Boeing 757 Cargo Door Conversion
In 2006, Kawak Aviation was contacted by Precision Aircraft Solutions of Beaverton, Oregon to help optimize their cargo door conversion for Boeing 757-200 jets which are converted for use as cargo freighters. The large cargo doors are installed into the forward section of the aircraft and are operated by hydraulics. These cargo doors which are controlled by a series of sequence valves, direct fluid power to the associated circuits to vent, lock, latch and lift the door which allows expedient loading and unloading of cargo.
The original design of the door utilized sequence valves that were soon discontinued by the original manufacturer, it was at this point that Kawak was contacted to analyze the current valves and subsequently create a drop-in replacement which would not only replace the discontinued part but out-perform them as well.
The unique system design constraint was that the entire hydraulic system operates using Phosphate-Ester hydraulic fluid which is commonly used on late-model aircraft for its reduced flammability properties. Phosphate-Ester fluid requires special seals to resist breakdown effects from the fluid. These seals are not commonly used or available and therefore not offered as standard parts in aviation, commercial or industrial uses. As part of the design process special seals were designed and manufactured.
Following this design process, at the request of the customer, Kawak performed extensive test of the valves according to stated DO-160 specifications. This program was initiated and completed with all testing and FAA certification in less than 12 months. Subsequent system reviews lead Precision Aircraft Solutions to award an additional contract to design replacement valves for addition functions in the hydraulic door system. These counterbalance and check valves went on to improve function and reliability of the system.
The completion of this programs in record time, cemented a lasting relationship between the two companies and lead to development of replacements for all the hydraulic cylinders which function to vent, lock, latch and lift the door for loading and unloading of the cargo pallets. The original cylinders were prone to leakage and seal failure. Kawak designed and developed replacement hydraulic actuators which were true direct replacements and which offered improved sealing and extended longevity due to the robust construction and use of quality materials and finishes. These hydraulic cylinders were tested to customer-specified DO-160 categories. Continuing development for improved seal technology is ongoing and supported by Kawak using a custom designed test stand.
As time passed, manufacturers continued to discontinue parts of the original system. The next part to experience this phenomenon was the 28VDC electric motor used to drive the hydraulic pump. Kawak developed a 400hz electric motor driven hydraulic pump which allowed Precision Aircraft Solutions to reduce wire gauge, thus decreasing installed system weight as well as improve system reliability. This new electric motor/pump combination was subjected to stringent DO-160 qualification supporting installation on transport category aircraft (FAR25). Its benefits included a more robust motor design which operated much quieter than the previous unit and was lighter and more compact. It was designed so that it could replace the previous design quickly and easily.
Kawak has, and continues to support Precision Aircraft Solutions by performing focused, unbiased testing on components which are suspected reliability points and continues work with Precision Aircraft Solutions to offer impartial review so as to help make informed decisions about their products.