Forum: F-35 Armament, Stores and Tactics

That is why the [ELP] informant is 'anonymous'. Very Happy

I guess we know where 'jeffb' is coming from also. AS IF we did not already guess eh.

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Quote:

jeffb
"Please explain"
In the words of a fictional Australian solicitor:
"Your honour...It's the vibe of the thing".

Didn't that Fictional Solicitor or his client also say something like "The law of common bloody sense says so your Honour."
On the Price - Don't you believe LM when they say it will cost $65m fly away once they are in volume production. [And pigs might fly also.]
I agree with you on how it will probably be used - as a bomb truck after other weapons clear all other defenses unless it is all you have.
Obvious why why the dropping of an "object" got no Press. "Yawn".
I can just see the headline. "F-35 drops a piece of metal shaped like a weapon." "Yawn"

rkap wrote:

I can just see the headline. "F-35 drops a piece of metal shaped like a weapon." "Yawn"

It's not a "piece of metal shaped like a weapon".

It was an inert Mk.83 bomb body with an attached KMU-559/B guidance section and tail assembly.

The particular weapon dropped was also fitted with a fuse and the standard GBU-32 JDAM aero-surfaces (strakes).

Describing it as nothing but a piece of metal, sells short what was achieved here.

This WAS a JDAM, just one without explosive filler...

Conan wrote:

Interesting that people always want more from than this program than reality allows.

I may just frame this one... Very Happy

Conan wrote:

rkap wrote:

I can just see the headline. "F-35 drops a piece of metal shaped like a weapon." "Yawn"

It's not a "piece of metal shaped like a weapon".

It was an inert Mk.83 bomb body with an attached KMU-559/B guidance section and tail assembly.

The particular weapon dropped was also fitted with a fuse and the standard GBU-32 JDAM aero-surfaces (strakes).

Describing it as nothing but a piece of metal, sells short what was achieved here.

This WAS a JDAM, just one without explosive filler...

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 Very Happy

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

The point of the test was not to test the weapon, per se, but to test the BRU-67, how it interacts with a JDAM, and the aerodynamic forces that act against the JDAM as it exits that weapons bay. They will then take all the collected data and compare it against the predicted values to better understand and improve the simulations.

rkap wrote:

Quote:

jeffb
"Please explain"
In the words of a fictional Australian solicitor:
"Your honour...It's the vibe of the thing".

Didn't that Fictional Solicitor or his client also say something like "The law of common bloody sense says so your Honour."
On the Price - Don't you believe LM when they say it will cost $65m fly away once they are in volume production. [And pigs might fly also.]
I agree with you on how it will probably be used - as a bomb truck after other weapons clear all other defenses unless it is all you have.
Obvious why why the dropping of an "object" got no Press. "Yawn".
I can just see the headline. "F-35 drops a piece of metal shaped like a weapon." "Yawn"

I expect a fly-by by an entire squadron of pigs the day the F-35 hits FRP rkap, each of them trailing a different color smoke from their little piggy butts.

SpudmanWP wrote:

The point of the test was not to test the weapon, per se, but to test the BRU-67, how it interacts with a JDAM, and the aerodynamic forces that act against the JDAM as it exits that weapons bay. They will then take all the collected data and compare it against the predicted values to better understand and improve the simulations.

Yeah I get that Spudman, but in this case do we know that the carrage system WAS a bru-67? I don't know how much force the ejector imparts on the store, possibly not that much. There only appears to be about 5 or 6 meters in the video between the bottom of the aircraft and the edge of the frame and the 'bomb' clears that frame in just a little over a second; that's not much more than a G of acceleration. Won't they need to test just letting the store FALL out of the aircraft at some point anyway?

BTW, are there any theories on why they've included the whole motor, compressor, manifold for the ejectors on the aircraft instead of just pre-charged gas reservoirs?

It's a BRU-67. There is no way for it to be anything else. No other system has been contracted for and testing anything but a BRU-67 would be completely senseless from a Flight Sciences aspect.

As to what force is applied, here are the specs on a per-weapon basis for the BRU-67/68.

My thoughts on the inclusion of pumps in the bay & pylons vs bottles is for reuse, quick turnarounds, variable charge states, etc.

To downloaded the original video in 1080 and played it back one frame at a time (via VLC). It was recorded at 29.9 fps and took only 21 frames from eject point to clearing the bottom of the screen. That is 2/3rds of a second to go 21 ft (based on ratio of F-35B length vs video frame size). The minimum (see pic above) is 15 ft/sec which it exceeded handily.

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.

SpudmanWP wrote:

To downloaded the original video in 1080 and played it back one frame at a time (via VLC). It was recorded at 29.9 fps and took only 21 frames from eject point to clearing the bottom of the screen. That is 2/3rds of a second to go 21 ft (based on ratio of F-35B length vs video frame size). The minimum (see pic above) is 15 ft/sec which it exceeded handily.

Great work Spudman, it was really just a passing remark made well past midnight just before I went to bed, I'm impressed you went to so much trouble. How did you determine which frame was "the eject point" as the door hides the store coming off the ejector doesn't it?

marksengineer wrote:

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.

Thanks for running the numbers on this ‘MarksEngineer’. There are just a couple of points that I’d make.

First, I don’t think I’ve seen any arguments ‘against’ the pneumatic ejector system as the advantages in relation to hazardous waste handling alone are, I think, self-evident. My concern was that the reliability of the new pneumatic systems might warrant a pyro based back up, especially in the case of the B version where bring back weight is of concern and a hung store may turn out to be a critical issue.

Second, the manufacturer is already “considering having off the shelf units pre-charged” which would argue that while achieving oil-tight connections with pre-charged units might be problematic, it certainly hasn’t been dismissed out of hand by the manufacturer as too difficult.

Third, your analysis seems to step around the obvious solution of simply installing the accumulators on the aircraft and charging them from a ground cart. This approach is cheaper, lighter, reduces system complexity, eases maintenance and removes a potential source of failure, so while the system as supplied may represent “a pneumatic system designed to best industrial practice” it doesn’t necessarily represent the best option for a new combat aircraft designed to “best industrial practice”.

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.

Last edited by SpudmanWP on Aug 18, 2012 - 08:15 AM; edited 2 times in total

jeffb wrote:

Great work Spudman, it was really just a passing remark made well past midnight just before I went to bed, I'm impressed you went to so much trouble.

Don't worry re:passing remark as I have made pleanty of those myself (yes, mostly after midnight).

jeffb wrote:

How did you determine which frame was "the eject point" as the door hides the store coming off the ejector doesn't it?

IIRC, I looked at the distance between the first visible and second visible frame and determined how many frames (one I think) to add to the total.

I will try to create an animated GIF with stopmotion and post it later.

--update--

Here is the animated gif.

I'm amazed this thread has gone this far. No one implied anything in this story other than the first AIRBORNE weapon release. Never said it was a live weapon. Never said it was guided. Never said the aircraft was tracking a target.

To downplay it to the level of 'using a string' to release it is also ridiculous.

It was an inert JDAM, released by the pilot, being carried on the ejector system the F-35 uses.

Forum: F-35 Armament, Stores and Tactics

F-35B First Aerial Weapons Release VIDEO + Pictures + Info