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35 votes

What is the white pattern on trim wheel for?

The white marks make it easy to see if the trim wheel is moving, which would be tricky if it was entirely black. But wouldn't the pilot always know if they was spinning the trim wheel? Remember that ...
60levelchange's user avatar
30 votes
Accepted

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

Trim pitch "wheels" as you describe date back to the time when turning that wheel actually pulled on steel cables that were connected to the hinge mechanism for the control surface itself. This ...
niels nielsen's user avatar
24 votes

What does "out of trim" mean?

In this context, it would mean the aircraft is loaded in such a way that the Center of Gravity is too far forward or aft. That's actually not the way we usually use the word "trim" in aviation but it'...
quiet flyer's user avatar
  • 22.2k
23 votes

Why do many light aircraft have a trim tab on one side of the elevator only?

A small propeller driven plane like that will have a bit of adverse yaw, rolling to the left, because of propeller effects (P-Factor, slipstream, torque, etc) The trim tab's effect is minimal because ...
abelenky's user avatar
  • 30.6k
20 votes
Accepted

Is trimming for constant speed equal to trimming for constant angle of attack?

Short answer: Yes Generally you are right. You are trimming the aircraft for a point on its polar, and that point is reached at a specific angle of attack. You say yourself we should neglect ...
Peter Kämpf's user avatar
20 votes

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

While the other answers are correct they are missing a key point: Because it was certified that way When an aircraft is certified with particular equipment, changing that can be difficult and may ...
Dave's user avatar
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17 votes
Accepted

Best way to correct for plane's natural tendency to turn left?

Always use rudder to keep the slip skid ball centered. Except when taking off and landing in crosswinds, that's all you ever do with it. If the airplane rolls with the slip/skid ball centered, that's ...
John K's user avatar
  • 130k
15 votes

Is a trimmed flight not always an unstable system?

But assume, there comes a wind gust, and the angle of attack will increase. This causes the center of pressure to move forward in front of my gravity location. So the aircraft will become instable ...
quiet flyer's user avatar
  • 22.2k
14 votes

Does static longitudinal stability require download on the tail?

For the impatient reader: The answer is no. Let me explain it in detail. For this, it is helpful to simplify things as much as possible and then add the complications step by step so I can explain ...
Peter Kämpf's user avatar
14 votes
Accepted

Does static longitudinal stability require download on the tail?

No, static longitudinal stability does not necessarily imply a download on the tail. Static longitudinal stability requires that the Centre of Gravity is in front of the Centre of Lift, indicated as ...
Koyovis's user avatar
  • 61.6k
14 votes
Accepted

Could a trim system conceivably manipulate only primary surfaces?

I assume by "primary surface" you mean the elevator, not the stabilizer, so we are not talking about moveable stabilizers. Most gliders with stabilzer/elevators, and a lot of homebuilts and ...
John K's user avatar
  • 130k
13 votes

Why do many light aircraft have a trim tab on one side of the elevator only?

The reason the trim is only on one side is cost saving; one trim tab is cheaper to build and simpler (therefore cheaper) to maintain. As for the rolling motion yes, the trim tab will cause a slight ...
GdD's user avatar
  • 53.3k
12 votes

Why is the CG envelope wider when the aircraft is heavy?

So if I understand that correctly the CG can be more forward when the aircarft is heavy. Not really, although I guess you could say the index can move "forward" because of the way the form ...
Terry's user avatar
  • 39.1k
12 votes

Why do most aircraft with variable incidence tailplane have the possibility to trim much more degrees for nose up than for nose down?

The wide negative trim range is for operation with lowered flaps. Fowler flaps shift the center of lift backwards both by adding wing area at the trailing edge and by increasing camber. Both effects ...
Peter Kämpf's user avatar
12 votes

Is a trimmed flight not always an unstable system?

I think you misunderstand how it works, and how you would respond to changes in wind. Increases in airspeed impact all flight surfaces, including the elevator, so a change in airspeed due to a gust ...
GdD's user avatar
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12 votes
Accepted

Could the pilots really not trim manually to overcome MCAS, as shown in the Netflix Downfall documentary?

The problem was they could not manually trim the a/c without performing the Boeing "offload the jack" procedure developed for the 737, which requires altitude to perform because you are ...
John K's user avatar
  • 130k
11 votes

Is a monobloc variable incidence wing viable (updated)?

Yes it is a viable way for roll control - aerodynamically that is. The mechanism you describe is a proper servo tab, where the aeroforces on the tab are fed back, and the tab acts like a lever on the ...
Koyovis's user avatar
  • 61.6k
10 votes

Why are airliners not inherently "speed stable"?

Light aircraft and transport aircraft behave exactly the same regarding trimming for speed. Trim is for angle of attack, but power affects that trim and phugoid oscillation occurs in speed and pitch, ...
Jan Hudec's user avatar
  • 56.2k
10 votes

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

The leading edge of the horizontal stab on jets is driven up and down for trim using a very large acme thread style screw jack. The Cessna 180/185 family and the Piper Cub/Super Cub/Pawnee family ...
John K's user avatar
  • 130k
10 votes
Accepted

Why doesn’t the A320 have any provision for manual aileron trim?

The normal flight law behaves as if it auto-trims the aileron, but there is no actual trim involved. The computer simply derives the desired deflection of ailerons using the pilot input and feedback ...
Jan Hudec's user avatar
  • 56.2k
9 votes

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

This makes sense and is approximately what happens if you reduce thrust during trimmed straight and level flight. The aircraft will go though a series of damped oscillations, called 'phugoid' until it ...
DeltaLima's user avatar
  • 83.1k
8 votes

Why do tailplanes provide down force, if not for longitudinal static stability?

Simple answer: To provide enough static stability and a wider center of gravity range. The lift on the tail will become negative if more stability is desired than what is achievable with no load on ...
Peter Kämpf's user avatar
8 votes
Accepted

When is aileron trim used?

Given your request to "answer with less smart words," it's hard to know what knowledge can be assumed, but I'll give it a try. Let's say you're hand-flying the airplane straight and level, and you ...
Terry's user avatar
  • 39.1k
8 votes

Why doesn’t the A320 have any provision for manual aileron trim?

There is no need for aileron trim because the flight control system keeps the bank angle constant if there is no lateral input on the side stick. The pilots use the side stick to roll the aircraft to ...
DeltaLima's user avatar
  • 83.1k
8 votes

Best way to correct for plane's natural tendency to turn left?

You really should talk to your instructor about this. Compensating for the inherent turning tendencies of propeller planes is a pretty basic skill that you should learn fairly early in your training. ...
HiddenWindshield's user avatar
8 votes

Could a trim system conceivably manipulate only primary surfaces?

Yes. Gliders usually have a coil spring in the pitch linkage, and if the horizontal tail is of the fully flying type, this spring will affect the zero-force position of that surface. Changing the ...
Peter Kämpf's user avatar
7 votes
Accepted

Is a monobloc variable incidence wing viable (updated)?

When changing wing incidence for roll control, it is important to have equal but opposite deflections on both sides. Otherwise you will add load factors to the results of your roll inputs. If you have ...
Peter Kämpf's user avatar
7 votes

Why are airliners not inherently "speed stable"?

The reason that large aircraft are often not exactly speed stable is that the line of thrust does not go through the centre of gravity of the aircraft. A change in thrust setting will therefore cause ...
DeltaLima's user avatar
  • 83.1k

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