Forum: F-35 Armament, Stores and Tactics

The arguments against the pneumatic stores ejection system don't take into account engineering realities. If you look at the schematics in the PDF file in the link supplied in this thread many of the questions are answered.

Based on the equipment descriptions and schematics:

1. System includes accumulators which are charged by the compressor. We don't know their size but from the looks of the system the volume of the pistons at full stroke appear to be between 7 and 10 cu. inches each with 2 pistons per station. That's a spherical volume of 1.85 inches in radius for an accumulator for each station. Four stations would require an accumuilator that was 10 inches long by approx. 4 inches in diameter assuming no other losses. That's not a large device.

2. The piston stroke is 7.5 inches. Assuming a 1 in. diameter piston and a 20 fps end velocity, the weight of the store and the number of frames in the film you can determine the force exerted. Using that number you can back out the amount of compressed air (cfm) that is needed to drive the piston less the valving losses. It's not a large number. Either way the accumulator size is small.

3. For all those who have worked on brake systems on their cars you all know that getting oil tight connections in a 5000 psi system isn't trival. Those compression fitting aren't easy at times to seat. That's why you don't want to use precharged bottles. Making those connections would be difficult using compression fittings in the field and designing a quick disconnect even tougher. Additionally the compressor (which is smaller in volume then many auto alternators) gives you the ability to provide a large number of charges to the system. The only question is how long would it take to recharge the system? Whatever the answer it still would be shorter than removing the spent cartridge and installing new ones as you would have plenty of time to recharge before you landed post mission.

4. The accumulators are protected from loosing pressure if the compressor fails by check valves (see schematic.) Also there is a manual dump valve and a relief valve in the system. The dump valve is used if you need to zero the pressure for maintenance or whatever.

Did not look close and it may not be in the schematic but you would use a cushion at end of stroke to reduce loads on the unit and extend component life.

The cfm flow rate is .35 or about 610 cu in per minute again a small number and it the 540 watts equates to 3/4 hp again a small number.

Pretty much a pneumatic system designed to best industrial practice.

But as pointed out, without all the necessary electronic wizardry that makes it a JDAM. Without all that wizardry it's just a lump of metal the same shape as a JDAM, useful for aerodynamic purposes but that's really about all. I note also that they don't mention in the navair press blurb that the "weapon" was released via the equivalent of a piece of string that the pilot had looped over the cockpit sill

Still, like they say, it's progress. But there's a lot more to do.

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Which leads me to believe that there is really only one reason why you would include a motor, compressor, etc. with all their known and undiscovered failure modes in a system that could easily be replaced with a simple accumulator and click-on-connector. A simpler system which, even if the accumulators were duplicated in parallel to increase reliability, would still be cheaper, lighter and easier to maintain than the system as installed and that reason is the Marine B version and its requirement for austere basing capability.

So this is another example of the tail wagging the dog, an overly complex system implemented because of the Marine variant and its “need” for austere basing capability.