Scales for Weight and Balance

[[email protected]]

Hello All,

Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?


Thanks!
Dennis Ballew
Vice President
Las Vegas Valley Soaring.

[Ron Gleason]

On Sunday, 3 May 2020 10:59:41 UTC-6, wrote:
> Hello All,
>
> Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?
>
>
> Thanks!
> Dennis Ballew
> Vice President
> Las Vegas Valley Soaring.

You may want to contact the SSA office or the head of the SSA contest committee as they have scales that move around from contest to contest. With most contests cancelled this year this would be a great use of that resource.

If you or anyone within your club has contacts in the automobile racing world you may be able to borrow some from them

[[email protected]]

Many repair and maintenance stations have them to loan out or use on-site. If memory serves me right, they need to be calibrated, which is a fairly straight-forward task.

[Bruce]

On Sunday, May 3, 2020 at 9:59:41 AM UTC-7, wrote:
> Hello All,
>
> Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?
>
>
> Thanks!
> Dennis Ballew
> Vice President
> Las Vegas Valley Soaring.

You might contact the local EAA chapter. Many of the clubs have scales for their members use, and would probably jump to help you out.

[2G]

On Sunday, May 3, 2020 at 6:55:17 PM UTC-7, Bruce wrote:
> On Sunday, May 3, 2020 at 9:59:41 AM UTC-7, wrote:
> > Hello All,
> >
> > Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?
> >
> >
> > Thanks!
> > Dennis Ballew
> > Vice President
> > Las Vegas Valley Soaring.
>
> You might contact the local EAA chapter. Many of the clubs have scales for their members use, and would probably jump to help you out.

Better yet, join the EAA - and their local chapter - and they will jump faster.

Tom

[[email protected]]

You'll still need scales, but can manage with smaller or less-suitable scales using the method below. I wrote this a couple of years ago for our club:

------------------------------

The weight and balance of gliders is critical to safety and handling in flight. The existing weight and balance sheets of many gliders are out of date or erroneous. Repairs, alterations and painting change the situation but are not always accounted for. Pilots who are smaller or larger than average adjust the seating, changing the CG location to an extent that is unknown unless the glider is weighed with the pilot seated.

We now have access to two scales of the sliding-weight type that are usable for the measurements needed to ascertain the weight and balance. One is a platform scale that measures to over 1200 pounds, the other to 130 pounds with more precision. But there are practical difficulties in a direct measurement of the assembled glider. The glider needs to be leveled (in pitch).. The platform is elevated, making it harder for the pilot to get into the seat. The tail would need to be elevated higher yet to level the glider. The vertical part of the platform scale may not fit under the wing. Any fall from the elevated perches may damage the glider. Electronic platform scales with no vertical parts are available for cheap these days, but their accuracy and longevity are in doubt.

Recently we came up with a trick way to accomplish a full measurement safely with the mechanical scales on hand, and successfully used it on one glider:

First weigh all the glider parts, separately. One wing at a time on the big platform, with padding. The fuselage needs a cradle that can roll out of the trailer, some gliders have that already, for others would need to improvise such. Set up a simple ramp and roll the the fuselage onto the platform scale. Put the small scale under the tailwheel. Weigh both points at the same time and add up the two numbers. The fuselage does not need to be leveled at this time, we're only seeking the total fuselage weight. Weigh the canopy separately or with the fuselage. Remember to include all the small pieces: removable tail, spar pins, battery, etc. Weigh the dollies and padding on their own, and subtract, to get the net weight of the various glider parts. Sum up the parts and get the glider's total empty weight. Compare with the pre-existing weight record.

Second, fully assemble the glider. With the main wheel on the ground, and wings held level, elevate the tail on top of the small scale to level the fuselage as per the manufacturer's directions. (It is safest to elevate the scale itself on top of a wide base.) Record the net weight at the tailwheel. Here's the trick: the weight at the main wheel is not measured directly, but can be computed by subtracting the tailwheel weight from the total empty weight (known from the first step above). From these numbers the glider's empty CG can be computed. Compare with the pre-existing record.

Next, weigh the pilot (with typical flying clothes, and with the parachute if it is to be used). Repeat the tailwheel weight measurement of the assembled and leveled glider, with the pilot seated and canopy closed. Again, the weight at the mainwheel can be computed by subtraction (empty weight plus pilot weight minus weight at tailwheel). Now the gross weight and the CG location can be computed. Check that the CG is within the allowed range. Can also deduce the actual location of the CG of the pilot, compare that with the location assumed in the manufacturer's instructions.

The calculations are best done in spreadsheet software. If you need help, ask a mechanic or one of the club CFIs. Trick question: does it matter where the "datum" is?

[[email protected]]

Admittedly this is crude, but the Duster designer told the builder to use 3 bathroom scales! Calibrate them with a known weight, then place a plank across two scales to weigh the main wheel with the most accurate scale used under the tail. Small errors on the main gear are not critical, but apply correction from calibration to all readings. Worked for the Duster and should be fine for other light ships like the 1-26.
JJ

[[email protected]]

"Does it matter where the datum is."

It matters that you know where it is as it was used to calculate the EW cg. Its best to use the manufacturers datum line location so there is no confusion later.

But, any datum location can be used to come up with the CG location as it relates to the position on the aircraft, relative to that datum line that is used.

[[email protected]]

On Sunday, May 3, 2020 at 12:59:41 PM UTC-4, wrote:
> Hello All,
>
> Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?
>
>
> Thanks!
> Dennis Ballew
> Vice President
> Las Vegas Valley Soaring.

Schweizer documentation indicated that, if no big scale is available, use 2 bathroom scales with a board across them.
FWIW
UH

[2G]

On Monday, May 4, 2020 at 1:16:42 PM UTC-7, wrote:
> On Sunday, May 3, 2020 at 12:59:41 PM UTC-4, wrote:
> > Hello All,
> >
> > Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?
> >
> >
> > Thanks!
> > Dennis Ballew
> > Vice President
> > Las Vegas Valley Soaring.
>
> Schweizer documentation indicated that, if no big scale is available, use 2 bathroom scales with a board across them.
> FWIW
> UH

Electronic scales that measure up to 300 kg are available for under $100. I calibrated a pair of bathroom scales by going to an immediate care clinic with a backpack loaded with about 50 lbs of weights. I asked to use their patient platform scale, which they gladly agreed to. I weighed myself with and without the backpack. I then weighed myself the same way on both bathroom scales (they were surprisingly accurate). The most critical measurement is the tail weight as it has the longest moment arm. I would check the scale this way as close as possible to the expected tail weight.

One thing to keep in mind is that any breeze will upset this measurement. Either find a hangar you can do this in, or go out early and do it on a calm day.

Tom

[Richard Pfiffner[_2_]]

On Monday, May 4, 2020 at 10:41:50 PM UTC-7, 2G wrote:
> On Monday, May 4, 2020 at 1:16:42 PM UTC-7, wrote:
> > On Sunday, May 3, 2020 at 12:59:41 PM UTC-4, wrote:
> > > Hello All,
> > >
> > > Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?
> > >
> > >
> > > Thanks!
> > > Dennis Ballew
> > > Vice President
> > > Las Vegas Valley Soaring.
> >
> > Schweizer documentation indicated that, if no big scale is available, use 2 bathroom scales with a board across them.
> > FWIW
> > UH
>
> Electronic scales that measure up to 300 kg are available for under $100. I calibrated a pair of bathroom scales by going to an immediate care clinic with a backpack loaded with about 50 lbs of weights. I asked to use their patient platform scale, which they gladly agreed to. I weighed myself with and without the backpack. I then weighed myself the same way on both bathroom scales (they were surprisingly accurate). The most critical measurement is the tail weight as it has the longest moment arm. I would check the scale this way as close as possible to the expected tail weight.
>
> One thing to keep in mind is that any breeze will upset this measurement. Either find a hangar you can do this in, or go out early and do it on a calm day.
>
> Tom

Buy 3 of these for $34.99 ea free Prime shipping. Make a ramp to use 2 on the main wheel and one for the tail. 440 lbs capacity ea.

https://www.amazon.com/Smart-Weigh-Shipping-Stainless-Readability/dp/B0153I0418/ref=sr_1_33_sspa?dchild=1&keywords=digital+scale+500+lb+capacity&qid=1588679443&s=hpc&sr=1-33-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzRlFVVlFNTVNIT1ImZ W5jcnlwdGVkSWQ9QTA2NzE3NDEzVERDNFhRNzZETTlBJmVuY3J 5cHRlZEFkSWQ9QTA0OTM1NTUzQ1RaS1IwNVpIRUpCJndpZGdld E5hbWU9c3BfYnRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm9 0TG9nQ2xpY2s9dHJ1ZQ==

Richard

[[email protected]]

> Buy 3 of these for $34.99 ea free Prime shipping. Make a ramp to use 2 on the main wheel and one for the tail.

Those look great. I think I would use some 3/4 plywood scraps to help out the force summer in each scale. Two square scraps for the tail wheel and 2 rectangular scraps to couple the two for the main.

(That's an old trick from the guys at a scale company I did s/w for)

[2G]

On Tuesday, May 5, 2020 at 4:57:52 AM UTC-7, Richard Pfiffner wrote:
> On Monday, May 4, 2020 at 10:41:50 PM UTC-7, 2G wrote:
> > On Monday, May 4, 2020 at 1:16:42 PM UTC-7, wrote:
> > > On Sunday, May 3, 2020 at 12:59:41 PM UTC-4, wrote:
> > > > Hello All,
> > > >
> > > > Las Vegas Valley Soaring is currently restoring our beloved SGS 1-26D and will need to establish a new empty weight CG once finished. Does anyone know where I might source a borrowed or rented set of scales?
> > > >
> > > >
> > > > Thanks!
> > > > Dennis Ballew
> > > > Vice President
> > > > Las Vegas Valley Soaring.
> > >
> > > Schweizer documentation indicated that, if no big scale is available, use 2 bathroom scales with a board across them.
> > > FWIW
> > > UH
> >
> > Electronic scales that measure up to 300 kg are available for under $100. I calibrated a pair of bathroom scales by going to an immediate care clinic with a backpack loaded with about 50 lbs of weights. I asked to use their patient platform scale, which they gladly agreed to. I weighed myself with and without the backpack. I then weighed myself the same way on both bathroom scales (they were surprisingly accurate). The most critical measurement is the tail weight as it has the longest moment arm. I would check the scale this way as close as possible to the expected tail weight.
> >
> > One thing to keep in mind is that any breeze will upset this measurement. Either find a hangar you can do this in, or go out early and do it on a calm day.
> >
> > Tom
>
> Buy 3 of these for $34.99 ea free Prime shipping. Make a ramp to use 2 on the main wheel and one for the tail. 440 lbs capacity ea.
>
> https://www.amazon.com/Smart-Weigh-Shipping-Stainless-Readability/dp/B0153I0418/ref=sr_1_33_sspa?dchild=1&keywords=digital+scale+500+lb+capacity&qid=1588679443&s=hpc&sr=1-33-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzRlFVVlFNTVNIT1ImZ W5jcnlwdGVkSWQ9QTA2NzE3NDEzVERDNFhRNzZETTlBJmVuY3J 5cHRlZEFkSWQ9QTA0OTM1NTUzQ1RaS1IwNVpIRUpCJndpZGdld E5hbWU9c3BfYnRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm9 0TG9nQ2xpY2s9dHJ1ZQ==
>
> Richard

Be careful. Here is one review:

this scale sucks! it is not accurate and got 5 out of 6 box weights wrong when I took them to the UPS they were all a few pounds over what the scale had told me. one of them was wrong by 8 pounds.

Using a scale so far off to do a W&B can lead to very significant errors if used to weigh the tail. A 1 lb error in measuring the tail weight of an ASH26e, for example, will result in a 3.3% error in the CG. An 8 lb error results in 26% error, which can be deadly.

Tom

[Mark Briner]

Ask the local soapbox derby crew. They have good calibrated digital scales usually.