▁built ▁by ▁them ▁with ▁the ▁assistance ▁of ▁the ▁Mun ich ▁branch ▁of ▁the ▁Bayern ▁Gl iding ▁Club ▁during ▁the ▁winter ▁of ▁ 1 9 2 0 - 2 1 . ▁They ▁were ▁aware ▁of ▁the ▁high - wing ▁mon op lane ▁gl iders ▁that ▁had ▁been ▁under ▁development ▁by ▁Friedrich ▁Har th , ▁assist ed ▁by ▁the ▁te en age ▁Wil ly ▁Mess ersch mitt , ▁since ▁before ▁ 1 9 1 5 . ▁By ▁about ▁ 1 9 2 0 ▁Har th ▁was ▁convinced ▁that ▁long ▁gl ider ▁fl ights ▁dep ended ▁on ▁energy ▁capture ▁from ▁g ust s ▁( ridge ▁and ▁thermal ▁lift ▁was ▁und isc over ed ) ▁and ▁the ▁Har th - Mess ersch mitt ▁designs ▁were ▁controlled ▁in ▁pitch ▁by ▁a ▁variable ▁angle ▁of ▁inc idence ▁wing ▁and ▁roll ▁by ▁wing ▁war ping . ▁Its ▁pilot ▁had ▁two ▁le vers , ▁one ▁for ▁roll ▁and ▁the ▁other ▁for ▁pitch . ▁The ▁tail plane ▁was ▁fixed . ▁L öß l ▁and ▁Fin ster wal der ▁took ▁these ▁ideas ▁a ▁stage ▁further ▁by ▁making ▁the ▁wings ▁separately ▁rot atable ▁and ▁controlled ▁with ▁a ▁conventional ▁column , ▁which ▁when ▁moved ▁side ways ▁rot ated ▁the ▁wings ▁in ▁opposite ▁directions . ▁ ▁The ▁fixed ▁tail plane ▁was ▁retained ▁but ▁the ▁conventional ▁fin ▁and ▁rud der ▁of ▁the ▁Har th - Mess ersch mitt ▁was ▁entirely ▁removed ; ▁instead , ▁y aw ▁was ▁controlled ▁by ▁the ▁opening ▁above ▁and ▁below ▁the ▁wing ▁of ▁little ▁wing ▁tip ▁trailing ▁edge ▁double ▁split ▁f lap ▁air