Since the untimely death in 2023 of MGC Life Member Roger Druce and Dr Ben Loxton moving to the USA in 2018, Melbourne Gliding Club has not had a member with authorisation to conduct a Weight and Balance Inspection of club aircraft. GGC and Beaufort were similarly bereft although, should we have a need, generous assistance was always likely from Trevor Hancock of Grampians Soaring Club, or perhaps Phil Organ or Paul Dilks of Bendigo GC.
(L-R) Colin Callum (GCV) leads the W&B of the GCV Duo Discus (VH-GCV) with George Schuitt (Southern Riverina GC), Murray Stimson (MGC) and Neal Bennet (Hunter Valley GC) at Benalla in Oct 2024.
By Murray Stimson, Melbourne Gliding Club
The vital importance of a correct Weight and Balance inspection may not be readily apparent to newer pilots. The purpose of the inspection is to ensure the aircraft is being flown within the correct range of the centre of gravity (c.g.) so that it remains stable and controllable in flight, as well as to ensure it is flown below the maximum mass limits (there are a few) so that critical points of the structure do not fail in flight.
Particularly dangerous is loading the sailplane beyond the aft limit of c.g. position, making entry to a stall/spin easier and recovery harder – potentially impossible. Trying to fly with too much weight forward of the c.g. could see the pilot run out of back stick to keep the nose up, or get the nose up on tow, also with potentially serious consequences. That is fundamentally important, right?
The registered operator of any sailplane is responsible for ensuring the correct placards are in place in a glider so that every pilot can load the aircraft correctly. Without those placards, the aircraft is NOT airworthy and must not be flown. A certified Weight and Balance Inspector is responsible for providing correct placards to the RO, and annual and daily inspectors are responsible for ensuring those placards are in place, and that the aircraft configuration still conforms to the W&B numbers being used.
A certification to conduct simple W&B inspections is gained through a course provided by GFA, with the prerequisites of holding a current certification to conduct Annual Inspections, and having conducted three W&B inspections under supervision.
The first course in at least 8 or 9 years was held at Benalla on the weekend of 26-27 October 2024. Seventeen candidates from gliding sites across Victoria, SA and NSW, including Lake Keepit and Warkworth, attended. Mike Durrant of GGC and I were the successful candidates from Bacchus Marsh. Trevor Hancock and the Vic/TAS Regional Manager Airworthiness, Dr John Wharington, assisted Anthony in delivering the practical component using four gliders provided by our generous hosts, Gliding Club of Victoria (GCV).
The main objective was to precisely weigh each glider on its main wheel and tail (or nose) wheel and precisely measure the horizontal distances between those points and the reference datum, usually the wing root leading edge. This involved setting up the gliders at the ‘level’ attitude specified in their Type Certificate, using plumb bobs to transfer the relevant locations for the hangar floor before using the tape measure. Using basic calculator functions produced the empty weight and the empty weight c.g. locations, from which cockpit placards can be developed. Sounds easy, right?
Anthony Smith, Chair of the GFA Airworthiness Department, who has been incredibly busy with airworthiness directives for all Pawnee tow plane wings over the last few months, had developed the new course from scratch with the help of Roger Druce and a few others. Anthony had been performing and supervising Weight and Balance inspections for over 30 years as an engineer at RAAF Edinburgh, SA, working mainly on the AP-3C Orion 4-engine maritime patrol aircraft.
The course is based on the new version of the MOSP 3 Airworthiness, and the new version of the relevant airworthiness instruction, AIRW-D011 Weight and Balance of Sailplanes. This instruction manual was also largely rewritten by Roger and Anthony Smith over the last few years and issued on 23 May 2023, only a few months before Roger died.
For any engineer, the concepts involved in Weight and Balance are quite simple, applying the well-known first year equation that the sum of the moments about any reference datum must be zero for any mass (i.e. sailplane) at rest. But it was quite another thing to deeply understand the rigorous application of the equations that result and allow the calculation of ballast masses (fixed, removable or disposable), fuel, oxygen bottles, tie-down kits and, of course, pilots and their drinking water, snacks and outlanding kits.
The final exam required a high mark to pass and involved some challenging problems, such that it took some up to 5 hours to be sure they had the right answers. Furthermore, a few of the class may need to sit a supplementary exam. A validated spreadsheet helps, but is only as good as the data entered by the inspector and was not available until the exam was successfully completed. This rigour is needed because the results directly affect the safety of pilots.
Under supervision across the next year, Mike and I each intend to complete three Weight and Balance inspections to complete our accreditation and ensure our gliders remain in conformance with the manufacturers’ limits.