Mar 21, 2020
You ask about a very interesting aircraft, however as others have already answered the ability reverse thrust wasn’t unique.
However the engines did have a unique feature.
Convair 990 Coronado — Wikipedia
The engines were also changed to the uprated General Electric CJ-805–23s, which were unique in that they used a fan stage at the rear of the engines, compared to the fan stage at the front of the engine found on the Pratt & Whitney JT3D that powered the 990’s competitors. The engine was a simplified, non afterburning civil version of the J79, used in military fighters. Like most versions of the J79, the CJ805 and CJ805–23 were smoky, although secondary operator Spantax eventually had their 990 aircraft refitted with smokeless combustion chambers in the 1970s.
A little more about this — General Electric CJ805 — Wikipedia
The unique feature of the -23 was the transonic single stage fan. NACA had done a lot of research on multistage transonic compressors during the 50s. Using this data, GE decided to design and test a high-pressure ratio single stage transonic fan. Much to their amazement the unit more than met the design target, including that of high efficiency. A modified version of this research unit was subsequently incorporated into the CJ805–23 aft fan. With no experience of transonic fan design and little time available, Pratt & Whitney had to resort to using 2 fan stages to produce a similar pressure ratio for their JT-3D turbofan. Although not an overhung design, the -23 transonic fan did not require any inlet guide vanes. There was, however, a series of structural vanes to help support the fan casing.
The a modified version of this aircraft also served as the Galileo astronautical research aircraft.
Not all project-management work at Ames came within the jurisdiction of Bob Crane and his Development Directorate. In 1963 a small group of Ames men had participated in an airborne (DC-8) research expedition to observe a solar eclipse along its path of totality, which lay in Canada. The group included Sheldon Smith, of the Physics Branch, and Ray Torrey, of the Guidance and Control Systems Branch. As participants in the expedition, this pair, with the aid of others at the Center, developed and built a rather unique gyro-stabilized camera for photographing the eclipse from the expedition’s airplane. A description of the camera is given in the July 1964 issue of the ISA Transactions in a paper entitled “A Stabilized Automated Camera for Airborne Eclipse Photography,” by S. M. Smith, M. Bader, R. A. Torrey, and M. E. Henderson.
The photographs of the eclipse obtained with the camera were quite good and the experience of the expedition gave Smith, Bader, and others the idea that Ames should have an airborne research laboratory of its own. Such a laboratory, it was felt, would provide ready observational accessibility to astronomical and other events occurring, sometimes on short notice in remote parts of the world. The idea of the airborne research laboratory was approved by Ames and Headquarters management and was shortly implemented by the procurement of a Convair 990, four engine, jet transport airplane.
Galileo astronautical research airplane, a modified Convair 990.
This video will tell you more about this interesting aircraft.
Before Concorde defined what it meant to fly fast, there was another airliner that tried to push the speed of air travel. With outside the box engineering, the Convair 990A cruised faster than any airliner before it. The Convair 990A is still the fastest non-supersonic commercial transport to have ever been produced.
While the Boeing 707 and Douglas DC-8 are recognized as the first American jetliners, Convair had also introduced a jetliner, the 880 around the same time. While Convair’s jet looked similar to its rivals, the company tried to capture a different segment of the market, betting that there was a market niche for a medium ranged, smaller, faster and more luxurious jet. Yet, airlines showed very little interest in the Convair 880.
But in 1958, Convair had another opportunity to try to establish itself in the jet airliner market. The company would work American Airlines to modify the 880 into an even faster jet, one that could cross the country at least 45 minutes quicker than its Boeing and Douglas rivals. But this proved to be a huge technical challenge, as airliners like the Boeing 707 were already flying near the limit of subsonic speeds. Between subsonic and supersonic is a speed regime called transonic. In this middle ground, drag on an aircraft dramatically increases. So Convair and its partner General Electric would innovate to produce the world’s first turbofan powered airliner and the first airliner with anti-shock bodies integrated into the trailing edges of its wings.
After numerous development setbacks, Convair engineer’s had built the world’s fastest subsonic airliner. However, by the time it took the skies, Boeing and Douglas were firmly established as leaders in the new jet age. Convair’s airliners, with their little bit of extra speed and luxury, at the cost of practicality, range and efficiency wasn’t what the market wanted. Reportedly, the company lost nearly half a billion dollars building their 880 and 990 jetliners, and they’d never build another one again. #Convair #990 Coronado #Airplanes #NotQuiteSupersonic
Additional information provided by Doug Green in a comment but worth sharing:
To return to the original question, no it wasn’t unique, and to fine tune the answer, I would point out that the “approach” refers, in the industry, the last few miles to the runway (definitions vary) and reverse thrust at that point would be (a) risky in case it wouldn’t stow, (b) a potential unwanted distraction and © symptomatic of significant neglect in planning/executing the approach! I.e. you’ve left it far too late to slow down.
To split hairs, engines are not reversed in flight. The engines turn the same way, but a proportion of the thrust is deflected partially forward (at about 45˚).
I was not aware that the 990 could select reverse in flight, but do know that the Hawker Siddeley Trident could on engines 1 and 3, and the Ilyushin 62M routinely came over the threshold with two of the four engines in reverse idle.
I haven’t flown Tridents or ’62s. The Trident had internal reverser doors and cascades, which did not protrude into the airstream. Selecting reverse idle in the Trident would have negated the residual forward thrust — I don’t know what % rpm was allowed in reverse to further increase the descent rate, but the limit would have been less than after landing.
In the IL-62, the later Soloviev engines of the -M and -MK versions had external clamshell reverser buckets, which contributed considerable drag simply by extending into the airflow (the original Kuznetsov engines had internal doors like the Trident).
Conjecturising, I suspect the deployment of reverse a few hundred feet above the runway was to cause drag, at idle rpm, much like the BAe 146 series routinely pops the tail brake at 100 feet.
The risk of course is the failure of thrust reverser doors to stow, in the case of a go-around. Ilyushin/Soloviev must have had supreme confidence in the reliability of the system. Industry standard is that a go-around/baulked landing is prohibited if any reverser has been selected, in case it doesn’t stow. At best, even if it does, it will delay the application of go-aound thrust which, if needed, is usually needed urgently!
If you like this answer you may also like some of my other answers below.
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