fastplane

I have a plane that requires control service movement in degrees. I only have a Great Planes AccuThrow to measure.
It only measures in inches or mm. How do I convert the degrees to inches/mm?

Or if I had a plane that requires inches/mm--- how to convert to degrees?
Also what do you do when the control service throw is greater then 2". (max of the AccuThrow)? Buy a different tool?
Thanks

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.

MustangFan

http://www.rcuniverse.com/forum/fb.a...c%2Cprogrammer

I deleloped a Xcell spreadsheet for the Hitec Programmer (LINK above)

If you have the capability to use it, the spreadsheet will convert both degrees to inches and inches to degrees.

You measure the width of the control surface, put in the inch movement and it will convert for you.

If you can't use it ... let me know and I will post the math for you.

fastplane

MustangFan, thanks for the link. I was able to download in Excel and it opened ok.
I do not have a HiTec programer so not sure yet if it will work for manual measurements.
Thanks,

Scar

My Feedback: (3)

Didn't you mean SIN? Or do I misunderstand the term "throw"? I thought it meant the vertical deflection of the tip of the control surface.

Best wishes,
Dave Olson

BillS

While the math approach works very will for me some problems are best solved with a 20-cent school protractor and a sheet of notebook paper.

Bill

fastplane

This is a lot of excellent work to determine measurements from you guys.
It has been a long time for me to remember my trig functions. But I thought that if we know two items for a right triangle, most of the other items could be calculated. So, if given the:
1. Arc segment length, which is the distance the control service moves when deflected. Measured on the circle circumference.
2. The radius of the right triangle, which is the cord dimension at point of measurement.

I was hoping that the angle of this right triangle could be calculated.

Or to do it the other way to find the arc segment if given the angle throw and the cord dimension.

As I said, I don't remember how to do all the triangle measurements and don't have a trig book.
Thanks,

Ed_Moorman

My Feedback: (1)

Get your scientific calculator.
Measure or get from the manual the control movement, 1/2" for example
Measure the control surface width or chord, say 2" for the elevator.

Divide the control throw by the width: .5/2 = .25

A scientific calculator will have a Sin to the -1 power. This is the inverse or arc sine, meaning it is the angle whose sine is the number you enter.
Usually you get the inverse Sin by using the 2nd key then the Sin.

With .25 showing, press 2nd, Sin for 14.48 degrees.

fastplane

Thanks Ed, I believe that was what I was looking for. Excel works pretty good also.
I set up a work sheet to do the same.

How to do the opposite? Go from degrees of throw and convert to the arc segment in inches or mm?

Newc

Why not simply use an angle locater such as sold by Ace Hardware or Sears? I have these and use them almost constantly while building planes for accurate settings of wings and horizontal stabilizer level, etc.

fastplane

I am not familar with an angle locator. How do you use it to do what I want?

JohnW

My Feedback: (6)

Sine... I see the point. I guess it depends on perspective on how the throw is to be measured. Maybe it is just me, but the whole idea of setting an angular throw by measuring inches just seems wrong.

I wouldn't bother with the angle locator. They aren't accurate enough and their weight will screw with your deflection reading. If you want a cheap and good tool for measuring surface throws in degrees that blows the socks off basically every other meter, just build the protractor gizmo I posted. These are so simple to make, cheap, and perform as well as commercial meters that cost 30 times as much. There is a picture of a small one on page 4 of the linked PDF. I'd suggest a model with a longer rod. You can make the $3 stick/protractor as precise and accurate as the $100+ laser meter shown in the same document.

http://www.bvmjets.com/Misc/BobCat_Trimming.pdf

Just to confirm, I'm not talking about the CRC meter shown in the PDF. They work ok, but aren't as accurate or precise as what I described.

Newc

Fastplane - Here's a picture of one of my angle locators. It's showing that it's sitting at a 5 degree angle due to one side being on the pad of paper. You can see how this can be used to show the angle of a control surface. In fact, the fixed surface doesn't even have to be at zero degrees to allow the use of this, as all you really are looking for is the difference in the angle from when the control surface is neutral versus at full throw.

Hope that this helps.

MustangFan

You do not need the programmer to use the spreadsheet to get your answer using the Excell Program

do this using the Desired Control Angle Know portion of the program.

1.) Using Line 1 ( any line really) enter the control angle desired. ( First Column)
2.) Under the column labeled "Width - Largest" enter the measurement in inches of the control at its largest point ( or point you wish to measure at)
3.) Under column "Control Throw" is the answer in inches (i.e. decimal 0.50 = 1/2 inch) of the throw you will use ( at the point measured)

The other portion of the program 'Desired Control Throw Known' works the same way but changes Inches to Angle.

Hope this helps

I constructed this program in part for the same question you had. Was always getting control throws in degrees ... wanted to measure with my trusty ruler or height gauge. I expanded when I got my Hitec Programmer and had trouble relating the programmer numbers to control surface movement desired.

Good Luck
Mustang Fan