Saab 105 64mm 3D Printed EDF Jet

[telnar1236]

As I was designing my 50mm EDF jet trainer, @FlyerInStyle pointed out that it resembled the Saab 105 quite a bit. The Saab is an amazing looking plane that also seems like it should translate very well to RC and also one that I had never even heard of much less seen modeled as an RC plane before which meant it immediately caught my interest.

My original thinking was to use twin 50mm fans and have a plane twice the size of my mini trainer jet, but at that point you end up with a plane that is getting larger than a practical park flyer size range and would require a paved runway for takeoff and landing, so instead I've opted to go with a single 64mm fan (since I had it sitting around anyways and have been trying to think of something to do with it). This size should still leave it possible to hand launch and belly land and keep the complexity more manageable. Currently, my thinking is to make it 4-5 channels with flaps optional, though the flaps might not end up happening.
This is what I have for CAD so far. It needs some additional details and some blending of some the corners to get everything closer to the real thing, but overall, the shape was surprisingly easy to achieve.

Because it's a lesser-known plane, the 3-views I could find to work from weren't particularly great and in the one I ended up using the top view didn't quite match the side view for a couple things. In addition, I couldn't find any section views of the fuselage which means the shape might be slightly off, but I think it's pretty close from what I can tell.

So far as size goes, it's pretty middle of the road for a 64mm design and is 1/12 scale to the real plane. Not substantially bigger than my 50mm jet trainer with a 35.5" length and a 34" wingspan (slightly larger than scale), it is, however, substantially chunkier which gives room for the larger power system. Weight will probably end up around 1.3 - 1.4 kg.

 

[FlyerInStyle]

would it be possible to make a version for a single 70mm edf? (I would love ot build this and I have one on hand) It is looking great though. I am thinking maybe a 70mm edf in the same size of plane, just because I like using 4s on my edfs which means a bit less thrust

 

[telnar1236]

would it be possible to make a version for a single 70mm edf? (I would love ot build this and I have one on hand) It is looking great though. I am thinking maybe a 70mm edf in the same size of plane, just because I like using 4s on my edfs which means a bit less thrust

What kind of 70mm EDF are we talking about? And what battery? With a 4s EDF and up to maybe a 3300 mAh pack, it should be pretty easy to design for, but with 6s the weight might start to get a bit much. The inlet area should be large enough and there is space to model for the larger nozzles, and the weight increase should be pretty manageable and well within what the plane can handle, no more than at most about 15%. Here's the size relative to my 70mm F-104 and a twin 50mm F-101 (roughly same FSA as a 70mm) I've been playing with the concept for, so the wing isn't really any smaller and the main difference is the length which won't really impact the ability to carry a larger power system.

 

[FlyerInStyle]

What kind of 70mm EDF are we talking about? And what battery? With a 4s EDF and up to maybe a 3300 mAh pack, it should be pretty easy to design for, but with 6s the weight might start to get a bit much. The inlet area should be large enough and there is space to model for the larger nozzles, and the weight increase should be pretty manageable and well within what the plane can handle, no more than at most about 15%. Here's the size relative to my 70mm F-104 and a twin 50mm F-101 (roughly same FSA as a 70mm) I've been playing with the concept for, so the wing isn't really any smaller and the main difference is the length which won't really impact the ability to carry a larger power system.
View attachment 252423

I am thinking exactly that, a 70mm edf (dont remember kv right now), with a 4s 3300 or 4000 pack, it just abrely powered my ft f-16 (it actually crasehd because the batt discharged some and it was underpowered enough that it crashed so now the edf is available) so as longa s it requires lelss power than that plane it shouldnt be a problem. As long as youc an design it to fit a 70mm edf instead of a 64mm one

 

[telnar1236]

I am thinking exactly that, a 70mm edf (dont remember kv right now), with a 4s 3300 or 4000 pack, it just abrely powered my ft f-16 (it actually crasehd because the batt discharged some and it was underpowered enough that it crashed so now the edf is available) so as longa s it requires lelss power than that plane it shouldnt be a problem. As long as youc an design it to fit a 70mm edf instead of a 64mm one

It should be able to fit either 64mm fan or a 70mm one without much trouble. The EDF mounting hardware was going to be separate from the fuselage regardless, so I modeled the nozzles at the 70mm size and will use inserts to reduce them for the 64mm version. This cross section shows a Freewing 70mm fan in place of the 64mm fan from my original concept. My only worry with a 4000 mAh 4s pack would be CG since I don't yet know where the CG without a battery will sit, but a 3300 mAh would probably work well.

If you can give me the brand and model of fan I can look up some drawings and make sure it will fit the mount I design, should only take about 5 minutes.

 

[telnar1236]

The CAD is starting to come together a bit more.

I didn't realize how weird the geometry around the jet exhausts and on the tail boom is until I started modeling in some more details and even in pictures of the real plane it looks like there is some variation in the shape between different versions of the aircraft.

The first parts probably won't be printed till this weekend at the earliest or maybe early next week, but the CAD is starting to resemble something a bit more workable.

 

[FlyerInStyle]

It should be able to fit either 64mm fan or a 70mm one without much trouble. The EDF mounting hardware was going to be separate from the fuselage regardless, so I modeled the nozzles at the 70mm size and will use inserts to reduce them for the 64mm version. This cross section shows a Freewing 70mm fan in place of the 64mm fan from my original concept. My only worry with a 4000 mAh 4s pack would be CG since I don't yet know where the CG without a battery will sit, but a 3300 mAh would probably work well.
View attachment 252435
If you can give me the brand and model of fan I can look up some drawings and make sure it will fit the mount I design, should only take about 5 minutes.

it was some random one off of amazon, I cant find the brand... jsut make it fit some sort of generic 70mm edf, Ill figure out the rest. I can tweak the design on my own to make it fit if you give me the cad. It s just some generic form factor so it should fit.

 

[FlyerInStyle]

The CAD is starting to come together a bit more.
View attachment 252437
I didn't realize how weird the geometry around the jet exhausts and on the tail boom is until I started modeling in some more details and even in pictures of the real plane it looks like there is some variation in the shape between different versions of the aircraft.
View attachment 252438
The first parts probably won't be printed till this weekend at the earliest or maybe early next week, but the CAD is starting to resemble something a bit more workable.

that is looking great! if you need more pictures, the prototype version was called the sk60, and it looked practically identical to the 105.

 

[telnar1236]

The nose of the Saab 105 is now printed. I didn't realize quite how wide the canopy is until I saw the physical part, but it makes sense since the full-scale plane had side by side seating.

Like all of my designs for the past couple of years, this plane is printed in modules which makes it easier to repair or replace parts in case of a bad landing or crash. In this plane, you have the nose, the main fuselage, the tail, the two wings, and the assembly of the horizontal and vertical stabilizers, each of which can be removed separately. Within each module, the servos can also be removed with a couple of screws and some other important bits and pieces can also be separated out.

Outwardly, the CAD hasn't changed too much, but you can see the internal structure is starting to be defined.

 

[L Edge]

it was some random one off of amazon, I cant find the brand... jsut make it fit some sort of generic 70mm edf, Ill figure out the rest. I can tweak the design on my own to make it fit if you give me the cad. It s just some generic form factor so it should fit.

Working with EDF's is a pain. Buy EDF, make a plane ---not enough thrust, go up by some S, now battery goes up in weight-plane shot, rebuild. Screwed. Repeat process.

So you need to get a feel about flying an EDF as well as matching an EDF and battery size and then design plane around that. A good name to buy in EDF's is Freewing. What size, minimum is 70 (the 64 can be substituted) and the key is lightweight for your plane. Printed is the way to go for a starter.

There are a lot of tricks with EDF's to get it to fly. @telnar1236 will agree. I chose 5 bladed 64 mm EDF and have designed (weight is super light to my success. Inlet ducting, exhaust location, 2 EDF's, all present problems you need to observe and solve.

 

[FlyerInStyle]

Working with EDF's is a pain. Buy EDF, make a plane ---not enough thrust, go up by some S, now battery goes up in weight-plane shot, rebuild. Screwed. Repeat process.

So you need to get a feel about flying an EDF as well as matching an EDF and battery size and then design plane around that. A good name to buy in EDF's is Freewing. What size, minimum is 70 (the 64 can be substituted) and the key is lightweight for your plane. Printed is the way to go for a starter.

There are a lot of tricks with EDF's to get it to fly. @telnar1236 will agree. I chose 5 bladed 64 mm EDF and have designed (weight is super light to my success. Inlet ducting, exhaust location, 2 EDF's, all present problems you need to observe and solve.

Yeah, that makes sense. If this EDF is underpowered and I do need to invest in a good one, I wouldn't mind doing so, I just don't want it to go to waste for now. I have not gotten to the stage of designing edfs, although I may try later on with my peregrine design that I started a thread on. I'll keep all that in mind .

 

[FlyerInStyle]

The nose of the Saab 105 is now printed. I didn't realize quite how wide the canopy is until I saw the physical part, but it makes sense since the full-scale plane had side by side seating.
View attachment 252457
Like all of my designs for the past couple of years, this plane is printed in modules which makes it easier to repair or replace parts in case of a bad landing or crash. In this plane, you have the nose, the main fuselage, the tail, the two wings, and the assembly of the horizontal and vertical stabilizers, each of which can be removed separately. Within each module, the servos can also be removed with a couple of screws and some other important bits and pieces can also be separated out.
View attachment 252458
Outwardly, the CAD hasn't changed too much, but you can see the internal structure is starting to be defined. View attachment 252459

That looks great! What are you printing it in? Pla or lw-pla, or something else? How big are the pieces? (Minimum what size printer)

 

[telnar1236]

Yeah, that makes sense. If this EDF is underpowered and I do need to invest in a good one, I wouldn't mind doing so, I just don't want it to go to waste for now. I have not gotten to the stage of designing edfs, although I may try later on with my peregrine design that I started a thread on. I'll keep all that in mind .

Unless it's quite weak for a 70mm fan, it should probably ok so long as the plane is taking off from a prepared runway. Probably 800g of thrust is all you need there. But hand launching might need something more powerful.

The overall design is intended for one of the more powerful 64mm fans out there with around 1.3 kg thrust, so most modern 70s should be overkill. My two "cheap" 70s from Amazon produce 1.5 kg of thrust and 1.8 kg of thrust which are both plenty.

 

[telnar1236]

That looks great! What are you printing it in? Pla or lw-pla, or something else? How big are the pieces? (Minimum what size printer)

Thanks, I'm using ABS primarily for the temperature resistance since I'm in Florida and anything dark colored and PLA lasts about 5 minutes in the sun, but normal PLA should work well too. All the pieces are designed to fit an Ender 3 style machine. The two largest pieces are the two halves of the core fuselage, both of which can be rotated diagonal to fit the print bed.

 

[FlyerInStyle]

Thanks, I'm using ABS primarily for the temperature resistance since I'm in Florida and anything dark colored and PLA lasts about 5 minutes in the sun, but normal PLA should work well too. All the pieces are designed to fit an Ender 3 style machine. The two largest pieces are the two halves of the core fuselage, both of which can be rotated diagonal to fit the print bed.
View attachment 252472

I am in a bit of a dilemma where I have 1 printer able to print 235^3 but it has a .6 nozzle and no enclosure, and one that has a .4 nozzle and an enclosure, but a 180^3 build volume. What do you think I should do? If I have to I will put a .4 nozzle on the bigger one but I would rather not given the chance. (That is when you hopefully release the files and I can build one myself)

 

[Mr Man]

My printer has a 150^3 Area…

 

[telnar1236]

I am in a bit of a dilemma where I have 1 printer able to print 235^3 but it has a .6 nozzle and no enclosure, and one that has a .4 nozzle and an enclosure, but a 180^3 build volume. What do you think I should do? If I have to I will put a .4 nozzle on the bigger one but I would rather not given the chance. (That is when you hopefully release the files and I can build one myself)

Unfortunately, pretty much the only option is changing out the nozzle on the 235x235 one to print this plane. There are a couple fuselage sections that are both too wide and too tall for a 180x180 machine. The design is far enough along that the amount of redoing work required isn't super practical and the core fuselage also can't really get any smaller while being able to fit a 70mm fan, all the required wiring, and the structure to support the wing since the fan has to fit through the middle of that structure. The bit in red has to fit through the bit in blue, and I can't make the fuselage smaller while leaving enough space without making the bit in blue too weak.

Fortunately, you shouldn't need an enclosure if you use PLA instead of ABS, so it should be doable, if a bit of a pain to change the nozzle.

 

[telnar1236]

The core fuselage is printed now. There was a bit of buckling in the skin on the wing root, so I'll need to add a bit more structure there, mostly for aesthetic reasons, but for the prototype, the print is good enough, and if I'm being honest, I likely won't change it out till I manage to break it.

The CAD also has the main landing gear now. It's a bit taller than scale, and the wheels are a bit larger, to improve ground handling, and obviously the gear struts are modified to be printable and easy to install and uninstall.

I've also been thinking about how to handle making an EDF mount that can work for both 70mm and 64mm fans, and this is what I've arrived at. The 64mm EDF slides back farther in the duct before being glued in place than the 70mm fan which means both can fit in the same part.

 

[FlyerInStyle]

Unfortunately, pretty much the only option is changing out the nozzle on the 235x235 one to print this plane. There are a couple fuselage sections that are both too wide and too tall for a 180x180 machine. The design is far enough along that the amount of redoing work required isn't super practical and the core fuselage also can't really get any smaller while being able to fit a 70mm fan, all the required wiring, and the structure to support the wing since the fan has to fit through the middle of that structure. The bit in red has to fit through the bit in blue, and I can't make the fuselage smaller while leaving enough space without making the bit in blue too weak.
View attachment 252485
Fortunately, you shouldn't need an enclosure if you use PLA instead of ABS, so it should be doable, if a bit of a pain to change the nozzle.

I dont know why I was complaining, I forgot my 235x235 printer was a toolchanger (stilla work in progress, but I can easily make 1 tool a .4) sorry for bothering you on that. Is petg a good material? I would think it has better crash resistance than pla or abs. how does infill and all that work on your planes, or do you jsut do it customa nd dont allow space for the infill? Its looking great so far though, and a great idea for the 2 eddfs sizes. I may have to steal that for my own plane design. where does the batt and the servos go?

 

[telnar1236]

No worries, I wouldn't be posting this stuff online if I didn't want to be asked questions about it.

PETG would probably work, but it's heavier than either PLA or ABS and despite its reputation, not as strong as PLA. If printing in PETG it will be about 200g heavier than ABS and about 70g heavier than PLA, so especially if you end up using a weaker 70mm fan with a big 3300 mAh pack, you could end up with something quite underpowered and heavy. Pretty much regardless of the material, if you crash, you'll end up replacing parts though. Really the only reason I see to use it is if you're worried about temperature resistance but don't have the enclosure set up to print in ABS.

The plane is a mix of areas requiring infill and not. Most of it is fully modeled, but there are some locations, mostly around bits that are more there for aesthetics, where infill is used. The majority of the parts use 0.4 - 0.8mm walls and 5% infill, but some more highly loaded bits like the landing gear use 1.6 - 2.0mm walls and 40% infill. When I release the files, there will be printing and assembly directions like with my F-104 with the required wall thickness and infill per part.

Thanks, pretty happy with how it's turning out so far. The battery is under the canopy and a bit back.

I don't have the servos modeled in yet, but it will use 7 of the common 9g servos most people have, 2 for ailerons, 1 for elevator, 1 for rudder, 2 for flaps, and 1 for nose gear steering. They'll be about here in removable pockets for easy replacement if needed. They're located as close as possible to the control surfaces to keep the length of the linkages reasonable.