Downwards ejection seats: the arguments in favour of them

[gumbyk]

Less stressful on internal organs and spinal cord: as a consequence of the first point, you don't need a very powerful and sudden thrust to leave the cabin. The direction of the thrust also does not compress the spinal cord and the organs.

It may produce less stress on the spine, etc, but more strain on the blood vessels in the eye and brain. Even -3g can cause damage to the eyes (retinal detachment, burst blood vessels), so at ejection forces (even downwards) you may be at risk of bursting major vessels in the brain.

Also, don't forget that the aircraft's trajectory is downwards - ideally you want to be above that. An aircraft in a spin has very little or no forward velocity to carry it away from a pilot under a chute.

 

[Joe Broady]

-Simple/More reliable? I'm thinking about the fact that also the canopy (or the cabin's roof) must be jettisoned. It means another ejection mechanism that must activate split seconds before the seat . A trapdoor unlocking and opening backwards (or being pushed by the seats itself) looks a simpler and more reliable mechanism.

I'm skeptical about that. In the B-52, for instance, all six ejection hatches have an initiator which fires when the hatch departs, thereby arming the seat. This safety feature prevents the seat from firing if the hatch fails to jettison. If the hatch initiator malfunctions, there's a "pin pull" control on the seat to override the initiator — after you make sure the hatch has departed! So in the B-52, at least, the ejection sequence involves a sequence of automatic steps whether the ejection is upward or downward.

The flight manual warns that if a downward ejection hatch is dropped when the plane is on the ground, the seat is armed and can fire.

Minimum downward ejection altitude is 800 feet in the B-47. In the B-52 you can escape successfully from 250 feet if the plane is not descending with respect to terrain and has at least 120 knots airspeed.

I don't know what's below the floor in a fighter, but I imagine a downward ejection system would impose annoying constraints on the layout of cables, plumbing, and linkages since there has to be a clear space for the hatch. Also, the structural design has to carry load around the hatch opening unless the hatch is a stressed, load-carrying component.

References:
1B-47E-1, Flight Handbook, USAF Series B-47B and B-47E Aircraft, 30 December 1955.
1B-52H-1, B-52H Flight Manual, 30 July 1980

A safety supplement in the B-52 manual warns that the 250 foot figure is valid only if the downward ejection seat is full forward. If not, the drogue parachute mechanism can be damaged during ejection. The man-seat separator is not affected, but without help from the drogue chute you must be at least 400 feet above ground. That was in 1980; I assume the deficiency has been corrected.

 

[msxyz]

Very informative post and interesting considerations. A downwards ejection seat wouldn't be possible in a plane where the wheel well is located under the cabin, or if there is an air intake. Also, the levers connected to the pedals and the yoke/stick would have to be routed around the hatch resulting in a more complicated arrangement.

 

[nuuumannn]

The much maligned Yak 38 had an automatic firing ejector seat if the pilot got into difficulties at landing

Yeah, initially this happened quite often, well comparatively as there weren't that many aboard the carriers, but Yak developed an autoland system for the aircraft, which was quite effective. It's worth remembering that the Yak-38 was not meant to be operated as a standalone aircraft, like the Sea Harrier, but as a weapons system employed from the carrier, which, strictly speaking is an Anti-Submarine Warfare Cruiser deployed with a specific role as part of a task force. The Yak-38s were to carry out strike operations against shipping and had a limited IR AAM capability. Nonetheless, it was limited in range and thus payload carrying capability.

 

[msxyz]

This drawing depicts the downwards ejection system of a soviet bomber (possibly the Tu 22). The pilot's and the other guy's seat slides on rails though a long shaft before being ejected. What a fun ride must have been!

 

[T Bolt]

I read somewhere pilots of the early F-104s were told that in case of an engine failed at take off they were to roll the aircraft upside down and eject.

 

[gumbyk]

I read somewhere pilots of the early F-104s were told that in case of an engine failed at take off they were to roll the aircraft upside down and eject.

That would likely just delay the inevitable. Excessive negative G, and trying to deploy the chute while 'inverted' is never going to end well. If they were told that, it was just to make them feel better.

 

[Thumpalumpacus]

That would likely just delay the inevitable. Excessive negative G, and trying to deploy the chute while 'inverted' is never going to end well. If they were told that, it was just to make them feel better.

The drogue chute isn't directional, is it? F-104 is before my time, but so far as I understand, the drogue-chute just goes in the wind to pull out chute, no matter the direction. And inverted and diving in would impart positive-G, no?

Am I missing something here?

 

[gumbyk]

The drogue chute isn't directional, is it? F-104 is before my time, but so far as I understand, the drogue-chute just goes in the wind to pull out chute, no matter the direction. And inverted and diving in would impart positive-G, no?

Am I missing something here?

Most ejection seats at that time had limitations on bank, as the drogue doesn't come out immediately.

You'd still impart quite a few G on your body ejecting downward, add 2 more if the aircraft was inverted and punching out the bottom, even if you were positive during the dive. Generally the human body isn't as resilient to negative g as positive. e.g. retinal detachment can occur as low as -3g.

 

[msxyz]

I think downwards firing ejector seats need to impart a much weaker thrust, not only because gravity is lending a hand but also because there is no tail to clear. The seat just needs to be pushed outside the aircraft, like a bomb or missile from an internal bay. But if the thrust is weak, ejecting upside down could cause the pilot to strike the fuselage due to the combined action of gravity and the airflow.