George,

I think Steve is talking about changing the moments of the plane. Moving the wing forward increases the tail moment thereby eliminating the need to place weight in the tail with a 4 stroke. This facilitates the installation of the gear where it usually goes. Steve, correct me if I'm wrong.

Blake,

the topic of stab anhedral (referred to as cathedral by Hanson) and its relation to wing dihedral was extensively tested by Hanson and Brown during that time. As George points out above, the wing cannot be flat topped as many pattern wings were (e.g., Deception) if the stab has anhedral - the model will just not fly well. Such interactions eventually materialized in the form of the Tipo's evolution into what became known as Dave Brown's design - the Illusion. The Illusion revised the anhedral to decrease it along with corresponding wing dihedral reduction and tucked the pipe into the belly of the fuse by raising the wing closer to the thrust line. This was no doubt an exploration of the statements made by Hanson in his article.

The introduction of stab anhedral into a design is to effectively lower its draft in the fuse and result in equal and opposite lift vectors on it when the rudder is deflected. Differential lift occurs because the usual negative lift produced by the stab is altered the moment the rudder is deflected. If one deflects left rudder, the negative lift on the left side of the stab is decreased and might even become positive lift. This causes the nose to pitch down or to the belly of the plane. Getting the anhedral angle right results in stab lift vectors that prevent pitching tendencies. However, there is one more problem. Since vectors are now equal and opposite on the stab with deflected rudder, the model is subject to adverse roll. When yawed it might be pitch neutral but not roll neutral and in level flight the model will seem unstable. In knife edge flight the model will tend to roll out to level flight. This can be taken care of by increasing the wing dihedral resulting in 3 axis neutral flight... or so one hopes!

These ideas are echoed by George in his simulator tests and evidently Steve has found that decreasing the wing dihedral while retaining the same stab anhedral does not work out too well. Tony Frackowiak recently had some comments to the effect of how Phoenix 7's flew with either side mounted exposed pipe engines vs vertically mounted engine and concealed pipe installations. Here is the thread in question:

http://www.rcgroups.com/forums/showthread.php?t=1509844

Jim Kimbro makes some related comments in his Deception article. As you likely know, the Deception is a design with a flat top wing and a symmetric, 0 degree incidence, 0 anhedral stab. It also has a rudder which is cut short of the bottom of the vertical. The rudder's deflection occurs entirely above the stab thereby eliminating the "blanketing" effect of the rudder on the stab as with the Curare/Tiporare design. Jim is emphatic about two things: 1) Don't build the Deception with stab anhedral and 2) Don't build it with a full length rudder. Both factors were explored and experimented with by him and he found out that the model flew best with the tail setup as recommended. An interesting aspect of the Deception design is also that the wing and stab are both set with chord lines equidistant from the thrust line. That was the main principle Jim wanted to follow in designing that model.

In short, if you build a Curare, I'd stick to what Hanno designed and what George also suggests. Then, set it up for SPA but stick a pipe on it for practice and see if the addition of the pipe vs a muffler has any effect on coupling tendencies of the model. It is possible that if a muffler is used instead of a pipe, that reducing stab anhedral and wing dihedral will result in an equally neutral aircraft. But as George says, it's a matter of how much... only experimentation can tell as well as the experience of people like Dick and Dave themselves. You might want to drop Dick a PM and see what he has to say.

David.