How do you weigh an airplane without a scale?

Answer 1

Well, if you know the thrust of the engines, and can measure the acceleration of the aircraft, you can calculate the mass of the plane.

Answer 2

You can't in practice. In theory there are a couple of ways it could be done. The landing gear shock struts are inflated with nitrogen. If you know the volume of the chamber and the pressure of the nitrogen inside the gear, you should be able to come up with a weight by measuring the amount of compression of the struts.
Second way is similar to the first using the tires, the area of the footprint should be a product of the pressure in the tire due to the force of the weight. Practically speaking, these can't be used because it's too inaccurate to measure the footprint of a tire and there are frictional forces in the shock struts.
To mathematically sum the individual weight of each part is ok in theory but not practice because this does not account for a variety of parts that go into an airplane like rivets, hi loks, wire bundles, etc. Also you will need to know the exact CG of the component and its exact location on the airplane to get the CG. When you weigh an airplane, you are getting the total weight but even more important, you are getting the CG of the airplane as a percent of MAC. Additionally, the FAA and DCAG would never approve the summation method. It is part of the aircraft's type certificate to be properly weighed on scales.

Answer 3

Quoted earlier "You don't. Three scales are used at the same time, or one is used three different times. Special heavy duty triangular-three legged jacks fit in to special jack pads, attached at structural hard points underneath the airplane in order to raise it up without damage. The three weights are either added directly or there is a formula for figuring the actual weight, that part I do not know, but I have seen it done at maintenance facilities at Hobby Airport south of downtown Houston, Texas.. "
Spot on, thats how I used to do it when I worked in Aircraft maintenance. It's normally carried out after major overhauls to check CG and overall balance. On small / light aircraft two pressure transducers are placed on top of jacks and the aircraft sits on these, usually on the jacking points at wing, a third is then placed under the nose wheel. There are some specifics that I've forgotton like the height the plane needs to be lifted, (enough to allow struts to fully extend) I think it has to be brought to a datum position where the longitudinal axis (nose to tail) is horizontal and this gives a true reading when the third scale / transducer is placed under the nose wheel.

Answer 4

You don't. Three scales are used at the same time, or one is used three different times. Special heavy duty triangular-three legged jacks fit in to special jack pads, attached at structural hard points underneath the airplane in order to raise it up without damage. The three weights are either added directly or there is a formula for figuring the actual weight, that part I do not know, but I have seen it done at maintenance facilities at Hobby Airport south of downtown Houston, Texas..

Answer 5

As 'planes are designed using CAD systems, for something like this where weight (mass) is a critical factor, the weight of each items is entered in the part record. The weight of assemblies and sub-assemblies are 'totted-up' by the CAD system. So the weight of any 'plane design could be arrived-at using this.

Answer 6

Basically what "Stillwater" said.

What you do is float a large rectangular or circular dock, measure the surface area of the dock & make a mark on the dock at the water level. Then, land the plane on the dock - the water level will change, now make another mark at this level. Calculate the height/distance between the two marks & multiply it with the surface area of the dock - this will give you the volume of water displaced. Multiply the volume with the density of water (1000 kg/cu.m) - this will give you the mass of the aeroplane.

Answer 7

The same way they weigh trucks.... each wheel goes on a scale, then a calculation is done to find its exact weight.

Answer 8

Weigh all the parts individually before putting together

Answer 9

Why u wanna weigh an airplane for? Haven't u got better things to do, like answering yahoo questions?

Answer 10

you can't weigh things without a weighing scale. just like you need to weigh trucks etc, they have special weighing scales/machines to do so.