Questions Answers
January 15, 2003

Bill Pritchard <billpritjr@yahoo.com> (#3)

Mr. Seykota-

Your replies prove interesting indeed, but I forgot the "real thing" that makes airplanes fly. MONEY. To cover jet fuel, airplane leases, insurance, overpaid & underworked pilots, etc.

So when a child asks "Daddy, what makes the plane fly?", the correct answer is MONEY.

All kidding aside, your arguments are compelling but I will remain stubborn in my position that Bernoulli's lift theory is correct, or let me clarify, with regard to wings and airfoils, it is the MORE correct theory. Although I am indeed intrigued and interested in your comments.

You are correct with regard to ice, it also increases weight of the wing.

I might offer a further note, that air is merely a liquid, like water, and if we were to take a garden hose and somehow perfectly spray an equal flow of water against the leading edge of the wing, or similar device, you would see that the flow above is indeed faster than the flow below. Again, your arguments are compelling, but if Bernoulli is wrong, well, we
better watch out because a lot of airplanes are going to be dropping out of the sky.

On the other side of the coin, one could take the position that the curve of the wing could "slow down" the airflow. Maybe this discussion is causing me to think too hard at this point....!

Ed, good talking to you and look forward to more of the same

Bill Pritchard

I recommend you check overview and the experiments I conducted. They show that Radial Momentum, not Fluid Velocity, accounts for lift.

Bernoulli's Principle is not wrong. It is an energy balance. It just does not apply to lift.

Air impacting the forward edge of the wing, above the mid point, deflects upward, causing a small downward force (negative lift) on the leading edge. Then, just behind the crest of the wing, there is an area of flow separation that causes a small upward force (positive lift). The net result of these is to twist the leading edge of the wing downward.

The net lift that supports the airplane results from the angle of attack of the wing, as air deflects downward off the bottom of the wing.

January 15, 2003

Bill Pritchard <billpritjr@yahoo.com> (#2)

Mr. Seykota-

I do indeed see your point, but I offer this for further consideration.

Recall that the wing itself, the physical wing, is traveling forward at XXX speed. Observe that a parked airplane (and its accompanying wing) cannot just "rotate" and get airborne. Well, give it 100 knots of gusting winds at the airport, it can, but for
our discussion, allow me to keep it simple to explain. Anyway, the wing must reach "rotation speed" or VR speed. Obviously then (obvious, but important to note for discussion purposes), the wing is physically cutting thru the air at XXX speed.

Subsequently, the airflow above the wing (which as we have observed is already traveling forward) is forced to curve across, while the airflow under the same wing (again, itself traveling forward) is not. The above airflow is faster, and this difference in speeds causes differences in pressure. Enough speed difference equals enough pressure difference to give us the end result called lift. So two parts of our equation "have speed" here, 1) The Wing has physical forward speed, and 2) The airflows over and under have their own personal speed

The pressure difference, as a result the different airflows, "becomes" lift at VR speed, or rotation speed, as the airplane takes off. (It could be further argued that the physical speed of the wing causes lift, and old hangar argument since that in
turn, causes the airflow differences). This is why ice, dirt, anything which affects the wing's shape can degrade takeoff performance.

Lets say a Boeing 727 rotates at 140 knots, with a "clean" wing. Our captain chooses Runway 25 at Reno because it is quicker to taxi to, the flight is late, and his believes his wing is clean and free of contamination. Runway 25 is the shorter runway at
Reno. Unfortunately, Reno had a strange ice storm that morning and the Captain did not look at the wings, he was busy checking his moving averages and volume from the market the day before, and hoping his idol Ed Seykota would help him retire early from the airline world.

In any event, during the takeoff roll on Runway 25, our jet clicks thru 138,139,140, the co-pilot says VR-rotate, and nothing happens.....141,143,150, nothing, now we are hard on the brakes and praying we don't go thru the fence. Our airfoil/wing was contaminated, and lift was not produced due to the problematic airflow. It could be argued that lift may have never been produced at all, at any speed.

Not to ramble, but physical speed of the wing is only one component. The critical angle of attack, which depending on airplane, is usually 15 to 18 degrees, is also important. Exceed this angle, and the airflow is interrupted with no hope of making lift. This is why every so often at air shows, a performer will be on the "bottom side" of a loop, traveling very fast, and in his desire to pull up quickly before the crowd, he exceeds the critical angle of attack. The airplane is still physically going thru the sky at a fast speed, but his wing is not producing lift, resulting in tragedy as the airplane plows into the ground.

Maybe the above scenarios help

take care!

Bill Pritchard
You can get to Incline Village from Reno, Nevada, the short way, by going up Mount Rose Highway, or, the long way, by going through Carson City and up route 50. Say two drivers leave Reno and travel to Incline, using different routes. According to your logic, the one who takes the longer route must, therefore go faster.

If a third driver went via Boston, he would have to, by your logic, travel at supersonic speeds. 

I suggest there is a problem with the logic and that there is no particular reason air flows faster just because it has to travel further.

Also, there is no particular relationship between the speed of separated air flows and their pressures, such as flows on either side of a wing. If this were the case, you could isolate a very separate flow, say a sealed jar of air, take it on a flight with you, get it going at, say, 600 knots relative to the ground, and thereby drop the pressure inside the jar.

Lift is, simply, a function of angle of attack. The curvature of the wing helps entrain laminar flow, reducing turbulence, and therefore converting more of the energy into thrust and lift.

Ice increases the weight of the wing, alters the angle of attack, effects turbulence and may also interfere with function of the deflection controls.

January 15, 2003

Bill Pritchard <billpritjr@yahoo.com>

Mr. Seykota-

I find your lift experiments very interesting. I might offer that, from the aviation standpoint, the Bernoulli theory is the "taught" theory, and supported by all major aviation industry bodies, to include NASA and the FAA.

To further your experiment, you might go up in a rented Cessna and study the effects of lift on the wing in different configurations. The wing has a critical angle of attack, usually 15-18 degrees, of which beyond this angle, lift is interrupted.

In your experiments, Bernoulli principle is referred to as "high velocity causes low pressure." The textbook definition is that (using airplanes again) the speed of the airflow above the wing is increased, or accelerated by the curve of the wing. As a result, this airflow is physically faster in velocity than the airflow under the wing, which is basically a flat surface. This difference in speeds causes the lift (according to Bernoulli). The faster-than-the-lower-airflow under the wing is not meant to indicate the airflow under the wing is "slow" or "low speed."

Again, your experiments are interesting indeed and one email cannot cover centuries of physics theory.  But those are my basic observations regarding lift, again, from the limited universe of airplanes, not other situations (as in hot air balloon, ok, hot air rises, that's fine, but what CAUSES the ACTUAL LIFTING)

Ed, take care and lets stay in touch.

Bill Pritchard

I see no particular reason that the air above the wing would have increased flow velocity. If anything, it would seem to slow due to deflection related losses. At any rate, it has a longer path to travel, so molecules that were "holding hands" at the leading edge would have to find new partners at the trailing edge.