The tailplane of the Bell X-1 had four evenly-spaced "bumps" on each side--what was their purpose? (Screen shot from The Right Stuff.)

Bell X-1

Another image

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If they're hinges for the elevators, then how come the rudder and ailerons have flush hinges?

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    $\begingroup$ They are indeed hinges, and I'm guessing (hence not an answer) that the tail airfoil just wasn't thick enough to handle hinges of the size required for the aerodynamic forces. $\endgroup$
    – Ron Beyer
    May 4, 2017 at 2:03
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    $\begingroup$ @RonBeyer: No, they hold the counter weight of the elevator, and to avoid flutter this counter weight is distributed over span. $\endgroup$ May 4, 2017 at 20:35
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    $\begingroup$ @PeterKämpf When they changed to the all-moving stabilizer did the retain the elevators or did they fix them to the stab? Getting confused reading about it. Some people seem to be describing it as a stabilator, but some seem to describe it more like a trimmable stab and elevator $\endgroup$
    – TomMcW
    May 4, 2017 at 21:18
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    $\begingroup$ Btw, there's a pic where you can see them closer here skytamer.com/1.2/2002/2136.jpg $\endgroup$
    – TomMcW
    May 4, 2017 at 21:21
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    $\begingroup$ @TomMcW: Trimmable stab and elevator is right. Stabilators were very unusual in the 1940s. $\endgroup$ May 4, 2017 at 21:31

1 Answer 1


This documentary is about the X-1 breaking the sound barrier. It shows that the bumps are indeed hinges, and that the horizontal tail was indeed originally designed as a trimmable stab and elevator. At 25:40 the control surfaces can be seen moving.

At 35:00 Chuck Yeager talks about losing control at M.94 with this configuration, and then having the tail config reworked into an all flying tail, directly connecting the stabiliser to the stick.

Update Aug 2019

The original clip has been removed, this is the new link. Starts at the movement of the all flying tail.

  • $\begingroup$ That youtube video has been removed. Is there another copy online somewhere? $\endgroup$ Aug 7, 2019 at 21:04
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    $\begingroup$ @CamilleGoudeseune looks like this one is similar, time stamps are a.bit later $\endgroup$
    – Koyovis
    Aug 7, 2019 at 21:24

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