F-35 internal fuel, range

[spazsinbad]

It's been stated on numerous occasions, that F-35As with full fuel, and full internal payload (i.e. >5000lbs) have 9G/50° AoA/M1.6 envelope. It's not even subject to debate at this point.

Clearly it's debatable, but your source is? On a general note, isn't it common for fighters to have AOA restrictions simply due to to the fact that CG is changing as weight is changing during the mission? Give me all yer best.

Why does the F-35 have to be 'common' to 4thGen fighters and their restrictions? Give me some idea please.

IS this it? Scorecard - A Case study of the Joint Strike Fighter Program April 2008 Geoffrey P. Bowman, LCDR, USN
http://www.f-16.net/f-16_forum_download-id-14791.html (PDF 238Kb)

BTW this is the 'airshow quote that most interested me:

""...2. Aircraft configuration and Fuel Requirements. The profile is flown in a standard configuration aircraft. Taking off with less than full fuel is authorized. Fuel load considerations include: divert requirements, cable availability, and density altitude. Typical fuel loads at engine start are: full fuel for a staged show…

[energo]

Secondly: please specify 'Basic Flight Design Gross Weight' and why refer to BOWMAN which is now old & speculative? AND to what BOWMAN document do you refer? Some links to your assertions would be great otherwise you rely on notes & memory from 11 years ago.

Now tell me why requirements cannot be surpassed. We are told plenty of times that the performance of the F-35 is better than expected/required/whatever. In 2008 the aircraft may have been designed but then surpassed what you say.

But now you are speculating.

According to LM Basic Flight Design Gross Weight is 60 percent fuel and two AAMs.

O'Bryan is an LM spokesperson. How do you account for the LM PR quote

That's pretty compelling, but I'm far from convinced as my info is not from the comms or PR department. Let's see how this plays out. Of course, there would be nothing better if LM had this all wrong in 2008.

Now consider this: the 29300 pound empty weight, which forms the basis of all the performance calculations, has not changed. So where would this substantial increase in performance come from? Four and a half tons of internal fuel makes huge difference, wouldn't you agree?

[spazsinbad]

Secondly: please specify 'Basic Flight Design Gross Weight' and why refer to BOWMAN which is now old & speculative? AND to what BOWMAN document do you refer? Some links to your assertions would be great otherwise you rely on notes & memory from 11 years ago.

Now tell me why requirements cannot be surpassed. We are told plenty of times that the performance of the F-35 is better than expected/required/whatever. In 2008 the aircraft may have been designed but then surpassed what you say.

But now you are speculating.

According to LM Basic Flight Design Gross Weight is 60 percent fuel and two AAMs.

O'Bryan is an LM spokesperson. How do you account for the LM PR quote

That's pretty compelling, but I'm far from convinced as my info is not from the comms or PR department. Let's see how this plays out. Of course, there would be nothing better if LM had this all wrong in 2008.

Now consider this: the 29300 pound empty weight, which forms the basis of all the performance calculations, has not changed. So where would this substantial increase in performance come from? Four and a half tons of internal fuel makes huge difference, wouldn't you agree?

Please provide a reference to the 'LM Basic Flight Design Gross Weight' you seem to be relying on your 'notes' and memory whilst this forum can see neither. And how am I speculating with sourced quotes? 'energo' you seem to think that we must believe your assertions circa 2008. 'Performance Calculations in 2008' are one thing but then there is FLIGHT TEST and the quotes quoted subsequently recently.

[energo]

Why does the F-35 have to be 'common' to 4thGen fighters and their restrictions? Give me some idea please.

Let's establish our baseline here: Are you saying changing weight does not influence CG and AOA on fighters? Can you refer to any examples where this does not apply?

IS this it? Scorecard - A Case study of the Joint Strike Fighter Program April 2008 Geoffrey P. Bowman, LCDR, USN
http://www.f-16.net/f-16_forum_download-id-14791.html (PDF 238Kb)

My apologies, I simply assumed you remembered the report. It has been debated in this and other forums. You even replied to it on at least one occation. But I agree it should not be taken as a defacto fact. I merely added it as it corroborates LMs own statements.

[spazsinbad]

UhOH. 'energo' you brought up this point so go ahead & prove it for the F-35: "Let's establish our baseline here: Are you saying changing weight does not influence CG and AOA on fighters? Can you refer to any examples where this does not apply?" I don't have to prove anything. I'm asking you to provide evidence with URLs etc for whatever F-35 info you have.

[energo]

'Performance Calculations in 2008' are one thing but then there is FLIGHT TEST and the quotes quoted subsequently recently.

You are speculating about flight tests. Sorry partner, but you have lost me there.

I will see if I can get an update on this.

[spazsinbad]

I see myself speculating on your speculations from 2008 NOT updated to today (or recently anyway). You can claim a lot of things but to have credibility you need authoritative sources - not just a note/memory of yourn from 2008. Meanwhile:

Semper Lightning: F-35 Flight Control System
09 Dec 2015 Dan “Dog” Canin (LM TEST PILOT) [pity no follow up]

"...The F-35 is an inherently unstable airplane, required to handle a wide range of CG. Its control surfaces are sized to meet the requirements of both maneuverability and low observability. As a result, the combinations of body rates, AOAs, CGs, Machs, and weapon bay door positions that define the controllable envelope of the F-35 are extremely complex – and the boundaries of that envelope are reflected, with all that complexity, in CLAW...."

Source: http://www.codeonemagazine.com/article.html?item_id=187

[lbk000]

Just as a point of reference we'll use Su-27SK, so this won't be exactly accurate to the Su-35S, but the deviation won't be dramatic:
Max operation G-loading is limited to 8.0 Gs @ 21,400 kg (47179 lbs)

Empty weight is ~38600lb
For an F-35 "equivalent" load:
2x 1000lb bomb equivalents (1100+lb FAB-500 + mounting) + 2x MRMs (700+lb R-27ER + rail), drop in 300+lb of ammo, you've got about 4100lbs of ordinance.
You get 4500lbs (!!!) of gas to match the F-35's airshow-out-of-the-bag capability. That's about 22% of the total possible fuel load. Again, this isn't even a realworld loadout as seen over Crimea or Syria which would be heavier, but it will put into context the Flankers seen with open pylons and 30% fuel.

Making allowances for a more realistic operational paradigm of 1. burning off gas to the mission and 2. ditching the A-G mission, you'll find there is no mission profile where you need a full tank of gas AND be at max performance maneuvering weight at the fight with the fuel needed to come back.
That's because a significant portion of the Flanker's gas tanks are by design for ferry use.

The central point I was trying to make, and that you willfully ignored, is that the Flanker's max operational fuel capacity is NOT its gross fuel capacity, so operational radius comparisons favor the F-35 even harder. No amount of pedantry over the F-35's weight limits here will change the balance.

[weasel1962]

Agreed on Sukhoi's range vs operational radius difference. Same goes with the F-35.

Su-30mk2: 3000km (1619 nm) range at cruise altitude with MTOW of 34,500kg (75,900lbs) and 9720kg (21,384lbs) max internal fuel with a load-out of 4 AAMs. Flight range is 1270km at low altitudes...

Source: Official numbers per rosboronexport catalog (site use at your own risk).
http://roe.ru/eng/catalog/aerospace-sys ... /su-30mk2/

Weasel's note: 1 engine vs 2 engine is less relevant since low power use at optimal cruising speed is probably imho roughly equivalent in terms of fuel usage (if similar TW, ceteris paribus and using simple logic. However carrying one extra engine does increase weight...). imho, F-35A should be able to achieve 1600+nm ferry range on the 15% less internal fuel. Drag from 4 AAMs is not that significant and suks are generally quite slick. Don't forget the Russians designed the Su-27 as an air superiority (not multi-role) fighter first.

The difference is that when one goes into air combat, the afterburner will have to kick in and that's where the fuel guzzling begins for the suk that will be far higher than the F-35. So the effective combat radius drops significantly because if the suk has to engage F-35s at 600nm, they won't be going home. Hit the afterburners, don't have the range to go home. Don't hit the afterburners, the F-35 goes into the combat with a significant energy advantage i.e. get shot down and still don't get to go home.

[wrightwing]

Let's establish our baseline here: Are you saying changing weight does not influence CG and AOA on fighters? Can you refer to any examples where this does not apply?

No, what we (and official sources) are saying, is that the F-35A/B/C has no envelope restrictions with full fuel/internal weapons. Pilots have routinely said that internal weapons have no discernable effect on flight performance/handling.
4th gen jets have envelope limits due to external mounted weapons, fuel, pods, which can have a big effect on DI, CG, etc... One of the big selling points for the F-35, is that in stealthy configurations, it can outperform 4th generation jets by a large margin.

[spazsinbad]

In the interest of backing up some of my so-called 'speculations' with sadly very dense material such as the CLAW quote above. Now for the really dense stuff about 'better than predicted/requirement' F-35 results from those who dun dood it.

F-35 Aerodynamic Performance Verification
25-29 Jun 2018 David G. Parsons, Austin G. Eckstein, & Jeff J. Azevedo LMers

"...Ultimately, the flight test results proved that the design of the F-35 aircraft exceeded requirements....

...II. Introduction
THIS paper provides a top-level understanding of the approach taken and analytical techniques used on the F-35 during our performance validation. With these we verified the conventional performance requirements of the F-35, with particular emphasis on the key performance parameters (KPPs) of the Joint Contract Specification (JCS). Our modeling and simulation-based verification process successfully validated the aerodynamics and performance databases used to calculate performance with a minimal flight test matrix. Ultimately, the process indicated that the mission performance of all three variants of the F-35 exceeded requirements....

...IV. Performance Management
At contract award, the F-35 program mandated the use of a conservative factor on aircraft performance calculations to cover risks in several aspects of the new design. The factor was implemented as a 5-percent increase in predicted fuel flow to cover immaturity in the design, among other things. It also covered the uncertainty in predicted aerodynamics and propulsion databases, as well as the possibility of weight growth during the maturation of the design. Further, it covered the potential for configuration changes resulting from discoveries during flight testing that could adversely affect performance. As the aircraft design matured and flight testing was accomplished, uncertainty in each of these areas was to be retired. In tandem, the factor was to be progressively reduced until no conservatism was to be applied for the final calculation of specification performance....

...VI. Flight Test Analysis Results...
...After completing all flight test analysis and obtaining the F-35 JPO’s concurrence, we used the validated aerodynamics databases to calculate the KPP mission performance for each variant. The results showed that each of the variants exceeded the JCS requirement for mission range by more than 10 percent, as illustrated in Fig. 15.... [attached]

...VII. Conclusion
On the F-35 program, we successfully implemented a modeling and simulation-based approach to aerodynamic performance verification. Applying conservatism to performance calculations early in the program protected against potential uncertainties in configuration, weight, or aerodynamics levels. Our rigorous process controlled aircraft weight growth and helped to ensure that the performance of the final F-35 design met the KPP requirements of the program specification. The efforts of a government/contractor team culminated in delivering a credible, flight test-based aerodynamics and performance database that accurately represents the performance of the F-35. This will be applicable for not only specification verification but also the operational performance products used by the fleet."

Source: download/file.php?id=27757 (PDF attached below)

[weasel1962]

Don't all planes have a flight envelope, at any fuel load?

[wrightwing]

Don't all planes have a flight envelope, at any fuel load?

The difference is that the F-35 has a full flight envelope with no restrictions, with full fuel and internal ordnance. 4th generation jets only carry external weapons, fuel tanks, pods, so their envelopes will vary greatly depending on the configuration and fuel status.

[weasel1962]

A flight envelope is perhaps in itself a restriction since that explains the upper limits of how an aircraft is expected to perform? Maybe the better way to describe is that the flight envelope of the F-35 at full fuel load would look like that of a legacy clean plus plus which itself has a significantly broader envelope than a legacy/suk either weighed down by EFTs or externally carried stores. A broader flight envelope could of course mean being able to fly faster at differing altitudes/weights, turn more at differing speeds, pull more Gs at certain speeds, fly higher etc.

[spazsinbad]

Tried to improve Fig.3 with subset MISSION PERFORMANCE because after all is not this thread about 'internal fuel, range'?

"...Performance requirements for the F-35 were defined in the JCS. The primary conventional aircraft performance requirement for each variant was the KPP design mission radius. The F-35B (STOVL) had additional KPP requirements for short takeoff distance and vertical landing bring-back to emphasize operations aboard Navy LH-class amphibious assault ships. The approach to verifying each of those requirements followed processes similar to those used for the conventional performance requirement approach presented herein. Vertical landing bring-back is a measure of the aircraft’s ability to recover to the ship with unexpended munitions and fuel. The F-35C (CV) had a separate KPP requirement for approach speed to emphasize operations on Navy aircraft carriers. The F-35 program used a modeling and simulation-based approach to determine and verify aircraft aerodynamics and performance...."