F-35 undergoes pit testing

[Esc8781]

EDWARDS AIR FORCE BASE, Calif. -- F-35 tail number AF-1 underwent stores static ejection testing at the F-22 Combined Test Force for the past three weeks. The aircraft is carefully positioned over a pit filled with foam, and instrumented inert weapons are released from the aircraft. This type of testing, also known as pit testing, allows the engineers to evaluate how the aircraft is physically affected by the release of the weapon, as well as the how the onboard stores management computers work. Pit testing is a pre-requisite to in-flight weapons release testing. The F-35 CTF tested both a Joint Direct Attack Munition (JDAM) and an Advanced Medium-Range Air-to-Air Missile (AMRAAM).

 

[Jango]

can somebody (Gambit?) explain this procedure more.

 

[gambit]

The weapons 'pit drops' is the first 'non-assembly line' weapons testing.

https://f35.com/news-events/news-releases.aspx

NAVAL AIR SYSTEMS COMMAND, PATUXENT RIVER, Md. – On June 14, F-35B Joint Strike Fighter test aircraft BF-2 completed the first test flight for the short takeoff and vertical landing variant with an asymmetric weapons load. Cmdr. Eric Buus flew BF-2 with an AIM-9X Sidewinder inert missile on the starboard pylon, a centerline 25 mm gun pod, and a GBU-32 and AIM-120 in the starboard weapon bay. Significant weapons testing for the F-35B and F-35C variants is in progress, including fit checks, captive carriage environment characterization, and pit drops. Aerial weapons separation testing is scheduled for this summer.(Lokheed Martin photo by Andy Wolfe).

Asymmetric load is not a desirable condition whether the load is bombs, missiles, or your average UPS/Fedex stuff. But it is a condition that all aircrafts have to deal with and all pilots have to fly with. In the old days, the burden of compensating for asymmetric load, internal and aerodynamic, the latter meaning load induced drag on one wing but not the other, rests upon the pilot. He has to use his understanding of the aircraft to hold the stick/rudder combination in precise position to maintain level flight. Not counting trim or even maneuvers. Not all aircraft behave the same way under the same conditions. We call them 'real pilots' back then.

Today, we have robots, aka avionics, to do that job.

What the 'pit drop' testing, which is quite static, does is to check for the structural response of the aircraft when confronted with a sudden appearance of an asymmetric load. Also checks to see how the flight control system respond.

We can simulate altitude and airspeed via the TTU-205...

TTU-205 Series Pressure-Temperature Test Sets | © 2012. TestVonics, Inc.

The TTU-205 is a rugged, self-contained flight line or hangar test system used to accurately simulate in flight pressure conditions by precisely controlling and measuring Altitude and Airspeed pressure to aircraft’s pitot-static system.

Basically, we plug up the pitot probe and create both pressure and vacuum to simulate altitude and airspeed. Then we check the FLCS computer to see IF certain voltages appears based upon our prediction on how and when they should appear to compensate for asymmetric load condition. The damn thing, even today's digital version, weighs nearly 100 lbs.

For the F-35, we already confirmed that the aircraft can take off and land with such a condition. Now we are testing to see how the aircraft would respond upon an unplanned and abrupt appearance of such a condition -- on the ground. The next test in the regime would be to see how the aircraft would perform in flight. The goal is to have the FLCS takeover so complete and transparent that the pilot does not even feel it, nor should he care about it. He just want to discharge his weapons, all or partial, and let the aircraft deal with the nitty-gritty of flying.

 

[Icewolf]

^^^ So basically balancing the aircraft out with the payload weight

 

[gambit]

^^^ So basically balancing the aircraft out with the payload weight

No. There are no 'balancing' here. If one out of two bombs are dropped. We are left with an asymmetric load condition. We can 'balance' out by dropping the other bomb. Same for missiles but less severe. The 'pit drop' tests several things other than avionics. We want to check the structural integrity of the weapons carriage system as well regarding materials, discharge mechanism speed, and recovery movements, if any, usually weapons bay door is part of the recovery movement.

 

[Juice]

One thing I wonder, Gambit...can the pilot still manually adjust the trim?

 

[BlueDot_in_Space]

LCA asymmetrical loading. Today, FBW takes care of such scenarios in flight

 

[gambit]

One thing I wonder, Gambit...can the pilot still manually adjust the trim?

Yes.

For the above example, we have the F-14D (top), F-16A (bottom), and F-18E (side) control sticks. The manual trim button is on top for all of them. Pitch and Roll trims are the most often needed so it is pretty much standardized the world over to place the trim button there while the rarely used Yaw trim is usually on the Flight Control panel.

 

[Esc8781]

Yes.

For the above example, we have the F-14D (top), F-16A (bottom), and F-18E (side) control sticks. The manual trim button is on top for all of them. Pitch and Roll trims are the most often needed so it is pretty much standardized the world over to place the trim button there while the rarely used Yaw trim is usually on the Flight Control panel.

Gambit can the pilot adjust for example the vertical stabilizer while the computer is adjusting the stabilizer?

 

[gambit]

Gambit can the pilot adjust for example the vertical stabilizer while the computer is adjusting the stabilizer?

If you mean rudder trim then yes, the FLCS computer is -- or rather should be -- fully capable of adjusting/compensating for both inputs: pilot trim command and its own.