Oz Report

Vortices

Goshawk, Barn and Tawny Owl

aerodynamics|Facebook

https://jeb.biologists.org/content/223/3/jeb214809

Here, by tracking up to 20,000, 0.3 mm neutrally buoyant soap bubbles behind a gliding barn owl, tawny owl and goshawk, we found that downwash velocity due to the body/tail consistently exceeds that due to the wings. The downwash measured behind the centreline is quantitatively consistent with an alternative hypothesis: that of constant lift production per planform area, a requirement for minimizing viscous, profile drag. Gliding raptors use lift distributions that compromise both inviscid induced drag minimization and static pitch stability, instead adopting a strategy that reduces the viscous drag, which is of proportionately greater importance to lower Reynolds number fliers.

Discussion: https://www.facebook.com/gary.osoba/posts/3681345908562773

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Fat Wings

Are those little vortex generators (seem to be in the wrong place)?

aerodynamics

A scaled version of the V-Wing made its first flight, showing that alternative designs could become long-distance aircraft of the future.

A scale model of the “Flying-V”, an experimental aircraft design with huge wings, took flight recently in Germany. The blended-wing aircraft concept is a project by Delft Technical University (TU Delft) in the Netherlands, with financial support by KLM Airlines. It was recently flown from a German airbase, with the support of a team from Airbus.

The Flying-V was designed as a fuel-efficient, long-range aircraft in which the passenger seating, fuel tanks and baggage hold are built into the wings. Research shows that the unusual design stands to gain up to 20 percent better fuel efficiency than an Airbus A350 jetliner, considered today’s most advanced design. It’s also about 15 percent more aerodynamically efficient than conventional aircraft. At full scale, the Flying-V would seat 314 passengers in two classes.

Don't let the wind hit your butt

http://imgur.com/PIOafIe

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Introduction to Aerodynamics

edX

aerodynamics

https://www.edx.org/course/mit/16-101x/introduction-aerodynamics/890

This is a course about aerodynamics, i.e. the study of the flow of air about a body. In our case, the body will be an airplane, but much of the aerodynamics in this course is relevant to a wide variety of applications from sailboats to automobiles to birds. Students completing 16.101x will gain a conceptual understanding of aerodynamic models used to predict the forces on and performance of aircraft.

Topics covered are relevant to the aerodynamic performance of wings and bodies in subsonic, transonic, and supersonic regimes. Specifically, we address subsonic potential flows, including source/vortex panel methods; viscous flows, including laminar and turbulent boundary layers; aerodynamics of airfoils and wings, including thin airfoil theory, lifting line theory, and panel method/interacting boundary layer methods; and supersonic airfoil theory.

How do wings fly?

And the bad theories that don't explain how wings fly

aerodynamics

http://www.grc.nasa.gov/WWW/k-12/airplane/right2.html

http://ozreport.com/forum/viewtopic.php?t=18362&postdays=0&postorder=asc&start=13

This is an excellent resource, much better than all the aerodynamics books that I read when I tried to figure this out years ago.

Blowing air over the wing and out the flap

(Cal Poly)

aerodynamics|landing|powered|tandem|technology

http://www.designfax.net/enews/20101123/feature-3.asp

Over-the-wing (engine) placement is a key design element because it enables very high lift while still providing the engine thrust necessary for take-off and high-speed level flight. It also offers important reduced-noise benefits.

…single wing flap is used in tandem with a novel element based on circulation-control technology. A narrow slot, capable of pneumatically blowing out air, runs along the entire trailing edge of each wing, just above the flap. This system is powered by its own compressed air source located inside the wing.

This procedure, called flap-blowing, performs two functions: it increases air velocity over the top of the wing, and it deflects the ambient wind stream downward so that it curls under the wing. The combined forces generate a lift coefficient that can be two to four times higher than a conventional mechanical flap.

During take-off and landing, air flow from the slot interacts with the engine exhaust and pulls this powerful exhaust blast down onto the wing. This process, called entraining the exhaust, greatly increases the velocity of the air passing over the wing and results in highly augmented upward suction and lift.

"This strategy allows an aircraft to be flying at a very low speed, while the wing is seeing much higher relative wind speeds on its curved upper surface due to this blowing and thrust-entraining combination," Englar says. "We have measured lift coefficients between 8.0 and 10.0 on these pneumatic powered-lift wings at a level flight condition during testing. The normal lift coefficient on a conventional wing at a similar flight condition is less than 1.0."

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Aerodynamics

of the ball

http://www.latimes.com/sports/la-sp-world-cup-ball-20100624,0,4874871.story

"So as the goalkeeper sees the ball coming, it suddenly seems to change its trajectory," McKeon said. "It's like putting the brakes on, but putting them on unevenly."

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Induced drag

Helical

aerodynamics

Does this device do anything?

http://www.minix.fr/english/planes_and_vortex.php

http://www.minix.fr/english/abstract.php

Flow

Order inside the chaos

(Monterey Bay, California)

aerodynamics

http://www.nytimes.com/2009/09/29/science/29chaos.html?hp

Over the past 10 years, scientists have made enormous strides in their ability to identify and make images of the underlying mechanics of flowing air and water, and to predict how objects move through these flows.

Assisted by instruments that can track in fine detail how parcels of fluid move, and by low-cost computers that can crunch vast amounts of data quickly, researchers have found hidden structures...

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Let's Twist Again

A fascinating, if highly technical and obscure, discussion of wing twist and lift distribution

aerodynamics

http://ozreport.com/forum/viewtopic.php?t=14586

I've been doing a fair bit of research into flying wing design and recently while reviewing a lot of info on model design I got a glimpse of the big picture and how important wing twist is in meeting stability and performance criteria. I may have uncovered some blind spots in current design concepts, but I don't have the hubris to suggest I know better than the current designers

This is the kind of discussion I love to see on the Oz Report forum. You don't have to register to read anything there (just to post a comment).

March 5, 2008, 10:08:32 +1100

Leading Edge Vortices

Bats do it, bees do it, ....

aerodynamics

http://www.nytimes.com/2008/03/04/science/04angi.html

In the latest issue of the journal Science, Anders Hedenstrom of Lund University in Sweden and his colleagues report that when a nectar-eating bat hovers in midair to sip liquid sugar, the mammal’s sharp-edged flexible wings generate the same sort of precision whirlwind lift detected recently in studies of insect flight. As the bat curls its membranous flappers in and out three times per second, a series of tiny cyclones form at the leading edge of each wing. The result? Even as gravity plucks at its heels, the bat’s homegrown tornadoes suck it back up toward Oz.

Other researchers have demonstrated that insects like honeybees and dragonflies rely on such leading-edge vortices to supply the major part of their lift, particularly during a hover or slow cruise. The new work shows that considerably heavier animals than insects can rally the power of quick-changing or “unsteady” aerodynamic tactics in their quest to stay high. The star of the current study, the Pallas’s long-tongued bat of Latin America, weighs maybe 12 grams, 120 times greater than the average bee. The researchers predict that hummingbirds will also be shown to have twister-tipped wings.

Flares

An animated view of how they happen

aerodynamics

http://www.ptone.com/flare/

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Thu, Jul 7 2005, 12:00:05 pm EDT

A guide

http://aerodyn.org/

You'll find many references to on-line guides to aerodynamics throughout past issues of the Oz Report.

Discuss Aerodynamics at the Oz Report forum

aerodynamics|certification|competition|Gerard "Gerry" Farell|job|Laurent Thevenot|safety|tail|tuck|tumble

john vernon <johnv@emvertec.demon.co.uk> writes:

This is my reasoning about the ATOS incident. You may think I have a point to make because I have made tail planes, in fact I have just restarted with the help of "Heli-Ben" Cope who does the main manufacturing now, or you may, like me, believe in the added safety a tail plane can give us :-

I think there are two discussions here 1) is whether the pilot was flying the glider too slowly and 2) is about whether the glider should have recovered.

As I don't fly an Atos and am quite happy thermaling at 23-25mph on the Tsunami I will only deal with 2).

The tail plane can provide us with improvements to our glider's stability by increased pitch damping and adding positive pitching moment at negative angles of attack. From these improvements we derive additional benefits of improved thermaling feel and damping out the effects of turbulence.

Floating, negative angle tail planes provide increased damping and increased positive pitching moment at negative angles of attack and do not change the pitching moment at +ve angles of attack. However they have the disadvantage of increasing bar pressure at speed, which is why I developed the "competition stop" which allows pilots who want to exceed 50-55mph, with a tail plane fitted, to do so. The above is true as long as the glider the tail plane is fitted to is not changed from its certified settings because the tail plane is fitted

Positive angle set tail planes (as I believe are fitted to the ATOS) increase pitch damping and depending on how they are designed and set can provide some increase in pitching moment at negative angles of attack and also can have a negative effect on pitching moment at positive angles of attack. Consequently they do not increase bar pressure at speed.

I assume that, in the case of the ATOS, the tail plane has now become an integral part of the glider's aerodynamics and the aerodynamics have been tuned to meet the certification requirements with it fitted. Consequently it seems to me that there will probably be no additional or only marginal additional positive pitching moment benefit derived from it as compared to the pitching moment safety margins required for the test i.e. the tail plane basically provides added pitch damping but provides no or only marginal extra +ve pitching moment.

When I wrote the article about tail planes in Skywings a couple of years ago (you can read it at www.slipstreamcomposites.com) it became obvious that the combination of increased pitch damping and added positive pitching moment over and above certification standards are necessary to improve our aircraft's tuck and tumble resistance.

Gerard Thevenot wrote in an email recently when questioned about tail planes

"Certifications say that above a line a glider is safe, under the line it is not. It is not a true fact, the more stable the safer the glider will be. A tail plane will improve the safety of a certified glider by a big margin."

In the incident in Spain it strikes me that the aircraft had enough airspeed to recover, it had passed through the first phase of rapid rotation and speed increase where the added damping had done its job, and not apparently gone past vertical, the pilot was still holding the bar and I think had moved his weight forward, at this point the glider should have pulled out and recovered, why didn't it?.

Added pitch up would certainly have been beneficial throughout the recovery and particularly at this point. I personally believe this was an incident where, with a tail plane fitted, the glider should have recovered.

Discuss tail planes and V tails at OzReport.com/forum/phpBB2

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aerodynamics|Angelo Crapanzano|book|history|Oz Report|photo

Got a great digital photo? Want to see it published in the Oz Report? Send it in with a funny caption (as though I didn’t have enough photos), and the best one gets a copy of The History of Aerodynamics by John D. Anderson, Jr. It is a great book, and was sent to me by Angelo Crapanzano.

Discuss the history of aerodynamics at OzReport.com/forum/phpBB2

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aerodynamics|Dave Brandt|helmet|Mike Tryon|nylon|site|sport

http://www.arcteryx.com

Dave Brandt <dave@prairiewalls.com> writes:

I have been flying with an Arc`teryx Sigma LT for a couple years now and it is a great flying jacket. The Gore Windstopper works great and the fit of the Sigma LT makes it very clean for flying.

Arc`teryx is a very cool company. They are continually pushing the entire high end outdoor clothing industry with their innovation. The products are not cheap, but they are worth it. I have been an Arc`teryx dealer for five years, they are a great company to work with.

Derek Poff <D.Poff@LabSafety.com> writes:

Flying up here in WI we get a great range of temperatures through the season and I use a Lycra stretch outer layer (BMX racing top) that seals up whatever layers I need under it. It is tight to the body and still very flexible. Works great, keeps the wind out and I found a couple at Goodwill for $2.00 a pop.

Mike Tryon <mtryon@ucsd.edu> writes:

Living in San Diego, I don't need much in the way of warm clothing but I have a jacket made by Mountain Hard Wear (http://www.mountainhardwear.com) that is very similar to the Arc`teryx Sigma LT. It is the best jacket I've ever had. Very windproof and comfortable through a very wide range of temperatures. It’s really too loose for use for flying - flaps around a lot unless it’s under speed sleeves.

Something that's better for flying is the tops made from "3SP" by Sport Hill (www.sporthill.com and http://www.sporthill.com/zone3/tops/pages/2002-DiscoveryTop.htm). I have the Discovery Top that is very nice for flying. Wind will get through it at high speeds, but up to about 35 it is really windproof. It fits almost as snug as speed sleeves. They are sized a bit large so go with a smaller size for a snug fit. All of these sort of tops have their limits in real cold. There is no substitute for insulation - you need thickness to really deal with cold. For summer flying (we commonly get 12-15,000 around here) I still put a layer or two of fleece underneath.

John Corry <john@neoncowboy.com> writes:

Moisture wicking base layer: these are readily available from Sierra Trading Post in all sorts of weights depending on your needs. The silk turtleneck from Terramar (http://www.terramarsports.com) is my personal favorite.

On top of that, I wear a big, cotton sweatshirt if it's cold. You may want to choose a mid-layer for insulation that is a little tighter than a sweatshirt (like Capilene) if you're concerned about bulk.

Next layer is a tight fitting, windproof nylon jacket by Pearl Izumi (http://www.pearlizumi.com/pearlizumi/site/catalog/productlist.aspx?iProductTypeSubID=30). This piece is the crucial windbreaker layer. It is small enough to pack down into its own zippered pouch and when packed, fits in my helmet with instruments to keep the instruments from moving around in transit. The only minus is that the sleeves are kind of flappy.

So the final layer is for additional warmth and aerodynamics. Just a tight fitting cotton turtleneck to keep all my layers of sleeves nice and tight.

That's what I wear. Keeps me warm and no flapping sleeves even on long flights at and above cloudbase.

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Fri, Apr 5 2002, 6:00:06 pm EST

Aerodynamics|Felix Ruehle|Gerolf Heinrichs|Rob Kells|Steve Pearson

Gerolf Heinrichs and Felix Ruehle have agreed to make short presentations on the aerodynamics of hang gliders just before the start of the Wallaby Open, or on a day that gets blown out during the meet (if that happens). Then the floor will be opened up to discussion and questions. Steve Pearson will be here, as well as Rob Kells, and many other knowledgeable pilots so I’m sure that we can get a free flowing discussion.

I’ll report on the results of any of the discussion, so that Oz Report readers won’t miss out.

Aerodynamics|Richard Miller

Aerodynamics|John "Ole" Olson|Richard Miller

(?-i)John "Ole" Olson|Aerodynamics|Richard Miller

Aerodynamics|John "Ole" Olson|Richard Miller

Richard Miller «richardmiller» writes:

Why? - to get back to the issue of the non-recognition of the upstream propagation. What reason for this? The shadow that intuition casts over any understanding of the mechanics of the bending of a stalk in the wind, or the fluttering of a leaf, is long and deep.

Half of all dynamic interactions in a free atmosphere are of a positive nature, involve positive dynamic pressure; the other half, their complement, are negative. Against this is the total intuitive disposition of the mind, intent on understanding, to see and to interpret the whole in positive terms, in terms of contact and impact. Classical aerodynamic theory from its origins in the Principia to the most recent article or book is testament to this.

This derives from our nature, or what we intuit our nature to be from our identification with the mass, motion, movement, momentum of a human body, and of the role that contact/impact play in the course of our lives. Everything we accomplish in life, with the minor exception of sucking beer through a straw, involves the manipulation of mass or the transmission of momentum by contact of some sort.

We are so deeply in the thrall of the intuition of contact/impact as to be far beyond any consciousness of it, which is exactly the definition of intuition. We are in the thrall of a congeries of intuitions that direct and misdirect our lives including the most insidious of all that we act, and think, as free, unfettered agents.

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Aerodynamics|Richard Miller

Richard Miller «richardmiller» writes:

As I was saying…

That pressure is propagated upstream, and at the speed of sound, is not my invention. It is orthodox science, an observed phenomenon, acknowledged as such, and referred to now and then. But the phenomena that appear on the stage of science, like actors, or clowns, are treated variously, and the upstream propagation of pressure is in the Rodney Dangerfield class. Rodney, so short as a child he tells us, he had to open his fly to see out. It's a little like that in this case.

Newton was aware of the phenomenon, but when he came to compose the second book of the Principia, the one that dealt with Fluid Mechanics, he saw no need to include it. When the bases of classical aerodynamic theory were worked out at Göttingen in the teens of the last century the emphasis, fore and aft, was on the downwash to the exclusion of anything that happened ahead of the leading edge of the wing. Nor has anyone had much to say about it since

I could easily have overlooked the upstream propagation of pressure myself. In fact I did, for quite a number of years, then, in Rodney Dangerfield terms, I found the zipper. "Hmmm!" quoth I, "What do we have here?"

In my own adventure in attempting to make sense of the observed phenomena - sense of what perceived, or imagined I did - I found that the upstream propagation of pressure had attracted so little attention as not even to merit its own nomenclature, and I was forced, in describing it to myself, to invent my own. Thus the Axis of Pressure Propagation, and The Initiation Point for the terminus of that horizontal line, described earlier, that does not end at the Stagnation Point.

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Aerodynamics|Richard Miller

richard miller «richardmiller» sends in the first of what may turn into a series of article on aerodynamics (we’ll see how it goes):

The fundamentals from which all determinations in fluid dynamics derive, like the 1 and 0 of software code, are a flow and a source of resistance to that flow. A rock in a stream, a glass or cup in the water draining in the sink, or around a rubber ducky in the bathtub, are all familiar examples of this. As with so many simple observations we tend to look no further than the surface, nor rarely have need to do so, except we are intent, as the expression goes, of probing the secrets of nature. Then we discover a lot more than ever we imagined.

Let us assume the flow to be uniform, horizontal, translatory, from left to right, of constant velocity, and of a homogenous, isotropic fluid; and the source of resistance as a round object in the right-hand portion of the flow field. Extending forward from the exposed face of this object, some distance into on-coming flow, we place a straight line representing the axis of the upstream propagation of pressure that occurs, at the speed of sound, when the designate conditions are established.

Again, that pressure is propagated upstream, and at the speed of sound.

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Peter Gasparovic|picture|tuck|tumble|aerodynamics

Peter Gasparovic «pegas», Air Force Academy in Kosice, Dept.of Aeronautical Engineering, http://pegas.oceany.cz writes:

The main difference between a hang glider and other aircraft is the lower stall speed of the hang glider relative to turbulent gusts. One is more likely to encounter turbulent gusts that can quickly reduce the hang glider’s air speed to below its stall speed. Therefore a hang glider is often found in flight regimes, where nonlinear aerodynamic characteristics are dominant (below stall speed).

There are also other non-linearities at lower angles of attack (AoA). These have to do with variation in wing twist and airfoil shape (wing flexibility). Good examples can be found at http://www.willswing.com/launch.asp?
theCategory=support&link=frmSupportPage.asp. More interesting is the effect on tumbling of the wing’s characteristics at high AoA (stalled wing), because they are inherently nonlinear (regardless of wing flexibility), and are very hard to quantify using the classic mathematical analyses.

Angelos's quest is for positive pitch at high AoA (roughly speaking). I claim that it is not possible to design glider with positive (stable) pitch moment about the hook-in point at high AoA (with a stalled wing). Why?

To explain this one should forget about the neutral point, pitch moment about some point, and so on. Concentrate on theCENTER OFPRESSURE (CoP). CoP is the point where the lift acts and where it can be totally balanced by our weight. In the next 2 pictures we see the movement of this CoP in first an unstable and secondly in a stable airfoil (glider). What can be seen, is that regardless of airfoil shape (similar to wing twist), CoP suddenly jumps aft to 50 % of the cord length at stall AoA. This leads to a strong pitch downward.

The third picture shows typical movement of CoP for both airfoils (glider). At angles above 45° drag becomes greater than lift and produces similarly strong pitching. Even though it is essentially impossible to eliminate this pitching (because of long arm), I think that in some way it could be improved by better stalling characteristics. It is desirable, that when CoP starts moving aft, lift should drop as soon as possible to as low a value as possible. In the forth picture, the blue curve represents potentially better glider. To be sure, we must also look at the location of CoP.

Unfortunately, stalling characteristics of airfoil can be affected only within a limited range of AoA, because fully separated flow is relatively insensitive to the airfoil shape. However, in the case of the whole wing it can be different. I don't have available any measurements of actual gliders at very high AoA. It would be interesting to compare these results for flex- and rigid wings.

There is a similarity in the requirements for good stalling characteristics to reduce the chance of tumbling and to increase the chances of having a good landing. The motion of a stalled glider is controlled by the loss of lift and by onset of strong pitch down forces. Loss of lift alone causes only slow curvature of flight path (tuck?), whereas pitching down rotates glider very quickly around the CG and moreover causes even greater loss of lift. In a tumble it is desirable to reduce pitch down moment, though at the expense of greater loss of lift. The same applies to landing. Lower pitching moment will result in smaller sensitivity to late pushing out, and it will not cause frontal whack after an early flare.

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