Weight and Balance

I've been building wings for the WACO NINE project while waiting for weather and viruses to cooperate with getting Fly Baby Flying.

I tried borrowing scales to do the weight and balance but the nearest scales were over 60 miles away.  Instead I bought one scale, an ADAM CPWplus 200.  It's good for 200 kg or 440 lb.

 To make it work I made 3 blocks, the thickness of the scale (2 1/4"), one for each wheel.  For the mains I added chocks to the blocks so the plane wouldn't roll off.  I also made a stack of shims 1/4", 1/2" and 3/4" to use for leveling the plane.

A stool turned out to be the perfect height for the tail wheel, with a 1/2" shim.

Level fore and aft.


 I had to put 1/2" of shims under the left main to get it  zeroed left to right. If I had brought the small air compressor I could have adjusted tire pressure also.

 With the plane level I then proceeded to measuring where things were along the axis of the plane.



The tape measure is zeroed under the center of the tail wheel.

 To do that I hung a plumb bob at a convenient spot forward of the stool.  Then I measured from the center of the tail wheel to the plumb string, 13 5/8".

Then I just slid the end of the tape back to where the plumb bob was at 13 5/8", making zero directly under the tail wheel center.

 The plumb bob was used to locate the axle, 169 7/8".


Then the firewall, our datum point, 185 3/16".  That makes the mains 15 5/16" aft of the datum

 I would like to replace the prop one day with a wood prop so I located it also, 212 3/8" or 27 3/16" forward of the datum.

 While I was at it I decided to measure the length of the plane.  The tip of the spinner was at 217 12".


The trailing edge of the rudder was 18" behind the tail wheel making the plane 235 1/2" long, 19 feet 7 1/2".

 I then swapped the scale for the block at each wheel and took the empty weights.  I also cross checked it with a second scale since I couldn't find 400 pounds of calibrated weights.  I eventually checked it with a third scale also.

Multiple readings were taken with each scale at each wheel.

 Same process for the left main.

 Then again for the right main.  It was a little slow but worked fine.

 I then wanted to weigh the plane with me in it to determine my CG location.  The scale won't read past 440 Lbs. so I decided to weigh myself then get in the plane and photograph the tail weight with me in it.  The remaining part of my weight is on the mains.  In 1976 we had the pilot CG at 40", I came up with 39.85".  I'd say we had it right on back then.

I preceded to do the same weighing process, with the help of my neighbor George, as we add fuel and checked the weight at 5 gallons, 10 gallons and full at 14.7 gallons.  The CG of the Gas Tank came out where I measured it so it looks like we got it right.

The data agrees very well with the 1976 data.  You also would have to work at getting to the forward or aft CG limits.  We're closing in on Flying this Baby.