| Re: Face to face with a 747
[Re: Boomer]
#53141 07/15/05 01:22 PM 07/15/05 01:22 PM |
Joined: Apr 2005 Posts: 473 Panama City, Florida Redtwin
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Posts: 473 Panama City, Florida | I do a lot of sailing in the east bay area of Panama City. We get some pretty low flying F-15 and various other Air Force aircraft. Thankfully, they are not low enough the hit us with their jet-wash. I think we would be a grease spot on the water if one of those hit us. Rob V.
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Panama City | | | Re: Face to face with a 747
[Re: Mary]
#53145 07/15/05 08:13 PM 07/15/05 08:13 PM |
Joined: Apr 2005 Posts: 473 Panama City, Florida Redtwin
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Posts: 473 Panama City, Florida | Yeah, it's noisy alright. We usually sail down the bay a little to get away from them. When they are taking off with full afterburner, you can't even hear yourself think. However, it is pretty impressive. Sounds like... freedom. Rob V.
Nacra 5.2
Panama City | | | Re: Face to face with a 747
[Re: Tornado_ALIVE]
#53149 07/17/05 04:11 AM 07/17/05 04:11 AM |
Joined: Nov 2002 Posts: 5,558 Key Largo, FL & Put-in-Bay, OH... Mary
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Posts: 5,558 Key Largo, FL & Put-in-Bay, OH... | If you have a window seat on a jet next to the trailing edge of a wing, in certain atmospheric conditions you can see the vortices spinning down like ghostly whirling dervishes. Heaven help me for asking this question of a bunch of engineers, but does this happen on a smaller scale off the trailing edge of a sail? Here is an excerpt from an e-mail from a friend of mine, partially on this subject: In the late 60s the A-cats and C's at Cabrillo Beach YC, Long Beach, CA, used "end plate" booms. Some used a wishbone down low with Dacron filling it in. Others used a normal, for the day, boom with Ocumme ply wings. We made sure that it was very slightly HIGHER at the clew. This was.....to compress the air and make the air lift. If the Park Avenue Boom thing angled down, we felt it would blanket part of the bottom of the sail.
The old Suicide class (ask Bill Roberts) was anything-goes in monohull, but with only 125 square feet of actual sail area, including mast. It became very efficient, using an A-cat style mast and wishbone main, 1950's and 60's materials, of course.
Tried was an end plate on the top of the mast.....for reducing tip vortex, although it was angled up on the front for the same reason the boom was angled down on the tack. The class ruled that they had to count the tip deflector as sail area, so it was quickly abandoned.(Most booms on dinghies are faster with the boom lower at the clew, It makes for leading edge foot, instead of trailing with its tip vortex and loss of pressure under the boom.) | | | Re: Face to face with a 747
[Re: Mary]
#53150 07/17/05 09:17 AM 07/17/05 09:17 AM |
Joined: Jan 2005 Posts: 6,049 Sebring, Florida. Timbo
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Posts: 6,049 Sebring, Florida. | To answer your question Mary, yes, on a much smaller scale it does happen off the back and tip of a mast/sail. The reason you can actually see the vortex when seated by a window in an aircraft is the much greater difference in pressure from the bottom to the top of the wing, which causes a lowering of temperature in the vortex to the dew point, forming fog, as the compressed air on the underside of the wing expands and cools going over the top. If the air is humid (like in Florida, all the time) you can see the vortex as fog. (if you sit near the front of the engine you can also see fog inside the engine cowling as take off power is applied, due to the reduced pressure inside the intake during engine acceleration) You can also see this as two streaming trails of fog off the wingtips if you sit at the approach end of any runway where big jets land in humid air.
The vortex's are much bigger when the wing is at a high angle of attack and "dirty" (flaps down, for take off or landing) as the wing is creating the most lift then. You don't see them at cruise as the wing is "clean" flaps up, fast and low angle of attack in dryer upper air. The vortex is still there but you can't see it in the dry air.
I have often thought of putting an end plate up there at the top of the sail but as the boat heals over, I think the end plate might become more drag than lift. If you were to capsize, it might also be more of a hindrance to righting. If you could keep the boat sailing with the mast straight up all the time, in theory, it would help reduce the tip vortex drag...in theory.
It is nearly impossible to measure how much it would help a sail boat, as the boat bobbs up and down over waves, which negatively effects the flow, in addition to the healing.
I think development of a soft-hard wing sail could yeild results. By this I mean a mylar/dacron wing sail with removeable battens/ribs, that looks like a hard wing, ala C cats, but then could be collapsed like an accordian back on the beach, for storage. The mast would be enclosed by the wing which would be raised around the mast, using the mast for support as a normal airplane wing uses the spar to support the ribs.
This wing sail plus boards/foils that lift the hulls clear, and the T foil rudders I think would make the next big advance in sailboat speed. We still have to figure out how to make the hulls get over the waves that come with big wind though...the Moth sailing up in the air looks cool, but can it be done consistantly in rough seas?
Last edited by Timbo; 07/17/05 09:40 AM.
Blade F16 #777
| | | Re: Face to face with a 747
[Re: Timbo]
#53151 07/18/05 06:56 AM 07/18/05 06:56 AM |
Joined: Mar 2002 Posts: 3,355 Key Largo, FL and Put-in-Bay, ... RickWhite
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Posts: 3,355 Key Largo, FL and Put-in-Bay, ... | I have often thought of putting an end plate up there at the top of the sail but as the boat heals over, I think the end plate might become more drag than lift. If you were to capsize, it might also be more of a hindrance to righting. Wow, that must be what makes the Hobie Wave so darned fast -- that Hobie Bob does wonders. And when capsized it makes the boat easier to right. So proud of my High-Tech Wave.., hmm! sailing in the Wave HT Class. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" /> Rick | | |
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