The GAU-22/A thread

[steve2267]

Reading between the lines of Dragon's post in the F-35 Updates thread:

http://www.edwards.af.mil/News/Article/ ... oward-ioc/

As of days ago, all Block 3F F-35A and F-35C WDAs have been completed, with only a single WDA for the F-35B remaining.

If all WDA's have been completed, it would seem that all accuracy / vibration issues with the GAU-22/A have been put to rest. Never did see a press release / announcement to that effect. The lack of any Gilmoresque wining, screaming, or gnashing of teeth would also seem a confirmation of sorts.

[steve2267]

F-35 Problems: Late IOTE, F-35A Gun Inaccurate, F-35B Tires, Threat Data, Cyber…

by Colin Clark, Jan 26, 2018

...

There’s another important problem which will make it very difficult for the Air Force to argue that it can replace the A-10 with the F-35A, as planned: “The F-35A gun has been consistently missing ground targets during strafe testing; the program is still troubleshooting the problems.” The gun shoots “long, and to the right.” The Marine’s F-35B and the Navy’s F-35C guns, which are not built in, are apparently performing better. “Initial accuracy testing of the F-35B and F-35C podded guns showed better results than that of the F-35A model,” Behler writes. “Both the F-35B and the F-35C gun pods exhibited the same right aiming bias as the F-35A, however the long bias is not manifested in the podded gun systems.”

The other bad news here is that “delays in completing the remaining gun testing and correcting gun-related deficiencies within SDD, especially for the F-35A, are adding risk to the IOT&E schedule,” the report says.

...

https://breakingdefense.com/2018/01/f-35-problems-late-iote-f-35a-gun-inaccurate-f-35b-tires-threat-data-cyber/

Since SDD has been concluded, I am unclear on to what extent, if at all, gun testing and deficiency corrections may have impacted the IOT&E schedule. My impression is that IOT&E is mostly affected by having enough airframes available to perform that testing.

That being said, I recall early "issues" with the gun system involving "vibration." However, I would think that "vibration issues" would tend to either affect firing rate, or decrease accuracy -- open up grouping size(s) -- that is, the gun wouldn't meet the required maximum dispersion specification. The gun consistently "shoot(ing) long, and to the right" sounds like an aiming problem. The pod is consistently shooting right, but not long. Perhaps "long" could be a design / installation issue? If it's consistent... then kentucky windage the thing in the aiming software.

Interesting that the gunpod was performing better than the -A's builtin gun.

Has anyone else seen any thing else gun related?

[sprstdlyscottsmn]

So, I may be guessing out my butt here... Hitting right sounds like CLAW trying to compensate for the offcenter A model recoil. Hitting long sounds like CLAW trying to compensate for low mounted pod recoil. I do not suspect I am correct by any means, but it sounds like the CLAW uses the same algorithm regardless of model and has too much rudder involved. I honestly expect to be wrong because that would be a rookie mistake.

[steve2267]

Spurts, sounds good to me, though the article noted the -A was long too... and the gun is above the a/c CG on the -A, isn't it?

Still, it sounds to me like something that is software fixable. If they were saying the gun was all over the place (e.g. shooting 10 mil dispersion diameter rather than the spec 5 mil diameter), then I'd say there were more serious issues a foot.

The F-35 is the first jet whereby man has aimed the cannon through a helmet mounted sight. i wonder if there could be some parallax kind of issues or just other HMS issues involved? Still... how much different is it projecting a dot or pipper out in space on an HMS vs a HUD?

The article is four months old, it's about the DOT&E report, so how much older might that information be? For all I know, all gun issues have been put to rest, but I've read no stories from the stellar aviation / aerospace press core about the resolution of any F-35 gun system issues. (They love to tell you when it's broke... not so much when the problem is fixed.) Given the lack of media harumphing over a broken gun, I'm guessing it is a non-issue and has been resolved... but...

[wrightwing]

SDD is complete, and no further issues have been mentioned with the guns.

[steve2267]

From FY2017 DOD Programs - F-35 Joint Strike Fighter (JSF), to which Spud had previously linked back on 1-24-18:

* Flight testing of the different gun systems on the F-35 (internal gun for F-35A and external gun pods for the F-35B and F-35C) revealed problems with effectiveness, accuracy, pilot controls, and gunsights displayed in the Helmet Mounted Display System (HMDS). The synopsis and assessment of specific HMDS problems are classified. The gun profiles include the testing and qualification of four separate 25 mm rounds in the two gun types. The F-35A internal gun testing includes the PGU-23 training round, PGU-47 Armor Piercing High Explosive Incendiary round, and the PGU-48 Frangible Armor Piercing round. The F-35B and the F-35C variants external gun pod testing is limited to the PGU-32 Semi-Armor Piercing High Explosive Incendiary round used by the Marine Corps.

p.42 of http://www.dote.osd.mil/pub/reports/FY2 ... f35jsf.pdf

Gun Testing

• Gun Activity
  
  • All three F-35 variants add gun capability with Block 3F. The F-35A gun is internal; the F-35B and F-35C each use an external gun pod. Differences in the outer mold-line fairing mounting make the gun pods unique to a specific variant (i.e., an F-35B gun pod cannot be mounted on an F-35C aircraft).
  • AF-31, the only Block 3F mission systems-capable F-35A test aircraft configured for gun testing, completed the first air-to-ground gun firing at Naval Air Weapons Station (NAWS) China Lake, California, in February 2017.
    
    • Helmet Mounted Display System (HMDS) alignment problems identified during the test event prevented further weapons demonstration activities with the gun until corrections were developed and tested. The test team accomplished a risk reduction test flight in March while awaiting resolution of the HMDS alignment and line-of-sight problems.
    • AF-31 completed an air-to-ground live fire accuracy event on September 27, 2017, and a gun lethality mission on October 5. Additional testing was ongoing at the time of this report.
  • BF-1 completed the first F-35B airborne gun firing on February 21, 2017. BF-1 then attempted more gun testing in March, but gun pod problems, weather, and range availability prevented the completion of the initial set of scheduled events.
    
    • BF-1 resumed testing in April, but gun pod seal problems and cracks at the FS 346.5 frame further delayed testing. BF-1 completed airborne gun firing in May to complete the flight sciences testing of the gun pod on the F-35B.
    • BF-17, the only Block 3F mission systems-capable test aircraft configured for gun accuracy testing, completed a gun lethality mission on September 12, 2017.
  • CF-3 performed the first F-35C airborne gun firing on June 6, 2017, and continued more gun testing throughout the month. It completed flight sciences testing with the gun pod in July.
• Gun Assessment
  
  • F-35A gun accuracy testing on AF-31 demonstrated uncharacterized bias toward long and right of the target. Also, the gunsight display in the HMDS was cluttered and slow to stabilize.
  • The initial F-35B strafing results with the gun pod have been better than those for the F-35A. The aim-point projection through the HMDS was more stable and the F-35B does not appear to have significant angular bias errors like the F-35A. The program will complete accuracy assessments; however, because the program used just a single aircraft per variant to assess compliance with specification requirements, the JPO will make more assessments with OT aircraft before and during IOT&E.
  • F-35C accuracy results with the gun pod to date have been consistent with those observed with the F-35B.
  • The JOTT and the Services will need to develop shot-kill criteria, possibly for each variant, to assess the effectiveness of simulated gun employment during training and test mission trials in IOT&E. Ongoing delays in completing the remaining gun testing and correcting gun-related deficiencies within SDD, especially for the F-35A, are adding risk to the IOT&E schedule.

p.43 of http://www.dote.osd.mil/pub/reports/FY2 ... f35jsf.pdf

So to summarize:

• sounds like gun system assessment to continue during IOT&E as there was only one -A, one -B, and one -C available for gun testing during SDD.
• -A had (has?) some HMDS display issues
• -A also has "significant angular bias errors" (someone needs to brush up on their trig? )
• The services still need to settle on what constitutes a gun kill

I find it significant that there was no mention of "vibration" issues that were made a (semi-)big deal of a year ago.

Sounds like normal development issues that are still being worked through -- I don't see any big oopses or major issues.

[archeman]

I never understood why the USAF didn't pony up the development cost to mod the external gun pod for the A model.

In one pretty simple move, the USAF could have silenced the 'Big Guns Win Wars' crowd and given the A-10 chest beaters something serious to chew on (dual GAU-22s) which would nearly double the A-10 rate of fire and nearly match the total A-10 kilojules of kinetic target impact.
A lesser but not unimportant note of course is that doubling the cannon fire of the F-35A it actually WOULD be a serious ground attack improvement. It wouldn't become twice as effective overall but when it did transition into ground strafe it would saturate the target area exactly 100% better than before.

[magitsu]

I never understood why the USAF didn't pony up the development cost to mod the external gun pod for the A model.

In one pretty simple move, the USAF could have silenced the 'Big Guns Win Wars' crowd and given the A-10 chest beaters something serious to chew on (dual GAU-22s) which would nearly double the A-10 rate of fire and nearly match the total A-10 kilojules of kinetic target impact.
A lesser but not unimportant note of course is that doubling the cannon fire of the F-35A it actually WOULD be a serious ground attack improvement. It wouldn't become twice as effective overall but when it did transition into ground strafe it would saturate the target area exactly 100% better than before.

Why would anyone in their right mind start ground strafing with F-35? If such a cozy airspace exists in the future, the likes of Tucano can handle it. Cannon isn't really that effective, almost a sideshow compared to PGMs with jets. There are certain platforms like AC-130 for it though.

[archeman]

I never understood why the USAF didn't pony up the development cost to mod the external gun pod for the A model.

.......

Why would anyone in their right mind start ground strafing with F-35? If such a cozy airspace exists in the future, the likes of Tucano can handle it. Cannon isn't really that effective, almost a sideshow compared to PGMs with jets. There are certain platforms like AC-130 for it though.

Apparently EVERYONE that purchased the F-35A is considering it's ground strafe capability.
They train pilots for ground strafe.
They design ammunition for ground strafe.
The have continued to work software and ground targeting issues related to ground strafe.

It is just another method and tool in the arsenal of democracy apparently. If you're going to have weapons at all, they should work well, and you should know how to use them.

[zhangmdev]

Why would anyone in their right mind start ground strafing with F-35? <snip>

There are videos of F-16 doing strafing run in anger as recent as 2013?

Strafing is still a part of Air Force pilot training

http://www.f-16.net/f-16-news-article2947.html

[wrightwing]

I never understood why the USAF didn't pony up the development cost to mod the external gun pod for the A model.

In one pretty simple move, the USAF could have silenced the 'Big Guns Win Wars' crowd and given the A-10 chest beaters something serious to chew on (dual GAU-22s) which would nearly double the A-10 rate of fire and nearly match the total A-10 kilojules of kinetic target impact.
A lesser but not unimportant note of course is that doubling the cannon fire of the F-35A it actually WOULD be a serious ground attack improvement. It wouldn't become twice as effective overall but when it did transition into ground strafe it would saturate the target area exactly 100% better than before.

Because PGMs and not guns, are the primary and preferred A2G weapons (including the A-10.l

[count_to_10]

Is the A’s gun door causing the problem?

[steve2267]

Is the A’s gun door causing the problem?

I've read nothing that states, let alone even suggests that. What are you thinking / why would you ask that?

As I ponder your question, though... I do wonder... could local flow perturbation caused by the door possibly cause the inaccuracy? Man, I have to think LM accounted for that -- that someone would have thought of it or otherwise considered it and accounted for such an effect.

But in the favor of a "gun door causing a problem" line of inquiry, the door always opens to the same position, so any effect (e.g. right bias) would be the same, and repeatable. On the other hand, flow perturbation effects (e.g. strength) could possibly change with airspeed, and at some critical Mach number, maybe 0.7M or 0.8M, I wonder if a local shock could be established by the door fairing. But would a projectile exiting the muzzle at > 1000m/s be sufficiently perturbed by such a local flow burble?

Still... it sounds like the gun bias is consistent. If it can be quantified and mapped vs flight dynamics variables, then it should be fixable via software kentucky windage.

[magitsu]

It is just another method and tool in the arsenal of democracy apparently. If you're going to have weapons at all, they should work well, and you should know how to use them.

There's a long way between use what you have and should've built a "GAU-8 Avenger -type" cannon pod.

Everybody and their mother has MANPADS these days, which makes sub 5k ft flight asking for trouble. So anything more than a backup cannon is a waste. Laser pod might make more sense, but probably not specifically for CAS as other uses might reach maturity earlier.

[gtg947h]

Is the A’s gun door causing the problem?

I've read nothing that states, let alone even suggests that. What are you thinking / why would you ask that?

As I ponder your question, though... I do wonder... could local flow perturbation caused by the door possibly cause the inaccuracy? Man, I have to think LM accounted for that -- that someone would have thought of it or otherwise considered it and accounted for such an effect.

But in the favor of a "gun door causing a problem" line of inquiry, the door always opens to the same position, so any effect (e.g. right bias) would be the same, and repeatable. On the other hand, flow perturbation effects (e.g. strength) could possibly change with airspeed, and at some critical Mach number, maybe 0.7M or 0.8M, I wonder if a local shock could be established by the door fairing. But would a projectile exiting the muzzle at > 1000m/s be sufficiently perturbed by such a local flow burble?

Still... it sounds like the gun bias is consistent. If it can be quantified and mapped vs flight dynamics variables, then it should be fixable via software kentucky windage.

This is why you do testing. Even with computers, sometimes you encounter things you never expected and find out things behave differently than you thought. Aerodynamic computation is still based off empirical models that need to be tweaked, refined, and validated with wind tunnel and flight testing. Structural fatigue involves a lot of statistics based off lots of empirical testing, from the coupon level up to whole airframe. And even then, once your airplane is in service you start finding cracks and issues elsewhere.

So as you said--"normal development issues".