USAF plans F-15 modernization

[SpudmanWP]

The original report that started the story said there was.

 

[LowObservable]

Because if someone writes in ALL CAPS it must be true.

Shanahan's been saying lots of stuff lately, some of which makes I larf...

BTW, getting back to the $65m unit cost that some have been throwing around. It's not actually crazy, although it's optimistic. FY19-20 flyway cost for a Shornet is under $70m (according to USN budget docs). Surprising as it may seem the OEW of an F-15E is less than that of a Shornet and it's a less complex airframe. The engines and EW system may cost more, but a lot of Shornets are two-seaters.

 

[TomcatViP]

They are absolutely not the same generation of airframe. And when assessing the cost of buying a bunch of new built airframe for the ANG, we have to remember that their usage is quite specific (continental AtA+ deployment) with constrained maintenance ressources. Hence 10 or 12 new built F-15 could potentially do the work done by twice more today (less maintenance hour per flight -> more mission rate / less logistic burdened deployment / more weapon carriage...). If now you start to look at the global picture and on the long term, add the reality of the fact that the Eagle is to be in service for many more years, you might get some cost cutting benefices buying some new airframe to replace a portion of the fleet that won't be phased out anytime soon.

 

[marauder2048]

Pentagon’s cost assessment and program evaluation shop presented analysis to the Air Force supporting the move.

Which tells you that it wasn't AF initiated since that analysis would have come from AFCAA.

The FY19-20 SuperBug flyaway costs have the MYP confound.

 

[LowObservable]

The FY19-20 SuperBug flyaway costs have the MYP confound.

Confound? This means what, in English?

 

[marauder2048]

The FY19-20 SuperBug flyaway costs have the MYP confound.

Confound? This means what, in English?

That someone who attempted to extrapolate cost based on the OEW of a fighter that's 13%
titanium by structural weight to an aircraft that's over 34% was likely an English major.

 

[LowObservable]

Thanks.

I hate doing math in public, but I'm sure that the use of a more expensive raw material for ~20% of the structure will totally drive the cost through the roof, even including engines and avionics. Particularly when much of the Ti is SPF/DB, which has the offsetting merit of reducing parts count.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.850.3043&rep=rep1&type=pdf

 

[LowObservable]

Latest news:

http://www.airforcemag.com/Features/Pages/2019/January%202019/Think-of-F-15X-In-Context-Of-Fighter-Recap-Donovan-Says.aspx

Donovan seems to have a fair number of F-15X-related talking points close to hand: "I can't tell you that we're buying more F-15s, but here's why we are doing it."

 

[sferrin]

Latest news:

http://www.airforcemag.com/Features/Pages/2019/January%202019/Think-of-F-15X-In-Context-Of-Fighter-Recap-Donovan-Says.aspx

Donovan seems to have a fair number of F-15X-related talking points close to hand: "I can't tell you that we're buying more F-15s, but here's why we are doing it."

After reading the article, I'll bet they wish the F-22 line was still up and running. I wonder what the incremental cost would be down to by now.

 

[marauder2048]

Thanks.

I hate doing math in public, but I'm sure that the use of a more expensive raw material for ~20% of the structure will totally drive the cost through the roof, even including engines and avionics. Particularly when much of the Ti is SPF/DB, which has the offsetting merit of reducing parts count.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.850.3043&rep=rep1&type=pdf

It's the material buy weight that matters here: current estimates for the advanced F-15s hover around
~70,000 lbs of titanium; I've seen numbers at low as 14,000 lbs for the Super Bug.

 

[lastdingo]

Those figures sure don't apply to individual airframes.

 

[marauder2048]

Those figures sure don't apply to individual airframes.

They do. The buy-to-fly ratio for titanium is....bad.

 

[sferrin]

Those figures sure don't apply to individual airframes.

They do. The buy-to-fly ratio for titanium is....bad.

And if you need it in forgings you'll be waiting in a LONG line..

 

[LowObservable]

I guess we'll see when the budget documents appear. By the way, both the F-15E and F/A-18E/F have forged and machined Ti bulkheads, which are the worst in terms of buy-to-fly. And even if the difference is 56,000 lb, it takes a pretty high raw material price to hit more than a few per cent of the total airplane.

 

[malipa]

Since the production rate is pretty low, why not 3D print them? then can even recalculate the shapes and make them lighter due to the freedom of the printing. The way lower use of raw materials will definitely pay for the investment. Also the forge and machining isn't cheap either...

 

[SpudmanWP]

Um, that F-15E (ie 70k) number is wrong. The empty weight of an F-15E is around 32k for EVERYTHING so 70k for Titanium is impossible.

I found a couple of things:

The F-15 airframe {classic} contains 25.8 percent titanium by weight, most of it concentrated around the engines and in the inboard sections of the wings.

https://www.f-15.nl/hist.html

----EDIT----
Damn, I need to stop posting before coffee. I missed that we are talking about raw-to-finished weights and NOT final weight.

 

[marauder2048]

Um, that F-15E (ie 70k) number is wrong. The empty weight of an F-15E is around 32k for EVERYTHING so 70k for Titanium is impossible.

For titanium, a very small fraction of the raw material (buy weight) ends up as a finished part (fly weight) on the airframe.
I've seen estimates of 8:1 - 12:1 for fast jets which is why additive, as mentioned above, is appealing since buy-to-fly
ratios between 3:1 - 1:1 look achievable.

 

[sferrin]

I guess we'll see when the budget documents appear. By the way, both the F-15E and F/A-18E/F have forged and machined Ti bulkheads, which are the worst in terms of buy-to-fly. And even if the difference is 56,000 lb, it takes a pretty high raw material price to hit more than a few per cent of the total airplane.

I could swear I saw somewhere that either the F-22 or F-35 had a titanium bulkhead that started as a 7,000lb forging and ended at 435lbs or thereabouts. I have no doubt there are many with a much worse "yield".

 

[sferrin]

Since the production rate is pretty low, why not 3D print them?

Because a 3D printed part isn't as strong as a forged one.

 

[SpudmanWP]

For titanium, a very small fraction of the raw material (buy weight) ends up as a finished part (fly weight) on the airframe.

Depends. Back when the F-15E bulkheads were being made they started with a solid block but modern systems like the F-35 start with a forging that is almost done.

Besides, they collect and reuse the shavings.

 

[sferrin]

*GASP*, *CHOKE* Just took a gander at a random titanium forging. 1175lb forging gets whittled down to a 45lb part.

 

[marauder2048]

The titanium buy-to-fly ratio on the F-35 CTOL is better than just about any other fast jet
and there was a very deliberate effort (per repeated and emphatic DOD guidance) to de-spec titanium
as much as possible.

 

[Colonial-Marine]

The titanium buy-to-fly ratio on the F-35 CTOL is better than just about any other fast jet
and there was a very deliberate effort (per repeated and emphatic DOD guidance) to de-spec titanium
as much as possible.

I know the F-35 wasn't designed to be a true air-superiority fighter but could the same be done for a fighter designed for that role? Have composites come that far or are the specs for aircraft like the F-15 and F-22 so demanding that titanium is still king?

 

[SpudmanWP]

Any modern fighter with the right industrial base can do it. Look at the photo in post 934 above. Note that little needs to be removed in relation to the old way of milling from a solid block.

As technology gets better then the size of the forging walls will get smaller & smaller (ie a better buy-to-fly ratio).



Damn, LN cooled CNC

https://www.youtube.com/watch?v=qfubbFtVilE

 

[LowObservable]

FWIW, remember that Ti has to be at $100/lb to make a $5m difference to unit cost, if M2048's numbers are accurate.

 

[sferrin]

FWIW, remember that Ti has to be at $100/lb to make a $5m difference to unit cost, if M2048's numbers are accurate.

I'd think a 10lb titanium forging would easily bust $1000.

 

[LowObservable]

But that's a component cost, not a raw material cost.

 

[TomS]

But that's a component cost, not a raw material cost.

Commercially pure Ti is running around $25 a pound these days. Aviation-specific alloys could easily be significantly more, especially with the DoD traceability/accountability requirements. I don't know specific pricing, but $100 per pound doesn't seem impossible.

 

[sferrin]

But that's a component cost, not a raw material cost.

Whoops. Fair enough. Carbon fiber isn't exactly cheap either though. (Nor is the core that goes with it.)

 

[sferrin]

But that's a component cost, not a raw material cost.

Commercially pure Ti is running around $25 a pound these days. Aviation-specific alloys could easily be significantly more, especially with the DoD traceability/accountability requirements. I don't know specific pricing, but $100 per pound doesn't seem impossible.

About a year ago I bought some 0.24" 6AL4V stock for testing. No certs. Came to about $46/lb. It was a relatively low quantity but it was from a remnant shop.

 

[Foo Fighter]

What is the potential for man made materials to replace the/some of the, titanium components?

 

[marauder2048]

Pentagon’s cost assessment and program evaluation shop presented analysis to the Air Force supporting the move.

Which tells you that it wasn't AF initiated since that analysis would have come from AFCAA.

Which is now confirmed. It was nothing more than an OSD diktat.

“Our budget proposal that we initially submitted did not include additional fourth-generation aircraft,”
Air Force Secretary Heather Wilson told reporters during a Feb. 28 roundtable at the Air Force Association’s Air Warfare Symposium.

Wilson’s comments confirm reporting by Defense News and other outlets who have reported that the decision
to buy new F-15X aircraft was essentially forced upon the Air Force.

https://www.defensenews.com/digital-show-dailies/air-warfare-symposium/2019/02/28/the-air-force-doesnt-want-f-15x-but-it-needs-more-fighter-jets/

 

[Phos]

For titanium, a very small fraction of the raw material (buy weight) ends up as a finished part (fly weight) on the airframe.

Depends. Back when the F-15E bulkheads were being made they started with a solid block but modern systems like the F-35 start with a forging that is almost done.

Besides, they collect and reuse the shavings.

Melting down titanium shavings back into ingot seems complicated considering how much titanium loves oxygen, but I'm no metallurgist so I dunno if that's a minor wrinkle or it's in "Might be cheaper to start with raw material" territory.

Of course, more recently I've been thinking that making something light is more about design and knowing what to leave out than material. For example, it's not rare for aluminum and fiberglass Lotuses to weigh less than cars with carbon fiber chassis. I know SpaceX is using the stainless steel chassis for its heat resistance as well but it feels along the same lines, but I guess even engine cradles don't get hot enough for titanium to lose out. Has me wondering, would a crashed plane would burn hot enough to destroy the important structural parts to prevent reverse engineering? Can jet fuel melt titanium spars?

 

[SpudmanWP]

Take a look at CNRP.

It's already being used in non-structural components of the F-35.

 

[Phos]

Take a look at CNRP.

It's already being used in non-structural components of the F-35.

Why would they use it non structurally when it's so strong and expensive? Nanotubes I imagine would outstrip the cost of carbon fiber with the same risk of rejection while also having similar health hazards as asbestos, that has to be super expensive. All I can think of is to get information on how it weathers, unless this is their weatherproof RAM? Is it a radar absorbing material?

 

[SpudmanWP]

They did not use it structurally in the F-35 because by the time they got the price cheap enough, the design & flight test work for the F-35 was too far along.

Expect to see it more on upcoming designs.

 

[marauder2048]

It's also not like you see a ton of composite sub-structure on fighters either.
What often keeps advanced materials out of those areas is lack of ballistic tolerance: it's what kept
the high-temperature aluminum off the F-22 though IIUC the latest alloys are better in this regard.

 

[sferrin]

It's also not like you see a ton of composite sub-structure on fighters either.
What often keeps advanced materials out of those areas is lack of ballistic tolerance: it's what kept
the high-temperature aluminum off the F-22 though IIUC the latest alloys are better in this regard.

They replaced several composite spars on the F-22 with titanium for this very reason. (Hydroshock when the wet wing was hit with ordinance was not kind to composite spars.)

 

[Triton]

"Buying new F-15X fighters for the US Air Force is unsolicited and unwise"
By: Gen. John Michael Loh (ret.)

Source:
https://www.defensenews.com/opinion/commentary/2019/03/04/buying-new-f-15x-fighters-for-the-us-air-force-is-unsolicited-and-unwise/

 

[Foo Fighter]

I have to say that having revisited the issue I can see the argument in a different light. If the cost per unit can be reduced and squadrons equipped faster, then the F-35 should be the sole acquisition over 4th gen equipment. Mainly this change of mind is driven by the growth of China as a threat and the goal of using money more responsibly. Sending pilots out in older, less capable aircraft should only be considered as a last resort and when the threat justifies it. Not much of a stretch to say that F-35 now has an improved ability to prove itself against alternatives.