Let's Try This Again! 3D Printed EDF Jet Trainer

[telnar1236]

My first attempt at a 50mm jet trainer was not very successful and barely flew. However, my reasons for it (wanting a cheap easy to replicate jet that flies well as factory options get more expensive) are still there, so I'm designing a new version that should hopefully be much better. It's based on my successful 70mm jet trainer with some substantial improvements and obviously reduced in size.

The low horizontal stabilizer should avoid deep stall tendencies which I am now scared of after the problems of the previous design. It also uses a more stall resistant airfoil than the previous design. And the wings should be very stall resistant between the Clark Y airfoil, wing fences, small leading-edge extensions, and 3 degrees of washout root to tip.

There's nothing particularly crazy about this design, and not attempting to make it look retro like a 50s fighter should remove a lot of the uncertainty from the aerodynamics, so I'm hoping it should fly a lot better.

 

[Houndpup Rc]

My first attempt at a 50mm jet trainer was not very successful and barely flew. However, my reasons for it (wanting a cheap easy to replicate jet that flies well as factory options get more expensive) are still there, so I'm designing a new version that should hopefully be much better. It's based on my successful 70mm jet trainer with some substantial improvements and obviously reduced in size.
View attachment 252015
The low horizontal stabilizer should avoid deep stall tendencies which I am now scared of after the problems of the previous design. It also uses a more stall resistant airfoil than the previous design. And the wings should be very stall resistant between the Clark Y airfoil, wing fences, small leading-edge extensions, and 3 degrees of washout root to tip.
View attachment 252016
There's nothing particularly crazy about this design, and not attempting to make it look retro like a 50s fighter should remove a lot of the uncertainty from the aerodynamics, so I'm hoping it should fly a lot better.
View attachment 252017
View attachment 252018

Good luck!

 

[telnar1236]

Everything is coming together a bit faster this time. The airframe is now mostly designed with the exception of the landing gear.

And it's rapidly approaching the point of being mostly printed too. Currently the prototype weight is looking to be about 950 g which should go down for the final version once I replace gyroid infill in the wings and tail with modeled internal structure.

 

[Houndpup Rc]

Everything is coming together a bit faster this time. The airframe is now mostly designed with the exception of the landing gear.
View attachment 252130
And it's rapidly approaching the point of being mostly printed too. Currently the prototype weight is looking to be about 950 g which should go down for the final version once I replace gyroid infill in the wings and tail with modeled internal structure.
View attachment 252131

Looking good!

 

[Mr Man]

Looks awesome!

 

[telnar1236]

And it flies! And in what might be a first for me I actually managed to video the maiden flight. Unfortunately, it was extremely nose heavy so as soon as I took off I realized I needed to land and so came back around and put it back on the runway. Apologies for the quality of the video - I tried taping my Runcam to my sunglasses to see if this would be an easier way to get good video but I didn't quite get it straight so the whole video is tilted.

The bounce on landing damaged the nose gear and this prototype is quite heavy so I didn't want to try hand launching, so I wasn't able to try to fly again with a more aft CG. The metallic gray PLA was also a bit too dark for the Florida sun, so it experienced some warping so I'll probably just move directly into building the version I intend to release with its significant weight reductions and some other changes to improve the building experience (like not forgetting the hole in the rudder hinge so you need to cut into it add one in for example).

Overall, I'm pretty happy with how this one is going. I went from a concept to a mostly working 3D printed design in a bit over a week which is a record for me.

 

[telnar1236]

The redesign is mostly done. There isn't really room to shift the EDF back so instead I shifted the wings and main gear forwards by an inch to shift the COP closer to the CG. It should result in a somewhat less close coupled design too which I'm somewhat ambivalent towards - personally I prefer close coupled designs, but I think a lot of people don't prefer them. I'm also changing up the color scheme since metallic colors of ABS seem to really suffer layer adhesion issues in my experience.

There are also minor changes to the wing root leading edge extensions, significant weight reductions of about 100g, mostly by fully modeling the internal structure, and some other minor changes.

 

[Mr Man]

That jet looks SO cool. Wish I had all the stuff for it. (My 3d printer is way to small, and is very old)

 

[FlyerInStyle]

I saw this and thought it looked very familiar... You may have accidentally designed something very similar to the saab105. Interesting how similar goals converged on very similar designs.

 

[Mr Man]

I saw this and thought it looked very familiar... You may have accidentally designed something very similar to the saab105. Interesting how similar goals converged on very similar designs. View attachment 252311

Close, the major differences I see are: Telnar’s canopy is farther forward, he’s got a traditional tail instead of a T-tail, and I think his fuselage might be a bit taller. They are kinda similar though. But imo Telnar’s is cooler 😎

 

[telnar1236]

That jet looks SO cool. Wish I had all the stuff for it. (My 3d printer is way to small, and is very old)

Thanks, I'm pretty happy with how it's turning out. 3D printer size shouldn't be a problem since it prints in sections, but it probably does need something a bit more modern with how thin all the parts are

 

[Mr Man]

Thanks, I'm pretty happy with how it's turning out. 3D printer size shouldn't be a problem since it prints in sections, but it probably does need something a bit more modern with how thin all the parts are

Yeah mine’s got a 150mm square build area. And I think it is almost 5 years old…. Maybe 6. (Qidi X smart)

 

[telnar1236]

I saw this and thought it looked very familiar... You may have accidentally designed something very similar to the saab105. Interesting how similar goals converged on very similar designs. View attachment 252311

That is pretty similar. Especially the wing design is almost identical and I almost went with a T tail on mine but ended up deciding on the lower tail to avoid potential problems with deep stalls. But like Mr Man said the fuselage is a somewhat different. I think mine is pointier which is probably aerodynamically worse, and it looks like the Saab design is a twin engine setup vs. the single motor in my one. That's a neat plane that I didn't know existed till just now

 

[FlyerInStyle]

That is pretty similar. Especially the wing design is almost identical and I almost went with a T tail on mine but ended up deciding on the lower tail to avoid potential problems with deep stalls. But like Mr Man said the fuselage is a somewhat different. I think mine is pointier which is probably aerodynamically worse, and it looks like the Saab design is a twin engine setup vs. the single motor in my one. That's a neat plane that I didn't know existed till just now

Yours is probably the better option for rc, but it was just cool to see the similarities, similar problem, similar solution. The Saab 105 was twin engine only cause they didn't have correct single engines, I believe it was proposed as a single engine first (although I may be remembering wrong).

 

[telnar1236]

Yours is probably the better option for rc, but it was just cool to see the similarities, similar problem, similar solution. The Saab 105 was twin engine only cause they didn't have correct single engines, I believe it was proposed as a single engine first (although I may be remembering wrong).

I've been thinking of building a twin 50mm F-101 since from some ground testing, two 50mm fans on 4s generate almost as much thrust as a single 70mm fan on 6s without drawing too much more current either. I'll admit, looking at the Saab 105, I almost want to build that instead - it would probably fly a good deal nicer even if it doesn't look quite as cool.

 

[Houndpup Rc]

I've been thinking of building a twin 50mm F-101 since from some ground testing, two 50mm fans on 4s generate almost as much thrust as a single 70mm fan on 6s without drawing too much more current either. I'll admit, looking at the Saab 105, I almost want to build that instead - it would probably fly a good deal nicer even if it doesn't look quite as cool.
View attachment 252365

Or the B-2........

 

[telnar1236]

Or the B-2........

Maybe at some point, but it's mostly the kind of model you have to fly around in circles and not do much with which makes it less fun, at least in my opinion. I had a model of a B-2 years ago (the twin 70mm from Banana Hobby) and it only flew well so long as you kept it in a fairly limited flight envelope - you could still loop and roll and do basic aerobatics, but it wasn't very fun to fly due to the lack of a vertical stabilizer. And some people at my flying field have brought out the twin 40mm version from Eflite which seems to fly terribly without the clear vertical fin which makes me worry that it might fly significantly worse as it gets smaller.

 

[Houndpup Rc]

Maybe at some point, but it's mostly the kind of model you have to fly around in circles and not do much with which makes it less fun, at least in my opinion. I had a model of a B-2 years ago (the twin 70mm from Banana Hobby) and it only flew well so long as you kept it in a fairly limited flight envelope - you could still loop and roll and do basic aerobatics, but it wasn't very fun to fly due to the lack of a vertical stabilizer. And some people at my flying field have brought out the twin 40mm version from Eflite which seems to fly terribly without the clear vertical fin which makes me worry that it might fly significantly worse as it gets smaller.

True....I know the Mig 29 is a really good one for more acrobatics.

 

[telnar1236]

The airframe is now rebuilt around the new wing position. Weather permitting, I'm going to try and fly it tomorrow. It currently is a bit of a patchwork since I didn't have time to reprint every part in the right color, but all the parts that I changed the design of are new.

It is now easy to achieve a more aft CG and the plane is 140g lighter, so it should hopefully fly a good deal better.

 

[telnar1236]

True....I know the Mig 29 is a really good one for more acrobatics.

Now that's an idea