O.K. I'm getting nervous!.... This Saturday morning I will be carrying out the all - important wing load demonstration on my homebuilt Adventurer. The LH wing panel (the one I havent covered yet) will be mounted upside down in a special jig, and approx 1.4 Tonnes of cement bags will be carefully loaded in increments on it.... This will demonstrate its capability of withstanding a minimum of 3.8 G (Normal category plus safety margin). Its not necessary pleasant, but worth doing. Interestingly in an anomaly in the CAA rules, Special category "experimental" or "Amateur Built" aircraft such as mine are not actualy obliged to have a wing load test, whereas class 2 (2 Seat) microlights are. Common sense suggests it is worth doing! I have a bunch of SAA mates coming along to stack cement for me and plenty of photos will be taken (some to be posted here) - its a big day for me. I am confident that the wing will handle the load OK, but still theres always a number of things that can go wrong Fingers crossed....
GOOD NEWS. the wing has sucessfully been demonstrated to no less than 4G - a total of 1.5 Tonne spread across the wing.
This should provide an operation limitation of +3 - 2 G with 25% demonstrated safety factor. 1.5Tonne is a LOT of cement - the wing did visibly bend,(as expected) but no structural damage ensued and everything returned to the correct shape afterwards. Heart rate and blood pressure of builder also returned to normal shortly afterwards! The only heart stopping moment was just as we were loading up over 3G, one of the dynabolts holding the jig to the floor sheared. No damage to the wing, but a loud bang gets everyones attention. fixed the jig after sending a helper down the road to get some bigger dynabolts and wedging in an extra brace, and the tests resumed.
The "empty" test rig - 90kg of plywood on the lower suface directs the load to the spars, Heavy duty cable puller attached to the portal truss to lift the wing. Mike Tunnicliffe (Mosquito builder and SAA mate taking baseline measurements
Paul Parsons records the data
the biggie - 4G - 1500Kg! (it should NEVER get to this load again - ever...)
The fixed camera shot shows some deflection - the reflective tape is the measurement datum.
Rear spar at 4G - another fixed camera
The load was then eased to max service 3G, and another 120KG added along the trailing edge (production sandbags) to simulate flap and aileron loads - Mike measures the deflection again
After that the cement was unloaded and re-stacked on the pallet for return to Mitre 10 (who kindly loaned it for the day) No permanent distortion found - but I am so glad I dont have to do that again - in some respects the first flight will be easy after this (there was a very real risk of something breaking...)
the other good news is that CAA have waived the undercarriage drop test requirement due to the fact the leg assembly and the axle / wheel sets exceed the requirements and are built by reputable commercial suppliers (Same company builds Maule UC legs)