I did find some "general" info, but nothing that'd help as far as sims go....
"I read an article about this awhile back, can't recall where ATM... maybe Sport Rocketry magazine?? At any rate, the idea is, that on "air-air missile" type rockets (like the Python and Sidewinder) that use forward fins (or TWO sets of fwd fins on Python) that makes the rocket VERY unstable... the further forward the fins are (closer to the nosecone) the more destabilizing they are for passive stability (typical model rocket) purposes. Rockets like AMRAAM with mid-mount forward fins are MUCH easier to make stable through simply shifting the CG with additional nose ballast and such, because the nose weight is further away from the fwd fins, and because the fwd fins, being further back on the body, don't bring the CP as far forward, meaning the CG doesn't have to be shifted as far forward to compensate. At any rate, the model in question used "pivots", essentially long dowel rods, to which the fins were attached. The forward fins, being essentially right triangles, were slotted for the dowel "axle" to be glued into the fin at about 1/4 to 1/3 of the root chord. Essentially, the further forward you can put the pivot, the better-- because basically all the fin area IN FRONT OF THE AXLE is STILL DESTABILIZING TO THE ROCKET. For fins shaped like a right triangle, with the axle at say the 1/3 root chord line, that puts only a small right triangle shape about 1/3 the size of the fin in front of the pivot point. IN flight, the airflow hitting this part of the fin tries to 'flip it over' the pivot point, but of course the larger area of the fin below the pivot point overpowers this tendency and keeps the fin pointing straight into the airstream. BUT, this area DOES generate forces that can be transmitted to the rocket, essentially moving the CP forward, only by a MUCH smaller amount than if the whole front fin were glued solid to the body tube. In flight, say the rocket experiences something that pushes it off course. The angle of attack to the surrounding airflow would, on a model with solid-glued forward fins, cause the same angle of attack to be presented by the forward fins, which would then generate lift at right angles to that angle of attack, tending to increase it, IE make the rocket go unstable. (This moves the CP forward with increasing angle of attack and makes the problem worse-- something that tends to cause extremely long rockets like super-roc models to go unstable in windy conditions). On the rocket with pivoting forward fins, when the rocket is perturbed from its path to an angle of attack to the airflow, the forward fin is presented the new angle of attack, but immediately pivots directly into the airflow, generating no (very little) lift, and therefore not inducing a destabilizing lift force into the airframe, or moving the CP forward. The fin pivots in relation to the rocket body by the same angle as the angle of attack (for all intents and purposes anyway). The main fins on the rear of the rocket can then create corrective forces to return the rocket to the proper flight path, and when the angle of attack goes away, the forward fins pivot back in line with the rocket body tube.
The main thing the article stressed is that the fins MUST be able to move freely-- if they bind up, the rocket WILL go unstable and crash! IIRC they used a combination of wood doweling for the "axles" and brass tubing glued into the rocket body tube for the axles to pivot within. Also, the fin root edges need some clearance from the body tube (using a small poly washer or other low-friction solution) to ensure the fins don't 'drag' on the body tube and are thus prevented from freely turning the direction the need to go to negate any angles of attack in flight."
) need to determine weather or not it'd be worthwhile to design them with free pivots as far forward on the fins as feasible vs simply fixing them in place. If it turns out the effect is negligible I won't waste a ton of time and effort on it. Thanks in advance..Oh, Btw, I have been searching, searching my arse off and drawing blanks....
