Forum: Program and politics

maus92 wrote:

The F-35A was only short of it KPP for radius of a few nms and the deficiency had been known for a while. There was talk of enlarging or adding a fuel tank, but a minor adjustment to a KPP seems to be a more prudent approach in this case - why spend a ton of money to achieve a marginal increase in range, with the possibility creating other problems (COG, W & B, GTOW, etc.) Also, these range values are still estimates.

The F-35A's deficiency was due to the added margin, of reserve fuel during testing, which wasn't counted towards range.

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wrightwing wrote:

maus92 wrote:

The F-35A was only short of it KPP for radius of a few nms and the deficiency had been known for a while. There was talk of enlarging or adding a fuel tank, but a minor adjustment to a KPP seems to be a more prudent approach in this case - why spend a ton of money to achieve a marginal increase in range, with the possibility creating other problems (COG, W & B, GTOW, etc.) Also, these range values are still estimates.

The F-35A's deficiency was due to the added margin, of reserve fuel during testing, which wasn't counted towards range.

That is true, but program officials also considered adding tanks, relocating valves to gain more usable volume and other tweaks that would likely have proven more expensive than simply changing the rules. At any rate, the 590 nm KPP is less than the 690 nm range estimated back in the day.

"One simple change under review is a software tweak that would maximise the amount of fuel taken onboard during in-flight refueling. Another relatively simple fix is to raise shut-off valves higher inside the fuel tank to create slightly more capacity, a source said, adding: “That gets you back a lot of the fuel that you need to recover” to meet the range mandated by the contract.

A more complex solution also being considered is to install new fuel tanks in a small number of hollow spaces within the aircraft’s structure.

But programme officials are also debating whether to change how the range of the F-35A is calculated, the source said. The equation does not include a buffer margin of 5% of fuel capacity, which is intended to be preserved through the end of the flight test period in 2016. Eliminating the buffer margin adds another 72.4km to the aircraft’s combat radius, the source said."

"This [2010 Selected Acquisition] report shows that Pentagon officials estimate the F-35A Air Force variant of the JSF will [not] meet its minimum combat radius requirement of 590 nautical miles. Granted, it misses the target by only six miles, but still, it’s missing the minimum performance metric. Program officials had estimated that the plane would have a combat radius of 690 nautical miles."

Read more: http://defensetech.org/2011/05/13/f-35a ... z1oGmHGMQh
Defense.org

Last edited by quicksilver on Mar 05, 2012 - 09:50 PM; edited 1 time in total

As usual, some of the reporting makes it sound like these jets are just barely eeking out range numbers. KPPs are calculated at min engine vice average engine which decrements thrust and increases SFC (ie makes it worse). Min engine is the thrust/SFC performance the engine has to produce in the last hour of its life before overhaul -- not when it first comes out of the can. CTOL profile also includes a substantial indirect routing factor.

The GR&A are generally very conservative.

'neptune' asked: "The enormous increases from 540, 550 to 600 seem a bit arbitrary in light of selecting "a number" and the LHA and LHD decks in the USN are 800'+ and with 20+ knots WOD...." I'll guess that it helps to have 200 feet in front (if starting from the extreme end) but also this '200 odd feet' allows takeoffs forward of the extreme end to allow other aircraft to be ranged behind, out of the immediate takeoff efflux perhaps. I recall seeing a lot of RN SHAR takeoffs where the aircraft are ranged (even one behind the other immediately) sucking down the exhaust of the STO Harrier in front. Perhaps USMC AV-8Bs do the same. I don't recall exactly. Videos will show examples I guess. This method of ranging aircraft closely allows quick takeoffs - no waiting or taxiing - so to speak.

neptune wrote:

The enormous increases from 540, 550 to 600 seem a bit arbitrary in light of selecting "a number" and the LHA and LHD decks in the USN are 800'+ and with 20+ knots WOD. Does anyone know what this requirement is based on? Why not 530, 510 or 480'? Shocked

They're simply letting the KPP distance reflect common operational practice. L-class tram line is marked in 50' increments for STOs. If the calculated deck run for a given load, OAT and wod falls above one of those numbers (eg 550, 600, 650 etc) the jet is always lined up at the next higher distance. For example, if the calculated deck run is 568', the jet would be lined up at the 600' mark.

spazsinbad wrote:

'neptune' asked: "The enormous increases from 540, 550 to 600 seem a bit arbitrary in light of selecting "a number" and the LHA and LHD decks in the USN are 800'+ and with 20+ knots WOD...." I'll guess that it helps to have 200 feet in front (if starting from the extreme end) but also this '200 odd feet' allows takeoffs forward of the extreme end to allow other aircraft to be ranged behind, out of the immediate takeoff efflux perhaps. I recall seeing a lot of RN SHAR takeoffs where the aircraft are ranged (even one behind the other immediately) sucking down the exhaust of the STO Harrier in front. Perhaps USMC AV-8Bs do the same. I don't recall exactly. Videos will show examples I guess. This method of ranging aircraft closely allows quick takeoffs - no waiting or taxiing - so to speak.

See video at link. IIRC, RN calls it an 'operational launch.' Not sure if F35 will observe similar convention.

http://www.youtube.com/watch?v=oaDcdGK2MHg

'QS' thanks. Good example video. From memory the SHARS have done some quick mass launches. I'll see what I can find.

"Pentagon Helps New Stealth Fighter Cheat on Key Performance Test"
By David Axe

"In fairness, it’s not unknown for capability standards, also known as “Key Performance Parameters,” to shift during a weapon’s development. But the shifts usually reflect the evolving needs of the military or some change in the operational environment, such as a likely enemy tweaking its own defense plans. In this case, the JROC gave the F-35 a pass that was apparently designed so the over-weight, over-budget, long-delayed stealth fighter could avoid yet another embarrassing scandal."

http://www.wired.com/dangerroom/2012/03 ... er+Room%29

quicksilver wrote:

neptune wrote:

The enormous increases from 540, 550 to 600 seem a bit arbitrary in light of selecting "a number" and the LHA and LHD decks in the USN are 800'+ and with 20+ knots WOD. Does anyone know what this requirement is based on? Why not 530, 510 or 480'? Shocked

They're simply letting the KPP distance reflect common operational practice. L-class tram line is marked in 50' increments for STOs. If the calculated deck run for a given load, OAT and wod falls above one of those numbers (eg 550, 600, 650 etc) the jet is always lined up at the next higher distance. For example, if the calculated deck run is 568', the jet would be lined up at the 600' mark.

Understood, but why was the original takeoff run KPP more restrictive? Rather than being arbitrary, there must have been some justification to set the original parameter at the lower figure.

No bias there Rolling Eyes

Salute!

I go with Cola.

On the programs I worked after hanging up the g-suit, the big problem was the military ADDING requirements and such. So the initial design needed more work ( $$$$) to meet the new spec. In some cases, the new requirement was not due to operational needs but "gee, wouldn't it be nice to......". So cost goes up. More testing. Longer time to production. And the beat goes on.

One stand-off weapon I worked on seemed a cost-effective way to take out enemy airfields at little cost to the aircraft integration and carriage capabilities of the aircraft for employment. And then the USAF started to demand a much longer range using a small jet engine versus the rockets the initial design used and demonstrated. Trouble was that the neat little engine cost as much as the full-up round with the rockets. Everything else was the same except the range increase, which was substantial - 200 or 300 KM versus 50 KM. Oh yeah, then the fuel tank and form factor and storage procedures and.....

The procurement specs should allow a few knots or miles or pounds here and there, but have fairly simple baseline numbers versus the "desired" numbers. Give the contractors a bonus if they beat a spec. Sure, there are a few bottomline specs, but most have some give and take. in the case of the JDAM ( I worked with the proof-of-concept folks), the thing reduced the estimated CEP by half within a year due to neat sfwe and filtering of the GPS data. Didn't cost a billion bucks. As an old attack puke, that thing would have saved many of my friends 40 years ago.

As far as range for the F-35 goes, I can tellya that pilot technique is as important as the aircraft's capabilities when flying the perfect profile in some kinda model. To get the real numbers, you put humans in the cockpit and they fly "x" miles with "y" gas and such and look at the data.

Gums sends...

Last edited by spazsinbad on Mar 06, 2012 - 12:55 AM; edited 1 time in total

Could not find what I was looking for but found this graphic (which is also somewhere on a thread about STO on LHAs on this forum) but repeated here to add to 'quicksilver' info above:

USS Wasp Deck Layout
http://www.robertheffley.com/docs/CV_en ... Manual.pdf
&
www.vtol.org/f65_bestPapers/testAndEvaluation.pdf

For comparison's sake here are some AV-8B (F402-RR-406 engine) STO performance figures for various configurations, 25kt headwind, standard day, SL:

Profile: HI-HI-HI
Clean Strakes, no pylons: 110 feet

Profile: CAS
6 MK-82SE (500lb), gun, ammo, 6 pylons: 425 feet

Profile: HI-LO-HI
6 MK-82SE (500lb), 2 300gal DT, gun, ammo, 6 pylons: 1,030 feet

Profile: HI-LOW-LOW-HI
6 MK-82SE (500lb), DECM pod, gun, ammo, 7 pylons: 460 feet

Profile: CAP
4 AIM-9, gun, ammo, 6 pylons: 275 feet

Profile: Ferry
4 300gal DT, 4 pylons: 975 feet

Source: NAVAIR 00-110AV8-4 (available on this site)

Interesting to me to see the close proximity of 'unconcerned' deck personnel to AV-8B STO jet efflux in this photo from [one may imagine similar 'unconcerned' chaps for F-35B STOs]:

http://www.sldinfo.com/harriers-operati ... or-2012-2/

"In the eighth photo, an AV-8B Harrier from Marine Attack Squadron 231 takes off from the USS Kearsarge Feb. 1 during Exercise Bold Alligator. The Harriers operated from the Kearsarge while conducting operations such as active air defense, combat air patrols, and close air support."

maus92 wrote:

"Pentagon Helps New Stealth Fighter Cheat on Key Performance Test"
By David Axe

"In fairness, it’s not unknown for capability standards, also known as “Key Performance Parameters,” to shift during a weapon’s development. But the shifts usually reflect the evolving needs of the military or some change in the operational environment, such as a likely enemy tweaking its own defense plans. In this case, the JROC gave the F-35 a pass that was apparently designed so the over-weight, over-budget, long-delayed stealth fighter could avoid yet another embarrassing scandal."

http://www.wired.com/dangerroom/2012/03 ... er+Room%29

The KPP was changed because the government changed the GR&A for what would be included in the OWE of the aircraft. Given that they have 750' of deck run and a lot more than 10 kts of wind to work with, an increase to 600' doesn't cost them anything.

Forum: Program and politics

KPPs being adjusted for F-35A & F-35B