Engineers took the design several steps further. Firstly a "triple engine" arrangement was planned to exercise the most power from the available technology. Beyond increasing performance, this engine arrangement increased reliability should one unit fail the pilot. It was planned to fit 3 x Westinghouse 24C series turbojets into the design, two in a ventral fairing (aspirated by the ventral intakes and exhausted under the empennage) and a third within the empennage section (aspirated by the side-mounted intake slots and exhausted under the tail fin). Placement of the engines in the body and tail of the aircraft meant that the nose section could accept all of the planned armament and centralize firepower on a given target.
Secondly, the group produce two working plans for the aircraft - the first was to feature a "bicycle style" wheeled undercarriage arrangement (retractable) and the second to sport a traditional, conventional tricycle undercarriage. For the former, this allowed the wings to be reduced in thickness, making them lighter, stronger and flexible for high-speed flight. When ground-running, the aircraft relied on outriggers - thin, simple wheeled legs - to hold up the edges of the aircraft's wings and thus keep the aircraft from tipping. In the more conventional tricycle undercarriage approach, a thicker wing was to be used to house the main landing gear legs.
The design team estimated their aircraft to feature a maximum speed of 657 miles per hour, a combat radius of 1,000 miles and a service ceiling of 47,000 feet. Both presented versions were estimated with roughly the same performance values.
At any rate, the Downey Penetration Fighter did not proceed beyond this planning stage for it was not accepted by USAAF authorities. After review, the design was thought to have grown too with its engine trio which also elevated maintenance requirements and complicated repair. There was no denying the estimated performance figures and reviewers appreciated the excellent vision for the pilot but there was some additional concern in regards to agility for such a large aircraft - a key quality of fighter types.
Selection moved on to a few different designs from competing sources - the McDonnell XP-88/XF-88 "Voodoo", the Lockheed XP-90/XF-90, and the North American YF-93 - but none of these were furthered beyond "fly-off" competition forms as the idea of a penetration fighter quickly fell to history and the idea of a dedicated penetration fighter also fell with it. Bombing enemy targets in their own territory took a back seat to intercepting incoming waves of nuclear-armed Soviet bomber formations.
Aircraft like the supersonic Convair F-102 "Delta Dagger" were pushed through as dedicated interceptors while the XP-88 went on to see its own ultimate evolution as the McDonnell F-101 "Voodoo" fighter - these offerings detailed elsewhere on this site.
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