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The X-26A	The X-26B

The X-26 program is among the smallest and more secretive of the X-plane programs, and comparatively little is known of its history or accomplishments. The X-26A was a stock Schweizer SGS 2-32 sailplane used by the Navy to expose novice pilots to the phenomenon of yaw/roll coupling. At least 3 of the X-26A's were destroyed in accidents, and one remaining X-26A is housed at the Army Aviation Museum, Fort Rucker, Alabama. The final example of this unpowered glider continues in use at the U.S. Naval Test Pilot School (TPS).

The powered X-26B was created in response to a requirement for a low-acoustical signature observation and reconnaissance platform for use in the Vietnam war. The X-26B was powered by a single Continental O-200A four-cylinder, horizontally-opposed air-cooled engine. A total of two X-26B's were built, though apparently no intact X-26B's survive. The X-26B was a Lockheed-modified Schweizer SGS.2-32 glider. The initial single seat QT-1 (Quiet Thrust) was never built, but it was the progenitor of three quiet-airplane designs. A pair of two-seat QT-2 aircraft were built, and underwent flight tests at a secret base in the Mojave Desert in August 1967. These were later modified to the QT-2PC Project Prize Crew configuration, which was tested in Vietnam combat beginning in January 1968.

The X-26B planes were prototypes of the YO-3A Quiet Star aircraft flown in Vietnam during the United States military action. The Lockheed "Q-Star" was a Schweizer sailplane, modified to a prototype silent reconnaissance aircraft with an engine behind the pilot. A long shaft was positioned above the cockpit, and a big propeller was fitted on top of the nose. The Q-Star used a Wankel-type rotary engine driving a slow-moving wooden propeller via a 10-foot shaft in an attempt to achieve audio stealth. One example of this direct follow-on to the QT-2 was built, which is currently on display at the Pima Air & Space Museum in California.

 

Specifications
	X-26A	X-26B
Manufacturer	Schweizer Aircraft	Lockheed Missiles & Space
Sponsor	USN	DARPA, USA, USN
Number Built	5	2
First Flight	3 July 1962	15 August 1967
Length	26 feet 9 inches	30 feet 9 inches
Wing Span	57 feet 1.5 inches	57 feet 1.5 inches
Height	9 feet 3 inches	9 feet 3 inches
Empty Weight	857 lb	1,576 lb
Gross Weight	1,430 lb	2,182 lb
Propulsion	none	Continental O-200A 100hp
Maximum Speed	158 mph	115 mph
Maximum Altitude	18,500 feet	13,000 feet

Global Security

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Q-Star (C) with Continental O-200 Engine

 

 

The X-26

U. S. Navy Test Pilot School (aka NTPS, TPS, and USNTPS) X-26 Program History by John H. Daly III. (Paraphrased and edited by Dale Ross Stith
 

Forward

 

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The X-26 program is among the smaller and more secretive of the X-Plane programs; yet is, by some accounts, the longest-lived of the X-Plane Programs.

Comparatively little was known of its history and accomplishments ‘til now. For example: Most, if not all, of us at Lockheed in 1967 did not know of the X-26 Program. Now, as we learn it, we are telling, and showing our history!

Mr. John H. Daly III prepared the initial text for the article: A veteran USMC aviator; Mr. Daly’s experience in high-aspect-ratio aircraft included flying gliders at eighteen years of age, the US Navy Test Pilot School (NTPS), the X-26 Program, the United Kingdom Empire Test Pilot School, and evaluation flights of German Grob 109 and 115 Motorgliders as quiet reconnaissance aircraft.

 

The X-26 Program

 

Quiet Star (W): With Cutiss-Wright RC2-60 Rotary (Wankel) Engine. An aviation 1st! Jerry & Chuck

Jerry, Jack, ? & QB (Ingress)

Q-Star (Wankel) over San Francisco

Bogus Advertisement (don't believe it!)

The US Navy commenced purchasing standard Schweizer SGS 2-32 Gliders in 1967.

Designated as X-26 Aircraft, they were used in the NTPS syllabus to train test pilots in the high-aspect-ratio flight envelope, spin training, and yaw/roll coupling.

The latter maneuvers, at jet aircraft speed, were known to be dangerous; so the X-26 was used to demonstrate the characteristics at much slower and safer speeds.

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

 

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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.












 

 

 

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