When maneuvering for position in air-to-air combat, pilots able to pull the most Gs without losing consciousness have an advantage. Engineers at Carleton Technologies Inc., a manufacturer of pneumatic components and oxygen systems, found a way to increase that advantage and save the U.S. Navy money.
The team designed an aircrew oxygen regulator that automatically applies positive pressure for breathing under higher G forces. Because it has fewer parts, the regulator costs about one-fourth as much as its predecessors and has proven reliability.
At the heart of the responsive, lightweight CRU-103 regulator design is a low spring-rate electrodeposited nickel bellows from Servometer (Cedar Grove, NJ). Worn on the parachute harnesses of Navy pilots and Naval Flight Officers flying tactical jets, the chest-mounted regulator weighs 13 ounces, and routes breathing oxygen under pressure to the wearer's oxygen mask and to an upper-body G-vest in response to aircraft maneuvers. The more Gs the pilot pulls, the greater the oxygen pressure applied to mask and vest.
Between the G-sensing air supply valve on the aircraft and the pressure valve in the regulator is a highly flexible metal bellows. As the bellows fill with air and expand, they close the regulator valve and increase the pressure of oxygen going to the pilot. "We could have used a piston or some other arrangement," explains Carleton Design Engineer Jim Talty. "But the bellows gave us the most mechanically efficient solution. Thin-walled electrodeposited nickel bellows provide exceptionally low spring rates for a quick, consistent response. It provided a reliable mechanical solution that was lighter and smaller than the alternatives."
After evaluating pistons and springs, Carleton partnered with Servometer on a solution based upon a precision metal bellows. Servometer engineers helped analyze the regulator requirements including travel distance with pressure change, and offered custom-designed electrodeposited nickel bellows with far lower spring rates to minimize resistance.
Bellows spring rate is a function of inside diameter, outside diameter, number of convolutions, material, and wall thickness. Electrodeposited nickel bellows typically provide one-fifth to one-tenth the spring rate of hydroformed brass bellows of the same size. "When they expand," Talty explains, "the amount of force you lose stretching the bellows is very low. The force also stays consistent from regulator to regulator."
Thanks to the regulator, pilots get exactly the oxygen they need without waste. Pressure to the mask and the compression vest is kept the same to maintain equilibrium inside and outside the pilot's chest.
Initially, the Navy issued the CRU-103 regulator only to the crews of the highest-performance fighters and attack aircraft. However, at $1,100 each, compared to as much as $4,000 for other regulators, the lower cost has led to the CRU-103 being used on all Navy aircraft.
Regulator production is ramping up from 1,000 to 3,000 a year, says Talty. "Fleet experience has been excellent. Our measure of success is reliability. With our design, the Navy has had far fewer regulator repairs." For more information about bellows from Servometer: Enter 537