| Dryden YO-3A has storied past July 3, 1998 Volume 42, Issue 12, Dryden Flight Research Center, Edwards, California
July 3,1998 The YO-3A has flown in Vietnam, served the FBI and now is used at Dryden for pilot proficiency flights. By Gray Creech
Aerospace Projects Writer From stealthy spy plane to Dryden research support aircraft, the YO-3A has a colorful past and is serving as a pilot proficiency aircraft until it is called upon for a new support mission. Dryden acquired the YO-3A, which arrived here in December 1997 from the Ames Research Center. Ames acquired the aircraft in 1978, from an airframe and powerplant mechanics school for use as an acoustic flight research aircraft to record the noise levels of other aircraft inflight. This is accomplished with the YO-3A's wing tip and tail-mounted microphones. Past NASA missions of the aircraft have included sonic boom sound measurements of a NASA SR-71 and various helicopter and tilt rotor noise measurements. " I've been working on the YO-3A since NASA acquired it," said Monte Hodges, the aircraft"s crew chief. "It was a major change to work on this airplane after working on modern jets." Lockheed developed the YO-3A from a Schweizer SGS-2-32 sailplane during the 1960s as an observation plane for use in the Vietnam War. The aircraftıs ultra-quiet design and large bubble canopy allowed pilots to move stealthly and at low altitudes over enemy territory to visually observe troop locations and movements, particularly at night. Somewhere between 13 and 15 of the aircraft were built. Drydenıs aircraft saw action in the war and is one of three still flying (the other two are privately owned). The FBI owned and operated two of the aircraft in the 1970s. Aircraft modifications greatly reduced the YO-3Aıs noise. A specially constructed and modified muffler system for the engine reduces engine exhaust noise. For non-sound measurement flights, the muffler system is not operated as it reduces the engineıs available horsepower. The aircraft uses a belt-drive reduction system, which is quieter than a gear reduction system. The system turns the propeller 3 1/3 times more slowly than the engine turns. This system is similar to an automobileıs timing and fan-belt system in that rubber belts link various mechanical parts rather than metal gears. Additionally, the YO-3A has extra in sulation applied to its firewall. The engine valve covers have a sealant to reduce valve ³ping.² The aircraftıs large custom-made wooden propeller also is much quieter than metal ones. It has a wider chord than the average propeller, allowing a lower rounds-per-minute rate which equates to quieter operation. It is also a handmade work-of-art made from Canadian Birch plywood layers one-sixteenth of an inch thick. The airplane isnıt the most responsive or the most comfortable airplane to take to the skies. The tandem seats are completely non-adjustable as are the rudder pedals, so pilot height differences cannot be accomodated. Instrumentation is very basic no Instrument Flight Rules (IFR) equipment to be found here. Also, being a ³taildragger² (only two main landing gear and a small tail wheel, as opposed to the more typical three main gear aircraft), taxi and takeoff can prove challenging for the most experienced pilot.The airplane doesnıt like to bank or turn very speedily, due to its basic sailplane-type cable-based flight control links. Range is limited to about 379 miles per fuel load, but this is greatly reduced on hot, thin-air days. "With the YO-3A Iıve learned about maintaining old aircraft. You have to think simple and direct, no computers," Hodges said. "A little patience doesnıt hurt either; the YO-3A is a very humble aircraft that requires alot of attention. It does offer a good view of life though low and slow."
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