It’s all about loads

I’ve been thinking about the layout of the spar in the center section and needed, thus, to consider the flight loads, again. About two years ago I started with an initial design of the spars, but for some reason I stopped and left the data and software in a lost and forgotten directory on my computer. Now it’s time get that programs up and running and look on the data again.

I started by sorting out the 24 cases that have to be considered to fulfill LTF-L (sorry for the German):


A short translation of the table header: Number, V-n-Point, Speed, C.G. nose(k)/ tail heavy(s), Load factor, Elevon deflection left/right, Wind gust. Here’s a V-n diagram to fill that up with some graphical information:


A Horten is quiet different to a normal tailed airplane, and herewith I mean not only the appearance. The lift distribution is obviously another, as stabilty about the pitch and yaw axes is obtained by reducing lift at the tips (bell distribution). Moreover, in a tailed airplane the main wing can be considered to be fixed unless ailerons are deployed. In a Horten, any elevator deployment results in a change of lift distribution, and thus inevitably, in a change of loads.This has as a consequence that the maximum lift coefficient CL depends much stronger on the speed (trim position) and that in the above V-n diagram the curve between VS1 and VA is not simply a parabola. And not forget the wings have sweepback and taper…

This all makes life harder when it comes to calculating aerodynamic loads. Anyway, this is why we have computers. I fed it with the cases and let it calculate lift, drag, side-force, pitching- and all other moments. Here are the most interesing distributions, lift and pitching-moment (for the 24 cases listed above):

load torsion

The pitching moment uses the C.G. as a reference and needs to be transformed to the shear center to get the shear stresses in the shear-web and D-tube. This center depends on the spar layout, needed also to calculate the axial loads in the spar caps. I have the software ready, but I have to re-check the layout before…