Starman's plane

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Starman

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The problem here is that you're looking at all this in a very simplistic manner without really understanding how all these variables figure into the whole nor how they inter-relate in all the aspects of stability and control, and performance.
Did it ever occur to you that it looks like that because of the limitations of writing in a place like this about a complex subject like that? Writing is so slow compared to speaking, and people misread so easily.
 

BBerson

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One thing I have noticed is that many of the people who can thoroughly understand the advanced airplane design books are usually people that have very little building skills. Quite a few airplanes have been designed by builders with little use of books. But generally these designs have been similar to existing designs. An unusual design, on the other hand, could use all the knowledge available and still have problems.

In the past I got upset by some of the comments on this and other forums, but not anymore. Everybody has a different view about things. Why get upset.

One airplane designer came to this forum about a year ago and got so upset by all the comments that he quit the forum. And he had already designed and flown his airplane.

BB
 
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orion

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Did it ever occur to you that it looks like that because of the limitations of writing in a place like this about a complex subject like that? Writing is so slow compared to speaking, and people misread so easily.
Yes it did however, those that know and understand a subject can discuss it clearly and with sufficient detail, even in a limited form and forum. In your very own discussion, the terms you use and the questions you ask clearly show that despite your reading you have missed numerous key ideas and concepts, without which your questions make little sense and cannot be answered in a meaningful manner. While this may be blunt, in my view it is better than giving you meaningless answers, or trying to take you by the hand and teach you the very basics of the subject matter. The former would be a waste of your time and the latter is not within the purpose or capability of this board. We do support each other here, after all, this is the mission of this space, but when someone's wrong, we do not hesitate to say so and for the most part that bluntness seems to be appreciated. But when you couple ignorance with arrogance, that's a bit more difficult to deal with. Sorry about that but at that point that's not our problem.
 

Jman

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Mod Note: Disagreements and criticisms are fine. Name calling will not be tolerated.
Starman,

I'm going to re-iterate what the moderator who edited your post had to say and take it one step further. If we have to edit your post for that reason again, you won't be welcome here any longer. The anonymity of the Internet does not give you the right to act that way on this website. I bet if we were to meet in person and discussed the same issue it would not end in name calling. Most likely we would agree to disagree, have a cold one, and that would be that. Let's keep it what way here as well.

If you think that your post may be taken as anything other than a polite disagreement.....DON'T POST IT. That goes for everyone.
 

BDD

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In your original post with 2 sets of 2-view drawings you had mentioned that the first version (with a scalloped trailing edge) was fabric covered "with fabric only on the top surfaces, completely open on the bottom". What was meant? Was it a single surface wing? Was just the wing open on the bottom?

As mentioned before, flying wings and delta wings stall just like any other wing. The maximum angle of attack will vary with aspect ratio though, as with any other wing. Delta planform wings tend to stall at a high angle of attack.
 

Starman

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In your original post with 2 sets of 2-view drawings you had mentioned that the first version (with a scalloped trailing edge) was fabric covered "with fabric only on the top surfaces, completely open on the bottom". What was meant? Was it a single surface wing? Was just the wing open on the bottom?
Both wing and fuselage open on the bottom.

As mentioned before, flying wings and delta wings stall just like any other wing. The maximum angle of attack will vary with aspect ratio though, as with any other wing. Delta planform wings tend to stall at a high angle of attack.
Yes, I know about how aspect ratio affects stall angle. It's when someone said that a flying wing is really different than a close coupled plan that I started wondering why. I always had thought flying wings could stall but due to that comment I wondered if maybe they had limited control effectiveness (to keep from stalling) and that's why they were so different, so I just put that out there. I realize thinking out loud makes me look stupid around all these experts.
 

Midniteoyl

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I realize thinking out loud makes me look stupid around all these experts.
No, its just confusing.. on the web, most people start a 'thinking out loud' session with : "Just thinking here", or "I'm wondering", or "Question:" or similar. You have to remember that in this world of text, voice inflections, body language, and emotions are not really transferable like in a face-to-face conversation. Thats why 'smilies' were invented :)
 

Starman

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That’s basically what I did in the situation mentioned, check it out.

I’ll make an attempt to salvage this and explain some of my stupid questions. I had to wait a couple of days to cool off because of my propensity for swearing, but I need to get this BS off my chest before continuing

Concerning the books that I apparently haven’t read: I bought those books about forty years ago and read them through several times and understood the concepts and the interrelationships quite well, but I haven’t looked at them much in the last thirty years. Since then I got many years of EAA magazines, all kinds of flying magazines, and internet research I have read and understood. I understood the interrelationships well enough to play around with all kinds of different designs but I knew I wasn’t going to build anything at the time so I didn’t NEED to go into a lot of minute detail with calculations, just some basic calculations. But anyway, I took Orion’s advice and bought a new design book, it's by Daniel Raymer, Yay!

So, you know, I’m getting old and I decided to do this thing, and I better do it fast too. So I came here as a place to get more in person advice. I got good advice about horizontal tail authority and a nice person provided the formula. I already knew about the relationships to wing area and chord, but I didn’t know what all the symbols meant, so another nice person provided that, but left out Sw so I asked about that. Boy was THAT a stupid question, no one wants to answer a question that stupid, because obviously, I’ll kill myself. When I stopped to think about it for a microsecond I realized w had to stand for wing and had to laugh at myself about it, but I had been in the mode of gathering info here and expected to get it that way so I didn’t think about it till later.

In any case, I didn’t think I needed to get exact numbers on the tail size before I start building the cockpit. That’s the kind of detail that can be worked out later, I though, in my humble opinion, I guess, I think, maybe, sometimes, who knows? I had no idea how insulting the idea of building the cockpit before knowing the exact tail size was to all the expert designers here.

Then a local well meaning rocket scientist informs me that I’m going to fail, and kill myself, because the control and stability of a scale model has absolutely no similarity to the aircraft that is being modeled. The silence of the lambs implied agreement, but maybe they were just waiting to see if I would say something stupid about that too :) Well, scale models being useless is exciting news. Someone should warn the scientists working at the **** NASA Wind tunnel that they’ve been doing it all wrong for the last sixty years.

But I went along with it, so I said something like: well if a model won’t work then how about X plane? Another stupid ignorant question, evidently I need a $50,000 program to do it right and X plane also has no similarity to the real world.

Now Dana’s thinking that in addition to being a liar I’m also a whiner :) and for Orion add ignorant and arrogant. So yes folks, I’m a lying ignorant arrogant whiney butt and don’t forget it. (By the way, does this forum have an ignore feature?)

I’m a very high energy person in spite of being older (see my intro), like a kid in some ways.

Then there’s the CG and center of lift issue. I couldn’t help but notice that ten million designers and builders have the CG and spar at the 25% chord point and that seems to work fine for them so that was my plan too, but all the talk in the spar location thread got me confused with the expert saying how bad it can get and basically that it’s too complicated far everyone but experts so better go buy a go cart instead. So I asked some more stupid questions and made some stupid comments about that. So I’ll be blunt about this, I don’t EVER want to know what my pitching moment is, or moment coefficient, or whatever the **** you call it. I know about slightly cambered and reflexed airfoils, and I’m building some freaking models, I don’t care what anybody says.

I do appreciate the people who told me the horizontal tail looked too small that was very helpful. I found that due to the wing center section being so big and there being no center section on the horizontal tail, that they had to be very large on the big wing model, which looks kind of fugly, and on the small wing model they actually need to be larger than the wings, which looks worse, So it was back to the drawing board after all. I looked into ducted fans to get more area in the rear but don’t like the looks. I could do the common thing of putting the horizontal tail on top of the verticals but that doesn’t appeal to me - quite yet. I’m examining making it into a flying wing. Kind of a blended wing/body. I figure that if the tails have to be so big I might as well just put them on the ends of the swept back main wings. The whole thing would then be simpler to make, lighter, and less stressed, and would meet my requirement for good looks. I have some neat ideas about how to arrange the landing gear; and yes, Gary, it will still use the same aluminum cockpit tub as originally planned with possibly minor changes to the attachment to the steel spar, so I AM going to go ahead with the aluminum. I’ve researched the many different ways of joining the aluminum to the steel and I think I have that method chosen.
 

Birdmanzak

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Starman:

Please stop taking things said on this site personally. Raymer (whose books I also highly recommend) puts it well when he says
Daniel Raymer said:
do not use the phrase, "They laughed at the Wright Brothers". We've all heard it before. Remember, "they" laugh at everybody...
That's from his site. I know you're getting a lot of recommended reading but allow me to add that page. It's not directly applicable to you but there's quite a bit in there that will help you get more help from places like this, and from the sorts of people you find here.

It doesn't matter if you're not familiar with the precise notation used in various books or predominantly around here; if you aren't aware that X-Plane is inadequate for testing new designs (especially unconventional ones); if you haven't seen the range of configurations that others have. It's ok not to know things you don't know. We already know that there's stuff you don't know: you're asking questions. People here are answering, not to highlight your ignorance, but because they generally want to help. I haven't seen any posts that were anything less than a genuine effort to help you. Being helpful includes being clear to the point of bluntness when answering. X-Plane simply isn't capable of doing what you hoped it would. Scale models don't necessarily answer the questions you think you asked of them, even when the Reynolds number is controlled to make them more accurate. Tall gear are heavy. Heavy things are expensive. The conventional notation used at HBA is common to most of the literature. There IS a lot you don't know. It might not be fun to read what you read here, but the lessons are usually worth the bruised ego.

Changing your design as you work through it isn't an admission of defeat, it's continual improvement. This is just my opinion, but I think that if your final design looks too much like your initial sketch you either have a LOT of experience in aircraft design, or you haven't analysed your design properly.

As for using the aerodynamic centre and pitching moment versus centre of lift, sure you can design a plane using centre of lift. The trouble is, no-one else does. The data that exists in the literature, the useful software (XFLR5, based on Xfoil, is quite helpful to me), and other people in the field almost exclusively use the AC and Cm. If you won't use that terminology, you're denying yourself access to most of the resources out there. AND you're making the maths far, far more complex than it needs to be.

Finally, I hope you don't leave the forum. I've learned quite a bit from your threads. I was lucky that a couple of my (many) misconceptions have been addressed in them. I've also had 'aha' moments where peoples's explanations have finally got something to click. If you can lose the chip on your shoulder you could get a lot from the HBA community, and contribute too.
 

BBerson

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Starman,

Like you stated, the CG of most airplanes is at or near 25% on full size or RC model.

But I recently started flying an RC model with the tail very close behind the wing similar to your proposed design. In order to make this short coupled model fun to fly, the CG is at 17% instead of 25%.
Lesson learned, I think short coupled or flying wing designs must have the CG more forward.

About X-Plane: I use it all the time. It is fun. You can learn quite a bit about performance, such as drag and power required. It will not predict stall behavior, but what does. Get an older version, you don't need or want fancy scenery.
Even Cessna just lost an airplane recently and I bet they had plenty of design tools that apparently failed to predict the spin recovery.
BB

P. S. I am not quite happy with Raymer's "Simplified design book for homebuilders".
The math is still too advanced and the book has some errors. I needed to consult a math professor friend, and that should not be needed in a "simplified" book.
 

Starman

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Hi everyone, I'm back from the mountains and on my computer, but only for a few hours then it's back to the mountains with a big steel gate I'm making today to keep hunters out of the canyon.

I won't quote Birdmanzack's post but agree with it, so thanks. I'm glad I could be of some help, don't hesitate to ask :) ... also, I just might look at pitching moments after all, but I hope not.

I found out that a single place plane without flaps and little CG travel can get by with the smaller range of horizontal tail volume and so the drawing I had posted of my design was exactly right on the money, perfect, ideal, and I had only eyeballed the sizes, this is the result of decades of getting a feel for such things. The fabric wing and small wing versions did look like the tail was too small but those were just like ten second modifications of the 'standard' wing size sketch for this forum to show possible directions the design can go in and I really didn't contemplate them due to my hurry to post them.

Anyway, since I freaked out about the tail volume I made the design even more adaptable :)

The aluminum tub fuselage front and cockpit are still the same tortured plate aluminum design with generally diamond shaped bulkheads. In order to make it more adaptable I have designed a main spar center section that will accommodate any wing planform be it conventional or swept or plank type flying wing, or delta, and possibly even a canard with a lot of weight and lift bias towards the front wing. It will be able to have straight, forward swept, or rear swept spars due to the main spar center section having a lot of torsional strength and also having wing root rib torsional attachment hard points. I also figured out how to prevent over controlling so it's not all twitchy and stuff but still has a lot of elevator authority.

So now that I've made it so adaptable I can't decide what wing type to make first. Right now I'm leaning towards the fabric but possibly like a plank or Fauvel style flying wing rather than conventional.

I also want to make the main spar center section so that a V8 can go inside it or under it, probably inside, more on that later.

BTW, the prop will be further back from the trailing edge of the center section than the drawing shows.
 

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Starman

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Here are some sketches of different possible spar center section designs I can possibly use. All of them are in steel, and provision for torsion is not shown in these sketches.

I'm playing around with making it big enough for a V8 so then any engine will fit.

The first one is a fabricated I beam with an additional beam flange going around the center circular opening, this one will be the most difficult to calculate but is the most elegant, I think. I like I beam style center spar sections because they already have the 'tabs' for bolting the wings on (Varieze style)

The second one down represents steel tubing, with the tubes represented as lines. This is the easiest to calculate and probably lightest but it doesn't have built in wing attach tabs and I don't like working with round tubing, possibly square tubing though.

The third one is a curved I beam with the engine hanging underneath. I like this and it won't be too difficult to calculate, but it adds a bit more height than the other two, and it also lowers the engine so that the engine may need to be inverted, but I don't want to go to the work of inverting the engine (yet). I guess I could put this type of spar under the engine, then it won't have the height issues but I don't want the engine high up, above the main structure, in case it comes loose in a sudden stop :)

So, what do you guys think?
 

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orion

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From a structural standpoint and since it's just downright attractive I like the first one. These types of full frame carry-through devices tend to be relatively easy to analyze (especially with FEA) and given that it's full depth, it will most likely result in a very efficient assembly. You however will most likely have to make the outer holes smaller and add vertical web reinforcement since you'll be dealing with the concentrated stresses of the wing attachment mechanism and the geometric kink you'll have there between the wing and this bulkhead frame.

The second one could be the "cheap" solution and it works quite well if properly designed and sized. It also gets benefit from the full depth configuration and let's face it, tube based steel structures are quite inexpensive to cut, jig and fabricate.

I'd probably recommend against the third one however since that does not give you a full depth carry-through. No, full depth is not necessary but using the maximum cross sectional properties when possible will give you a substantial weight advantage over something like this.
 

BDD

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Option #1 will have stress concentrations at the center and will have to be designed to carry the maximum bending moment and shear forces where there is the least material. There is very little web there for the shear loads and this is the point where bending stresses and shear stresses will be at their maximum. The radiused curves at the center section are necessary to avoid extremely high stress concentrations. With that very deep spar section bending stresses will be helped but that deep section will also need to be analyzed at the spar caps and webs for buckling. You will need web stiffeners. I suppose that you could also have a stiffener that runs around the large hole that the engine goes through. As Orion said a FEA would be useful here.

Option #2 should be designed as a truss and could have the web members meeting at points (by moving the vertical tubes outboard a bit) or there will be some bending moments in the tubes which can also be designed for.

You can carry the wings torsional loads by having a two spar wing.
 

BDD

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......I found out that a single place plane without flaps and little CG travel can get by with the smaller range of horizontal tail volume and so the drawing I had posted of my design was exactly right on the money, perfect, ideal, and I had only eyeballed the sizes, this is the result of decades of getting a feel for such things. The fabric wing and small wing versions did look like the tail was too small but those were just like ten second modifications of the 'standard' wing size sketch for this forum to show possible directions the design can go in and I really didn't contemplate them due to my hurry to post them.

.......and possibly even a canard with a lot of weight and lift bias towards the front wing. It will be able to have straight, forward swept, or rear swept spars due to the main spar center section having a lot of torsional strength and also having wing root rib torsional attachment hard points. I also figured out how to prevent over controlling so it's not all twitchy and stuff but still has a lot of elevator authority.

So now that I've made it so adaptable I can't decide what wing type to make first. Right now I'm leaning towards the fabric but possibly like a plank or Fauvel style flying wing rather than conventional.
Your description of a canard with a lot of lift bias towards the front wing sounds more like a tandem wing configuration rather than a canard configuration. They have less longitudinal stability than a conventional layout. Depending on it's vertical location this horizontal tail would have reduced effectiveness due to the wing's downwash. It could also be blanketed by the wing's wake in a stall which would reduce control and stability in a stall.

As for "not over controlling" I would think that pilot induced oscillation could be an issue. The concentration of the engine weight near the center of the plane would also further lower the angular momentum of the plane and would add to the "twitchiness" about the lateral axis. Something to consider.

If it is a flying wing or a flying wing with a hybrid tail added on pitching moments and exact C.G. location and travel are extremely critical and will have to be analyzed. This is true of a conventional layout too but even more so for a flying wing. The airfoil selection is also critical for these.

If you are thinking of a fabric covered wing and fuselage you should certainly also cover the bottom of the wing and fuselage. A 2 spar wing, very beefy box spar taking all loads, or D-cell structure would also be required.
 
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orion

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Option #1 will have stress concentrations at the center and will have to be designed to carry the maximum bending moment and shear forces where there is the least material. There is very little web there for the shear loads and this is the point where bending stresses and shear stresses will be at their maximum. The radiused curves at the center section are necessary to avoid extremely high stress concentrations. With that very deep spar section bending stresses will be helped but that deep section will also need to be analyzed at the spar caps and webs for buckling. You will need web stiffeners. I suppose that you could also have a stiffener that runs around the large hole that the engine goes through. As Orion said a FEA would be useful here.
If we look at a shear - moment diagram we find that the maximum moment of any wing structure is at the wing root at the side of body. At that point the lift is sheared out into the fuselage so the applied moment from that point across the body is constant. True, this is an oversimplification and it does depend on how the carry-through is mated to the body shell but for the sake of this discussion I'll assume that to be the case.

As such, the load imposed onto this carry-through is simply a moment, which at the centerline can be resolved into two forces (compressive and tensile). As such, there is less need for a web at the centerline except that which is needed to stabilize the top and bottom caps. Ideally, the assembly here would have the caps, the web, and another "cap" running around the periphery of the centerline hole. The gauges would be designed to carry the resolved load.

What the FEA analysis would check is the effect the geometry has on the whole since the structure is not a straight line so there would be certain stress risers and deflections as the carry-through curves around the top and of course as the angle of the cap changes at the root from that of the wing to that of this frame.
 

BDD

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It looks to me as if the spar here is the fuselage frame at that location and all loads go into it.
 

Starman

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I need to apologize for the simplistic drawings. I design with pen and paper, and I don't like to take the time to make accurate drawings with my computer, for posting, because they leave too much information out. From now on I'll take pictures of my paper drawings and post them instead.

Anyway, I'm going to use a fabricated I beam type center section where it circles the engine and the outer parts of the spar will be tubing.

The steel spar center section is connected to the aluminum fuselage tub at only two points, one on each side of the inner ring, which will have it's own inner spar cap, as I mentioned earlier. Actually, the loads transferring between the spar / fuselage connection at that point nearly cancel each other out so there is almost no stress at there. I know it sounds crazy.
 
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Starman

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Starman,

I recently started flying an RC model with the tail very close behind the wing similar to your proposed design. In order to make this short coupled model fun to fly, the CG is at 17% instead of 25%.
Lesson learned, I think short coupled or flying wing designs must have the CG more forward.
Thanks, I'll remember this

P. S. I am not quite happy with Raymer's "Simplified design book for homebuilders".
The math is still too advanced and the book has some errors. I needed to consult a math professor friend, and that should not be needed in a "simplified" book.
The book doesn't have much in the way of info I wasn't aware of but it has some nice reminders and is put together well. It was nice to be reminded of the elevator blanketing the rudders in a spin and how to avoid that.

I hope the errors in the book aren't too serious, I haven't noticed anything yet that stood out.
 

Starman

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Your description of a canard with a lot of lift bias towards the front wing sounds more like a tandem wing configuration rather than a canard configuration.
So then is a Quickie type plane technically a tandem wing rather than a canard?

As for "not over controlling" I would think that pilot induced oscillation could be an issue. The concentration of the engine weight near the center of the plane would also further lower the angular momentum of the plane and would add to the "twitchiness" about the lateral axis. Something to consider.
Pilot induced oscillation is what I was thinking about. I think that giving the elevator control a lot of travel will help. Some pilot reports say it takes just a bit of pressure on the stick to control the plane. I want a lot of movement for and aft, like 12" or maybe as much as 18" for starters. Also I was thinking of a proportional control, where more movement of the control near the center produces less movement on the elevator surface, this would mean that near the ends of the control travel less hand movement would produce more elevator movement. Is this reasonable, to make the control less effective in the center of the travel?

It would probably require a trimming system build into the bellcrank so that the center of the stick travel stays near the center of the elevator travel no matter what speed the trim is set for.

If you are thinking of a fabric covered wing and fuselage you should certainly also cover the bottom of the wing and fuselage. A 2 spar wing, very beefy box spar taking all loads, or D-cell structure would also be required.
I don't think you appreciate what I'm trying to accomplish with this first fabric version and I suppose you think i'm referring to conventional fabric stitched to ribs, etc. but that's not it.

I mentioned before that it would be like an ultralight but that didn't explain it well. What I meant was that it would be like a hang glider type ultralight. My goal is to have a huge wing area and make it super simple to build. It's just going to be temporary, to fly slowly and practice while I make some fiberglass wings and body panels.

I'm just going to throw some cheap stuff at it and see what sticks, like maybe use some two by fours and an old tablecloth. Haha, just kidding. No, maybe some of that 8" diameter bamboo for wing spars and some plastic hardware tarps for surface. I'll call it the Tiki Hut version. I'll show you guys quick and cheap :)

Not really. Probably what I'll use is a couple of floor joists, boxed, or a single floor joist with a D cell for stiffness and some used sailcloth for the fabric. Used sailcloth shouldn't be too hard to find in this port town. NO airfoil shaped wing ribs, not one single wing rib anywhere, just some tie down points. I'll let nature make the airfoils.

This shows a thirty foot span, and the wing area ahead of the prop is about 280 square feet. The dotted line represents the hinge line for the elevators and I'm thinking of putting a hinge on the wing tip bow to provide aileron action. The round circles represent the tie down points to attach the fabric to the structure. Top surface only, all the machinery will be hanging out in the breeze underneath for easy access.

If I use a fabric leading edge like this drawing shows then it would need to have a stranded wire reinforcement for strength inside some plastic pipe for leading edge radius
 

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