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Covering Developments by Lutz Schramm

In Uncategorized on August 29, 2013 by nicholasandrewray

Covering Developments by Lutz Schramm

Some time ago, Current F1D World Champion Lutz Schramm kindly sent me some images of his latest covering methods, and seeing pictures of Nick Ray’s elliptical dihedral F1D prompted me to put this series together for INAV. I hope all is self-explanatory as I have not discussed the fine details with Lutz.

Lutz has used elliptical dihedral on F1D models for some years and he originally applied the covering film with a curved frame. More recently, in pursuit of perfect wrinkle free results, he has developed a system using a purpose built vacuum box.

Figure 1. The jig used to build the dry wing structure. The top surface is made from a sheet of thin flexible plywood.

Figure 1. The jig used to build the dry wing structure. The top surface is made from a sheet of thin flexible plywood.

I assume that the curved spars, tips and ribs are built separately beforehand and this jig is used only for final assembly. Ribs and main spars typically have boron top and bottom. Note that the wing above has six ribs while that in the sequence below has seven.

Figure 2. The vacuum box used to cover the completed wing frame is shown below. The completed dry structure is presumably tacked to the balsa carrier, which locates into slots on either side of the jig for exact positioning. The hole in the side of the box is to accept the clear plastic tube seen in figure 4 and the top of the box is covered with soft thin porous fabric.

Figure 2. The vacuum box used to cover the completed wing frame is shown below. The completed dry structure is presumably tacked to the balsa carrier, which locates into slots on either side of the jig for exact positioning. The hole in the side of the box is to accept the clear plastic tube seen in figure 4 and the top of the box is covered with soft thin porous fabric.

Schramm.3

Figure 3. The wing frame is removed and a sheet of well-crinkled film is then brushed out over the top surface of the jig. This film appears to be Y2K.

In the image below, the clear plastic tube can be seen on the far side of the box, leading to whatever provides the suction.

Figure 4. In the image above, the clear plastic tube can be seen on the far side of the box, leading to whatever provides the suction.

Figure 5. The wing frame is then reintroduced on top of the film.

Figure 5. The wing frame is then reintroduced on top of the film.

Figure 6. Presumably, the adhesive to glue the film to the structure has already been applied.

Figure 6. Presumably, the adhesive to glue the film to the structure has already been applied.

Figures 7.

Figure 7.

Figure 8. The two images above show the underlying top surface of the box, carved as an exact match to the compound curvature of the wing. A matrix of small holes allows suction to pull the covering film down and hold it in place.

Figure 8. The two images above show the underlying top surface of the box, carved as an exact match to the compound curvature of the wing. A matrix of small holes allows suction to pull the covering film down and hold it in place.

Figure 9. Excess film is removed in the normal way.

Figure 9. Excess film is removed in the normal way.

Figure 10. Lutz also uses this system to cover tailplanes.

Figure 10. Lutz also uses this system to cover tailplanes.

Nick Aikman. 25.08.2013.