Solved my journey to 3D print a JAS 39 gripen

[NeonGreen]

I’m trying to model and 3D print a roughly 1-meter-long JAS 39 Gripen RC model for a school project. I’ve been researching online and working on the modeling process, but now that I’m trying to determine if it can actually fly, I’m struggling.

According to the simulations I’m running in SolidWorks, the model has no chance of getting off the ground. However, when I look at similar models on YouTube, it seems like mine should be able to fly. When I import the model into Bambu Studio, it estimates a weight of about 710g at 5% gyroid infill. Based on that, I’ve been roughly estimating the final weight to be between 1–1.5 kg.

The issue is that my flow simulations indicate almost no chance of achieving lift. With a convex airfoil, I’m only getting about 0.8N of lift at 15 m/s, which I doubt will be enough. To improve this, I redesigned the wings to have roughly twice the surface area, using a thicker and more aggressive airfoil. With this new design, I achieved 2.7N of lift under the same conditions. The original wing has a total area of 0.098 m², while the larger-winged version has 0.18 m².

I’m mainly looking for feedback from more experienced individuals on whether this model seems flyable. Additionally, I’d appreciate any suggestions on airfoil selection—what type to use or how to design one that suits my needs. Any advice, suggestions, or feedback would be greatly appreciated!

 

[Mr Man]

I’m trying to model and 3D print a roughly 1-meter-long JAS 39 Gripen RC model for a school project. I’ve been researching online and working on the modeling process, but now that I’m trying to determine if it can actually fly, I’m struggling.

According to the simulations I’m running in SolidWorks, the model has no chance of getting off the ground. However, when I look at similar models on YouTube, it seems like mine should be able to fly. When I import the model into Bambu Studio, it estimates a weight of about 710g at 5% gyroid infill. Based on that, I’ve been roughly estimating the final weight to be between 1–1.5 kg.

The issue is that my flow simulations indicate almost no chance of achieving lift. With a convex airfoil, I’m only getting about 0.8N of lift at 15 m/s, which I doubt will be enough. To improve this, I redesigned the wings to have roughly twice the surface area, using a thicker and more aggressive airfoil. With this new design, I achieved 2.7N of lift under the same conditions. The original wing has a total area of 0.098 m², while the larger-winged version has 0.18 m².

I’m mainly looking for feedback from more experienced individuals on whether this model seems flyable. Additionally, I’d appreciate any suggestions on airfoil selection—what type to use or how to design one that suits my needs. Any advice, suggestions, or feedback would be greatly appreciated!

I actually like the look of the second one better.

 

[Mr Man]

Now, it mostly depends on your power system, as almost any plane is capable of flying. You just might need more power to do it. And proper CG of course.

 

[NeonGreen]

Now, it mostly depends on your power system, as almost any plane is capable of flying. You just might need more power to do it. And proper CG of course.

im currently eyeing a 64 mm edf fan that should give about 1.5 -2 kg of thrust, and then im hoping to ballance the cg trough either small weights or moving around the battery

 

[Mr Man]

im currently eyeing a 64 mm edf fan that should give about 1.5 -2 kg of thrust, and then im hoping to ballance the cg trough either small weights or moving around the battery

So far everything is looking good, just remember that 15m/s (33mph) (53kph) is pretty slow for a jet. 50mph (80kph) (22 m/s) is the average speed of an edf jet.

 

[Mr Man]

I also don't see any control surfaces, are you going to have full moving canards or elevons?

 

[NeonGreen]

So far everything is looking good, just remember that 15m/s (33mph) (53kph) is pretty slow for a jet. 50mph (80kph) (22 m/s) is the average speed of an edf jet.

will be using that speed later if i decide to do any further simulation. and i wanted to make sure the plane could fly before making cutouts on the wing for elevons since i would have to remake them if i down the road realized that the current wing wheren't suiteble.

and when you said the second one looked better, did you mean the second picture which would be the one with the smaller wings

 

[Mr Man]

will be using that speed later if i decide to do any further simulation. and i wanted to make sure the plane could fly before making cutouts on the wing for elevons since i would have to remake them if i down the road realized that the current wing wheren't suiteble.

and when you said the second one looked better, did you mean the second picture which would be the one with the smaller wings

Oh, I see, I was going off of order of pictures. You could also design it to be capable of High Alpha.

 

[NeonGreen]

Oh, I see, I was going off of order of pictures. You could also design it to be capable of High Alpha.

my hope is to be able to throw the plane into the start, maybe do some air manouvers altough thats optional. and other than that just speed and style

 

[Mr Man]

my hope is to be able to throw the plane into the start, maybe do some air manouvers altough thats optional. and other than that just speed and style

Ok, I would recommend putting some landing gear on it, so it can build up speed on take-off.

 

[NeonGreen]

Ok, I would recommend putting some landing gear on it, so it can build up speed on take-off.

will do, do you have any recomendations on what kind of airfoil that would look good and work well?

 

[quorneng]

I would have two suggestions for a basic EDF.
1. Don't 3D print it. It will come out heavier than almost any other form of construction and EDFs are heavy enough already
2. Keep it simple. A basic EDF delta is compact, robust, relatively easy to build and is fully controllable using just two servos! The simplicity of construction means it will be light. If light enough a hand launch is perfectly possible.
One further advantage of a simple delta is generates most of its lift from vortex generation so the wing section is not critical. The very board root chord also means almost any wing section will have sufficient depth for strength.
If you want it to look scale pick something like a Douglas Skyray. The full size way built to install the maximum size turbo jet into the smallest airframe. A pretty good basis for an simple EDF.
I have 4 home design scale plain delta EDFs including a 36" span Douglas Skyray built from 3 mm sheet foam.

At 554g (20oz) all up and 4 sqft of wing area makes it is an easy hand launch. The ground effect of the wing means landing is a non event

And yes it uses just two servos mixed as elevons!

 

[Mr Man]

I would have two suggestions for a basic EDF.
1. Don't 3D print it. It will come out heavier than almost any other form of construction and EDFs are heavy enough already
2. Keep it simple. A basic EDF delta is compact, robust, relatively easy to build and is fully controllable using just two servos! The simplicity of construction means it will be light. If light enough a hand launch is perfectly possible.
One further advantage of a simple delta is generates most of its lift from vortex generation so the wing section is not critical. The very board root chord also means almost any wing section will have sufficient depth for strength.
If you want it to look scale pick something like a Douglas Skyray. The full size way built to install the maximum size turbo jet into the smallest airframe. A pretty good basis for an simple EDF.
I have 4 home design scale plain delta EDFs including a 36" span Douglas Skyray built from 3 mm sheet foam.
View attachment 247814
At 554g (20oz) all up and 4 sqft of wing area makes it is an easy hand launch. The ground effect of the wing means landing is a non event

And yes it uses just two servos mixed as elevons!

will do, do you have any recomendations on what kind of airfoil that would look good and work well?

I’m building a f-16 falcon using a 64mm edf, it is Incredibly light, 4s will be plenty of power. As far as airfoil, I think a flat bottomed airfoil would be good for slower flying, and a symmetrical airfoil for higher speeds. And I agree, 3d printing will be too heavy.

For advice on 3d printing planes, I would ask @telnar1236

 

[Houndpup Rc]

I’m building a f-16 falcon using a 64mm edf, it is Incredibly light, 4s will be plenty of power. As far as airfoil, I think a flat bottomed airfoil would be good for slower flying, and a symmetrical airfoil for higher speeds. And I agree, 3d printing will be too heavy.

For advice on 3d printing planes, I would ask @telnar1236

I saw once that a slimmer airfoil will give you less drag (for speed) but less lift, whereas a more pronounced airfoil will give you more lift but more drag. For example a heavy bomber would have more airfoil but a racer would have a thinner airfoil.

 

[Mr Man]

I saw once that a slimmer airfoil will give you less drag (for speed) but less lift, whereas a more pronounced airfoil will give you more lift but more drag.

That’s true.

 

[NeonGreen]

I would have two suggestions for a basic EDF.
1. Don't 3D print it. It will come out heavier than almost any other form of construction and EDFs are heavy enough already
2. Keep it simple. A basic EDF delta is compact, robust, relatively easy to build and is fully controllable using just two servos! The simplicity of construction means it will be light. If light enough a hand launch is perfectly possible.
One further advantage of a simple delta is generates most of its lift from vortex generation so the wing section is not critical. The very board root chord also means almost any wing section will have sufficient depth for strength.
If you want it to look scale pick something like a Douglas Skyray. The full size way built to install the maximum size turbo jet into the smallest airframe. A pretty good basis for an simple EDF.
I have 4 home design scale plain delta EDFs including a 36" span Douglas Skyray built from 3 mm sheet foam.
View attachment 247814
At 554g (20oz) all up and 4 sqft of wing area makes it is an easy hand launch. The ground effect of the wing means landing is a non event

And yes it uses just two servos mixed as elevons!

I’m building a f-16 falcon using a 64mm edf, it is Incredibly light, 4s will be plenty of power. As far as airfoil, I think a flat bottomed airfoil would be good for slower flying, and a symmetrical airfoil for higher speeds. And I agree, 3d printing will be too heavy.

For advice on 3d printing planes, I would ask @telnar1236

Thanks for the feedback! Unfortunately, for my chances of succeeding, the two main building blocks of this project are 3D printing and form factor, so I’ll have to work with the extra weight and reduced wing area.

I looked around for some airfoils on AirfoilTools and found a few options. The first picture shows the airfoil I originally used since I had heard that the Gripen used a convex airfoil, so I tried to come up with something similar. The second picture is of a NACA 2408 airfoil, which I thought looked similar to the one used by a guy who built his own 3D-printed Gripen. His model seems to be roughly the same size as what I want to make. However, I think the airfoil looks a bit thick, so I might adjust the thickness slightly to see how it looks. The third picture is of a NACA 0006 airfoil, which I like for its thin profile and symmetrical shape, as you suggested for higher speeds. However, I believe the extra lift from the one with the flatter bottom might be necessary.

When looking at my model, I started to doubt the size I had chosen because the walls are quite thin—around 1 cm. I believe this will make it quite fragile, making it difficult to support landing gear, and I won’t be able to create channels for wire management.

At first, I considered using a smaller EDF, but the only ones I found were 50mm, and according to the manufacturer’s specs,gave a significantly less amount of thrust. So, I’m thinking about scaling up the model, which would increase the wing area but also make it heavier. That said, I don’t think the weight increase will be too drastic since I still need to hollow out the front for the electronics, and I plan to make the model more hollow when adding the wire management channels.

I plan on reaching out to @telnar12346 about the problem as you suggested, but any insight into the matter would be greatly appreciated!

 

[Mr Man]

Thanks for the feedback! Unfortunately, for my chances of succeeding, the two main building blocks of this project are 3D printing and form factor, so I’ll have to work with the extra weight and reduced wing area.

I looked around for some airfoils on AirfoilTools and found a few options. The first picture shows the airfoil I originally used since I had heard that the Gripen used a convex airfoil, so I tried to come up with something similar. The second picture is of a NACA 2408 airfoil, which I thought looked similar to the one used by a guy who built his own 3D-printed Gripen. His model seems to be roughly the same size as what I want to make. However, I think the airfoil looks a bit thick, so I might adjust the thickness slightly to see how it looks. The third picture is of a NACA 0006 airfoil, which I like for its thin profile and symmetrical shape, as you suggested for higher speeds. However, I believe the extra lift from the one with the flatter bottom might be necessary.

When looking at my model, I started to doubt the size I had chosen because the walls are quite thin—around 1 cm. I believe this will make it quite fragile, making it difficult to support landing gear, and I won’t be able to create channels for wire management.
View attachment 247823
At first, I considered using a smaller EDF, but the only ones I found were 50mm, and according to the manufacturer’s specs,gave a significantly less amount of thrust. So, I’m thinking about scaling up the model, which would increase the wing area but also make it heavier. That said, I don’t think the weight increase will be too drastic since I still need to hollow out the front for the electronics, and I plan to make the model more hollow when adding the wire management channels.

I plan on reaching out to @telnar12346 about the problem as you suggested, but any insight into the matter would be greatly appreciated!

You actually don't have to use landing gear, you could also build a launch trolley or hand launch it.

 

[Mr Man]

What filament are you planning to use?

 

[NeonGreen]

What filament are you planning to use?

colorfabb lw pla at 5% gyroid infill is the plan. haven't printed with any lw pla yet so going to do some testing once i get some.

 

[Mr Man]

colorfabb lw pla at 5% gyroid infill is the plan. haven't printed with any lw pla yet so going to do some testing once i get some.

Ok, just checking.