What's new
Van's Air Force

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

Best scales on a budget

Maxrate

Well Known Member
Looking for input on a set of good scales to weigh a -7 that won’t break the bank. New aircraft scale prices are all over the map.
Thanks.
 
Used race car scales. Check your local SCCA chapter website.

Used race car scales work well. Somebody will have them.
 
Or check with your local EAA chapter. Many have scales for the use of their members, and membership dues are low.

I weighed mine with the EAA 302 chapter (Conroe, TX) scales. They do charge a small fee for use that covers the annual re-calibration of the scales.

Cheers,
 
+1

I bought the same scales as Galin and they worked fine for my -9A. Cheap enough on Amazon you can buy a set of three and loan them out to your RV buddies. Weight limit is too low for C172's.
 
Consider renting the scales from your local industrial supply store if you want to save the $ and not have equipment that rarely gets used lying around the hangar.

Erich
 
I wonder (but haven't done the math) how much accuracy is really required. If each of the scales is accurate to say within three pounds, and in the unlikely event that all the errors are in the same direction, is a nine pound error tolerable? (I don't know the specs for "certified" aircraft scales.) Also, at one point, factory built airplanes were not all weighed when they were built, but only every tenth airplane or so... Gross weight is important, but keeping the c.g. from going too far aft is really important...
 
I wonder (but haven't done the math) how much accuracy is really required. If each of the scales is accurate to say within three pounds, and in the unlikely event that all the errors are in the same direction, is a nine pound error tolerable? (I don't know the specs for "certified" aircraft scales.) Also, at one point, factory built airplanes were not all weighed when they were built, but only every tenth airplane or so... Gross weight is important, but keeping the c.g. from going too far aft is really important...

A three pound error in the accuracy of the weight on the tailwheel would have a serious impact on the CG calculations. Depending on the direction of the error, it might reduce your (theoretical) baggage allowance by 15+ lbs or it might fool you into flying with the CG aft of limits.
 
Last edited:
The scales suggested by Galin are accurate to 0.2 pounds each at the 660lbs setting. That's 0.03%.

Anyone know how accurate are aircraft scales???
 
I believe the ones I used on the military were 0.1% of the reading. So a 500 lb weight would be 0.5 lbs. A 30,000 lb wheel would be 30 lbs.
 
My Intercomp scales are rated at (1500 lb capacity ea):
Accuracy ± 0.1% of Reading or 0.02% of Load Cell Capacity– Whichever is Greater
 
Remember, if you find yourself trying to land with an adverse aft cg condition, apply full nose down trim and leave it there throughout the landing. While not the best landing condition you want, it will give you the maximum elevator authority you can have under these circumstances. Don’t ask me how I know!
 
I believe the ones I used on the military were 0.1% of the reading. So a 500 lb weight would be 0.5 lbs. A 30,000 lb wheel would be 30 lbs.
The percent error is only at max weight, unless otherwise indicated. So a 600lb scale with a 1% error means an error of 6lbs, across the entire range. Using these scales to weigh a 10lb object can still give the 6lb error. That is why you must be careful to use scales of appropriate capacity.

FWIW a "rule of thumb" is to weigh no less than about 60% of max scale capability. So for accuracy, a 600lb scales should not be used to weigh anything less than about 360lbs. In my case the main tires were 532/544lbs while the nose tire was 363lbs.

:cool:
 
Last edited:
Offset versus gain (deviation). Accuracy claims are meaningless. Only a full cal yields anything reliable.
 
The percent error is only at max weight, unless otherwise indicated. So a 600lb scale with a 1% error means an error of 6lbs, across the entire range. Using these scales to weigh a 10lb object can still give the 6lb error. That is why you must be careful to use scales of appropriate capacity.


FWIW a "rule of thumb" is to weigh no less than about 60% of max scale capability. So for accuracy, a 600lb scales should not be used to weigh anything less than about 360lbs. In my case the main tires were 532/544lbs while the nose tire was 363lbs.

:cool:

We used the intercomp 30-60 scales, and the accuracy is always given as a percent of the reading. There is usually a smaller max error like walt posted buried in the tech manual, but if the scales are sized right, you're almost always using the indicated reading error range.

https://www.intercompcompany.com/aviation-scales/platform-scales/ac30-60

We also used the same rule of thumb that goes with torque wrenches, which was avoid 20% on each end. So a 10,000 lb scale would be used for anything between 2,000 and 8,000 lbs. If you needed the end of the range, you had to verify the accuracy against the previous calibration sheet.
 
Last edited:
Take care that the bathroom scale style sometimes has a "tap to wake" and an automatic timeout that will kick in at the most inopportune time... Like just after you've got the plane all positioned on it and before you've crawled underneath to read the numbers. And with the weight on it, you can't "tap" to wake them up.

Indeed. And I think it's even "tap to turn on and calibrate" for some scales.
Also appears that some scales are sensitive to where he weight is placed on them (and possibly side loads).
When weighing my RV-4 on low profile glass scales I built a platform for the tail wheel and layers of wood for the main wheels so I could roll the airplane back and forth. Took a dozen readings to get repeated numbers within a pound or two.

Finn
 
Take care that the bathroom scale style sometimes has a "tap to wake" and an automatic timeout that will kick in at the most inopportune time... Like just after you've got the plane all positioned on it and before you've crawled underneath to read the numbers. And with the weight on it, you can't "tap" to wake them up.

good point. Something to consider when I get to that stage in a couple years... I imagine I can scrounge up a few old smart phones with cameras on record and appropriately pointed so I don't need to crawl around.
Another poster pointed out "side load". That's a bit more difficult to solve...
I can see these klugey workarounds quickly becoming more convoluted and adding complexity and unreliability to the mix...
 
Side loads

If rolling the level plane on and off the scales, side loads probably won't be an issue. Anyway, that is solved by placing a garbage bag on the scale. Low friction between the two sides of the bag ensures the tire settles with no side load.

Others have mentioned vinyl floor tiles.

Finn
 
Joe Ruggless sold his scales for race cars years ago. Certainly someone still has a set lying around that they’d sell cheap. Here’s an old link but some checking around should reveal more. https://grassrootsmotorsports.com/forum/parts-sale/ruggles-scales-fs/179236/page1/

This works fine. Before we got our race car scales our EAA Chapter used a home made version of them. BUT..You need to remember that any error in the scales is multiplied by the length of the lever arm.
 
Back
Top