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Picture 1 shows the pieces, but it does not show a complete thing. When I assembled it I found that the push rod getting in the opening between the side plates might jam if something flexed under load and the face of the rod got against the edge of the side flap. Maybe I am paranoid but I felt better adding a backwards extensions of the side flaps with gradually increased distance between the walls, call it a funnel, which guided the push rod smoothly into the gap between the side plates. Now even if something flexed it is impossible to jam it. Unfortunately I did not make a picture of the thing with the "funnel". |
Next two pictures show the dog leg arm attached to the transversal tube. Please note that I increased the number of bolts to five, and to accomodate the bolts I machined the arm with a cylindrical extension around the tube. The hole at 90degrees away from the line of five holes is a set screw. It does not do anything good after you finished with everything, but it is invaluable when you are drilling the first hole in the tube using one of the holes as a guide - it assures that everything would stay where it was set. |
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For the flaps "in" the horn of the hand actuated lever, connected to
the push rod, is roughly at right angle to the push rod resulting in the
longest effective lentgh of the horn, while the dog leg lever is all the
way forward over the back spar resulting in a small effective length of this
lever, roughly equal to the length of the arm from the center of the tube
to the corner. In this position the angular transmission rate is the same
as in the old design, but with the arm twice as long as original the force
is reduced roughly by a factor of 2.
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When the flaps are totally "out" which corresponds to approximately 45 deg, the horn of the hand actuated lever's is at ~20 degrees to the horizon reducing effective length of that horn, while the dog leg arm is moved up and it utilizes the whole distance between the pivot points as the effective arm. This way the force on the handle is reduced by an additionl factor of ~2.5 in addition to the former factor of 2, That should result in a factor of ~5 decrease of force on the handle, or increase of force transferred to the flaps, for the full deflection of flaps. Of course nothing comes for free, and the flaps move out slower vs motion of the handle as you reach large deflection angle. |
| The other set of pictures shows position of the hand lever for the flaps "in" and the first, second and third steps "out". I checked if it is ergonomic moving it while sitting there. It seems to be ok. in all positions. | |
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| I installed more bolts to attach the arms to the tube for these
reasons:
(1) If one uses two bolts in the side arms and only two bolts in the central arm, it is obvious that the central arm transferring all torque from both side arms is the weakest point of the construction. Why not to make equal stress in all joints? (2) The infamous British analysis has shown that the strength of the joints, especially for the central arm is marginal (for their assumed maximum load) (3) I wanted more flap deflection and it was obvious that that would increase forces. The additional long bolt attaching the side arm is shown on the picture. It goes at right angle to the original bolts and between them, going into a tight thread in the arm. I will use a locking wire to immobilize the bolt in place. It is likely that I will not need full 45 degrees but I will have an easy way to limit it. Trying to increase it in the old construction is not easy. |
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