Tuesday, 16 August 2022

Reasons for the Bf 109 'tall tail' aufgestockte Leitwerk - Calum E. Douglas on Twitter

reposted using the Twitter 'embed' code and comments

..I had always assumed the 'tall tail' on later 109s - the so-called aufgestockte Leitwerk - was about providing increased lateral control at high speeds and reducing stick forces. It enabled the incorporation of Flettner tab(s) controllable from the cockpit. First variant equipped was the G-6/AS (with AS engine). Being able to better keep the sight on the target as a consequence was obviously very useful for a gun platform too. Otherwise, as usual with the Bf 109, the reasons are not always entirely clear. 

..and on the long-defunct '109 Lair' site this report (partial title page above) details high-speed flight tests with a Bf 109 F fitted with a tall tail following incidents in service of  "..overcompensation of the ailerons and insufficient effect of the elevator at high Mach numbers ". Conclusions right at the bottom;

 ".. diving with power applied at speeds from 800 km/h the aircraft is no longer stable around the vertical axis. At the same time the aircraft made violent 'fishtailing' movements - overlapping movements around the longitudinal axis and around the transverse axis (sliding roll moments, Paddelbewegungen - I'm assuming this is what is referred to a 'Dutch roll' - a combination of rolling and yawing oscillations ). One is tempted to counteract this with the ailerons and it is suspected that many of the incidents reported thus far can be traced back to not applying adequate rudder corrections. It is recommended that  (1) with increased speeds as planned enlarge the tailfin/rudder assembly on series production of the G-version and (2) limit aileron deflection as a safety measure by up to 50% of current values if over-compensation should occur.."

Report posted on the 109Lair here Click on the pages to move through the report.

also on this blog;

Jukka Juutinen review of Calum E.Douglas' "The Secret Horsepower Race" here