VGC News/Newsletters - Lakes Gliding Club

Sheet metal parts ofthe new Ol/furs cut by Lase,: PhotoPeter WellsThe rest ofthe Ot1fur bits, Photo Peter Wells.The tests carried out on this rig proved our 'Ossie' cousinsabsolutely correct, a worn Ottfur would not meet JAR 22 butthen, JAR 22 did not exist when the Ottfur unit was conceived.Probably more importantly it was found that although thegeometry of the over dead-centre lock was indeed important,the condition of the hook profile, caused by release ring wear,could result in excessively high release pull loads and incertain circumstances, the inability to release at all! A unitrecently returned from Denmark exhibited exactly such afault.With a good hook profile and over dead-centre geometrygenerally within an overall 2,0 mm tolerance, release pullloads fell within the requirements of BCAR Section E. Thesewere the parameters against which the Ottfur had been originallydesigned and at last there was a basis to work from but,just to provide some extra incentive, another problemappeared.The original hook was manufactured by placing threel4swg (.080") steel plates together which were then weldedaround their outer edge. In one sample, hook corrosionbetween the plates had weakened the assembly to such anextent that the beak of the hook had broken off completely.Cutting through other samples showed this Was a commonproblem with the three plate method of fablicat,ion and in consequence\looks will in future be manufactured ~rom solidplate using a suitably hardened and upgraded material. Thisapproach should also reduce profile wear.The tests conducted also revealed two other points worthyof comment. It was found that in the higher l'ange of cable testloadings, origiJJaI Ottfur release rings showed s,igl1s of ringdistortion and, in a few cases, weld failure. Bearing in mindthat the rings are contemporary with the release unit this wasnot too surprising. However, the Ottfur rings are manufacturedfrom relatively narrow bar stock (1/4") and in consequence,very high point loadings are generated where the ring is incontact with the hook profile. Only one test run in the higherrange produced an indentation on the hook profile which, assubsequent tests proved, significantly increased the pull loadsrequired to achieve release. It follows dlat rings manufacturedwith larg,er diameter stock are to be preferred.It is a cause for some concern that the sheer longevity ofthe Oufuf means that there could be some units in the fieldwhich may be potentially dangerous. On the other hand, thereare those gliding enthusiasts who have the skills and resourcesto carry out servicing and repair work over and above theroutine, but without some manufacturing, or what might bebetter termed 'second line support' the future for the Ottfurwould be very uncertain.Therefore the objective of this support project is to ensurethat the Ottfur will last as long as its host glider and now,some ten months after Colin's initial suggestion, it is hoped tohave a second line service in place by the end of 1996. Well intime for the Northern Hemisphere's C. of A. season and hopefullyalso in time to ensure the long term future of the goodold British OttfuLYou may well ask what happened to my oath of all thoseyears ago. Well, after ten months of further frustration, somevery interesting research and design work and, with the assistanceof Bob's special assembly tools, a lot less physical violence,just let's say -I'm Hooked!Pete Wells, Worthing.August /99622