Lockheed Martin is developing a spoiler for F-35C Joint Strike Fighter flight test aircraft to counter potential wing drop in transonic turns.

Wing drop in high rate transonic turns is a problem because it results in a turn becoming a roll.

Because leading and trailing edge flaps may not be enough to counter this phenomenon, the carrier variant F-35C will have a 4.5kg (10lb) spoiler added to the centre of its outboard wing for the test programme.

The issue of transonic turn wing drop was a lesson learnt from the Boeing F/A-18E/F Super Hornet programme.

The same issue has been studied in wind tunnels for the F-35 programme.

Despite the addition of this control surface Lockheed does not expect a radar cross section signature impact.

At the American Institute of Aeronautics and Astronautics' 45th Joint Propulsion Conference in Denver Colorado Lockheed Martin's F-35 development vice president JD McFarlan III told Flight International, "[the spoiler] has been designed to be LO compliant."

In other developments for the programme, the first short take-off and vertical landing variant's flight test is planned for September at Naval Air Station Patuxent River. Pratt and Whitney is to deliver five production F135 engines later this year and has delivered 12 of its contracted 18 test engines, five of which are for STOVL flight.

The General Electric/Rolls-Royce F136 engine will have maximum afterburner tests later this month and the engine's three variants have now achieved more than 800h of test time.

While the F135 engine has achieved over 12,000h of 14,250h planned test hours, over 5,750h of which are for the conventional variant and another 2,300h-plus for the STOVL.

McFarlan added that the F-35's inlets have been designed for 10% engine thrust growth and that higher temperature fuels were of interest to enable the fighter's fuel to become a better heat sink.

Source: Flight International