Discussion First UAV airframe question

[Groucho-14E]

I’ve been into RC for a couple years, and now I’m researching airframe options for my first UAV. I want to use the ArduPilot system in an electric powered, high-wing aircraft with landing gear. A few different aircraft have caught my attention, the StevensAero SOARStik, NitroPlanes Cessna 337, and E-Flite Alpha 450.

I’d like to hear what experiences you’ve had with these aircraft and which you’d recommend or advise against. If there's another good choice I've missed I'd like to hear about it.

On a separate note, I’m also curious about flying-wing UAVs that I’ve seen online and in some academic papers. What are the pros and cons of this configuration?

[rich smith]

IMO flying wings are not good for first time UAV efforts. I prefer self-stable designs because it allows far less complex hardware and software. Almost and order of magnitude difference in cost and weight. Important considerations if you lose as many planes a I did starting out.

PS By self-stable I mean you can go way up, invert or spin dive, then let go of the stick and plane will recover.

[Groucho-14E]

I wasn't planning on starting with a flying wing, just curious about them. I'm a big fan of stability.

[jtprouty]

There are some very stable flying wing designs out there that work very well and are fairly rugged. An autopilot will give additional stability which will tame unstable airframes as well. I use an Atto V1.8 and it corrects for an untrimmed plane and will even correct for the plane being grossly out of trim (nose heavy or tail heavy.)

If you like flying wings there are some EPP kits on the market that would work well and are, of course, bouncable.

One plane that I think would work well but isn't a flying wing is Graupner's ELEKTRO-TRAINER S RC Plane (OVERSIZE). It's fairly complete and only costs $185 from Hobby Lobby. Anyone seen one fly?

Jimmy

[Gary Mortimer]

I have flown two different wings autonomously, a zagi and one of our own design. The advantage is that they can cope with wind a little better, not having so much side area for the wind to get hold of and they are very simple, just two servos! The disadvantage is that they are flipping hard to see and its also difficult to mount cameras for oblique shots, vertical is easy.

Jimmy is being modest he has a very nice design, the Osprey http://attopilot.ning.com/page/osprey-1

G

[rich smith]

My problem was cost. If you can afford to blow a grand then high end autopilots with IMU etc like the Atto make sense. One of the original design constraints dictated by my client was the autopilot setup complete w/plane could not even "cost hundreds". I succeeded but self-stable was one characteristic that could not be sacrificed.

Needless to say, like Gary indicates, I cannot fly in conditions that regular RCers have no problem with. Mainly just before dawn and on those really hot windless summer days. ASOS is my friend.

I had high hopes for Attopilot, Paparazi, Arduino, etc. that initially started as low cost projects for the beginner but quickly bloomed in cost and complexity well out of my range. So back to the drawing board, inherent airframe stability being the key cost reduction measure in my case.

[wbuttry]

well get a easy star the most stablest planeon the market you dont want a wood kit or if you just want a wing try a ritewing a 60 inch or a 54 in zephyr they are epp and can be fiberglassed in no time go to ritewing.com

[jglenn]

rich: why can't your autopilot fly just before dawn and on those really hot windless summer days? What is ASOS?

Wood planes can be very rugged, and not so hard to repair. Every time a
foam plane busts, it gets heavier from the glue to repair it. Wood planes
bend and flex and you can use CA. Usually epoxy fixes foam better, maybe.

Actually I am flying a 1/2 HP wing top mounted pusher, specially designed to
survive crashes, hence the pusher. You can see a pic of it in the parachute thread, dropped a chute well. The fuse is wood, wing is foam, hybrid!

A trick I use is sandwiching a 2" thick piece of EPE foam sticking out from the nose. It is the best energy absorbing foam I have found, used for packing expensive machines for shipping.

This plane can slam into the ground and just bounce. You pick it up and fly again. Earlier versions were tested by flying into a brick wall at full power.

One weird problem is a shock wave propagates thru the fuse, and the rudder snaps off sometimes, with an intense hit. But the rest of the plane is OK.

[rich smith]

Originally Posted by jglenn

rich: why can't your autopilot fly just before dawn and on those really hot windless summer days? What is ASOS?

Just the opposite. I fly only at those times. Sorry I didn't phrase that correctly.

ASOS=Automated Surface Observing Systems. Reliable up-to-the-minute info on local wind speed using aircraft radio.

Originally Posted by jglenn

Wood planes can be very rugged, and not so hard to repair. Every time a foam plane busts, it gets heavier from the glue to repair it. Wood planes bend and flex and you can use CA. Usually epoxy fixes foam better, maybe.

Just the opposite. Consesus among those who have tried both is wood is fragile and foam is not.

The fact that you even consider using CA and epoxy on foam says a lot. Hot Glue is very popular too but not much better. While something can be said for some of the contact cements like UHU etc. nothing competes with PU (Gorilla, Sumo, etc) for adhesion, strength, and weight.

Originally Posted by jglenn

A trick I use is sandwiching a 2" thick piece of EPE foam sticking out from the nose. It is the best energy absorbing foam I have found, used for packing expensive machines for shipping.

It's rare for EPE (Expanded Polyethylene) to be used for foamies. Expanded Polypropylene (EPP) is more common for shock absorption but is ridiculous flexible. I don't like it because it is too flexible and impossible to use w/o reinforcment. Expanded Polystyrene (EPS) is not a serious building material either due to it's extreme brittleness. Good for toys.

The main issue with crash damage is not flexiblilty or toughness anyway but weight. Few hobbyists recognize this but it's true.

Extruded Polystyrene (XPS aka FFF/Depron) is not only significantly more flexible than wood but more importantly is lighter. A LOT lighter even compared to balsa.

Originally Posted by jglenn

Actually I am flying a 1/2 HP wing top mounted pusher, specially designed tosurvive crashes, hence the pusher.

1/2 HP???? Elizabeth! Elizabeth Honey! I'm comin'... Elizabeth!

You are right about pusher configuration though. Either that or have a HUGE box of spare props and motors handy.

At one point in time this was more of a hobby for me as I was hired to study these issues for clients involved with air sampling. I spend many hours and built hundreds of foamies for these guys. Things that make little difference to most hobbyists saved thousand$ and made the difference between the project being viable or not.

[jglenn]

Rich: thanks for comments, sorry if I seem backwards sometimes, will try to adapt to modern techniques, am an old balsa fan, from the 1960's, before there were foam planes, not even in the 1980's do I remember that. From a structural standpoint, every material has its advantages and drawbacks, whether foam, wood, carbon fiber, aluminum, or even titanium. It is how you combine them, to take advantage of each ones strong points, that matters.
For example, balsa wood is available in many grades. An old trick is to use
"C" grain for the leading 1/3 of the wing (hand launch glider or rocket plane),

and light weight variety for the other 2/3. Many new expensive 3D plane kits
have carbon fiber parts fused to wood and even foam parts.

Have heard of Gorilla glue, will check it out. EPE I do not use for the main structure, just a "shock absorber" built into the nose, about an inch of the foam sticks out, from between the balsa sides. This has been refined over dozens of flight tests and crashes. Necessary because I am not always the
best pilot, or plane designer. The 1/2HP is just for fun, overpowered so much I need to get a better battery to handle full power without voltage droop, can only run at 80% without ESC cutout now.

The foam planes are easy, fly out of the box, but I think you can beat
the efficiency of them with a built up wood wing (GASP)

cover with this stuff they call Super Monocoat, speaking greek to you
foamie guys. The transparent colors are neat, not sure how to get light
to shine though a EPP sheet, and foam is really heavy if you look at it.

The hotliner speed planes are all carbon fiber, I think.

[rich smith]

I go way way back, started with balsa over half century ago because, of course, that's all there was. I did get a kick out of spritzing that tissue! However drifted away from the hobby because of the time and patience required. Foam and electric were like a breath of fresh air to me and revived my interest. The brushless/lipo revolution just added fuel to the fire.

Of course you are right about every material having advantages. Balsa for me can't be beat when used as a low cost framework for sub-gram micro to stretch that OS film across (called that because it's so thin it only has One Side ). CF is stronger but more costly and can be VERY difficult and dangerous to work with. For normal size planes I've gravitated toward FFF, specifically PB3 from Lowes. Pennies per plane and extremely resistant to damage. When I do finally manage to destroy a plane I just crack up and laugh because it's so easy to repair or just build another.

You might like Polyurethane. It's only drawback is slow setting time. However if you mix a little water or whiteglue it sets in minutes and foams up big time. Even though many newcomers complain about the foaming in my opinion this is one of it's main advantages.

[jglenn]

Wow, you are an old timer too. I can almost remember the rubber band powered escapements, but not the single vacuum tube radio. There were foam planes decades ago, the really crummy stuff, big cells, broke easily, heavy.

I still remember my first built up 2 meter sailplane, CraftAir Drifter, had washin,
wash out, turbulators, other tricks, would hand launch about 200', way further than any foam plane I had.

The lightest covering I have used is jap tissue, with dope.

Is FFF like Depron?

Will ask my foam addicted pal about polyurathane glue, never heard of that.

Keep 'em flying!

[rich smith]

Originally Posted by jglenn

Is FFF like Depron?

Will ask my foam addicted pal about polyurathane glue, never heard of that.

FFF is just a comercial version of Extruded PS like Depron but much cheaper and easier to obtain here. The PB3 vesion has a skin on one side that makes it much stronger than Depron. The obsolete 2 side version (Blucor) had skin on 2 sides and was stronger still but very hard to glue for that reason.

I'm sure you must have heard of PU, aka Gorilla, Sumo, Elmers Ultimate, Elmers Nano, etc..

[jglenn]

My pal Ivan plays around with foam a lot more. He says the FFF is fan fold, made by Dow. Sometimes he scavenges the blue and pink foam sheets used in building construction. We made a hot wire cutter with various cutter bits that is fun, and a long wire stretched for wide slices. Here is a plane he is working on:

[rich smith]

Beautiful! The planes I build are toys compared to that. I probably couldn't fly that either as I'm not good enough for low wing or ailerons yet.