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Last Updated: Mon Jan 27 11:18:09 UTC 2014

F-35A CTOL JSF: The Biggest Loser

Air Power Australia - Australia's Independent Defence Think Tank

Air Power Australia NOTAM

  16th April, 2007

Peter Goon, BEng (Mech), FTE (USNTPS),
Head of Test and Evaluation, Air Power Australia

Contacts: Peter Goon
Carlo Kopp

Mob: 0419-806-476 Mob: 0437-478-224

Update: By November 2011, the official Not-to-Exceed (NTE) design target empty weights of the JSF designs, including a redefined set of design margins to IOC, for all variants had again increased. As best can be determined, this makes the fifth, possibly sixth time the NTE design empty weights for the JSF family of aircraft have been increased since contract award back in 2001. At a new NTE design empty weight of some 34,868 lbs, the F-35C Carrier Variant JSF is now the biggest loser, with a projected 16% increase in its design target empty weight since 2002 and weighing in at around 5,500 lbs heavier than the former holder of the title, the F-35A CTOL JSF variant (Artwork courtesy Rod Emmerson).

A feature common to most Tier 1 air combat/fighter aircraft is the ability to takeoff with full internal fuel and full payload.  Most have a margin in excess of this ‘total load’ figure which allows for growth in weight over the aircraft's service life.

Weight is one of the easier aspects of aircraft design to understand, unlike others which are often made intentionally confusing by the maker, his statements then being unfortunately taken on face value and repeated by the potential purchaser. Such design characteristics include the more emotional 'stealth', 'supercruise', 'network centric system of systems', and advanced radars such as 'AESA Radars', which makers describe in confusing technical jargon, implying capabilities to their aircraft which they do not have in the true sense.

What is called the aircraft's Empty Weight is one of the most basic and important aspects of aircraft design.  This is the weight akin to what is seen at a ‘Biggest Loser type weigh in; the ‘down to your skivvies’ weight, which for aircraft is without fuel or other payload such as bombs or missiles, sensor pods, external fuel tanks, or crew.  The Empty Weight is fundamental to how well the aircraft will aerodynamically perform, how much fuel and payload it will be able to carry, and how much growth it can accommodate throughout its life.

Weight, however, is such a predominant design objective/factor that it may alone determine whether or not an aircraft will proceed to the production stage. In these cases, the designer just cannot meet the operational requirements within the maximum weight constraint. Where the designer strikes serious weight problems, it behoves the potential purchaser to exercise more than usual caveat emptor, that is exercise greater due diligence when monitoring the program.

Not surprisingly, the JSF Program has had weight issues.  In 2003, the STOVL JSF was declared overweight and the SWAT (STOVL Weight Attack Team) was formed to perform a Biggest Loser miracle.  At the end of 2004, the SWAT declared they had removed ‘over 2,700 lbs’ off the STOVL aircraft's weight, with commensurate weight reductions for the other two models; the Carrier Variant (CV) and the one which Defence and the Government say we will buy, the Conventional Take Off and Land (CTOL) variant.  The news that the JSF had faced its Biggest Loser weight challenge and won was spread far and wide by the manufacturer's men and those of the prospective customers alike.  Now that all the hoopla, hype and weight reduction dust has settled, a look at the “weigh in”records of all three variants shows a somewhat different story -

Design Configuration Design Target Not-to-Exceed (NTE) Empty Weight (incl. 3% IOC Margin) #240-1
% change since 2002 Max Fuel Load (Internal)
Weight Growth Factor Inverse Payload Factor
CV JSF 30,049 30,700 32,072 6.7% 20,120 Classified Negative >0.75
STOVL JSF 29,735 30,500 32,161 8.2% 13,966 Classified Negative >0.75
CTOL JSF 26,500 27,100 29,036 9.6% 18,448 Classified Negative >0.75

Design Empty
Weight [lb]
Max Fuel


Payload Factor
F-22A Raptor 31,670 (AV) +
10,262 (ENGs) = 41,932
18,385 (Normal)
20,649 (Maximal - Est)
66,470 (MTOW)
83,500 (Maximal -Est)
< 0.65

These weight figures are from the JSF Program Office annual presentations to the US Air Force Association and are the design target weights for the three aircraft variants.  With an overall increase of 2,536 lbs (about 10%), the CTOL JSF is certainly not going to win the Biggest Loser competition.  In fact, all three aircraft designs have shown progressive and steady increases in their design target empty weights over the past 4 years.  Columns for the other two important weight parameters - maximum internal fuel load and maximum take off weight (MTOW) - are shown with MTOW, somewhat surprisingly, being declared to be ‘classified.   MTOW being held so close is a sure sign of an aircraft development program with weight problems.

Back in 2002, when the then senior Defence leadership convinced the Government that the JSF was the way to go, the MTOW was stated as 60,000 lbs. In the recently posted RAAF data sheet on the CTOL JSF, the MTOW is stated as in excess of 22,700 kgs (50,000 lbs).  Splitting the difference (55,000 lbs) makes for some interesting hypotheticals, which will become high risks for Australia if they turn out to be true.

Even at a MTOW of 60,000 lbs, none of the three JSF model designs present with an aircraft that is able to take off with full internal fuel and its full external payload, let alone internal and external payloads, together. The latter would not be possible even if the MTOW were 66,000 lbs.  Similarly, all three variants have a negative weight growth factor, that is, there is no margin in the design for increases in weight over the aircraft's life, whereas aircraft like the F-22A, F-15C/E and F-111, as well as the Russian Su-27/30 family of aircraft, have significant margins for growth.

The other parameter shown in the above table is referred to as the Inverse Payload Factor which is an engineering means of comparing different aircraft on the basis of their payload capability relative to fuel load and combined structural/systems weight.  A factor of 0.7 or less is common for aircraft that have distinguished themselves in service, principally due to efficient and effective design, with aircraft like the F-15E and F-22A scoring well at less than 0.65. In fact with the additional considerations of significant thrust available and a maximum zero fuel weight of around 48 klb, the design latitudes within the F-22 present an aircraft of awesome capabilities and growth, both for now and into the distant future.

What does this all mean?  Well, put simply, all the claims about the JSF being able to carry more weapons than, say the F-22A or the F-111 and do so more efficiently and effectively go the way of most things that are simply not true –- out the window.  The real concern now, given the above data, should be whether the JSF is going to be able to lift a useful combat payload with its fuel tanks full or, like other small air combat aircraft, is going to produce a heavy reliance on tanking just to stay in the game. This should be of particular concern for the devotees of the Carrier Variant because the weight characteristics are trending towards those of programs that have not made it on to the boat, for instance, the ubiquitous A-12 (planned A-6 replacement). Those who are not CV devotees should not ignore these trends because a ‘no show’ of the Navy Carrier Variant puts higher cost and schedule risks on their buys.

Those with experience in defence capability development know that the 5% that the Minister can't tell us about, because it is 'classified', will not in any way change design fundamentals when comparing the capabilities of the JSF with those of the F-22 or the Evolved F-111, or equally importantly the Su-27/30 family of aircraft.  Even the 'shrouded in secrecy' weapon system going into the JSF - now being marketed through highly classified presentations as 'likely to revolutionize the battle space'- will not change any design fundamentals.  In simple terms, it will still be a system like any other and so can be fitted to other platforms, including aircraft more capable than the JSF, which is, unfortunately,  turning into an overweight design with no weight growth and limited air-to-air capabilities  - the very advantages we need to ensure regional air superiority.

This brings us back to the other 10% - the growth in weight -  that the Minister and his Departmental bureaucrats do not wish to discuss, and their overwhelming dependence upon a 'system of systems' concept to assure Australia's air combat edge over the next 30 years or more.  The Chief of Air Force expressed it as: 'The RAAF's air combat power is not a function of any particular aircraft, but how all elements combine to support a multi-level net-centric warfare concept'. This is inverted thinking, and dangerous.  Firstly, it assumes that we can get away with second tier aircraft by maintaining an offsetting network-centric superiority - that is, we will always be ahead of any adversary.  Secondly, it ignores the reality that systems are designed to enhance a platform's basic capabilities, not replace them.

The 'system of systems' concept where 'the capabilities of the whole are greater than the sum of the parts' is laudable in theory and can be quite effective in practice, PROVIDED that it is not used to justify building a system using parts of a lesser capability. As the former aerospace industry chairman/CEO whose escalating costing prediction for future fighter aircraft started this whole JSF genre, Norm Augustine, was also heard to say, "when trying to turn a sow's ear into a silk purse, 'tis best to start  with a Silk Sow".  The strength of any chain is measured by its weakest link and the currently weakest link in the new air combat capability debate is the inability of the Minister and his Department to see that 'systems' will come and go, but the platforms that make these systems effective must serve us well for over 30 years.  Systems do not an aircraft make, they only enhance or reduce its ability to do the job efficiently and effectively.


APA has sought comment from both the JSF developer/manufacturer and the Department of Defence on the issue of JSF weight and the results of its analysis but, to date, has yet to receive any response.

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