Failure Analysis of In-Flight Refuelling System of Super Sonic Aircraft's Hose

In the pursuit of attaining cutting technologies it is a prudent and efficient way to have an airborne fuel station and in-fight refuelling feature added to the advanced generation of aircraft. The ‘in-flight’ refuelling system essentially consists of hose (flexible pipe), drogue chute, receptacle and the winding cage. The hose is integrated with the mother aircraft refueling system on the air platform structure which is kept in a rolled condition over a roller with guiding mechanism for uniform winding of the hose all over the roller width. The end of hose is connected to the mother aircraft refueling tank while the other end which comes out of the aircraft through a drogue chute. This drogue chute uses its aerodynamic drag in a moving air platform to the receiving which flies at little lower altitude so as to allow the hose in being unrolled to come in contact with to receiving ATF (aviation turbine fuel) through the mid air refuelling port. After the refuelling is complete the mother aircraft pulls back the mid air refueling hose to once again pack it on the roller through the guide mechanism. An operator of one of advanced generation aircraft having the feature of mid air refueling hose was stationed at DMSRDE Kanpur for a major defect / failure, making the hose unserviceable which occurred during one refueling exercise wherein the top most portion of the Elastomeric layer had given way to cleavage with exposed helical and braided reinforcement provided for avoiding formation of kink which was deformed and damaged. The assigned objective was to determine the cause of this failure and suggest design modification in hose construction to avoid recurrence of this kind of failure which has a very critical rolled to play from strategic angles . The aerodynamic assessment was done and the material was put to various test such as DSC, TGA, SEM, EDAX and we analysis. Based on the aerodynamic assessment it indicated that the maximum splashing of the hose occurred during rolled backed of the hose in view of roll back tendency against the G-effect (Gravitational effect) and the aerodynamic drag. The elastomeric covering also was studied in detail with the most advanced instrumental techniques having the likely hood of ageing phenomena. Although the elastomeric layer was found to be chemically in good compositional condition still the permanent set in the rubber lining which is under maximum stress during winding being the outer most lining was found to be significant and thus the permanently stressed zone leading to reduction in resilience of the elastomer . Further the compression set is a temperature dependent phenomenon, which is high in tropical country and thus is the most likely cause of failure. Also as the drag is proportional to the square of relative air speed therefore a reduction of the fuel transfer IAS (Indicative air speed) can prevent such a phenomenon. Therefore an improved rubber lining with lower drag coefficient and suiting Indian conditions where the average temperature are high as compared with the temperate conditions with lower platform cruise speed till the refueling hose winding is complete can prevent recurrence of such a phenomenon.