Dropping the Bomb on Hiroshima: Why the Need for a Sharp Turn?

Colonel Tibbits, the pilot who dropped the bomb on Hiroshima, wrote:

I’m not following this. I understand the need to get away from the impact as quickly as possible, but how does turning away help? I would have thought that whether they continued to fly straight, or turned, they would still be travelling the same distance from the point of impact? What am I missing?

Inertia; the bomb is traveling at the same speed as the plane when released, so if you keep going straight you’ll be roughly in the same place when it detonates I’d imagine.

Edit: Okay, I imagine that since the plane becomes lighter after the load it would become a bit faster, but I’m not sure if it would be by enough of an amount to make a difference, maybe in a light headwind that blew the fallout in the opposite direction.

Edit2: It’s basically the “fire a gun/drop a bullet” problem, ironman edition if you want to think of it that way.

You are correct, Inertia.

Plane traveling west at 300 MPH, drops bomb. Plane traveling now 325 MPH bomb slows to 275 Mph. This means the plane is moving away from the bomb at 50 MPH.

Same case but plane turns away at 325 but because of turn slows to 250 MPH. Plane now traveling away from bomb at 525 MPH.

my numbers are off but the idea is there.

In other words, without turning away, the bomber will only be about 35,000 feet away from the blast (almost directly above the bomb).

I googled ww2 bomb footage, and there is a couple videos shown as if taken through the open bomb bay, and the bombs stay in view all the way to the ground. (I assume the plane stays over the drop to get info for post strike analysis, propoganda, and training footage.)

Turning away will put some horizontal distance between the bomber and the blast.

Would it help if you started the turn before you released the bomb?

IIRC a plane can “lob” a bomb onto a target (not sure of proper term). Essentially the plane turns and then releases the bomb which arcs away from the plane and onto its target. This was done to avoid overflying the target (perhaps because of too much AAA or something). Accuracy would suffer I’d think and I am not sure if this was ever deemed an appropriate tactic or just something they tried to see how viable it was.

That said I do not think a bomber can do it (done with small tactical bombers) as releasing from the bomb bay in this way would probably smash the bomb into the side of the plane. With externally mounted bombs this is not a problem.

Ditto inertia.

You’ve also got to take into account the enormous diameter of the affected zone. Once that bomb goes off, you do not want to have to fly back over the area to return to base.

The explosion produced a shock wave, which would weaken by an inverse-square relationship with distance. The farther away the plane was, the less potential damage it would take when the shock wave caught it.

The bomb was intended to produce an air burst to cause the maximum damage, so a delay fuse to buy the plane more time was not an option.

Probably not… The bomb isn’t going to curve; it’s always going to fall straight forward in whatever direction the plane is going at that moment.

If your turn has to start shallow for some reason and can only gradually get tight, then theoretically, you could improve the speed of turning away from the bomb path by not releasing the bomb until you’re in the tighter part of the turn, but it’s hard to imagine a real-world case where it matters. Certainly not enough to make it worth the hassle and aiming difficulty involved in releasing the bomb partly through a turn.

In the 50s, B-47 crews trained in the Low Altitude Bombing System (LABS) technique, otherwise called toss bombing, in which they basically would have released the nuke at some point in the vertical part of an Immelmann and got the hell out of Dodge. Put a lot of stress on the airframe, though.

Next week on Mythbusters…

Nobody had ever airdropped one before - so putting as much distance between it and the plane must have seemed sensible. As I recall it was parachute retarded - but still … and you don’t want to waste fuel travelling on in the wrong direction.

Their approach and return was simple enough to be manageable and calculated enough to ensure their safety.

It appears that any more complexity was completely useless, if not endangering.

Former bomb-dropper here. Various folks have introduced a bunch of valid ideas, but also a bunch of red herrings for the specific case at hand.

When dropping bombs from high altitude and a level delivery, like every B-17 or B-29 footage you’ve ever watched …

The bomb(s) will continue to travel forward after dropping, albeit slowing their forward progress as they fall. The airplane can often gain some speed from the reduction in weight or drag, but this is negligible over the time scale we care about.

From the ground’s point of view, the bomb(s) will carry forward along the pre-release flight path some distance before impact. For WWII altitudes, speeds, and bomb designs this might be 2-ish miles from release to impact.

From the airplane’s POV, the bomb will begin to trail the aircraft and the trail will be getting larger faster all the way to bomb impact. For WWII altitudes & speeds, this might be 1/4 mile at impact.

For non-nuclear bombs and WWII high altitude deliveries, the bomb explosion is of no concern to the aircraft. Pretty to watch, but neither the shock wave nor the shrapnel, nor even secondaries if you’re bombing an ammo plant have any potential to get you.
Now for nuclear deliveries, escaping your own weapons effects was a big deal in 1945 and remains a big deal today.

As described by others above, for the high altitude level delivery, turning aggressively away was the best way to put distance between the bomber and the bomb. And at high altitude near the limit of the B-29’s capability, they needed to make a descending turn to be able to maintain flying speed in an aggressive (for a B-29) manuever. They lost a few thousand feet in altitude but gained a couple extra miles of separation. Net, net, that’s a winner. So that’s what they did and why they did it.
Now for bombing missions other than Hiroshima / Nagasaki, both before and since, there are dozens of additional tactical considerations and hundreds of variations on altitude, aircraft, tactics, weapons etc. This thread http://boards.straightdope.com/sdmb/showthread.php?t=403006 includes a writeup by me on a different set of nuclear delivery tactics invented later.

The applied practical physics of unguided bombing is actually a pretty interesting topic. It’s a bit difficult to explain or understand without diagrams, which is why I’ve shied away from a complete treatment in the various threads we’ve had.

Modern bombs prefer the term “parachute mentally challenged.”

Parachute challenged is more like it.