Building Lasers

[Wayne Galligan]

Keith,

On the square for lining up the rudder post.   
If you have perpendicular lines layed out on your table you just lay the square on the line that is perpendicular to the fuse.  This way you can tilt the square forward or back(in the case of a canted rudder post) and still have a square post.  Of course a scribed line in the center of he post is needed.  I use the Great Plains center scribe for this as it will make a center line that will conform to a tapering hinge area.

Wayne G.
  ----- Original Message ----- 
  From: Keith Black 
  To: discussion at nsrca.org 
  Sent: Monday, October 25, 2004 1:24 PM
  Subject: Re: Building Lasers


   think lasers are hugely helpful in some cases. I find them particularly helpful when trying to draw a straight line on an unlevel surface, or a particularly large area such as a line across an entire room. An example of an unlevel surface for modeling would be drawing a straight line right down the center top of a fuselage from the top of the fin to the front of the nose, or when drawing a line down the side of the plane. In both of these cases you're working with a curved surface and the laser will follow the contour (be sure it's lined up correctly). 

  The down side to lasers I've found are: One, the laser I have has a relatively thick beam as compared to the accuracies we need, between 1/16th" and 1/8th" depending on distance. It's harder to be exact that you would think. Second is that you can sometimes be misled when the beam goes across surfaces that curve further away or closer to the source of the beam. This will distort the beam unless it's exactly even with the location you wish to draw the line. 

  After messing with lasers in the past to try and do alignment I feel the best way to align the stab is to have a level table, put a scribe line on the rudder post and use a square to make sure the fin is perfectly perpendicular to the table. Then when mounting the stab use a height gage to make sure the stab is exactly the same height from the table at all points (front corners, back corners, center fronts, center backs). This will yield a perfectly aligned stab, height wise at least. You also need to make sure the stab tips are aligned equal distance from some center point in the front of the plane (I won't go into this, the best bet is to buy Bob Noll's tapes).

  What I sometimes find difficult in this process is eyeballing the square and the rudder post to make sure indeed the fin is exactly 90 degrees to the table. In some cases you can butt the square right up to the rudder post, but in other cases you can't do this, or the rudder post is at an angle. This is when my eyes play tricks with me since the square isn't up against the scribe line. In this case a laser may be useful, however remember that the laser must be perfectly lined up behind the rudder post (side to side) or the angle of the laser combined with an angled rudder post will cause the line not to be true.

  For the alignment of the main wing it's necessary to use some type of measuring gadget, like Bob Noll describes, to make sure the wing tips are equal distance from the stab tips, but when it comes to the wing tips being lined up height wise to the stab tips I think this can be done more accurately using the eyeball than with any measuring tool (at least the tools I have). If you stand ten of fifteen feet in front of the plane and position yourself exactly in the middle of the fuse you can raise and lower your head and see if the wings are even with the stab. Also do this from behind the plane. This can be done with incredibly accuracy. In fact, I've done it using measuring tools and afterwards found that my tools couldn't get it as accurate as my eyeball. And since you've made sure the stab is correct it's a good measure for the primary wing (I set my stab first). 

  I've used the a laser to confirm my eyeball measurements for the wings being level with the stab, but due to the thickness of the beam, and the fuzziness around the edge of the beam, it's tough to get it to the accuracy of my eyes.

  BTW, I didn't pioneer these methods. It's thanks to other modelers that have shared their approaches to doing things that I know this. Out of all the different methods that have been suggested to me these are the ones that I find work the best.

  For anyone who's new to building, or just wants more tools for their building arsenal, I strongly recommend Bob Noll's tapes. The one for alignment is called "Perfect Airframe Alignment". You can order them at 610-746-0106. He has a set of four tapes that go through many of the difficult parts of building a pattern plane.

  Keith Black
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