757 CARGO DOOR CONVERSION HYDRAULICS
In 2006, Kawak Aviation was contacted by Precision Conversions 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 valves that direct fluid power to the associated circuits to vent, lock, latch and lift the door are all controlled via sequence valves.
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 it as well. A unique design constraint for the program was that the entire hydraulic system operates on Phosphate-Ester hydraulic fluid which is commonly used on late-model aircraft for its reduced flammability properties. Phosphate-Ester fluid is extremely corrosive and requires special seals to resist breakdown effects from the fluid. These seals are not commonly used and therefore not typically offered as standard parts in aviation, commercial or industrial uses. As part of the design process special seals were manufactured as there were and still are no standard parts for this use. 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. Ongoing system review and testing ultimately lead Precision Conversions to award an additional contract to design additional valving which would improve function and reliability of the system as a whole.
The completion of this program 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 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 and are continuing life-testing to-date with over 50,000 cycles logged without failure.
Continuing work included design for a replacement 400hz electric motor driven hydraulic pump which was also subjected to stringent DO-160 qualification. 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. No plumbing or electrical changes were required
We’ve supported Precision Conversions over the years by performing focused testing on additional components that were suspected potential failure points and worked with Precision Conversions to offer impartial review so as to help our customer make informed decisions about their products.