What is a good explination of trim when reffering to flying a plane?

Question

I have had one lesson and as i remember, the trim wheel was used to ............ sort of take the pressure from the yoke during a climb so that, once "properly trimmed" you could let go of the yoke and the plane would still climb.

If that is a correct recollection from m lesson 6 odd years ago, how does that work? What actually happens?

Answer 1

Some airplanes have such light control forces that they don't have a flight adjustable trim tab.

The tab is there to reduce the control forces so you can concentrate on flying the airplane without wearing yourself out against the trim forces.

Changes in power setting, and speed will change the trim forces you feel in the controls; so you trim the forces out if you're going to maintain the new flight condition.  So also will changes in the aircraft C.G.  As the fuel burns off the trim will need to be adjusted.  

In light aircraft you can put the controls out of trim by moving one foot or one arm forward or aft by six inches or a foot.  I flew cross country with my wife in a 182 several years ago and couldn't figure out why the airplane wouldn't stay trimmed until I noticed that it went out of trim every time my wife moved an arm or leg.  After that I was able to maintain altitude quite exactly without touching the yoke by countering every move of my wife with an opposite move of my own.

Answer 2

Well Friend,

Here is the SIMPLEST explanation.

In flight, an airplane is subjected to a variety of aerodynamic forces. Some try to pitch the nose up and some try to pitch the nose down.

Now, depending on whether your airplane tends to pitch up or down in flight, you cannot keep holding the joystick back or pushing it forward to maintain straight and level flight for the entire flight.

This is where trim comes in.

THINK OF TRIM AS AN IMAGINARY HAND THAT HOLDS THE AIRPLANE IN THE DESIRED ATTITUDE, WHILE ELIMINATING THE PRESSURE YOU APPLY ON THE FLIGHT YOKE / JOYSTICK.

That is, say, if your airplane tends to pitch down, you pull back on the flight yoke to maintain your desired pitch. Now, you use your pitch trim tab to apply some nose - up trim. Then you release the pressure on the joystick and watch for any deviations from your intended flight attitude. You may have to repeat this process several times before your aircraft is properly trimmed. Same goes if your airplane tends to pitch up. It takes practice before you develop an instinctive feel about the amount of trim you need to hold a specific flight attitude in your airplane.

I prefer to use the VERTICAL SPEED INDICATOR (VSI) needle as a pitch trim reference , since it is very sensitive. Simply, if the needle goes clockwise, you are climbing; and if the needle goes anti - clockwise, you are descending.

Now if you intend to fly straight and level, in the simplest possible terms, it boils down to keeping the VSI needle in the middle.

If you were to climb (or make any changes to flight attitude) , remember this rule of thumb:

ATTITUDE - POWER - TRIM

This means, select your desired flight ATTITUDE, apply appropriate POWER, and TRIM for this attitude.

Many airplanes have trim for bank control, which is sometimes necessary when the wing's fuel load is unbalanced or you have heavier people sitting on one side of your airplane.

Anyways, no matter how well your aircraft is trimmed, it will OSCILLATE up or down slightly, varying it's altitude by a few hundred meters. Periodic adjustments (MINOR) are required

Hope this helps.

God Bless

Answer 3

Trim is actually set differently at different times. Trim can be used as you mention to set a rate of climb or slow descent on landing. Primarily however, trim is used to set the plane into equilibrium at cruise. Once cruising altitiude is reached, the trim is adjusted so that constant control input is not necessary in order for the plane to remain more or less straight and level neither gaining nor losing altitude (pitch). The trim you refer to here is of course elevator trim. Some aircraft also have rudder trim as mine does so to adjust yaw, particularly helpful when cruising with a cross wind. Some also may have aileron trim to help set roll stability.

Answer 4

Okay. I can't tell you the whole mechanical process, but I know that what you said is true. If you are on a very long flight and are at the correct altitude, you don't always want your hand on the joystick. So, you let go and if the plane starts gaining altitude, you turn the k**b down untilit flys straight. It just adjusts a couple of small flaps on the tail wing up or down, like the elevators on the main wings. Hope this helped!

Answer 5

The trim wheel adjusts the elevators(the horizontal flaps at the rear of the plane)  At take-off you adjust the trim for gaining altitude, for level flight go back to 0 for descent you go to neg numbers.  If not properly adjusted, the plane could go into a stall or a dive.  A few yrs back there was a plane crashed outside of Houston due to not adjusting the trim after take-off, the plane stalled out and crashed.  Killed the people on board.

Answer 6

Trim compensates for small deviations in flight caused by outside influences. Each panel is equipped with a "trim tab". This tab "flys" it's corresponding panel. If for example if the aircraft tends to roll in level flight then the aileron trim is adjusted,the tab moves the opposite direction of the unwanted roll moving the aileron in the direction of the unwanted roll to bring the aircraft level again.  Roll,pitch and yaw can all be fine tuned this way. Crosswind can be compensated for using the trim system to lighten the load on the "stick" especially on long flights. The auto-pilot system on many aircraft are a function of the trim system. SAS or stability augmentation system is a computer controlled trim system to compensated for rapidly changing crosswind conditions using the aircraft gyroscopes,correction is almost instant. The control panels are as follows,ailerons control roll,they are on the wings,elevators are on the horizontal stabilizer and control pitch,the rudder is on the vertical stabilizer and control yaw. Of course we could get into other types of control systems like ruddevators or elevons,slats and slots or attenuators, but, that is another chapter.

Answer 7

You are right about the basics.  You want to trim the pressure out so you can let go and it won't change much.  There is another angle to explain it: an airplane will always seek the speed for which it's trimmed.  If you vary the power the nose attitude will change to seek the speed it's trimmed for.  

I have a story about trim: once I did a flight from Portland OR to Novato CA.  It was a night flight in winter.  As I attempted to level off the trim would not move; it was FROZEN.  That was a very uncomfortable situation for about 3 hours in a Piper Saratoga.  On descent the trim freed up as I went down through the freezing level.  I didn't tell anyone cause I didn't think they would believe me. You never forget things like that.