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Remove the smoke oil and any fuel in the tanks, leave the oil in the engine. Make sure you weigh the plane in a closed hangar. The slightest air movement will cause inaccurate weighing. If you make small ramps it will make it easy to push the plane on to the scales, just make sure that you have a chock on the scale to stop the planes motion. No use learning a new language if it rolls off and you have to start again.
Don't forget to subtract the weight of the chocks, at each location.
I "shimmed" to level just by leaving air out of the high tires.
When I lift the plane on to the scales, I use greased nylon sheets (gift from a friend - a set that I used to set wheel alignment…) to make sure I don’t put any side loads on the scales. You do sort of have to guess where things are going to end up when you do it that way, but its not hard.
Yes. I forgot that tip. It's a great method to adjust level a little. On mine the mains were much higher and even a flat tire wouldn't level it.
Beringer recommends 4 atmospheres for Michelin tires they use. I go slightly higher as it’s easier to remember. (60 psi) at 40 psi I refill using N2. Only do it once a year. Really nice wheels and brakes ! Never had a shake or wiggle.
Exactly. It's more than most are used to inflating. The tire/bead sealing dependent on the pressure. If allowed to drop, the tire instantly goes flat.
Lots of different definitions of weight out there. I don’t recall what FAA defines but I would weigh with the unusable fuel and engine oil as Bob says. In my old day job that was called “operating weight empty” (OWE which is BEW + required fluids) and my opinion best as you can’t fly without those fluids. Again not looking up FAA guidance, I would use the 8 quarts of oil even though you can fly with a lot less. Just make sure you document the exact configuration of what you weigh so you know where to add/subtract from for each flight.
I did the same but was hesitant to jack one wing at a time. So I made some simple lightweight ramps using 1/4” ply laminated at various lengths. Ramp length is 4’ overall and I can easily roll most RVs (tailwheel) onto the scales by myself. Works great and is less exciting.
I'm really curious to try scales on top of roller dollys to eliminate side load, as jacking the plane is much more convenient for the amount of lift I need to achieve to level the longerons.
I did that and works well if carefull. i have them laying around from car/truck alignments i do at home.
Yes. If tail dragger you only need two.
if the smoke tank is will be removed from time to time, weigh with it out. If permanent, weigh with it empty. This is variable and should be calculated for each flight. Like fuel.
IMO you need 3 scales to do WB accurately. I also will only do it with empty fuel.
Don't want to get too in the weeds and derail the conversation, but I'd like to hear your argument for why it needs to be empty. I've only tried full, with a subtraction for calculated fuel weight. My assumption is that variance in fuel density by temp is negligible, or could also be calculated.
Weighing with full fuel is valid if you know the fuel weight and the arm of the fuel. Fuel weight is dependent on the fuel density (as delivered from the refinery) and the temperature. Regular large aircraft weighing kits often include fuel densiometers to determine the actual fuel weight per gallon. On these aircraft a small error in fuel weight per gallon doesn’t is multiplied by thousands of gallons it can make a significant difference.
I think this device should be simple if not widely available. Might look for one.
This is a good point but I also think it varies more with in flight pitch attitude (just based on fuel float variability at different speed/attitude when nearing empty). I wonder if Vans used a margin of safety in their station to account for slosh.
I'm not sure I agree with this analysis for weight. All the things you mentioned (uncertainty of how full is full, etc) apply equally well to to the gross weight of an aircraft with a BEW measured empty (well, actually with unusable fuel on board, another issue). In the end the actual weight is just as uncertain either way.If you measure the weight with full tanks, at least there's no question of the total weight (usable and unusable) of fuel onboard.
Yes but empty CG can and does vary based on many factors so that doesn’t hold true for all 8’s.
I thought it was "what can't be pumped". Drain the remaining to measure it. EAA Test cards detail the process quite well. Mine was 2oz.Just to head further down the rabbit hole, is the “unusable” fuel determined by what can’t be “drained” using the wing drains or what can’t be “pumped” using the fuel pump? I used what could not be pumped, as we did in my day job, but wonder how many use drained and how big a difference that makes.
I spent a lot of time working with weight engineers and they love to get into this type of discussion.
Still... Even if the empty CG moved through a 2“ range across multiple aircraft, the CG of the fuel is so close to it that a small variation in volume would have no practical effect on accuracy. We're talking about CG's in tenths of an inch here, when none of us are making any real world change if it's 76.5 or 76.6 inches. Do what you can to minimize error, yes, but don't incur unnecessary risk by draining and then hoisting and pouring up to 20gal per side. If the owner fills the tanks, at least the "full" point is likely to remain relatively consistent while that owner has the plane.
Agree completely
We'll, I hope you drained the oil, too. Or filled it with a graduated eyedropper. Was your brake fluid reservoir full, or down .5“? And you and your passenger stand on a scale before every flight, right?
You need to tell Van's to revise their procedure then because it doesn't really matter.
Just add helium to the low side?
Using Walt’s process (per Van’s reference) keeps BEW data valid for all RV- owners looking at that model RV.
That's how I did it, but to expand on Walt's method, the builder really should measure the arms and validate the distances. They can be different. I doubt it would fall out of the sky, but as long as we are being precise, one might as well go all in.
