sub diving plain positioning

thanks guys.

On the subject, why did the US switch from sail-mounted planes to bow mounted planes on the Improved LA class SSNs?

Under-ice operations I believe. For reasons best known to the designers the planes on the early models could not pivot through 90°. This made surfacing through (thick) ice impossible. That’s what I read, anyway.

Well, when you figure that the manuvering comes from any set of horizontal planes the best positions for maximum manuverability would be at the extreme front and extreme rear. Putting planes on the sail alleviated pressure on the tower during ice breaching because it gave a sharp edge to aid the dull surfaces otherwise topside. Of course, sail-mounted planes are not the traditional placement but obviously deemed necessary for a given period of time. I’ve heard that passive sonar statement before, as well. That actually seems to be the best given reason for placing them up there, however. It sure doesn’t help the boat much when it’s above water!

Yup, the 688I, Seawolf, and Virginia all have bow mounted planes.

On the subject, why did the US switch from sail-mounted planes to bow mounted planes on the Improved LA class SSNs?

I think he might have been temporising a little with you there Mixtec.

The bow planes, on a Traf for example, are set halfway back to the conning-tower from the bows and are pretty well clear of the sonar array. Certainly the physical seperation between the bows mount and a 688-style tower mount isnt a tremendous one.

Most flow noise over a hull is generated by the bows piercing the water and, whilst it is true that the interaction between the bow wake and the planes generates noise at speed, passive sonar performance degrades at speed anyway. To a highly sensitive sonar planes-turbulence 30ft back from the array is no more disruptive, in practical terms, than a tower mounting 60ft back and 20ft up!.

This link makes some interesting reading about what I was talking about in terms of easier construction and maintenance:

http://www.chinfo.navy.mil/navpalib/cno/n87/usw/issue_22/kentucky.htm

I was told by a US submariner that they are mounted on the sail purely for decreased sound interference with the bow passive array. And he said that having them mounted on the forward part of the hull gave greatly increased leverage for ship control.

cheers jonesy.

The pitch response of hull mounted planes is meant to be a bit quicker and the benefits of hull planes compared to conning-tower mounted ones is very clear for under-ice operations. When surfacing through ice planes on the side of the tower can be quite vulnerable to damage.

The main advantage of tower-mounted planes is in the initial ease of construction and the reduction of one more penetration through the pressure hull.

As to which is the ‘correct’ positioning I’d say that the hull mouting is right, with the retractable planes seen on the Kilos’ etc probably optimal, a belief seemingly supported by the design of the new US Virginia Class boats.

thanks ja, but i still think there should be some reason for a design team to choose one configeration over another, do you know the reason for the emergence of the two designs in the first place?

There’s not reeally that much of a difference, except in the nose performance, if they are on the bow, then the nose will rise slightly quicker, but for the most part, with Subs, it really doesn’t make a difference since ballast is the work horse of diving and submerging.

What is more interesting is the difference between Ballast control on Western Subs and ballast on Russian subs, as they both have different ways of controlling it, the Western way is more complex. Look it up, i have it in a book somewhere about here, should be on the net too!

Not to sure about Chinese types, but since most of their subs have derived from Russian, it stands to reason that they’d use the Russain ballast controls.