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Old Sep 15, 2013, 04:43 AM
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Help!
Want a fpv wing design wingspan ~ 3 meter

Hello everyone

I want to scratch build a fpv capable wing with following features

1. Huge wingspan around 2.5 to 3 meter
2. Wing area atleast 1500 Sq. In
3. Tons of lift. Most important.
5. Low power required to keep in the air ~60w
4. Stiff design, crash resistant
5. Light as much as possible
6. Can be made from foam epp
7. Slow flyer. Capable of thermal flight

Please give me your suggestion. I previously made a fpv49 wing with kfm 2 airfoil. The wing is awesome. But I want to build something bigger.
If I want enlarge a wing design let's say fpv49. How do I do that? Is there a simple formula or something?

Thanks in advance
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Old Sep 16, 2013, 01:52 PM
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You're going to run into some problems.

First off EPP is not that light. For a big model the volume of the wing adds up quickly and so does the weight of the foam. One option is to use foam only for parts of the wing or use a foam core but cut out big lightening holes or use a second cut to make the core hollow.

The idea of a forward "U" shape and a rearward "V" shape isn't actually a bad way to go. With a wing this big you HAVE to use a proper spar to withstand the flight loads anyway so it is a natural to glue on a front "U" shape and a rear "V" to produce the airfoil.

Your wing doesn't need "tons of lift". What it needs is to use an airfoil which is able to operate in the lowest lift to drag portion of the performance envelope at the speed and weight for the model. This all relates to the Coefficient of Lift (Cl) vs Coefficient of Drag (Cd).

With low weight to give you a light wing loading and an airfoil that produces low drag at the normal angle of attack for how you'll be flying you will minimize the power needed to fly. Look around at some of the articles on solar powered model airplanes and you'll find that with efficient glider like planforms that it's possible to climb at more or less an "uphill glide" with as little as 6 to 10 watts per lb if the design is efficient. And with that in mind level flight should be practical for cruise at down around 3 to 4 watts per lb.

To be fair though most folks won't be able to do well with what amounts to an uphill glide as a climb rate. Little bobbles in turns due to poor control coordination will produce a sink rate instead of a climb. So it becomes hyper critical in how you wiggle the sticks. So to give yourself some fudge factor room I'd suggest that you figure on a motor and pack that gives you 30 to 40 watts per lb so you can climb at around a 20 degree angle when required but still throttle back to around 3 to 6 watts per lb for level cruising.

In terms of light weight and big wings be careful what you wish for. If you manage to achieve a wing with 1500 sq inches and keep the weight down to 4 lbs you'll have a very light 4.6 oz/sq ft wing loading. But you'll also have a model which can only be flown in calm to light wind conditions for the most part. With care and skill you can fly it in up to 8 to 10 mph winds but it won't be much fun. More a matter of survival. And you can forget about flying in anything over 10 mph. Keep in mind what you feel on the ground gets stronger 50 feet up.
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Old Sep 16, 2013, 09:23 PM
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thank you for the very elaborated reply,

I think i would be able to keep the weight down as much as possible by making rib structure using depron and carbon rods like this person http://www.rcgroups.com/forums/showthread.php?t=1050008

the above link shows a 14 feet wing with 3.5lb weight, IMO that is too light for a wing this big and the structure has so much strength that it can be lifted from the tip.

considering that i would be making a 8 ft wing the weight wouldn't be that much of an issue

now all I need is a effective, efficient and exact design plan to make this happen, as I have no experience in designing a wing. and little experience in building. I don't have in depth knowledge of the aircraft design structure.

Also I would be implementing solar panels on this wing. If you know or can calculate exact dimensions (root chord, tip chord, sweep, airfoil ) that would be a great help to make this a reality.

thanks
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Old Sep 16, 2013, 11:39 PM
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Quote:
Originally Posted by electrolics View Post
thank you for the very elaborated reply,
...........as I have no experience in designing a wing. and little experience in building. I don't have in depth knowledge of the aircraft design structure.

Also I would be implementing solar panels on this wing.....
I'd suggest learning to dog paddle before you try to swim the Channel for a new record time.

For this first time around skip the solar panels. That can come later in a new build. Keep your first adventure as simple as possible as the mountain you're climbing is already steep enough. That wing of Bill's in your link is clearly not his first time building something.

As for the design I'd suggest you slavishly plagiarize something that is already a proven design. If you're more comfy with Depron and carbon by all means go that route. But copy something that has already been done. You'll still be learning lots along the way.

To get ideas study all the threads and links in searches you can on projects such as Bill's. You'll learn a little more from each read.
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Old Sep 17, 2013, 01:42 AM
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http://www.gobookee.net/get_book.php...4gTGVuZyAuLi4=

I haven't opened this,but it looks as though it could be of interest
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Old Sep 17, 2013, 10:55 PM
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With regards to solar power. The last guy who managed to do it successfully spent 10 years getting the power setup just right. And spent a lot of money doing it - mostly buying solar cells that he discovered were not usable on an RC plane - too heavy, generates too little power etc. You can read up on his project here: http://www.rcgroups.com/forums/showthread.php?t=1954492

In the end he ended up flying with a 20-22 watts setup. For a comparison, a 2S setup at 22 watts translates to around 2.6 amps. You'd need a very efficient and light (low wing loading) airframe to fly with just 2.6 amps.

Is it doable? Yes, certainly - as proven by the guy in the linked thread. But treat it as a long term project where each build you do is like baby steps to learn how to build planes light and strong and able to fly with minimal power.
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Old Sep 18, 2013, 02:12 AM
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Are there any methods or formulas for calculating the wing dimension and other perimeters given the power and weight?
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Old Sep 18, 2013, 12:31 PM
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Not really. There's no one perfect answer for any of this. Other than obviously you want a low wing loading and a good airfoil. Instead it's actually a pretty broad bell curve sort of thing.

But it's more than that. It's a set of overlapping requirements that all fight each other. We want a light weight and low wing loading to get a slower sink rate. But that requires lots of structure. So we need to be skilled and knowledgeable to design and build a light enough but still strong enough structure to achieve this. But how do we know how strong it needs to be? There's just no good answer for that other than to build models and when they are too light they break up so we try again but this time build a little stronger.

But strength isn't just adding material. It's as much HOW the material is used which also counts. You can learn more about this by studying various plans. In particular look at free flight model designs to see more examples of doing a lot with very little.

In the end though you don't learn all this and make the perfect first model. If you think you can you may as well give up now. It's a skill as much as a study. And the skill portion can only be learned by doing.

The solar model in that link came in at only 26oz with a 104 inch wing span. That is light by any measure. The design and building techniques are straight from the classic free flight school of light weight yet reasonably strong. 26oz is 1.6lbs. So with 22 watts of power it's flying the way we see in his videos with only 13.7 watts/lb. The videos will thus give you some idea of what flying at this sort of modest power level provides.

In any event since you haven't built much of anything yet I still suggest you shelf the solar power idea for now. Learn to build and learn to fly first. By "learning to fly" I mean learning to fly such that you're super smooth and do not waste energy in the model from using excessive control inputs and by entering and exiting turns smoothly with no speed change due to mis-coordinating the controls. Learning to fly in this manner will set you up for future very low power flying.

Keep in mind too that very low power and slow flight that gives the longest duration for every watt of power carried aloft will also be kicked around in windy conditions. That huge 17 foot glider you posted the thread for in your first post is going to be in that sort of situation.
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Old Sep 18, 2013, 01:33 PM
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thank you for the reply,

I understand the points you mentioned and totally agree with you on this. this is not an urgent build I just started working on it. I am reading stuff about plane structure, design and optimization available on the interne.

i know that this kind of stuff can be achieved from years of experience, learning and experimenting. But solar powered rc planes are not new. A lot of successful work has been done on it. Many of the solar plane airframe were based on glider or sailplane. while I am more into flying wings and feel quite easy building and flying them. I am still trying to figure out if solar flying wing would be better than the conventional plane design.

I am just trying to make cheaper yet effective version with little modifications of other designs. just couldn't find one yet?

well I got inspired from many projects like this one
FPV, 80km and back. 2.4Ghz RC. (3 min 34 sec)


http://www.rangevideo.com/forum/show...-my-Maxi-Swift

in this project the solar panels can provide up to 5A at 12V, while the 4kg wing needed 8-10A to stay leveled. I believe that if I only cut down the weight to at-least lets say half, the wing should require even less power to stay leveled.

what do you think?
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Old Sep 18, 2013, 03:36 PM
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Low weight with lots of wing area is always the answer to low power flying. The key is, as I described above, to achieve that while still providing a strong and resilient airframe.

On things like solar powered planes a major portion of the weight is taken up by the required gear to provide the power and guidance. So you're stuck with that fixed payload right off the bat. With the airframe already being less than half the total all up flying weight cutting the overall weight by 50% is simply not doable. You might manage to cut down the airframe itself by half but if the airframe was already only 40% of the total weight then you only save 20% of the total.

Looking at the fellow in sbletman's link of his solar powered model the other issue is that it's apparent that we needed to wait for the weight vs power efficiency ratings on cells improved to where a reasonable model could carry enough cells at a weight which allowed for an airframe to fly. If you're patient YOUR attempt might just be using the next generation of cells. In the meantime by all means build up some models and test for the power needed to maintain level flight under realistic values and designs. Then you'll be ready.

The measure of the lowest power needed to fly level is also the sailplane's parameter for lowest sink rate. That is the airspeed at which the design takes the longest to sink back to earth. On a powered model this is also the speed which requires the least power to fly level.

But with flying wings we run into issues with using highly cambered airfoils which allow for higher lift coefficients that still have reasonable drag coefficients.

For example there's a very good reason why world championship FAI free flight models use thin and highly cambered airfoils. It's because they offer the lowest sink rate. But such airfoils have strong pitching moments. On a conventional layout this isn't a big issue. On a flying wing a strong negative pitching moment requires more washout and/or more sweep angle if the wing is to remain positively stable in pitch.

Now you CAN twist the wing enough to be stable with such airfoils. But the tips will end up operating at a highly negative angle and likely end up adding more drag than you save. So there's going to be a happy middle ground in terms of airfoil choice. What is that happy middle ground? Damn'fi'know. But it's something that you could play around with and build some models to test and learn. And learn you will. About aerodynamics, stability, flying, and power systems. If your fourth model isn't head and shoulders over your first then you are either not learning anything or you got DARN lucky on your first attempt.
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Old Sep 18, 2013, 09:12 PM
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Originally Posted by BMatthews View Post
Looking at the fellow in sbletman's link of his solar powered model the other issue is that it's apparent that we needed to wait for the weight vs power efficiency ratings on cells improved to where a reasonable model could carry enough cells at a weight which allowed for an airframe to fly. If you're patient YOUR attempt might just be using the next generation of cells. In the meantime by all means build up some models and test for the power needed to maintain level flight under realistic values and designs. Then you'll be ready.
Actually such cells already exist. Indeed, if you look in the thread I believe there was one solar cell salesman who was promoting his cells. The thing we need to wait for is for the prices to drop to affordable levels (depending on your definition of "affordable").

If money is not an issue you can use the cells they use on this:

http://titanaerospace.com/platforms/solara-50/

They claim flight duration of up to 5 years without landing. So the cells not only provides power for flight but also recharges the batteries for night flying.

Heck, if money is not an issue you can buy the Solara. They take a month on average to build but there's already four orders so if you order now you can have yours in January or February.
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Old Sep 21, 2013, 06:27 AM
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Mr BMatthews, I think you have understood my problem and situation quite well. kindly suggest me a 2.5m WS light flying wing plan to begin experimenting with. I believe you are a builder and have much greater knowledge and experience.

i want to first practice a Rib structure wing using styrofoam and carbon rods
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Old Sep 23, 2013, 12:18 PM
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I had to think a bit on this answer. Really there isn't any one good way to go. You want to fly at moderate speeds. So really any thermal flying design should work for you. But you want to carry some payload in terms of FPV stuff. Which means the wing loading would go up. But there are very few designs of this sort.

There are a few different places on the web that have information about flying wing designs. If you google for "flying wing plans" and "flying wing models" and a few other similar combinations of keywords.

There have also been a few design threads on RCG by other modeler's that wanted a flying wing planform that could carry a camera. Do a search in RCG for "flying wing camera" and sit back to do some reading.

Styrofoam for a classic rib and spar setup is a poor choice of material. The foam is simply too weak and prone to compression damage or snapping from tension to perform well. Balsa wood is a far better option as has been proven by 100 years of aeromodeling. If you really MUST use some new fangled foam then the best option would be Depron. But even then it's a poor second or third place compared to balsa for suitability to use in rib and spar classic construction. To make it work well you really need to cap the edges of the ribs so that the Depron becomes more a core to support the banding on the edges of each rib. This make the project more time consuming than using straight balsa.

In the end you're trying to do a lot all at one time. You're not only going to climb a mountain worth of skill and knowledge just over the building of the model but you're also packing up your back with a lot of needless ballast in connection with wanting to put cameras and other payloads into the model all at once.

Instead I'd suggest you start by simply building a model to fly. Never mind cameras, solar cell assist or anything else. Simply build up a somewhat smaller 1.5 meter or 2 meter model designed by someone else and fly it. With that base of knowledge you'll then get a feeling for how much bigger you need and you can try flying the model with ballast equivalent to the weight of the FPV gear.

After all, jet fighter pilots don't just step into the cockpit of a front line fighter. They practice and train through a basic trainer, advanced trainer and then finally the front line fighter. And most things in life are like this. So take your time and start with something more basic and with a single focus of learning to build and fly a flying wing. Leave off the additions until later for your second, third or even fourth effort.
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Old Sep 23, 2013, 09:21 PM
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Originally Posted by BMatthews View Post
Styrofoam for a classic rib and spar setup is a poor choice of material. The foam is simply too weak and prone to compression damage or snapping from tension to perform well. Balsa wood is a far better option as has been proven by 100 years of aeromodeling. If you really MUST use some new fangled foam then the best option would be Depron. But even then it's a poor second or third place compared to balsa for suitability to use in rib and spar classic construction. To make it work well you really need to cap the edges of the ribs so that the Depron becomes more a core to support the banding on the edges of each rib. This make the project more time consuming than using straight balsa.
Having actually built rib and spar depron wings I have to disagree slightly.

Firstly, depron rib and spar construction is not the same as classic balsa rib and spar construction. It is more similar to balsa sheeted foam core construction - the loads are borne by the skin rather than the internal structure. In foam rib and spar construction what you're building is not a rib and spar wing, what you're building is a hollow foam wing which is significantly lighter than solid foam wings but with comparable stiffness.

Up to 1.5m span I've successfully built wings with foam spars. The secret is to use fiberglass tape as spar caps taped to the insides of the foam skin, not the spar. It's the tape that's actually acting as spars with the foam "spar" acting as a very weak shear web.

I've been meaning to build a 2m wing with 1.5mm balsa glued to the foam spar to make it a better shear web but it will have to wait till next year due to all the other projects I'm currently working on. I suspect it's possible to build rib and spar foam wing with balsa shear web for up to 3m before I need to consider using carbon fiber anywhere on the wings.

One big advantage of foam over balsa is the cost (at least to me). I understand that the cost of depron or depron-like sheet foam varies depending on where you are but at least for me for the cost on one balsa plane I can build twenty foam planes.

You do have to use slightly thicker airfoils though when building this way because you lose a lot of stiffness with a thin airfoil. Some of the thicker MH airfoils work quite well. I typically use airfoils with 10% to 12% thickness.

Also, due to the thickness of the skin and the softness of the ribs the airfoil you end up building is fairly inaccurate. You can improve things a bit by making sure you've allowed for the skin thickness when cutting the ribs. Fortunately most thick airfoils are fairly tolerant of inaccurate building techniques.
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Old Sep 23, 2013, 09:43 PM
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I'd have to agree about building a simple model (flying wing or otherwise) first and then keep improving in small steps. The advantages are numerous:

1. The initial cost is significantly less. Whatever you do you're not going to eliminate ongoing expenses in this hobby. So you can either spend large sums rarely or small sums often. On average you'll be spending roughly the same amount either way.

2. FPV is in itself a full hobby - in addition to your RC flying. Whatever time you spend on understanding flight and building planes you'll be spending almost the same amount just fiddling with video equipment. Learn how to build planes first so that when it comes time to delve into FPV you have one thing less to worry about and can concentrate on debugging your video gear.

3. You WILL make mistakes. The first mistake that you're almost guaranteed to make is building your plane too heavy. Some people make the opposite mistake and build them too fragile and light but that's extremely rare. Fragile and heavy also happens a lot. The good news is that you will learn from your mistakes if you keep building. If you're like me and like to design your own planes I suggest building other people's planes from plans from time to time. Sometimes you can't see what you're doing wrong unless you take a look at other people's work.

4. The most significant benefit is that you'll be flying! Now or next week or by the end of the month. You'll be flying instead of waiting. This has two primary advantages. First and most importantly is you'll be having fun! Second is you'll get practice flying (and crashing) so that when it comes time to fly your FPV plane you'll have better confidence and better understanding of how that plane responds to your input.
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