The Fish: A scratch built slow flier

by RaptorTech | May 29, 2014 | (15) Posted in Projects

Introducing The Fish! A scratch built dollar tree plane for beginners.

 

Building The Fish

When I set out to design and build this plane, I had several goals in mind

  • Stability
  • Slow flight capabilities
  • Light
  • Robust to crashes and rough landings
  • Easy to control
  • Cheap (mostly spare parts)

These characteristic were all important to me because I planned to use the plane to teach people to fly. For this particular plane, I was not interested in looks, speed, flight time or acrobatics (though I would argue that I ended up with all of those but speed anyway!).

Wings

Although I didn't really have a grand build plan, I began with the wings, because at least those seemed pretty straightforward to me. Characteristics that I figured would be important for a slow flying wing were undercamber and being extremely light. I also wanted my design to be simple so that others would be able to reproduce it if everything went well.

First I cut out 5 formers from a scrap piece of dollar tree foam board. (Ignore the crease. This one's a template)

I scored a 10 inch by 20 inch piece of foamboard lengthwise at 2.5 inches and 5 inches and glued the piece over two of the formers. I repeated this process with two 10 inch by 10 inch squares which each received one former. The two 10 inch squares (with some trimming for looks) went on to the sides of the larger piece to form the wingtips for a nice polyhedral wing.

Strips of fiberglass packing tape and some hot glue reinforce the joint between the central portion of the wing and the tips. The angle was established by shaving away some of the foam at an angle on the wing tips where it meets the main wing. I added a strip of tape along the top just to have some color.

Wings done. They are incredibly light and decently strong.

Fuselage

Now for the hard part: the fuse. I wasn't entirely sure what I wanted from this plane, but I knew I wanted a puller prop and I knew that prop would be an 8x4 because I had a bunch of cheap 8x4s laying around.

I was tempted to attempt something like this because I liked how the prop was proteced somewhat by the fuselage and it's pretty unique.

However, the front "boom" was liable to be weak, and I wanted to keep weight low so extra reinforcement wasn't an option. I still wanted the prop to be off the ground on landings though.

I ended up playing around with a drafting program just to get something acceptable, and came up with a fuselage tall enough to get the prop entirely off the ground. The tall fuse meant that I could have my center of gravity well below the plane of the wings, which is very effective for stabilising the plane. Having a tall fuse also turned out to be really nice because it meant tons of space for electronics.

As usual I began building without concrete plans, but I had an idea of what I wanted.

I simply used strips of foam on the top and the bottom of th plane and two identical "walls." Without any reinforcement, the box could have been fairly weak, but I had many angles in the foam which greatly increased the strength.

Testing out the fuse with the wings

It seemed to fit well and looked proportional to me.

I hot glued on the other side of the body to close it up. This proved to be quite difficult as I made the mistake of trying to glue it all at once, so when it wasn't a perfect fit the already cooling hotglue didn't really bind. Squeezing more glue into the cracks seemed to help though.

I also added a tail with a rudder and an elevator. 

The vertical stabilizer and rudder needed to be fairly large to overcome the large surface area of the side of the fuselage.

Taking inspiration from the SkyWalker FPV plane, I cut a door on the side of the fuse and installed some 8g servos I from an old PNF 800mm Mustang. Here's where having all that extra space in the fuse was nice.

I ran pushrods from a decomissioned AXN Floaterjet through the tail boom and out to the tail surfaces. This airplane would have no ailerons, so for the sake of caution I made the throws on the rudder pretty big.

I added a simple plywood and foam motor mount at the front and ran two wooden dowels through the fuse just in front and behind the wing to string rubber bands over and hold the wing on.

I threw in all the electronics with velcro inside of the massive fuse, and The Fish was ready to fly.

 

Parts list

Electronics (all from HobbyKing):

  • 8x4 electric slowfly prop
  • 2200 kv AXN Floatjet replacement motor
  • 800mAh 2s all the way up to 2200mAh 3s (Lithium Polymer)
  • 6 Channel Parkfly Receiver (only 3 channels are used)
Materials:
  • Less than 2 sheets of Dollar Tree Foamboard
  • Packing Tape
  • 1' of 1/4" wooden dowel (mounts for the rubber bands over the wings)
  • 4 rubber bands (to hold on wings)

 

Flying The Fish

Although I usually fly at the athletic fields by my highschool (space is 2 baseball fields and a football field), for this plane I decided I could probably get away with a maiden flight in my backyard. My backyard is about 60x40 feet surrounded entirely by trees, so it was a pretty cramped space for a paper airplane, let alone an RC plane with with a wingspan of 40 inches.

As soon as the plane left my hand I knew the space wouldn't be an issue. A good bit of down trim and I was cruising around in tight ovals with no problem. Even without aelerons, I had no worries of rolling the plane because it centered out as soon as I took my hands off the sticks. Content with the performance, I took the plane down after about 2 minutes and invited some friends with zero flying experience to come over and try it out. We headed down to the highschool with The Fish and an FT Viggen.

Results and Comments

The good

The fish is unlike any of my other planes in that it can be made to fly almost at a walking pace. With a solid headwind, this plane can fly backwards quite comfortably. Now that's not to say that it can't handle the wind, however. Just throw in a 3s pack the plane becomes a different animal with unlimited vertical and a pretty good top speed.

I was astounded by the versatility of this airframe. It can be at once the easiest plane to fly (first timers had no problem keeping it aloft) and incredibly acrobatic (loops, wingovers, hover, etc.). The plane is super stable, so you can take your hands off and it will just fly in a straigh line off into the sunset, but if you have a bit of experience its also really manuverable. I love flying this plane in cramped spaces with tons of obstacles, because it's almost like the thrill of tearing through the forest with one of those little Blackout Quads.

The plane also amazed me with the variety of batteries it would accept. I maidened it with a 2s 800 pack (the type I use in my TX), but soon found that it will fly happily with anything up to a 3s 2200 (almost 3 times more weight). No wing flex at the bigger packs and very little change in minimum airspeed.

Overall, this is an incredible plane, and I am very happy with it's versatility. It's become one of those planes that I bring to the field every time, because I know I'll always enjoy flying it.

Things to improve on

I was thrilled with the way this plane performed, but there are a few things I would change for a "Version II"  

First, the motor mount was simply not strong enought. It was not a major flaw with the design of the plane; I just cut some corners to save weight. I also made the mistake of putting a sheet of foam between the motor mount and plywood firewall and running the screws through all. The motor wasn't going to come off, but it was not very tight and could be easily shifted or angled.

Second, the surface area of the side of the fuselage meant that in high winds, the plane would actually point away from the wind rather than crab into it. This was no problem for cruising around in regular conditions, but above 15mph winds, it became a major issue. Of course, the plane is very light and not designed for high wind, but the large fuse didn't help. For a Version II I would probably cut doors on both sides of the fuse and just leave them open so that air can pass through the side of the plane.

And third, the tail boom was not quite strong enough. It held up fine in flight, but in crashes (well really when my friend grabbed the plane out of the air) it got slightly bent where it joined the fuse. Some popsicle sticks were able to easily remedy the bending, but I'm sure I could change the shape of the fuse to avoid this issue in the first place.

Conclusion

Plane kicks butt. I love it, and The Fish V2 is even better!

I haven't made any plans yet, but I suppose if several people express interest, I'll do that. Maybe a build video as well.

I have had the opportunity of instructing 4 elementary school students in building this plane, and they got it done in only a few hours. If 10 year olds can do it, so can you!


—————————————————————RaptorTech—————————————————————

Thanks for reading! This was one of my first FT articles, so let me know how I did and what I could improve on. Comments appreciated!

I plan to post more content both here and on YouTube, as well as on my own website

YouTube Channel: https://www.youtube.com/channel/UC5bTux0AVaN9tBEbeR8rmHQ

My Website: izzybrand.com

COMMENTS

kb0bnz on July 5, 2014
Verry nice plane. some landing gear like the lazey bee would be nice. would love plans

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RaptorTech on July 5, 2014
I actually had some landing gear on this one for a while! I used lego wheels on a lego axle, so it was really easy to remove them from the plane. I guess they were pretty similar to the Lazy Bee. They were fun, but the plane can take off from the ground without them anyway just sliding along on its belly.

As for plans, I am already looking into making some (it will be my first time making plans and I want them to be usable, so I'm trying to get stuff right!)
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RaptorTech on November 13, 2014
Here are the plans.
https://www.dropbox.com/sh/r1xu16glgol0ey1/AAD_MxKDa9h3A-Vfes4CDfX3a?dl=0
Note that I have not tried building the plane according to these plans yet. My friend will be building a fish this weekend and he'll let me know if everything fits alright.
Also, I plan to make a video showing some build tips and more flight footage (at night) when the plans are finalized, so if you're patient you can expect at least an update if not a full blown build video.
Thanks for waiting!
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yeahsure on July 5, 2014
Great article! The fuselage and undercambered wing reminded me of MikeysRc's slow flyer: https://www.youtube.com/watch?v=oaLFmjus3Hg
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RaptorTech on July 5, 2014
Thank you! That was actually one of the planes that inspired the fuselage. I really liked how he could squeeze a camera in without having the prop in view. On The Fish, an upside-down GoPro actually seems to work similarly, but I was not so enthusiastic about more or less landing on the lense, so I never flew with it. - See more at: http://flitetest.com/articles/the-fish-a-scratch-built-slow-flier#sthash.VZuuGUNP.dpuf
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apnewton on July 6, 2014
Good article, you're on the right track. Keep them coming.
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pkertt on July 19, 2014
really love the plane....please think about plans..even some dimensioned sketches would work if you post them. thanks for the design,,,
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RaptorTech on November 13, 2014
Here are the plans.
https://www.dropbox.com/sh/r1xu16glgol0ey1/AAD_MxKDa9h3A-Vfes4CDfX3a?dl=0
Note that I have not tried building the plane according to these plans yet. My friend will be building a fish this weekend and he'll let me know if everything fits alright.
Also, I plan to make a video showing some build tips and more flight footage (at night) when the plans are finalized, so if you're patient you can expect at least an update if not a full blown build video.
Thanks for waiting!
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Vaidotas on September 25, 2015
I built it, but where is CG? How should I balance it?
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Vaidotas on October 11, 2015
I tried different setups and it works then cg is 10% till even 50%. My favorite 35%. Great design, flies great but I added tail support with few rods :) it can go very very slow.
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Floatflyer on June 13, 2016
Just saw this little plane and I think I want to build it. I have a couple of questions and I also wonder if this thread is still active or is DOA? Thanks, Floatflyer
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planecrazysam1 on August 14, 2016
great job! Is there plans anywhere for this awesome plane! Keep up the good work!
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jazzyal on November 10, 2016
I would very much like the planes that will be used at the local Boys and Girls Flight program
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asanga on October 11, 2016
I scratch build 50% scale mini Fish with EPO and Depron Foam. Its very slow flyer and can be flown with hands free!! https://www.youtube.com/watch?v=Jk_PMePz4W4
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matjey on November 21, 2016
What was the AUW it will be if using 1800 or 2200mah lipo with it? To my understanding, if using prop 8x6, it much better to go with 1400kv motor. Would it work?
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dkuzmin on May 7, 2018
Hi RaptorTech,

This is my first build and I'm having trouble visualizing how the servos should be attached to the control surfaces, the rudder in particular. Do you have any close up photos or diagrams that I can use as a reference?

Thanks,
David
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bracesport on May 19, 2018
we were looking for a plane that we could build and learn to fly on when we stumbled on the fish! We decided to try an build one and finished it this morning. Sadly it is too windy this weekend! here are some pictures so far from the build https://www.dropbox.com/sh/0l1jqmmjokv33f4/AADqbteB5WcAdHvv6OWzCIA2a?dl=0
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The Fish: A scratch built slow flier