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Weight and Balance Input?

D

dvalle

Well Known Member
Changing the panel so much and had to drain the fuel so decided to do a new weighting of the aircraft and looking for input. I am finding the plane significantly heavier than the original paperwork shows and my changes are minor (lighter) in comparison. Sure looks like the previous owners numbers were off? Input would be appreciated? He also has max at 1660, is that normal? Also, anyone have the arm for the mains and nose handy?

My numbers below. My total 1082, his 1031.

left main 428
right main 409
Nose 245



Thanks
 
Could very well be that the original builders numbers were off. I've heard of many folks using two bathroom scales to weigh an aircraft instead of certified aircraft scales - such an approach seems pretty inaccurate. Aside from that, aircraft tend to gain weight over time and lots of RVs have had improvements added to them by the builder without a W&B update because the additions seemed pretty minor.

The arms for my gear are 29.50" for the nose and 85.06 for the mains, BUT I would suggest measuring yours as they seem to vary slightly from aircraft to aircraft.

Regarding the max gross weight, that is a number that Van's suggests (1650) but builders are free to set their own, and many do. Numbers between 1750 and 1800, often with caveats such as +3.8/-1.5, maximum landing weights, and so on.

You probably did this, but just to make sure: the plane was leveled and canopy closed when you weight it, right? That won't affect the total weight, but will screw up the balance figures.

Good luck!
 
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ChiefPilot said:
The arms for my gear are 29.50" for the nose and 85.06 for the mains, BUT I would suggest measuring yours as they seem to vary slightly from aircraft to aircraft.
Click to expand...

Correct

Two airplanes are rarely the same and it is pointless to go through all of the trouble to re-weight and calculate a new W&B without using valid arm positions so that you get a valid result.
 
Weight and Bal input

Thanks, appreciate the input. Looks like I'll have to get into the books/drawings as I have been unable to find info for Wt and Bal...like what is the panel? Looks like measuring in space somewhere is the answer (in front of the wing):)??
 
Main gear measurement?

Brad

How the heck did you measure to the hundredth of an inch (85.06)? We could to that at work anywhere on a car with a massive coordinate measuring machine but obviously, I don't have access to that type of measuring equipment.

Thanks
Dan
 
I bought my rv6 and the logbook stated 1010lbs. I fixed a fuel tank leak and weighed it on race car scales. It came out 1044lbs. I would not be surpried at all if an accurate weigh in from the orginial will differ by 20-30 lbs.

My problem is extreme tail heavy. I bought a 20lb crush plate from sabre for my new catto prop, but can't get it to run smooth to save my life. I have it in a box while trying to to figure out how to get the cg more forward. I have 20lbs of dive lead straped to the engine mount.

The rv6 was designed for an 0-320, standard starter, standard gen etc. i have lightweight everything and it is problematic. It reallys need a 55lb hartzell c/s prop hanging on the nose.
 
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titanhank said:
I bought my rv6 and the logbook stated 1010lbs. I fixed a fuel tank leak and weighed it on race car scales. It came out 1044lbs. I would not be surpried at all if an accurate weigh in from the orginial will differ by 20-30 lbs.

.....
Click to expand...

Can you tell from the logs if it was weighed before painting, and the later paint job weight ignored?
 
dvalle said:
Brad

How the heck did you measure to the hundredth of an inch (85.06)? We could to that at work anywhere on a car with a massive coordinate measuring machine but obviously, I don't have access to that type of measuring equipment.

Thanks
Dan
Click to expand...


It's just to the nearest 1/16" inch.

I built some platforms for the main gear to get it as close to level as possible (paying attention in trig finally paid off!), then adjusted the tire pressures to get it as exact both laterally and longitudinally. Next the aircraft centerline was plotted on the floor, then the datum was laid out using the centerline and distances from each wing root. Several plumb bobs made this pretty easy.

Again using a plumb bob, I located the center point of each axle on the platforms and dropped it to the floor. Measuring the distance from that point to the centerline then duplicating that distance on the datum marker in front of the aircraft, I was able to keep the tape square to measure the distance from the datum to the center point of each axle.

Once that was done, I weighed it using aircraft scales after reinstalling the wheel fairings (again being careful to get it leveled both directions and keeping the canopy closed). From there the rest was easy.
 
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az_gila said:
Can you tell from the logs if it was weighed before painting, and the later paint job weight ignored?
Click to expand...

From the building picture log, it was up on the scales without wheelpants and gear fairings. I am not sure if this accounts for all of the weight gain, but it can't help. The tail surfaces were also rebuilt with new .020" metal about a year before i bought it. I plane on changing to a lightweight tailwheel, moving the battery to the firewall, moving the elt to the old battery location, moving the strobe box to the inside of the firewall and trading someone my nice light skytech starter for an orginial heavy boat anchor starter. This will be about all i can do to move the cg and will have to live with the results.
 
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My 7 is tail heavy and I have a IO360 and a Hartzell CS prop! Empty ARM is 81.25 and it is almost impossible to fly dual aerobatics and be in the aerobatic category limits! 2-180lb men and 20 gal of fuel puts me in the 1600lb aerobatic weight limit but CG is slightly aft of category limits.....Solutions I have pondered on are a lighter tail wheel, taking out my Classic Aero tonneau cover and the EXPERIMENTAL cover in the back, and polishing all the paint as much as possible everywhere aft of CG.....By the way, does anyone know where I can find a 120 lb aerobatic instructor?
 
rvbuilder2002 said:
Two airplanes are rarely the same and it is pointless to go through all of the trouble to re-weight and calculate a new W&B without using valid arm positions so that you get a valid result.
Click to expand...

Just out of curiosity, how much variation have you seen between aircraft? Are we talking +/- 1/8" from plans, or +/- 1" from plans, when comparing datums?

Consider how people will be loading the airplane, there's a wide variation in where you can put people and baggage... The seat backs can move +/- 2", the baggage can move +/- 10" depending on where in the compartment you load things... Getting your datums within 1/8" may not really be significant in a practical sense?

Maybe it's more important to know where you are relative to gross weight, understand how the CG will move with loading, and understand the effects of being really close to either end of the CG limits?
 
Weight

My -8A was weighed unpainted. Not sure how much, but paint will add more than a few pounds. Didn't worry about CG implications - paint was mostly distributed over entire aircraft.
 
pvalovich said:
My -8A was weighed unpainted. Not sure how much, but paint will add more than a few pounds. Didn't worry about CG implications - paint was mostly distributed over entire aircraft.
Click to expand...

On a conventional aircraft, paint will always move the CG aft. There is much more surface area aft of the CG. A new weight & balance is required after paint.
 
pvalovich said:
My -8A was weighed unpainted. Not sure how much, but paint will add more than a few pounds. Didn't worry about CG implications - paint was mostly distributed over entire aircraft.
Click to expand...

I weighed my -6A before taking it in for paint then again after bringing it back from the paint shop (because I wanted to use the same scales etc.).

My paint added 25 lbs and moved the CG aft by 0.80".
 
It's four colors (two main, two trim) PPG DELFLEET two stage. Clear coat buffed to a high shine. Done by the great folks at Midwest Aircraft Refinishing in Hibbing, MN

9684270408_99df7e67c0.jpg
 
Weight and Bal

The last one funny:)

Thanks for all the input, I'll get at it again soon, been off for girlfriend duties....

Dan
 
To the original poster:

Weigh your airplane on another set of scales. It could be that the ones you recently used were poorly calibrated. Or it could be that the ones the original owner used were uncalibrated. You'll get a better idea of the situation if you cross check by weighing again.
 
titanhank said:
and trading someone my nice light skytech starter for an orginial heavy boat anchor starter. This will be about all i can do to move the cg and will have to live with the results.
Click to expand...

I was thinking the same way. My old starter caused a kick back and shattered some teeth. I bought an old prestolite, but couldn't get it fast enough and bought a Skytech. I never installed the prestolite, as it the Skytech spins the engine SOOO much better (longer on a charge and faster). I would never go back. Ended up putting a 19# crush plate on to deal with the aft CG.

Happy to sell you the prestolite for the $20 I paid for it.

Larry
 
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