Real Aicraft - Trim wheel rotation limits?

[Guest seanw]

Hello all,Does anyone know how much rotational travel an actual aircraft trim wheel have, say in a cessna or a similar aircraft? In other words, how many turns or degrees can you turn it from neutral to nose-up trim, and from neutral to nose down trim before the trim wheel ACTUALLY STOPS SPINNING?And last but not least, how do you determine what the take-off trim setting is? provided it's not marked. (for example when flying the cessna in the simulator).ThanksSean W.

[Guest PeterK]

PeterK In the Mooney I took apart the trim wheel turned a threaded shaftthat went about 10 turns each way...this shaft pushed thetrim rod that went to the tail....This shaft also went toa indicator mounted on the nose wheel well..It was a steelcable that moved the indicator...Basically you rotated the wheel until the indicator went to the Takeoff position...In flight you then turned the wheel to the Up or down into position...Basically the same as in FS2002s cessnaor Baron... Last week I went up in a Cessna 152...during flight the trim wheel was rotated about 3 times up or down to get the controls to feel nutural and you turned it to a indicatedtake off position on the indicator on the dash..Trim on a simulator can done with a 10-20 turn 25K potThats what i use...Put in line with the elevator controlby building a 15pin breakout box before the game port... I Dont use USB but it would be the same thing you wouldjust splice in right off the control pot..Now ..how do you get an indication,,,You have to stiring itlike an old radio the pot has to feed some kind of indicator...like a older am/fm radio indicator but verticle...pete http://home.comcast.net/~fs-boneyard

[Guest seanw]

Hi Peter,Thanks for the detailed response.If I understood you correctly, you stated that on C152, you turned the trim wheel 3 times to neutralize the controls. So does it mean it can rotate more than 3 times (360 Deg. x3) from neutral to nose up and from neutral to nose down?Secondly, you stated that you were using a 10 ~20 turn pot. I assume that a wire wound type pot.Thanks again for the reply.Best Regards,Sean W.

[tigert]

>Hi Peter,>>Thanks for the detailed response.>>If I understood you correctly, you stated that on C152, you>turned the trim wheel 3 times to neutralize the controls. So>does it mean it can rotate more than 3 times (360 Deg. x3)>from neutral to nose up and from neutral to nose down?Make it rather turn more than too little, as it makes it more precise to trim to level flight.The "3 rotations" means you pull the wheel up or down 3 times, but since you only see a slice of the side, one "pull" probably rotates 1/4th of a turn or so.>Secondly, you stated that you were using a 10 ~20 turn pot. I>assume that a wire wound type pot.Potentiometers have one nasty issue: if you ever want to use the autopilot to hold altitude, that uses the trim also in FS. Now, if your trim is connected via a pot, the pot keeps it value, and if the pot has even a small "shaking" movement (due to wires getting interference or such) it will fight with the autopilot and resets the trim to whatever position the pot happens to be at, and the autopilot corrects and starts to trim back, until the pot "moves" again a tiny bit..IF you can use rotaries, use those for the trim. My setup uses FSBUS and I have a rotary controller as the trim, wired via keyboard events even, so that the trimwheel only does "trim up" or "trim down" commands. Then you can have an indicator gauge or something that shows the amount of trim you have and the takeoff position.This way you can also have the trim wheel rotate freely, and you can tune the sensitivity (how many turns from end to end) to fit your own taste and plane too.Hope this helps,Tuomas

[rickalty]

I dropped by tonight on the way home, and checked it. On a Cessna 172, it was four full turns from the physical stop at full down trim to the physical stop at full up trim. The takeoff position was 1 1/3 turn from full up.Rick

[Guest PeterK]

PeterK I guess when i said turn you would think 3X360 degree'sNo ...a turn is probably 1/3 to 1/2 a rotation...The mooney was 5X360 each way...so 10 turns sounds like alot too...the mooney wheel is is a 8 -10 inches in diameter aluminum wheelwhere the cessna is a plastic wheel which is about 5-6 inchesin diameter...more or less my mistake in explaining...SeanThe pot i belive is wire wound inside..it has a bit of a feelon the shaft as you turn it that the contacts are runningacross a wire wound coil...another way to track its positionis using some geared number displays that mount over the potshaft..I got some off a surplus Military panel....IM flying GA planes on the seat of my pants so i dont use the auto pilot ...I know that a 20K pot does nuturalizeout the upward or downward drift when using an analogjoystick....A real airplane the trim affects your feel on the stick..In fs2002 your more or less looking at the window outsideor the artificial horizon to know the trim issue...Pete http://home.comcast.net/~fs-boneyard

[Guest PeterK]

PeterK I looked in a 1959 172 at lunch...the trim was on the floorwith the indicator also...3 turns down 360 from Takeoff. 2 turnsfrom take off for Up...I made an over explination to sean about the trim wheel...A turn is about 1/3-1/2 not 360 on the wheel...pete

[Guest seanw]

Thanks for all the work and info. It helped out a lot. Now I have an idea on how to setup the trim wheel on the GA panel I am going to start building.THANKS AGAIN!APPRECIATE ALL YOUR HELP & FEEDBACK!Best regards.Sean W.

[tigert]

>A real airplane the trim affects your feel on the stick..>In fs2002 your more or less looking at the window outside>or the artificial horizon to know the trim issue...Well. Nothing stops us from making a mechanical trim that just adjusts the yoke centering position by moving the centering springs or bungee cord. Does not need to go to FS at all, just mount a mechanical trim position indicator that is connected to the centering adjustment mechanism.Anyone have good ideas for such a thing? :)Tuomas

[Guest Guyzer]

>IF you can use rotaries, use those for the trim. My setup uses>FSBUS and I have a rotary controller as the trim, wired via>keyboard events even, so that the trimwheel only does "trim>up" or "trim down" commands. Then you can have an indicator>gauge or something that shows the amount of trim you have and>the takeoff position.>>This way you can also have the trim wheel rotate freely, and>you can tune the sensitivity (how many turns from end to end)>to fit your own taste and plane too.>>Hope this helps,>>Tuomas>Hello Tuomas. Thanks for your explanation. Using rotaries seams to be the right direction for a trim wheel. However, I have a couple questions regarding your trim wheel set up. Does your trim wheel have full up and full down stops?If so, I can't seam to grasp how it would work? Example: Lets say you have it trimmed all the way to the bottom and the auto pilot trims it towards the top. As soon as you turn the AP off and trim the wheel up, wouldn't the position of the trim wheel be inaccurate compaired to FS's position?Maybe I've got it totally wrong. I think the only way for it to work is if there were no Up and Down stops and it would spin freely in both directions? That way it would still allow you to adjust the trim and it wouldn't matter what position the wheel was. Defiantly not 100% accurate to real life, but some compromises must be made in some areas if we can get our cockpits complete in our life times. ;-) I also think it would be a lot easier to build using rotaries instead of a pot and some gears.Thanks Tuomas!!Regards Guy

[tigert]

>Hello Tuomas. Thanks for your explanation. Using rotaries>seams to be the right direction for a trim wheel. However, I>have a couple questions regarding your trim wheel set up. >>Does your trim wheel have full up and full down stops?>>If so, I can't seam to grasp how it would work? Example: Lets>say you have it trimmed all the way to the bottom and the auto>pilot trims it towards the top. As soon as you turn the AP off>and trim the wheel up, wouldn't the position of the trim wheel>be inaccurate compaired to FS's position?No, it is just a freely rotating switch that FSBUS can use as an encoder.http://tigert.gimp.org/vatsim/cockpit-stuff/trimwheel.jpgBasically it just triggers a pulse for each "notch" (I removed the springs and small bearings from inside the switch so it doesnt "click" but rotates freely. The foam is there for friction, but needs to be replaced by something else, it makes an annoying noise. The thing works fine though.The events get passed as keyboard presses to Flight Simulator. This is important as if you use a potentiometer or a rotary to control the FSUIPC value directly, we get just the problem you describe: the trimwheel itself has a "position" that gets out of sync when autopilot does trimming (or if you trim from a gauge in your FS panel)So the trim events get passed as just normal keystrokes to FS (FSBUS can generate keyboard events) - this makes it better because then the wheel itself does not have any idea of position, it just tells FS to trim "up" or "down".>Maybe I've got it totally wrong. I think the only way for it>to work is if there were no Up and Down stops and it would>spin freely in both directions? That way it would still allow>you to adjust the trim and it wouldn't matter what position>the wheel was. Defiantly not 100% accurate to real life, but>some compromises must be made in some areas if we can get our>cockpits complete in our life times. ;-) I also think it would>be a lot easier to build using rotaries instead of a pot and>some gears.Yea. I am going to make a trim indicator gauge with the servo controller card of FSBUS though - then it doesnt matter since I can see the real position from the gauge. The only problem is that it doesnt stop, but then again, you very rarely trim to the very end of the trim wheel travel in normal flight anyway. What matters is that you have big and precise enough wheel to do trimming. Everything else is just eyecandy and not relevant to actual flying. Tuomas