Are all your airfoils obsolete?

[TomM]

http://www.bicambertechnology.com/index.htm

I've been reading this site trying to figure if it's a real benefit for modeling or not, what types of applications like speed range and size, good for sailplanes, AP platforms, heavy lifting??? The more I read the more I wonder if it's snake oil. Can't find much info other than the self promotion sites and patent info. I'm wondering if anyone has tried modeling a design like this.

[Sparky Paul]

Build that "bi-cambered" wing that fits on a plane whose flying qualities you know well.. and fly it.

[Jim_Marconnet]

For a little more info, look up US patent No. 5,395,071

Airfoil with bicambered surface

Abstract:
An improved airfoil using bicambered surfaces to promote laminar flow, attached flow, reattachment of flow, delayed flow separation and to achieve high angle-of-attack performance. Bicambered surfaces introduce alternating favorable and adverse pressure gradients to achieve enhanced flow control.

Inventors: Felix; Frederick L. (Camp Douglas, WI)
Appl. No.: 08/119,353
Filed: September 9, 1993

I found it easily at: http://www.uspto.gov/patft/index.html

It's available in full text and also the images, but my QuickTime is acting up, so I did not get to see the images.

Hope this helps!
Jim

[rcjetpilot]

An interesting concept for sure.

Bob.

[JetPlaneFlyer]

Some very impressive claims made for sure... However there is a complete lack of objective evidence to back up the claims.

I'm not dismissing the concept but if the claims of 60% improvement in lift were true I'd have expected to see some solid evidence... Independant wing tunnel tests or something.

Just my thoughts..........

[JetPlaneFlyer]

I thought that it would be interesting to run the Bicamber section through a wind tunnel simulation... I have a great little program called Profili which is ideal for this. I downloaded the image of the Bicamber airfoil from the web site and traced it very accurately in CAD... I then imported this into Profili. Profili reported the section as having 4.4% camber and 11.6% thickness, so I selected a few conventional airfoils that were a close match to these figures. I then ran Coefficient of lift (Cl) and Coefficient of drag (Cd) graphs for these airfoils. The resultant graphs are shown on the attached image.

CL graph:
You will see that all the airfoild are matched quite closely which is to be expected given similar camber and thickness. The Bicamber section is generally mid range with a small peak at 8 Deg AoA before levelling off.

Cd graph:
The conventional sections are grouped tightly however this time the Bicamber does stand out from the crowd but for the wrong reasons... Is shows a much higher CD (ie much more drag) all the way from -5 Deg AoA right to +9 Deg AoA. Above plus 9 Deg it groups up with the 'worst' of the conventional airfoils.

These results do have to be taken with a pinch of salt as they are no substitute for proper wind tunnel testing but they are interesting none the less. Until proper wind tunnel tests are published they are more objective than anything I saw on the web site.

[TomM]

You're smart AND quick. I was thinking of putting it in Profili, but my thought was that if they're so tight lipped about test data, and the shape is patented, I wonder if the picture is an accurate cross section of the airfoil. Good work.

[The Other Dave]

I wonder if the picture is an accurate cross section of the airfoil. Good work.

If you are patenting somthing you want to have the description accurate
otherwise someone can come along with the "real" thing and patent it as well.

Unfortunately that is the problem with patents...get one and everyone knows
what you are doing..that's why most real corparate secrets are never let out these days.

[Sparky Paul]

Most airfoils have similar lift slopes.. it's at the high alphas where they seperate..:)
It is the drag part that counts, and in this instance.... the shape appears to have a permanent bubble, right where a plane would be using it.
Other than being more difficult to manufacture, it has no redeeming qualities. :(
Don't buy the stock.

[biber]

That bicamber thing is just funny,
some of the statements on that internet site seem to prove it nonsense to me.

Must be sort of an engineer's joke.

Or a joke on engineers, maybe? :rolleyes:

biber

[Sparky Paul]

It reminds me of the "Kline-Fogelmann" airfoil, which uses turbulence from the air trapped by the step on the airfoil to provide "thrust".
A seperation bubble top and bottom can't be good! :)

[BMatthews]

It reminds me of the "Kline-Fogelmann" airfoil, which uses turbulence from the air trapped by the step on the airfoil to provide "thrust".
A seperation bubble top and bottom can't be good! :)

Funny, I was just getting ready to type about that one as well until I saw your reply.

And remeber the terranced airfoil? A series of flat facets on the trailing edge that looked like a staircase.

As you said and as the charts show, they are all great until the going gets tough.

Now used in a far more viscous environment like water the results may well be totally different. Also even in air there's some past precidents. Remember the area rule fuselages that let the old early jets with the strongly swept wings go from just under to just over the sound barrier? But the reynolds numbers of a full sized fuselage operating at transonic speeds is a tiche higher than OUR usual operating range.

[biber]

They claim, the void between the two bumps will even lower the topsurface pressure,
because: with the excess space the air has to fill up to avoid vacuum. :rolleyes:

Generally I would expect the opposite: that excess space to increase pressure,
as only bumps/convex shape tend to lower pressure.

And in case of a separation bubble, why not fill up the dead air with airfoil?
Of course that would lead to a common style airfoil wich is not so well suited for patent... ;)

Oh, and to explain the better structural properties of the bone shaped airfoil
they take the shape of an I-beam like in a spar.
Only that their sort of 'spar' is tilted by 90°,
so that it is useless for carrying the main stresses on a wing (resulting from lift).
But if you fear, your wing could sweep unintendedly, then it is perfect!... :rolleyes: ;)

biber

[vintage1]

I simply look at bird wings..which have evolved into as near perfect wings for the purpose as its possible to get. Soarers?..look at a gulls wings. About what a sailplane has..want high lift but small turning circle and shorter wingspan..? look at the slotted tips on raptor wings..


I am sure if bumps worked, birds would have 'em.. They DO have quite 'rough' surfaces tho..

[Airboatflyingshp]

One word Bumblebees. ;) they shouldnt but they do............insects did the flight thing first Dragonfly's are tops.........but the relative viscosity gets to be more akin to a liquid the smaller you get. :D

[Flyingwingbat1]

This reminds me of the "pinched" airfoils that Dr. Drela uses for his sailplane tails to allow for more control authority (maintaining a smoother curve around the hingeline while fully deflected). But I'm not too sure about the reduced stall resistance/ higher Cl claimed. W/ real airfoils, especially our low RE ones, you can't curve them too much or the air separates. The 2nd outward bulge means the aft upper portion of the foil must plunge down STEEPER than a single slope going from a forward high point, and airflow tends to hate steep "backside" slopes on foils from what I understand. The downward sloping trunklid of the '96 Ford Taurus INCREASES that vehicle's drag compared to a more normal trunk profile (in addition to cutting trunk space, but that's another thread topic!)

[KSU Flyer]

Oh yeah???

I just applied for a "tri-cambered" airfoil patent! Take that bicambertechnology.com!

-Mike

[Flyingwingbat1]

Your tri-cambered wing will not beat my quad-cambered design made from unobtanium and impossibillium alloys (not to mention Composite Aggregate Reinforced D-board). It's so light it floats in air.

[biber]

Nothing beats a true multicamber!

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\_
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/

:p

biber

[Flyingwingbat1]

HA! Biber, your multi-camber airfoil is just a flat-plate at heart (draw a mean camber line to see what I mean) HERE's an even better foil...

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

The angle of attack of each segment is roughly 60 degrees which equals HUGE LIFT!! Don't bother me with facts, my theory is perfectly adequate to me. Not only that, the airfoil begins to spin and generate extra lift with ethanol supplementation (for the pilot). Doubt me? Just tape a pic of this airfoil design on the ceiling, and keep drinking...it will start spinning and soon be even farther above you.

[biber]

Naaaw, I say multicamber was just the beginning...

I proudly present...

The Magical Circular Eternit-O-Camber:

<I@I>

:eek:

biber

[Neil Walker]

It's just a matter of time until Apple comes out with iCamber, isn't it?

[MacMyers]

It's just a matter of time until Apple comes out with iCamber, isn't it?
This is a very amusing thread. Great work guys.

[Flyingwingbat1]

Introducing the end-all to end-all, the revolutionary CamberSphere. That's right, no matter which way you go on this perfectly spherical airfoil, there's always plenty of camber to be found! Optional fractal bumplets ensure it always has plenty of extra camber lines, no matter what scale you observe it at! Order yours today for only $2999.99!*







*CamberSphere does not prevent brain cancer, lung cancer, heart disease, erectile dysfunction, or tax hikes. Do not use under a physician's guidance. CamberSphere has a optional 3 year/36,000 mile warranty available for $599.99 extra. See dealer for details. Void in HI, WY, WA, CA, MA, WI, OH, IL, MN, SC, LA, AK.

[biber]

Ok fwb1, you win... ;)

biber

[Flyingwingbat1]

Hey, the Fwb1 sounds like a German fighter flown in WWII...I should build one! Now, should I use a bicamber technology or CamberSphere for the wing?

[biber]

Well, as there was plenty of weird technical details they tried out at that time,
it wouldn't surprise me if they already had such stuff too.
So it could be sort of hypothetically scale, I guess.

biber

[TomM]

HA! Biber, your multi-camber airfoil is just a flat-plate at heart (draw a mean camber line to see what I mean) HERE's an even better foil...

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

The angle of attack of each segment is roughly 60 degrees which equals HUGE LIFT!! Don't bother me with facts, my theory is perfectly adequate to me. Not only that, the airfoil begins to spin and generate extra lift with ethanol supplementation (for the pilot). Doubt me? Just tape a pic of this airfoil design on the ceiling, and keep drinking...it will start spinning and soon be even farther above you.


Now THAT one makes sense. The first airfoil grabs the air molecule. The second one lifts the molecule, while the third shears it off below stall level. The remaining airfoils apply lubricant and conditioner for a smooth flight.

[TomM]

Since the airfoil is patented, I decided to work on a "zero-drag" fuse.

The only problem is I went through 4 rolls of covering and I can't find the seams.

I thought the new wheel would solve axle alignment problems, but you actually gain speed every time you touchdown.

[Sparky Paul]

Introducing the end-all to end-all, the revolutionary CamberSphere. That's right, no matter which way you go on this perfectly spherical airfoil, there's always plenty of camber to be found! Optional fractal bumplets ensure it always has plenty of extra camber lines, no matter what scale you observe it at! Order yours today for only $2999.99!*


*CamberSphere does not prevent brain cancer, lung cancer, heart disease, erectile dysfunction, or tax hikes. Do not use under a physician's guidance. CamberSphere has a optional 3 year/36,000 mile warranty available for $599.99 extra. See dealer for details. Void in HI, WY, WA, CA, MA, WI, OH, IL, MN, SC, LA, AK.
.
Strictly speaking... a sphere has zero camber..
Now, an oblate spheriod can have camber!

[Flyingwingbat1]

No no Sparky, you got it wrong. You see, I'm measuring the sphere's camber at the surface; pretend it's a highly cambered, cupped wing that is exaggerated so much the LE, TE, and wingtips meet again at the bottom. The air will keep going round and round,producing lift all day long. See? My logic is infallible :p

[Sparky Paul]

No no Sparky, you got it wrong. You see, I'm measuring the sphere's camber at the surface; pretend it's a highly cambered, cupped wing that is exaggerated so much the LE, TE, and wingtips meet again at the bottom. The air will keep going round and round,producing lift all day long. See? My logic is infallible :p
.
I'd say your logis is more like.... dare I say... circular!

[MacMyers]

The first airfoil grabs the air molecule. The second one lifts the molecule, while the third shears it off below stall level.


HAHAHAHAHA ... thanks! I needed that. :D

[jkettu]

Originally Posted by Flyingwingbat1:
Introducing the end-all to end-all, the revolutionary CamberSphere. That's right, no matter which way you go on this perfectly spherical airfoil...

But symmetrical airfoils need positive AoA to generate lift. How are you supposed to get that? :confused: :p

[nmasters]

But symmetrical airfoils need positive AoA to generate lift. How are you supposed to get that?

Use a positive pitching moment airfoil. When the nose lifts it will act like backspin on a golf ball :rolleyes: Or put backspin on your symmetrical section to make it act like it has camber. Yaknow... like Flettner (http://images.google.com/images?hl=en&rls=com.netscape:en-US&sa=N&resnum=0&q=flettner%20rotor&ie=UTF-8&oe=UTF-8&tab=wi) :cool:

[Flyingwingbat1]

But symmetrical airfoils need positive AoA to generate lift. How are you supposed to get that? :confused: :p

Hey, go find your own balloon to pop :p

[Vegas_flyer]

Gone fishing

[Sparky Paul]

It'sa looka likea dis..

[Vegas_flyer]

Gone fishing

[Flyingwingbat1]

ah, a Ballistically Actuated, Linear/Logarithmic, Ovoid Operational ExpaNdable device. I made one of those once. Unfortunately, the concrete mixture proved too heavy and it broke through the outer finish...

[Flyingwingbat1]

Here is a drawing of one....

Color may vary....

I see the problem, you should've used a Klein nozzle on the end. It results in much better directional control, and better flight efficiency (the air can simply circulate around the B.A.L.L.O.O.N. to provide continuous thrust)

See the attached picture.

[BMatthews]

This reminds me of the "pinched" airfoils that Dr. Drela uses for his sailplane tails ....

Since I've got nothing funny to add I guess I'll go after this one.... :D

If you look at Dr Drela's designs I think you'll find that the hinge line of his conventional rudders and elevators is placed at the leading edge of the second "hump". This is done so that when you deflect the surface the air flows over a more rounded shape and tends to remain attached rather than separate from trying to follow around a sharp hinge line discontinuity.

So while it sort of looks like the bicamber it's not done for the same reason at all.

[Flyingwingbat1]

Since I've got nothing funny to add I guess I'll go after this one.... :D

If you look at Dr Drela's designs I think you'll find that the hinge line of his conventional rudders and elevators is placed at the leading edge of the second "hump". This is done so that when you deflect the surface the air flows over a more rounded shape and tends to remain attached rather than separate from trying to follow around a sharp hinge line discontinuity.

So while it sort of looks like the bicamber it's not done for the same reason at all.

Yeah, that was how I saw it; I didn't mean to imply that he used the same reasoning as the folks at bicambertechnology.com. I thought of using his idea on a combat flying wing some time ago; right now I'm out of the R/C "thing" due to financial constraints, but that reminds me of what's so nice about semi-freeflight (aka indoor slope soaring); it's cheap!

P.S. posts here are invalid unless there's something funny in them; you better come up with something clever real quick! :D

[biber]

Of course the germans had already multicamber,
but unfotunally they failed to apply it in the propper direction...

biber

[Flyingwingbat1]

LOL, those Germans thought of everything it seems! :)

[eflightray]

I remember a long time ago on TV they showed a yacht with a parallel chord 'wing' sail, that had a varying airfoil camber for easier tacking.

I have done a rough sketch below. I hope it's self explanatory.

But like a lot of new inventions brought out to replace the old tried-and-tested, you don't seem to see them again.

[biber]

It looks cool, but I guess it's a solution to an nonexistent problem. ;)

biber

[macboffin]

There was a world war 1 airplane (a quadraplane, ie four wings instead of three like a triplane) called the Morse produced in 1917 using this section.High climb rate but very draggy, the section was patented at the time.The actual airplane still exists in a private museum near Bournemouth England in company with a few other more modern aircraft.Saw it in 1971.

[macboffin]

There was a world war 1 airplane (a quadraplane, ie four wings instead of three like a triplane) called the Morse produced in 1917 using this section.High climb rate but very draggy, the section was patented at the time.The actual airplane still exists in a private museum near Bournemouth England in company with a few other more modern aircraft.Saw it in 1971.

[Julez]

Hi!

A friend here told me some time ago about this kind of concept. Many airfoils have a laminar separation bubble.
See first drawing here. (http://www.mh-aerotools.de/airfoils/bubbles.htm)
The attempt was to make a dent into the airfoil at the position of the bubble. The bubble was supposed to fill up the dent, so that the original airfoil shape was restored.
The problem is: Laminar separation bubbles move depending on the Reynolds number and the angle of attack. Hence, the "dent- concept" only was successful at one airspeed with one angle of attack.
In all other situations the dent- airfoil was inferior to the original shape.

Nowadays, there are more promising concepts for eliminating separation bubbles. The best I know of is the bubble- ramp. The airfoil's layout makes sure that the pressure rise in direction towards the trailing edge is very smooth. This helps a lot. Mark Drela's sucessful airfoils use this concept.


To sum the whole thing up, these multi- cambered airfoils seem to promise more than they can keep.

Cheers,

Julez

[Julez]

Just for kicks, I modified the well- known Clark Y Airfoil to become a bicamber version. As expected, bicamber sucks big time in most situations.
However, it has advantages in the Re50k range below cl0.8, where the normal Clark Y is obviously stalled.

I defined a turbulent transition at 20% on the normal Clark Y and ran the Re50k test again. What a surprise: Bicamber looses.

In the polars shown below, "Clark Y" ist the Bicamber version while "Clark Y Airfoil" is the normal version.

Cheers,

Julez

[Julez]

http://www.sunny-boxwing.de/tandempropeller.htm

Quite interesting: This website claims, that, when used on a propeller blade, the dent in the shape produces a suction due to centrifugal effects, which slightly increases the propellers efficiency, as the laminar separation bubble is sucked away.

[Batmanwpg]

JetPlaneFlyer
Your test in Profili @ 200K Re might be low for this full size section. Bump up the Re and lets see what it does?

[MarkusN]

If you are patenting somthing you want to have the description accurate
otherwise someone can come along with the "real" thing and patent it as well.

Unfortunately that is the problem with patents...get one and everyone knows
what you are doing..that's why most real corparate secrets are never let out these days.

Actually that's the deal with Patents: You provide the public domain with a clear description how your stuff works. In turn you get protection for a limited timespan.

That way inventions don't get lost and the inventor has an incentive to publish it.



I have serious doubts if these profiles deliver what is claimed. However, checking them with current digital wind tunnel software is probably not such a good idea, since these are based on theories that lead to the current profile designs. So if the concept does work, Profili could probaly not calculate the results properly.

[JetPlaneFlyer]

There is not one jot of evidence to support the incredible claims made for this airfoil however I think the most telling fact is that the patent was filed about 14 years ago but there is still no significant uptake of the technology and no hard factual data on its performance...
Maybe I'm just too cynical :rolleyes:

Steve

[macboffin]

Comment one ; "Bullxxx baffles brains". Comment two. During World War 1, a guy called Morse produced a prototype fighter with this wing section, with similar claims. Climb performance was good, but other wise no good. High drag in cruise, and dangerous stall characteristics. Aircraft were a Triplane version and a Quadraplane version. The Army didn't buy them! The quadraplane version is in an aircraft museum in Southern England, near Bournemouth, as an interesting relic.

[rroyce]

It reminds me of the "Kline-Fogelmann" airfoil, which uses turbulence from the air trapped by the step on the airfoil to provide "thrust".
A seperation bubble top and bottom can't be good! :)

Not quite the way it works. The step creates a downflow into the stepped area and it sticks to the wing a bit better and increases the distance the airflow travels over the top of the wing when used on the upper surface of the wing.
There is a good tread on this wing on the scatchbuilt foamie section of this group. There are many happy users. They don't seem to care how it works but only that it does work.