Setting Propellor Pitch using laser light tool

Using this method of setting prop pitch is easy and very accurate. All you need is a small laser light tool available from Ebay for a couple of £’s or $’s. Once you have the laser light it needs to be mounted on a simple board/card which will hang on the leading edge of the prop. (see pic) I made mine from hardboard. I glued two strips on the front to hold the laser light itself and 3 blocks on the reverse side, 2 to ‘hook’ over the leading edge of the prop and the 3^rd small block to rest against the prop face. If you don’t glue this 3^rd block on, the flat card tends to rock on the curved face of the prop. Use tape to hold the laser light in place once the glue has gone off. Make sure you can press the ‘on’ button when it’s taped in place. 

I also attached a piece of string to mine to ensure the whole thing doesn’t drop on the floor if it slips off the prop blade. Just loop the string over the prop blade before you hang the tool on the leading edge.

 First things first…

1. Set plane on flat ground
2. Ensure plane is chocked and will not move.
3. Remove one set of plugs so engine turns over easily.
4. remember to disable ignition. (you don't want the engine to fire up whilst you are turning the engine over!!)

You will now need to ‘chock’ the prop blade in a known position to take the first reading. Find a piece of wood or something similar and set it under the prop. It doesn’t matter how you do this as long as you do it exactly the same way for both blades. I have a piece of wood I use with a little groove in it and a mark so I can set the tips in exactly the same place. Set the bottom of the chock in the same place on the floor each time. I drew round the piece of wood on the board with a pencil. That way, when I came to swing the prop round to do the second blade I could set the chock in exactly the same place.

Now you are ready to take a reading of the first blade.

Hang to laser tool on the back of the blade and using a ruler or tape measure set the tool at a known distance from the tip. Again it doesn’t matter too much exactly where you measure from, just so long as you do it exactly the same for both blades. I used 8” if I remember correctly. I suggest that when you try this you remember to loop the string over the blade. (Not like I did here) It gets annoying when the tool falls off the blade to the floor.

Put the tape down and then gently hold the laser tool in place on the blade and press the button. The light will shine on the floor. At this stage its handy to have placed a piece of lined paper or graph paper right there on the floor where the light is shining. I personally use a magazine with plenty of text on the page. When the beam shines on the text, you can remember the word it shines on. Easy. Make a note of where the laser beam is shining.

In the pic below you see the beam shining just below the number 21 in the middle of the page.

 Now carefully swing the prop round, chock the second blade and repeat the whole process.

 The idea being, you want the light to shine in the same place for each blade. The task now is you may need to slacken the hub and adjust the blades to set them the same.

 I have used this process to check and set numerous ground adjustable props and also my GSC inflight adjustable prop. Checking it and finding that the pitch was out was the easy bit. Adjusting it was the interesting part. That may be described in another article. 

Joe Kynaston.  March 2005