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Topaz

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Topaz, I see you added more to your earlier post. You're starting to talk me into it, or out of it, depending on how you look at it :)

I DO like deltas a lot.
I can't vouch for the flying qualities, and any tailless design is considerable effort in learning, above and beyond that required for a more conventional configuration. Trust me on this. However, it can be done, and designing an airframe that can accomodate one set of wings and tails is probably orders of magnitude easier than trying to design one that can fly effectively and safely with radically differing performance qualities, flying surfaces, and structures.

In the time it takes you to adequately design and build the "ultralight" version of the airplane, you could have your pilot's license and quite a few flight hours under your belt. If you want an ultralight, build an ultralight. If you want a higher-performance airplane, do that. I can certainly understand the mental temptation to try such a 'morphing' model, and your reasoning behind it, but transitioning the same airframe from one realm to another is going to be a bigger challenge, IMHO, than even designing a tailless airplane in the first place.
 

Topaz

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There's actually very little design information on that website for tailless aircraft. If you know what you're looking for, you can glean quite a bit from the pireps and some of the experiment reports, but that foreknowledge is what you need to design your own tailless airplane anyway. So at best this site can only confirm or deny your theories within the limited data available there. It's also is no longer connected with Jim Marske at all, despite the fact that they haven't removed his name from the page properties part of the code. Jim Marske's actual site is here, but he doesn't share design information at all anymore.

The "Basic Design of Flying Wings" link at the bottom of the "Flying Wings" page on this site is a good primer, but nothing more than that. It only gives basic pitch-axis stability information and neglects quite a few significant practical factors in the interests of brevity.

I was going to refer you to the "On the Wing" newsletter archives, but the site appears to be down? Norman? Know anything about this or where it might now be located?
 

Starman

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Thanks for all the links guys, I have seen and studied those, except for the Marske site (love that Genesis glider!)

I can't vouch for the flying qualities, and any tailless design is considerable effort in learning, above and beyond that required for a more conventional configuration. Trust me on this. However, it can be done, and designing an airframe that can accomodate one set of wings and tails is probably orders of magnitude easier than trying to design one that can fly effectively and safely with radically differing performance qualities, flying surfaces, and structures.
Yes it is more difficult, and I did it :) Doing the difficult part in my head and making my hands do the easy part is what I like.

In the time it takes you to adequately design and build the "ultralight" version of the airplane, you could have your pilot's license and quite a few flight hours under your belt. If you want an ultralight, build an ultralight. If you want a higher-performance airplane, do that. I can certainly understand the mental temptation to try such a 'morphing' model, and your reasoning behind it, but transitioning the same airframe from one realm to another is going to be a bigger challenge, IMHO, than even designing a tailless airplane in the first place.
Aha, so you figured me out. That's right, I don't have my license yet. I found and dusted off my old log book, last entry in 1980. I have about 15 hours and 64 landings and a solo. I was a natural. I'm going to start in again here pretty soon. I learned 95% in a Piper Tomahawk because I don't like high wing planes but there don't appear to be any of those available now so it's back to the 152. If you give those planes more throttle they just make more noise, don't go any faster. Anyway the first fabric option is beginning to look less worthwhile.

My problem is that being an analyzer, when faced with too many choices I become catatonic, and how many choices are there in aircraft design? That's why I like to leave it open ended till the last possible moment. Lets say my brother, who may not be interested, wants a conventional plane that looks like an F16 rather than a delta. OK then that can be done easily, differences in control system noted; but the front end of the control system, in the fuselage front, would be the same for all possibilities, the differences in the control system would all happen behind the cockpit so I'm going ahead with the fuselage front end as soon as I get windows and doors on the place in the mountains. As I mentioned earlier I have made a plywood mockup of the fuselage front, next step is fitting and making patterns for the outsides of the cockpit to fit the mockup (inner sides). Flying wing, big delta, little delta, no problem, they'll all use the swept back spar, and the main difference is different wing spans. Another thing is that since I'm flexible and an analyzer (Taoists call it yielding) that if someone I respect, like my brother, were to say: "Steve, I want you to make your first airplane a conventional one", then I'll probably do that, if he sez tailless delta (subset of flying wing) I'll probably do that.

One thing about the big delta wings is that their chord is so large that it may actually be a little difficult to reach the middle of the wing while doing glass work. I would be using VariEze style methods on the wing because I have the plans and I like the concepts, except I would really like to avoid all the exterior finishing work.
 

Starman

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Also on their site is this link to the Rohr 71x (2-175) that Orion has talked about:

Rohr 2-175 Fan Jet

Bruce :)
I looked at that, while I don't like the style that much I noted that the gross weight is close to my concept and the wing area of theirs is smaller than my first one would be if I make a delta first. I didn't see where it gives the stall or landing speeds, which is what I want to know so I can get a closer idea of what wing area I want to start with. Is there info on this forum about that kind of thing?

Another thing I noted is that it has a spin recovery chute. Is that because they were in test mode? I guess a delta can stall and spin if the CG is too far back but I didn't think they could spin because they can't stall, if the CG is right. That is/was one thing I found attractive about deltas, is inability to spin.
 

Starman

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My fuselage front will have a hard chine, like an SR71 or F18. I read elsewhere in this forum that for vortex formation you need a rounded chine. Is that correct? Do I care about having the vortex for something with conventional wings? Evidently the SR71 and the F18 don't think so (I'm referring to low subsonic here) and they are both conventional and delta.

I think a hard chine that is almost longitudinal will still form a vortex at high AOA, and where it transitions to the wing there will be a rounded leading edge.
 

Topaz

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Thanks for all the links guys, I have seen and studied those, except for the Marske site (love that Genesis glider!)
The Genesis is quite an airplane. Very nice. Despite the little 'horizontal tail', it's really tailless when you look at how it's stabilized. That little 'tail' is basically the elevator only, and doesn't significantly contribute to the stabilization of the airplane.

Yes it is more difficult, and I did it :)
I don't mean any kind of offense by this, because I've not seen your work in that direction, but based upon your statements and questions in this forum, I don't think you've got the right questions figured out to adequately design a tailless airplane. Some of your statements regarding stability and control are in contradiction to the practices that would be used for such work.

I'm not at all saying that you can't learn it - if I can, you can - but that the way the design factors interrelate is very difficult compared to a conventional airplane, or even a canard to some extent. The link I gave earlier is a good primer on the subject of pitch-axis stability and control for tailless airplanes, but is only a starting point. Run through that, and then we can give you some more resources that are worth pursuing if you want to go this way. Norman here is another excellent resource for tailless designs, and of course our local experts (Orion, Billski et al) can tell you the "why" answers better than most people anywhere.

Aha, so you figured me out. That's right, I don't have my license yet. I found and dusted off my old log book, last entry in 1980. I have about 15 hours and 64 landings and a solo. I was a natural. I'm going to start in again here pretty soon. I learned 95% in a Piper Tomahawk because I don't like high wing planes but there don't appear to be any of those available now so it's back to the 152.
Almost precisely my own first experience with flying, too. Including flying Tomahawks, which were what the local Piper flying school was using at the time. Now I'm learning in sailplanes.

My problem is that being an analyzer, when faced with too many choices I become catatonic, and how many choices are there in aircraft design? That's why I like to leave it open ended till the last possible moment. ...
I have the same tendency towards 'analysis paralysis', as many here will attest. And they're right. However, one lesson I learned over the years is that simplicity is the highest virtue in almost anything. And that includes the design process. I completely understand how 'leaving it open ended' seems like a great idea at the meta-level, but the practical result is a morass of design and learning tasks as you try to accomodate all the various permutations of the design. The work grinds to a halt under its own weight and volume. If I could make one suggestion to you above all others (and one that I'm trying very hard to enforce upon myself these days - much easier said than done for those such as ourselves) is that you stop, stand back, and pick one small permutation and design/build that. Something that, on the surface and at the beginning, seems stupidly simple to execute. You'll be simply amazed how much work puffs up out of even the most basic airframe, and you'll gain valuable design and construction experience to match your theoretical and conceptual background. I know you've got a lot of hands-on experience in other crafts, but airplane design and construction really is a different animal. It pays to give yourself a little practice piece first - an 'etude' as they call it in the music world.

One thing about the big delta wings is that their chord is so large that it may actually be a little difficult to reach the middle of the wing while doing glass work.
Yep, an interesting dilemma. I'm sure you'll figure something out.

I would be using VariEze style methods on the wing because I have the plans and I like the concepts, except I would really like to avoid all the exterior finishing work.
Wouldn't we all. :gig:
 

bmcj

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That is/was one thing I found attractive about deltas, is inability to spin.
No plane is 100% immune from stalls or spins. No matter how well you augment the stability, someone somewhere will figure out a way (intentional or otherwise) to stall it. Once in a stalled condition, any asymetric flow over the wings will cause a tendency to spin. The trick to the design is how difficult is it to reach a condition suitable for stall/spin, and how quickly does the design tend to naturally extract itself from a stall or spin.
 

Starman

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Yah, I figured that if the CG was too far back that deltas could stall, so let's change the question a bit. (My question asking ability sucketh)

What I should have said:

If the CG is well ahead of the NP in a delta (see, I said NP instead of Center of lift :speechles ) to make the plane have real good longitudinal stability, then it is very very unlikely to stall. Right?
 

Starman

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I don't mean any kind of offense by this,
No offense taken at all, your bedside manners are much nicer than Dana's, who doesn't know what I don't know :)

because I've not seen your work in that direction, but based upon your statements and questions in this forum, I don't think you've got the right questions figured out to adequately design a tailless airplane. Some of your statements regarding stability and control are in contradiction to the practices that would be used for such work.
Well I hope you or someone will point those out so I can learn. Frequently I understand a concept pretty well but I've read something somewhere that seems to contradict it and so I ask questions that imply I have the wrong ideas, other times I simply write questions and statements poorly, sometimes I realize this but don't bother to edit :gig:

Other times, no doubt, I do have the wrong idea.

I'm not at all saying that you can't learn it - if I can, you can
That's why I'm here.

- but that the way the design factors interrelate is very difficult compared to a conventional airplane, or even a canard to some extent. The link I gave earlier is a good primer on the subject of pitch-axis stability and control for tailless airplanes, but is only a starting point. Run through that, and then we can give you some more resources that are worth pursuing if you want to go this way. Norman here is another excellent resource for tailless designs, and of course our local experts (Orion, Billski et al) can tell you the "why" answers better than most people anywhere.
OK lets try this on for size. I read the sites earlier and digested and understood the concepts pretty well I think, but I don't bother doing the math yet because I don't need to. I get a good feeling for what will work and I allow for that and I'll get to the hard numbers when the time is ripe for making the wings and locating the CG by moving some of the heavy stuff around. I'm going to keep reading those sites and taking it a little further into the numbers each time.

Concerning the Rohr delta, if it was to be competing against the 172 then they had to have a pretty slow landing speed, which means I may not need as much wing area as I was worried I might need.
 

Starman

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I have the same tendency towards 'analysis paralysis', as many here will attest. And they're right. However, one lesson I learned over the years is that simplicity is the highest virtue in almost anything. And that includes the design process. I completely understand how 'leaving it open ended' seems like a great idea at the meta-level, but the practical result is a morass of design and learning tasks as you try to accomodate all the various permutations of the design. The work grinds to a halt under its own weight and volume. If I could make one suggestion to you above all others (and one that I'm trying very hard to enforce upon myself these days - much easier said than done for those such as ourselves) is that you stop, stand back, and pick one small permutation and design/build that.
I agree, but this is the other side of the story of analysis paralysis as it relates to my design and me knowing myself.

This design concept thing has been stuck going around in circles for years precisely because of analysis paralysis so I decided that the buck stops here and I'm starting NOW. First I'm making the aluminum fuselage front/cockpit. Since I removed the spar from it and am making the spar part of the steel subframe then this single place cockpit will be perfect for any of the airframes I might want to attach to it, and if it limits my choices downstream in any way then that's great! While I'm making the cockpit tub I'll be thinking about the planform more and the steel subframe that holds it all together. If I'm still undecided about the planform the steel subframe/spar I have planned for so far will still work for most anything I would want but it may not be optimal since right now it's optimized for a relatively straight wing, aiming at 10Gs for a 20 ft span (5gs @ 40 ft, etc). If I'm sure I want a delta before I start on the steel frame then I will adapt it to optimize it for that instead of a straight wing.

Something that, on the surface and at the beginning, seems stupidly simple to execute. You'll be simply amazed how much work puffs up out of even the most basic airframe, and you'll gain valuable design and construction experience to match your theoretical and conceptual background.
I agree, and am way too aware of how something that seems simple before I start making it causes me to stay up all night or two to meet a deadline.

So this is how I deal with my analysis paralysis, pay now, buy later, or something.

I'm going mountain climbing for a few days to give you guys a break, here's a trip report in case you want to see pictures of beautiful mountains: Mount Maude. That forum makes automatic thumbnails, so click the pic to get the big picture.
 
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BDD

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Yah, I figured that if the CG was too far back that deltas could stall, so let's change the question a bit. (My question asking ability sucketh)

What I should have said:

If the CG is well ahead of the NP in a delta (see, I said NP instead of Center of lift :speechles ) to make the plane have real good longitudinal stability, then it is very very unlikely to stall. Right?
Delta wings stall just as all other wings stall. They stall when at a certain angle of attack the airflow separates from the wing surface and lift is greatly reduced. Delta wings just stall at a higher angle of attack than do higher aspect ratio rectangular or tapered wings.

The C.G. location will have a big effect on longitudinal stability but doesn't usually prevent a plane from stalling.

If the C.G. is far enough forward (as you just mentioned) and the elevator power is low enough then it's possible that you can't (in most circumstances) change the angle of attack enough to stall the wing but in that case you have very reduced pitch control and that isn't a good thing. You could then be lacking control you later need to recover from a maneuver or from a stall or spin (that you thought would never happen), and you would not be able to rotate the wing to take advantage of maximum lift and minimum speed while landing which is one of the advantages of a delta wing.

It could also affect your ability to rotate on take off which can have disasterous effects on delta winged planes. This depends on the thrust line location, langing gear configuration, etc.

The stability will also be effected by power on or off conditions, the fuselage shape, the design of the horizontal stabilizer, etc.

You could also effectively stall the wing by flying too slow to produce enough lift, by certain maneuvers that increase the relative angle of attack on part of the wing, or by pulling high G's and raising the wing loading over the amount of lift that is actually being produced.

Certain wind gust conditions or turbulence could also stall a wing that has limited elevator power and then where are you?

There are many ways to "stall" a wing.
 
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Starman

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Thank you for the explanation BDD, that makes sense. I certainly do want to have plenty of control authority. I got this idea about deltas not stalling because I've read a few magazine articles that said deltas don't stall, that they just mush. Like, you know, mush means develop a fast sink rate but still have control.

I still like deltas, and I do want to have strong rotation ability and be able to fly at minimum speed.
 

bmcj

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Deltas reach stall and max lift coefficient at very high angles of attack. That is why you see them landing with such a nose-high attitude, and it is what has fooled many into believing that they will not stall.
 

BDD

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In fact, F-16's have a problem in that it is possible to enter a "deep stall" from which it is very difficult to recover. The plane tends to stay "locked" at the high angle of attack while falling vertically.
 

wsimpso1

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Stall of a delta wing is kind of interesting - With a normal wing, the air on top starts separating, and as the separation proceeds across the wing, drag takes off as the lift peaks and declines. With some airfoils and some wing designs, this can occur rather abruptly...

In a delta wing, the same tendencies are there, but the lift does not drop off abruptly, and the drag does not take off so much either. It has been described to me as spreading out the lift peak while the induced drag parabola just keeps getting higher and steeper. While it will seem all very nice to be at high AOA and under control, the drag can drive a huge sink rate. Not a corner of the envelope that I would want to find myself in at 50 feet. Might be OK to get inches from touchdown at nominal AOA, and then keep holding it off with back stick until it just won't stay airborne anymore. It might produce some positively low touchdown speeds. Then you can hold the nose way high to keep the drag big to shorten the rollout.

Now as to control, stalls, and stability, I want to clear up a few things. Please do not confuse stability, damping, and control. They are seperate things.

Stability is a primarily a matter of where the CG is relative to the neutral points. If we start by assuming that we have enough authority to hold an attitude, the neutral point is one place with the stick held, and usually a little further forward when the stick is free. Less static margin... This is for the simple reason that the elevator surface may tend to trail and contribute only part if its area, lift, and pitching moments when the stick is free. Other than this effect, elevator area and travel have little to do with stability. Got that?

Damping goes the same way. We all would like deadbeat response to control inputs, and when damping is big enough, we get that. Otherwise, when you pull and then release the stick, the airplane will oscillate more before settling down than if you held the stick after the pull. Why? Well, damping is a function of the second moment of inertia of the planform (in pitch), which is a fancy way of saying add up all of (area* (arm to CG)^2). Yeah, the areas furthest from the CG have huge effects. Fixed elevators will contribute quite a bit, and a trailing elevator will contribute less. And delta wing aircraft tend to have relatively short arms to the elevators.

Then there is control, which is all about area, deflection angle, and arm length to the CG. You need this to leave places like deep stalls, to rotate for take off, to flare for landing, and to execute fun maneuvers! And while control authority can be the thing that puts you into deep stalls, there are (as was pointed out earler) other ways to get there too. Like faster pitchup rates, discovering that the NP is further aft than you thought (!), etc. Me, I can tolerate being able to stall the airplane as long as it does not snap roll or depart easily, so I would opt for plenty of control authority.

Now, Cherokees and Ercoupes and Cirrus all exist with somewhat limited pitch authority. But they had their fun being developed too. I suspect (perhaps someone else can confirm) that they started out their test programs with more elevator or stabilator travel, and it was reduced during the test program. Joe Average may never have flown these birds when the pitch travel was still big... Might have been fun, might have been scary.

Oh, and all of the things said about pitch can be applied to yaw with appropriate extensions...

Billski
 

Starman

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This is for the simple reason that the elevator surface may tend to trail and contribute only part if its area, lift, and pitching moments when the stick is free. Other than this effect, elevator area and travel have little to do with stability. Got that?
Yes sir, got it. I was thinking about just this sort of thing (your whole post) while I was in the mountains and figured that the full span elevons which I drew previously wouldn't contribute to stability or dampening. I figured that in order to have stability that it should have a fixed (trim tab) section on the inboard part of the trailing edge. Either that or it could have little 'cheater' tabs on the tops of the tails, to get more lever arm, but that seems inelegant to me.

I don't think I care much about the dampening as I'm not planning on slapping the controls and then letting go, and I sort of like sensitive twitchy things, like for example I like to do some two or four wheel drifting around corners on dirt roads in the mountains, just for practice. Not that I want my plane to be too twitchy or sensitive, but I don't see much need for a lot of dampening for a plane intended primarily for fun flying unless you or someone can provide some motivation along those lines.

Concerning control authority, I want plenty of that so given a limited lever arm, that simply means more surface, not a problem.

Concerning the NP being farther back than I thought, what about that sharp edged chine at the front sides of the fuselage, does that raise any warning flags for you? The fuselage is a lifting body type, or you could say the whole plane is a double delta. The fuselage being lifting moves the NP forward quite a bit so the wing needs to be that much further back to balance it. To be safe it would probably be best to assume that the fuselage front is lifting, and if it ends up not lifting that much then that means more stability, possibly too much, but I'll be having to make a model to check that when the time comes to plan the wings. Also, it would probably be a good idea, for safety sake, to make the control surfaces extra large to begin with. It would hardly add anything to drag, and they could be trimmed smaller or remade smaller later if that seemed like a good idea

I am liking the idea of a delta more these days. Only two wings and two surfaces to make, not counting the verticals. That, and I like the way they look. Earlier I was thinking they were to 'hot' to handle, but now I think not.

So now, about the stalling ability of deltas, the way you described it, which is how I thought it happens, doesn't sound like a stall to me. OK, technically, part of the wing is stalling and part isn't, but when I think of stall I think of the plane suddenly stops flying and the seat drops out from under you and it's YAAaaaa..... falling, while dropping a wing. I don't like that! Maybe because I'm a beginner, but simply developing a fast sink rate while having control would feel very different, and acceptable to me.
 

BDD

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The C.G. of the delta winged version that you have sketched will be much further aft from where it is shown.

This is a flying wing and for longitudinal stability you will need an airfoil with a positive pitching moment with the C.G. ahead of the aerodynamic center of the wing.

The pitch stability in this case would come from a positive pitching moment and how far ahead of the aerodynamic center of the mean aerodynamic chord the C.G. is.

This would be a reflex airfoil with trailing edges that are reflexed upwards. That part of the airfoil and the airfoil's reflexed camber produce the positive pitching moment.

I would think that part of the wing's trailing edge should not have control surfaces so that the reflexed part of the airfoil is always maintained.

I don't see the part of the fuselage that is in front of the wing developing much lift. It would detract a bit from longitudinal stability and would be balanced by the c.g. location, pitching moment, etc.
 

Starman

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The C.G. of the delta winged version that you have sketched will be much further aft from where it is shown.
I was wondering about the CG location so thanks for bringing it up. actually the one in that drawing is another casualty of a ten second computer sketch, that CG location was 'left over' from the straight wing drawing :) and I hadn't analyzed it at the time, I am now.

This is a flying wing and for longitudinal stability you will need an airfoil with a positive pitching moment with the C.G. ahead of the aerodynamic center of the wing.

The pitch stability in this case would come from a positive pitching moment and how far ahead of the aerodynamic center of the mean aerodynamic chord the C.G. is.

This would be a reflex airfoil with trailing edges that are reflexed upwards. That part of the airfoil and the airfoil's reflexed camber produce the positive pitching moment.

I would think that part of the wing's trailing edge should not have control surfaces so that the reflexed part of the airfoil is always maintained.
Definitely, I mentioned in my previous post the idea of having the 'fixed' part of the trailing edge also do double duty as trim tabs. Trim tabs are essentially fixed, and they would always be reflexed upwards to some degree, to whatever degree is needed for stability actually (assuming the CG is correct), so it's another one of those variable/adaptable scenarios that I like. Automatic perfect reflex for any speed and CG location by cranking on the trim.

There's another way to provide reflex, possibly, even if the elevons are full span, and that is to have a spring trimmer built into the controls. Some airplanes use an adjustable centering spring connected to the stick to provide artificial feel and to provide trim as well, so that could work. I guess I'll use both to start with.

I don't see the part of the fuselage that is in front of the wing developing much lift. It would detract a bit from longitudinal stability and would be balanced by the c.g. location, pitching moment, etc.
I'm making some drawings to locate the CG, using a couple of variables that apply to this delta, and then I'll post them here and we can have a vote as to which one looks the most correct :)

I've read in many places that you calculate wing area as if the 'imaginary' part of the wing that goes through the fuselage also counts as wing area. I'll put up some more drawings later today so it will be easier to discuss it.

The Rohr delta has a wing loading at gross of 8 pounds per foot, so I'm figuring on 200 square feet of area hich will make the wing loading a little bit less.

Another thing I'm thinking is that since you don't count the horizontal tail as part of the wing area in a conventional wing that in order to err on the side of safety I won't count the elevon area as part of the wing on this delta either.
 
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