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Terminal velocity
- Thread starter Antoon
- Start date
Seems reasonable to me....but there must surely be some other criteria around the height from which it is dropped, and hence density of the air its falling in.
If the Austrian chap, Baumgartner, that jumped from the high altitude balloon reached mach 1.25 in freefall, then I can't see why a streamlined bomb wouldnt reach Mach 1.75 (2019Km/hr)
Im not a physicist...so happy to be corrected
Rich
If the Austrian chap, Baumgartner, that jumped from the high altitude balloon reached mach 1.25 in freefall, then I can't see why a streamlined bomb wouldnt reach Mach 1.75 (2019Km/hr)
Im not a physicist...so happy to be corrected
Rich
Tony Williams
Well-Known Member
I certainly don't claim to be an expert on this subject, but I know enough to realise that it isn't straightforward.
One key number is the BC (Ballistic Coefficient) of the bomb, which describes the aerodynamic drag. The problem here is that there is no one figure for BC for any projectile; there is one figure for subsonic velocities, then the air resistance goes up sharply around Mach 1, before dropping again to a figure below the peak (but still higher than at subsonic speed). What this means is that a bomb might accelerate quite easily to just subsonic velocity but then find it very hard to get through the sound barrier as the air resistance is too great.
The other issues are of course the dropping height and the release velocity. If the bomber is flying very high at supersonic speed when it drops the bomb, and the bomb is well-shaped to achieve a good BC at supersonic speed (which is a different shape from the optimum at subsonic velocities) then it might stay supersonic all of the way down (I'm guessing here). But a bomb of similar weight and diameter, but shaped to be most efficient at subsonic velocities and dropped at lower altitudes and speeds, probably would never get there.
One key number is the BC (Ballistic Coefficient) of the bomb, which describes the aerodynamic drag. The problem here is that there is no one figure for BC for any projectile; there is one figure for subsonic velocities, then the air resistance goes up sharply around Mach 1, before dropping again to a figure below the peak (but still higher than at subsonic speed). What this means is that a bomb might accelerate quite easily to just subsonic velocity but then find it very hard to get through the sound barrier as the air resistance is too great.
The other issues are of course the dropping height and the release velocity. If the bomber is flying very high at supersonic speed when it drops the bomb, and the bomb is well-shaped to achieve a good BC at supersonic speed (which is a different shape from the optimum at subsonic velocities) then it might stay supersonic all of the way down (I'm guessing here). But a bomb of similar weight and diameter, but shaped to be most efficient at subsonic velocities and dropped at lower altitudes and speeds, probably would never get there.
imaokie2000
Well-Known Member
Is that Martian? Google couldn't translate it!
Slick
Well-Known Member
Might as well be(Martian). I did try to figure the sample bomb, but didn't have all the numbers. Made some up. Couldn't cipher a viable Vt. Went back to playing Cubis2.
I have to tender my apologies to the Air Ministry typsetters. Having had a brief look through AP1661B I was surprised to find most British bombs had a terminal velocity in excess of 1000 ft/s. The GP bombs seem to have a terminal velocity of around 1440 ft/s. Most surprising was the 4,000 lb bomb which has a terminal velocity of 2,400 ft/s (estimated).
It seems odd that most of these bombs, where aerodynamics appear to have been of secondary considered have a much higher terminal velocity than that of the 'Grand Slam' where aerodynamics were almost the primary consideration.
TimG
It seems odd that most of these bombs, where aerodynamics appear to have been of secondary considered have a much higher terminal velocity than that of the 'Grand Slam' where aerodynamics were almost the primary consideration.
TimG
glevum
Well-Known Member
My understanding is that the Tallboy was designed to be dropped from 40,000 feet to enable it to reach terminal velocity.
The Lancaster could only get to about 20,000 feet with one onboard so the bomb did not reach terminal velocity before it hit the ground, hence the lower speed at impact.
The Lancaster could only get to about 20,000 feet with one onboard so the bomb did not reach terminal velocity before it hit the ground, hence the lower speed at impact.
Now from what I always figured it is as follows........." For practical purposes, terminal velocity is achieved micro-seconds before detonation !"
To rationalize, I figured that if your the dropper, It ,doesn't matter 'cause it's delivered............If you're the receiver, it doesn't matter if it achieved the optimum velocity............'cause your TOAST ! :tinysmile_shutup_t2
Just my 2 cents worth...........Mike
To rationalize, I figured that if your the dropper, It ,doesn't matter 'cause it's delivered............If you're the receiver, it doesn't matter if it achieved the optimum velocity............'cause your TOAST ! :tinysmile_shutup_t2
Just my 2 cents worth...........Mike
In the book of Wolfgang Fleischer "German Air-Dropped Weapons to 1945" such effect is mentioned for German P.u.W. bombs. Designed in 1916, these bombs were tested in the end of 1920s - early 1930s, being dropped from faster and higher flying planes than in WW I. The researchers found that when dropped from the height of 4-4,5 km (13.000-15.000 ft) or more, P.uW. bombs usually break up in the air and only small fragments fall on the ground. It was explained by complex interaction between torque and aerodynamic forces. Initially, Germans try to improve old bombs by strenghened shell/fin connection, or modified fin angle, but they found it not very effective. Meanwhile they also reveal other defects of P.u.W bombs (over-stabilization or no stabilization, shell break up when hit hard soil, dangerous fuzes) and finally designed entirely new family of bombs.
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Terminal velocity matters when you have to calculated the penetration depth and offset from a bomb that has not detonated. So a buried UXO.
Greetings Antoon
butterfly
HONOURED MEMBER RIP
Terminal Velocity is very important for the bomb aimer. It varied from bomb to bomb and you need to know the TV of the bomb you are dropping in your calculations when setting up the bomb sight computer.
Kev
Terminal velocity of WWII era bombs needed to be subsonic because as the bomb reaches speed of sound, lugs would cause appearance of skew shock waves which would then disturb in flight stability of the bomb.
That is the main reason why Russians designed drag ring on the ogive of their post WWII bombs- to keep bomb subsonic.
That is the main reason why Russians designed drag ring on the ogive of their post WWII bombs- to keep bomb subsonic.
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