Tuesday, July 29, 2014

Herr Champ Update

There was an inquiry recently about how my Herr Engineering Champ was flying and if there were any pictures of it in flight. So far for me this plane has not flown very successful and in my opinion the airplane is just too heavy for the wing area. I had tried some test flights with 3/32” rubber and the plane would not climb at all, switching to 1/8” rubber the airplane would climb slowly but appeared to me always on the edge of a stall. Downthrust and nose weight were added which did help some, washout in the wings was recommended but that did not help much either. It was suggested that the airplane needed more power so I tried 3/6” wide rubber and now the plane was climbing easily but the number of turns in the rubber that could be used was reduced. If the airplane was not launched just right it would hit the ground harder and finally one wing half broke off.

Herr Engineering Champ

At this point I took my Guillow’s Super Cub out again to fly for a comparison; it flew much better like it always has. The climb is smooth with no hint of a stall, sometimes there is a slight wobble in the flight path. Extra dihedral was used on this airplane, maybe too much. After building a not very successful Guillow’s Cessna 180 I concentrated on building the Super Cub lighter, especially in the tail. No noseweight was needed for the Super Cub, total weight with rubber was 25 grams. With noseweight and heavier rubber in the Champ total weight was almost 22 grams.

Champ Wing Half on Top of Super Cub Wing

Some approximate math calculations were done to compare the wing loadings between the Champ and Super Cub. Wingspan of the Super Cub is 20” with a chord of 3” while Champ has 18” span with 2 ½” chord. Both planes have rounded wingtips but I used the area of rectangular wings and the calculated the wing loadings which showed that the Champ had a 16% greater wing loading. 

Super Cub Chased by a Gull

Someone with success with the Herr Champ had built to 14 grams total weight, at that weight I would expect the Champ to fly well. The design of the kit looks good like it should be light but the strips of wood felt heavy to me as I was building, I should have substituted some lighter wood. 

Bill Kuhl

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