Range question

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steve2267

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Unread post17 Feb 2017, 06:04

When a brochure like the F-35 program Fast Facts states that the F-35B has a range of 900nm and it carries 13,500lb of fuel internally, how do they calculate the range?

Is that a range that comes from flight planning a one way, no wind, trip at optimal cruise altitude and cruise speed, landing with the NATOP specified reserves in the tank?

Or does that range come from some marketing weenie taking 13,500 lb of fuel and dividing by best cruise fuel burn and then multiplying the resulting hours by optimal cruise speed?
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Unread post17 Feb 2017, 06:19

Fast Facks of LM has been around for a wery long time. Any objections to content have been ignored for similar very long time. :roll: It is what it is. One imagines that whatever criteria was used applies also to the other variants - for purpose of comparison.

Lest We Forget. This is a new military aircraft with many secrets - that is still under development. We are all mushrooms. An Oz Parliamentary Enquiry was told by former F-35 head honcho that early figures for range were done with a penalty for 'end of life' scenarios - engine that is. As more and more data is obtained then these 'range' figures (unknown to shroooms) would be recalibrated. There is a reason why not a lot is known in exact detail about various aspects of the new F-35. One day if we live long enough we may know more. I'm always surprised by the amount of old info online about older miljets in service today. Perhaps that is just me.

Range has been discussed endlessly in the past on this forum. There are old criteria about missions and how benchmarks are created with no clue how these may apply to the F-35. Some old F-35 brochures specifically for the B/C variants give some range figures but without the supporting detail these scenarios don't mean much. Be Happy - Be a Mushroom :mrgreen:
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vanshilar

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Unread post17 Feb 2017, 06:42

steve2267 wrote:When a brochure like the F-35 program Fast Facts states that the F-35B has a range of 900nm and it carries 13,500lb of fuel internally, how do they calculate the range?

Is that a range that comes from flight planning a one way, no wind, trip at optimal cruise altitude and cruise speed, landing with the NATOP specified reserves in the tank?

Or does that range come from some marketing weenie taking 13,500 lb of fuel and dividing by best cruise fuel burn and then multiplying the resulting hours by optimal cruise speed?


There usually is a flight or mission profile in mind. It's not always stated though (and in fact is usually left out). For the F-35, typically it's going to be an air-to-ground mission, which means enough fuel for taxi, takeoff, flying toward target, perhaps not at optimal cruise altitude/speed, drop bombs (from internal bays), perhaps do some combat (simulated as several 9 G turns with max afterburner for example), return home which may or may not be at optimal cruise altitude/speed, land, and have enough reserves. The F-35 program was also required to consider "end of life" engines so it was something like 5% more fuel burn and 2% less thrust or something like that.

The reported range depends a lot on the mission profile. For example, the F-35A's combat radius (that's both to and from a target) is given in its SAR as around 625 nm, but its combat radius in an air-to-air profile is stated in a presentation to Israel as being 760 nm. From Lockheed's own presentation, the Super Hornet on an air-to-air mission with 3 fuel tanks can get to a combat radius of around 800 nm, but the Super Hornet's official SAR shows its official interdiction combat radius (with 3 fuel tanks and 4 1000-lb bombs) as 489 nm. That's how much of a difference the assumed mission profile can make. (Usually, air-to-air missions will assume optimal cruise conditions going both to and from the target location -- though they will also assume some combat maneuvering at the target location.)

For the F-35B, its SAR combat radius is around 467 nm or so I think, which means its brochure-given 900 nm is a one-way trip. Of course, note that it always say ">900 nm" because the actual amount is not publicly available -- so all we know is that it's somewhat north of this figure.
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Dragon029

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Unread post17 Feb 2017, 08:09

steve2267 wrote:When a brochure like the F-35 program Fast Facts states that the F-35B has a range of 900nm and it carries 13,500lb of fuel internally, how do they calculate the range?

Is that a range that comes from flight planning a one way, no wind, trip at optimal cruise altitude and cruise speed, landing with the NATOP specified reserves in the tank?

Or does that range come from some marketing weenie taking 13,500 lb of fuel and dividing by best cruise fuel burn and then multiplying the resulting hours by optimal cruise speed?


Range itself is simply calculated to be the combat radius x2 - it's not an accurate measure, but customers are interested in more detail data than what's presented on the Fast Facts documents.

Also, it should be noted that the combat radius figures in the Fast Facts documents are threshold requirements, not actual performance figures (current estimates for those figures those can be found in the annual SAR: https://fas.org/man/eprint/F35-sar-2016.pdf#page=16 )

Those combat radius figures are based on specific mission profiles; attached is the one that (to my knowledge) represents the F-35B's mission.

F-35B Mission Performance.jpg


You may notice that the optimum Mach and altitude for cruise are not given; I'm not sure what they are. There's also factors such as routing factor (how much extra distance the jet must cover to avoid threats, etc); the F-22 has a 6% routing factor for example, as well as things like weather which you mentioned. Different payloads mean different radii as well, so do different threats, etc.
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Unread post17 Feb 2017, 08:38

There is a diagram for the F-35C also which is just as informative. Dr. Paul Bevilaqua - Lockheed presentation 4.4Mb PDF: http://www.aereo.jor.br/wp-content/uplo ... tation.pdf

These graphics from 2010 presentation and other 'range' info are scattered all over the forum....
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F-35CrangeBevilaqua2010.gif
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Unread post17 Feb 2017, 09:16

From same Bevilaqua 2010 presentation 'Design Missions' the INTERDICTION graphic with two more to follow....
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BevilaquaDesignMissionsInterdiction.gif
BevilaquaDesignMissionsDECKintercept.gif
BevilaquaDesignMissionsCAP.gif
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Unread post17 Feb 2017, 14:21

Looks like she has long legs, especially the C and I'd presume the A...

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