Jeffro & Otto
You say you see the holdback cable fastened to something on the catapult. The other end of the holdback is fastened to the underside of the aircraft? Are there fuses at both attachements? In video clips you’ve seen of A-4 launches, the holdback cable stays fastened to the attachment on the deck and the cable and attachment seem to stay with the aircraft and follow the aircraft as it is launched. Does the holdback cable stay on the deck? Also, how does the holdback cable separate from the aircraft?
Well I can understand how you might be confused by various descriptions offered about the catapult. Being there helps, and years stomping around the pointy end of the boat shooting planes off amidst loud noises and other stuff helps learn and does concentrate one's attention . . . so, here is the straight poop.
First off, perhaps nomenclature may be clogging up the situation somewhat. There are basically three parts to the A-4 holdback system:
There is no "fuse" . . . a connotation of something explosive going on . . . (altho' occasionally it may seem that way).
The so-called fuse is the tension bar ( and years still further back it was a 'tension ring" ) . The holdback bar, or tension bar, is a machined steel bar about 5+ inches long for the A-4. I'm sitting here looking at a chromeplated A-4 holdback bar given me by my cat crew . . . With the trusty ruler the bar measures exactly 5 7/16"; that's 13.9 centimeters. Weighs about 2 pounds and looks sort of like a dumbell, except that in the middle of the slender portion is a precisely machined semicircular annular groove. (There is a similar bar, different weight, strength and dimension, for every type aircraft, ie, A-4, F-4, A-6, ....etc.)
The system works simply, but very effectively and safely. Prior to launch, as the aircraft is being readied, a tension bar is placed in the holdback box on the plane's underside, where it just rides along with one end in the box and the other end hanging out a couple inches. So far, so good. As the aircraft taxis into position on the cat, a cat crew member attaches the holdback cable to the free end of the tension bar ... by means of a holdback box/fitting exactly the same as on the aircraft, but with an extending cable and cleat. The cable is then hooked into the holdback track.
As this is taking place, the bridle is being attached to the two hooks on the underside of the wings, and is held in place by hand .... so the bridle doesn't drop off ...until the aircraft is 'tensioned' . The pilot is signaled to release his brakes - gently - as the catapult shuttle with the launching bridle attached is moved forward slowly. When the plane & shuttle can move forward no further, because of the restraining holdback, the catapult and aircraft are said to be "tensioned up"
The holdback bar is machined such that the bar is designed to fail (break at the annular groove) under an exact, pre-determined amount of tension. There is sufficient strength in the bar to hold the plane against the tension of the shuttle, as well as the static tension from the aircraft engine, even at full power, when the pilot applies full throttle prior to launch. But when the steam cat is fired, the holdback bar breaks at an exact designed pressure, and KABLOOM!! ..... a couple seconds and 130 knots later, "WHEEE.... we're flying!"
The spent half of the tension bar still attached to the plane gets a free ride until after landing, when it's removed and given a heave overboard. The rear half was already removed from the holdback, which dropped to the deck upon launch, and tossed overboard.
I mentioned that the pilot is signaled to release his breaks gently. This is so that the aircraft is eased against the holdback - and is not brought to a hard stop by the holdback .... which if done, may cause the tension bar to be prematurely weakened or even cracked. Such could result in a 'cold cat' shot that, when occurring, can spoil your whole afternoon! So to prevent such, the plane has to be pushed back, the bridle dropped, a new tension bar inserted and the whole operation done over! 'Push backs' have the affect of causing great consternation among the cat crew, and giving rise to unseemly aspersions being cast upon the pilot's legitimacy, etc. They also occasion great beating of breasts by the Air Boss, the CAG, and the Captain! (Who occasionally try not to show their angst. But the dentist can tell .... all their rear molars have been ground down to gum end before cruise end!
Jeffro pointed out that things have changed just a bit from the "old" days (sorry, guys, but bridle launches are NOT the norm anymore!). The bottom line is this -- we now use "throw-away" bridles. Reason for this is that the CV's no longer have the extension at the end of the cat to keep the bridle from slapping the front of the CV. The throw-away bridles have a rope "lanyard" as part of their make-up to keep them from hitting the main mounts on the acft as it goes flying off the front end of the CV. That's the "slack" cable you see hanging down. The holdback assembly remains the same as always.
Since the A-4 is about the last to still use a 'bridal' to attach the plane to the catapult shuttle, and since carriers no longer have a 'bridal arresting' system, the A-4 bridals are throw-aways.... ending up well ahead of the ship with a nice splash on each launch. Bridle arresters were made unnecessary with the advent of the 'nose tow' used by all current operational carrier aircraft. This system accomplishes the tension/holdback evolution with an integrated nosewheel tow/shuttle hook-up arrangement which eliminates launch bridals and hold back systems (except for the older aircraft such as the A-4) (The long 'horns', seen in photos of carriers of a few years back, extending forward of the catapult tracks on the axial & angle decks, were part of a system designed to arrest the bridals, which were then retrieved to be used again.)