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Wide aft fuselage and vertical tail interference


Well-Known Member
Supporting Member
Aug 10, 2014
Recently, our member @Bill-Higdon posted a video about some lesser known transport planes:

Five Weird Cargo Planes You've Never Heard of

I thought that a separate thread would interfere less with the original one. We can see that at least two models (Evangel 4500 and Ahren AR-404) had a wide slab-sided aft fuselage (especialy the AR-404) that, at a first glance, could disrupt the airflow around the vertical tail at high AOA, in a stall or spin. One other example would be the Casa 212 and going further we could notice a somewhat similar situation with the F-16 and A-5. Although these two don't have a boxy fuselage, there's a single vertical tail in the middle of a wide aft fuselage, to put it simply.

I tried the NACA reports server but the keywords 'fuselage' 'interference' and vertical tail' did not seem to return anything useful. Chris Heintz wrote in his book that a slab-sided aft fuselage helps with spin recovery, but nothing more.

Are there any guidelines on how to incorporate a wide slab-sided fuselage without interfering with the vertical tail? Or a fuselage width to tail thickness ratio somewhere? But apparently, the Evangel, Ahren AR-404 and Casa 212 all flew well enough. Meanwhile the Short Skyvan (and 330), with its boxy fuselage had its vertical tails away from the fuselage, probably to get them out in clean, undisturbed air. So where is the decision made between an H-tail and a classic configuration with a wide/boxy aft fuselage? Also, notice that the Evangel, Ahren and Casa all have a dorsal fin.