Twilight of the F-35

Twilight of the F-35

by David Archibald

24 March 2021


There were two articles on the F-35 in today’s The Australian newspaper. One reported that the RAAF had cut the flying hours of our 33 F-35s by 36%, from 8,204 to 5,205 hours per year, while the operating cost for the whole fleet remained much the same at $258 million per annum.

It means that the hourly operating cost had risen from A$32,545 to A$49,568 which converts to US$24,409/hour and US$37,176/hour respectively. It seems that reality has caught up with the RAAF. The F-35 has been costing US$44,000/hour in US service, possibly now near US$37,000/hour.  The US Air Force wants it down to US$25,000/hour, what a new F-15 costs to operate, which it can afford. So A$32,545/hour was a dream number provided by Lockheed Martin which our RAAF swallowed. Now the RAAF is confessing that the real number is 52% higher.

The way it works in places like the RAAF is that the annual budget remains the same so the flying hours get reduced, in this case from 20 hours/month to 13 hours/month. Pilots need 20 hours/month to maintain proficiency. As shown by recent USAF results, when flying hours drop below 20/month the accident rate rises.

Bad news for our pilots — they will be flying an undefended light bomber into combat and not even be proficient in operating it.

In the second article, Robert Gottliebsen continues to point out the deficiencies of the F-35, including the fact that its normal operating altitude is 30,000 feet lower than the Chicom and Russian stealth fighters, the J-20 and Su-57 respectively. In combat the F-35 will be fighting uphill against those two fighters. The faster and higher a fighter is flying, the greater the range of its radar-guided missiles which fly a ballistic arc towards their targets. This gives the Russian and the Chinese fighters the ability to fire at the F-35 and then turn around before the F-35 can fire back.



The reason why the F-35 flies at 25,000 feet instead of 55,000 feet is that it is optimised for bombing surface-to-air missile sites. Actually it is worse than that. The measure of the efficiency of a jet engine is its thrust-specific fuel consumption (TSFC).  This is its fuel consumption per unit of thrust, and for U.S. jet engines is measured in pounds per hour of fuel per pound of thrust.  The TSFC of the F100-PW-229 engine that powers the F-15 and F-16 is 0.726 lb/Hr/lb.  The F-15 first flew in 1972.  More than 40 years later, the TSFC of the F-135 engine, which powers the F-35, is 0.889 lb/Hr/lb. This is 22% higher than the F-15’s fuel consumption despite all the decades of engine development in between.  If the F-35’s engine were as efficient as that of the F-15, the F-35 would be able to fly 22% farther on its fuel load.  This is a big deal, so what happened?

It all goes back to the original sin of the F-35 in that it was sold as something that would satisfy the needs of all three of the U.S. services that have fighter aircraft.  For the Marines, this meant an aircraft that could take off and land vertically — which places a particular constraint on the engine used to achieve that.  For normal jet aircraft, once they start rolling down the runway to take off, there is a ram effect of air being pushed into the engine, aiding the engine’s efficiency. For vertical take-off and landing of aircraft, though, with no ram effect, the engine must suck in an enormous amount of air to generate the necessary mass of exhaust.

This requires a wide engine with lots of core mass flow.  That big core mass flow in turn requires an equivalent amount of fuel, as kerosene-air mixtures will burn in only a narrow range of mixtures near the stoichiometric ratio (the ideal ratio that leaves no unburned fuel or unused air).  This means that all the F-35 variants — the F-35A for the USAF, the F-35B for the Marines, and the F-35C for the USN — have a wide, draggy, thirsty engine with a range penalty.  That engine is optimized for the F-35B — a small percentage of the total fleet of F-35 variants, and only for a few moments of the F-35B’s flight regime. It has been said that the F-35 is optimised for operating at 25,000 feet for its ground attack role. The engine though is optimised for operating at 0 feet, zero air speed.


 Vertical take off: this is why the F-35 engine sucks


The F-35 is Australia’s biggest problem, because without a proper fighter aircraft we are defenceless. The USAF has relegated its F-35s to delivering cruise missiles to the edge of the combat area and then running away. The USAF is patching its F-35 problem by buying more F-15s and F-16s. The US Department of Defense signed a contract for 1,000 new F-16s with the initial batch at US$54.4 million per copy. No doubt we will be offered the F-16 too but Australia should turn it down because we can buy something a lot better at much the same price.

The solution to our F-35 problem that Mr Gottliebsen puts forward is to resurrect the F-22. That is a nonstarter for a number of reasons. There were F-22 supporters in the U.S. who pressed for a congressional inquiry into restarting production. The inquiry duly found that the unit cost would be US$205 million and the enthusiasm for the F-22 died. The F-22 has a multitude of other deficiencies beyond its sticker price.

The optimum solution to the F-35 problem remains the Gripen E from Saab in Sweden. The Gripen E has 80% of the combat effectiveness of the F-22 at a quarter of the capital cost and 15% of the hourly operating cost.

The standard for combat effectiveness is set by the F-22 which combat simulation modelling indicates will shoot down two Su-35s for each F-22 lost. The rate for the Gripen E is 1.6 Su-35s shot down for each Gripen E lost. Using Lanchester’s square law for relative effectiveness, it takes 1.5 Gripen Es to do what one F-22 can do. So the work that a force of 100 F-22s, costing US$20.5 billion, could do would be achieved by 150 Gripen Es costing US$8.4 billion.

We don’t have much time left before China’s war starts. The first thing we should do is panic buy the 50-odd Gripen C and D versions that the Swedish Air Force has parked up.  To have an operating air force at the end of a conflict, you have to start with a force that is larger than the number of aircraft shot down (and pilots killed) in defeating the enemy.