measurements for W&B

[prkaye]

For the weight and balance, they have you make a series of measurements for the distances to each of the wheels from the datum (which is 70 inches forward of the leading edge). I'm wondering why this is necessary... with the pre-punched kits, should these values differ in any appreciable way from Vans' numbers (i.e. the numbers given in their "Sample Weight and Balance")? They give 34.5 inches to the nosewheel and 91.88 inches to the mains. I jsut wonder if the difference due to builder variances would likely be smaller than the error with which I could physically make the measurements...

[Mel]

There WILL be differences airplane to airplane due to weight and building tolerances. You need to make you own measurements.
BTW, there is nothing sacred as to the datum. That's your choice. 70" is just a suggestion from Van's. Some people seem to have trouble working with negative numbers. Personally I use the leading edge of the wing for the datum.

[frazitl]

I did my W&B before the first flight and again at the first condition inspection. Of course she gained a little weight, but the measurements for the nose and main wheels changed enough to make a noticeable difference in my overall W&B calculations. The distances are a little hard to measure, and have a large impact on the final calculation. With the deflection of the relatively springy gear legs, the distance measurements seem pretty critical. My advice is to CAREFULLY do your own with a couple plumb bobs...

[rv9av8tr]

I just did the station measurements on my -9A per plans... INTERESTINGLY, my measurements came out EXACTLY 1" different than the plans (Mains 90.88 and Nose 33.5). Trust me, I checked and rechecked this several different ways, and it is 1" "off". I asked Van's about this and they said, yes, it can be different for a host of reasons. It just feels "odd" to me to be EXACTLY 1". By the way, my fuse and wings are QB's, so it's not something as a result of my work.