The positioning of dive planes on the sail itself doesn't actually have to do with snap roll. Any plane scheme which can impart a counter torque around the hull axis will accomplish that objective. Positioning the planes on the sail, instead of on the hull axis, has advantages when it comes to fine depth control at periscope depth, as depth can be controlled with a single set of planes acting over what is essentially the center of mass and center of buoyancy of the vessel. A tertiary benefit is that these planes are clear of the hull when coming to alongside, and may not need to be retractable.
Stern fins are necessary to add stability to an axisymmetric hull form traversing the water at speed. At low speed, bow and stern planes are necessary to control vessel pitch, with the bow planes predominately controlling depth, and the stern planes predominately controlling pitch angle. As vessel speed increases, the stern planes become dominant in dynamic control, and the bow planes essentially become superfluous, adding unnecessary drag.
A low velocity vessel, such as most PSubs, will not benefit greatly from dynamic control surfaces (other than for yaw / azimuth control), because both the vessel's transverse stability and fore and aft stability are large in comparison to the vessel's inertia and resistance to water flow. The instability of the axisymmetric hull form at speed does not present itself in a small submersible because the combination of form drag and inherent stability moments are sufficient to stabilize the vessel at the speeds typically encountered by such a vessel. At typical operating speeds, the control surfaces would need to be quite large (and hence, introduce significant drag) in order to counter the natural stability moments enough to be useful.
-Sean
On Sep 13, 2009, ShellyDalg@aol.com wrote:
In a message dated 9/12/2009 9:30:30 P.M. Pacific Daylight Time, hc.fulton@gmail.com writes:I have uploaded a few photos of the internals and bits on the projects page under “Hugh Fulton” Comsub.Hi Hugh. I like the new pictures. That's a beautiful sub. Good luck on the re-fit.As for dive planes, I've always thought that unlike a surface boat, a submarine should have a kinda "fish" shape. The big Nuke subs are something like a whale and it's the most efficient shape.If you look at most fish they have little fins about midway down their bodies and they rotate the leading edges of those little fins much like we do with the dive planes on our boats. The big subs have them on the sail like you said to counteract the snap roll thing.Some subs have dive planes in the back to act I assume like the tail on a whale. I know that's not very scientific but it's an observation.Frank D.Frank D.