The next comparison was from the work of Raspet showing some performance figures for gliding of a Horten IV and a black buzzard. He moved on to the Reimar Horten s Piernifero, one of his most picturesque flying wings, which Phil was able to locate in Argentina in 1984 during one of his visits. He actually dressed himself with the aircraft and found that it was very heavy. However, as you began running with it at low angles of attack all of a sudden the weight seemed to disappear. This presented the question of why Horten wings are so interesting while at the same time giving us an opportunity to study them in order to try and find something related to birds.
Horten wings have sweep and a tremendous amount of washout or twist.
This can reach nearly 15 degrees when you add together the aerodynamic and geometric twist values, but results in good stability and no stalling at the tips. Horten commented that he had shown he could get thrust from the tips at very high lift coefficients, however, Phil noted he has never seen anything in writing on this. The next slide was a rough drawing of a wing panel with the lift and thrust vectors shown. The root section shows the velocity vector coming in from the front and the lift vector perpendicular to it, but due to circulation you get an induced velocity at the AC towards the tip. At the tip it becomes a very powerful upwash depending on how much the lift is, and this upwash tilts the lift vector forward yielding thrust.