
- 227
1
vote
2
answers
140
views
Trimmed unstable aircraft [duplicate]
I am wondering which conditions are possible and what they mean:
Aircraft is statically stable in pitch and there is a trim point (for a specific surface deflection)
--> So in this situation my ...
- 11
15
votes
3
answers
4k
views
Best way to correct for plane's natural tendency to turn left?
I am a new private pilot in training. I've only had about two hours of flight lessons so far, so I'm still quite new to this.
In a single engine, PA-28-181 Archer, I found that the plane has a natural ...
- 1,137
7
votes
6
answers
3k
views
Is a trimmed flight not always an unstable system?
As soon as I am flying in trimmed flight condition, my pitching moment around the center of gravity becomes zero. So my center of pressure has to be located in the center of gravity, so that there is ...
- 71
5
votes
1
answer
868
views
Why do most aircraft with variable incidence tailplane have the possibility to trim much more degrees for nose up than for nose down?
Probably the question will be a little bit confusing but I'll try my best to make it clear.
Due the position of the CP with respect of the AC, symmetrical airfoils don't produce pitching moments, but ...
- 51
6
votes
3
answers
3k
views
Why doesn’t the A320 have any provision for manual aileron trim?
To eliminate the need for pilots (human or automatic) to maintain continuous force on their aircrafts’ yoke/joystick and rudder pedals while flying, aircraft generally have some sort of trim mechanism ...
- 28k
3
votes
1
answer
1k
views
Why is the CG envelope wider when the aircraft is heavy?
I mean, the same aircraft, but empty or on MTOW. According to MAC, those limits are the same, but the indexes are different. So if I understand that correctly, the CG can be more forward when the ...
- 31
2
votes
2
answers
112
views
What happens without trimming a statically stable aircraft?
if I have a statically stable aircraft, it will always return to its neutral position. What happens now if I do not trim my aircraft? Will it move/osicallate around its neutral position and be ...
- 21
0
votes
2
answers
576
views
On large aircraft, why do flaperons not run the full length?
This is a 777 flaperon. It looks rather tiny, compared to the flap.
There have been air disasters where the airplane rolled uncontrollably for one reason or the other. It seems to me that a larger ...
- 3,524
1
vote
2
answers
361
views
Is there an advantage to combining trim function with yoke?
SUMMARY: What if the yoke didn't require constant pressure, as is the case with the current "trim" function?
In all cases that I know of, airplanes have had the yoke (which you need to apply ...
- 3,524
1
vote
3
answers
116
views
Power changes and trim forces. related to position of Center of Mass (CoG), or Center of Pressure?
Theoretically (and Actually) do power increases cause a pitching tendency (and a need to adjust pitch trim), because the thrust line is not aligned with the Center of pressure, or, as I understand it, ...
- 5,546
6
votes
2
answers
538
views
How did pilots maintain the Vomit Comet's parabolic trajectory?
How did the Vomit Comet maintain its free-fall trajectory? Careful trimming? Custom autopilot software? Or just good stick and rudder technique?
Wikipedia, citing references but without ...
- 10.5k
8
votes
1
answer
330
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
votes
4
answers
712
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?
- 31
3
votes
1
answer
3k
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 ...
- 28k
6
votes
4
answers
2k
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
votes
3
answers
9k
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 ...
2
votes
1
answer
321
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:
...
- 28k
2
votes
2
answers
86
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 ...
- 461
3
votes
1
answer
419
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 ...
- 2,484
6
votes
2
answers
7k
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 ...
- 1,258
8
votes
4
answers
750
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
votes
3
answers
376
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 ...
- 16.4k
2
votes
1
answer
1k
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 ...
- 53.5k
3
votes
1
answer
815
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 ...
- 16.4k
1
vote
1
answer
520
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
votes
2
answers
7k
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) ...
- 16.4k
3
votes
1
answer
2k
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 ...
- 33
11
votes
3
answers
3k
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 ...
- 151
2
votes
5
answers
956
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 ...
- 43
5
votes
1
answer
4k
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 ...
- 5,759
5
votes
1
answer
3k
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 ...
- 247
2
votes
2
answers
5k
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 ...
- 16.4k
1
vote
2
answers
383
views
Why is airspeed different in climbs and descents although the AoA doesn't change?
Here are the background facts:
This excercise has the objective to familiarise the student with the slow flight characteristics.
The steps are:
1)Establish straight and level, 90% RPM, 15 units AoA, ...
- 21
4
votes
2
answers
2k
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 ...
- 28k
8
votes
1
answer
2k
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 ...
- 3,932
6
votes
2
answers
2k
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 ...
- 163
2
votes
2
answers
2k
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 ...
- 1,348
7
votes
1
answer
1k
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 ...
user14897
1
vote
3
answers
7k
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?
- 123
14
votes
3
answers
5k
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?
- 141
4
votes
1
answer
4k
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?
- 195
4
votes
2
answers
2k
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). ...
- 149
5
votes
1
answer
3k
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 ...
- 153
8
votes
1
answer
7k
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 ...
user14897