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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 ...
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30 votes
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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 ...
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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'...
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22 votes
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Why don't we use elevator trim as the primary flight control?

Proper trim control technique involves exerting control pressure to attain the desired attitude then using the trim to alleviate the requirement of holding that pressure. There can be a temptation for ...
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22 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 ...
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20 votes
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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 ...
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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 ...
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19 votes
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What is the relation between trim setting and constant airspeed?

Your friend is right. Elevator trim isn't setting a pitch, it is compensating for control forces on the elevator, which vary with speed. If you are trimmed for level flight at 100 kias and reduce ...
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19 votes
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Why couldn't Air Moorea Flight 1121 use pitch trim to land safely?

All quotes in this answer are from the English translation of the BEA accident report. The elevator cable broke at "an altitude estimated at between three and four hundred feet",(p. 7) and there were ...
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  • 6,004
16 votes
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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 ...
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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 ...
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13 votes

What are the reasons to evolve from trim tabs to moving the entire surface (e.g. stabilizer)?

Trim is used to zero the stick forces at the desired flight condition, and with the small, slow early airplanes, an adjustable spring somewhere along the control cables would do. When speed increased, ...
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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 ...
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12 votes
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Can the design for neutral stability reduce trim drag?

Terminology first: Trim drag is the drag component added by adjusting the incidence of the horizontal tail rsp. the deflection angle of the elevator for trim. The increased parasitic drag of a larger ...
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12 votes
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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 ...
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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 ...
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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 ...
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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 ...
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11 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 ...
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11 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 ...
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11 votes
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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 ...
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  • 104k
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, ...
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  • 54.1k
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 ...
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9 votes
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How does trim work on an A320?

The faster an aircraft is, the wider range of elevator deflections it needs. And so do aircraft with large change of weight (amount of fuel used) during flight. However larger elevator deflection ...
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9 votes
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What is trimming the fuel tank?

Just like normal trimming. However trim the fuel tank use aft fuel tank to achieve the trimming effect. Fuel is pumped between main tank and aft tank to shift CG around to a desire position during ...
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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 ...
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9 votes
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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 ...
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8 votes

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

The main reason for having trim is to modify the forces felt by the pilot to relieve strain, or as you say, 'trim away' the constant forces. There are various reason for not using the trim as the ...
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8 votes
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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 ...
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