Large War Bird Weight and Balance

[Rod Schneider]

I've done several weigh jobs on airliners for my employer, using load cells with axle jacks. I'm curious about how it would be done on something like a B-17. Is it possible to weigh it in three point attitude with the tail wheel on the ground, or do you have to lift the tail to level the plane? How would one go about supporting the tail if you had to raise it to level attitude? On the airliners, we usually just change the inflation on the nose strut to get the plumb bob centered..........

[The Inspector]

It will need to be leveled and a tailwheel support fabricated to hold the tail up @ the Tailwheel so it gets weighed too and the weight of the support subtracted as 'TARE WEIGHT'( note the weight of the support and write that on the support so eveyone using it will know it weighs 'XX', it's also a good idea to re weigh it every couple of years and update the info/date of verification on the support so there are no questions, we had to re weigh our cement drums of TARE every year they always came up 1245 lbs. and the date/weight was noted every year to keep the blue coats happy). The support will need some vertical adjustment built in (like a mobile home leveling jack). There should be two nutplates on the side of the airframe, and using screws as resting points to place a good quality level on. You'll need to know where DATUM is (no MAC since it's not a swept wing) then everything usually forward of DATUM is a negative number or value and everything aft of DATUM would be a positive value. I HATED doing W&B on large convential airframes because you have to remove, note the location, and weigh everything in the airplane, both negative and positive and calculate the W/A/M for all of it and subtract it then add it back in.
All the procedures should be in the maintenace/erection manual and be sure you have read through them, have them right there when you do the deed.

[Cvairwerks]

The designers got smart when Plant 4 was built. Out in our Experimental Building, floor scales were incorporated into the hangar floor. Pull the a/c onto the scales, drive them to level the a/c and read the weights. They did the same thing when all of our fuels buildings were constructed. Now it only takes a few button pushes to level and weigh the a/c. The weights guys have all the data in file on a laptop and complete a W&B within about 5 mins now. One of the guys got really smart a couple of years ago and took our suggestion to produce a calculation routine that used checkboxes for doing weights when equipment was removed at the time of weighing. If we have to weigh an incompete aircraft, all he has to do is uncheck the boxes for equipment not installed at the time. Really speeds things up for them.

[The Inspector]

Hope someone bought that guy a great lunch! Whale of an idea!!!!!!!

[The Inspector]

And-all your numbers will be positive as they would be aft of Datum so it's just WxAxMx3 and the manual should have the divisor formula to divide your final moment calculation into a meaningful number, I'd weigh it three times rotating the cells to eliminate 'drift'.