Saturday, July 12, 2008

The Planes of Mojave: Gate Guardian

Sitting silently and guarding the main entrance to the Mojave Air and Spaceport is a former four-engine airliner in fading NASA blue that confuses a lot of folks. I've had people ask about the "707" at the front gate, or give directions to the airport refering to the "DC-8" at the turnoff. But this old gal is neither a DC-8 nor a 707, it is a much rarer breed, a Convair 990A, and though almost no one remembers it, the 990 actually had a name, the Coronado.

The 990 was a growth variant of the Convair 880, produced at the request of American Airlines, who wanted a faster jet to go coast to coast. The 990 was equipped with odd-shaped bulges on the upper trailing edges of the wings, called "K├╝chemann carrots", after their inventor, the German aerodynamicist Dr. Dietrich K├╝chemann. These "anti-shock devices" served to reduce transonic drag, allowing the plane to fly at a higher Mach number, .91, making it the fastest commercial airliner of its time.

The choice of engines was also critical to the aircraft's speed goals. The designers took the 880's General Electric CJ-805-3 turbojet engine (itself a simplified version of the oft-used GE J-79 jet fighter engine) and turned it into one of the first turbofan engines with the addition of bypass ducts and a fan stage, and called it the CJ-805-23. Unlike today's turbofans, though, the -23's fan stage was mounted to the back of the engine.


The 990 entered production in 1961, and it quickly became apparent that the design didn't deliver on the designer's promises. American Airlines was unhappy, and the 990A was produced to try to fix the issues, but it still didn't live up to the performance targets. American began backing out of its orders, and by 1963, it was clear that the plane was a marketing failure. Production was cancelled with only 37 airframes built. Mojave's 990A, serial 30-10-29 (meaning the 29th built), was delivered on May 11, 1962 (5 days after I was delivered!) to American Airlines as N5617 (click here for an image of the plane in American colors from 1966).

When American divested itself of its 990 fleet, serial 29 was picked up by Modern Air Transport and named Berliner Baer. NASA acquired the plane in 1975, where it joined two other 990s, the first and last built. Serial 01 was lost in a mid-air collision in 1973 and ship 29 was bought as a replacement; serial 37, which was destroyed in an aborted takeoff from March AFB in 1985. Serial 29 was reregistered as N713NA (later as N710NA) and was based at NASA Ames, where it was used as a medium-altitude atmospheric research aircraft, studying wildlife migration patterns, ice-floe movements, monsoon behavior in the Indian Ocean and making archaeological surveys of Mayan ruins. In 1983 it was flown to storage at Marana, Arizona.

In 1989 NASA needed to refine the design of the Space Shuttles landing gear and braking systems, and Ship 29 was pulled out of storage and modified as the Landing Systems Research Aircraft, or LRSA; it also became N810NA, and assigned to Dryden. The aircraft's center section was modified with a mounting for a shuttle main wheel assembly, and aft of the main gear well, protective structure to guard against airframe damage from disintegrating tires. To facilitate all this, the aircraft's landing gear retraction system was disabled. From April 1993 to August 1995 it flew a total of 155 flight tests at Dryden and Kennedy to study shuttle tire wear and for flight testing landing gear upgrade developments. The test flights were flown by two-time shuttle astronaut C. Gordon Fullerton. The shuttle tire retraction system held the test article retracted until the 990's main gear made contact with the runway. Allowed loads of up to 150,000 pounds to be imposed on the shuttle tire. Results of the flight tests allowed the crosswind limits of the shuttle to be increased from 15 to 20 knots.

Above left: the results of a shuttle tire that burst on landing. During the last series of tests, the tires were deliberately flattened to evaluate roll-on-rim failure characteristics. Above right: landing during the last shuttle tire test flight in August 1995 at Edwards' Rogers Dry Lake. (NASA photos)

Above left: the shuttle gear mount as it exists today. Above right: the remains of a test tire.

After retirement in 1995, Ship 29 was flown to Mojave, escorted by a NASA F/A-18 and trailing the type's signiture black engine exhaust. (Cathy Hansen photo Mojave Transportation Museum collection.)



NASA images and information

3 comments:

Ben Brockert said...

Hi,

Thanks for this post, and the blog. I'd been meaning to go look at that plane since I got here, but never stopped. Yesterday I went and checked it out, and the plane next to it. Interesting history.

I also got bit by an ant and a thorn through the heel of my foot, so watch your step if you're wandering around out there.

Ben Brockert
Masten Space Systems

Aleta said...

Welcome to the desert: everything bites or has thorns or is poison, or any combination thereof. :-)

And no, I did not order the Arizona monsoons. It _never_ rains here in July. Weird.

Sikiri - OST/EBOS (Belgium) said...

Nice storie. Hopefully we get the story about the CV880 converted freighters that were stored at Mojave long long time ago. I always wondered if one of the converted ones flew in commercial operation.