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-   -   Capricorn - the ultimate flying boat. (https://www.wattflyer.com/forums/showthread.php?t=26120)

Larry3215 10-28-2007 06:16 AM

Capricorn - the ultimate flying boat.
I keep getting requests for plans and building instructions for my Capricorn flying boat so I decided to do a build thread. This will save me re-typing and e-mailing the same stuff over and over :)

I had originally done a long thread on RCGroups with all the details, but I deleted all my posts from that thread.

This design was inspired by the Robbe Gemini. However, the Gemini had several things wrong with it that I didnt like. It was too small, mostly unavailable in the US, over priced and it was the wrong astrological sign!

Since I am a Capricorn, I decided to re-engeneer the entire thing into something better - or at least something that I like better :D :D

I have all sorts of planes from small 3D shock flyer types, 3 different "Hydros" of various flavors including a 4Q and my flying Batboat, flying Batcar, 2 EDF's, some heli's and larger balsa planes up to a 3200 watt, 30% Yak.

This is now the ONE flying machine that goes in the truck no matter what else Im taking out. It goes on grass, pavement, snow, mud, gravel, indoors, in strong winds and of course - water :)

Im on my 5th or 6th one now - version 4 or 5 in the development. Since I built the first one last winter, there are now 12 or 13 of them in our club.

Edit:For those of you just starting and wanting to get straight into the building - 97% of what you need to know is in the first 40 posts or so. Plans are in post 2.

If you read thru post 60 you will have 99.99% of the important details.

You dont really
need to read the whole thread - BUT along the way, there are many small items explained in more detail, lots more pictures, many questions asked and answered and then answered with a different option.

There are also a great many modifications, options and variations discussed as well as pictures of how other folks have done theirs. There is even a VT version by Leadfeather about 1/2 way thru.

I think there is some good info that is worth taking the time to search out.

Here are a few videos to get you started.


And my current second favorite version - the Mini-Capricorn.

This is a video of the latest and favorite version - Mega-Capricorn. Its a giant scale version 87" long and 59" wide.

This is the Mega on the water - my favorite!

Larry3215 10-28-2007 06:23 AM

basic plans
6 Attachment(s)
Here are the basic "plans". Im not much of a plans drawing guy as you can tell, but all the basic info is there, though its not to scale.

I'll post some more build pics in a few...


Edit: As requested Ive added the plans drawn by Skylar. They are metric so deal with it :D

If any new plans are posted I'll put a copy here.

I recommend you build the standard sized one to begin with. It is the easiest to fly and is most tolerant of using slightly heavy gear. The Mini is the most dificult to fly and is more sensitive to exta weight. The Mini is NOT the best bet for indoor flying. The standard sized one will fly much slower.

One set of plans is for the full size version and the other is for an 85% sized version.

As of July 2008 my current favorite is a Mini-Capricorn that is sized at about 60% of the full sized version. (edit: I've changed my mind - the mega version is now my favorite - at least for now!) Details are further along in the thread starting about post 405. I added another video of the mini version above. Its a totally different bird than the larger one.


Here are the specific dimension of the mini as shown in post 441.

I just got home - the main panels are 5.5" wide. The length from hinge line to the tip of the extended nose is 23". The nose is swept back at a 45 deg angle.

The elevons are 4" wide at the shortest point extending to 6" at the swept tips. The inner pair are 4" and the outer pair sweep from 4" to 6".

The rudder is about 10" tall and about 14" long. That is measured from about 1.5" below the center 'V' to the top of the rudder and from the forward most point to the tip of the swept point. The hinge point is about in line with the 4" wide elevons so you can get a minimum 45 deg throws. I like 60 deg better :)

Those dimensions of the movable surfaces are not critical - but dont skimp :)

The sponsins are 11" long, 2.5" tall, 1.5" wide.

Bottom brace acroiss the center V is 4" wide and I made it from 3mm.

By the way - Skylar says they call this the flying 'wobbleU' in Africa, so I changed the file names ;)

For those of you just starting - 97% of what you need to know is in the first 40 posts or so. If you read thru post 60 you will have 99.99% of the important details.

You dont really need to read the whole thread - BUT along the way, there are many small items explained in more detail, lots more pictures, many questions asked and answered and then answered with a different option.

There are also a great many modifications, options and variations discussed as well as pictures of how other folks have done theirs. There is even a VT version by Leadfeather.

I think there is some good info that is worth taking the time to search out.

New addition:

Lee has done a great tutorial with tons of pics and explanations on his thread. He has - like everyone else so far - done things a bit differently on some of the details. Its well worth looking through!


Here are links to the various drawing by DBacon in this thread. Sorry I took so long to get them added!!!!!!!!!!!

Mini drawings

Standard size drawings

Mega Cap drawings

DBacons FMS Capricorn files.

Larry3215 10-28-2007 06:25 AM

Waterproofing your electronics with CorrosionX
I keep answering the same questions over and over about waterproofing also, so here is the basic info you need. Its not as bad as I make it sound :)

If you plan to fly off water - get some CorrosionX water proofing stuff. They have it at the Ace hardware/lumber yard next door to the hobby shop. It can be found in most Ace hardware stores and many Marine supply stores.

If your not going to fly off water you don't need it. If you are - its essential to protect your rx and speed controller and motor and connectors. Infinitely better than baggies, balloons or rubbers or any other method I have tried.

Get the standard (NOT the heavy duty) Marine or Aviation CorrosionX. I prefer the pump spray bottle and not the aerosol spray can, but either will work. The pump spray is a lot easier and neater because you can take the lid off to poor it into a jar for use. The aerosol can is a lot of trouble to get some into a jar for dunking. You will waist a lot.

This stuff is like medium weight oil - about 20-30 weight or so.

Poor some into a large mouth glass jar or small deep bowl. Make it enough to completely cover the parts. Dunk the rx, speed control and motor into the jar and swish it around so that the stuff penetrates all the nooks and crannies. Take the rx case off, if you can, so the gunk can get to the electronics easily. It needs to contact and coat the electronic circuit boards.

Make sure it gets inside the heat shrink on the speed controller too. Get all the air bubbles out. Also be sure all the connectors get a dose.

Once the part is all coated remove it from the oil - I use long nose pliers - and let most of the stuff drip back into the jar. I then put the parts onto several layers of paper towels and let them drain over night. Turn the stuff a couple of times to try to get as much of the oil to drain out as possible. Wipe the outsides of everything off as best you can with more paper towels. Then wipe it again - then wipe it again - then wipe it again and again etc etc.

Be warned - this stuff stinks some (my wife hates it) and if you get any onto something else you will never get glue or tape or paint to stick to that place again. Its a good idea to wash your hands very very well after using it and before touching anything else. Its persistent stuff!

You may think you have drained the part very very well and then lay it down on your wife's pretty new kitchen table - your doomed because another drop will decide to drain out just then :)

If you want to use sticky back Velcro on the rx or speed controller, you will need to wipe the outside of the case or shrink tubing down with alcohol to get it as clean as possible or the sticky will never stick. Don't get the alcohol on the electronics as that will remove the waterproofing. It also may kill the circuit.

Sounds like a lot of trouble but it will save you blowing up a speed controller or rx if (when) it gets dunked under water. Believe me - if you fly off water it will end up upside down at some point!

I have deliberately run treated motors and controllers and rx's while they were completely under water. Amazing stuff. The TV commercial shows them treating a TV set then tossing it into a swimming pool and watching TV under water.

I put a lid on the used CorrosionX left in the jar and keep using it till its gone. Keep a lid on it as it stinks and may evaporate over time. If you can get the bottle instead of the can you can poor it back in.

I re-treat my stuff once a year and it is doing great. The only things that it didn't work well on were servos. 1 out of 3 or 4 went bad when treated.

On my Capricorn, its not unusual for the plane to get blown over upside down in the water (its the wind - not dumb thumbs ;) . More often than not, that same wind will catch it and blow it right side up again. So far, I have been able to wait a few moments and fly off the water again as if nothing had happened. I have had the plane upside down for as long as 15-20 minutes with the receiver, controller and motor completely submerged the entire time. When it flips back upright again - off I go with no issues. I have found that sometimes it doesn't work. If water is touching the pins on the receiver crystal it will de-tune the receiver and it wont work until the water drains off the crystal. If that happens, just remove the crystal and blow on the socket and you good to go again.

I do NOT treat servos as mentioned above. Too many of them die on me. I also do NOT treat my batteries. There is tape covering the electrical contacts on most all battery packs. The CorrosionX causes the tape to stop sticking and uncovers the contacts. Not a good thing.

After a dunking I do NOT use that battery pack again that day. I take it home and put the battery in front of a fan to dry it out as best I can. I leave it there for at least a day before re-charging. So far, after many many dunkings, I have had no battery problems.

Do NOT fly off salt water. It will kill the battery packs in just a few minutes and I don't know how well the CorrosionX would work on protecting the esc's and RX's in salt conditions. They use it for Marine electronics, but they don't normally expect a complete dunking in salt water.

CorrosionX is truly amazing stuff.


P.S. Do NOT be tempted to run your motor while its under water with a prop attached to try to 'motor boat' back to shore. The water has soooo much extra resistance compared to air that the motor will draw huge currents and over load. You will probably kill the controller or battery if you try it.

As always with electrics - the FIRST thing to do if you crash - on water or land - is kill the throttle.

Larry3215 10-28-2007 06:31 AM

2 Attachment(s)
Here is the build info. Its actually pretty simple and none of the dimensions or angles are really all that critical. Ive built many variations on this theme and they all fly well, tho these numbers are the best so far.

Jed has a new variation on the "wing" shape that looks interesting. Once I get some pics of it I'll post them or get him to. It looks a lot sleeker and faster even when its flying slow :)

This pic shows the basic wing shape your after and the main wing panels all cut out.


Larry3215 10-28-2007 06:39 AM

8 Attachment(s)
Thats all for now - I'll post more details over the next few days. Feel free to ask any questions if you want.


Larry3215 10-28-2007 07:47 AM

I almost forgot about Jeds video of his ARF version. Jed is running with a much larger power system than I do on mine so his tend to fly a lot faster and handle a bit differently.

He has also changed a few of the construction details and esthetics.


CHELLIE 10-28-2007 08:04 AM

Great Job Larry on making the hydro Foam, very creative , what motor and prop do you use to power it, I think its one of the best atvs I have seen, take care, Chellie

Larry3215 10-28-2007 11:21 PM

Any small brushless will work fine if it can put out 100 watts or more peak and you could probably fly "sport" with as little as 60 watts.

The wing loading of a typical shock flyer is about 4.5 ounces per sq foot. A Tensor 4D is down to about 3.5 oz/ft. The Capricorn is about 2.5 oz/ft at the lightest.

My latest version weighs around 16-18 ounces all up and I like flying it on a Mikrodan 2505 motor with a 3S TP 1320 pack. It draws about 9 amps for around 100 watts peak with a GWS 9x5 prop. Its more than light enough to fly in the smallest spaces or indoors yet still has plenty of power for wild manovers and water or wet grass takeoffs and is a hoot to fly outdoors in the wind.

The vast majority of each flight is spent well under 1/2 throttle.

I have used motors up 250 watt range with much larger packs. Infact I even flew it in an All Up/Last Down contest with a MikroDan 2510 and 6ea 3S 2100 TP packs in paralell. It still flew fine with the extra weight but wasnt nearly as "floaty" :)

Jed likes to use much larger motors. He is using Torque motors and running 2100 sized packs. I believe he is averaging more like 200-250 watts peak on his setups.

They are heavier, but a lot faster too. Different styles of flying.

This planform is very forgiving as far as weight and also CG.

I like flying with my CG about 9-10 inches back from the leading edge. I have flown it as far as 15" back but thats a bit much :eek:

Jed and most other folks prefer being about 7-8 inches back - right at the rear of the sponsons. Its a lot more stable and tracks better with it forward at that point.

However, if you want to do those super tight loops you need it further back :)


Larry3215 10-28-2007 11:27 PM

By the way, the MicroDan motors are among the best on the market. Very smooth and very powerfull and efficient.


Im also a big fan of CustomCdrom motors.



CHELLIE 10-29-2007 01:26 AM

Thank You Larry :ws: for the information, I am going to try to make one soon, I just have to finish a few nagging projects that I started and have not finished yet :red: Take care and have a great week, Chellie

Larry3215 10-29-2007 02:20 AM

I know what you mean! There are tooooo many good ideas for planes waiting to get built!

I have a partially cut out smaller 3mm version of the Capricorn I've been working on for the indoor season - 2S with a hot wind CCDr motor. Im hoping to get the wing loading under 1 oz/ft, but Im still not sure thats possible :)

Im also doing repairs/mods on my 30% yak, still working on my second 84" BIG foamy and Ive had the wings folded for a mid-sized full fuse/full airfoil plane for months and I recently started on a twin with articulated wings ala the Jinx.

I think its a genetic condition..... :)


Larry3215 10-29-2007 02:40 AM

main wing joint details
1 Attachment(s)
1)After you cut the main wing parts out, bevel them as per this drawing.

2)Start with the 2 panels on one side and bevel then tape the outside of the joint while its laying flat.
3)Turn it over and add glue to the joint.
4)Weight the inside piece and prop up the outside tapered piece 4" to 5" off the table. That will give the proper angle. Brace it some way so it cant move while the glue cures. I use scraps of depron and some pins.

<deleted note>

5)As the polyurethane glue cures, it will expand up out of the joint. Durring the first 1/2 hour or so you can run a popsicycle stick over the joint and scrape off the excess as it comes out. You will end up with a nice joint if you stay after it from the beginning. Wait too long and you'll have to sand it or try to cut it off.

Once the outer panels are done, you can do the center joint the same way. I put glue in the joint then flip it right side up and put braces at each end then let the glue cure. I dont bother scraping out the excess as it foams up because it will not show and its impossible to get to using this method anyway :)

You can pre cut the slots for rudder and motor mounts or do them afterwards.

More later...


Larry3215 10-30-2007 06:19 AM

A note on the angle of the outer panels - it doesnt matter :)

I just checked and I have 3 different bend angles on various versions. Prop up the outer panels anywhere from 4" to 5". They all fly fine ")


RocketMan 11-02-2007 01:19 AM

I am very interested in this model. I realize that this is made out of depron (having looked at the titles of the thread and deleted posts on RCG) but would you mind providing a bit more details on the materials you are using?

I am in search of the ultimate winter weather plane and the Capricorn is the best I have seen...


Larry3215 11-02-2007 03:55 AM

Hi RM. You will like it, if I do say so myself :)

The main wing and controll surface material is all 6mm Depron. Guys have used blue fan fold sucessfully but its not as stiff as the Depron so you may want to scale down a bit.

You could probably use the foam poster board, but I have never tried that stuff so I dont know how strong it is in comparison to Depron.

Hinge tape is 3M Blenderm medical tape. Other tapes wil work, but nothing beets Blenderm.

The sponsons are made from 2" thick pink building insulation board. I get mine from Home Depot in 2' wide x 8' long sheets for about $20 or so IIRC. Its enough to build a few dozen sets of sponsons :) If you find a broken sheet they will often sell it to you way cheeper or even give it to you. Regular lumber yards often carry the pink foam as well.

I have also used pool toy "Noodle board" foam for the sponsons. It has the advantage of being similar to EPP foam in that it bends and springs back after a crash. The down side is that is a pain to work with as far as getting glues to stick and it only comes in ugly colors :)

I think white EPS might work but it would be more fragile.

One of the guys in the club is planning to try pipe insulation foam tubes on his sponsons. Havent seen that yet so dont know how well its going to work.

I cover the bottoms of my sponsons with plastic cut from large jugs of cat littler. I glue it on with 3M 77 spray adhesive. It lasts forever and is very slick. Works better on grass and snow than duct tape, tho Duct tape will work and is cheep and easy. It wears out fast on pavement but is easy to replace.

Others have had good luck with the thin baking sheets from Target. I think they are made from teflon or something similar. Very slick and reasonably tough but a little pricey. I forget what they were using to glue them on with.

For glue on the main wing joints - Gorilla brand glue or any similar expanding Polyurethane type glue will work best by far. I like the Sumo brand because its white and looks the best. It has the worst bottles tho. Very tough to squeeze. I have used CA and epoxy but they seem to be more brittle and the joints have broken easier.

I usually use foam safe CA on the motor mount and to glue in the rudder but the PU or epoxy will work as well.

Ofcourse, CorrosionX is the best at water proofing.

Thats about it I think :)


Larry3215 11-02-2007 03:58 AM

It occurs to me that if you go by an Insulation company you may be able to get scrapes of the 2" pink foam free. They are bound to have left overs.


Larry3215 11-02-2007 04:03 AM

A note on winter flying...

Last winter I was flying with the same 3 guys in the video above at the same lake on a very cold day. There was a thin skin of ice that started about 100 feet off shore and covered the entire center of the lake.

I eventually got nerve enough to land on the ice and the Cap went very well as you'd expect. However, the ice was thin and when I tried to go from the water onto the ice, the model stopped like it hit a brick wall!

The edge of the ice sheet actually cut into the edge of one sponson pretty deep! One of the other guys landed on the ice pretty hard and broke thru the crust and got stuck for a while, but moving the controlls freed it up enough to take off again.

The moral is that thin ice is tricky!


RocketMan 11-02-2007 04:20 AM

Thanks Larry that was very helpful and I am now in search of 6 mm depron! (looks like rcfoam is the place to get this as they ship internationally). I am also sold on CorrosionX so I have to order some of that also.

I have some really good teflon strips that I will use for the bottom of the sponsons. They seem to be virtually indestructible and very low friction.

It will be a while before we get snow here so I have time to prepare :-)



RocketMan 11-05-2007 12:00 AM

I have depron on the way from rcfoam and it should get here by the end of next week I suppose.

I will post my progress on the Cap! I will beat winter into submission this year :-)


Larry3215 11-06-2007 02:20 AM

Yeah, RCFoam is one of the last places to get Depron now that DepronUSA has closed down.

Keep us posted on your build :)


RocketMan 11-06-2007 02:33 AM


Originally Posted by Larry3215 (Post 299833)
Yeah, RCFoam is one of the last places to get Depron now that DepronUSA has closed down.

Keep us posted on your build :)


Thanks Larry. I am looking forward to getting the Cap together. I will probably have a million questions along the way. I suppose that will make for a good build thread :-)



Larry3215 11-06-2007 09:49 PM

Your right about that!

I've built so many of them that things I think are obvious and easy may not be so appearant to someone building it for the first time.

Ask away!

One thing that occurs to me now - I just got asked the question at the field a while ago - is how to do the controll horns and linkages.

You could just use your favorite foamy technique and you'll probably be fine - I have seen them done 4 or 5 different ways succesfully.

However, these surfaces are wider than the normal foamy surface and there are some leverage issues you may run into. I have a couple of ways of doing it that I think work very well.

I'll post some close up pics later.


RocketMan 11-07-2007 05:32 PM

Hi Larry, I've been going over your drawings and they seem pretty clear. It sure would be great however to have some close up pictures of a finished model and particularly the control linkages as you suggest. It took me a while to figure out that the electronics can be 'hidden' in the space between the center fold and the center brace and that you make some kind of hatch once the CG is determined. Do you seal this compartment at the front to the keep the water out (I'm thinking mostly about protecting the battery as the receiver and ESC will be waterproofed) or leave it open for air flow?

My depron is somewhere en route from Atlanta. I'm tempted to just try foam poster board as a prototype to start with but then I'll probably want to try and make that fly so I better wait :-)



Larry3215 11-07-2007 06:43 PM

I will try to get that done tonight when I get home :)


Larry3215 11-07-2007 07:02 PM

As far as putting the packs in the space between the deck and the under brace - you will probably have to make the brace peice wider to create a larger space.

On my current version, the space is too smal for a TP 3S 1320 pack to fit all the way inside. You would have to leave any "hatch" off or build up a deeper pocket for the packs.

As far as cooling - the way I fly mine with the motor Im useing, my packs never get warm even in the summer. If I put my packs inside the pocket, I'll probably seal up the front for the same reason you mentioned.

In the winter it would probably help keep the packs warmer so you would actually get better performance on very cold days.

Be sure to leave the back end open so any water that does get inside can drain out.


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