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Riggerrob

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Cool video. Apparently the nickname of the plane was ‘Monica’, on the account of the large intake…

im not sure I understand how the LE vortex generators enable a flatter approach. My understanding is that the f-18 LE vortex generators enable high AOA because the vortex helps keep the flow attached to the top of the wing. The facetmobile needs a high AOA for slow approach and decent descent rate.
To be precise, the leading edge flaps on Cf-18, HAL Tejas, Sukhoi 57, Boeing 727 and Boeing X-32 are not vortex generators. They are merely leading edge flaps that droop to increase wing camber. Increased wing camber increases lift. They are easy to identify by their hinges at the REAR of the LE flaps.

OTOH Kasper's vortex generators hinge at their leading edge so that they rise more like spoilers. Kasper tailored his LE spoiler sto generate predictable span-wise vortexes that further decreased low pressure on the top skin.

Master Corporal Rob Warner, retired CF-18 wrench-bender.
 

henryk

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and Boeing X-32 are not vortex generators.

-this one (X32-A ) ?

=post #1=
=Kaspers LE VORTEX generators...
 

SamP

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To be precise, the leading edge flaps on Cf-18, HAL Tejas, Sukhoi 57, Boeing 727 and Boeing X-32 are not vortex generators. They are merely leading edge flaps that droop to increase wing camber. Increased wing camber increases lift. They are easy to identify by their hinges at the REAR of the LE flaps.

OTOH Kasper's vortex generators hinge at their leading edge so that they rise more like spoilers. Kasper tailored his LE spoiler sto generate predictable span-wise vortexes that further decreased low pressure on the top skin.

Master Corporal Rob Warner, retired CF-18 wrench-bender.
Sorry Rob, I was actually trying to refer to the leading edge root extensions on the f-18 when I said LE vortex generators. sorry for the confusion. Both the Apex laps and leading edge root extensions create vortices, just in different directions. The LEX helps with high angle of attack by keeping flow attached to the upper surface, the other increases effective camber for greater lift. I’ll be more precise next time
 

rotax618

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The inboard root extensions/strakes on jet fighters do produce powerful vortices at high alpha, they are actually de-stabilising, which is a good feature on a fighter plane, but not real good on a lightweight homebuilt.
From my experiments and if you look at the planform on the FMX4-5, Barnaby has observed the same characteristics. It is an advantage that the sweep at the root is less than the sweep at the tip, the greater the sweep the stronger is the vortex. It is better that the strong vortex lift is aft of the CG at high alpha so the craft doesn’t stall tail first.
I built a series of LAR faceted models some 12 years ago, I was obviously inspired by Barnaby’s pioneering work in this field,
 

Aviacs

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I read all the posts; and tried to watch/skimmed through the lecture video so may have missed it.

Understanding that the flat surfaces and arrises don't significantly reduce lift (WTTE stated on one of the early pages or references);
Are they essential to how the lifting body produces lift (or stability)?
Or merely convenient artifacts of a simple built and structural process?

My thought is that with modern cnc routers, a tab-'n-slot eggcrate structure and sheathing could be generated to make curved surfaces be more structural; gluing the whole thing out of 1/16" plywood. (E.g. D-tube leading edge: a flat piece of 1/16" ply has little strength in any direction. Curve it into a partial roll & constrain with formers, the construction becomes stiff and strong along that axis as well as across it).

smt
 

rv7charlie

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As I understood BW's explanation, the corners don't cause flow separation as long as the angles aren't too sharp, and the lack of curves makes fabrication dirt simple. I suspect that the problem with trying to use plywood (or even aluminum) on curved surfaces for this type of shape is that it's effectively a compound curve. That would require some type of stretch forming for ply or aluminum.

He did talk about various covering methods, and fabric came out the winner in the weight dept. Did you catch the mention of the proposal he did for NASA about 15 yrs ago? That design was for what amounted to tab/slot honeycomb core aluminum sheet (still a faceted airfoil, though).

What I haven't seen him talk about is whether the concept can scale upward in the speed category. Does the current 2 seat design he's working on hit a aero 'wall' beyond LSA speeds, or could adding HP and/or reducing lifting area make it go faster (RV-x speeds) even if we accept moving the stall up to RV range.

Also, would it scale to 4 seats at reasonable cruise speeds.
 

Riggerrob

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I read all the posts; and tried to watch/skimmed through the lecture video so may have missed it.

Understanding that the flat surfaces and arrises don't significantly reduce lift (WTTE stated on one of the early pages or references);
Are they essential to how the lifting body produces lift (or stability)?
Or merely convenient artifacts of a simple built and structural process?

My thought is that with modern cnc routers, a tab-'n-slot eggcrate structure and sheathing could be generated to make curved surfaces be more structural; gluing the whole thing out of 1/16" plywood. (E.g. D-tube leading edge: a flat piece of 1/16" ply has little strength in any direction. Curve it into a partial roll & constrain with formers, the construction becomes stiff and strong along that axis as well as across it).

smt
Barnaby Wainfain has mumbled about a "SMOOTH MOBILE' with curved flying surfaces. He has encouraged anyone who wants to ... to build a Smooth Mobile and compare its performance with the Facetmobile.
Wainfain maintains that Facetmobile fuselage operates at such large Reynolds numbers that sharp corners add insignificant drag at slow airspeeds.
 

Aviacs

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Right.
I immediately registered that per Mr. Wainfan's analyses, the flat surfaces and arrises had no significant penalty.

My curiosity relates to the apparent fact that in current configuration, at current speeds and loads, fabric on tube is the most efficient and lightest construction. OTOH. if a person were to explore adding strength through stressed skin ("moncoque" construction) so as to perhaps facilitate higher loads and airspeed, cnc'd eggcrate interior parts combined with curved surfaces might well facilitate that at similar or lower structural weight. So long as there is not an aerodymanic penalty using curved surfaces, which was my question.

That would require some type of stretch forming for ply or aluminum.
I dont' know about aluminum, perhaps stamping with a rubberform to do effectively? But i am sometimes called on to do mild compound curves in the course of my woodworking. In my case, 1/8" birch plywood, or "various species" veneer build ups. Curves similar to what could cover a facetmobile type surface. If 1/16" ply is considered, it should be more or less easily possible, though pieces might have to be cut and spliced along a few contours.
 

rv7charlie

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He indicates that the aluminum tube/fabric is a homebuildability thing, to keep weight/cost low while still being achievable by the average builder.

And compound curves can take a hit in the strength dept. A rolled cylinder is strong in compression on its long axis, but has little strength at right angles, in its curved axis. A curve has less strength in both compression and tension than a straight member.
 

mcrae0104

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He indicates that the aluminum tube/fabric is a homebuildability thing, to keep weight/cost low while still being achievable by the average builder.
Yes.

A curve has less strength in both compression and tension than a straight member.
No; a curved surface offers increased resistance to bending and buckling compared to a flat surface. Any schoolchild with some stiff card stock can prove this to his own satisfaction with a few minutes of play. Compound curves can be even better in this regard. The argument that curved surfaces are weaker than flat ones is one that could perhaps be explored in a different thread focused more on mechanics of materials, but for the purposes of this thread, I'll just say that I would be very surprised if the designer chose a faceted shape because he felt that curved surfaces are weak compared to flat ones (but of course he can speak for himself should he choose to do so.)
 

rotax618

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The internal structure of the Facetmobile takes all of the loads, the skin is fabric. The internal structure is essentially a spaceframe, that is all members are either in tension or compression, you must therefore consider the buckling of non concentric struts when designing, curved or non-concentric struts are far weaker than straight ones for the same minor axis size - that is why it is faceted.
 

Aviacs

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The question (post #85) was about changing the structure to a monocoque.

Largely because the shape suggests it as an efficient option at the cost of complexity.
I sometimes build light 3D contours with thin plywood for architectural apps.
Modern cnc routers can generate thin plywood formers for an eggcrate support/forming structure complete with reduced sections and lightening holes/cut-outs, that would essentially snap together, bonded with epoxy. Then skin with more thin ply
At which point egg-crate construction and curved surfaces become stronger.

Partly in pursuit of speed.

So long as there is no aerodynamic penalty or increased risk for stability issues.
 

rotax618

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The problem is not one of aerodynamics, a LAR “smoothmobile” would fly just as well or perhaps better, the problem is one of weight. The very large surface area requires a very lightweight skin, and if a monocoque, very stiff covering. I have toyed with various types of skin sandwiches and different internal structures, for a 1/2 tonne TOW only fabric works. This type of machine is only efficient with a very low wingloading. If you scale the idea up and add lots of power, who knows?
 

Aviacs

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With a Sonerai 2 project sputtering along, and too many other projects in other areas, this was not a serious consideration for action.

That said, the quick though process was that 1/16" marine Okoume weighs 5lbs/4' x 8' sheet.
given the planform of the facetmobile, that is 20 sheets of skin. Double that for internal structure and add epoxy, could come in at 250 lbs similar to current airframe, albeit much greater complexity. Does not include hardpoints for engine, etc. Just a quick "well, is it impossible from a materials weight perspective?"
Possibly not impossible if enough materials have been imagined for adequate structure.

So the next step would be "Is there a structural configuration that would work with those materials and process"
Possibly not. I don't have the experience to work that out on the back of an envelop.

Of course one would at that point have to consider "how 'bout cnc'd plywood stations with lightening holes as the formers/hotwire guides, bonded between what weight and configuration of foam blocks, to be finished with how much fiberglass might work?

:)

smt
 
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Ozthruster

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Yes.


No; a curved surface offers increased resistance to bending and buckling compared to a flat surface.
What he said is correct, he just left out one instance of the word "member", a bent stick is weaker than a straight stick. Trusses (spaceframes) are always made with straight members. OTOH a curved sheet is stiffer along axis than a flat sheet.
 

Urquiola

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Nice thread! About David Rowe's UFO, a guy added a video in YouTube of the machine flying in Australia as this, an alien UFO, it's a bit the Milt's 'Little bird', a downscaled version of Arup Flying wings, built as two shells, upper and lower, Uttar and Undra they would say in India, 'bolted' togheter.
I wonder if the Wainfan PAV could be built in 'Pladur' boxes, covered by plywood, no idea if weight could be affordable.
The patent US1887411, 'Method for construction of airplane', Richard B Johnson, in my personal icon, is a bit as the Rowe flying disc.
Blessings +
 

WINGITIS

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-this one (X32-A ) ?

=post #1=
=Kaspers LE VORTEX generators...
Thanks for pointing out those inner rising aero devices, I had not seen them before.

They have named them "Vortex Flaps" in the diagram attached:

x-32 number LEADING EDGE 11 vortex flaps.jpg
 
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