rand robinson
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KR2S

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The KR2S Project

Flaps


The flaps on this KR2S are going to be a split flap arrangement.  For those who do not know, a split flap is one where the trailing edge on the underside of the wing hinges down as a flap.  The most beneficial split flap size is 20-25% of the chord and operated at angles up to 60-70o.  Invented in 1920 by Orville Wright and J. M. H. Jacobs and patented soon after, it is very simple by design and simple to build.  
A bonus for the KR2S is the split flap increases drag for reduces the landing speed and thus the landing roll as well as lowering the nose of the aircraft for a better view on approach.  However, it adds close to zero additional lift in a typical take off configuration which is not an issue in the KR2S as its take off roll is relatively short anyway.


flap kr1 The initial part of the flap build can be seen on the stub wing page .  A piano hinge with removable pin  attaches it to the rear spar.
The flap will be operated via a linear actuator behind the seat which will rotate a torque tube.  This tube will exit the fuselage just aft of the rear spar and pivot the flap down via an arm attached to rod end bearings and in turn, the flap.  It will be a similar set up to that of Jeff Scott's.   
loctite Here I have joined 2 HF-2A rod end bearings with a piece of 5/32" thread and some Loctite.  These bearings are smaller than the MW-3 ones used on the elevator and rudder and were in the AS&S bargain bin for under a buck each.  I bought 10 knowing they would come in handy one day......sure enough!
lever point The edge of the flap has a 1/4" layer of flox beneath the full length and a 1 1/2" deep pocket of flox where the bolt hole has been drilled and the double ended bearing screwed in.
piano hinge I use the grinder to scuff up the piano hinge.  It gives the flox better "bite".
torque tube The good old nylon breadboard makes a fantastic bearing surface for the flap torque tube.  The fuselage has a 3/4" drilled through and the round cut nylon bearing has a 5/8" hole.