W&B Tip

[FLY6]

I was helping a friend do a W&B on his RV7A today. We jacked the plane up, zeroed the scales and slid the scales under the wheels. We were having a problem getting consistent results. After scratching our heads for a bit, the builder who had done a W&B on his 6 when he built it remember an important fact; the person who was helping him stated he needed some sort of material under the wheels to allow the main gear to slide outward as the weight was put back on the wheels. We put some heavy weight oil between some pieces of aluminum and placed them under the main wheels. When we lowered the plane back down, the wheels moved out about an inch on both sides and low and behold, we got consistent results.

If you are using ramps to get the plane on the scales, you will not require these slip plates.

Hopefully this info can eliminate someone else from experiencing the same problem we were having.

If this a repeat subject, my apologies.

[Pilot135pd]

Interesting. Didn't know it would weigh more because of not having the wheels out a few inches, you live and you learn.

[DennisRhodes]

It may be more of the wheels placing side load onto the load cells than the position of the wheels being a bit more outboard. ie Possibly the load cell not being able to measure correctly with side load applied.

[Kyle Boatright]

Originally Posted by Pilot135pd

Interesting. Didn't know it would weigh more because of not having the wheels out a few inches, you live and you learn.

It won't weigh more, but the "unrelaxed" gear's lateral forces may play some trickeration on the scales, which are designed for vertical forces.

[Pilot135pd]

I guess it depends on the scales. Haven't seen that problem with the ones I use. I did it on the 172 and now on the RV-8.

[rv7charlie]

The greased plate technique was well documented back in the days of spring style & counterweight style scales. If you can find some old EAA docs, you'll almost certainly see it described, along with the caution that omitting them will cause erroneous readings.

[Pilot135pd]

Not saying it?s not true, just saying we lifted it onto the scales and also drove it on because my mechanic had heard about the issue previously but it made no difference on these particular scales.

[WingsOnWheels]

An easier alternative to the metal plates, just put a bit of oil inside a ziploc freezer bag and use that. Quick and easy.

[FLY6]

The oil in a baggy does seem a little easier.

I understand people finding it hard to believe the weights could be effected that much, but it definitely did make a difference, at least with the scales we were using. Once we put the slip plates in, our numbers would duplicate every time where as before, there was quite a variation on the mains. As one poster mentioned, maybe the side loads plays trickery on the scales.

[BillL]

I just made a ramp and rolled the plane on to avoid the side loading. Scales are not made for side loads. Meaning: a strong frictionless sliding action. I borrowed the scales and did not want to damage them. $$$$