Mechanism for the control surfaces of the B-29

[Jenisch]

Hello,

I'm wondering how the control surfaces of the B-29 were operated. They were mechanic or hydraulic?

 

[krieghund]

Here's some excerpts from the flight manuals with the autopilot hook up showing mechanical controls

 

[Siegfried]

Hello,

I'm wondering how the control surfaces of the B-29 were operated. They were mechanic or hydraulic?

They were not hydraulic. They were geared spring tabs also known as geared servo tabs. Not to be confused with trim tabs.

In servo tabs, also known as flettner tabs after their German inventor Anton Fletner, the pilots controls only operate small tabs on the ailerons that then move the main surface. In spring tabs the controls are connected not only to the tabs but effect force on the aileron via springs. Geared spring tabs reduce the effect at high speeds to prevent over control that can allow a pilot to over stress an airframe. The B-36 used a similar system. The B-29 however had a reputation for heavy controls. In event of hydraulic failure aircraft such as the 707 and 727 had backup spring tabs.

I'm aware that some German aircraft such as the He 177, Ar 234, Me 262 used spring tabs. The P 38L received hydraulic boost. The Dornier 335 had it and so may the Fw 190D-13 and He 162. The C-54 also had hydraulic boost.

Spring tab systems are vulnerable to vibration flutter and over balancing at high speed, the also feedback forces to the pilot and can cause a dangerous thing called pilot coupled oscillations (loss of dh 108 swallow)

Spitfire was almost cancelled in mk 20 version in part due to elevator spring tab issues.

Me 109 had excellent roll rate at low to medium speed however stiffening at speed induced some supply of Me 109 aileron spring tabs though documentation is elusive. Late war corsairs and hellcats received geared spring tabs.

Some info on b29 spring tabs, though Schairer had them replaced on the b17e.
http://history.nasa.gov/monograph12/ch6.htm