Weight and Balance

A professional aircraft weighing company (Planeweighs Ltd) was visiting our airfield, so we took the opportunity to get G-STRV weighed.

It has not yet been possible to install the interior, since we’re waiting for a harness crotch strap to be delivered … it had been accidentally omitted from the order, and I only noticed when I started to install the cockpit floor … grrr!

Obvious Top Tip … always check everything in the box when it’s delivered!

So I had to temporarily position all the interior components ready for the weighing.


IMG 9244

It took a while to attach all the various components to the plane … spats, fairings, access covers etc.

We also filled the engine with 7 US Quarts of oil, and positioned another Quart bottle to approximately account for the oil cooler oil capacity.

Scales were initially positioned under each wheel with the tail down … this allowed the AUW to be calculated.


IMG 9242

The Centre of Gravity in is calculated with the plane in its flying attitude. We raised the tail until the canopy rails were horizontal.

This now increases the weight on the front wheels, but by adding these and taking the result away from the first AUW measurement, the reduced weight on the tailwheel can be calculated.


IMG 9247

The floor was marked with a laser and chalk to indicate where the wheels touch the floor, and also the vertical position below the wing leading edge.

Since the datum is defined as a point 72″ in front of the wing leading edge, after measuring the various distances it is now a simple moment calculation to work out the C of G.


I had been concerned that G-STRV’s weight would be a bit high, and the C of G aft … I was remembering all my priming, lighter EXP119, lightweight EarthX battery, Yaw Damper servo etc.

But thinking of all this, we had opted for the MT Propeller with counterweights. Also the 6″ wheels are slightly heavier.

Anyway, I needn’t have worried … with more luck than judgement I was pleasantly surprised with the following figures:

Empty AUW: 1278.5 lbs (580 kgs)

C of G: 80.94″ (205.6 cm) Aft of Datum

This allows two 190 lb (86 kg) pilots, full fuel load of 50 US Gallons (189 litres), and 94 lbs (43 kgs) of baggage whilst complying with the max take off weight of 2050 lbs.

Two 190 lb (86 kg) pilots with 40 US Gallons (150 litres) will be be within the aerobatic aft C of G limit and max aerobatic weight of 1900 lbs.

The nicely forward C of G also means that I’ve not been able to calculate a realistic loading configuration which puts the aircraft C of G out of limits (82.08″ to 88.24″)

Another Happy Dance!

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1 Comment on "Weight and Balance"

  1. Paul Folland | June 18, 2022 at 11:11 am | Reply

    Seriously impressed and left in awe of Tim and you on this project Steve. Is there a kudos button somewhere?!

    Can’t wait to see Team G-STRV at the airfield! 👍

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