Shawn
Do you have a drawing of Manta somewhere?
[ Different subject: Member Profiles: Not sure about the rest of you, but I sure would like some place on the PSUB web site where I could go and see a profile for each member, including there current design, previous projects and professional background. It'd be helpful to know when I am reading something from a marine engineer as oppossed to a back yard hobbist like myself, not that I would take the engineers advice any better :) ]
As to roll: I added a tail to my design but only because I plan to use it as a snokel and give me a imporved turns when submerged, but I have not even considered roll. I figure at 2 mph with a ton of weigh just over the keel and all of the displacement over 1 foot above the weight, roll is not going to be an issue. Does that sound right? Seems like a tail is just one more thing to get snagged.
Thanks
Doug J
In a message dated 3/20/2004 4:54:51 PM Central Standard Time, NeophyteSG@aol.com writes:
In a message dated 3/19/04 1:02:21 PM Pacific Standard Time, emuller@naic.edu writes:
The reason for the tail is to provide a useful torque for pitching.
The V shape is to maximise rolling stability while reducing the
resistance to pitch.
The more torque, the more powerful the pitch and the less energy necessary.
This is all hand-wavey stuff of course.
Erik, no handwaving in front of the ADHD kids ... we get nothing done. ;-)
In a message dated 3/19/04 12:41:02 PM Pacific Standard Time, DJACKSON99@aol.com writes:
What is the criteria for deciding if you need a tail?
*Great* question and one I'm still defining with Manta (my design). We have six degrees of freedom possible; three linear and three rotational. For each of those freedoms you want to have control over you have to have a force, whether thruster, buoyancy, or control surface. Short, non-hand-wavey answer: You generally use a tail/control-surface if your primary mode of travel is forward at a fairly good speed.
You'll notice that Alvin, the K-series, and similar subs which tend more toward hovering/loitering operations don't have control surfaces because they use vectored thrust at relatively low speeds -- generally one per degree of freedom.
At higher speeds, control surfaces like tails and fins are used to convert part of the craft's forward thrust to rotational thrust (pitch, roll, yaw), more or less taking the place of one or more thrusters in an Alvin-like sub. The farther the distance of the control surface (e.g., tail) is from the center of the craft's rotation point, the smaller it needs to be. The disadvantage of control surfaces is that you have to be moving for them to work.
Warm Regards
Shawn
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