Typically the wheel, brake, and bearing assembly slides over the axle. Which axle is threaded on the outboard end. Then a 2 to 4" castle nut is threaded on and torqued down. When properly torqued, the castle slots align with a transverse slot cut into the axle. A smaller bolt is then run through the castle slots, the axle slot, and is cinched down with a small castle nut. Which may itself be safety wired to the large castle nut.
If steps are forgotten, the large nut quickly spins off due to friction. Then the wheel/tire/brake/bearing assembly falls off the aircraft. If it’s torqued too much, the axle eventually develops a fatigue crack and maybe this is the flight it parts in two and the outer half of the axle, the nicely secured nuts, and the wheel / tire, etc fall off. If it’s undertorqued, the whole wheel may wobble and something may tear out.
If the large nut is overtorqued, there may be excessive drag against the rotating tire. Which tears through the small bolt that secures the large nut in place. Now the large nut is free to be spun off. Followed by the wheel / tire / etc.
It’s real secure. Until it isn’t. Checking all that stuff for proper assembly and no sign of unexpected wear on parts that shouldn’t be moving is part of the pilot preflight. And presumably maintenance’s preflight as well.
Despite all the checking and all the redundant fasteners, sometimes stuff just breaks.
Thanks. I missed that at first but see it now. Before, I was wondering about the sudden pitch down change, but the arresting hook explains that, and the navigator talks about it too.
Ranger Jeff said this as well. I did not remember this in the models I built in my youth, so I thought it was not common. Thanks for setting things straight.
So, not just a set of lug nuts like a typical car, but a large center nut like in some racing and performance cars. I wonder what happened in this case.
Statistically ejections have about a 10% fatality rate. If done perfectly within the ejection seat’s envelope, it’s still about 5% fatality rate.
While some F-111s use seats many of them used a whole cockpit ejection capsule. The video indicates this particular plane had the capsule system, since the seats did not have the yellow striped ejection handles above each headrest characteristic of F-111s with ejection seats.
The capsule ejection system proved less reliable than seats. The capsule was chosen due to the F-111 ability to maintain very high speed (Mach 1.2) at sea level. The wind blast from a Mach 1+ seat ejection at that air density would likely be fatal, whereas the capsule would protect the crew.
I once saw a museum display of ejected F-111 crew modules. IIRC (and it was a long time ago) minor spinal injuries were pretty much the norm (or even the least degree of likely injury. You wouldn’t eject unless the alternatives were even more deleterious.
My brother who flew F-111s said that the flight manual discusses the variety of landing gear malfunctions you can have. During the academic part of his training they would show videos of landings similar to that RAAF situation. Those were from the 1970s, and back then the technique they used to avoid the fire hazard was to lay out huge amounts of foam on the runway. He guesses somewhere along the line it was decided that this was more of a mess than the benefit it gave.
ISTM the tailhook makes a belly landing relatively safe, moreso than an ejection. Whereas a no-hook belly landing presents a significant chance of the plane getting sideways and rolling/tumbling, or veering off of the runway (e.g. if there’s a crosswind), the tailhook ensures that the plane will travel nose-first and upright until it comes to a complete stop, and will remain on the runway. Seems like it probably confers better odds than ejection.
I think you can see one of those in that video – something small & dark seems to be dragged along behind the plane (goes out of view on the right as they zoom in to the plane).
The vid says the pilot made several passes before finding just the right approach and landing. Perhaps dumping fuel would have caused him to run out before he got it right. Coming in with dead engines would have been more dangerous than landing with the fuel.
I was an F-111 mechanic for 8 years in the USAF. I saw two belly in similar to the video. In both cases the aircrews got out OK and one aircraft was successfully repaired.
One of the aircraft was on fire due to a hydraulic line chaffing an electrical cable near the main wheel wheel. Therefore the gear wouldn’t come down. It hit the approach end cable with the arresting hook. The runway was foamed. Due to the fire, that aircraft was pretty much a write-off.
The second one that I observed has a mechanical malfunction that prevented the main gear from extending. It slid to a stop without use of the arresting hook. That aircraft was eventually repaired. I saw a third F-111 have a main tire explode and slide down the runway grinding away part of the landing gear. Unlike the other two which were declared emergencies with everything prepped in advance, this was quite a surprise and the runway wasn’t foamed. There was a fire truck on duty near the runway though, but only the one.
Foaming of runways stopped when the USAF did studies that showed it didn’t really help and cost a lot of money. There were some environmental concerns also. The stuff sure smelled bad; rumor had it that it was mostly pigs blood.
Unlike many commercial aircraft, fighter aircraft don’t have thrust reversers to slow them down when landing. Many fighter and bomber aircraft also had substandard brakes especially if trying to stop with a full load of bombs and fuel during an aborted take-off. That’s why the often had tail hooks and also drag chutes to assist during braking. Drag chutes also could help pull an aircraft out of a spin.
I apologize as the span of time made me make a couple of mistakes. The second and third incidents above were the same one. Also according to the book F-111 Down by Hyre and Benoit, the first aircraft mentioned was repaired.
Actually, yes, at one time it was. Processed and refined, to get the shape/type of protiens that would form the impermiable vapor barrier on top of the fuel. The Nav used it too. Then they shifted to AFFF (Aqueous Film-Forming Foam) and never looked back; A-triple-F is vastly superior.
There are a couple of different systems in use. As you say, one was just WWII Navy anchor chain laying alongside the runway which would be drug along by the aircraft until the airplane was slowed to a stop. It was laid out opposite the direction of travel so the farther your drug the chain, the more links were being pulled. That gives a progressively increasing stopping force.
The fancier systems were actually modified aircraft wheel brakes set into the ground on each side of the runway and connected to spool of very heavy fabric tape. A cable stretched across the runway and connected the two spools. The brakes were adjustable for how hard they’d resist paying out their spool once something snagged the cross-cable and started pulling on it.
These were for more permanent installations where the cross-cable was permanently connected, but sat below the surface of the runway in a recessed slot. On command from the tower, solenoid or pneumatic devices spaced across the runway would lift the cable a few inches above the surface. So for normal ops the cable was protected from wear and airplanes didn’t have to worry about damage from hitting a raised cable. But in an emergency the tower controller could press a button and the cable would be up and ready to grab a hook in just a couple seconds.
