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Old Jun 28, 2012, 06:07 AM
Registered User
United States, TN, Farragut
Joined May 2012
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Help!
Converting degrees to mm or inches

Anyone know a conversion on degrees to mm or inches. Trying to setup throws on a couple of my planes and don't have a protractor handy. Have my great planes throw meter but t only reads in inches and millimeters.Usually just use a builders protractor but mine seems to be lost. By the way, the plane is a 3DHS 72 Extra. I know you need the surface measurement (ie...aileron,elevator for an accurate measurement) but looking for a formula
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Old Jun 28, 2012, 06:14 AM
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pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
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SOH CAH TOA

The most relevant one here would be angle = sin^-1(throw/chord)

The windows calculator does the inverse sin function.
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Old Jun 28, 2012, 08:10 AM
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rjstrickjr's Avatar
United States, NC, Faison
Joined Jan 2011
683 Posts
Metric converter

I like this one. It's free and will do more than just leanths.

http://www.worldwidemetric.com/measurements.html
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Old Jun 28, 2012, 08:52 AM
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mikmerl's Avatar
Athens, Greece
Joined Apr 2010
453 Posts
Try doing it this way
Degrees are increments of a circle or arc.
To simplify the exercise treat your control surface as something that will make full 360 degree motion.
Using the following formula:
Diameter x Pi, (3.14159), divided by 360 for 1 degree.
The diameter of the circle in our case will be the width of your control surface x2.

Then multiply the degrees travel with the above result to get travel in mm.

Eg: Let us say that we need a elevator deflection of 40 degrees for the example
width of elevator=50mm (that is the radius of your travel circle)
multiply that by 2 to get your diameter.
result is 100mm.
multiply 100 by 3.14= 314
divide 314 by 360 = 0.8722mm
multiply 0.8722 x 40 degrees
34.88 is your travel distance in mm

hope this helps
mike
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Old Jun 28, 2012, 09:15 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
16,667 Posts
Quote:
Originally Posted by mikmerl View Post
Try doing it this way
Degrees are increments of a circle or arc.
To simplify the exercise treat your control surface as something that will make full 360 degree motion.
Using the following formula:
Diameter x Pi, (3.14159), divided by 360 for 1 degree.
The diameter of the circle in our case will be the width of your control surface x2.

Then multiply the degrees travel with the above result to get travel in mm.

Eg: Let us say that we need a elevator deflection of 40 degrees for the example
width of elevator=50mm (that is the radius of your travel circle)
multiply that by 2 to get your diameter.
result is 100mm.
multiply 100 by 3.14= 314
divide 314 by 360 = 0.8722mm
multiply 0.8722 x 40 degrees
34.88 is your travel distance in mm

hope this helps
mike
Since we can't measure arc length that is the basically the small angle approximation, x = sinx. (X in radians of course)
40 degrees is not a small angle , so you should have said ~35 degrees. (Makes no sense to do 4 digits when the answer is out by ~8%)
True answer for 40 degrees is 50*sin(40) = 32.14

Close enough I suspect, but since everyone has a calculator on the PC, why not just do the sin?

Personally I usually just eyeball it anyway

Pat MacKenzie
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Old Jun 28, 2012, 10:42 AM
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United States, NC, Faison
Joined Jan 2011
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I am LMAO!

You fellas just went so far over my little brain that I did'nt even see you go over!

Well said by all and I think I will just use the eyeball technique!

Max out the control surfface and only use what you need by the input of the gimble is what I do.
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Old Jun 28, 2012, 11:25 AM
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dgliderguy's Avatar
United States, WA, Snohomish
Joined Mar 2001
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Quote:
Originally Posted by pmackenzie View Post
Since we can't measure arc length that is the basically the small angle approximation, x = sinx.

Personally I usually just eyeball it anyway

Pat MacKenzie
NO KIDDING!!! I never measure my control throws, I just stand behind my model when programming and eyeball my throws, and I get comfortably within the ballpark just about every time. Maybe I will fuss with dual rates sometimes, but it is always through experimentation (flight test) rather than with physical measurements.

Soapbox speech: In all my years (and I have had nearly 200 models over the years-- check my blog, they're all listed there), I have never once measured my control throws. First of all, we really should be measuring angles, not inches (or mm's), as control surfaces don't always have a constant chord. Second of all, why should I accept someone else's values, when my personal preferences may be different? Thirdly, control sensitivity is a function of airspeed, so what may work at cruise speed may not be enough on approach, or in a thermal at minimum sink speed. Flight testing is still the best way to determine control throws, and eyeballing the throws in preparation for the first flight has always worked out just fine for me.
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Old Jun 28, 2012, 10:10 PM
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United States, TN, Farragut
Joined May 2012
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Thank you for all the replies. I usually set the control surfaces as a starting point an go from there. I have gotten some good ideas.
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Old Jun 29, 2012, 03:19 AM
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mikmerl's Avatar
Athens, Greece
Joined Apr 2010
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Gentlemen

The man asked for a way to measure control surface deflection and you’re describing your bionic eyeballs to him.

mike
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Old Jun 29, 2012, 06:42 AM
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United States, TN, Farragut
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Guess if I want it easy and exact I should order the throw meter from aero works. It is in degrees. Lol.
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Old Jun 29, 2012, 06:45 AM
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Mike thank you for your replies. I think your method will be the easiest.
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Old Jun 29, 2012, 07:52 AM
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United States, NC, Faison
Joined Jan 2011
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Mik, you are absolutley right.

I will share this, the only RC plane that I have needed to actualy measure deflection of a control surfface on was a Tocanno .60 by World Models. I had used the ole eyeball technique as discribed above and almost lost the plane on landing. The Tocanno is very pitch sensitive and requires very little elevator to move it up or or down. Once I got it back on the ground I adjusted to the recommended throws with a Great Planes throw meter, and she flew fast and straight! The GP throw meter has inches and MM on it so it can be used for bothe SAE and Metric.
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