Lockheed Missiles & Space Co. (LMSC, now part of Lockheed-Martin Co.), in an expedited manner through liaison with the Chief of Naval Operations (CNO); acquired two of the X-26s (ordered but not yet built) for use in its Quiet Thruster (QT) Program.
The X-26s (Chassis Numbers 46? and 47?) were assigned non-standard Navy Bureau Numbers 67-15345 and (perhaps) 67-15346.
The QT Program, under the auspices of the Defense Advanced Research Projects Agency (DARPA) and sponsored by the U.S. Army with Navy and Marine Corps participation, was created in response to a requirement for a low-acoustical signature observation and reconnaissance platform. Mr. John S. Foster, Director of Defense Research and Engineering (DDR&E) made the initial request to the technical community.
Anticipating added weight for a power-plant and their intended use, the aircraft were constructed at Schweizer Aircraft USA (SACUSA in Elmira, NY) with flush rivets and thicker wing spars and skins (8G for a standard 2-32).
The QT-2s were built and flown within six months of “Go-Ahead” (First flight on 8/15/67). They were designated as experimental Lockheed QT-2s (N2471W and N2472W).
After wining a “fly-off” competition, they were ordered to be converted to tactical military aircraft and sent to Vietnam within 90 days for the Prize Crew Operational Evaluation.
They were then identified as QT-2PCs (with only #1 or #2 on the vertical empennage).
A third X-26 was acquired during that period and modified to Lockheed Q-Star Aircraft configuration: The Q-Star (N5713S) was a Lockheed “house aircraft” used for research and development for the YO-3A while the QT-2PCs were in Vietnam.
The QT-2PCs and aircrews (Phases I and II) flew at low altitudes (800 to 1200 ft AGL) in Vietnam throughout most of 1968, almost exclusively at night.
The QT-2PCs were transferred back to the NTPS in 1969 and designated as X-26Bs.
Note: Until that time, the NTPS (2-32) gliders were designated as X-26s. Adding a power plant to the gliders caused them to be re-designated X-26As and the powered (QT) aircraft to be designated as X-26Bs.
One X-26B (Tail Number “5345”) was flown and, as no spares were available, the other was used for parts.
The X-26B Aircraft, using a propeller mounted on a pylon in a tractor configuration had, as an unwanted effect, a “fixed-rudder” mounted on the wrong end of the aircraft!
The design resulted in, not only yaw-roll coupling, but adverse yaw-roll coupling (yaw-roll divergence).
Note: LMSC earlier added approximately four Sq-Ft of surface area to the vertical empennage to ameliorate the condition, but that did not correct the problem.
NTPS exploited this flight characteristic to teach adverse yaw-roll couple phenomenon.
Other X-26B Uses. During the early 60s, the U.S. Navy was concerned about the noise generated by H-2 and H-3 helicopters when they hovered over water to “sonar dip” and in slow-speed Anti-Submarine-Warfare (ASW) flight operations. Potential detection of the helicopters, by the submarine(s) being prosecuted, was the concern.
So, a series of tests were conducted over the Chesapeake Bay near NTPS:
1. A stationary boat was used to collect the noise data from the hovering helicopters.
2. The X-26B was used to collect noise data from single-rotor helicopters while hovering and in slow-speed (i.e., up to 40 knots) flights over water.
The X-26B was chosen as an acoustic sensor platform for the following reasons: (1) It presented a low level of noise contamination: A low amount of propulsion power was required to maintain level flight. (2) It was stable in low-speed portions of the flight envelope.
The data gathered from these tests was used later in the Army’s RAH-66 Comanche program and in a DARPA program to reduce of helicopter acoustical noise signatures.
I was fortunate enough to fly the last series of flights gathering the acoustic data.
John H. Daly III
Post Script:
Recent credible reports place at least one QT-2PC at Pt Mugu, CA in 1969. Nothing is yet known about its operations there.
The X-26Bs were declared surplus to the Navy in 1973 and were then used by the Army for a sensor test.
A LMSC employee (Cutrer) reported seeing the X-26B at the Naval Air Museum in Pensacola, FL, but a record of it being there has not yet been found.
The surviving X-26B (67-15345/QT-2 N2471W/QT-2PC #1) is now in storage at the U.S. Army Aviation Museum (USAAM) at Ft. Rucker, AL in the care of Mr. Steve Maxham, Director/Curator.
The other X-26B (67-15346?/ QT-2 N2472W/QT-2PC #2) has been returned to a (nominal) SGS 2-32 configuration and is operated at Mile High Glider School in Boulder, CO in the care of Mr. Dave Mencin.
