sail aerodynamics

Just for general info - one of the most important functions of airplane flaps is to allow a steeper (up to 10°-12° more than a clean wing) and slower approach path during landing. That is made possible because of the combined effect of high lift and much lower L/D ratio of the wing with fully extended flaps.
Cheers

 

On my aft-mast design I was able to put a mizzen sail on one of my primary backstays (the one that goes down to the base upon which the mast is stepped). That was better in my opinion that having that mizzen sail blanketed by a mast itself.

I don't think Chris has any intentions of placing a mizzen sail on that aft mast of his.

One of my original inspirations for the aft-mast design of mine was an experiment carried out on a Morgan Out Island ketch, where the traditional mainsail was removed and a staysail (might be termed a mizzen staysail) substituted in that area
http://www.runningtideyachts.com/sail/
"I once had a copy of a test on a Morgan 41' Out Island ketch , where upon removing the mainsail, the boat lost only 1/2 knot of speed, but cut its leeway in half (from 11 to 6 degrees). A staysail was then rigged between the masts in place of the mainsail, and the boat regained 1 knot of speed while retaining its decreased leeway."

I think there are a number of other examples here:
http://www.boatdesign.net/forums/multihulls/main-less-rig-21274.html

He is looking for more efficiency from a lower aspect sail plane, along with total feathering of those mast shapes without 'reefing' them.

I believe he is utilizing round section mast shapes hidden inside the foil shapes, and those outer foils are free to rotate 360 degrees so they are not venerable to worst conditions.

 

My post about -aoa giving lift was intended to beg the question about coming away from a dock with an on dock breeze.

Also, would a -aoa + lift mast section develop enough circulation to be of interest to a jib set in front of it? Especially if there was less drag than a mast with mainsail?

Paul

 

You're not the only one.

The wings can be useful for springing off the dock in a crosswind, producing forward or aft thrust to push against a spring line to rotate the boat away from the dock. However, in this case the force pushing the boat into the wind comes from it pressing against the dock. But there's no way the wings can pull the boat into the wind without any other outside interaction.

 

I'm not sure what you mean by "-aoa + lift mast section", but the influence of the wing on the jib will be similar to a mainsail producing the same spanwise lift distribution. The main difference is the lift on the wing is produced further forward and may make the jib act as though it has more overlap than it actually does.

There's a widespread misconception that jibs are more effective per square meter than mainsails because they are staysails and not mast-mounted. This leads to the conclusion that one should remove the mainsail and concentrate the area in the jib.

Instead, it's the case that the jib benefits from favorable interference from the mainsail, and the mainsail sacrifices lift because of interference from the jib. But the combination of the two is better than either one alone. If you remove the mainsail, the superiority of the jib disappears. If you remove the jib, the mainsail looks better. This is why development classes that only limit sail area and make no distinction as to how the area is used (A & C class catamarans, for example) evolve to cat rigs, not mast-aft rigs.

 

Tom, I meant this by -aoa +lift (just as an example, first one I found, no editing, I'm sure there are better ones, don't know if it would generate enough lift to get off a dock when pinned):

http://www.worldofkrauss.com/foils/784

Sorry for confusion. Low battery. Race against current, as it were.

Paul

 

Biplane Wing for Supersonic Flight

...this could upset the apple cart in understanding aerodynamics of flight...or at least show there are some 'unexplained phenomena' with dealing with these subjects

Cheaper, quieter, and fuel-efficient biplanes could put supersonic travel on the horizon, according to MIT engineers.


By Jennifer Chu, MIT

For 27 years, the Concorde provided its passengers with a rare luxury: time saved. For a pricey fare, the sleek supersonic jet ferried its ticketholders from New York to Paris in a mere three-and-a-half hours – just enough time for a nap and an aperitif. Over the years, expensive tickets, high fuel costs, limited seating and noise disruption from the jet’s sonic boom slowed interest and ticket sales. On Nov. 26, 2003, the Concorde – and commercial supersonic travel – retired from service.

Since then, a number of groups have been working on designs for the next generation of supersonic jets. Now an MIT researcher has come up with a concept that may solve many of the problems that grounded the Concorde. Qiqi Wang, an assistant professor of aeronautics and astronautics, says the solution, in principle, is simple: Instead of flying with one wing to a side, why not two?

Wang and his colleagues Rui Hu, a postdoc in the Department of Aeronautics and Astronautics, and Antony Jameson, a professor of engineering at Stanford University, have shown through a computer model that a modified biplane can, in fact, produce significantly less drag than a conventional single-wing aircraft at supersonic cruise speeds. The group will publish their results in the Journal of Aircraft.

This decreased drag, according to Wang, means the plane would require less fuel to fly. It also means the plane would produce less of a sonic boom.

“The sonic boom is really the shock waves created by the supersonic airplanes, propagated to the ground,” Wang says. “It’s like hearing gunfire. It’s so annoying that supersonic jets were not allowed to fly over land.”

Double the wings, double the fun
With Wang’s design, a jet with two wings – one positioned above the other – would cancel out the shock waves produced from either wing alone. Wang credits German engineer Adolf Busemann for the original concept. In the 1950s, Busemann came up with a biplane design that essentially eliminates shock waves at supersonic speeds.

Normally, as a conventional jet nears the speed of sound, air starts to compress at the front and back of the jet. As the plane reaches and surpasses the speed of sound, or Mach 1, the sudden increase in air pressure creates two huge shock waves that radiate out at both ends of the plane, producing a sonic boom.

Through calculations, Busemann found that a biplane design could essentially do away with shock waves. Each wing of the design, when seen from the side, is shaped like a flattened triangle, with the top and bottom wings pointing toward each other. The configuration, according to his calculations, cancels out shock waves produced by each wing alone.

However, the design lacks lift: The two wings create a very narrow channel through which only a limited amount of air can flow. When transitioning to supersonic speeds, the channel, Wang says, could essentially “choke,” creating incredible drag. While the design could work beautifully at supersonic speeds, it can’t overcome the drag to reach those speeds.

Giving lift to a grounded theory
To address the drag issue, Wang, Hu, and Jameson designed a computer model to simulate the performance of Busemann’s biplane at various speeds. At a given speed, the model determined the optimal wing shape to minimize drag. The researchers then aggregated the results from a dozen different speeds and 700 wing configurations to come up with an optimal shape for each wing.

They found that smoothing out the inner surface of each wing slightly created a wider channel through which air could flow. The researchers also found that by bumping out the top edge of the higher wing, and the bottom edge of the lower wing, the conceptual plane was able to fly at supersonic speeds, with half the drag of conventional supersonic jets such as the Concorde. Wang says this kind of performance could potentially cut the amount of fuel required to fly the plane by more than half.

“If you think about it, when you take off, not only do you have to carry the passengers, but also the fuel, and if you can reduce the fuel burn, you can reduce how much fuel you need to carry, which in turn reduces the size of the structure you need to carry the fuel,” Wang says. “It’s kind of a chain reaction.”

The team’s next step is to design a three-dimensional model to account for other factors affecting flight. While the MIT researchers are looking for a single optimal design for supersonic flight, Wang points out that a group in Japan has made progress in designing a Busemann-like biplane with moving parts: The wings would essentially change shape in mid-flight to attain supersonic speeds.

“Now people are having more ideas on how to improve [Busemann’s] design,” Wang says. “This may lead to a dramatic improvement, and there may be a boom in the field in the coming years.”

“There are many challenges in designing realistic supersonic aircraft, such as high drag, efficient engines and low sonic-boom signature,” says Karthik Duraisamy, assistant professor of aeronautics and astronautics at Stanford University, who was not involved in the research. “Dr. Wang’s paper presents an important first step towards reducing drag, and there is also potential to address structural issues.”

Published March 2012

 

Thanks, Brian-most interesting!

 

Read that at gizmag and also had thoughts for bi-sails, caravan effect between cat hulls saved some pics thinking I better be a supersonic expert

 

Arvel Gentry's passing & a Legacy of His Articles

Arvel Gentry has just recently passed away, but thank goodness someone has taken the job on to preserve his numerous papers. Check out the forum subject thread with a number of links to his papers:
http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/arvel-gentrys-site-49806.html#post678461

As is mentioned on the first posting of this subject thread that old website link is no longer valid. Rather have a look here for some fascinating articles of his:
http://arvelgentry.jimdo.com/articles/

 

Thanks for the info, Brian.
Best wishes.

 

Since the thread was active, I thought I'd add a result we recently plotted - the distribution of the driving force (Fx) and the heeling force (Fz) in the vertical direction, up along the mast.

Although the side force distribution is very similar, this is not the lift distribution - both lift & drag distribution in the vertical direction can of course be deduced from here, considering the apparent wind angle 23,5 deg.

 

Thanks Mikko, I'll be back to this discussion when i have a bit more time
Brian

 

Thanks Mikko, nice picture!
Does it include vertical gradient of TWS?
What are the total drive and lateral forces?
Interesting to see the low contribution of the bottom part of jib and top part of mainsail.

 

I found that interesting also. Still very important to the rest of the sail, but I guess it makes sense when sailing not do dwell too much on the top and bottom other than as end plate. This summer I think I will focus more on the middle two quarters of the sail, for shape etc.