ORIGINAL: BMatthews
The first or first few models of 104 had downward seats. And possibly a few other craft at the time. The why for it is because they couldn't ensure a safe punchout at supersonic speeds over the high T tail of the 104. But it obviously meant that the pilot needed quite a distance under the keel before ejection was safe. Rolling to the side was an option of course but that's hardly a good thing to do during takeoff and the initial portion of the climb when speed is low. It was the best they could do at the time.
Mr. Matthews is quite correct in his reasoning on the why of the F-104 down seat. I worked on both the F-104 and on ejection seats as an engineer and perhaps can add some additional insight.
Early ejection seats used a ballistic cartridge (think, "cannon shell") for propulsion. Basically, the seat and it's occupant got a gigantic bang to separate them from the airplane. As you might imagine, there is a limit to how much of a jolt the human body can withstand. Later in the evolution of ejection seats, rocket propulsion came along. The rocket motor imparted a lower force on the pilot over a longer period of time, thus getting him higher and farther from the airplane while hurting him less.
The F-104 can be truly said to be an airplane that was ahead of its time. Many of the internal systems and components were not up to the performance potential of the airframe. With only ballistic propulsion being available for the ejection seat, Lockheed did the only thing that could be done they made the seat go down rather than up.
When you examine the overall performance envelope of an airplane such as the F-104, there wasn't much difference between a ballistic seat going up versus one going down. The upward or downward velocity component of the airplane's flight path is a giant consideration on a safe ejection. If the airplane is descending rapidly, it doesn't make much difference whether the seat goes up or down you will still hit the ground before your parachute opens. Likewise for the case where the airplane is climbing. It you have a large upward speed component when you eject, either the up or the down seat will do the job.
Is an upward seat better? You bet. Once rocket propulsion became available, changing to the up seat was a no brainer. The up seat extended the safe ejection envelope to lower altitudes in combination with higher sink rates. It also gave the ability to eject at ground level as long as there was no sink rate involved.
Today we have ejection seats in which a crew member can escape at zero altitude and zero airspeed and expect no back injuries. But things were not always that sweet. The F-104 came along slightly before the big seat improvements were available. We also retrofitted the T-33 trainer with a rocket seat. The F-80/T-33 first appeared with no ejection seat at all, so it went from a "climb over the side" airplane, to a "ballistic seat" airplane and ultimately to a "rocket seat" airplane.
Dick Fischer