Today on science friday on NPR they were discussing lift as it relates to airplanes. The speaker said that Bernoullies principle doesn't completely account for the lift that the air flow over an airplane wing generates. He said that according to Bernoullies principle a commercial jet would have to achieve 400knots to generate enough lift for takeoff. He said that this idea is a point of contention among scientists but the lift generated is as simple as air flow over the top of the wing being enough to push downward towards the earth. He cited examples such as a helicopter and the fact that fighter jets mount missles under their wings because the air flow there isn't that important. Anyone out there familiar with this "controversy"?

There is two theorys on flight. Bernoullie, and Newtononian. Newton says it's from the air particles hitting the bottom side of the wing. Bernoullie says it is from a difference in pressures. The air traveling over the top of the wing has farther to travel so it is moving faster creating an area of lower pressure. The pressure difference is what creates the lift. The reality is that they don't fully understand how the lift is produced, only how to manipulate it. I only have limitied exposer to lift from the handfull of aviation classes I took when I was going to school for ATC.

I think it has more to do with airflow than lift. When you get on the highway next time, put your hand out the window traveling at speed. Change the angle and see what happens. You hand is not creating lift, but, the angle of attack is high enough that the air flowing above and under your hand forces your hand to go up or down. This force is not lift, but airflow. This is all about elevators, flaps and trim tabs. I am sure TIMBO can instruct much better on this.

Just like a rudder, a rudder without water flow is NOTHING, just an object in the water. Once the boat starts moving the rudders start doing there job.

I cant believe I just replied to this. This is what RUMS does to you.

MERRY NEW YEAR! <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

There are many books and websites that go deep into details I have long since forgotten, and I'm not about to get too deep here, I have things to do, but when it comes to a comercial airliner getting off a runway, it's not only the lift from the wing, there is also some -push- (we call it thrust) from the 2 (or 3 or 4) engines. The basic equation is; Lift + Thrust > Drag + Weight. The Thrust is added to the lift, to overcome the weight plus drag.

In a large comercial airliner, on take off, as you pull the nose up, (at say, 150 kts) the engines are now pointing down, at the runway, and they are "thrusting" (no dirty jokes here) the jet into the air, that thrust adds to the lift of the wings and helps get the airplane into the sky. Also, at takeoff, the wing is in a "high lift" configuration, with leading edge devices and flaps, all of which add to the camber of the wing. As the airplane accelerates after getting airborne, the flaps and slats are retracted to the high speed configuration.

And no comercial airliner wings that I am aware of are rated to much more than 360 knots (I'm talking indicated airpseed, and not the old, faster, 727's that could go above 380, but the newer stuff, since the 757) so the "have to go 400 to get airborn" remark isn't valid, we never go near 400 indicated, even though the true airspeed at altitude is about 480knots, or Mach .83, our indicated airspeed is only about 250 at cruise (35,000').

You have probably seen the videos on YouTube of the fighters going straight up, doing all kinds of impossible aerobatics. That's usually done on thrust, not lift. If you have an engine that puts out 50,000 lbs. of thrust in a plane that only weighs 40,000 lbs. you can put it on a rack, point it straight up, and launch it. No lift coming off the wings at all. Throw a rock striaght up, see? All thrust, no wings or lift needed.

My Supersonic Aero instructor once said, "If you put a big enough engine on it, you can make a barn door fly...but they had to put two of them on the F4!" (The F4 was known as the lead sled, big engines, kind of heavy, stubby wings) Take a look at the F104 sometime too, one of the fastest fighter jets of it's time (Viet Nam era) All engine, tiny wings, fast as hell, all on thrust.

Even with the propeller type aircraft there are many unlimited competition type acro planes that can just about hang on their prop, suspended in mid air, no airflow over the wing yet it can still do all kinds of stuff, so flying isn't limited to lift generated by the wing. Thrust is a big factor. The Space shuttle on launch has no airflow over the wing as it lifts off the pad, yet it still lifts off the pad.

Recommended reading:

And I like Frank Bethwaite's "High Performance Sailing". He was a pilot in the RAF (is that what they call the Aussie AF?) as well as a competition glider pilot, and a great sailboat designer, racer, etc.

You guys are all wrong! It's very simple: Money ($), and lots of it, make an airplane fly. <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />

Read chapter three of the free online book "See How It Flies" by John Denker. It has the information you want and demonstrates why some common misconceptions are wrong.

My favorite quote in regards to money and aviation, "How do you make a million dollars in Aviation? Start with 10 million..."

I was out flying a little plane last week, the fuel is up to $4.56/gallon for 100LL. Yikes! We need to get on that coal-to-jet fuel conversion thing right away!

Coal to jetfuel.. Or: http://en.wikipedia.org/wiki/Gossamer_Albatross <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

What I would really like to see is an electric motor powered type of glider, the wings covered with solar panels. Self launched using the electric motor and a batery, climb up above the clouds, fly around up there for ever, or until you have to pee... <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />

I used to buy av gas for $2.50/gal for my race quad. What a tradgedy.

I'm paying 7.5 US/gallon for my car. You guys ain't seen nothing yet !

Wouter

Yeah, you also pay 90% taxes

Karl why don't you do your homework first before posting

From Wikipedia:
"Netherlands
The sale of fuels in the Netherlands is levied with an excise tax. A 1995 excise was raised by Dutch gulden 25 cents (€0.11), the Kok Quarter (€0.08 raise per litre gasoline and €0.03 raise per litre diesel), by then Prime-Minister Wim Kok is now specifically set aside by the second Balkenende cabinet for use in road creation and road and public transport maintenance. The 2007 fuel tax was € 0,684 per litre or $ 3,5 per gallon. On top of that is 19% VAT over the entire fuel price, making the Dutch taxes one of the highest in the world."

I would venture to say that the fuel taxes in NED are more than 90% of the base cost of the fuel.

You should do your research before posting, Dave. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

And if that wasn't expensive enough, in July diesel tax will go up another 3 cents. <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />

HAAA HAAA. Bout pee'd my pants. Thanks Matt.

Guys,

You are getting off track, my compliments to "TIMBO" on his explination. If only my Professor for "GasDynamics" at Drexel Univ could have explained it so simply. Instead it took alot of chaulk dust and calculus with Greek symbols to get it through our young and impressionable minds.

Question: do you think the cats (if used) for the AC Regetta will have rotating masts so as to promote aerodynamics/lift at the higher boat speeds and apparrent wind velocities that a (90')? multihull could theroretically reach???

Harry

Every once in a while a revert back to this article to remind me about sail shapes etc. http://www.northsailsod.com/articles/article6-1.html