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Measuring new (elastomer style) nose gear arm

Draker

Well Known Member
The new elastomer nosegear for the -7A has a little back-and-forward pivoting movement when off the ground. This pivot accounts for a 1-3/8" difference in measured nosewheel arm, in other words, when on the ground, the nosewheel is 1-3/8" forward of where it is in flight, relative to the datum. Which arm makes sense to use for the purpose of weight and balance? Since the purpose of calculating the moment arms is to compute the C.G. in actual level flight, I would assume the correct arm measurement is with the nosewheel hanging down as if in flight. The only problem with that is when weighing the plane, the nosegear is obviously in it's pivoted-forward on-ground position.

Strangely enough, neither of my measured nosewheel arm length comes even close to the example numbers in the manual. Perhaps the examples are based on the old style nosegear.
 
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CG is CG

The old style nose gear also allows the nose wheel to move forward and back.
I really don't think this movement materially affects the actual CG. Methinks you may be overthinking this! :)
 
The old style nose gear also allows the nose wheel to move forward and back.
I really don't think this movement materially affects the actual CG. Methinks you may be overthinking this! :)

In my plane, the final C.G. difference between the two possible ways to measure nosegear arm is 3/8". I suppose you're right. Still, it would be nice to know the theoretically correct way to do it.
 
In my plane, the final C.G. difference between the two possible ways to measure nosegear arm is 3/8". I suppose you're right. Still, it would be nice to know the theoretically correct way to do it.

Theoretically, and even practically, it could be proved by calculating the moment arm for the nose wheel in the two positions on the scale. The flying position could be simulated with a cord between the tail tie down and the nose wheel to pull it back 3/8". I'm pretty sure the moment arm will be the same in both positions. The scale will show a slightly different weight for each position, corresponding to the slightly different arm.
 
Weight and balance is calculated by using the known weight values obtained with it on scales factored against the arm positions when it’s sitting on those scales when you get those weights. What the nose gear does when it’s lifted off the scales/ground is irrelevant.
 
Weight and balance is calculated by using the known weight values obtained with it on scales factored against the arm positions when it’s sitting on those scales when you get those weights. What the nose gear does when it’s lifted off the scales/ground is irrelevant.

Yep, think retractable gear, good luck doing a W&B with the gear up :D
 
What the nose gear does when it’s lifted off the scales/ground is irrelevant.

I cannot disagree more. Clearly, if the battery was to come loose and slide into the tailcone, the cg would change. It’s incumbent on the aircraft designer to come up with cg limits which are safe with any aircraft configuration expected, e.g., gear up or down.
 
I cannot disagree more. Clearly, if the battery was to come loose and slide into the tailcone, the cg would change. It’s incumbent on the aircraft designer to come up with cg limits which are safe with any aircraft configuration expected, e.g., gear up or down.

This is an RV forum after all, and there are no retract gear RV's (at least not factory designed... so the issues related to those are up to the builder).

The movement of landing gear on any RV when it becomes unloaded would have a negligible effect on the actual in flight C.G.
If someone wants to pick nits, we would have to do a compensating calculation for all the RV's because with aft sweeping legs, the wheel position changes longitudinally as well as laterally when unloaded.
 
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