Lift Produced Where Wing Transects Fuselage

[Jane-DoH]

I don't know exactly what you call this, but I remember hearing that to some extent the area between the left and right wing "counts" for producing lift

[Lord Spandex Masher]

OK. Thanks.

[Jane-DoH]

Well what do you call this?

[FlightPathOBN]

its the wingbox...

Wingbox - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Wingbox)

[Mad (Flt) Scientist]

Wingbox is a structural term.

I'm not sure there is a specific aerodynamic term for what you describe - wing-body lift would include all of the wing contribution, not just the 'carry through' term. The wing does get some benefit (or decrement, if you considered an isolated wing) from being on a fuselage (or vice versa if you prefer) but the theoretical wing planform in the fuselage is purely that - theoretical.

[Jane-DoH]

Mad (Flt) Scientist

I'm not sure there is a specific aerodynamic term for what you describe - wing-body lift would include all of the wing contribution, not just the 'carry through' term.

So wing-body lift includes both the lift of the wing and the part that is "in the fuselage"?

The wing does get some benefit (or decrement, if you considered an isolated wing) from being on a fuselage (or vice versa if you prefer) but the theoretical wing planform in the fuselage is purely that - theoretical.

What variables increase this benefit? I assume a fuselage that was flattened where the wing intersects it, had wing-body fairings to blend it together and/or it's intakes were flatter than deep (if they were in the wing-root) would have better overall wing-body lift?

[grity]

have a look at this nice picture, it shows, through condensation, the distribution of lift on an airplane during a high-g maneuver
http://home.comcast.net/%7Eclipper-108/Image26.gif
it is from:
A Physical Description of Lift (http://home.comcast.net/%7Eclipper-108/lift.htm)

and the lift over the fuselage in this case looks not like in some more teoretical pictures with lift over the fuselage

http://t3.gstatic.com/images?q=tbn:ANd9GcTCLKZmiZzLdekpLXBH6EKV1OcqnaViUS-6Os_YT1ZT8qk3nUljSw

[balsa model]

In my naive wing model, it goes like this:
The extant fuselage length, trailing behing the wing box, interferes with the development of lift vorteces from this part of the wing. No vortex, no lift.

Lifting body would not be a counter-example because in that topology, the fuselage is not really trailing. The lengths are balanced.

(Definitely waiting to be corrected - I'm still mentally struggling with the role of viscosity - I know it's essential)

[bearfoil]

Hi Jane-doh

Hope you are safe. I was about to bring up 'lifting body', parasite fighter, and 'gremlin'.

Many folks disapprove of lifting body, NASA liked it well enough to base the Shuttle on it.

Problem? Intuitively, and visually, things that don't look like wings make Bernoullians anxious.

Newton. Deflected energy can "lift". Simples. Bernoulli was a Swiss 'plumber'.

[Mad (Flt) Scientist]

@Jane-Doh

So wing-body lift includes both the lift of the wing and the part that is "in the fuselage"?

No. Wing-body is the term we use at my current (and indeed former) employer to mean the total lift of both wing and body, but excluding the tailplane contribution. Taill-off is commonly tested in wind tunnel development so it's useful to have a term for that condition. It therefore includes the TOTAL fuselage contribution.

What variables increase this benefit? I assume a fuselage that was flattened where the wing intersects it, had wing-body fairings to blend it together and/or it's intakes were flatter than deep (if they were in the wing-root) would have better overall wing-body lift?

Generally, wing/body interface design, at least in the commercial world, is concerned more to address drag than lift. If you need more lift its generally better to add more wing than to make the fuselage lift more - the fuselage is a poor lifting device. Obviously the fuselage does generate some lift, and you wouldn't want to throw it away, but it's not a design criteria usually.

@grity

Interesting pic, but be careful of assuming that the low pressure region is directly proportional to lift. The fuselage is relatively long chord, so a much lower pressure drop will, integrated over the longer "chord", create proportionately more lift. But, yes, the diagram of the SEP is over simplified - usually a fuselage degrades lift compared to the isolated wing.

[barit1]

Interesting historical trivia:

Benny Howard's DGA-8 through DGA-12 SE 4-place cabin aircraft were 38' span high-wing monoplanes. The wing area was quoted as 185 sq. ft.

Then the DGA-15 was derived from the earlier ships. Same 38' span, same chord, but now the area was quoted as 210 sq. ft.

I have determined that the difference of 25 sq. ft. corresponds to the "wing box" area - the wing chord times the fuselage width. So the difference is simply a difference in method of calculation.

[Mad (Flt) Scientist]

The ESDU data sheets used to contain various variants on the calculation of wing area, depending on what you planned to use it for.

[grity]

Interesting pic, but be careful of assuming that the low pressure region is directly proportional to lift. The fuselage is relatively long chord, so a much lower pressure drop will, integrated over the longer "chord", create proportionately more lift. But, yes, the diagram of the SEP is over simplified - usually a fuselage degrades lift compared to the isolated wing. I think the cloud over the wing shows an "3D iso-presure-surface", you are right it says nothing over a mayby slower lift above or below the fuselage, but it shows that in this case, the lift over the inner part of the wing is reduced

[bearfoil]

It is such a disappointment to learn of the lack of relationship (directly) in the area of Lift indicated by the "Cloud".

May I use Drag, instead? It seems a natural: greater drag, less integrity of the 'cloud'?

[boguing]

Jane-DoH

You have a record of asking some very interesting questions.

This one has me thinking that we are both querying the same accepted theory.

Feel free to pm.

[FlightPathOBN]

Jane...

My experience in these design parameters is in the subsurface realm, but the principles of air being thin water should apply.

Bernoulli's principle is generally explained by the argument that the faster speed of the air along the top of the wing leads to reduced air pressure above and hence produces a lift.
Given this, simplistically, one would rationally surmise that the fuselage negates this basic couple.

If we look at Bernoulli's Laws, or what is the common explanation of wing aerodynamics. Airfoils are curved on top and flat below, and therefore the air follows a longer path above than below. Since the upper surface of the wing is longer, it causes the upper air to flow faster than the lower, which (by Bernoulli's principle) creates lower pressure above. According to this pure principle, a wing can create lift at zero attack angle, and do not deflect air, the air behind the wing is flowing the same as the air ahead. Are there any real time examples of the wing section at zero angle providing lift?
We have all seen the diagrams, with the airflow coming together nicely at the back of the wing, in a straight line with the air from below.
http://www.allstar.fiu.edu/aero/images/FOIL.gif
To add further issue, given what we have seen in wake vortex creation, does that seem plausible?

Then again,
If we look at Newtons Laws, using principles of Newtonian Angle, wings are forced upwards because they are tilted and they deflect air. The air behind the wing is flowing downwards, while the air far ahead of the wing is not. Both the upper and lower surfaces of the wing act to deflect the air. (which would answer your question regarding the surface between the wings creating lift) The upper surface deflects air downwards because the airflow "sticks" to the wing surface and follows the tilted wing, called the "Coanda Effect" (marine thrusters and ducted fan UAV's). (note: while flaps radically effect lift, they add no surface length over the wing, this appears counter to Bernoulli)
For this to be applicable, air's inertia is critical, so after the wing has passed by, air must remain flowing downwards...sound familiar, ie wake vortex creation?
http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/04/wirbelschleppe1-300x190.jpg

Given that....

Newton and Bernoulli do not contradict each other. Newton's Laws based on air deflection explain 100% of the lifting force. Bernoulli's Laws based on air velocity also explain 100% of the lifting force.

Hope this helps. :D

I will be appearing here from 9 to 10 Monday thru Friday, please tip your servers....

[Jane-DoH]

grity

have a look at this nice picture, it shows, through condensation, the distribution of lift on an airplane during a high-g maneuver

That's an F-14. As I understand it, the pancake produces the most lift at high alphas, at supersonic speeds with the wing swept back...

and the lift over the fuselage in this case looks not like in some more teoretical pictures with lift over the fuselage

What if the wing's in the middle of the fuselage?


bearfoil

Hope you are safe. I was about to bring up 'lifting body', parasite fighter, and 'gremlin'.

Gremlin?

Many folks disapprove of lifting body, NASA liked it well enough to base the Shuttle on it.

Problem? Intuitively, and visually, things that don't look like wings make Bernoullians anxious.

Well, the laws of physics are what they are regardless of what you believe them to be. If I believe the sky's green and it's blue, my belief doesn't change the sky's color; the sky's blue.


Mad (Flt) Scientist

No. Wing-body is the term we use at my current (and indeed former) employer to mean the total lift of both wing and body, but excluding the tailplane contribution.

The tailplane reduces overall lift doesn't it?

Taill-off is commonly tested in wind tunnel development so it's useful to have a term for that condition. It therefore includes the TOTAL fuselage contribution.

So the term "tail off" includes total fuselage contribution to lift? I assume it doesn't include the tail... (Not to sound stupid, but I want to know if I'm wrong).

[CliveL]

If I may cut in ...

The distribution of lift across the span from fuselage centreline to wing tip on a typical subsonic airplane looks like this:

http://i1080.photobucket.com/albums/j326/clivel1/spanloading.jpg (http://www.pprune.org/%3Ca%20href=)">

The bit over the fuselage is usually described as 'wing/body carryover' It comes about because the airflow cannot tolerate a sudden drop in pressure where the wing root flow 'passes by' the fuselage so there is a 'smearing' of the pressure through a spanwise pressure gradient. Where the LH gradient meets the RH gradient pressures are equal.

You can have any definition you like for wing reference area so long as you stick to it. Some use a line across the fuselage joining the two wing root LE points (and/or TE root) others use the projection of LE and TE through to the centreline.

Wing body lift is just that - wing plus body without tail or nacelles. Just a remark that at normal civil aircraft AoAs, even up to stall, the fuselage lift per se is pretty small, although there is lift in the wing region as above.

That picture of the F14 is showing condensation in the wing vortices. This is associated with the drop in static pressure in those vortices. The drop is biggest at the centre of the vortex so the 'outer' boundary is just a region where the pressure has not dropped enough to cause condensation - it doesn't mean that there is no lift from the aircraft surface underneath that point.

[bearfoil]

Sorry Miss Doh.

goblin

Blue? By agreement only! Observation creates reality?

[Jane-DoH]

bearfoil

Well, the sky's coloring is kind of a bluish color in day-time with some white and gray (clouds) and yellow if you're looking at the sun, very dark blue to black at night excepting the stars, various shades of red, orange, pink and so forth during sunset.

The point is that no matter what you believe the color to be, the sky is a given color in a given location. These colors can be measured in terms of wavelength.


R.C.
"That being said, I'd like to remind everybody in a manner reminiscent of the SNL bit on Julian Assange, that no matter how I die: It was murder (even if there was a suicide note or a video of me peacefully dying in my sleep), and should I be arrested or framed for a criminal offense, or disappear entirely -- I think we all know who to blame for it"

[bearfoil]

If you are truly fearful, and fear a trip to "jail", do not wear shoelaces, belts, or ropish jewelry.

"She must have hung herself with her _______".

What about the lumps on her head?

discretion is the better part.........

[Mad (Flt) Scientist]

Mad (Flt) Scientist
No. Wing-body is the term we use at my current (and indeed former) employer to mean the total lift of both wing and body, but excluding the tailplane contribution.
The tailplane reduces overall lift doesn't it?


CliveL answered the other one, and provided a very nice picture, so I'll just answer this one.

"contribution" may be positive or negative, but wing-body doesn't include it, whichever it is. Because it's generally a wind tunnel test thing, and you simply leave the tailplane (and indeed, anything else that takes your fancy) off the model.

Even when the tail IS fitted, wind tunnel models aren't (usually) tested with trimmed tailplanes, but rather with a range of tailplane angles to enable the tail effectiveness to be determined, so there certainly will be cases of both upload and download in most tunnel test sets.

[Jane-DoH]

bearfoil

If you are truly fearful, and fear a trip to "jail", do not wear shoelaces, belts, or ropish jewelry.

"She must have hung herself with her _______".

What about the lumps on her head?

discretion is the better part.........

What are you talking about?


[b]Mad (Flt) Scientist

"contribution" may be positive or negative, but wing-body doesn't include it, whichever it is.

What about the area of the tailplane that transsects the fuselage?

Because it's generally a wind tunnel test thing, and you simply leave the tailplane (and indeed, anything else that takes your fancy) off the model.

Even when the tail IS fitted, wind tunnel models aren't (usually) tested with trimmed tailplanes, but rather with a range of tailplane angles to enable the tail effectiveness to be determined, so there certainly will be cases of both upload and download in most tunnel test sets.

Aren't there issues with scaling effects?

[CliveL]

What about the area of the tailplane that transsects the fuselage?

Same rules as for wing.

Aren't there issues with scaling effects?

Not as regards how you specify wing and tail areas.
Of course there are the normal problems with overall forces and moments affected by the difference between wind tunnel and flight Reynolds Numbers, but they aren't relevant to your original question.

[Jane-DoH]

CliveL,

Same rules as for wing.

Understood

[HazelNuts39]

CliveL,

I wonder how the graph you reproduced in your post #18 is produced. Is it just an "artists impression", or perhaps an integration of a measured pressure distribution, or by calculation by CFD?

[Jane-DoH]

I just thought of something -- why didn't anybody (before area rule was implemented in the traditional sense) think of the idea of flattening the fuselage in between the wings?

It would make the carry-through area more "wing-like" and generate more lift out of the fuselage.

[FlightPathOBN]

If you look at a section of the wingbox, you will see the 'flat' portion you are curious about...

[FE Hoppy]

Wingbox is an internal structural term. Not applicable in this case.

Jane, the idea was explored in many ways from Parasol Fokker D.VIII and PBY catalina to the flying wings of Horten and others.

There will always be a compromise between structural requirements of the fuselage in terms of strength, volume and shape and the desire to get the most out of the wing.

[Jane-DoH]

FlightPathOBN

If you look at a section of the wingbox, you will see the 'flat' portion you are curious about...

I'm not talking about the internal structure. I'm talking about the fuselage section in between the wings. Evidently, depending on the shape of that structure there is a lift contribution in some cases -- I was basically curious if anybody pre area-rule contemplated flattening the fuselage in between the wings to help make it more "wing-like", effectively deriving more lift from the fuselage.

Understand?


FE Hoppy

Jane, the idea was explored in many ways from Parasol Fokker D.VIII and PBY catalina to the flying wings of Horten and others.

I didn't know that's why the PBY was designed with a parasol wing, I guess it makes sense though.

I know about flying wings, but many of them had bad handling characteristics in one way or another (bad-stall characteristics for one, sometimes instability, a tendency to wallow in flight) unless there was fuselage in the middle

There will always be a compromise between structural requirements of the fuselage in terms of strength, volume and shape and the desire to get the most out of the wing.

I thought flying wings were excellent structural designs unless pressurization was an issue as the fuselage frames are effectively the same as the wing's spars and share each other's loads.

[cwatters]

Surprising how much lift the wing box area can generate..

Old hands will have seen this "F-15 landing with one wing" vid before..

F-15 landing with one wing. Real story. - YouTube

[FlightPathOBN]

I guess I just considered that entire area, connecting the wings to the fuselage, the center wing box...I guess it is just the center wing...

perhaps a little OT... but the center wing on the 787 is mentioned in wikileaks...

Cable reference id: #08NAGOYA15 (http://www.cablegatesearch.net/cable.php?id=08NAGOYA15)

[barit1]

Jane-DoH:I just thought of something -- why didn't anybody (before area rule was implemented in the traditional sense) think of the idea of flattening the fuselage in between the wings?

It would make the carry-through area more "wing-like" and generate more lift out of the fuselage.

Several Beechcrafts - Models 18 & 35 e.g. - have a flat fuselage bottom from the wing aft. Don't know what this equates to aerodynamically.

Inverting the thought - The Monocoupe high-wing of the late 20s onward had a flat fuselage top continuous with the wing upper surface. Race pilot Benny Howard deduced this was the reason he "kept seeing the Monocoupe from the wrong end", and stole the idea for his highly successful Mister Mulligan.

[boguing]

My guess on the Catalina is that, intuitively, the area of wing adjacent to the body is pretty well compromised by the slow (relatively) air arriving at it. So to free it from the fuselage gives the centre section a clear view of still air.

The reason for my interest in this thread is that as of about five or so ago, I read that Boeings Kray-hosted CFD could model wings and fuselages, but not both.

My design interest is mainly sailing boats. Our foils have to work both ways up, as it were. Keel mounting in cruising boats is often a grp moulded keel moulded with the hull, and filled with heavy stuff.

Racing yachts and cheap boats have a bolted on keel.

Over the years I have noticed that the moulded grp keels are filleted, bolt-ons are not. Reason being that grp would have to be massive if a hard point were introduced. Fillet distributes the strain more evenly.

So as a young man working at a British Shipbuilders towing tank facilty at the time of Dr Pieter VanOosanen and Ben Lexcen's remarkable "upside-down" and winged keel on Australia III, I got to thinking. At the same time, we were running some submarine tests and used foils to hold it submerged. I wondered if it might be a good idea to separate the keel from the hull entirely because, surely, the water in the region of the non-fillet couldn't be that helpful.

Fast forward again to when I read of Boeings' computer problem.

The New Zealand America's Cup boat was revealed with a 'dillet'. Reverse fillet, so that water arriving at the hull/keel join was encouraged in by the low pressure. Made sense to me, and seemed to work for them.

Back to 'planes. Fillet might add strength if it were integral with the body/wing skins, but I suspect that it's not really.

So why fillet, and why not dillet on the top side? Get the air speeded up a bit.

[FlightPathOBN]

Here is a pic of the Kiwi, sorry, but it was taken with 35mm, then I had to scan it...

http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/04/SKMBT_C45108052810581.jpg

[boguing]

Different boat altogether.

http://mox.polimi.it/fulltext.php?file=10-2007.2007.pdf

Page 11 shows what I'm talking about, but at the bottom end where the lifting foil meets tha ballast bulb.

[FlightPathOBN]

I see and understand..

in reality, when the wings are added to the mix, the rollup of the vorticies acts much differently in the composite structure...

I would also note the pure laminar flow of the modelling, which in surface vessel, between the attack angle, currents, and the flow from the wings, isnt very realistic, just as in aircraft modelling software, laminar flow from the wings is simplistic and incorrect.

As soon as the vessel is sideslipping or crabbing, in regards to the current, the upstream surface of the keel will create one vortex, while the shielded side will create a different vortex. Modelling software typically deals with the effect of the current on the vortex, rather that the vortex effect from the current...same for aircraft...

[Chu Chu]

Maybe the parasol wing on the PBY has something to do with keeping the propellers out of the waves?

[Matari]

Jane D'Oh,

I was basically curious if anybody pre area-rule contemplated flattening the fuselage in between the wings to help make it more "wing-like", effectively deriving more lift from the fuselage.

You mean like this?

http://www.bibliotecapleyades.net/ciencia/fouche/sr71_high.jpg

[Machinbird]

On supersonic aircraft such as the SR-71 and F-18, my understanding is that lift is generated by every square inch of the aircraft planform during supersonic flight, rather than just the wing area which is more the case during subsonic flight.

Since the Aerodynamic center moves from its 1/4 cord point back to the Centroid of the Area as you go supersonic, the fuselage area ahead of the wing helps reverse the increase in stability which would tend to increase stabilizer (stabilator) "trim" drag and create excessive nose heaviness.

So the SR-71 example is a lifting fuselage, but it is done for stability reasons which improves aircraft efficiency during supersonic flight.

[grounded27]

As I understand as an aircraft (commercial) operates at closer to trans mach speeds the center of lift moves inboard and aft.

[chrisN]

Jane, I doubt if anyone is more careful with wing/fuselage drag minimising and (if possible) efficient lift production than high-performance glider designers.

AFAIK, they concentrate of getting lift from the wings, not at all from the fuselage, but focus greatly on fillets where the wing joins the fuselage to minimise drag. These are, of course, slender fuselage aircraft and operating at low Mach numbers.

An example of testing to show the effects is referred to at:
http://web.archive.org/web/20030419045435/http://www.ssa.org/Johnson/80-1996-06.pdf

“The oil flows showed little or no signs of airflow separations on the top surface, except possibly for a suspiciously stagnant area near the fuselage at about .7 chord (see photo)”

(Dick Johnson conducted independent tests of many gliders over the years, developing carefully calibrated methods, and became a legend in gliding circles for his analyses and recommendations as to how to improve glider wing efficiency.)

By the way, I know little about airliner aerodynamics, but AIUI all conventional (not canard or flying wing type) glider tailplanes always generate DOWNWARDS lift in steady flight. It is a stability thing.

Chris N.