hcobb@cs.utexas.edu (Henry J. Cobb) (11/20/89)
From: ut-emx!walt.cc.utexas.edu!hcobb@cs.utexas.edu (Henry J. Cobb) On this subject, does anyone got any leads on hydrofoil carriers that would use the speed of the ship rather than a catapult to launch and recover the aircraft? Henry J. Cobb hcobb@walt.cc.utexas.edu
budden@manta.nosc.mil (Rex A. Buddenberg) (11/21/89)
From: budden@manta.nosc.mil (Rex A. Buddenberg)
Henry,
I haven't heard of anyone proposing a hydrofoil as hull form, but
there has been a continuing discussion of non-conventional hull
forms for large ships, especially carriers, in the Naval Institute
Proceedings for several years.
The most ballyhooed hull form was SWATH and the naval engineers
finally weighed in with some substantive answers and some homework
to back it up. Both SWATH and hydrofoil use hull forms that rely
on means other than displacement shift to handle displacement changes.
To explain. In a conventional hull, as weight is added and
subtracted, the hull immersion changes -- automatically. And
conventional hull forms are such that fairly substantial displacement
changes result in fairly minor draft and handling characteristic
changes. And with the exception of submarines, there is no dynamic
compensation mechanisms required on any major class of warship today.
Non-conventional hulls such as hydrofoils, SWATH,...and submarines,
must use dynamic compensation systems -- as in parts that can break.
SWATH (and submarine forms) require dynamic displacement compensation --
that is, as weight changes, the hull form can't rely on displacement
shifts to compensate. When the weight changes are sudden -- as in
aircraft launch/land, this presents a major problem which has ruled
out SWATH use for aircraft-capable ships anytime in the near future.
Hydrofoils have similar problems. Foilborne operation is
a high-dynamic operation anyway, so if you could scale to the appropriate
size, the problems presented by aircraft could probably be managed.
But that theoretical speculation is overwhelmed by the difficulties
in getting that big. The Pegasus class foils have an underwater
(foilborne) form somewhat larger than the hull -- call it wingspan
if you must. And a significantly larger maintenance bill comes
along with that wingspan. Somehow scaling what works for a 200 ton
vessel up to an 80,000 ton one seems to me to present some major
problems in strength of materials and stress control.
Worse, I'm not sure what payoff there would be. CVs can
crank out 30+ knots when working aircraft. Hydrofoils advertise
55+ knots. What good is a 25 knot increase when dealing with
aircraft that operate at 300+ knots?
Rexraymond@io.ame.arizona.edu (Raymond Man) (11/22/89)
From: raymond@io.ame.arizona.edu (Raymond Man) In <11596@cbnews.ATT.COM>Rex A. Buddenberg asked > CVs can >crank out 30+ knots when working aircraft. Hydrofoils advertise >55+ knots. What good is a 25 knot increase when dealing with >aircraft that operate at 300+ knots? It is as good as having a catapult, since approximately (V - U)^2 = 2 a s V = Launch Speed U = Wind over deck a = acceleration s = take off run and if the take off speed is 90 knots, then (90 - 30)^2 =:= 3 * (90 - 55)^2 So for the same take off run the effect is like having a 3g catapult. It is actually better because the relative landing speed will also be lower and hence the sink rate, the deck structure, risks etc. The crust of all this is both take off run and dynamic pressure on the wings are proportional to the square of relative velocity. Just call me `Man'. Uh-oh. I don't know. raymond@jupiter.ame.arizona.edu
steve@uunet.UU.NET (Steve Nuchia) (11/24/89)
From: nuchat!steve@uunet.UU.NET (Steve Nuchia) In <11596@cbnews.ATT.COM> budden@manta.nosc.mil (Rex A. Buddenberg) asks: > Worse, I'm not sure what payoff there would be. CVs can >crank out 30+ knots when working aircraft. Hydrofoils advertise >55+ knots. What good is a 25 knot increase when dealing with >aircraft that operate at 300+ knots? There is a lot of payoff. While the aircraft can go fast, they land at more moderate speeds, like 70-120 knots (guessing). Thus the difference in relative speed in the approach is much greater than you've indicated. More available speed also allows more freedom in setting the course of the ship during air ops, for given wind. And, of course, knocking 40% off the time to reach a trouble spot from wherever you happen to start would be nice. Overall, I think if it could be done reasonably they'd do it. -- Steve Nuchia South Coast Computing Services (713) 964-2462 "Man is still the best computer that we can put aboard a spacecraft -- and the only one that can be mass produced with unskilled labor." - Wernher von Braun
terryr@ogccse.ogc.edu (Terry Rooker) (11/25/89)
From: terryr@ogccse.ogc.edu (Terry Rooker) The discussion about hydrofoil carriers has been interesting, but their are some physical limitations to hydrofoils that limit their usefulness. This from memory, but given enough time I could probably dig up the specific reference. According to a text on ship design the power requirements for a hydrofoil are exponential which effectively limits the displacement to a destroyer sized vessel. since it was an older text I belive destroyer sized was on the order of 2-4000 tons. Considering the power requirements it seems that most of the hull volume would be dedicated to power plant and fuel. Even if excess volume was available, you can't operate many aircraft off of a 4000 ton hull. Terry Rooker terryr@cse.ogc.edu