Pterodactyl

[herk1]

A Pterodactyl design posted on RCG caught my eye (link). I decided to take a stab at making it, using Dollartree foamboard. The design looks attractive and well thought out, with tabs and slots to take the guesswork out of assembly. I used some of the techniques from Flitetest plane-building for the build -- for example doing the elevons by a score-cut followed by a bevel-cut followed by sealing/reinforcing the paper hinge with a thin layer of hot-glue.

There was a bit of a challenge at the outset, in that the plans are just .jpg images not PDFs, and there is no scale shown...so the first decision was how big to print out the plans. I figured that a 400 percent printout (from Windows Paint) would nicely fill up a 3x3 matrix of 8-1/2"x11" sheets of paper for each sheet of the plans, and then each of the merged sheets would fill out a 20"x30" DTFB perfectly. And better yet: at that size, the printed assembly slots came out just the right width for DTFB-thickness tabs. The resulting assembled model has a 44" wingspan.

The only modification I did to the design was in the motor mount area. I omitted the cutouts/notches in the center-aft of the wing and main body, and installed a plastic stick-mount onto the center-aft surface of the wing instead. It would also be pretty simple to modify the design to accept a swappable pod of the "mini" variety (like with the FT mini Scout), if you wanted.

For a power system, I chose a 1700kv "Blue Wonder" motor -- which turned out to be a good match...if anything, a little overpowered. I have been flying the Pterodactyl mostly using 40 to 50 percent throttle. The joy of this plane is just having it gently soar around and look cool. This plane design is a work of art! I especially like the curving claws detail in the feet.

 

[jimmymc2286]

Great work, This may be one of those have to builds.

 

[jamboree1]

That's pretty neat looking, if you like that bird you will love this one http://forum.flitetest.com/showthread.php?17616-The-Eagle-has-landed-or-is-it-flying

 

[herk1]

Actually I've had the Flyparty EPP Eagle for years, which that one looks quite similar to, except not V-tail.

 

[FPVology]

From the pics it looks like the wing tips fold down/in. Is this for flaps? Looks like a kickass phoenix to me! awesome build man love it!

 

[herk1]

FPVology - In order to fit both wings onto one foam sheet, the wingtips were broken out into separate parts, and those parts are notched for a secure, foolproof fit like the other parts. They're just glued on; they don't move.

 

[FPVology]

ahh gottcha

 

[ZoomNBoom]

Looks great!
Im a little skeptical about how it will fly, as its essentially a tail less flying wing without wing sweep to speak off, and that nose with the cute thingy sticking out, risks being a wind vane that will cause yaw instability with not much to compensate for it, but my intuition has been proven wrong before and if you give anything enough thrust, it will fly . Looking forward to your maiden

 

[herk1]

Like I said in the last paragraph of my first post...I've already been flying it, mostly enjoying just watching it soar around gently at 40 to 50 percent throttle. It flies surprisingly "normal" and easy, after getting the CG sorted out. And speaking of CG: figuring out the proper CG is what made the maiden flight pretty hairy...

The plans don't tell you much. Each part has a number on it telling you how many of that part you need to make. Other than that, there is only one two-character Chinese word on each sheet of the plans. On the sheet with the wing parts, that word falls right on the thick drawn line of a wing spar. My first assumption was that that word just meant "spar." It seemed awfully close to the leading edge for a CG balance point. So I balanced the plane for a CG of about a quarter-inch aft of the spar. Then on the maiden flight, the plane acted bad tail-heavy. It wanted to sit on it's tail, and it was touchy and difficult to control. So I carefully brought the plane down and put more weight on the nose, bringing the CG up to the front edge of the spar. Then I launched for a second flight -- and the plane was transformed! It flew beautifully and was gentle and easy to fly.

When I got home, I got on the internet to test a hunch I had about those Chinese characters on the spar. I went to Google Translate, set up for English-to-Chinese translation, and input "center of gravity" into the English block. Sure enough, Google spit back the exact same two Chinese characters that are printed on the spar on the plans! Doh!

 

[herk1]

Looks great!
Im a little skeptical about how it will fly, as its essentially a tail less flying wing without wing sweep to speak off, and that nose with the cute thingy sticking out, risks being a wind vane that will cause yaw instability with not much to compensate for it, but my intuition has been proven wrong before and if you give anything enough thrust, it will fly . Looking forward to your maiden

Oh I forgot to mention: if by 'tail less' you mean lacking in a vertical stab, it actually does have multiple vertical stabs -- in the large, mostly underslung vertical "legs" (see attached photo of the underside for a better view of the legs/feet). So there's plenty of yaw stability built in.

Another interesting oddity: since the wing is just a flat plane, I at first assumed that some "up" reflex in the elevons would be necessary, and I set it up that way before the maiden. But after I got the plane sorted out and trimmed, all that "up" elevon was trimmed out and the elevons are ruler-straight inline with the wings. So what holds the wing up into a positive angle of attack to counteract gravity? The "feet" are parallel to the wing, and the head is parallel. But the NECK angles upward. So I think that the horizontal braces for the neck, even though they are not very wide, have a canard effect to push the wing into exactly enough angle of attack so that no reflex is needed. Some serious thought must have gone into this design!

Yet another quirk: the hinge-lines on the elevons are not perpendicular to the wing...they are at an angle. I think this was done for two reasons: 1) if you were to instead cut some squared-off elevon sections out of the gracefully curved trailing edge of the wings, it would detract from the enchanting "bird" illusion inflight with every control deflection from neutral, and 2) it acts as a speed brake when you pull a lot of elevator, due to the opposite-rudder effect...which consequently protects from overstressing the wing (which is particularly weak in the middle-aft section between the feet and body). As a result, the model resists any attempt to loop it.

 

[ZoomNBoom]

it acts as a speed brake when you pull a lot of elevator, due to the opposite-rudder effect...which consequently protects from overstressing the wing (which is particularly weak in the middle-aft section between the feet and body). As a result, the model resists any attempt to loop it.

This is fairly typical of delta wings. Because the elevators (well, elevons) are on the main wing, as you pull up, the entire wing loses lift and tends to (high speed) stall. My last purchase was a hobbyking Me163 and its a good example of that. Nice plane, but the only way to loop it is make HUGE loops and be very careful when you pull out. Nearly crashed it on the maiden when I did a split S. Takes some getting used to, it rolls >1000 degree per second, but loops like a 747 .

 

[xviper]

Video

Finished building mine and did the maiden today. This is the video of the second flight. I made it out of Dollar Store 5mm foamboard, 20" X 30". It's powered by a Turnigy 28mm, 2200kv outrunner, 40amp FMS ESC, 7 X 5 prop, 1300mah, 3s battery. It required quite a bit of lead weight under the chin to balance at the spar. Launched using Frisbee throw, moderate throttle, no drama, but needed fair amount down elevator and a small bit of aileron to trim for level flight. The elevens were set up dead level to start. This thing flies way better than I expected. Rolls very nicely and loops are easy and effortless. Inverted flight a bit twitchy but that will get better with practice. I think the CG may need adjusting to fly inverted well but this may affect normal flight. More testing is required. Elevator response is odd. At first, it seems very sluggish and numb but at a certain point, it just jumps up or down. This may also have something to do with CG. It flies quite well at slow speeds and it floats well but also has the power to go very fast. Landings are soft and easy.
https://www.youtube.com/watch?v=XBA7-1cOPZg&feature=youtu.be

 

[herk1]

Nice job! I like the red highlights against bright green. Looks like you did a firewall-type mount per the cutout notches in the plans, instead of the stick-mount I did on mine. Which would make it easier to adjust the thrust angle. Mine climbs a little when adding power...so ideally it could use a little downthrust. Not too bad though. I also put quite a bit of balance weight on the chin of mine...four 1/4-oz. stick-on lead squares, for a total of one ounce. I'm using an 850 mAh 3S LiPo and a smaller motor, and I get eight-minute flights with a comfortable reserve. But like I said, I fly mine mostly puttering around slowly, at half-power or less.