Comments by "Valen Ron" (@valenrn8657) on "'This is what sovereignty looks like': PM celebrates new F-35A Lightning Fighter" video.
-
2
-
2
-
2
-
2
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
@WarblesOnALot
https://www.quora.com/Why-does-the-US-Air-Forces-F-35-stealth-fighter-have-heat-issues-when-flying-supersonic-and-whats-overheating
With the completion of developmental flight testing, the F-35 no longer has any heat issues when flying within its design flight envelope (with a top speed of Mach 1.6).
In the past however there were 2 sets of speed restrictions:
In the FY2015 Director of Operational Test & Evaluation (DOT&E) report for the F-35, it was noted that the program had an airspeed restriction in place where F-35s were not permitted to fly at speeds equal or greater than 500kts below 5,000ft, 550kts between 5,000–15,000ft and 600 knots between 15,000–25,000ft, for more than 10 minutes at a time without opening the weapon bay doors to vent the air inside them. Above 25,000ft there were no restrictions (aside from the Mach 1.6 top speed).
The reason that this restriction was put in place was because an electronics system that was moved into a weapons bay for easier maintenance access had not been tested and fully certified to last an acceptably long life in high temperatures. When the F-35’s engine is producing high levels of thrust, it produces a significant amount of heat which is transmitted into the weapon bays. This can result in the weapon bays reaching temperatures of over 80C / 176F, so if a circuit board was only previously tested to 85C / 185F, it would require re-verification.
Since that report’s release years ago, those flight restrictions have been removed.
When the F-35’s afterburner was used for extended periods of time it would cause heat damage to the inner surfaces and coatings of the horizontal stabilisers (which extend out behind the jet, either side of the exhaust plume.
This problem was particularly an issue for the F-35B and F-35C variants which accelerate slower and therefore need more time using afterburner to reach speeds such as Mach 1.6.
In the first half of 2018 however, all 3 variants of the F-35 were certified to fly their full flight envelope, and the latest DOT&E report has no mention of this issue remaining, or of afterburner usage restrictions being imposed.
As for the F-35’s Mach 1.6 speed limit, this is purely a placard limit, where the manufacturer was only contracted to develop a Mach 1.6 capable fighter and no funding or requirement has been made to test whether the jet can exceed Mach 1.6 by a non-trivial amount.
Diagrams of the F-35’s flight envelope suggest that all 3 variants can fly faster than Mach 1.6, with the F-35A’s diagram appearing to suggest a top speed of around Mach 1.8 or higher, but this is speculation, and Lockheed cannot guarantee the jet will continue to be safe to operate to (eg) Mach 1.8 without studies and flight testing. In any case, top speeds are not very relevant to real world combat (due to how quickly jets will drain their already partially-depleted fuel tanks trying to reach them) and there could be thermal issues (either with even hotter weapon bays, or additional horizontal tail heating, or with aerodynamic heating causing issues for the jet’s stealth coatings).
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1
-
1