Monday, October 4, 2010
Barriers and Barricades, One More Time
I recently read an excellent history of a carrier-based airplane but noted that the author, in the captions, did not bother to differentiate between barriers and barricades. It is a minor quibble, but the nomenclature is specific and illustrates a two-step set of changes to carrier-deck equipment forced by the introduction of jet airplanes, one element of which was retained on angled-deck carriers.
Barrier
The configuration of the Davis barrier changed over time but the principal remained the same.
Barricade
The original barrier was introduced at the very beginning of carrier operations to stop an airplane when its tail hook had missed all the arresting wires. First one steel cable and then two were strung across the deck about three feet high at each barrier station. They were attached to stanchions which could be folded down to place the cables on the deck so airplanes could taxi past the barriers. An operator was stationed at each barrier to raise and lower it.
The steel cable barriers were very effective.
Unfortunately, the original barriers were not safe to use to stop airplanes with nose landing gears and to some extent, with twin-engine airplanes. The steel cables would wipe out the nose landing gear, raising the potential for the cables on the next barrier forward to slice the canopy off the airplane, and with it the pilot's head.
There was also the potential on a twin-engine propeller-driven airplane for the nose gear to pull the cable forward, allowing a propeller to hit it an angle and cut it, rather than skip off of it and past it. A tightly stretched steel cable when cut could wreak all kinds of havoc, not to mention not stopping the airplane.
The Davis barrier solved those problems by having the cables laying flat on the deck. A canvas strap was strung across the deck about three feet up using the same stanchions used for the original barrier. When the airplane's nose gear (or a "retractable barrier guard" in front of the windscreen if the nose gear had collapsed) hit the horizontal strap, vertical straps between it and the cables pulled them up off the deck to engage the main landing gear, thereby stopping the airplane. There were about six or so barriers on a carrier, so some were rigged for props and some for jets. They could also be reconfigured or replaced fairly quickly. Four barriers are shown in the following picture, two prop (lying on the deck) and two jet/AJ, i.e. Davis, one that has been activated but didn't snag the main landing gear because the jet had hooked a late wire so was going too slowly (barrier operators were cautioned not to drop their barriers too quickly) and the other in the ready position.
The Davis barrier worked acceptably after some development, although it was recognized that if the airplane were going too fast when it hit the Davis barrier, the cables might not be pulled up high enough, fast enough so they didn't get above the main landing gear tires and snag the landing gear struts before the main landing gear had passed by. There was also a problem with the steel cables being cut by airplane appendages at the higher landing speed of jets as well as pilots defeating the purpose of the barrier with a late and unsuccessful wave off as pictured above. After a few incidents in the fleet with jets not being stopped by the Davis barrier, a really big canvas net hung from scaled-up barrier stanchions was introduced as the last-chance layer of protection for the men and aircraft forward of the landing area. This was the barricade.
With the advent of the angled deck, barriers were no longer required. However, the barricade was still necessary if a jet had a landing gear or tail hook problem and couldn't land ashore. It is only rigged when required and the deck crews periodically practice erecting it on short notice and in only a few minutes.
Barrier
Davis Barrier
The configuration of the Davis barrier changed over time but the principal remained the same.
Barricade
The original barrier was introduced at the very beginning of carrier operations to stop an airplane when its tail hook had missed all the arresting wires. First one steel cable and then two were strung across the deck about three feet high at each barrier station. They were attached to stanchions which could be folded down to place the cables on the deck so airplanes could taxi past the barriers. An operator was stationed at each barrier to raise and lower it.
The steel cable barriers were very effective.
Unfortunately, the original barriers were not safe to use to stop airplanes with nose landing gears and to some extent, with twin-engine airplanes. The steel cables would wipe out the nose landing gear, raising the potential for the cables on the next barrier forward to slice the canopy off the airplane, and with it the pilot's head.
There was also the potential on a twin-engine propeller-driven airplane for the nose gear to pull the cable forward, allowing a propeller to hit it an angle and cut it, rather than skip off of it and past it. A tightly stretched steel cable when cut could wreak all kinds of havoc, not to mention not stopping the airplane.
The Davis barrier solved those problems by having the cables laying flat on the deck. A canvas strap was strung across the deck about three feet up using the same stanchions used for the original barrier. When the airplane's nose gear (or a "retractable barrier guard" in front of the windscreen if the nose gear had collapsed) hit the horizontal strap, vertical straps between it and the cables pulled them up off the deck to engage the main landing gear, thereby stopping the airplane. There were about six or so barriers on a carrier, so some were rigged for props and some for jets. They could also be reconfigured or replaced fairly quickly. Four barriers are shown in the following picture, two prop (lying on the deck) and two jet/AJ, i.e. Davis, one that has been activated but didn't snag the main landing gear because the jet had hooked a late wire so was going too slowly (barrier operators were cautioned not to drop their barriers too quickly) and the other in the ready position.
The Davis barrier worked acceptably after some development, although it was recognized that if the airplane were going too fast when it hit the Davis barrier, the cables might not be pulled up high enough, fast enough so they didn't get above the main landing gear tires and snag the landing gear struts before the main landing gear had passed by. There was also a problem with the steel cables being cut by airplane appendages at the higher landing speed of jets as well as pilots defeating the purpose of the barrier with a late and unsuccessful wave off as pictured above. After a few incidents in the fleet with jets not being stopped by the Davis barrier, a really big canvas net hung from scaled-up barrier stanchions was introduced as the last-chance layer of protection for the men and aircraft forward of the landing area. This was the barricade.
With the advent of the angled deck, barriers were no longer required. However, the barricade was still necessary if a jet had a landing gear or tail hook problem and couldn't land ashore. It is only rigged when required and the deck crews periodically practice erecting it on short notice and in only a few minutes.
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