F-35 Wet Runway Testing Edwards AFB [SRVL Relevant?]
Salty Dogs & Funky Jets Oct 2015 Mark Ayton
"...Wet Runway Testing
It’s strange that wet runway testing must be conducted at Edwards Air Force Base in the Mojave Desert. Annual rainfall on America’s east coast requires runways to drain away quickly and does not provide sufficient time to conduct wet runway tests.
The main Edwards runway is ideal for wet runway tests. It has a flat section that allows a sheet of water an eighth of an inch thick and a layer of AFFF (aqueous film forming foam, which is used for fire fighting) to be laid down. This gives a window of about five minutes when the runway is wet enough to meet the runway condition rating (RCR) criteria.
The pilot runs the aircraft up to the wet section at which point he applies moderate braking. Cdr Ted Dyckman explained: “That represents 60% peddle deflections while tracking down the runway to see how it stops to determine anti-skid performance. We have directional control points that indicate where the pilot enters the wet section and corrects back to centre line from an off set of 20 feet.
“We conduct two verification flying points. First we fly and land in the wet section to make sure there are no directional control issues. The F-35A and the F-35C each use similar types of main tyres but the F-35C’s double nosewheel configuration gives slightly better tracking performance than its single-wheel stablemates. The team conducted wet runway tests with normal field service tyres and carrier surface tyres. The latter simulates catapult launches and arrested landings back on the ship.
To prevent carrier surface tyres from rolling on the deck because of the side forces applied they are inflated to a higher pressure which makes them track well but hydroplane. They also take further to stop because the tyre’s surface area in contact with the deck is reduced by the higher pressure. The field service tyres also tracked well and stopped in the same distance.
Test points were conducted at 60, 90, 110 and 130 knots using wet sections measuring 2,500, 3,000, 4,000 and about 6,000 feet respectively. As soon as the RCR meets the test point (measured by an instrumented truck tracking down the side of the section to avoid the painted centre line which would give a very inaccurate value) criteria, the pilot runs down the wet section replicating a landing run, conducts the braking test and clears the area. The truck remeasures the RCR value and records the time between the two for an average figure. During the directional test, when the main tyres run over the centre line, the aircraft skids slightly because of the effect of reduced friction on the paint. The test team completed the trials in mid-April."
Air International OCTOBER 2015 Vol.89 No.4