10
$\begingroup$

When Boeing switched over from the B-52F to the B-52G in 1959, they (among other changes) lopped off the top 2.4 meters (8 feet) of the aircraft's vertical tail:

Original-height tail (here on a B-52F)

B-52F, with original tail

(Image by the United States Air Force, via David Legrand at Wikimedia Commons, edited by Denniss, Hohum, and Ralf Roletschek at Wikimedia Commons.)

Pruned tail (here on a B-52H)

B-52H, with decapitated tail

(Image by the United States Air Force, via Trevor MacInnis at WIkipedia, via Rcbutcher at Wikimedia Commons.)

Why did they chop off the tip of the vertical tail, thereby decreasing the aircraft's directional stability and rudder authority?

$\endgroup$
6
  • 2
    $\begingroup$ You can have too much directional stability, which gives an airplane a strong spiral tendency because the airplane wants to weathervane immediately before dihedral effect can do its thing. That was probably the case here. $\endgroup$ – John K Nov 14 '19 at 5:04
  • 1
    $\begingroup$ Of because there was a hangar it needs to fit inside of $\endgroup$ – ratchet freak Nov 14 '19 at 12:09
  • $\begingroup$ "decreasing the aircraft's directional stability and rudder authority" Do you see how small of a rudder the B-52 has, especially in the upper part? I'm guessing that this has more to do with the 1964 Savage Mountain Crash and the test where the tail broke off. $\endgroup$ – Ron Beyer Nov 14 '19 at 13:02
  • $\begingroup$ Elephant Mountain crash also shows that there were structural issues with the B-52 tail. $\endgroup$ – Ron Beyer Nov 14 '19 at 13:12
  • $\begingroup$ @RonBeyer: The teeny tiny rudder makes it even more surprising that they would give up some of what little rudder authority they had to begin with. Also, if the tail is prone to breaking off, the usual course of action is to make the tail stronger, thus fixing the problem at its source without introducing new ones. $\endgroup$ – Vikki - formerly Sean Nov 14 '19 at 21:35
2
$\begingroup$

The fin was shortened to lessen the structural loads (torsion and bending) when flying low (thicker atmosphere). That and using a spoilers-only roll control presented issues:

To reduce aerodynamic loads on the rear fuselage in low-level flight there was a 91-inch reduction in the height of the vertical stabilizer. This stubbier fin had been tested on the first B-52A. In practice, the short fin combined with spoilers-only lateral control induced a tendency to Dutch-roll and low level handling was more sensitive than on earlier B-52s.

— Davies, Peter E., Tony Thornborough, and Tony Cassanova. Boeing B-52 Stratofortress. Crowood, 1998.

Related: Did the "feeler" ailerons of the B-52A-F make air-to-air refueling easier than with the B-52G/H?

The structural reason is also mentioned in an AeroTime article:

The shorter vertical fin was intended to prevent the aircraft crashes caused by the original tall fin failing in turbulent air.

On Wikipedia's B-52 article, there are at least two such accidents:

  • On 24 January 1963, a B-52C on a training mission out of Westover Air Force Base, Massachusetts, lost its vertical stabilizer due to buffeting during low-level flight, and crashed on the west side of Elephant Mountain near Greenville, Maine. Of the nine crewmen aboard, two survived the crash.
  • On 13 January 1964, the vertical stabilizer broke off a B-52D in winter storm turbulence; it crashed on Savage Mountain in western Maryland. The two nuclear bombs being ferried were found "relatively intact"; three of the crew of five died.

While those accidents were on older models, they took place after the change. That does not mean the structural integrity was not apparent from regular maintenance or from manufacturer data. The list is also not exhaustive, there could very well have been minor failures that did not make that list of "notable accidents".

$\endgroup$
4
$\begingroup$

Boeing B-52G Stratofortress

In the design of the B-52G, considerable attention was paid to reducing the structural weight. Different materials were used in the construction of the airframe, and the wing structure was extensively redesigned. The most visible difference was a vertical tail which was reduced in size. The height was reduced from 48 feet 3 inches to 40 feet 7 inches, and the chord (width) was increased. The new tail was tested on the first B-52A (52-001) and perhaps also on either the XB-52 or YB-52 before being adopted as standard for the B-52G.

$\endgroup$
4
  • 2
    $\begingroup$ This confirms that it was indeed made smaller, but doesn't really address the "why"... $\endgroup$ – Ron Beyer Nov 14 '19 at 12:59
  • 4
    $\begingroup$ When I read the entire linked article, it seems to imply that many weight saving changes were made, and the smaller tail was just the most visible "weight saving change". $\endgroup$ – Mike Sowsun Nov 14 '19 at 13:12
  • $\begingroup$ What that article is missing is that the mechanical yaw damper was invented and they were able to use artificial stability to help reduce the needed tail size. The short tail is one of the reasons the re-engine attempt in the 1990s with 4 RB211s was abandoned, as it would make engine out controlability poor. $\endgroup$ – OSUZorba Feb 19 '20 at 2:55
  • $\begingroup$ You might want to add that the 52G was redesigned for low-level bombing and that on several occasions with earlier versions the tail broke off in low-level flight. $\endgroup$ – Peter Kämpf Apr 9 at 18:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.