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woolen thread or slip indicator?
#1
hi,
I noticed that in the flight sbandometro (ball) never coincides with an indication of the wire on the windshield.
if in forward flight the ball I keep it in the center, the wire is conspicuously tilted to one side, if I hold the wire in the center the ball is on one side.
I do not know who to give straight to the ball or to the wire
who can explain me the reason for this?
thanks
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salve,
ho notato che in volo lo sbandometro (pallina) non coincide mai con l'indicazione del filo sul parabrezza.
se in volo traslato la pallina la tengo al centro, il filo è vistosamente inclinato da un lato, se tengo il filo al centro la pallina è da un lato.
non sò a chi dare retta, alla pallina o al filo
chi mi può spiegare il motivo di questo?
grazie


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#2
So someone else can chime in that flies airplanes with a turn coordinator but here's what I'm thinking. You are comparing two different (gauges) The woolen thread is an indication of airflow over the windscreen. If you are tracking straight the thread is straight. The other is a turn coordinator. Measures angular relationship. You don't really need this on a helicopter. All you need is the woolen thread and keep it straight. This indicates you are in trim and flying straight. Not crabbing. The last thing is do not mount the thread too far down the nose. You may be getting weird eddies from the nose geometry. Try moving it up the windscreen and then see if they track the same.
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#3
Cam,

I think you make a great point. The R-44 I fly occasionally has a inclinometer ball installed and sometimes the thread and the ball are not exactly synced, but I do not think anything of it.  That is because like Cam points out the woollen string is measuring the angle of wind hitting the string based on you relative wind (  you movement through the air) where the inclinometer is measuring the amount of centripetal acceleration vs gravity ratio, which is shown in either a "slip" ( not enough turn) or a "skid" (too much turn).  The inclinometer was designed to show a coordinated turn with "bank", but will still show which way your out of trim in level cruise flight.  Of course this is accomplished by "stepping on the ball" to coordinate the flight condition.  I have noticed in the R-44 of differences in the string and ball when in cruise, but very minute and insignificant.  I believe the R-22 and Schweizer were the same way.  Most of the turbine helicopters I have flown didn't have a string to compare.  When in cruise flight with both the ball and string sometimes "slighty" out of sync, this is when you have to trust the seat of your pants and other indications to see when your "truley in trim."  A few common sense ways to figure out if you are in trim.  Ask yourself when are you and the helicopter most comfortable.  You can even note slight differences in airspeed as being out trim is not as slippery aerodynamically as being in trim.  Wind from either door is another huge obvious give away in a helicopter with no doors.  Both the trim string and inclinometer both will tell you when you are out of trim, but they are getting their information obviously from different sources.  While I am very use to inclinometer's from my airplane flying, I tend to agree with Cam that the Woolen String is probably more appropriate for the helicopter since in much of its normal flight envelope it will be out of trim.  It is kind of nice to have both for long cruise, especially with passengers in larger helicopters, but depending on where the inclinometer is mounted can also change your view of what is "ball centered", so be aware of that.  In mosquito terms, a ball would be neat, but I wouldn't worry about it.  I had the MGL Enigma in my ship before I sold it, but I did not have the AHRS installed to get any indication.  The trim string worked great, and just good old "seat of the pants." feel worked just fine.
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#4
ok, from now on I will refer only to the wire wool (red), but as you can see from the video it's hard to keep it straight, maybe not in the right position?

https://www.youtube.com/watch?v=Y2iARt...

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ok, da ora in avanti farò riferimento solo al filo di lana (rosso), ma come si vede dal filmato è difficile mantenerlo sempre rettilineo, forse non è nella posizione giusta?
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#5
Both are the same there used for coordinated flight.In sailplane terms woolen thread is referred to as a YAW string.on my mosquito the yaw string doesn't seem accurate. who knows what type of eddies you getting from the rotor. If i had to choose i wold use the winter , no outside interference.


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#6
Awesome video. I always put my yarn on a suction cup. That way I can move it if I have to. I find for cleaning the windscreen it is nice just to pop it off. Try moving it up the windscreen. I don't remember mine dancing around like that. Try the small suction cup. Then you can move it around easily.
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#7
Thanks Cam, I made some tests and indeed you were right, if the wire is held higher is much more stable

https://www.youtube.com/watch?v=JjK7uY...
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#8
That's awesome!!!!!!!! You ought to be able to tell when you are in trim now with all those trim strings. LOL. WHAT A GREAT EXPERIMENT.
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#9
Brilliant... One video answers lots of questions!
Richard, NZL  /// C? Test Dummy \\\  "I used to be a hang-glider pilot. Yeah, I remember that... day!"
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