Solved my journey to 3D print a JAS 39 gripen

[Mr Man]

Is that a actual concern..?

Yes, @telnar1236 has to be very careful in the summer.

 

[Mr Man]

Is that a actual concern..?

Black is a bad color for 3d printed planes.

 

[NeonGreen]

Black is a bad color for 3d printed planes.

ok, luckily i made some good color choices

 

[AIRFORGE]

Dark colors absorb heat/sunlight more easily than lighter colors.
It's always a good idea to not leave printed planes in direct sunlight, or in a closed vehicle when it's hot, regardless of color.

 

[telnar1236]

It depends on where you live how big the risk is. I'm in Florida where inside cars it can get up to 150 or 160 degrees Fahrenheit most days in the summer and you can literally cook eggs on the asphalt on occasion. Down here, even printing a plane in black PLA at all is a recipe for disaster. My modular trainer jet was originally black, and after flying it once on a sunny day, it came back warped. Even my mostly gray ABS F-104 originally had a PLA nosecone. I painted the black antiglare strip on it and within a few flights, it had collapsed too, and I needed to replace it with ABS as well. The biggest thing is not to leave PLA planes in a hot car. They will be totally destroyed and unflyable in minutes. Further north, I expect it is better and damage will occur more slowly, but as a whole PLA has pretty poor tolerance for sunlight. It's why I'm slowly trying to switch over to fully ABS planes despite ABS being so much harder to deal with. You can boil ABS, and it won't break a sweat.

 

[AIRFORGE]

It depends on where you live how big the risk is. I'm in Florida where inside cars it can get up to 150 or 160 degrees Fahrenheit most days in the summer and you can literally cook eggs on the asphalt on occasion. Down here, even printing a plane in black PLA at all is a recipe for disaster. My modular trainer jet was originally black, and after flying it once on a sunny day, it came back warped. Even my mostly gray ABS F-104 originally had a PLA nosecone. I painted the black antiglare strip on it and within a few flights, it had collapsed too, and I needed to replace it with ABS as well. The biggest thing is not to leave PLA planes in a hot car. They will be totally destroyed and unflyable in minutes. Further north, I expect it is better and damage will occur more slowly, but as a whole PLA has pretty poor tolerance for sunlight. It's why I'm slowly trying to switch over to fully ABS planes despite ABS being so much harder to deal with. You can boil ABS, and it won't break a sweat.

Absolutely! Heart-O-Texas heat for me, brother!

 

[NeonGreen]

After tuning the printer settings for LW-PLA, I initially thought that 240°C with a 0.38 extrusion would be ideal. However, after a test print, I realized this was probably pushing the limits of the material. The bed adhesion wasn’t very good, and the part felt fragile.

On a positive note, the expected weight with these settings was 550g, but since the print felt flimsy, I checked the expected weight using a 0.5 extrusion, which was 720g. That seems like a better weight. I also noticed some imperfections at 0.35 extrusion.

 

[NeonGreen]

it's all coming togheter now.

 

[Houndpup Rc]

it's all coming togheter now.
View attachment 248789 View attachment 248790
View attachment 248788

Man! that's cool! Great job!

 

[telnar1236]

Looking good!

 

[NeonGreen]

did some testing with the edf and got about 700g worth of thrust when it is in the plane. going to do some testing to see if i can get more by giving it better airflow

 

[NeonGreen]

did some mock up testing inorder to get a feel for how i should mix the servos.

 

[telnar1236]

did some testing with the edf and got about 700g worth of thrust when it is in the plane. going to do some testing to see if i can get more by giving it better airflow

EDFs definitely need plenty of air. If you don't have cheater inlets already, it's worth adding them in. What's the final weight?

 

[NeonGreen]

EDFs definitely need plenty of air. If you don't have cheater inlets already, it's worth adding them in. What's the final weight?

The fuselage alone, without the battery, weighed 906 grams. Adding the 215-gram battery and the wings, which weigh about 60-70 grams, brings the total to 1,272 grams. I this doesn't includes the nose or the rudder, so I'd say 1,300 grams is going to be the final weight

 

[NeonGreen]

i

EDFs definitely need plenty of air. If you don't have cheater inlets already, it's worth adding them in. What's the final weight?

I do already gave some small cheater holes but im going to try having just one cheater hole instead of multiple small ones.

 

[NeonGreen]

did another thrust test but carved away to make abigger hole for more airflow. this resultet in 100grams less force from the edf. Now im no aerodynamics expert but my guess is that the simple design of the bigger cheater hole creates too much turbulance and/or the air gets sucked in at the bottom of the edf meaning that most of the edf isn't getting enough air. corrently printing one more with a big hole but that hopefully allows the air to be better distributed around the edf (looks somewhat how the red line goes)

Old cheater hole design

 

[NeonGreen]

did another thrust test but carved away to make abigger hole for more airflow. this resultet in 100grams less force from the edf. Now im no aerodynamics expert but my guess is that the simple design of the bigger cheater hole creates too much turbulance and/or the air gets sucked in at the bottom of the edf meaning that most of the edf isn't getting enough air. corrently printing one more with a big hole but that hopefully allows the air to be better distributed around the edf (looks somewhat how the red line goes) View attachment 248985
View attachment 248978 View attachment 248979
Old cheater hole design View attachment 248986

di another test with the new cheaterhole. got even worse results. this makes me beilive that it is the difference in battery level that is having a big impact even though the voltage has only droped slightly.
15.3V first test ≈700grams 15.1V second ≈600 grams 14.9 = 550grams

im using a 2300mah 45 C battery

 

[Mr Man]

di another test with the new cheaterhole. got even worse results. this makes me beilive that it is the difference in battery level that is having a big impact even though the voltage has only droped slightly.
15.3V first test ≈700grams 15.1V second ≈600 grams 14.9 = 550grams

im using a 2300mah 45 C battery

Yes, always test with a fully charged battery.

 

[Mr Man]

Yes, always test with a fully charged battery.

I mean if you’re doing thrust and efficiency tests.

 

[telnar1236]

di another test with the new cheaterhole. got even worse results. this makes me beilive that it is the difference in battery level that is having a big impact even though the voltage has only droped slightly.
15.3V first test ≈700grams 15.1V second ≈600 grams 14.9 = 550grams

im using a 2300mah 45 C battery

I was wondering about that. Sounds like the battery is nearly empty. Testing at 16.8 V should give you much more thrust. It's a very rough approximation, but for a given EDF unit, thrust should scale with about the square of the voltage. That said, the voltage of a pack sags under load, and it sags much worse when it's almost empty so that's probably why you're getting so much worse performance. From the sounds of it, the cheater might actually not do much, so you might be able to get away with not having it, though having it couldn't hurt.