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trimming the elevator

Old 03-27-2006, 11:47 PM
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luisfc1972
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Default trimming the elevator

what exactly are you looking for when trimming the elevator? dont i just make sure the elevator is even with the front wings before i attach it to the pushrods? i read somewhere that a properly trimmed beginners plane will right itself when you let go of the controls. i assume they are referring to both the rudder and elevator.
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Old 03-28-2006, 12:59 AM
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Sky Sharkster
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Default Trimming Control Surfaces

Hi Luisfc1972, welcome to Wattflyer! The general rule for setting up control surfaces is to align them with the flattest part of the fixed component, in other words, lay a ruler across the stabilizer and the elevator should be even (flat on the ruler) at "Netural". For the rudder, a straight edge aligned with the fin is the "netural" line for the rudder. For flat bottom wings with ailerons, a straight-edge placed along the bottom of the wing should align the ailerons at "netural". Do not align the elevator with the wing unless you're flying fully-aerobatic models or supersonic jets! Trainers and most sport-type models have a built-in angle (difference of angles) between the wing and stabilizer/elevator. This angle is called Decalage, angle of incidence or longitudinal Dihedral. It is there for a reason, it allows the wing to fly at the proper angle (angle of attack) to provide the correct amount of lift with the least drag. So until you've flown the model, go by the manufacturers recommendation for settings. Later you may want to shim the leading or trailing edge of the wing to change a flight characteristic, like making it more maneuverable, faster, slower, etc.
Good Luck!
Ron
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Old 03-28-2006, 03:13 AM
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Hi Sky Sharkster,

I also have a question about this. I have a PZ P-51 that I have yet to maiden. I've been flying a J-3 to get used to flying again. When aligning the elevator and ailerons on the P-51, since they are tapered, is it correct that they should be level with the top or bottom of the wing or should they follow the taper of the wing and horizontal stab? I hope that was clear.

Tom
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Old 03-28-2006, 03:27 AM
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luisfc1972
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thanks sharkster. i dont think i was clear though. i mean once up in the air i see how trimming the rudder to make the plane to fly straight makes sense. but once in the air what am i looking for to trim the elevator? why even trim the elevator in the air? just pull up or down if you have to makes sense to me.
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Old 03-28-2006, 03:39 AM
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Hi Luisfc,

Don't mean to jump in the middle here but if I understand your question, when the elevator is trimmed correctly in flight, the plane should fly level without holding the stick up or down. This also applies to the rudder. This will change as you increase or decrease throttle. Once you find the speed you like to cruise at, get several mistakes high and let go of the sticks to see if it flys straight. If it wants to nose down, add a little up trim and the opposite if it wants to climb. Do the same for the rudder so it flys straight. You are correct that most trainers will correct themselves if you let go of the sticks provided it is trimmed out correctly and you are high enough.

You never want to run out of airspeed, altitude and ideas at the same time. Hope this helps.

Tom
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Old 03-28-2006, 10:34 AM
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Default Elevator Setting

To Luisfc, guess I didn't understand your question. By flight trimming- as opposed to static trimming, which is what I explained in my first post- you correct any tendency for the plane to climb or dive at normal flight speeds. Tom is right, this will change with different speeds, but for now, let's say we have a normal flight airspeed, not too fast to control, not so slow the plane is staggering around, ready to stall. We'll call that speed "cruise" speed, OK? Once the plane is flying, we usually cut the throttle back, it takes more power to take-off, then we ease the throttle back until it maintains a level flight attitude (angle). At this speed, if you take your hand off the stick, the plane should not pitch (climb) up nor should it dive. It should maintain altitude. If it doesn't, gently move the elevator trim control until it flys level. You don't want to be correcting an out-of-trim model with the control stick, there are way too many other things to worry about just flying the plane! Use the trims, that's what they're for. Full-size aircraft have'em, they are an important part of the aircraft trimming process. Same for the rudder; If the model constantly diverges (turns) one way or the other, use the rudder trim to correct it. It's a little bit of a balancing act, finding the correct cruise speed and elevator setting to achieve level flight, it helps to have an experienced pilot with you.
If your radio has a "model memory" function, be sure you enter that model name, so the radio will remember the trim settings. If the radio doesn't have "memory" and you fly more than one model on the same radio, the best thing to do is put the trims on the model! In other words, after you fly and trim the model, say it needs two "clicks" of right rudder and one "click" of down elevator to fly straight and level. OK? Now you aren't going to remember every setting and if you fly a different model with that same transmitter, likely you'll change the trims for the next model. What happens when you go back and fly the first model? Trims are set different, you crash! At the end of the first flight, look at your trim settings. Unclip the rudder clevis from the control horn and put the equivalent of two clicks of right into the model. Same with the elevator. Now the model should fly straight and level with the transmitter trims set at netural because you've trimmed the model (they're permanently set into the aircraft) not the radio. Hope this is clear, it's a little hard to explain.
Hi Tom, that's a good question about the tapered control surfaces, with a flat surface it's pretty easy. The neutral setting should follow the curve of the airfoil. Another way to explain it; If you could see a side view of the wing (or tail) airfoil, like when the wing is made in two pieces and needs to be glued together in the middle (usually with dihedral added) you can look at the wing center airfoil (root airfoil). Imagine a line that splits the airfoil in half vertically, between the top curve (upper camber) and the bottom surface (lower camber). This line is called the "mean camber line" and is an important part of airfoil analysis. If you extend that line through the control surface (a line through the middle of the surface) that's the neutral setting for the surface. Follow the mean camber line. Hope this helps!
Ron
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Old 03-28-2006, 01:07 PM
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Thanks Ron,

You explained it perfectly and that's how I have done the static trim.

Thanks again.

Tom
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Old 03-29-2006, 12:53 AM
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Default Setting Control Surfaces

Hi Tom, thanks for the kind words, glad I could help, Good luck with the P-51!!
Ron
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