Forum: F-16 Simulators

Hi Guys
I am not sure if this is the place to post this question, but here goes. I have built a simulator pictured here and am having a small issue that I hope someone here can help me resolve. I am using Falcon BMS [Link pending approval] software and it simulates the WOW switch almost perfectly for takeoff and landing. After touchdown, the WOW is triggered as well as on take-off. The computer sends out a signal to an interface card that I have installed to activate the landing gear box [Link pending approval] have a real landing gear box installed and the solenoid lockout works along with the permission button. The problem is that when landing for example the computer triggers the WOW switch very rapidly till the plane settles down on the runway. This causes the solenoid to flutter and could burn it out as the real ones have a very short duty cycle, something like 15 seconds on to 10 minutes rest!!! My question is: in the real F16, is there some kind of delay before the signal is re-sent to prevent the same issue? I hope this is clear. IOW, If you bounce a bit on the landing does the WOW switch re-trigger rapidly as I am describing? We are trying to make the simulator software react exactly like the real plane and these details are really important.
Here is my pit:

I will try to make a video of the problem.

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Based on the F-16 crash recorder data I looked at during my employed years, normal flared landings with subsequent two-point aerodynamic braking didn't produce a weight-on-wheels signal until well after touchdown. In those cases there was no rapid switching of the weight-on-wheels signal. It came on when the main gear compressed far enough to turn it on and then it stayed on. If the pilot made a firm landing, weight-on-wheels could be triggered for a fraction of a second, but it would then go away until it came back again as described above. If it was a firm landing with a bounce to another firm touchdown, there could be two brief weight-on-wheels signals before the final one. I never saw the signal re-trigger rapidly multiple times as you describe. I don't know how the F-16's WOW switch mechanization achieved that stability. I'm guessing it has to do with the nature of the main gear shock strut design and the compression point chosen to indicate weight-on-wheels.

What about rigging it in a way so that it only takes the signal from the nose landing gear WOW? Would this not solve the problem?

Larry (as usual) is correct. It is typical to see a couple of intermittent WOW transitions on landing. Remember, the WOW switches are old-style mechanical plunger switches that are adjusted manually on installation, so the adjustment of the WOW switches also has a lot to do with when they "trigger" WOW.

All of which does not solve your problem. I think the only thing you can do is modify your program so that the solenoid only gets the WOW signal if it is persistent, i.e., present for more than a second or two.

Changing to the nose WOW won't work; too many other things use the RMLG WOW. For example, your landing display on the HUD wouldn't be correct.

Best Regards,

Thanks guys you answered my question with enough info to relay it to the coders. After some more thought on what exactly happens to a wheel strut when it contacts the runway it occurred to me that one thing not being modeled or perhaps accounted for is so simple I cant believe I didnt think of it before. The shock absorber damping will slow the return of the oleo. This must inherently allow the leg to stabilize lower than the trigger point for the switch. Is my logic OK here?
Also, our WOW is triggering almost the instant the tire touches the runway which judging by what exitsafety posted, seems way too soon. This is probably what the real problem is. Joe, your solution looks best and thank you again for the insight. We are trying hard to get BMS exactly right and some things like this dont show up until we have real hardware hooked up.
Thanks a LOT for the replies guys, this is a huge help.
Nigel

Nigel - Glad to be of some help. Today I contacted the retired engineer who is basically the "father" of the F-16 landing gear. He pointed out that there is considerable hysteresis in the weight on/weight off wheels mechanization. After weight-on-wheels occurs, the gear must extend farther than the weight-on-wheels point to go back to weight-off-wheels.

Forum: F-16 Simulators

Triggering WOW switch