Robert CarrÆs Intenal Wing

[joedunai]

Robert Carr has patented his idea about internal wings in 1986 (US Patent # 4,568,042; and US Patent 4,579,300) which can be found on the page

http://www.rexresearch.com/carrcoan/carrcoan.htm

.

The man is obviously not an expert of fluid dynamics, but his idea is still interesting. There is a good reason why his internal wings didn’t replace the conventional airfoils even after 2 decades.

Consider the Fig. 4 of US Patent # 4,568,042 which is attached to this post. A high velocity air stream is injected over the curved surface at the bottom of the internal wing. This supposed to decrease the pressure over the surface, and establish a vertical pressure gradient. The pressure at the top of the duct claimed to be higher than that at the bottom, thereby generating a vertical lift.

My question is whether it would be indeed possible to generate a significant lift and/or torque with this setup? If yes, then would it still work if the duct would be very long compared to the cross section (like in an infinitely long duct)?

 

[rb1957]

as a wing i see this as being impractical ... a wing is a large surface ... to add the "duct over the top of it would mean a very high drag, no?

as a duct, surely it can be profiled to compress the airflow, and gas and you have a ramjet (a la V1). the airflow does work against the duct, work supplied by the combustion explosion. typically the ducts are symmetric. if it was unsymmetric would there be a net force ? not so sure, but if the symmetric duct applies the work symmetrically, then an unsymmetric duct would apply the work in an unsymmetric dist'n ... but looking at the set-up from outside, i don't see anything different as far as the rest of the world is concerned (between a symmetric and unsymmetric duct).

 

[KENAT]

Cylindrical/Annular wings have been investigated before.

http://en.wikipedia.org/wiki/Wing_configuration

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[btrueblood]

At least one of the heavy-lift cargo planes for the USAF uses blown flaps, so the idea isn't too nuts, and the idea of a blown wing or blown flap extends at least back to WW2 (I think there was work done by Messerschmidt on the ME109?). But I don't see how adding a duct over the top of the blown wing adds much, other than drag as rb notes. I think the proportions of his internal wing/duct are way too elongated also, i.e. any low-pressure region created by his blower is going to decay pretty rapidly, so most of his duct (as depicted in said Fig. #4) seems like wasted space/volume.

 

[rb1957]

blown flaps are one thing ... de havilland did a project with NASA which converted their DHC-5 Buffalo to an advanced STOL with bolown flaps ... worked a treat, except the fuselage was Full with ducts (cross-ducting the blown system in case of an engine out).

boundary layer suction is another different thing that'll come to mind ... see the UK's Blackburn Buccaneer ... a very successful ground attack plane designed in the 60's.

one confusion i had is the sketch shows a section through the fuselage, but the "internal wing" structure will have to extend the full span.

 

[KENAT]

I took the implication to be that you'd have a 'flying body'. Essentially no wings as such.

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[IRstuff]

Some of the verbiage seems to be at odds with physics. How do you get thrust from a passive system? Conservative of energy and momentum would seem to violated.

TTFN
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[joedunai]

Thanks everyone for the comments.

As rb1957 pointed out, the internal wing is certainly impractical as the main source of lift for an aircraft, due to dead weight of surfaces that don’t generate lift.

The remark of btrueblood that “the idea isn't too nuts” is also important, because the pressure drop over the blown bottom surface is a valid physical phenomenon. Checked out the “Blackburn Buccaneer” and the blown flaps on Wikipedia, but they mention only one reason for blowing air over the surface, namely to reduce airflow separation.

The full description of the patent of our concern US Patent # 4,568,042 with more figures can be found at the middle of page:

http://www.rexresearch.com/carrcoan/carrcoan.htm

. Let’s skip the other two articles above this patent for now, because those indeed contain some “verbiage that are at odds with physics” as IRstuff mentioned. The patent doesn’t claim that the internal wing as a passive system would generate thrust. The thrust and the compressed air blown over the bottom surface of the internal wing are provided by the jet engine. The brave claim that “This arrangement of airfoils reduces drag, enhances lift and thrust output” is in the article at the top of page referring to a different wing structure (triple airfoils). Let’s ignore these articles for now for better focus.

Nevertheless, even if the invention is not practical as an aircraft wing, and even though the inventor’s understanding of fluid dynamics is lacking, the basic idea may be still useful for other applications. The ultimate answers could be obtained by building and testing the structure in real life which is out of question for now. The second best, to perform a CFD analysis is under consideration, but before doing so, it makes sense to ask CFD expert opinion. With sufficient experience a CFD expert can assess fairly well the pressures, forces and torques at least qualitatively even prior to running the simulation. I don’t have this level of CFD experience and expertise, so best to ask those who have it.

Let me define more clearly what I am interested in. Let’s approach the structure of interest step by step.
1.) First we have high velocity air (or other fluid) blown over a curved surface resembling an airfoil. Due to Ventury effect there will be a reduced pressure area above the surface which generates lift. In this setup the upper wall of the duct is either missing or is very far away from the examined bottom. I suppose that this far we are correct.

2.) In the second step let’s modify the setup by introducing the upper wall of the duct, and move it towards the bottom decreasing the gap. As the gap decreases the pressure difference between the bottom surface of the top wall and the upper surface of the curved bottom wall will decrease, i.e. the lift will decrease. Let’s find an optimum distance which will not require an impractically large duct, but still yield a significant lift.

3.) In the third step let’s extend the length of the duct to be much longer than the effective curved blown surface which generates lift. We could imagine a theoretically infinitely long duct allowing the injected air to escape through holes on the side walls at a long distance from the injection. Another option is to make a toroid duct having the inlet and outlet connected. In this case the injected air could be extracted at a point 180 degrees from the injector on the sides of the duct.
Here comes the big question:
a) do we still have a lift on the duct?
b) do we have any torque on the duct?

Or generally at what step of our imaginary experiment do we loose the lifting force and/or torque on the duct if it is lost? What will cause the counter force/ counter torque that would cancel the lift and torque measured in the first step?

Perhaps I should have posted this thread in a section specialized for CFD analysis, but hope the experts will find it here as well.

 

[thruthefence]

How can you guys argue with a "thumb over a garden hose" analogy?

I'm ready to invest.

 

[KENAT]

1) I'm not sure you're correct. It's not fundamentally the curve of a typical aerofoil that generates lift.

Also joedunai, you seem to have a slight misunderstanding of the difference between an aerodynamicist and their potential use of CFD. CFD is not the be all and end all.

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[rb1957]

me, i'm keeping my money.

there may be something in an asymmetric venturi duct ... a symmetric venturi causes symmetric work on the airflow, compressing it uniformly; the work done on the opposite sides of the duct cancel out each other. would an asymetric venturi prodcue a net force ? i don't think so.

 

[btrueblood]

It would need to be a short duct, to prevent the local pressure gradient from being "felt" on the opposite wall. So, optimizing...shorter is better, and a distant or no upper wall is better...which leads to the blown wing that Rb describes.

My bill for the highly parallel CFD processor installed between my ears is a pint, please.

 

[IRstuff]

Look that it this way: will this system have as good lift as a plane with a single wing with the same surface area?

> No, because the upright sections that hold the structure together don't generate any lift, and is therefore dead weight
> No, because the uppermost wing, at best, generates the same equivalent lift, but potentially generates less lift because of the faster flow of air under this wing.
> No, because the lowermost wing has downward moving air impinging on it, thereby applying a negative lift force against that wing, partially negating any lift it might have generated by itself

The end result is barely one half of the incurred weight can produce lift, so it's inefficiency causes the weight of the plane to increase with little added benefit.


TTFN
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[KENAT]

I'm far from convinced it would fundamentally work at any significant level (rb1957 thinking about unsymmetrical venturi kind of captures my doubts though btrue makes valid points regarding proportionate length of duct) however, if it does vaguely work I could imagine it might have more applicability in motor racing or something than in aircraft.

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