"Curiouser and curiouser" said Alice.

Have you talked with the manufacturer?

I would seal the le's on the fins for starters.

With the elevons on the way they are, is the te of the elevon at or inside the te of the fins? Is this the way that the elevons are fitted on the plans? Are the fins fitted according to the plans?

The reasoning here is that it looks like there is little difference between Viper and the Canterbury Jazz that I was trying to fly. On the Jazz a big part of the stability is the fact that the fins act as tip plates over the end of the elevons. The elevons on mine (one of the early ones) were parallel, but I believe that the Jazz Extreme now has the reverse taper elevons.

I am past the end of my meagre knowledge with this - was the kit made on a Monday? No, only joking.

As a matter of interest, how does the airfoil on the Viper look? The Jazz had a long flat on the underside rather than a smooth curve. Looking at the profiles it seems that this is consistent with many of these wings. I must go take a look at a Viper at the LHS...