doxilia

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Nice looking T-120 Christian! I take it that is an OS 120 AX? How do they perform together? Your Tipo is shy of 12 lbs if memory serves?

Illusion it is. If you plan to go with a RE YS, then you'll simply have to make a small recess in the FW about 1" wide x 1/2" deep semicircular to pass the header alongside the fuse. Since you'll have a glass fuse, you'll end up with a gap between the FW and the opening you'll make in the fuse to pass the header. You can fill this gap with a big wedge of tristock between the FW and fuse side and then sand the groove into it per your opening in the FW. Once carved and sanded to shape, you glass the notch with 6 oz cloth and blend it with the fuse side. Evidently you'd use the smooth belly pan for this setup.

As for anhedral on the stab, Dick Hanson's discussion refers to the original T720. All Tipo's had different amounts of anhedral per Dick's recommendations. The Illusion did too and Don might have those instructions and can send you a copy with his kit. Basically the Illusion anhedral was reduced to the case of "no pipe under the wing" for the T720 since the pipe was concealed in Dave Brown's models. For a pipe running along the side, the same rule would apply so you'd build the stab and wing stock per Dave Browns instructions (technically it is DB's design not DH's...).

If using a 65 AX built along the lines of your T-120, how much anhedral you put into the stab is a bit your call. You could add more per T720 instructions to compensate for the pipe (and accordingly also add wing dihedral) but you could also leave it stock per Illusion instructions (less stab anhedral and wing dihedral) since the pipe would actually not materially increase the frontal area of the model given the pipe is beside the pan rather than under it.

The real difference between a T720 and an Illusion amounts to four things: 1) less stab anhedral, 2) less wing dihedral, 3) wing and stab chords equidistant from thrust line (hence, the higher wing position) and 4) 30 more squares on the wing (probably a few more on the stab too). The Illusion was really an "exercise" in the various experiments that Dick and Dave were playing with at the time to find the best configuration for the design. The thing is that Dave was a great pilot and since he flew the Illusion competitively, it just made sense to release this particular "Tipo configuration" as well.

Not to dissuade you but they eventually concluded that the bottom wing position of the Tipos with underslung pipe produced a better flying model. I believe that TonyF who also flew these birds competitively at the time agreed on that. You could ask for his input. I believe that he has also recently stated that the same underslung pipe position works better on the P7 (no anhedral stab in that design) than a RE engine configuration with pipe on the fuse side. The aerodynamics just seem better and some of it might have to do with the disturbance of the flow around the fuse with a pipe on the side. Dick argued that the indent on the fuse sides separating the canopy line, if you will, contributed to a greater "effective side area" which improves KE manouvers.

Whew! I've lost track of how many times I've made these comments over the years...

Hope it helps,

David

P.S. My nickel's worth on the ideas: If you are going to build an Illusion, use the 65 AX. Use the YS Classic in a proper RE design such as an Arrow or better yet, the tested but rare and cool design I'm working on! (Still 6 months out I'd say before production).