Vertical / rudder area on our stunters: Does it even matter? On one hand there's the Skyray 35 with what seems (to me at least) to have a large surface area for the vertical surface in proportion to the fuselage. Then on the other hand there's the Genesis, with what seems to have almost no vertical area. (OK, OK, I know it has some area; it's just not tall).

My real question: Say I'm building a model such as the Skyray. Could I cut-down the size of the vertical without adverse effect? I see some repaired models (presumably landed inverted) where the owner just cuts-off the damage to the vertical and presses on. So what's the real deal? 

Vertical / rudder area on our stunters: Does it even matter? On one hand there's the Skyray 35 with what seems (to me at least) to have a large surface area for the vertical surface in proportion to the fuselage. Then on the other hand there's the Genesis, with what seems to have almost no vertical area. (OK, OK, I know it has some area; it's just not tall).

My real question: Say I'm building a model such as the Skyray. Could I cut-down the size of the vertical without adverse effect? I see some repaired models (presumably landed inverted) where the owner just cuts-off the damage to the vertical and presses on. So what's the real deal? 

  You are perhaps missing the fact that the rest of the fuselage is pretty small. A Genesis, scaled down to Skyray size, is probably just about as stable. That's because even though there is no explicit fin/rudder, the nose is pretty small, and the area behind the CG is substantial due to the deep fuselage, and dorsal fin. The Skyray has a huge canopy, a very small fuselage, and a pretty good-sized fin.

     It probably won't hurt anything to reduce it a bit, but I would mostly leave it alone, or reshape it to make it look better.

    What you can't tolerate is much if any rudder offset, DO NOT use the offset shown on the plans.

     Brett

We were impressed as kids when our Ringmasters flew better after the vertical tails broke off.

 Same thing with Noblers. Of course, removing the fin also removed the offset and airfoil, which is almost certainly an improvement in most conditions.

    Brett

  You are perhaps missing the fact that the rest of the fuselage is pretty small. A Genesis, scaled down to Skyray size, is probably just about as stable. That's because even though there is no explicit fin/rudder, the nose is pretty small, and the area behind the CG is substantial due to the deep fuselage, and dorsal fin.

When I built a Fancherized Twister with a Genesis profile (called "Sister Jenny", which is what "Twister Genesis" turns into with the addition of enough beer). I actually ran the numbers (to the best of my ability) on the strength of that big flat fuselage as a vertical stab -- my calculations showed me that the yaw stability of a Genesis is roughly comparable to the yaw stability of the Fancherized Twister that I otherwise followed.

Since then, I had the occasion to make my own-design stunter with a too-small tail -- the effect is obvious and noticeable.  So -- yes, experimental results bears out the notion that the Genesis has yaw stability from that fuselage profile.

So -- no, I don't think you could build a Skyray and go to town on the tail without ill affect.  You may be able to cut the fin down somewhat, but I suspect that at some point you'd start suffering from underdamped yaw response, and you wouldn't like that.