AC-130 gunships

OK, so they circle, but why not something sticking out of the other (starboard?) side?

According to the nytimes, the AC-130 gunship

When these craft are in action, they are turning fairly tight circles (for a plane of its size) at pretty high bank angles.

The starboard side would be looking at the sky most of the time.

Because you keep the bad guys on one side of the plane? Sure, you could have cannons on both sides. But that would dilute your firepower. The idea is to be able to concentrate fire on any one point. You keep the bad guys to the port side and slowly circle around them, blasting away. If you had guns on the other side they wouldn’t be able to bear. If you put all the guns on one side you can get twice as much firepower from that side. So all you have to do is make sure you face the correct side.

The AC-130 is only useful if the bad guys don’t have any anti-air capability since it is slow moving and cumbersome. But for fire support you WANT to be slow moving so you can loiter in one area. But since this is a fixed wing aircraft you HAVE to keep moving, and so the circling, and so you put all the weapons on the port side.

Port side is the pilot’s side. The weapons are aligned on the pilot’s side so he can level the firing platform (the plane) at the target with the good old Mark I. The weapons themselves have a restricted field of fire and can only be accurately trained at the target by the gunners once the Spectre itself is properly aligned. Thus, both pilot and gunner play a role in aiming the weapons. Weapons on the starboard side of the plane would obviously be facing skyward when the port side is firing, and cannot be as accurately aimed by the pilot because he has to look through the cockpit instead of straight out the window.

EYEBALL, MK.I, NSN 0001-01-001-0001

The good ol’ Mark I is often used with the TLAR* sighting system, BTW.

[sub]*TLAR = “That Looks About Right”[/sub]

In the statistics field we have (that would be the royal we) “interocular tests” like the “interocular test of curve fit”. We (again, royal) also have the TLAR Index of item distribution, which often rivals the (skew/std.error) index.

Trust the dopers to give a straight answer. Or is it nifty circular reasoning?

Anyway, thanks for the elucidation.

Cool site here on all of the AC-130 models.

Metafilter has some other interesting links and comments about the AC-130. (Hope I’m not banned for disloyalty.)


"Brig. Gen. Carl A. Hagan of US Army Forces Command, speaking at an Air Force Association symposium in February 1990, shared a soldier’s view of the awesome power of the Air Force gunship. Hagan’s son Steve, a captain in the 82d Airborne Division, had taken part in Operation Just Cause in Panama in December 1989. On the first night, his unit found itself in a difficult spot.

Fortunately, the captain told his father, there was an AC-130 gunship overhead: "We explained our situation and the guy [in the gunship] said, ‘Where are you?’ and we showed him, and he said, ‘Where are the bad guys?’ and we showed him that. There was a pregnant pause for a couple of seconds, and then he said, ‘You need to move back 18 feet.’ "

“They did that,” the elder Hagan reported, “and the AC-130 did its thing and eliminated all opposition. Now, that’s close air support.”

The inspiration for the gun ship supposedly came from australian mail. Myth or not the similarity is illustrative.

In the outback mail planes learned they could drop a bucket on a rope and keep it in the same place while circling so mail could be retrieved or posted without landing. Similarly, circling allows the AC130 pilot to keep the target stationary with respect to the airplane.

Um, Ned? No offense but I have my doubts about that. To keep the “bucket” relatively stationary would require the plane to turn inside it’s own wingspan. I doubt a puddle jumper could do that, let alone a monster like the C-130.

However, the AC-130 probably can turn tightly enough that the cone of fire from the guns tends to loiter at a central “pivot” point as the plane circles.

The turning radius would not need to be less than the wingspan, just equal to the length of the side of the triangle formed by the rope, and the ground. Still some fancy flying, though.


“No flying machine will ever fly from New York to Paris … [because] no known motor can run at the requisite speed for four days without stopping.” ~ Orville Wright ~

It’s easy enough to put an aircraft in a bank (30-40deg.)at an altitude of a couple thousand feet, deploy a “bucket-on-a-rope”; the end result is a bucket that’s basically stationary over a stationary point on the earth.

TACAMO birds use the same principle to stabilize the major leg of their antenna.

Small/slow aircraft (like a Cessna-150) would be able to do the same from a fairly low altitude.

Think of this principle as a reversal of the cowboys’ lariat.

Help me out here. I’m having a hard time envisioning this bucket deal. If the airplane is flying a tight banking circle and it’s got a bucket on a rope hanging from it, why is the bucket staying in the center of the circle instead of experiencing the centrifugal force pushing it outside the plane’s circular travel path?

With the lariat, the cowpoke’s hand is swinging the lariat around. In the airmail scenario described it sounds like the bucket is swinging the plane around.

Just a guess, but the mail bucket’s on the ground, not hanging? Think instead of one of those model airplanes where the operator stands in one spot and rotates, with the control lines leading to the plane circling around. Now replace the control lines with a stream of shells, and you’ve got a gunship.

That’s not the way I read the scenario described.

I’ve got no problem with the gunship’s targetting, I’m trying to digest the bucket tangent, which does not make sense to me at this point.

Take a small plane on a totally windless day…

this plane is in 40 degree bank at 1000 ft above ground,

and the plane traces a circle above a fixed point.

Now, deploy 2000 ft (or so) of line with any sort of weight at the end and the end result is the end of the line/weight will hang around/above the ground depending on how long the line is and how stable the plane is flown.

(reverse cowboy lariat; think about it a sec)

I remember seeing this in a very old Nat Geographic that concerned either Africa or Australia; the technique was used to deliver radio batteries in remote locations.

Maybe I’m brain dead tonight (it’s happened before), but I still don’t get it.

If an airplane is in a tight banking turn and releases an object, that object, from the point at which it was released from the airplane, is going to travel a straight course tangent to and away from the circular course of the airplane until such time as the rope is fully deployed and capable of exerting on it the centripetal force from the airplane’s continual turning. At that point it will resume a circular travel path with a radius greater than that of the airplane’s circular travel path. It is not going to proceed to the center of the circle.

How can it? What forces act upon it to overcome centrifugal force?

I’ve read about the low-freq planes doing this with the antenna. I suspect that drag has a lot to do with it.

Let’s go with the antenna version. It has very low mass compared to its drag. When it’s fairly short it tends to simply trail the aircraft. As it gets longer it reacts more slowly to the motions of the aircraft. Eventually, as the plane circles, dragging the wire around, the forces cause the wire to settle into the center of the circle.

The bucket on a rope would be very similar. Since the mass is so low it doesn’t end up getting slung to the outside of the circle.