Use as laser incidence meter, to measure the angle of attack of an airfoil in degrees.
Mostly on model planes when setting up the wing.
commercial unit here Accupoint
Step 1: The Meter's Components
the meter consists of:
1. the body, (simple aluminum curtain rail) to attach the othe components
2. the freely swinging laser cradle
3. the legs (for gripping surfaces)
4. the scale (marked in degrees)
Firstly the legs, made out of scrap wood and miscellaneous hardware for the swiveling action.
Step 2: The Laser Cradle
I used bearings from an old armature off an electric motor for the laser to pivot on, and glued (CA) the armature shaft to the laser body. This way the laser swings freely for accurate measurements.
Coarse adjustments are made via the friction fit ply cradle, and the fine adjustment is done using the threaded weight.
A bit of heat formed perspex keeping the lasers push button on for use, a quick rotate of the perspex and its off. Sweet and simple.
Step 3: More About the Cradle
these pics show the fine and coarse adjustments as well as the amount of coarse travel
Step 4: The Scale
The critical part of any meter is the indicator scale. This one is dependant on the length between the laser pivot and the scale.
For example, on my piece of track, the distance between the laser pivot and scale is exactly 745mm so that would equate to 1degree at the laser being 13mm at the scale.
This I sucked out of Modern Mathematics for Std 8 by J.J. Dreyer.
In the trigonometry section it says tan theta = opposite /adjacent side
So in my example the angle I want is 1 degree, the side b we have already said
was 745mm and we're looking for side c the opposite side.
Therefore c = tan 1degree x 745mm = 13.0040mm according to Bills calculator.
Bobs yer uncle, an accurate laser meter to a 1/4 degree for less than a tenth of the cost of the commercial unit.
Of course you could make the track longer for greater accuracy, the commercial unit is 508mm long, but dont forget to take flex into account, it just might reduce the accuracy of the unit.
Step 5: Using to Check the Trueness of a Wing
Checking the trueness of a wing
First sandbag the wing, (to prevent the wing moving) then zero the laser on the center section. Now gently transfer the meter to the wing tips without knocking out the zero setting. As a matter of principle I always face the laser to the back of the wing or plane so that when the laser reads above the zero line it indicates positive degrees.
The laser is very visible in daylight, you can actually see it glow right through the
2mm balsa that I use for mounting the scale markings, unfortunately my batteries have gone flat.
Step 6: The Usual Caution
NB As with all laser devices exercise extreme caution when using and dont look into the device when on, it can damage the eye very quickly.