I understand the Software Development Problems, what I am unsure about is if the structural problems, particularly with the B have been resolved, any update.

Currently, the “B” structural life tests are being evaluated for second lifetime testing (16,000 hours). Previously, testing had to be stopped due to wing carry-through bulkhead failing at 9,000+ hours. The F-35C has wing spar/ titanium bulkhead failures that have halted lifetime testing. Overall, only the “C” is not meeting the 8,000 hour airframe life and fielded aircraft will require extensive modification. The F-35A is undergoing third lifetime testing (24,000 hours). The “B” is no longer the problem child of the litter. The “C” which is lagging behind the others in testing (though it will be the last to IOC) is proving to be challenging.

Do you have a source for that?

Reading the FlightGlobal article one gets the impression that there is a delay:

HASC March 23rd hearing on the F-35. The lots 9 & 10 contract negotiations have been ongoing for over a year now.

Also if this is for a/c delivered in 2015 and 2016, isn’t it a bit odd that they have not yet agreed on the contract? Since he refers to “value for taxpayers” one does get the impression that price is somehow involved as factor in the “dragged-out” negotiations. (and why do they use the term “dragged-out negotiations” if everything is proceeding according to plan as you seem to imply…?)

No, the Lot 9 & 10 won’t start deliveries until mid 2017-2018. (production was about 2 months behind schedule for Lot 7) , Lot 8 deliveries are starting now.

Edit- sorry didn’t answer the second part of your question. One snag is the delay in 3F configuration. Lot 10 is being held back until they have assurances that 3F will be ready.

Now you guys contradict yourselves a bit.. Is the stealth design determined by shape or by internal structure, in your books? And if you answer “both”, then which one is dominant?

Shape, but not all of the RF energy can be redirected. This is not an area that I’m well versed in but I can point you to a simple explanation (not a scholarly article- more a “stealth for dummies” more my speed in this topic)
http://www.harpoonhq.com/waypoint/articles/Article_021.pdf

The idea of stealth is to reflect the RF energy back in some very discrete angles, as far as I understand it. That means you get almost no return in all except few peaks which are then extremely high. These angles have to be avoided during the mission..Second, it is about absorbing the radar energy.. that means all those features which are invisible to the naked eye (honeycombs, composites, various special coatings, RAM) – but these can be applied even to a flying barn door..

The problem with the F-117’s shaping is twofold: 1. It is not aerodynamic 2. as the aircraft maneuvers, some of those facets become flat surfaces pointed right at the antenna.
The idea is to reduce reflectivity to a few peaks, those are treated with RAM. Not all surfaces (like leading and trailing edges) have enough RAM, nor are all surfaces reflective at all wavelengths so the materials and shaping of internal structure is important as well.

Back to the original question, which of that is dominant? If you say shape, then the F-117 cannot be less “stealthy” than F-22 because the smooth curves of the F-22 feature so many angles to provide at least small reflection from that it’s nearly impossible to find any optimum other than head-on (which is obviously optimized to the greatest extent). If you say “structure”, then, of course, you can design even a Gripen to be stealthy, all it takes is to retain the shape and let radiation be absorbed in internal honeycombs.

Yes, the F-117 can be less “stealthy” and by reports is less so. The second part of this quote is silly. Treating an aircraft like the Gripen, or F-16 with RAM and incorporating RAS materials and techniques into areas like the wings can reduce RCS considerably but it isn’t possible or practical to build an aircraft with enough to convert all RF energy,

Here is the article about TACIT blue which explains the difference between the faceted shape of the F-117 and the use of Gaussian surfaces in subsequent designs.

http://www.airforcemag.com/MagazineArchive/Pages/1996/August%201996/0896tacit.aspx

Quite on the contrary, I have seen claims that the Hopeless Diamond is by far the most stealthy one due to presence of few concentrated angles contrary to smooth surfaces of the F-22 or F-35.. The only problem is that it was designed without any compromise towards aerodynamics which didn’t cope too well with the air superiority role..

Go figure.. but this explanation does make sense to me..

Right after the proof of concept for the F-117 flew (HAVE BLUE), computing power allowed for LO properties to be developed beyond the mathematical theories of Pyotr Ufimtsev. That led to Tacit Blue that proved that airframes with curvature could meet or exceed the RCS of the “hopeless diamond” and be more aerodynamic. First the B-2 (with the classic all aspect RCS shape), then the F-22 developed on this, and the advancement of RAM and RAS, learning to build structures that radiation could pass into and be absorbed such as the internal honeycomb common in most modern fighters wings.

As to the “stealthier” question? The F-117 had a lower RCS from some angles, but the problem with the angular shape was that certain angles were exposed to reflect. The development of planform alignment with curvature and internal RAS that trapped radiation as well as RAM that was both more durable and had better absorption properties at higher temperatures was critical to the F-22. The issue still facing LO aircraft today (which answers the oft asked question of why there aren’t stealthy AAM missiles) is that most RAM becomes reflective as temps rise.