Foamboard SAAB JAS-39 Gripen EDF (images, plans, build)
- Thread starter Widkin
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- edf gripen saab scratchbuild
Bayboos
Active member
Not everything is permanent yet; but I had to put the pieces together to figure out next steps. It looks like I will have to have the bottom half almost completed before I can start to build up the top one; and that in turn means the EDF will have to be glued in permanently. That's not something I was hoping for; but I can still live with that. I hope I will not have to replace it anytime soon.
Bayboos
Active member
So I glued the wings on today, and then cut the spar slot and installed the carbon rod inside. Only after that I flipped the fuselage bottom side up and realized that something just doesn't look right. As I understand the plans, I believe the line from the wing's "inlet slot" (the cutout for the inlet part of the fuselage) inner corner should go straight to the inner side of the angled section of the tail cutout, barely touching the EDF spacers - that's because this line marks the inner edge of the fuselage cover/skin. Instead of that, the aforementioned line touches the EDF spacers, but "misses" the tail cutout by approx. 6mm (the thickness of the foam).
And that's on the "better" side; the other one does not even touch both spacers and misses the cutout even more.
I know why the "worse" side is this way: the rear spacer "slipped" just a tiny bit to the outside when the glue was curing. Obviously that's not something that can't be fixed; but it just begs for a slight change in plans so this would never happen again. I'd also love to have the wings designed in a way that allows joining them together and installing the spar before attaching them to the fuselage; but for this particular plane it's too late for that anyway.
Now it's time for a razor blade, a sanding block, and a hope other parts will fit better.
And that's on the "better" side; the other one does not even touch both spacers and misses the cutout even more.
I know why the "worse" side is this way: the rear spacer "slipped" just a tiny bit to the outside when the glue was curing. Obviously that's not something that can't be fixed; but it just begs for a slight change in plans so this would never happen again. I'd also love to have the wings designed in a way that allows joining them together and installing the spar before attaching them to the fuselage; but for this particular plane it's too late for that anyway.
Now it's time for a razor blade, a sanding block, and a hope other parts will fit better.
Bayboos
Active member
I just figured out that the "inlet slot" in the fwd part of the wing panels is too short to make the inlet skin fit the fuselage properly. In fact, I believe the inlet skin should have a matching pair of slots; but there is nothing like this to be found on the plans. Instead of guessing the slot position on the inlet skin, I just made the the wing slots longer 
I also figured out the "height" at which the inlet should meet the wing based on the width of the straight parts of the upper/lower fuselage skin parts.
After all this figuring out, I just used some more razor blade moves and a ton of glue; and here's the result:
(don't worry about the closed cockpit, please. It's just a part of "technological process" and will be cut open; but I'm leaving it for my 6 yr old son to do it tomorrow. He asked for it himself, so I can't let him down).
From this point I can finally (and correctly this time) determine how much I need to correct the EDF mounting spacers. After that it will be just a matter of glueing the EDF itself in and more skin panels around it. And that's basically it in terms of the "business end" of the plane.
It's time to start figuring out the "pointy end"; and here's the problem: I can't imagine how the mid-nose (or front-cockpit, if you like) part joins the fuselage. I think that the two triangular slots in the belly skin play a role in the joining thing; but I have a hard time imagining it. It would probably become clear if I would just cut the parts and try to assemble them; but since I need to modify most of the parts, I'd rather see how it is supposed to look like before any cutting is done.
Can anyone provide some close-up photos of the bottom of the plane in the cockpit area, and preferably inside the cockpit as well? That would be very helpful. Thanks in advance.
P.S. Weight check-in showed ~100g at this point. Assuming 150g for the remaining foam/glue, the calculations show approx. 800-850g AUW of the completed plane. In this case the design buffer is around 100-150g; so I'm now moderately positive about the overall results.
I also figured out the "height" at which the inlet should meet the wing based on the width of the straight parts of the upper/lower fuselage skin parts.After all this figuring out, I just used some more razor blade moves and a ton of glue; and here's the result:
(don't worry about the closed cockpit, please. It's just a part of "technological process" and will be cut open; but I'm leaving it for my 6 yr old son to do it tomorrow. He asked for it himself, so I can't let him down).
From this point I can finally (and correctly this time) determine how much I need to correct the EDF mounting spacers. After that it will be just a matter of glueing the EDF itself in and more skin panels around it. And that's basically it in terms of the "business end" of the plane.
It's time to start figuring out the "pointy end"; and here's the problem: I can't imagine how the mid-nose (or front-cockpit, if you like) part joins the fuselage. I think that the two triangular slots in the belly skin play a role in the joining thing; but I have a hard time imagining it. It would probably become clear if I would just cut the parts and try to assemble them; but since I need to modify most of the parts, I'd rather see how it is supposed to look like before any cutting is done.
Can anyone provide some close-up photos of the bottom of the plane in the cockpit area, and preferably inside the cockpit as well? That would be very helpful. Thanks in advance.
P.S. Weight check-in showed ~100g at this point. Assuming 150g for the remaining foam/glue, the calculations show approx. 800-850g AUW of the completed plane. In this case the design buffer is around 100-150g; so I'm now moderately positive about the overall results.
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Widkin
Member
Looking good! If you can get AUW as low as you estimate, I think this will perform very well.
The front part is just glued on to the rest. The two thin slots are just to create some separation between the inlets and fuselage, so only for show.
You need two firewalls, and they are glued together. Don't glue too much, the idea is that the front part should break off in case of a bad crash.
Pictures coming later, can't upload from my phone to FT forums.
The front part is just glued on to the rest. The two thin slots are just to create some separation between the inlets and fuselage, so only for show.
You need two firewalls, and they are glued together. Don't glue too much, the idea is that the front part should break off in case of a bad crash.
Pictures coming later, can't upload from my phone to FT forums.
Bayboos
Active member
Here's what I'm working on right now.
It's (obviously) not glued in yet; I want to figure out the ESC location before. Originally, I wanted to put it in the "triangle" part of the cabin; but it will make it difficult to replace/upgrade in the future (no access to the cable connectors without cutting the fuselage open). I can move it forward, closer to the inlet area (which will also help with CG and make connecting the battery easier); but that requires soldering cable extensions I don't have enough materials for at this point.
On the other end, front part of the cockpit is also glued together:
This one required a lot of "adjusting" and still did not came out perfect; but I'm not worried about that much since it's very likely that I'll need to rebuild it soon anyway
It's (obviously) not glued in yet; I want to figure out the ESC location before. Originally, I wanted to put it in the "triangle" part of the cabin; but it will make it difficult to replace/upgrade in the future (no access to the cable connectors without cutting the fuselage open). I can move it forward, closer to the inlet area (which will also help with CG and make connecting the battery easier); but that requires soldering cable extensions I don't have enough materials for at this point.
On the other end, front part of the cockpit is also glued together:
This one required a lot of "adjusting" and still did not came out perfect; but I'm not worried about that much since it's very likely that I'll need to rebuild it soon anyway
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Bayboos
Active member
Latest news from the building front:
1. Fan's power leads extended up to the cockpit area (no image) - this will allow installing the ESC in a place where it can be reached for temp check/replacement (if needed)
2. Fan glued in place:
3. additional "fences" (triangle stripes of 6mm depron) glued in to help with installing the air duct skin:
Both pictures above show the bottom half of the plane. Those "stripes" will not affect the final look since they will be covered by the fuselage-wing "fairings". The bottom half of the fuselage skin is in the glueing process right now, I will post the photos of the final product when the glue will cure.
1. Fan's power leads extended up to the cockpit area (no image) - this will allow installing the ESC in a place where it can be reached for temp check/replacement (if needed)
2. Fan glued in place:
3. additional "fences" (triangle stripes of 6mm depron) glued in to help with installing the air duct skin:
Both pictures above show the bottom half of the plane. Those "stripes" will not affect the final look since they will be covered by the fuselage-wing "fairings". The bottom half of the fuselage skin is in the glueing process right now, I will post the photos of the final product when the glue will cure.
Hahaha!
I have a 6 month little boy here and he takes all my time right now, but
Im building a F16 from LX, I hope it's ready for spring
Time very well taken and invested
Hahaha!
I have a 6 month little boy here and he takes all my time right now, but
Im building a F16 from LX, I hope it's ready for spring
Time very well taken and invested
Bayboos
Active member
My ESC will be installed in the floor of the aft part of the cockpit. It will not be protruding into the air duct; rather than that, it will stick "outside" and will be cooled by the outside air.
Back to the work bench:
As you can see, the bottom skin is already glued in and the upper one is in the process. And the fuselage cross-section looks AWESOME from behind I just need to complete the exhaust tube and the nose cone; and the fuselage will be basically done. I will probably not be able to complete the plane before the weekend (just a tiny drop of self-irony ), but I'm hoping it will fly in a couple of weeks.
Back to the work bench:
As you can see, the bottom skin is already glued in and the upper one is in the process. And the fuselage cross-section looks AWESOME from behind
I just need to complete the exhaust tube and the nose cone; and the fuselage will be basically done. I will probably not be able to complete the plane before the weekend (just a tiny drop of self-irony ), but I'm hoping it will fly in a couple of weeks.
Bayboos
Active member
Don't worry, I will not forget about them. In fact, wing root fairings are essential to hide some "fitting imperfections" along the fuselage
Some more "fitting magic" happened during the last two days:
As you can see, the "thrust tube" (as cut exactly from plans) turned out to be too "short". I decided to leave it this way and will fill out the gap later as this will make the bottom of the tail a bit stronger. This will definitely help with tail's durability in case of slow (high alpha) landings.
After glueing that part together, I decided to cut out the "exhaust nozzle" longer and fit it on the plane; and this turned out almost perfect. A couple of "cone joining tricks" later the nozzle was in place.
Now it's time for "aesthetics" (nose cone, wing fairings etc.) and electronics; which will probably take longer than everything else...
P.S.
At this point the plane weights 330g, with the EDF unit already in place. The designated battery weights 225g, ESC - 50g, 2 servos - 20g. I'm not sure how much the receiver and leads will add to the mix, but with the "known total" around 625g I still have 175g to the designed AUW. Looks promising.
Some more "fitting magic" happened during the last two days:
As you can see, the "thrust tube" (as cut exactly from plans) turned out to be too "short". I decided to leave it this way and will fill out the gap later as this will make the bottom of the tail a bit stronger. This will definitely help with tail's durability in case of slow (high alpha) landings.
After glueing that part together, I decided to cut out the "exhaust nozzle" longer and fit it on the plane; and this turned out almost perfect. A couple of "cone joining tricks" later the nozzle was in place.
Now it's time for "aesthetics" (nose cone, wing fairings etc.) and electronics; which will probably take longer than everything else...
P.S.
At this point the plane weights 330g, with the EDF unit already in place. The designated battery weights 225g, ESC - 50g, 2 servos - 20g. I'm not sure how much the receiver and leads will add to the mix, but with the "known total" around 625g I still have 175g to the designed AUW. Looks promising.
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