Pentagon Slackens Difficult-To-Achieve JSF Performance Requirements

Inside Defense ^ | 3/3/2012 | inside Defense

[U-238]

The Pentagon last month relaxed the performance requirements for the Joint Strike Fighter, allowing the Air Force F-35A variant to exceed its previous combat radius -- a benchmark it previously missed -- and granting the Marine Corps F-35B nearly 10 percent additional runway length for short take-offs, according to Defense Department sources.

On Feb. 14, the Joint Requirements Oversight Council -- in a previously unreported development -- agreed to loosen select key performance parameters (KPPs) for the JSF during a review of the program convened in advance of a high-level Feb. 21 Defense Acquisition Board meeting last month, at which the Pentagon aimed to reset many dimensions of the program, including cost and schedule.

Pentagon sources said a memorandum codifying the JROC decisions has not yet been signed by Adm. James Winnefeld, the vice chairman of the Joint Chiefs of Staff and the JROC chair.

Sources familiar with the changes, however, said the JROC -- which also includes the service vice chiefs of staff -- agreed to adjust the "ground rules and assumptions" underlying the F-35A's 590-nautical-mile, combat-radius KPP.

Last April, the Pentagon reported to Congress in a selected acquisition report that "based on updated estimate of engine bleed," the F-35A would have a combat radius of 584 nautical miles, below its threshold -- set in 2002 -- of 590 nautical miles.

To extend the F-35A's combat radius, the JROC agreed to a less-demanding flight profile that assumes near-ideal cruise altitude and airspeed, factors that permit more efficient fuel consumption. This would allow the estimate to be extended to 613 nautical miles, according to sources familiar with the revised requirement.

[Uncle Ike]

Well, now we know where all of those Atlanta teachers got new jobs....

[HiTech RedNeck]

You canna change the laws of physics!

[HiTech RedNeck]

Man. How do they expect this thing to hit that “near ideal” trajectory. If they had also come up with some kind of guidance system to support that, like maybe miniature drones with sensors to fly ahead of it to help plan its path, it would be more credible. But it’s going to be like “good luck, GI.” Engine bleed. What the heck does that mean. Either it goes where they planned, or it doesn’t.

[diogenes ghost]

This monument to military procurement stupidity can't meet it's design goals....again.

So they simply change the goals....again.

Suddenly this POS is considered a great success.....who woulda thunk it?

[USNBandit]

Depending upon the engine and the aircraft, some amount of air is "bled" off the engine to support other systems. That bleed air has a negative effect on thrust performance and thus reduces range.

The most obvious bleed demands for a fighter would be the environmental control system, cockpit pressurization, and onboard oxygen generating system. Without any background in the F-35 program I would still imagine the ECS system would be fairly demanding in all models due to the electronically scanned radar system.

As far as computing an ideal trajectory to achieve the 590 nm radius goes, that should be pretty easy for the flight computer to tell you what altitude to fly at for optimal performance between gross weight and fuel burn. It won't be some vertical arc through the sky, but probably a stair step up to altitude at fuel is burned on the way to the target. 590 nm is nothing to laugh at and is way better than the legacy hornet, an aircraft that failed its combat radius spec miserably.

[HiTech RedNeck]

They’re talking about beating the 590 nautical mile range by counting on the more ideal trajectory — but if the computers could already figure out this trajectory with high reliability then why was it ever an issue. Maybe it has to dodge artillery on the way there too? That problem would not go away.

When I first saw nm I thought that meant nanometers... brain fart.

[USNBandit]

There is a fixed profile that they use as a yard stick for combat radius. There are slightly different profiles depending on the type of mission. It has been a few years, but from what I recall they include an altitude and a speed for the enroute portion to the target and a certain amount of maneuvering for the mission and a max range profile home. In a way that first enroute segment doesn't help newer aircraft because as engine performance has gotten better they would do better at higher altitudes. I flew F-14s with the Pratt engine (sucked) and had they made that enroute segment higher we would have been sucking with any kind of load out. The legacy hornets would hate being that low because they were always sucking for gas and like to go high where their fuel burn was less.

For the Navy a number like 590 nm would be way better than the legacy hornet it is replacing.

[HiTech RedNeck]

I’m not saying this puppy isn’t worth pursuing. Maybe combat radii need to be rejiggered. Certainly those who fly the craft would know how to milk the maximum miles from it.

[USNBandit]

It is just a measuring stick to compare platforms. You won't see the pilots actually flying that profile. They will be flying their best profile just about everywhere they go.

Personally, I like the idea of about 20 of these guys doing the job we used to have send 100 planes to do in Vietnam.

[HiTech RedNeck]

If I was trying to realistically compare craft, I’d look at how they are actually most likely to be used, not some dusty outmoded benchmark that hurts the estimates about the best craft available.

[SunkenCiv]

Thanks U-238.