Relieving stress by implementing stuff from textbooks

An F-35C coming in for landing is usually at about 11 to 13 degrees nose high so that when it hits the carrier deck, it looks something like this:

Now, program note: for personal circumstances, I left the F-35 program entirely in mid 2012 only to return a little less than two years later to the same job. So I wasn't there to see this in 2013:

We also got an all new hook shoe! This one looks much more like a scoop, to catch the wire even if it's down low on the deck. The new hook profile in red, old in blue, the arresting cable shown in purple:

It was clear that the hook needed a redesign. The new hook has much stronger hold down damper, an all new damper for the upstroke, a better lateral limiter, and improved instrumentation that didn't break on every arrestment. Here's the new hook:

But what actually happened is that the wire stayed down and the hook skips over the wire. What isn't shown is how FAST the tailhook would rebound into the jet. The readings were so high that the test team believed the accelerometer was broken, but it wasn't.

Now the aircraft continues to move forward. We have a wave propagating in both directions along the wire, causing the wire to lay mostly flat against the deck. The wire dynamics model said that what should happen next is that the wire rebounds off the deck..

To understand *how* it didn't work, back to Brick's article. When an aircraft performing an arrestment lands, its main and/or nose tires hit the wire first. This starts a wave in the wire that moves away from the tire. Here's an example, the nose gear has just hit the wire.

Here's pretty much what we were looking at in this conversation. Why was it like this? Because the engineers at Northrop Grumman engineered to a computer model that can simulate how an arresting wire acts when used for arrestment, and the model was wrong.

"Boss," he says to me, "This fucker ain't gonna work. Look at this thing. It's short, it's too close to the wheels, and look at this dumbass hook shoe they got on it. If the wire don't hit it exactly right, it's just gonna go under the hook and you'll bolter."

It was interesting to see it play out this way. I heard it predicted first, by, of all people, one of our instrumentation technicians on November 6, 2010 That was the day CF-01 arrived at Pax. We went to look at the jet. I remember standing with this tech, looking at the hook.

After things like Jet Blast Deflector compatibility testing, we get down to testing the hook. Brick tells us, in a masterful understatement (seriously, this man has a wicked sense of humor and can be amazingly sarcastic, so he HAD to know ):

We began serious carrier suitability testing with F-35C at Lakehurst NAS in the summer of 2011. We would hold our briefings in the same hangar that the Hindenburg was trying to reach when it crashed. This is a level of irony that took zoomers another ten years to reach.

The tailhook is designed to decelerate an aircraft during carrier landing by engaging a wire. The F-35C hook is stowed in a bay that’s covered by clamshell doors during flight. The hook is electronically controlled and moved by hydraulics. And originally, it didn’t work.

Primary source here is “F-35C Carrier Suitability Testing” by Tony “Brick” Wilson, who gives us one of the greatest flexes in an AIAA paper I’ve ever seen.

F-35C Tailhook thread 🧵