Savannah S empty aircraft weight.

[IBob]

Some headscratching locally over Savannah S empty (no fuel, brand new ) weights, as taken at the initial Weight & Balance.

My S, with standard steam gauges, long range tanks, extended baggage, carpet, adjustable seats and Condor tires (next size up from standard) came in at 314.8Kilos
 

I'd be interested to know numbers from other builders/owners.

 

Thanks!

[Neil_S]

 

My Savvy S with standard steam gauges, long range tanks, carpet, adjustable seats, centre stick, manual flaps and 15x6.00-6 tyres is 310.5 kgs.

 

Cheers,

Neil

Edited May 2 by Neil_S
added manual flaps

[IBob]

Thanks Neil_S. It's been pointed out to me that a similar thread was run here some years ago, but it delivered a surprising scattering of results.
Having said that, weighing can have it's challenges, and I'm of the opinion that unless you can do multiple weighings with almost exactly the same result, something is wrong with the weighing process.
We do know that lowering main UC wheels onto scales doesn't work well, as the UC then spreads and the scales don't respond well to that sideways force. I got round that by putting a strop across the lower UC (then subtracting the strop weight when I got finished). That gave me excellent repeatability.

Rolling on does sound like an excellent alternative, but in practice it needs fairly long and wide ramps and pads that will stay put as the aircraft is manhandled. And again the aircraft has to be moved without inducing any UC spread or flex.

 

[turboplanner]

2 minutes ago, IBob said:

Thanks Neil_S. It's been pointed out to me that a similar thread was run here some years ago, but it delivered a surprising scattering of results.
Having said that, weighing can have it's challenges, and I'm of the opinion that unless you can do multiple weighings with almost exactly the same result, something is wrong with the weighing process.
We do know that lowering main UC wheels onto scales doesn't work well, as the UC then spreads and the scales don't respond well to that sideways force. I got round that by putting a strop across the lower UC (then subtracting the strop weight when I got finished). That gave me excellent repeatability.

Rolling on does sound like an excellent alternative, but in practice it needs fairly long and wide ramps and pads that will stay put as the aircraft is manhandled. And again the aircraft has to be moved without inducing any UC spread or flex.

 

I had squares of 12 mm ply cut, fitted roller bearing castors and sat the scales on the ply. That let the tyres push where they beeded to and was able to get repeatable figures ........................on a level concrete floor.

[turboplanner]

* needed to

[Lukeh]

11 hours ago, Neil_S said:

 

My Savvy S with standard steam gauges, long range tanks, carpet, adjustable seats, centre stick, manual flaps and 15x6.00-6 tyres is 310.5 kgs.

 

Cheers,

Neil

Neil, is there a parachute in 310,5kg?

[Neil_S]

17 hours ago, Lukeh said:

Neil, is there a parachute in 310,5kg?

Hi Luke,

 

No - no parachute.

 

Cheers,

Neil

[IBob]

Conducted  minor experiment with digital scales:

Weighed self on the flat, then placed scales on rigid board, chocked up at one side so scales are no longer hortizontal, and weighed self again.
As the board is tilted up, the scales progressively underweigh.
So unless something is done to ensure no lateral load on the scales, the scales will underweigh.
Which could explain some of the unlikely low weights reported in other threads.

In the case of the Savannah, if lifting and lowering the main UC wheels as I did for successive weighings, that means either preventing the UC from spreading when the wheel comes down, or arranging for the scales to move sideways, as Turboplanner did above. Or rolling on, provided that can be done smoothly.

[IBob]

Further experiment and correction to above:
Weighed self on flat, then weighed again with scales flat but leaning shoulder on slippery wall: this is closer to the Savannah situation, where the weight is on the wheel, but there may also be side thrust as the UC spreads.

In this situation, the scales over-weigh.

 

In both the above scenarios, the scales tolerated a small amount of tilt or lean without over or underweighing. How much probably depends on the design and construction of the particular set of scales.

[Marty_d]

Is there a best practice for aircraft weighing,  on normal scales?

[IBob]

Assuming you want accurate weights (and in my view you'd be nuts not to) it starts with certifying or calibrating the scales. I checked mine with a range of certified test weights at a local industrial breadmaking business.
After that you can either raise and lower a wheel onto the scales (I used a small hydraulic jack) with the other two wheels packed up (I put a strop across to prevent the UC spreading).......
Or you can roll the aircraft onto the scales, which is not as simple as it sounds unless you have nice big pads for the other two wheels and a good sized lead-in pad for the scales. In theory at least this gets you away from the problem of the main UC spreading and putting side load on the scales. I believe this is how it is normally done.

However you do it, you need to take multiple weighings and they should deliver very consistent results. If that is not happening, something is wrong with your setup.

 

Edited May 4 by IBob

[BC0979]

Final assembly before the airworthiness inspection. Single set of wing tanks. Viking 130. 808 lbs empty 366kg

Paid $250 for a guy with certified scales. Tried the digital bathroom scales without success,  my readings were much lower and inconsistent, tried 4x.

 

[IBob]

A note to add here:

The ICP manual says to weigh for W & B with no fuel in the aircraft.
You cannot fully empty the wing tanks with the aircraft sat level.

Also just lifting the nose a bit (I had it on a bit of 4 x 2 so 2" high) does not renew the flow to drain the remainder, probably due to unavoidable undulations in the pipework in the wings.
To fully drain the wing tanks. sit the aircraft back on it's tail.

Edited Saturday at 10:30 PM by IBob

[BC0979]

FYI if you have not witnessed this method.

 

The certified professional weight and balance guy I hired had ramps for each of the three electronic scales.  The ramps and scales of each wheel were at the correct height for level flight, the top of the rear fuse. We rolled the S onto the scales. Then there was a Temperature compensation step before the final numbers. 

[BC0979]

One more addition.

Be careful with the ARM values, the location of the wheels to the leading edge of the wing. My W&B guy used a plumb Bob and our ARM values were not the same as published in the ICP manual.