Weight & Balance Question RV14-A

[Lizard Lips]

Going down the short list, preparing for the Airworthiness inspection I ran into a situation that defies explanation, at least to me. The W&B readings on an empty airplane show the left main wheel weighting 66 pounds heavier than the right. Fuel tanks are empty, so nothing there. All is built according to t he plans rand instructions and, to my knowledge, there is nothing on the left side that would cause this condition. CG calculates to be within normal limits.

First: Anyone have any ideas about what could be the cause and,

Second: Other that maybe being a little wing heavy does anyone see where it might be an unsafe condition?

Joe
Longview, TX

RV 14A Almost complete. Awaiting inspection by DAR

Arion Lightning-LS1 Flown regularly

Dues paid for 2020

[rkbrown819]

Well, now you know where all those missing bucking bars went.

More seriously, I suspect the weight measurements are simply wrong. Possibilities might be 1) a number was transposed when the readings were recorded, 2) a zero value or tare value was stored incorrectly on the scale, 3) the airplane was out of level around the longitudinal axis while it was being weghed. There are probably other plausible explanations, but in any event, I would suggest repeating the weight measurements.

[Ron B.]

Did you have three scales, then one might be off a bit. Also I found that you need to have something in place to allow the wheels to slide sideways. If you jack up your plane to put it on the scales , the weight is off the mains and the wheel base is less because of this. When the wheels are lowered on the scales the gear spreads out and I find this effects some scales in their readings. If you grease between two boards and place the boards on the scale and lower the wheels onto the greased boards the grease will allow the wheels to slide out to their correct wheel base and present no side load in your scale.
Also if weighing with only one scale , the height of the blocks need to be exactly the same height as the scale with the weight of the aircraft on it. Aircraft must be perfectly level to be accurate.

[KeithB]

Also, note that in flying attitude (how you should weigh - longeron level), the nose wheel needs to be lower than the mains. While this sounds minor, it definitely changes the nose/mains distribution. This doesn?t give you a heavy left main, but is a common weighing error (ask me how I know).

[Lizard Lips]

Originally Posted by rkbrown819

Well, now you know where all those missing bucking bars went.

More seriously, I suspect the weight measurements are simply wrong. Possibilities might be 1) a number was transposed when the readings were recorded, 2) a zero value or tare value was stored incorrectly on the scale, 3) the airplane was out of level around the longitudinal axis while it was being weghed. There are probably other plausible explanations, but in any event, I would suggest repeating the weight measurements.

Not missing any bucking bars, but I suspect I made some errors in the readings. I was using three automotive electronic scales which are supposed to be quite accurate. I swapped the scales to see if maybe one was giving me an incorrect value but got the same numbers each time.

I am now convinced that I did not make the measurements properly which gave bad numbers. I built ramps so that I could pull the plane up on the scales. I put boards under the mains in an attempt to level the plane. Lateral was exactlly level, but the longitudinal was slightly nose high. I made the mistake of saying "good enough" and proceeded to record the values.

I'm going to do the W&B again taking pains to assure the plane is level. It wasn't out much before, but it wasn't perfect which probably contributed to the error.

Thanks for all the ideas. I'm going to keep doing it until I get it right. Otherwise, "Beatings will continue until moral improves."

Joe
Longview, TX

[rvbuilder2002]

I have weighed and done the W&B calculations on a LOT of different RV's

Pretty much universally the weight difference between left and right main wheels is 5 - 10 lbs. I have never seen a delta of more than 15 lbs.

So, regarding your question of unsafe condition..... I think the concern should be that your results have an error. Depending on the severity of the error, it could be an unsafe by causing you to fly with the C.G. outside of the accepted range when you think you are not.

Some potential causes of the error could be one scale being wrong, the airplane not actually being level laterally while weighing, or maybe one tank having some fuel in it when you thought it was empty.

[rvbuilder2002]

Originally Posted by Lizard Lips

Not missing any bucking bars, but I suspect I made some errors in the readings. I was using three automotive electronic scales which are supposed to be quite accurate. I swapped the scales to see if maybe one was giving me an incorrect value but got the same numbers each time.

I am now convinced that I did not make the measurements properly which gave bad numbers. I built ramps so that I could pull the plane up on the scales. I put boards under the mains in an attempt to level the plane. Lateral was exactlly level, but the longitudinal was slightly nose high. I made the mistake of saying "good enough" and proceeded to record the values.

I'm going to do the W&B again taking pains to assure the plane is level. It wasn't out much before, but it wasn't perfect which probably contributed to the error.

Thanks for all the ideas. I'm going to keep doing it until I get it right. Otherwise, "Beatings will continue until moral improves."

Joe
Longview, TX

Longitudinally exactly level is the important one.
Any amount of error here will cause you to calculate an erroneous empty C.G. position.
Even having the canopy open will induce an error.

[Bavafa]

For a reference, here is mine which the R side is 5.6lb heavier than the left side.
Lmain 456.8
Rmain 462.4

My ELT is on the right side of the plane under passenger seat.

[dpansier]

Just a little bit of breeze can make a difference, I opened the hangar door when I weighted mine and saw a difference on the main gear from just a very light wind.

[KeithB]

One tip I have used for fine tuning longitudinal leveling (since nose is a bit high on the 14) is to let some air out of the nose wheel - much easier than adding wood under main tires. Just remember to add it back.