What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Weighing Aircraft and CG

Frankster13

Active Member
It is time to weigh my newly completed RV-14A. I have access to scales but wondering if there is a quick and easy way to do this. I have not been able to find resources but I'm sure they are out there. I need the form to calculate and satisfy DAR inspection. Any suggestions?
 
Last edited:
Weighing a homebuilt is quick and easy. But there is no getting around tape on the floor, plumb bobs, tape measures, and shuffling load cells to ensure repeatability.

The key to making the process go fast is planning - but there's no avoiding the grunt work of data aquisition.
 
The key is getting the fuselage level per the plans before weighing to get the proper c/g location. For the 14A if you deflate the nose tire completely it should give you the proper level line (but always check) so the nose weight comes out correctly.
 
The key is getting the fuselage level per the plans before weighing to get the proper c/g location. For the 14A if you deflate the nose tire completely it should give you the proper level line (but always check) so the nose weight comes out correctly.
Might not even need to deflate the tire. After weighing the entire airplane in three-point attitude, simply remove the scale under the front wheel and let it drop until the plane is in level flying attitude. Shim it there if you have to. Then read the weights off the main wheels, and subtract from the previous total weight to get the weight on the nosewheel in flying attitude.
 
Weight Scale Central Florida?

I'm almost at the point of weight the aircraft. Just to start working things out, I would like to take profit of this thread (instead of create a new one) and ask if there's anyone in Central Florida that have a scale?
I tried the EAA Chapter that I'm part of, but they don't have one.
Just trying to plan things ahead of time.
Thank you!
 
Be sure your plane is also level side to side if only using one scale. You will have to shim the wheel without the scale under it. Makes a difference in weight. 3 pad car scales work best.
 
Just as a general question, would it be ok to weigh the airplane with fuel in the tanks (if you have a well-calibrated fuel totalizer)?

It might be better to weigh the airplane in a typical operating configuration and then back out the known weights and moments to obtain empty weight. That would eliminate some of the potential errors caused by estimating moments for various fuel loads etc.
 
OK, Me too...

I am just about ready to weigh my RV-14A here in Richmond, VA. I have tried everything I can think of to find scales including:

Called my local EAA chapter (which I am a member of)
Called several local car race shops
Reached out to other local builders

I really don't want to spend $1000 or so to get a set of scales that I likely will use one time.

Does anyone on here have access to a set of scales I can use? I will pay a reasonable rental cost and pay for shipping.

Thanks!
 
Just as a general question, would it be ok to weigh the airplane with fuel in the tanks (if you have a well-calibrated fuel totalizer)?

It might be better to weigh the airplane in a typical operating configuration and then back out the known weights and moments to obtain empty weight. That would eliminate some of the potential errors caused by estimating moments for various fuel loads etc.

You can weigh it either with full tanks or empty tanks, any other fuel load would be guestimating as far as C.G. is concerned.
 
Don't try and skimp doing the weighing or calculations. Take the time to do it properly and learn. Also do it in a hangar with the doors closed, the slightest breeze will change the weights. I have seen too many planes not done properly and too many accidents because the owner/pilot did not take the time to fully understand the weight and balance of their plane.
 
Vans lays out the formulas well in their examples, re-create their format on a spreadsheet. Easy to do, or easily adapted from another RV builders (any A model) spreadsheet version.
Have a few friends there to help move the plane up onto the scales, & off. Doing a W&B is 90 minutes of preparation for a 2 minute job!
 
I am just about ready to weigh my RV-14A here in Richmond, VA. I really don't want to spend $1000 or so to get a set of scales that I likely will use one time.

Does anyone on here have access to a set of scales I can use? I will pay a reasonable rental cost and pay for shipping.

Thanks!

I bought two High Capacity Digital Bathroom Scales off of Amazon when I did mine. Takes a little longer getting everything setup properly, so that you can do the mains and then shim again to then do the nose. But I feel that the W&B ended up very accurate. Want to make it even easier buy three. I think the ones I bought went to 550 lbs. can't remember. I think they cost about $40-50 each.
 
I bought five identical bathroom scales from Amazon. I weighted myself on each one repeatedly to confirm that they were repeatable and reported consistent weights, and did the same against my scale at home for a sanity check.

I then leveled the aircraft by jacking up various places and sliding sheets of thin plywood under each wheel until it was level in both axes.

I then jacked up each wheel and slid the scales under. I put one scale under the nose wheel and two under each main gear, with a sturdy piece of wood to spread the load across the two scales under each main gear.

My scales only showed their values for a minute or less before going blank, so once I was all set, I jacked a wheel up to take the weight off the scale and then lowered it back on to get a reading. I did this a few times for each wheel and confirmed I got consistent totals on each wheel.

Later I added a weighted crush plate behind the prop and reweighed out of paranoia. I was pleased to find the results measured on another day aligned well with my calculations.

As long as you are comfortable with the math of weights, arms, and moments (multiply and add), there's no need to have a special W&B form. My DAR accepted a piece of paper showing the measurements and calculations. If you aren't comfortable, figure it out or get help because this could kill you if you do it wrong.

David
 
Ditto on what Bobby Hester did, except that I only bought one scale. When it was time to weigh the plane, I cut two blocks of wood that were the same height off the floor as the loaded scale. As I recall this was about two inches. I then put the two wheels not being weighed on the blocks and jacked the plane up enough to slide the scale under the remaining wheel. Push the button on the scale to arm it and then let the jack down.

I went around twice taking a total of six measurements, but the first three matched the last three exactly, so there was no point in taking an average.

Bonus: my scale has a talking feature so I didn't even have to read the number. I still have the scale and I keep it in my hangar where it gets occasional use when I get curios about the weight of something going into the baggage compartment. Cheers!
 
Side load on the scales can cause them to read incorrectly -- it's easy to get a side load if you lower your plane onto the scales rather than rolling it on.

A common trick to eliminate this to put a few layers of trash bag plastic on the top of the scale. It's slippery enough to relieve the side loads effectively when the plane is lowered.
 
Side load on the scales can cause them to read incorrectly -- it's easy to get a side load if you lower your plane onto the scales rather than rolling it on.

A common trick to eliminate this to put a few layers of trash bag plastic on the top of the scale. It's slippery enough to relieve the side loads effectively when the plane is lowered.

Wow! I wish there was a like button. This is what I love about this site. I was scratching my head for a week why my plane was weighing in "too heavy". Exactly what I did. Jacked it up but was concerned about side loads. This post not only confirms that this might be the issue but also offers a solution. 10 out of 10 for this post!
 
Back
Top