Help me with an airframe idea please.

[JeffElecRC]

Hi there, I've recently been building up a paparazzi autopilot, and I've been thinking about building the airframe I want to put it in (for now its being tested in a magpie AP).

My goal is to do aerial photograpy so I want to be able to mount a down-looking camera (that can tilt side to side) and also a front-looking CMOS camera for fun on the video downlink. I'd also like a 20-30 minute flight time on E-power (doesnt need to go fast).

My current idea for the airframe is to take a commercially available wing and convert it into a twin-boom pusher setup. I'll modify the wing with hardpoints to attach the tail-booms. I want to make the fuselage out of a 3" to 4" diameter carboard tube. The tube will attach to the wing via straps or bolts with reinforcements as neccesary. At the back of the tube will be an AXI motor and prop mounted to a woodeng firewall, at the front a dome-camera. The full-size digital camera will lie on its belly looking down through a notch in the tube, so that it can pan side to side with the help of a servo.

I was hoping to get some feedback from you guys on this idea. I think the sleek tube design will look alot like the scan-eagle but with a twin-boom tail and standard empennage.

My first question is if there are any thoughts on a good wing to use. I want ailerons and relatively low dihedral (the autopilot will take care of stability). Right now I'm looking at the Telemaster 40 Wing (73") so thats about the size I want the plane to be. I also considered the Electra/Gentle Lady wing, but it has an aggressive pohlyhedral and no ailerons.

Could anyone offer some suggestions on how I design for endurance. The airfoil of the telemaster wing is flat-bottom and looks pretty curvey on the top. This will be good at low speed right? but what about in a pusher setup, would soemthing like a glider wing be more appropriate? What sort of wing-loading should I consider for good flight times and decent flying characteristics? I'll come up with a weight estimate soon, assuming a power system equivalent to an E-Telemaster 40.

Anyway. Thanks for reading. I hope to hear some great suggestions. :D

[Unterhausen]

I want to do the same thing with the extra wing I got with my Stevens Aero Squirt. Twin boom pusher.

The lack of dihedral isn't necessarily a good idea. Life is much easier if the airframe is stable and self-righting to some degree.

The rest of your questions deserve better answers than I can give. But I'll take a shot anyway. I really don't see why it would matter if you go to a pusher over tractor. Granted, the airflow is different, but not that much. If you really want a lot of endurance, the glider wing is probably your best bet. I'm just saying that from observing endurance aircraft. This leads to low wing loading.

[LukeZ]

This is what I have been thinking about lately as well. Fuselage, empenage, drive system are all easy to put together; it's the wing that's the challenge. To design my own wing I'd have to first pick an airfoil, and although I've done a lot of reading, I probably don't even myself quite yet know exactly what my needs are going to be, at least not sufficiently such that I'm going to pick just that right airfoil that gives me some kind of super advantage over a regular sailplane wing. So I've been thinking I could save myself a bunch of work and probably have pretty good results by building a glider wing from a kit, dumping the rest, and building my own fuse.

I can't give you any advice on the Telemaster wing, but as you know the guy named Workshop on these forums is using a Telemaster and he can probably give you some thoughts on it. It seems to me it is a very high-lift wing, which means (to my mind), low speed and probably high drag. You'll need a decent powerplant (ie, expensive for electric) and don't expect to go extremely fast. The good thing is you should be able to lift a pretty good-sized payload (as he has, if you read his thread).

A higher-aspect ratio wing, such as the Gentle Lady you mentioned, would give you a wider operating speed range and probably require less power to lift. The Gentle Lady may not really be your best choice - as you mentioned, it has no ailerons and does have aggressive poly. Check out the Spirit 100 (http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJ598&P=7), it comes with ailerons and the parts to build optional flaps. It has dihedral (and actually it even has polyhedral as well, but very little), so it should be stable, but also maneuverable. In fact, I know it is, because I've built two of them. Only thing about Great Plane kits is they build like tanks. If you're not going to be zoom-launching your UAV you might want to seriously consider lightening the wing structure to save weight.

I just now thought about the Spirit 2M Elite (http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNH96&P=7) - the wingspan is more in line with what you're talking about (78"). The wing can be built with ailerons and even flaps if you want, or you could leave those out. Probably not much need for flaps on a UAV.

Both the Spirits mentioned also come in ARF versions - would save you some work, but again, expect the building to be a tad on the heavy side.


Luke

[JeffElecRC]

Thanks for the input gentlemen. Unterhausen, the reason I say that I don't want dihedral/polyhedral is that the Paparazzi autopilot has been proven on alot more unstable airframes (i.e. microjets and 4-rotor helicopters) so I think eliminating the dihedral will allow the autopilot to do its work better and make a for more responsive/maneuverable UAV.

LukeZ, I checked those those gliders, they are definately about the right size (at least the 2M elite is). I'm afraid of loading up a glider wing too much. I guess I can't make a judgement until i come up with a weight estimate.

I'll probably keep posting here with new info/ideas.

BTW: do a search for a thread called "aerosodle". Someone has built a very nice twin-boom pusher tube-design. His model is a bit small for the weights I'd like to lift, but I asked him for his autocad drawings, maybe I could scale it up to suit my needs.

[kd7ost]

BTW: do a search for a thread called "aerosodle". Someone has built a very nice twin-boom pusher tube-design. His model is a bit small for the weights I'd like to lift, but I asked him for his autocad drawings, maybe I could scale it up to suit my needs.

http://www.rcgroups.com/forums/member.php?u=53193

Thats Scott, AKA typicalaimster. Good builder and pilot to talk to.

Dan

[meles meles]

'ello 'oomans !

We're embarking on a similar project too - we need a UAV to keep an eye on you all as part of our masterplan to overthrow 'oomanity. We started out with the idea of going for a canard design but the clever 'oomans on the Modelling Science forum persuaded us to go for a twin boom pusher with a moderate aspect ratio wing... Check out our thread here (http://www.rcgroups.com/forums/showthread.php?t=546249) - we'll definitely be keeping a beady eye on this one. We've already proven our camera and video links at ground level, now we just need to develop the air platform and GPS guidance.

[typicalaimster]

A bit late here...

There was Aerosodle (http://en.wikipedia.org/wiki/Aristotle) that would do fine at the 2-3 lb weight limits. That had a flight time of about 10 minutes. It was built more as a video platform more than a camera platform. I've pulled the plans off the net for now for "release management reasons". I may release it as a "FPV Trainer Kit" in 2007. That's still a work in progress. I have plans in CAD but I'm very hesitant on who they go to. There have been issues with manufactures in other countries stealing plans and selling the kits on Ebay. If you go to www.profili2.com and search under plans for Bib Brother that will give you an idea of how someone else did it.

Later on came Aerosade. It was built as a glow powered system that would fly with a 50 to 70 sized 4 stroke for 30 minutes and would be in the 4-8 lb catagory. Rev 1 of Aerosade had a gear structure problem, and Rev 2 had an issue with the 4 stroke I was using. Lessons leared I could either build a Rev 3 or move on to a different design.

Mostly these two were based off of Aerosonde (http://www.aerosonde.com/) and the Pioneer UAV (http://www.puav.com/home.asp) . However I wanted something quick and simple. I knew I needed to have something to mount my equipment to.. I then needed something to cover that equipment up to protect it. Thus the profile and body tube designs. However I didn't think a couple things through all the way.

I took a summer break and worked on some swept wing designs (http://www.rcgroups.com/forums/showthread.php?t=531474&highlight=xj) with my dad. I also played around with a few delta's while I was at it. I'm now working on another design dubbed Infinity (http://en.wikipedia.org/wiki/List_of_Ghost_in_the_Shell:_Stand_Alone_Complex_ep isodes). I'm still trying to draw out the plans to the craft. This one would have the swept wing like the Scan Eagle.. It would also have the twin booms and a V-Tail for a bit of stability. Some may laugh but after you fly a tailless airplane you soon realize what it does. With the "Infinity" design I'm trying to shoot for a very robust design. It will basically be the next step after Aerosodle. Currently I'm shooting for a 500 sq/in wing. I'm trying to come in under 2lbs with the airframe itself. The plane will go up with a E-Flight '32' sized motor and take a 3700mah - 4000mah pack 4 cell pack. If my calculator is correct I think we're talking about 820 - 880 watts of power.

A few other things to note...

I want ailerons and relatively low dihedral (the autopilot will take care of stability).

Very good points... Sparky Paul (http://www.rcgroups.com/forums/showpost.php?p=5815730&postcount=26) is using a polyhedral wing on his twin boom design. This will allow the plane to correct itself hands off. I'm using a flat wing with no dihedral along with a FMA CoPilot. I went this route so I could do 'light aerobatics' with the plane. I don't know if you saw the video (http://video.google.com/videoplay?docid=-1152229394797388906) in the AP forum, but I wanted the plane to be very nimble for this exact reason.

I want to make the fuselage out of a 3" to 4" diameter carboard tube. The tube will attach to the wing via straps or bolts with reinforcements as neccesary. At the back of the tube will be an AXI motor and prop mounted to a woodeng firewall.

You are on the right track here. Loc Precision puts out 3.90" rocket tubes and nose cones (http://www.launchpad2000.com/parts-body.html). The problem is the nose cone and tube itself will cost you about a POUND of weight. Use the tubes structure to your advantage! I found out later about how strong the tube was. I think I wasted about a pound of wood building out my airframe. I'm still debating if I want to go the tube route on "Infinity" or start over with something new. I may start out with a tube in the beginning and move to a balsa build out later down the road. Another mistake I made with "Aerosade" was not mounting the engine flat on the back. I tried to be crafty and make the engine mount part of the fuse. This lead to the 4 stroke getting a bit hot and blowing a valve.

Right now I'm looking at the Telemaster 40 Wing (73") so thats about the size I want the plane to be. I also considered the Electra/Gentle Lady wing, but it has an aggressive pohlyhedral and no ailerons.

Many of us in the forum have started off with a prefab wing and gone from there. I believe Canadian Goose and W4UAV (http://www.rcuniverse.com/forum/m_3588416/tm.htm) went the same route on their RPV/UAVs. Don't be afraid to roll your own wing. I was helping instruct one of George Town Universities engineering students on flying. From what he said they are building a 20' twin boom pusher very similar to my plane. After he saw me flying my plane and asked a few questions about it. He was very shocked when I told him I chose the airfoil "because it looked pretty in the simulations". Wing design may sound hard but there are programs like Profili out there that will help you. There is also a design spread sheet by Lee Van Tasel that will give you ideas. I still use my own modified version of Lee Van's spread sheet to design my planes today.

Lastly I do apologize if it seems like I may have blown you off in messages going back and forth. There are many of us that have spent hours on designs. I know I've been woken up by the computer beeping at me 'cause I was sleeping on the keyboard a couple times. I'm very hesitant on 'giving up the goat' when it comes to the design. I'd be more than happy to collaborate with you on here and help give you some ideas to steer you in the right direction. There is a lot of talent in the forum that will help you along the way. More help than I had when I started into this mess ;) Do keep up with the questions! I'll attach some food for thought. If you have questions throw them in the forum.