Post by AAC_Maj. Hubbabubba on Nov 7, 2012 16:18:51 GMT -5
~S~All
Since practise bomb runs at range #3 have started, a certain confusion as to "how to bomb" has been raised.
As to make things clear (or, at least, clearer...), here are the main specifications;
Altitude: 60 feet AGL (Above Ground Level)
Speed: 240 MPH IAS (Indicated Air Speed)
Distance: 425 yards from the wall
Location: Center of the wall at right angle.
Without going into details (a good site for that would be www.thedambusters.org.uk/index.html), I will try to explain briefly the reasons for these specs.
Altitude was governed by two main reasons. If dropped too high, the "Upkeep" would disintegrate and, if dropped too low, the aircraft dropping it would. First trials took place at 150 AGL but the bombs, at the time covered with a spherical wooden structure, would loose their timber envelope as they hit the water. It was nevertheless observed that despite that, the metal casing which would contain the explosives (TORPEX) was resisting to the shock. Some footage of experimental drops doing just that are available on the aforementioned site. Wallis decided to try drops without the wooden external structure from the same height but the metal drum, without the softening effect of the disintegrating wooden ball, would not resist the impact.
It is said that Barnes Wallis "calculated" the altitude to drop safely the Upkeep as being 60 feet precisely. My humble opinion is that it is a bit of hype. Too many variables exist to determine precisely the rupture point of a metallic container and, even with the spots "trick", getting and maintaining an aircraft "precisely" at 60 feet was humanely impossible. If anything, it is easier to maintain altitude in CFS1 than it would be in real life. We have control not only over the aircraft, but also over wind, and we can trim our elevators to perfection with auto-pilot.
In my opinion, that "precise 60 feet" was obtain by trials and was basically the lowest possible altitude, with a certain margin for safety, at which the bomb could be dropped and survive its first contact with water. By experience, dropping below 40 feet will result in the destruction of your aircraft. Dropping over 75 feet will mean almost certain overshooting.
Speed was decided by the distance and the number of "hops" necessary to reach the dam wall. If going too fast, the intervals between bounces would be too long and the Upkeep would risk going over the dam or hit the parapet, literally exploding in your face. If going too slow, the bomb would simply sink before reaching the dam wall, causing very little damage, if any, to it.
In "real life", the pilot was keeping his Lancaster at 240 MPH by looking at his airspeed indicator dial. No historical mention is made of any special device to keep precisely that speed. I doubt that a difference of ± 5 MPH would matter much. The pilot had the luxury of having his hand constantly on the throttles but, in CFS1, we have other things to do than to fiddle with throttles while preparing to drop the Upkeep. This is why I have added digital/analog airspeed indicators and throttle percentage indicator to the bomb-aimer panel. This is also why "dry runs" should be made prior to the drop to evaluate which percentage of throttle will get you over the drop point at 240 MPH. Individual aircraft performance, sustained damages, and topography of the target will dictate which settings you should get.
Distance, as stated just above, is in direct relation with speed. The Upkeep should be dropped ideally at 425 yards from the dam wall, give and take 25 yards. In CFS1, we can compensate one by the other, but it was impossible in real conditions to do so. The Upkeep would sink too soon or jump over the wall. If used proficiently, the special bombsight should give very good accuracy.
This brings us to location. Although last cited, it is as important, if not more important, than everything else. I can't emphasized it too much; LINE-UP, LINE-UP, LINE-UP!!!
The more acute is your approach angle, the closer will the two dam towers appear in the bombsight, inducing late drops. In real life, this was even more problematic. If the barrel-shaped charge was not hitting "squarely" the wall, chances were that it would tumble or disintegrate. If not well centered, the Upkeep could still cause damage, but the charges had been calculated for maximum blast effect at the center of the gravity dam, where the weigh of water is heaviest.
In my next post, I will indicate what it specifically mean when practicing at bomb range #3.
Since practise bomb runs at range #3 have started, a certain confusion as to "how to bomb" has been raised.
As to make things clear (or, at least, clearer...), here are the main specifications;
Altitude: 60 feet AGL (Above Ground Level)
Speed: 240 MPH IAS (Indicated Air Speed)
Distance: 425 yards from the wall
Location: Center of the wall at right angle.
Without going into details (a good site for that would be www.thedambusters.org.uk/index.html), I will try to explain briefly the reasons for these specs.
Altitude was governed by two main reasons. If dropped too high, the "Upkeep" would disintegrate and, if dropped too low, the aircraft dropping it would. First trials took place at 150 AGL but the bombs, at the time covered with a spherical wooden structure, would loose their timber envelope as they hit the water. It was nevertheless observed that despite that, the metal casing which would contain the explosives (TORPEX) was resisting to the shock. Some footage of experimental drops doing just that are available on the aforementioned site. Wallis decided to try drops without the wooden external structure from the same height but the metal drum, without the softening effect of the disintegrating wooden ball, would not resist the impact.
It is said that Barnes Wallis "calculated" the altitude to drop safely the Upkeep as being 60 feet precisely. My humble opinion is that it is a bit of hype. Too many variables exist to determine precisely the rupture point of a metallic container and, even with the spots "trick", getting and maintaining an aircraft "precisely" at 60 feet was humanely impossible. If anything, it is easier to maintain altitude in CFS1 than it would be in real life. We have control not only over the aircraft, but also over wind, and we can trim our elevators to perfection with auto-pilot.
In my opinion, that "precise 60 feet" was obtain by trials and was basically the lowest possible altitude, with a certain margin for safety, at which the bomb could be dropped and survive its first contact with water. By experience, dropping below 40 feet will result in the destruction of your aircraft. Dropping over 75 feet will mean almost certain overshooting.
Speed was decided by the distance and the number of "hops" necessary to reach the dam wall. If going too fast, the intervals between bounces would be too long and the Upkeep would risk going over the dam or hit the parapet, literally exploding in your face. If going too slow, the bomb would simply sink before reaching the dam wall, causing very little damage, if any, to it.
In "real life", the pilot was keeping his Lancaster at 240 MPH by looking at his airspeed indicator dial. No historical mention is made of any special device to keep precisely that speed. I doubt that a difference of ± 5 MPH would matter much. The pilot had the luxury of having his hand constantly on the throttles but, in CFS1, we have other things to do than to fiddle with throttles while preparing to drop the Upkeep. This is why I have added digital/analog airspeed indicators and throttle percentage indicator to the bomb-aimer panel. This is also why "dry runs" should be made prior to the drop to evaluate which percentage of throttle will get you over the drop point at 240 MPH. Individual aircraft performance, sustained damages, and topography of the target will dictate which settings you should get.
Distance, as stated just above, is in direct relation with speed. The Upkeep should be dropped ideally at 425 yards from the dam wall, give and take 25 yards. In CFS1, we can compensate one by the other, but it was impossible in real conditions to do so. The Upkeep would sink too soon or jump over the wall. If used proficiently, the special bombsight should give very good accuracy.
This brings us to location. Although last cited, it is as important, if not more important, than everything else. I can't emphasized it too much; LINE-UP, LINE-UP, LINE-UP!!!
The more acute is your approach angle, the closer will the two dam towers appear in the bombsight, inducing late drops. In real life, this was even more problematic. If the barrel-shaped charge was not hitting "squarely" the wall, chances were that it would tumble or disintegrate. If not well centered, the Upkeep could still cause damage, but the charges had been calculated for maximum blast effect at the center of the gravity dam, where the weigh of water is heaviest.
In my next post, I will indicate what it specifically mean when practicing at bomb range #3.
