JAS-39 Gripen Owners/Build Thread
12-19-2014, 06:09 PM
#1002
Interesting observation about the rails Jim. I ran into a similar issue with my F-16. I really wanted the rails angled down (I think it's 3deg on the f-16) but because the wing doesn't have the scale washout then rail looked noticable off. In the end I ended up angling them at an angle that was a compromise to something that was close but didn't looke weird in relation to the wing. No compromise is not likely in your Gripen competition vocabulary so I watch with interest to see what you do. Btw, i wonDer if that is why'd the holes are drilled as they are, so the rails can be angled down? Or am I giving the mfg to much credit?
i wonder how yellow handle it on the large f-18....that's in my to-do list.
i wonder how yellow handle it on the large f-18....that's in my to-do list.
12-20-2014, 01:15 AM
#1005
Sean,
It wasn't quite as bad as I thought. I spent $12 for batteries for my digital level (I was using a less accurate analog level last night). The kit rail seems to have a bit more washout that I originally thought, about 1 degree, though it was pretty tough to take the measurement since I only have two hands and I didn't feel like gluing the kit rail on just to take a measurement.
Bottom line, it isn't scale (1.85 degrees), and it would be noticeable. No compromises (unless absolutely necessary, LOL).
The F-16 missile rail has a rectangular cross section where the leading edge of the wing at the tip is centered on the rail in the pic below. I suspect the trailing edge is centered too. This would have made it obvious that there was a problem with your kit if you tried mounting your rail at the correct angle so I feel your pain.
The Gripen missile rail is curved on the inboard side in the region where it attaches to the wing. This makes it a lot less obvious if the angle of the missile rail matches the washout in the wing. The rail is centered at the front, but at the back I really can't tell and I've got thousands of Gripen pics.
The main issue though is the completely unscale kit missile rail. Using photos and Corel Draw I was able to get the length-wise dimensions of the major features of the missile rail as detailed below.
The width and height of the missile rail would be very hard to determine from photos. However, in May 2013 I hired two photographers to go to the open house at Caslav Airbase outside of Prague and take 32 specific photos at specific angles of the Gripen. This was one of them.....
The RB74 missile (equivalent to an AIM-9) has a body diameter of 5 inches and from this the height and width of the rail, as well as he launch tracks and other features, can be scaled.
As for the hole locations in the Airworld rail, like you I initially thought the holes were off centered so the rail could be angled down. Nope, one of the holes is so close to the edge of the wingskin that there is no space to install a threaded insert. It's just bad workmanship. :-( Regardless, I will use them initially for test flying and replace them with home made scale rails before Top Gun.
In the dimensioned side view photo above, I saw that there are three holes in the Gripen missile rail. I'm not sure what they are for on the full scale, but they are the perfect size and location for countersunk bolt holes to mount the rails to the wingtip of the model. I spot glued a ply strip to the wingtip to hold the threaded inserts at -1.3 degrees and potted them in place with Hysol through injection holes in the top & bottom of the wing.
These hole locations do not interfere with the existing 6mm holes in the AW missile rail so I'll just patch the 6mm holes and drill new holes (offset on the inboard side to get the extra .55 degrees of washout) for the 6-32 nylon bolts.
Regards,
Jim
It wasn't quite as bad as I thought. I spent $12 for batteries for my digital level (I was using a less accurate analog level last night). The kit rail seems to have a bit more washout that I originally thought, about 1 degree, though it was pretty tough to take the measurement since I only have two hands and I didn't feel like gluing the kit rail on just to take a measurement.
Bottom line, it isn't scale (1.85 degrees), and it would be noticeable. No compromises (unless absolutely necessary, LOL).
The F-16 missile rail has a rectangular cross section where the leading edge of the wing at the tip is centered on the rail in the pic below. I suspect the trailing edge is centered too. This would have made it obvious that there was a problem with your kit if you tried mounting your rail at the correct angle so I feel your pain.
The Gripen missile rail is curved on the inboard side in the region where it attaches to the wing. This makes it a lot less obvious if the angle of the missile rail matches the washout in the wing. The rail is centered at the front, but at the back I really can't tell and I've got thousands of Gripen pics.
The main issue though is the completely unscale kit missile rail. Using photos and Corel Draw I was able to get the length-wise dimensions of the major features of the missile rail as detailed below.
The width and height of the missile rail would be very hard to determine from photos. However, in May 2013 I hired two photographers to go to the open house at Caslav Airbase outside of Prague and take 32 specific photos at specific angles of the Gripen. This was one of them.....
The RB74 missile (equivalent to an AIM-9) has a body diameter of 5 inches and from this the height and width of the rail, as well as he launch tracks and other features, can be scaled.
As for the hole locations in the Airworld rail, like you I initially thought the holes were off centered so the rail could be angled down. Nope, one of the holes is so close to the edge of the wingskin that there is no space to install a threaded insert. It's just bad workmanship. :-( Regardless, I will use them initially for test flying and replace them with home made scale rails before Top Gun.
In the dimensioned side view photo above, I saw that there are three holes in the Gripen missile rail. I'm not sure what they are for on the full scale, but they are the perfect size and location for countersunk bolt holes to mount the rails to the wingtip of the model. I spot glued a ply strip to the wingtip to hold the threaded inserts at -1.3 degrees and potted them in place with Hysol through injection holes in the top & bottom of the wing.
These hole locations do not interfere with the existing 6mm holes in the AW missile rail so I'll just patch the 6mm holes and drill new holes (offset on the inboard side to get the extra .55 degrees of washout) for the 6-32 nylon bolts.
Regards,
Jim
Last edited by rcjets_63; 12-20-2014 at 01:26 AM.
12-21-2014, 02:37 PM
#1007
Then things suddenly got very real.
Many thanks to fellow SVF club member and Jet Team USA Sponsorship Director for lending me his NIB Kingtech K-210 to do fit checks and pipe measurements (I'll buy my K-210 next month).
You know what they say about borrowing things: "My toothbrush, sure. My wife, maybe. My turbine, never!" so Dan is a great guy!
Regards,
Jim
Many thanks to fellow SVF club member and Jet Team USA Sponsorship Director for lending me his NIB Kingtech K-210 to do fit checks and pipe measurements (I'll buy my K-210 next month).
You know what they say about borrowing things: "My toothbrush, sure. My wife, maybe. My turbine, never!" so Dan is a great guy!
Regards,
Jim
12-22-2014, 07:41 PM
#1009
I have to keep the weight of the plane (dry) below the 20 Kg limit of the JWM. The weight of a couple Gripens built by others with a bit of scale detail were 19Kg with a P200SX and 21.5 Kg with a BF300. I plan on adding a lot of scale detail so I need to save weight wherever I can (besides, lighter planes fly better).
I really don't like the pipe the AW supplies with this kit. It is 28-1/8" long overall, with a 140mm diameter funnel, the OD is 4-1/2" and the ID is 4" which is too large a diameter for a 200N turbine (might be OK for a BF300 though). It is also far heavier than it needs to be.
One of the reasons I went with the Kingtech 210 (and sold my P-200SX) is that the 210 weighs about a pound less than the P-200SX. In the Gripen, the engine is mounted farther rearward than most planes so a heavy engine will require more components (and hopefully not lead) in the nose. A heavy pipe only makes matters worse.
With Dan's Kingtech K-210 turbine installed about as far forward as comfortable, I measured the distance between the aft end of the nozzle and the scale exhaust cone nozzle to be 27-11/16" and I called up Tam to order a pipe.
The Tam pipe will have an ID of 3-3/8", an OD of about 3-3/4", and an overall length (including the 3/4" bellmouth) of 27-3/16" to give a 1/2" gap between the nozzle and bellmouth per his recommendation. Tam knows pipes and neither he or one of his pipes has ever let me down so I'll install it per his numbers.
With that issue handled (thanks Tam - Merry Christmas) I returned to the fuselage and molding the canopy frame (see posts 979 for the issues with the AW frame). The balsa "plug" I built turned out pretty good and has the scale reinforcement along the side as well as the scale transition between the fuselage curvature and the canopy.
as opposed to the AW frame 
I masked off the fuselage around the canopy frame, applied 4 coats of Partall wax, and laid up the female mold of the new canopy frame (layer of 1/2oz, 3 layers of 4 oz, 1 layer of 10oz) which should be good enough for one or two uses.
It seems to me that this is way beyond what should be required of the builder especially for an $8000 kit.
Regards,
Jim
I really don't like the pipe the AW supplies with this kit. It is 28-1/8" long overall, with a 140mm diameter funnel, the OD is 4-1/2" and the ID is 4" which is too large a diameter for a 200N turbine (might be OK for a BF300 though). It is also far heavier than it needs to be.
One of the reasons I went with the Kingtech 210 (and sold my P-200SX) is that the 210 weighs about a pound less than the P-200SX. In the Gripen, the engine is mounted farther rearward than most planes so a heavy engine will require more components (and hopefully not lead) in the nose. A heavy pipe only makes matters worse.
With Dan's Kingtech K-210 turbine installed about as far forward as comfortable, I measured the distance between the aft end of the nozzle and the scale exhaust cone nozzle to be 27-11/16" and I called up Tam to order a pipe.
The Tam pipe will have an ID of 3-3/8", an OD of about 3-3/4", and an overall length (including the 3/4" bellmouth) of 27-3/16" to give a 1/2" gap between the nozzle and bellmouth per his recommendation. Tam knows pipes and neither he or one of his pipes has ever let me down so I'll install it per his numbers.
With that issue handled (thanks Tam - Merry Christmas) I returned to the fuselage and molding the canopy frame (see posts 979 for the issues with the AW frame). The balsa "plug" I built turned out pretty good and has the scale reinforcement along the side as well as the scale transition between the fuselage curvature and the canopy.
I masked off the fuselage around the canopy frame, applied 4 coats of Partall wax, and laid up the female mold of the new canopy frame (layer of 1/2oz, 3 layers of 4 oz, 1 layer of 10oz) which should be good enough for one or two uses.
It seems to me that this is way beyond what should be required of the builder especially for an $8000 kit.
Regards,
Jim
Last edited by rcjets_63; 12-23-2014 at 09:58 AM.
12-23-2014, 08:34 PM
#1010
The female canopy frame mold came out pretty good. It wasn't too hard popping it off the fuselage either. I trimmed it down a bit to clean up the edges and had to sand off a bit of resin flashing. Next was removing the balsa "plug". Then I applied 3 coats of Partall paste wax to the inside of the mold and the fuselage exterior followed by a coat of PVA mold release.
Photo 1 shows how it looks prior to doing the lay up for the frame. The female mold I made forms the sides of the canopy frame mold and the flanges around the cockpit form the mating flanges.
A mixture of resin and micro balloons was injected around the perimeter of the frame and then 4 layers of 4 oz cloth were added to form the new scale frame. See photo 2. Can't wait to pop it out of the mold tomorrow morning.
Regards,
Jim
Photo 1 shows how it looks prior to doing the lay up for the frame. The female mold I made forms the sides of the canopy frame mold and the flanges around the cockpit form the mating flanges.
A mixture of resin and micro balloons was injected around the perimeter of the frame and then 4 layers of 4 oz cloth were added to form the new scale frame. See photo 2. Can't wait to pop it out of the mold tomorrow morning.
Regards,
Jim
12-24-2014, 10:25 AM
#1011
The scale canopy frame came out fantastic! Here are some pics:
Photo 1: Frame laid up and still in the mold
Photo 2: Female outer mold removed revealing the frame and fuselage
Photo 3: Excess fiberglass cut/ground away from canopy opening and fuselage flanges
Photos 4 & 5: Canopy frame showing scale notches along right side
Photo 6: Canopy positioned in new frame. A bit of final trimming of the canopy itself and the opening in the frame is still needed but you get the idea.
Like the rear canopy, the windscreen (forward canopy) is also supposed to be glued over the white canopy bow. :-( As such, the white canopy bow will be cut away, and the female mold and canopy frame will be used to make a new canopy bow so that the windscreen can be glued to the interior of the bow and fuselage.
Regards,
Jim
Photo 1: Frame laid up and still in the mold
Photo 2: Female outer mold removed revealing the frame and fuselage
Photo 3: Excess fiberglass cut/ground away from canopy opening and fuselage flanges
Photos 4 & 5: Canopy frame showing scale notches along right side
Photo 6: Canopy positioned in new frame. A bit of final trimming of the canopy itself and the opening in the frame is still needed but you get the idea.
Like the rear canopy, the windscreen (forward canopy) is also supposed to be glued over the white canopy bow. :-( As such, the white canopy bow will be cut away, and the female mold and canopy frame will be used to make a new canopy bow so that the windscreen can be glued to the interior of the bow and fuselage.
Regards,
Jim
12-25-2014, 10:14 AM
#1014
Merry Christmas,
I had a bit of time yesterday afternoon and this morning between Christmas celebrations with the family so I was able to lay up the canopy bow and get it trimmed to size.
The clear canopy and windscreen needs some final trimming and I have a few air bubbles in the frame/bow to fill but I thought it came out pretty good and certainly much more scale than before the modifications.
I hope everyone has a great Christmas,
Jim
Photo 1: Canopy bow cut off and fuselage sanded to feather the transition between old/new fiberglass
Photos 2 & 3: Three layers of 4 oz cloth laid up against the fuselage mold and the rear canopy frame
Photo 4: Fuselage mold removed. Perfect fit between new canopy bow and canopy frame
Photo 5: Canopy frame and bow trimmed to size. Clear canopy and windscreen test-fitted.
I had a bit of time yesterday afternoon and this morning between Christmas celebrations with the family so I was able to lay up the canopy bow and get it trimmed to size.
The clear canopy and windscreen needs some final trimming and I have a few air bubbles in the frame/bow to fill but I thought it came out pretty good and certainly much more scale than before the modifications.
I hope everyone has a great Christmas,
Jim
Photo 1: Canopy bow cut off and fuselage sanded to feather the transition between old/new fiberglass
Photos 2 & 3: Three layers of 4 oz cloth laid up against the fuselage mold and the rear canopy frame
Photo 4: Fuselage mold removed. Perfect fit between new canopy bow and canopy frame
Photo 5: Canopy frame and bow trimmed to size. Clear canopy and windscreen test-fitted.
12-26-2014, 12:06 PM
#1016
I wanted to give a big shout out to B1-Bob, Henry Nguyen, and Dan Gill for all their suggestions and help with molding the canopy frame and bow. These guys are molding experts and their advice was a big part of getting good parts made.
The canopy saga continues but hopefully this is the last chapter. The full scale Gripen has a distinct curved flange that extends along the front of the canopy as seen in these pics:
The windscreen on the AW kit was intended to be glued to the exterior of the fuselage and this flange was kinda-sorta molded in but it really didn't look right. My windscreen will be glued to the inside surface of the fuselage, so having the flange will make the plane more scale but will also provide a larger surface to which the windscreen can be glued.
I simply wrapped the windscreen in a couple of layers of Saran Wrap, put two layers of 4oz cloth & resin around the front of the windscreen as a mold, and put the windscreen in place with magnets. When the resin dries, the canopy can be easily removed and the flange trimmed to shape.
Regards,
Jim
The canopy saga continues but hopefully this is the last chapter. The full scale Gripen has a distinct curved flange that extends along the front of the canopy as seen in these pics:
The windscreen on the AW kit was intended to be glued to the exterior of the fuselage and this flange was kinda-sorta molded in but it really didn't look right. My windscreen will be glued to the inside surface of the fuselage, so having the flange will make the plane more scale but will also provide a larger surface to which the windscreen can be glued.
I simply wrapped the windscreen in a couple of layers of Saran Wrap, put two layers of 4oz cloth & resin around the front of the windscreen as a mold, and put the windscreen in place with magnets. When the resin dries, the canopy can be easily removed and the flange trimmed to shape.
Regards,
Jim
12-26-2014, 08:03 PM
#1018
Hey Guys,
Thanks a lot for the words of encouragement, they really help me keep at this project which is quite the handful.
The windscreen fairing hardened and was trimmed to size and seems a close match for the full-scale once I do a bit of final shaping.
I was trying to figure out what to tackle next when the USPS man rang the doorbell and brought me this:
Wow Tam, I ordered the pipe Monday at about 11am and it was delivered Friday early afternoon. I would normally call that fast service but Christmas was in there too so I'd have to call it phenomenal service. Your next little green bottle is on me.
Regards,
Jim
Thanks a lot for the words of encouragement, they really help me keep at this project which is quite the handful.
The windscreen fairing hardened and was trimmed to size and seems a close match for the full-scale once I do a bit of final shaping.
I was trying to figure out what to tackle next when the USPS man rang the doorbell and brought me this:
Wow Tam, I ordered the pipe Monday at about 11am and it was delivered Friday early afternoon. I would normally call that fast service but Christmas was in there too so I'd have to call it phenomenal service. Your next little green bottle is on me.
Regards,
Jim
12-27-2014, 10:26 AM
#1019
Pipe & Exhaust Cone Mounting
Shipping this jet over to Germany is likely going to be a pricey endeavor so I wanted to make the fiberglass exhaust nozzle and the pipe easily removable as this would shorten the crate by about 6" and hopefully save some $$$.
To mount the pipe, I cut some L-shaped plywood pieces and glued them to the rear side of the aft former and the inboard side of the turbine mounting rails. A 1/2" gap was left between the aft end of the turbine nozzle and the front end of the pipe bellmouth. The pipe tabs are screwed to the plywood using two #4 screws which can be directly accessed from inside the engine hatch.
To mount the nozzle, I used the method of attaching the nose cone on the SM Cougar. I ground off the rear fiberglass flange and glued a plywood ring in its place. This was drilled and tapped for 6-32 SHCS. Four mating smaller plates with keyhole cutouts were glued around the inside of the nozzle. The nozzle is simply inserted over the SHCS and rotated a few degrees to engage the SHCS in the slots. A long ball driver can be used to tighten the SHCS, if desired, but a friction-fit is likely OK.
To support the aft end of the pipe, I cut a 5-1/2" diameter circle out of 1/8" Lite-Ply and glued it inside the nozzle about 1-5/8" from the aft end. The ply circle has an ID of 4" (the OD of the outer pipe) and 3/8" diameter holes were drilled every 15 degrees around the ID to allow air to flow around the pipe and out of the jet.
Regards,
Jim
Shipping this jet over to Germany is likely going to be a pricey endeavor so I wanted to make the fiberglass exhaust nozzle and the pipe easily removable as this would shorten the crate by about 6" and hopefully save some $$$.
To mount the pipe, I cut some L-shaped plywood pieces and glued them to the rear side of the aft former and the inboard side of the turbine mounting rails. A 1/2" gap was left between the aft end of the turbine nozzle and the front end of the pipe bellmouth. The pipe tabs are screwed to the plywood using two #4 screws which can be directly accessed from inside the engine hatch.
To mount the nozzle, I used the method of attaching the nose cone on the SM Cougar. I ground off the rear fiberglass flange and glued a plywood ring in its place. This was drilled and tapped for 6-32 SHCS. Four mating smaller plates with keyhole cutouts were glued around the inside of the nozzle. The nozzle is simply inserted over the SHCS and rotated a few degrees to engage the SHCS in the slots. A long ball driver can be used to tighten the SHCS, if desired, but a friction-fit is likely OK.
To support the aft end of the pipe, I cut a 5-1/2" diameter circle out of 1/8" Lite-Ply and glued it inside the nozzle about 1-5/8" from the aft end. The ply circle has an ID of 4" (the OD of the outer pipe) and 3/8" diameter holes were drilled every 15 degrees around the ID to allow air to flow around the pipe and out of the jet.
Regards,
Jim
12-28-2014, 02:16 PM
#1021
Nose Gear Side (Clamshell) Doors
Hinging of these doors on a Gripen can be problematic (especially the 1/7 scale versions on the gun side) due to the curvature but at least on this large kit there is a bit more room which gives you some options.
The doors on the full scale are actually externally hinged. Yep, the hinges hang out in the slipstream and they have little cones at each end for drag reduction.
The AW kit comes with a G-10 sheet that has been cut out with all kinds of fancy shapes. Some of these are probably for hinges using the slot/pin method used on the main gear doors. While that will work, it isn't scale, and I'm trying to do it right (or at least as right as possible). You can also use offset hinges, though you will have to cut away the inner liner of the doors and a bit of the wooden longeron that runs along either side of the wheel well.
I opted for the scale style external hinge method described herein. First thing I had to do was to shorten the clamshell doors by about 1-1/4" to make them the scale length. You might recall from an earlier post that I relocated the nose gear 1-1/4" aft to the scale location. I used Corel Draw and the full scale photo above to get the fore/aft location of the hinges and cut slots into the fuselage. Good old-fashioned Dubro hinges were used as this seemed to be the closest match to scale. A piece of 1/32" ply sandwiched between the longeron and the hinge aligned the hinge inboard/outboard in the slot, and a .048" diameter music wire laid along the exterior skin aligned the hinges up/down. The doors themselves were also slotted and then sanded at an angle so the hinge would contact the door flange and the door liner. CA was used to spot glue the hinges to the door then V-poxy was injected into the gap between the hinge and the door. Once it dried, the excess hinge was cut off.
I then made L-shaped pieces of music wire as hinge pins which were held in place with BVM screws into the longerons.
Next up will be filling the 1-1/4" gap between the forward door and the fuselage so the forward door can be mounted.
Regards,
Jim
P.S. I just noticed, I got the doors mixed up, the door with the aft vent hole is supposed to be on the right side, not the left side next to the gun. Crap. Oh well, gotta get out the filler. It's always something!
Hinging of these doors on a Gripen can be problematic (especially the 1/7 scale versions on the gun side) due to the curvature but at least on this large kit there is a bit more room which gives you some options.
The doors on the full scale are actually externally hinged. Yep, the hinges hang out in the slipstream and they have little cones at each end for drag reduction.
The AW kit comes with a G-10 sheet that has been cut out with all kinds of fancy shapes. Some of these are probably for hinges using the slot/pin method used on the main gear doors. While that will work, it isn't scale, and I'm trying to do it right (or at least as right as possible). You can also use offset hinges, though you will have to cut away the inner liner of the doors and a bit of the wooden longeron that runs along either side of the wheel well.
I opted for the scale style external hinge method described herein. First thing I had to do was to shorten the clamshell doors by about 1-1/4" to make them the scale length. You might recall from an earlier post that I relocated the nose gear 1-1/4" aft to the scale location. I used Corel Draw and the full scale photo above to get the fore/aft location of the hinges and cut slots into the fuselage. Good old-fashioned Dubro hinges were used as this seemed to be the closest match to scale. A piece of 1/32" ply sandwiched between the longeron and the hinge aligned the hinge inboard/outboard in the slot, and a .048" diameter music wire laid along the exterior skin aligned the hinges up/down. The doors themselves were also slotted and then sanded at an angle so the hinge would contact the door flange and the door liner. CA was used to spot glue the hinges to the door then V-poxy was injected into the gap between the hinge and the door. Once it dried, the excess hinge was cut off.
I then made L-shaped pieces of music wire as hinge pins which were held in place with BVM screws into the longerons.
Next up will be filling the 1-1/4" gap between the forward door and the fuselage so the forward door can be mounted.
Regards,
Jim
P.S. I just noticed, I got the doors mixed up, the door with the aft vent hole is supposed to be on the right side, not the left side next to the gun. Crap. Oh well, gotta get out the filler. It's always something!
Last edited by rcjets_63; 12-28-2014 at 02:24 PM.
12-29-2014, 02:04 AM
#1023
Thanks Sebastian, that's my new avatar.
Nose Gear Forward Door
First thing was to fill in the 1-1/4" gap between the kit nose door cutout and the correct location. The recess around the cutout was about 3/32" deep so I had spot glued a piece of 3/32" balsa under a thick balsa block, cut the block to shape, and used the fuselage skin and forward door as sanding guides to sand it to the right curvature. The 3/32" balsa strip was then removed, the block was wrapped with Saran Wrap and then spot glued in place where it sat pretty much flush with the recess around the door cutout. 2 layers 4oz, 3 layers of 10 oz, 2 layers of 4oz glass cloth/resin were laid up to fill in the hole (That is more glass than required for strength but the intent was to build up the new skin thickness to match the original skin, and the flange on the forward side of the door was also about 3/32" thick). A layer of yellow rip-stop nylon was added on top to act as a peel ply. A bit of light sanding was needed to blend the edges into the fuselage and the notch cut for the forward door.
I checked the full-size Gripen and found that it has two offset-style hinges used to mount the forward door.
Airpower offset hinges proved to be a very close match for the full-scale hinges with only some minor trimming and sanding required. I did have to cut away the door liner (it wasn't very scale anyway) and it will be replaced with 3/32" balsa with chamfered edges (as seen in the photo above) and glassed. I drilled the hinges out to receive a .078" music wire pin which was used to align the hinges when they were glued to the fuselage and door. The single pin was then replaced by two pieces of music wire bent into L-shaped pins for easy removal of the door. The final result is a pretty good match for the full scale.
Regards,
Jim
Nose Gear Forward Door
First thing was to fill in the 1-1/4" gap between the kit nose door cutout and the correct location. The recess around the cutout was about 3/32" deep so I had spot glued a piece of 3/32" balsa under a thick balsa block, cut the block to shape, and used the fuselage skin and forward door as sanding guides to sand it to the right curvature. The 3/32" balsa strip was then removed, the block was wrapped with Saran Wrap and then spot glued in place where it sat pretty much flush with the recess around the door cutout. 2 layers 4oz, 3 layers of 10 oz, 2 layers of 4oz glass cloth/resin were laid up to fill in the hole (That is more glass than required for strength but the intent was to build up the new skin thickness to match the original skin, and the flange on the forward side of the door was also about 3/32" thick). A layer of yellow rip-stop nylon was added on top to act as a peel ply. A bit of light sanding was needed to blend the edges into the fuselage and the notch cut for the forward door.
I checked the full-size Gripen and found that it has two offset-style hinges used to mount the forward door.
Airpower offset hinges proved to be a very close match for the full-scale hinges with only some minor trimming and sanding required. I did have to cut away the door liner (it wasn't very scale anyway) and it will be replaced with 3/32" balsa with chamfered edges (as seen in the photo above) and glassed. I drilled the hinges out to receive a .078" music wire pin which was used to align the hinges when they were glued to the fuselage and door. The single pin was then replaced by two pieces of music wire bent into L-shaped pins for easy removal of the door. The final result is a pretty good match for the full scale.
Regards,
Jim
12-30-2014, 03:28 PM
#1024
Fuel Tank Mounting
The fuel tank that Airworld supplies for the Gripen is made from two of their MiG-21 fuel tanks spliced together. It's kind of a funky shape, but it will work and has a capacity of 176oz. It costs 222 Euros ($270) plus shipping. Here are some pics of it from Airworld:
Since I'll be using a Kingtech 210, I wanted a larger fuel tank. Roy Maynard suggested a Jet Tech tank for the Mibo A-10 but it has a capacity of 170oz. I spoke with Gary at Jet Tech, and he was able to use his existing mold to make an extended version of the A-10 tank (1-1/2" longer) with a capacity of 193oz for $200 with free shipping! Not only that, I received the tank only 8 days after I placed the order.
The tank is 12-1/4" long, 7.9" wide, and 4.8" high. Gary sent me a scale drawing of the tank and I cut a blue foam copy of it to check the fit. It is a tight squeeze, but you can get in into the plane through the main gear door and it clears the retracted main tires by about 3/8". The tank was also customized to have a single clunk fitting (the standard A-10 tank has two) and Gary made the tank without a vent (per my request - I'm not sure where I would like the vent fitting) but included a straight and 90 degree fitting.
Mounting the tank was a bit of a head scratcher. With so little room between the tank and the tires, the mounts had to be pretty low profile. Airworld uses formers glued to the upper fuselage above the tank to cradle the tank and four mounting pads glued to the fuselage skin.
I didn't like this method because their tank is forward of the C.G., the wheel/tank clearance leaves no room for a cradle/former, and the fuselage skin would oil can or buckle (particularly under G-loads while flying) at the tank mounts. I wanted the tank to be centered on the C.G. (the Gripen already has problems rotating for take-off, why make it worse with the forward positioned tank), easily removable under contest conditions (Scott had a crimped line at the JWM in Switzerland which, fortunately, he was able to fix between rounds), and mounted securely to the airframe.
I made small 1/4" plywood formers which are glued to the upper fuselage next to the model's very stiff spine. The rear former has a 1/8" x 3/4" slot to receive aluminum angle Hysol'd to the rear of the tank. Two aluminum angles are Hysol'd to the front of the tank and are screwed down into pads on the front former. Strips of 1/16 balsa were temporarily spot glued to the upper fuselage to support the tank while it was being Hysol'd to the aluminum angles.
The all up weight of the mounts is 1-7/8 oz which is pretty good considering that they will support 1-1/2 gallons of fuel which weighs about 10-1/2 lbs static and 50-70 lbs during aerobatic G-loading.
Regards,
Jim
The fuel tank that Airworld supplies for the Gripen is made from two of their MiG-21 fuel tanks spliced together. It's kind of a funky shape, but it will work and has a capacity of 176oz. It costs 222 Euros ($270) plus shipping. Here are some pics of it from Airworld:
Since I'll be using a Kingtech 210, I wanted a larger fuel tank. Roy Maynard suggested a Jet Tech tank for the Mibo A-10 but it has a capacity of 170oz. I spoke with Gary at Jet Tech, and he was able to use his existing mold to make an extended version of the A-10 tank (1-1/2" longer) with a capacity of 193oz for $200 with free shipping! Not only that, I received the tank only 8 days after I placed the order.
The tank is 12-1/4" long, 7.9" wide, and 4.8" high. Gary sent me a scale drawing of the tank and I cut a blue foam copy of it to check the fit. It is a tight squeeze, but you can get in into the plane through the main gear door and it clears the retracted main tires by about 3/8". The tank was also customized to have a single clunk fitting (the standard A-10 tank has two) and Gary made the tank without a vent (per my request - I'm not sure where I would like the vent fitting) but included a straight and 90 degree fitting.
Mounting the tank was a bit of a head scratcher. With so little room between the tank and the tires, the mounts had to be pretty low profile. Airworld uses formers glued to the upper fuselage above the tank to cradle the tank and four mounting pads glued to the fuselage skin.
I didn't like this method because their tank is forward of the C.G., the wheel/tank clearance leaves no room for a cradle/former, and the fuselage skin would oil can or buckle (particularly under G-loads while flying) at the tank mounts. I wanted the tank to be centered on the C.G. (the Gripen already has problems rotating for take-off, why make it worse with the forward positioned tank), easily removable under contest conditions (Scott had a crimped line at the JWM in Switzerland which, fortunately, he was able to fix between rounds), and mounted securely to the airframe.
I made small 1/4" plywood formers which are glued to the upper fuselage next to the model's very stiff spine. The rear former has a 1/8" x 3/4" slot to receive aluminum angle Hysol'd to the rear of the tank. Two aluminum angles are Hysol'd to the front of the tank and are screwed down into pads on the front former. Strips of 1/16 balsa were temporarily spot glued to the upper fuselage to support the tank while it was being Hysol'd to the aluminum angles.
The all up weight of the mounts is 1-7/8 oz which is pretty good considering that they will support 1-1/2 gallons of fuel which weighs about 10-1/2 lbs static and 50-70 lbs during aerobatic G-loading.
Regards,
Jim
Last edited by rcjets_63; 12-30-2014 at 03:36 PM.