MIflyer
1st Lieutenant
Here is a story from Corky Meyer, originally published in Flight Journal:
The engineers were trying to build the lightest airplane with the biggest motor and still make it capable of surviving carrier landings. To do this, they designed the wings lighter and weaker than normal but intended to shed about three feet on each side should it be overstressed. It could fly back to the carrier and land, even if only one wing separated. The concept worked in testing, and everyone was happy until it hit the fleet.
Pilots loved the airplane because it was fast and had the fastest rate of climb of any propeller-driven fighter in the War. Unfortunately, after a few weeks of glowing operational reports on the Bearcat, word came back that a pilot had shed one of its two wingtips in a dive-bombing-run pull-out and had augured in. Several similar occurrences followed, and the Navy and Grumman became greatly concerned. The flight envelope of the Bearcat was severely restricted, and it was immediately removed from carrier operations.
The Navy and Grumman agreed that a better way to guarantee the wingtip separation was to put a 12-inch strip of prima cord (an explosive rope used to detonate dynamite) just outboard of both wing break joints and have a set of electrical microswitches at both break joints. These microswitches would activate the other tip's explosive device at the instant the first wingtip came off. (We called them "icebox" switches, which shows where we were in technical antiquity!) The ground tests were spectacular, to say the least. Lots of noise, smoke and flying airplane pieces.
After several successful ground tests, we rigged up a Bearcat with this "Fourth of July" system, and I was sent off to do my job as a test pilot.
One of the tips was structured to come off at 5G, and according to theory, the icebox microswitch in the other wing would electrically activate the prima cord and blow the other tip off at the same instant. Three hundred and twenty knots at 7,500 feet altitude in a 30-degree dive angle was selected as the demonstration point. To record the action, we had photographers in chase airplanes on both sides of my Bearcat. I pulled 6G to ensure the 5G rivet joint would fail and activate the other tip explosive.
Lo and behold, the genies of fate again urinated on the pillars of science. With an impressive flash of fire, smoke and debris, one weakened tip left the airplane as predicted at 5G, but the other remained as fixed to the wing as ever.
From the cockpit, a Bearcat appears to be nothing more than a huge engine with tiny wings. However, to look out and see that not only has one short wing become even shorter but also that the other one is full of holes gets your immediate attention.
One of my chase pilots came in and inspected the wing damage. He saw a large hole in the bottom surface, proving the prima cord had indeed fired, as predicted, but the wingtip had remained firmly attached even though the 12-inch hole was in the most critical stress area—the lower skin, or tension area. Good old Grumman Ironworks! Fortunately, the 12-inch hole did not cause any aerodynamic disturbance as might have been expected, and I had already landed the F8F with single tips removed and was ready for the experience, so the landing was uneventful. Back to the old drawing board.
The project engineer suggested 26 inches of prima cord be used on the next flight, after ground tests were run to check whether that amount of explosive would affect proper wingtip severance. On the next flight, when I pulled 6G, both tips departed as planned amid much smoke and parts flying off the airplane.
Both chase pilots were much more excited than I was by the visual effects; I hadn't seen them because my eyes were glued to the accelerometer in the cockpit. They said it looked as if the airplane had blown up when both tips blew and both the ailerons and wingtip sections departed the bird. There were two very smoky explosions as two wingtips and two aileron halves came off in very rapid succession along with much shattered metal. The wingtip ends were cleanly severed as hoped for. There weren't even small pieces of metal outboard of the end rib to suggest an explosion had done the surgery. The test was considered a great success by Grumman and the Navy. More important, I had survived the tests, which I considered an even bigger success.
The engineers were trying to build the lightest airplane with the biggest motor and still make it capable of surviving carrier landings. To do this, they designed the wings lighter and weaker than normal but intended to shed about three feet on each side should it be overstressed. It could fly back to the carrier and land, even if only one wing separated. The concept worked in testing, and everyone was happy until it hit the fleet.
Pilots loved the airplane because it was fast and had the fastest rate of climb of any propeller-driven fighter in the War. Unfortunately, after a few weeks of glowing operational reports on the Bearcat, word came back that a pilot had shed one of its two wingtips in a dive-bombing-run pull-out and had augured in. Several similar occurrences followed, and the Navy and Grumman became greatly concerned. The flight envelope of the Bearcat was severely restricted, and it was immediately removed from carrier operations.
The Navy and Grumman agreed that a better way to guarantee the wingtip separation was to put a 12-inch strip of prima cord (an explosive rope used to detonate dynamite) just outboard of both wing break joints and have a set of electrical microswitches at both break joints. These microswitches would activate the other tip's explosive device at the instant the first wingtip came off. (We called them "icebox" switches, which shows where we were in technical antiquity!) The ground tests were spectacular, to say the least. Lots of noise, smoke and flying airplane pieces.
After several successful ground tests, we rigged up a Bearcat with this "Fourth of July" system, and I was sent off to do my job as a test pilot.
One of the tips was structured to come off at 5G, and according to theory, the icebox microswitch in the other wing would electrically activate the prima cord and blow the other tip off at the same instant. Three hundred and twenty knots at 7,500 feet altitude in a 30-degree dive angle was selected as the demonstration point. To record the action, we had photographers in chase airplanes on both sides of my Bearcat. I pulled 6G to ensure the 5G rivet joint would fail and activate the other tip explosive.
Lo and behold, the genies of fate again urinated on the pillars of science. With an impressive flash of fire, smoke and debris, one weakened tip left the airplane as predicted at 5G, but the other remained as fixed to the wing as ever.
From the cockpit, a Bearcat appears to be nothing more than a huge engine with tiny wings. However, to look out and see that not only has one short wing become even shorter but also that the other one is full of holes gets your immediate attention.
One of my chase pilots came in and inspected the wing damage. He saw a large hole in the bottom surface, proving the prima cord had indeed fired, as predicted, but the wingtip had remained firmly attached even though the 12-inch hole was in the most critical stress area—the lower skin, or tension area. Good old Grumman Ironworks! Fortunately, the 12-inch hole did not cause any aerodynamic disturbance as might have been expected, and I had already landed the F8F with single tips removed and was ready for the experience, so the landing was uneventful. Back to the old drawing board.
The project engineer suggested 26 inches of prima cord be used on the next flight, after ground tests were run to check whether that amount of explosive would affect proper wingtip severance. On the next flight, when I pulled 6G, both tips departed as planned amid much smoke and parts flying off the airplane.
Both chase pilots were much more excited than I was by the visual effects; I hadn't seen them because my eyes were glued to the accelerometer in the cockpit. They said it looked as if the airplane had blown up when both tips blew and both the ailerons and wingtip sections departed the bird. There were two very smoky explosions as two wingtips and two aileron halves came off in very rapid succession along with much shattered metal. The wingtip ends were cleanly severed as hoped for. There weren't even small pieces of metal outboard of the end rib to suggest an explosion had done the surgery. The test was considered a great success by Grumman and the Navy. More important, I had survived the tests, which I considered an even bigger success.
