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Old May 13, 2015, 11:07 PM
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About that golf ball design

So I'm thinkin' they've been playing golf for quite a while now. And I wonder about when did they decide to put dimples on them. I doubt if they did wind tunnel tests or had any type of graphic simulation. What ever made them decide to dimple 'em ?
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Old May 13, 2015, 11:43 PM
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Build straight - Fly twisty
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The early golfers noticed that the ball went a greater distance when it had been dented all over due to repeated bashing.
So they started to make new balls already dented.
Scientists did not come up with the concept but they were able to explain the effect that had been observed by the players.
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Old May 14, 2015, 01:52 AM
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Ha Ha, Thanks ! They were pretty observant. I wonder if they had little guys with little tap hammers peening them to put in the dimples after they figured it out
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Old May 14, 2015, 03:10 AM
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"Use the foam, Luke!"
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Quote:
Originally Posted by Dickeroo View Post
SpaceDrydock-22....

In the 1930s, a German aerodynamicist shocked the racing world when he chopped off the rear end of a tear-dropped shaped racing car. He was told that it would never work. Instead, the flat rear end of his racing car proved to be more efficient. Today, most cars come with blunted rear ends. Even the hybrid cars, because they are more fuel efficient. The Boat-tail rear end creates a trapped vortex. So it does seem to work on a full scale object.

In the 1950s, Detroit couldn't understand why their station wagons were more fuel efficient than their sedans. It was the Kamm Effect which was invented by Wunibald Kamm back in the 1930s.

That was a terrific video you produced with your ribbed wing.
Interesting stories about the Kamm Effect. And thank you about your kind words of the video.
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Old May 14, 2015, 03:25 AM
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"Use the foam, Luke!"
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Quote:
Originally Posted by zsumo View Post
SpaceDrydock-22

The test glides in the beginning of the video perfectly illustrate what I said about good balance producing a straight glide - although there is a very slight aft CG in the trim which then shows up in the powered flight section as a slightly droopy tail. This could also be due to what appears to be a zero degree angle of incidence to the main wing ... when flying it goes to a positive angle of attack to develop lift, which drops the tail a bit ...
You are just right about your observations.


Quote:
Originally Posted by zsumo View Post
The golf ball stuff I had encountered before (used to play to 13 handicap) good links there, thank you - will study with interest. The principle extends to some interesting stuff in the animal kingdom. I will relate some detail about sharks in my next post. But now we are entering very interesting biomimetic territory ...Try these links to shed some light on what is happening with your fluted wing ... dragonflies apparently know a thing or two about flight at low Reynolds numbers ...

http://engineering.jhu.edu/fsag/wp-c..._Exp2005VA.pdf
I have these two files attached here from my archive of interesting research docs ...
dragon flies ... and humpback whales are getting in on the act as well ! ....
I am familiar of the dragonfly wing research docs and I am going to build a wing with that profile in bigger scale and test how it will work with rc plane. I think the result is a real slow flyer.

The humpback whale document is new to me, very interesting stuff. Thank you!
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Old May 17, 2015, 05:01 AM
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I crashed my plane today because of a trouble with the video link.

So no kfm airfoil tests will be done before a long time I'm afraid...

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Old May 17, 2015, 08:39 AM
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Are you sure it was not pilot error? That is the most common cause.

We'd probably accept it as a contributing factor at the least...

Jack
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Old May 17, 2015, 03:15 PM
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Well, maybe I could have anticipated the video failure, but in FPV with no video there was little I could do...

The plane will fly again, but I have now to spend some time understanding the reason of the video failure
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Old May 17, 2015, 07:59 PM
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I'm sure you will, and it it was not clear I meant that as a joke. I read it now and it reads like I was accusing you of telling a lie. I didn't use enough smilies or something!

Jack
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Old Yesterday, 05:32 PM
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Here is a paper that introduces a jet flow on two different airfoils....

ICABB 2014 : 16th International Conference on Applied Biomaterials and Biomechanics September 2014

http://www.waset.org/abstracts/10869

EFFECT OF CO-FLOW JET ON KLINE FOGLEMAN AIRFOIL
Authors:
Shibin Mohamed Jeevan J
Abstract:
An airfoil section, which is the essential part of a wing, has its primary task as a lift generator. The proper functioning of the airfoil is the prerequisite to the satisfactory performance of the lifting surface. CO-FLOW JET technique is the most efficient flow control technique researched till date to effectively delay the flow separation thereby increasing Lift, the operating AOA & the Stall margin. The CFJ (co-flow jet) utilizes tangentially injected air at the leading edge and tangentially removed air at the trailing edge to increase lift and stall margin and also decrease drag. The mass flow rates of the injection and suction are equal, so there is a zero net mass flow rate. Kline Fogleman airfoils were initially tested by NASA and were found to offer little or no advantages when compared to the conventional Airfoil and was claimed to have high drag accordingly with lift. In the present study, computational simulations were carried out to verify the performance Characteristics of the co-flow jet principle which when applied on to a Kline Fogleman Airfoil. The NACA 23015 airfoil was selected for the analysis procedure. It was initially converted into a Kline Fogleman type-2 airfoil by making a top cut or a step at 50% of its chord length. The airfoils thus drafted by CATIA software were meshed and analyzed using CFD Fluent software. Analysis was carried out with and without CFJ for both airfoils at different Angles of Attack of -5, 0, 5, 10, 15 & 20 degrees. Sea level conditions were assumed for the computations. The flow was assumed to be 36m/s (subsonic). It was observed that a considerable increase in lift was observed by the application of CFJ & also among the conventional and Kline Fogleman Airfoils the Kline Fogleman Airfoil displayed a greater increase in lift. The turbulent viscosity contours for each airfoil at different Angle of Attacks was observed. The CFJ aided in vortex trapping in case of the Kline Airfoils thereby increasing lift.
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Old Yesterday, 05:47 PM
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Quote:
Originally Posted by Dickeroo View Post
Here is a paper that introduces a jet flow on two different airfoils....

ICABB 2014 : 16th International Conference on Applied Biomaterials and Biomechanics September 2014

http://www.waset.org/abstracts/10869

EFFECT OF CO-FLOW JET ON KLINE FOGLEMAN AIRFOIL
Authors:
Shibin Mohamed Jeevan J
Abstract:
An airfoil section, which is the essential part of a wing, has its primary task as a lift generator. The proper functioning of the airfoil is the prerequisite to the satisfactory performance of the lifting surface. CO-FLOW JET technique is the most efficient flow control technique researched till date to effectively delay the flow separation thereby increasing Lift, the operating AOA & the Stall margin. The CFJ (co-flow jet) utilizes tangentially injected air at the leading edge and tangentially removed air at the trailing edge to increase lift and stall margin and also decrease drag. The mass flow rates of the injection and suction are equal, so there is a zero net mass flow rate. Kline Fogleman airfoils were initially tested by NASA and were found to offer little or no advantages when compared to the conventional Airfoil and was claimed to have high drag accordingly with lift. In the present study, computational simulations were carried out to verify the performance Characteristics of the co-flow jet principle which when applied on to a Kline Fogleman Airfoil. The NACA 23015 airfoil was selected for the analysis procedure. It was initially converted into a Kline Fogleman type-2 airfoil by making a top cut or a step at 50% of its chord length. The airfoils thus drafted by CATIA software were meshed and analyzed using CFD Fluent software. Analysis was carried out with and without CFJ for both airfoils at different Angles of Attack of -5, 0, 5, 10, 15 & 20 degrees. Sea level conditions were assumed for the computations. The flow was assumed to be 36m/s (subsonic). It was observed that a considerable increase in lift was observed by the application of CFJ & also among the conventional and Kline Fogleman Airfoils the Kline Fogleman Airfoil displayed a greater increase in lift. The turbulent viscosity contours for each airfoil at different Angle of Attacks was observed. The CFJ aided in vortex trapping in case of the Kline Airfoils thereby increasing lift.
Not bad my friend. Not bad at all.
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