Flapper (oz4346)


Flapper (oz4346) by Art Horak 1945 - plan thumbnail

About this Plan

The Flapper. Ornithopter. National record holder.

Quote: "Junior and Senior Record Holder Ornithopter. The Flapper, by Robert Horak.

AFTER designing and building several ornithopters following the general indoor trend of design, I reached the conclusion that indoor types were not adaptable for outdoor flying. I then set about trying to develop an ornithopter which would turn in successful outdoor flights. After trying various ideas and different aero-dynamic setups I finally arrived at the following conclusions:

1. It must have a large stationary sur-face with a high lift airfoil set at a high angle of incidence.
2. It must be extremely light but strong in the right places.
3. It must be streamlined in order to permit fast flights. Speed is essential since lift increases with the square of the velocity. In other words, a model producing 5 oz of lift at 5 mph will produce 25 oz of lift at only 10 mph.
4. It must have sufficient flap area to obtain the very necessary forward speed.

I designed the model presented here with these ideas in mind. The model presently holds both Junior and Senior National Records.

Read the article carefully, studying plans until all details of construction are clear. Lightness should be paramount throughout the entire model. Select materials indicated. Original model only weighed 1-1/2 oz.

Fuselage. Select four pieces of 3/32 sq medium hard balsa for the longerons. Pin longerons in position placing pins on either side of the wood and not through it as this weakens the structure. Next select a length of soft 3/32 sq stock. This is to be used for the crossbraces and uprights. Finish one side of the body and let it dry thoroughly; then place a piece of wax paper over it and build the second side directly over the first..."

Direct submission to Outerzone.

Update 28/02/2017: Added article pages, thanks to George.

Supplementary file notes



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Flapper (oz4346) by Art Horak 1945 - model pic

  • (oz4346)
    by Art Horak
    from Model Airplane News
    July 1945 
    38in span
    Rubber F/F
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 07/05/2013
    Filesize: 251KB
    Format: • PDFbitmap
    Credit*: ErikJohnson
    Downloads: 2242

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User comments

Having built Dr. Lippisch's 48 inch version, which probably preceded Horak's version by 10 or 20 years (unlikely he was a Dr. yet), I'm naturally interested in the Flapper. I can plod my way thru it, but a text would be really helpful if there were any available.
ArtHoltzman - 13/08/2013
This plan (and article) is in the July 1945 Model Airplane News.
George - 28/02/2017
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