170 S. Schuster and H. Schwanecke 
Fig. 24. Arrangement for rotary instability tests 
of a dihedral foil 
To sum up: 
1. Rolling into the inside of the curve for hydrofoil boats as well as for planing craft 
and airplanes such that the principal plane coincides with the apparent perpendicular is 
more disadvantageous relative to security than is rolling into the outside of the curve as 
occurs with displacement craft. 
2. Hydrofoils already rolling to the outside at the beginning of the curve will run a 
tighter circle (with higher sideslip angles) than those rolling to the inside. 
3. The preceding result contradicts the conception that in a circle a foil rolling to the 
outside will stall easier because of the higher load. Therefore the whole situation needs a 
thorough investigation. 
