Foamboard JAS-39 Gripen EDF Part 1 (model + plans)

by Widkin | January 13, 2014 | (10) Posted in Projects

2014-02-09 Update 

  • I corrected dimensions on detail 56, 68 & 70, see new plans at the end of the article. The details were too small due to incorrect calculation of the folds of the foam. 

2014-01-29 Article updated (scoll down)

  • Added weapon hardpoints and wing root covers for more detail
  • Updated plans with more notes and details
  • Added full-size plans 40x30 inch

Intro

Ever since I saw the awesome JA-37 Viggen made by David Windestål, I've been thinking about making an EDF-jet of my own. However, I did not want to mess around with all those formers and hot-wire cutters, since it seemed so time-consuming and seemed to be more a work of art than easily replicable. I therefore wanted to see if it would be possible to make a good-looking scale jet out of regular Dollartree foamboard instead.

Since I am a Swede too, I wanted it to be a Swedish jet. Since the Viggen was already done, it felt natural to make the JAS-39 Gripen. I also really wanted it to have fully articulating canards, something that the Gripen has but the Viggen does not. 

I recently caught up on the Flitetest podcasts and believe that there might be something like a foamboard EDF jet already in the works. It's going to be very interesting to see how David has solved the design, but until then, here's my idea. I hope someone likes it, and maybe even tries to build it along with me. Tips and suggestions on improvements are naturally very welcome. I should also, for the sake of transparency, note that I am not an experienced pilot, nor an experienced builder, and have only been into RC for the last year or so. There's a not-so-slight chance that this might go very wrong on the maiden, but hey, mistakes brings you experience too, right? 

The model

Pic 1: Render of model. Bluecore nose cone, foamboard body

I guess I should tell you at this point that I work as a design engineer with focus on house construction, and therefore have access some pretty useful 3D CAD-software. I have actually modelled this plane using the same features I would use to create steel plates, which basically involves planar elements with cuts, bevels, bends and chamfers, joined together. It worked perfectly, and made it possible to automatically generate plan drawings from the 3D model. Above is a render of the model. 

Because of the 3D capability, I have started in the opposite end of many other scratchbuilds I've seen, where the plans are published last. I have the complete model and all the plan drawings already available, for download here: PDF plans This also contains a fully interactive 3D PDF, for those that want to check the model out more closely. Please note, the grey pyramid out front of the model is the viewport of the Sony actioncamera, which I placed inside the canopy. 

The drawings are plotted in scale 1:1 on A3, A2 and A1 paperspace, depending on the size of the parts, but you can print the plans on any paper you have available, using Adobe Reader's "tile"-functionality. You just have to tape them together. 

Stats

Since I used a 3D CAD program that can handle materials, I assigned a density for the foamboard and weights for all the components, which means I have a pretty good estimate of the final weight: 

Plane, just foamboard (no glue): 460g
74mm mercury EDF unit: 236g
2x2200mAh 4S LiPo: 2x216g=432g
80A Plush ESC: 100g 

This amounts to 1228g. Add a couple hundred grams extra for cables, receiver, glue etc and I suppose this plane should stay under 1.5kg. Compare that to the static thrust of 20N (2kg) from the Mercury EDF-unit, and we get a thrust to weight ratio of 2:1.5, or 1.33:1. Pretty nice I think. I guess it might be possible to use a smaller battery to get even better ratio with reduced flight time, but that depends on if I need the weight in the front or not. Using a lighter, plastic EDF unit will also enable this to be a really light plane. 

Design

The plane consists of a number of parts of foamboard, illustrated with different colors below. (Please see the full PDF document for plans and numbering for assist in assembly.) The nose was decided to be bluecore foam (depicted in light blue), since the cone can be sanded to a nice shape using a power drill, as demonstrated by David in his Viggen build. I also have a couple of pieces that fit between some foamboard, and I intend to use the foamboard as formers and simply cut off the excess with a hot-wire cutter. I would prefer not to use hot-wire at all, but I don't think I can get a smooth and nice enough shape with just foamboard here, and covering a former with thin paper, like with a canopy, would be too weak. 

 Pic 2: CAD model with different colored parts. 

The curves of the fuselage are made by using multiple scored lines and gently folding it, like the wing folding technique shown in many Flitetest scratch builds. It does actually work very well, as seen on the pictures later. 

Build log so far

I have started assembling the model now, and it works surprisingly well! So far, I have spent perhaps half a day, and most of the model is already done. I have spent far more time honing the 3D model, which took about a weekend of 3D modelling and a couple hours on an evening after work tinkering with the drawings. All in all, a pretty OK work load I think. 

I will put up a build log once I'm done, but for now, here's a couple of pictures as proof that it is indeed possible to build. 

Pic 3. Mockup of parts. Front top fuselage not glued yet, waiting for electronics to arrive. 

Pic 4. Inlet area of the two inlets are about the same as EDF fan area, maybe a little bit larger. I hope it's enough. 

Pic 5. Quite roomy in the pod. Here you see the 4mm carbon fiber rod and steering wheel arm that will attach to a servo and make the canards articulating. 

Pic 6. EDF goes here, inside a foamboard tube. Waiting for EDF to arrive from Hobbyking before I finish this. 

Pic 7. Wingtip

I theorize that using leading edge flaps like the real Gripen, it will create an undercamber effect on the wing tip and prevent tip stalls, much like what was observed in the FT spitfire and FT cruiser. With functional canards, it should be possible to deploy the elevons as flaps to some extent while still maintaining pitch control, which might make for some really interesting maneuverability. 

Summary

This is as far as I've come. I do feel like I want to share the work at this stage, though, since the plans and everything is ready for anyone who cares to join me in this build. I'm currently waiting for components to arrive from Hobbyking China, and hope that they will arrive next week. 

I will create a part 2 in this project once the parts arrive, detailing the build, and then of course a part describing the maiden and (hopefully) successive flights. I do need to wait for some snow to melt, or waterproof the plane before I maiden it. I have just bought some airbrush stuff for that occasion, so well see what happens. 

If you've read all this way, I thank you. This is my first article on Flitetest, and as such I'm sure it needs working on. I humbly appreciate any feedback, be it comments on improvements, tips, questions, or just what you think of the project.

Until next time.

 

Kind regards,
Niklas

 

Update 2014-01-29

As requested, I have updated the plans to "full size" with 40x30 inch versions. I also took the time to make some modifications in the plans, such as a better fit of the top and bottom front fuselage parts as well as some more instructions on the drawings.

I have added weapon hardpoints and a cover for the wing root to blend the fuselage with the wing. 

I have also uploaded the CAD model in DWG and DWFX for those that are interrested in those. Was not able to before due to some file restrictions, but placing them in a ZIP worked. 

Here are some new renders for you to enjoy. :)

Pic 8. Render. Note hardpoints and wing root covers

Pic 9. Render. 

Pic 10. Render

 

Files

See forum thread with latest plans

Updated plans 2014-02-09

Updated plans 2014-01-29

DWG is the source model. Opens in almost any CAD program. DWG Trueview is a good, free viewer. Also opens in Autodesk 360 on Android, iOS or in browser. 

Old plans

  • 3D PDF model (old)
  • PDF mixed size drawings (old)

Links

If you, like me, have trouble finding the type of foam that Flitetest uses over in Europe, I found that it's called "kapaskiva" or "cellpannå" in Sweden. I bought it from Svexo pappersmarknad. It's more of a $8-foamboard than $1 for 700x1000mm, but that's the best I could find. 

COMMENTS

TehMaxwell on January 22, 2014
A great all round article, I can't say there is anything wrong with it! Also a very interesting build, I am keen to hear of the results! :D
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Widkin on January 23, 2014
Thank you, glad to hear I did not completely screw up. :-) I'm still waiting for the HK parts to arrive. Apparently, express mail service is not registered, so I have no idea where they are at the moment.
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Jaxx on January 22, 2014
This is awesome! This is impressive work. Thanks for sharing the plans. Is there any way the plans could be posted in a single, non-tiled format?
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Widkin on January 23, 2014
Thank you for the comment. With non-tiled plans, I assume you mean that one paper contains one part of, say, the main wing, and then another paper the next part of the wing and so on? If so, what paper-size do you need it on? I can have a look and do some cut-and-pasting of the plans if necessary.

Just out of curiosity: did you try to print them in Adobe reader as "tiled"? Just wanna know if there was any trouble with that method.
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Jaxx on January 23, 2014
Widkin,

First, let me say; you did an excellent job with the article! I'm not sure I understand how to print the plans in order to get the parts 100% scale. I send my plans to a print shop to get them printed on a large format printer. They print them on 1 or 2 large sheets of paper, depending on how big the plans are. This way I don't have to tape the parts together. FliteTest usually post their plans in 2 formats: full-size and tiled. I use the full-size plans, and was trying to figure out how to print these plans so that the parts are the right size. When I checked the properties and it said the paper size is 11 x 8.5 inch, but I just realized it may just be the size of the first page. I was wondering if it was possible to cut and paste more parts onto a single page like the FliteTest full-size plans. Thanks again for the great article.
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Widkin on January 28, 2014
Thanks! My original idea was to print the drawings with 100% scale and no "fit to margin" or similar, and simply have Adobe reader "tile" the print.

http://helpx.adobe.com/acrobat/kb/print-posters-banners-acrobat-reader.html

I have thought about how to make the plans on a single sheet, and it will ultimately depend on how large sheets your printing company can print. I'm leaning towards making the PDF sheet the same size as the foamboard I use, which is 1000x700mm. I think that's what FT uses, too, although I can't be certain. A single sheet would fit most of the plans, but not all - the model uses just a bit more than a full sheet of foamboard.

I have also updated the current plans with a scale bar so that it's possible to scale the prints properly, and also verify that it is indeed correct on paper. I will update the article with all these things today or tomorrow. Not sure if the article needs to wait for re-approval, though.

Again, thanks for the interest and feedback!
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Jaxx on January 28, 2014
I'm the one who should be thanking you for the great article, and all the work you put into this project. Your effort is shown by level of detail in these plans. The foam that FliteTest uses is 30 x 20 inches (762x508mm). The printing company I use is limited to a document that has a width of 36 inches (914.40mm) for the type of prints that I get. The document can be any length. If all the parts don't fit on one sheet, that's not a problem. Some of the FliteTest plans require as many as three sheets. The key is trying to keep the width below 36inches (914.40mm). For example, the FT Cruiser plans require three pages, and the dimension for each page is 34.38 × 28.66 inches (873.25x727.96mm). Thanks again for sharing this project. I look forward to building it.
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Widkin on January 29, 2014
This is good info, thank you. I have updated the article now.

I had some trouble fitting the plans on 30x20 inch so I chose double that size. So, each plan is now exacly two FT foamboards. I hope that is a working compromise for most people. I guess your printing company can print the plans rotated 90 degrees to keep the width under 36 inch. :)

I also modified the plans a bit and added some more details like weapon hardpoints and wing root covers. If the renders are anything to go by, I think it's going to look really sweet with the extra detail.

Cheers!
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Jaxx on February 8, 2014
Widkin,
This is perfect! The way you put these full-size plans together should work for most people who get them printed at a print shop. Thanks again for the extra time and effort you have put into modifying these plans! I'm glad you were able to use the information I provided. Like I said before, this is very impressive work.
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Widkin on February 9, 2014
Jaxx,
I hope you have not sent the plans for printing yet. I just updated detail 56, 68 & 70. They were too small due to an error in the calculation of the folds, which I've now corrected. If you have sent them for printing, please make sure you add about 31mm to the length (circumference) of detail 56 & 68, and 7mm to the width of detail 70. See new plans for details.
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Jaxx on February 13, 2014
I have not sent the plans for printing yet, so I will download the updated version. I'm really looking forward to building this bird. Thanks again.
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teteorp on January 23, 2014
It looks amazing!!! I´m so excited about the Gripen!! I´m from Brazil and our government announced last December that the Gripen NG will be the next fighter jet of the Air Force. Since then I´m searching for builds of it. Keep doing the great job and keep posting pictures and videos!!!
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Gravitysucks on January 23, 2014
Sweeeeet. Swedish planes rocks. Eller vad säger ni ? ;)
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QuantumSponge on January 24, 2014
Awesome Awesome AWESOME!

Well don Niklas!

What 3d CAD program are you using?

I have no experience in EDF myself but have been researching for the past 6 months or so with the idea of modifying a pusher prop design for EDF. Your design looks amazing though so I think I'm going to loose my EDF virginity to your Grippen lol.

I think I'll probably aim to get this model to around 1000g or just under with less battery and the "Alloy DPS 70mm 5 Blade EDF- Light Weight Version 4000kv" PRODUCT ID: 107000093. Be looking at 1 to 1 power to weight ratio or just over in favor of power which would be plenty of performance for me.

One last question, what is the weight of the foam board your using? Gram per square inch?
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Widkin on January 25, 2014
Hello, and thank you for the praise. Very glad to hear that someone else also wan't to join in the build. I also think you have a good point in choosing a ligher EDF and battery. :)

For CAD, I use AutoCAD 2014 with an additional software on top for Steel Detailing, called Advance Steel.

http://www.autodesk.com/products/autodesk-autocad/overview
http://www.graitec.com/en/as.asp

I'm sad to say that together they are in the price range of 16,000-17,000 USD for a single user, so I'm afraid it's not an option for most people. I have access to it from work. It is possible to just use the Advance Steel software without AutoCAD, albeit with some limitations, but that would still be about 10,000 USD. :-/

The weight of the 5mm foamboard I use is about 0,36g/in2, or 5,6g/dm2. I averaged it by weighing 9 sheets, to account for variations in the foam, so I think it's pretty accurate. As it says in the article, I calculated the weight of the used foamboard to be 460g. The model is now as 415g, excluding the nose cone and canopy, but including glue and tape, so I think it's pretty spot on.
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rcflyer729 on January 29, 2014
nice
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Starssadar on February 9, 2014
Very very nice!

Here in Switzerland we will soon have Gripen for our air force, hence my interest in your project.
Is yours finished? Have you tried it?
On what paper size must we print the plans?
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Widkin on February 9, 2014
Hi, and thanks. Yeah, I've heard that Switzerland has made one of the larger orders of the Gripen NG. :)

It's not finished yet, I have a few bits to do, and are still waiting for the electronics. Stupid HobbyKing. :(

The plans are in 30x40inch, but you can print them on whatever size you want using Adobe Reader and the poster/tiled print.
http://helpx.adobe.com/acrobat/kb/print-posters-banners-acrobat-reader.html

It's only the big details that needs to be tiled, though. The smaller details can easily be printed using another PDF viewer: Bluebeam Vu, which has the ability to print a selection of the page. I usually just print them one by one on whatever paper I have available, usually A4 and A3. Just make sure you have no scaling on (or at 100%).
http://www.bluebeam.com/us/free-viewer/
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wingnutzster on October 26, 2016
Very nice design, structurally and aesthetically...if I may though can I ask why the strange planform of the wings? We fly the Gripen in South Africa as our primary front line fighter and she is among our most beloved types, the shape is unmistakable and beautiful...the leading edge is a straight sweep to the dog tooth, the dog tooth has a slightly higher sweep than the inboard leading edge. Besides that your design is quite likely one of the more scale parkflyer Gripens hence my question re the wing shape. Great work and a magnificent subject.
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Widkin on October 29, 2016
Hello, and thanks for the feedback. I did not have the full detail of the wing at the time of publication. Also, i did mot bother folding the leading edges on CAD, but i did so on the real model. Please see the forum thread for a lot lore info on the model. Personally i do mot fly it at the moment, but others have built the model with pretty OK results.

http://forum.flitetest.com/showthread.php?8289-Foamboard-SAAB-JAS-39-Gripen-EDF-(images-plans-build)


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Nandan on October 16, 2020
Thanks WidKin. I am a big fan of SAAB Gripen... this by far is the best info I got about building a foam Gripen. Not sure if our (me and my dad) skills are good enough to get one made. No harm attempting.

me flying depron model https://www.youtube.com/watch?v=zW8mlcCHERo

Will post a video in a few weeks from now
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Widkin on October 17, 2020
Hello Nandan,

Thank you. I'm glad you will try out the build, it a great looking plane both on the ground and in the air.

Please see the link to the forum thread, at the end of the article. Several people have built this plane, one of them in depron as a super light weight variant. The forum should give you more info and also people willing to help out in case you run into trouble. (I'll try to answer if/when I can as well, of course)

Good luck with the build!

Kind regards
Widkin
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Foamboard JAS-39 Gripen EDF Part 1 (model + plans)