Note: The drawing shown above is dimensioned in 20:1 scale but actual size when printed is roughly 40:1.

The plan shown is one of several structural configurations of the general planform. As dimensioned, it is a 1:20 scale of a 31 3/4 foot span man carrying aircraft that is intended to be converted to flapping after it is test flown. You may notice that the plan is similar to Jim Thesis' NightHawk. This is true but it is not a copy of the NightHawk. Copying the same prototypes from nature independently developed this configuration.

The full size is intended to have a variable sweep angle to control pitch trim and CG position. The position of the wings shown is the most forward sweep limit. Notice the lighter line perpendicular to the centerline at the junction of the leading edge and the wing root. This line also intersects the wing leading edge again 3" outboard from the wrist in the wing position shown. The wing would be cut from the fuselage and swept so that this perpendicular line intersects the leading edge 1 1/2 inch outboard of the wrist joint in the normal slow flight position. You may wish to redraw the planform in this configuration. This "normal position" is the baseline that I generally test from and would be the recommended configuration for starting the following experiments.

For a first experiment you may want to cut a 1:40 scale or 1/2 the size dimensioned (about the same size as this will print on 8.5 x 11 paper) from a piece of 8.5 X 11" heavy paper. Add a paperclip for a nose weight after folding gently at the centerline and along the rib line at the wrist joint to give it a little dihedral and a gull wing effect. It Should not need any reflex at the tail and should be pitch stable without it. However, if necessary give the proper elevator trim effect after the CG placement has been corrected.

It is not intended to be necessary to change the sweep of the first prototype. However the provision is incorporated into the design so that when flapping is added the ability to flex in sweep is available to absorb the varying thrust load while smoothing out the jerkiness that might otherwise occur. The tubular structure and flexible trailing edge is intended to simplify construction and allow for an aeroelastic twist that will be evident when we double the size of the shown drawing to a 3' span, 1:10 scale, model for the follow on experiments.

Separate project:

Flapping Escapement I have designed a three crank flapping escapement mechanism that is ready for the construction development stage. I will share the design with anybody willing to build models and refine the design into a working unit. A brief description follows. The device is intended to be used for rubber powered ornithopters. It is an improvement on the traditional crank arrangements in the following areas. 1. It powers one side of the stroke only. The other half of the stroke is to be self-powered through gravity or other methods. 2. There are three cycles per revolution. 3. The load on the rubber is relatively constant as there is no dead area at TDC and BDC where the rubber is untwisting and the wings are unable to absorb the work input. The primary design features are the method of capturing and releasing the crank at the proper times in the cycle and restraining the crank from rotation while the unpowered portion of the cycle is in progress.

Any help with further development of either of these projects would be appreciated.

Grant Smith emailaoa@juno.com