JohnW

My Feedback: (6)

You need trig. Scentific calculator will work, including the one in Windows. You may have to change the view in the Windows calculator, i.e. top menu: View: Select Scientific.

You need to know two things to convert a degree throw to inches. The degrees which you already know, and the distance from the hinge line to the trailing edge at the location you intend to place your throw meter. So measure the chord of the control surface, say it is 2 inches.

Now for the math, don’t worry, it is easy with a calculator. In the Windows calculator, verify you have selected “Degrees”, not radians or grads. Make sure the INV and HYP boxes are not checked. Also verify you are working in base 10, i.e. DEC, not hex, oct, etc.

Now enter in your degrees, say it said 25 degrees. Enter 25 then press the TAN function in the lower left corner. Notice it changes your 25 to 0.466 etc. Now multiply this by your chord measurement. Click on the “*” for multiply, then enter “2” from our example, and press “=” to compute. You should get 0.93… This is the throw in inches at the location you measured which equates to 25 degrees. I hope this was clear.

As for throw meters, you can build a very precise meter that reads in degrees. Degree throws tend to make more sense to me as they are comparable from plane to plane and aren’t size specific. Inch throws really don’t make much sense unless you know exactly which plane and what size. I’m sure vendors list inch throws for kits because they obviously know exactly which plane and what size, and inches are easier for most measure.


To make a very precise throw meter that reads in degrees, you only need two things. A stiff rod with a known length (small carbon fiber rods work great) and a protractor. Make a rod, say 12” long. I tend to glue a pin to one end to get a finer indicator. Take the protractor, and copy/blow it up such that the distance from the center to the graduations is 12”. I tend to just draw these in autocad, but a copy will work. You don’t need the whole protractor copy, just the area around the center (90 degrees), say 30 degrees either way, depending upon what you want to measure. Take the protractor copy, and glue/tape it to some wood or the like. Make a stand (I use a 2 by 4 wood base and a dowel) and attach your readout to the stand such that it is adjustable both up and down as well as tilt.

To measure, simply tape your stick to the control surface, with one end aligned with your hinge line. Take care to align the stick at a right angle to the hinge line. Won’t matter where to put this spanwise. Now bring in you meter and align it such that you match your stick length, i.e. the general idea is you want the hinge line to be the center of the protractor. Be sure you don’t have the meter cocked and some funny angle. This is why tilt is nice. You could do without the tilt I suppose if you level the model. Now you can read in degrees surface throw. Again, I hope this was clear… kinda hard to describe without pictures. I have two 18” versions of this kind of meter I made for about $3 each. They are extremely precise and accurate, well under a quarter degree. Most don’t need that much precision, but you’d be surprised how far off you can be with other meters. Just a degree off and most sport planes won’t fly as well. Translated to inches, assuming a 1” chord aileron, 1 degree error is only 0.017 inches, or about 1/64th of a inch. No way you can set that precise with those clumsy inch throw meters.