JAS-39 Gripen Owners/Build Thread
01-10-2015, 11:41 PM
#1051
Speed Brake Detail
The recessed area behind the speed brakes has the three "ribs" like the full scale, but that's about it. The ribs as well as the perimeter of the cutout have a draft angle in order to get the laid up fuselage out of the mold. The kit detail doesn't look bad, but it just isn't accurate enough, particularly for a competition model.
To fix this I had to grind away anything that didn't look like a Gripen. That was just about everything in the recess and some of the speedbrake itself so I used a coarse bit to save time. Once the periphery was cut away, I lined the cutout with .060" G-10 sub-formers/longerons. If you look closely at the full scale, you'll see the recess is deeper at the front than the back. The front sub-former is 1/2" from inside radius to outside radius while the aft former is 3/8". The longerons are tapered accordingly. Yes, Roy, I made you templates for everything.
Once the periphery was done, it was easy to glue a 0.010" G-10 sheet to the inside. Three cutouts were made in the upper and lower longerons for the three ribs. The ribs and the forward doubler sub-former were cut to shape and glued in place. A 5/32" wide strip of 0.010" G-10 was added as the outboard flange of the ribs and doubler.
All in all, it matches the full scale structure pretty closely. Later, I will add further details (the small brackets, rivets, tube, etc) but this will do for now.
Regards,
Jim
The recessed area behind the speed brakes has the three "ribs" like the full scale, but that's about it. The ribs as well as the perimeter of the cutout have a draft angle in order to get the laid up fuselage out of the mold. The kit detail doesn't look bad, but it just isn't accurate enough, particularly for a competition model.
To fix this I had to grind away anything that didn't look like a Gripen. That was just about everything in the recess and some of the speedbrake itself so I used a coarse bit to save time. Once the periphery was cut away, I lined the cutout with .060" G-10 sub-formers/longerons. If you look closely at the full scale, you'll see the recess is deeper at the front than the back. The front sub-former is 1/2" from inside radius to outside radius while the aft former is 3/8". The longerons are tapered accordingly. Yes, Roy, I made you templates for everything.
Once the periphery was done, it was easy to glue a 0.010" G-10 sheet to the inside. Three cutouts were made in the upper and lower longerons for the three ribs. The ribs and the forward doubler sub-former were cut to shape and glued in place. A 5/32" wide strip of 0.010" G-10 was added as the outboard flange of the ribs and doubler.
All in all, it matches the full scale structure pretty closely. Later, I will add further details (the small brackets, rivets, tube, etc) but this will do for now.
Regards,
Jim
Last edited by rcjets_63; 01-10-2015 at 11:58 PM.
01-11-2015, 10:13 PM
#1053
Drop Tanks
I've had a lot of fun with the drop tanks on my BVM Rafale and Reaction-Phantom and wanted to install drop tanks on the Gripen. Several people have asked me what mechanism and method I use. The way I did it on the Gripen is pretty typical so here it is, with lots of details/photos so this post is a bit long.
The first thing you will need is a pylon(s). The AW Gripen comes with pylons but, if you don't have any, they are really easy to make from 1/16" plywood sides with a carved balsa block at the front & back for the streamlined shape. I recommend installing a centerline belly pylon rather than wing pylons as dropping one tank is simpler and less risky than dropping two tanks and you don't have to worry about asymmetric drag if one tank fails to drop. Here's the homemade pylon I made for the Reaction-Phantom
The pylon has a strip of plywood at the top and bottom. The top strip has a couple of through holes for the 4-40 socket head cap screws that are used to mount it to the belly of the plane. The bolts are inserted through the oversized holes near the front & back of the pylon. The bottom strip of ply also has the cutout for the release system. I use the BVM EZ hanger to for droppable ordnance.
In the case of the Gripen, I fitted the inboard pylons with EZ hangers. The full scale pylons have a dual clamp/release mechanism to hold ordnance. I chose to install the EZ hanger at the rear position because it was closest to the CG of the tank. A 17mm wide (the internal width of the pylon) piece of 1/8" plywood was cut about 3/8" longer than the purple frame for the hanger. A couple of pieces of 1/16" ply were laminated at the mounting holes to give a bit more thickness locally and the holes were drilled/tapped for the 4-40 screws provided with the hanger, squirted with thin CA, and then re-tapped. The slot in the middle is for the pneumatic line to the cylinder.
The tough part is correctly positioning the plywood mount in the pylon and I have a little trick that makes it easy. The plywood plate needs to be 3/4" deep into the pylon (5/8" isn't enough, particularly if you have a round tank as the screw at the back of the hanger can interfere with you tank). I cut a 3/4" wide balsa strip and SPOT glue it to the plywood. The plywood/balsa assembly is inserted into the pylon and short pieces of thin plywood (popsicle sticks work great) are glued to the balsa. The assembly is then pushed down into the pylon such and the popsicle sticks keep the plywood the right depth and parallel to the bottom of the pylon. A bit of the balsa can be carved away, if necessary for access, and the plywood is spot glued to the pylon using CA. The balsa/popsicle sticks are then snapped off than the plywood and the plywood is then glued fully along both sides to the pylon.
Next, a slot needs to be made in the side of the pylon for the manual release. I typically put it on the inboard side so it is hidden. The EZ hanger is temporarily placed in position with the 4-40 screw for the wheel collar sticking out through the slot in the base of the pylon. Move the cylinder by hand and mark the range of travel of the 4-40 bolt. Transfer these marks to the side of the pylon. The centerline of the slot is 3/8" above the base of the pylon.
Next, jam a piece of 1/4" ply into the EZ Hanger to keep the cylinder rod all the way back. Remove the 4-40 screw from the wheel collar, and insert it through the slot in the side of the pylon and back into the wheel collar. Tighten the screw to lock the wheel collar on the cylinder rod so there is about 1/16" gap between the collar and the cylinder to give the correct movement of the rod.
Next is mounting the tank. This will vary from tank to tank, but you want the eye screw to be at or slightly aft of the C.G. of the tank. Some tanks have internal wood structure already installed and it's a simple matter to drill a hole and install the eye screw. In my experience, most tanks don't have the structure in the right place and you have to add something. In the case of the Gripen, I drilled a 1/16" hole in the top of the tank, and found nothing there behind the fiberglass. I then drilled a slightly oversized 5/8" hole (for a wood dowel) and was pleasantly surprised to find that the tank had a nearby wooden structure. All that was required was adding a piece of 1/8" ply to the side of the wood structure to bring the edge even with the 5/8" hole. A 1-1/2" long piece of dowel was prepped by sanding a slight flat spot and a some short holes (to give more contact area for the glue). I installed the small eye screw (that comes with the BVM hanger) near the edge of the dowel. The eye screw acts as a handle to hold the dowel when gluing it in place. The dowel can then be drilled for the big eye screw.
Although the tank can now be attached to the pylon, a second support is required to keep the tank pointed forward. Basically, you need to add a pin or plywood tab elsewhere on the top center of the tank to engage feature on the pylon. The Rafale tank had 1/2" wide piece of 1/8" ply glued near the back of the tank. The ply tab fit into a slot in the bottom of the pylon. The Reaction/Phantom tank had a small vertical fin near the rear of the tank. The two little tabs at the aft end of the pylon (as seen in the first photo of this post) capture the fin and keep the tank straight. The method you use is up to you; just make sure that there is a bit of play so that it doesn't bind. You want your tank to release cleanly.
Continued on next post.....
I've had a lot of fun with the drop tanks on my BVM Rafale and Reaction-Phantom and wanted to install drop tanks on the Gripen. Several people have asked me what mechanism and method I use. The way I did it on the Gripen is pretty typical so here it is, with lots of details/photos so this post is a bit long.
The first thing you will need is a pylon(s). The AW Gripen comes with pylons but, if you don't have any, they are really easy to make from 1/16" plywood sides with a carved balsa block at the front & back for the streamlined shape. I recommend installing a centerline belly pylon rather than wing pylons as dropping one tank is simpler and less risky than dropping two tanks and you don't have to worry about asymmetric drag if one tank fails to drop. Here's the homemade pylon I made for the Reaction-Phantom
The pylon has a strip of plywood at the top and bottom. The top strip has a couple of through holes for the 4-40 socket head cap screws that are used to mount it to the belly of the plane. The bolts are inserted through the oversized holes near the front & back of the pylon. The bottom strip of ply also has the cutout for the release system. I use the BVM EZ hanger to for droppable ordnance.
In the case of the Gripen, I fitted the inboard pylons with EZ hangers. The full scale pylons have a dual clamp/release mechanism to hold ordnance. I chose to install the EZ hanger at the rear position because it was closest to the CG of the tank. A 17mm wide (the internal width of the pylon) piece of 1/8" plywood was cut about 3/8" longer than the purple frame for the hanger. A couple of pieces of 1/16" ply were laminated at the mounting holes to give a bit more thickness locally and the holes were drilled/tapped for the 4-40 screws provided with the hanger, squirted with thin CA, and then re-tapped. The slot in the middle is for the pneumatic line to the cylinder.
The tough part is correctly positioning the plywood mount in the pylon and I have a little trick that makes it easy. The plywood plate needs to be 3/4" deep into the pylon (5/8" isn't enough, particularly if you have a round tank as the screw at the back of the hanger can interfere with you tank). I cut a 3/4" wide balsa strip and SPOT glue it to the plywood. The plywood/balsa assembly is inserted into the pylon and short pieces of thin plywood (popsicle sticks work great) are glued to the balsa. The assembly is then pushed down into the pylon such and the popsicle sticks keep the plywood the right depth and parallel to the bottom of the pylon. A bit of the balsa can be carved away, if necessary for access, and the plywood is spot glued to the pylon using CA. The balsa/popsicle sticks are then snapped off than the plywood and the plywood is then glued fully along both sides to the pylon.
Next, a slot needs to be made in the side of the pylon for the manual release. I typically put it on the inboard side so it is hidden. The EZ hanger is temporarily placed in position with the 4-40 screw for the wheel collar sticking out through the slot in the base of the pylon. Move the cylinder by hand and mark the range of travel of the 4-40 bolt. Transfer these marks to the side of the pylon. The centerline of the slot is 3/8" above the base of the pylon.
Next, jam a piece of 1/4" ply into the EZ Hanger to keep the cylinder rod all the way back. Remove the 4-40 screw from the wheel collar, and insert it through the slot in the side of the pylon and back into the wheel collar. Tighten the screw to lock the wheel collar on the cylinder rod so there is about 1/16" gap between the collar and the cylinder to give the correct movement of the rod.
Next is mounting the tank. This will vary from tank to tank, but you want the eye screw to be at or slightly aft of the C.G. of the tank. Some tanks have internal wood structure already installed and it's a simple matter to drill a hole and install the eye screw. In my experience, most tanks don't have the structure in the right place and you have to add something. In the case of the Gripen, I drilled a 1/16" hole in the top of the tank, and found nothing there behind the fiberglass. I then drilled a slightly oversized 5/8" hole (for a wood dowel) and was pleasantly surprised to find that the tank had a nearby wooden structure. All that was required was adding a piece of 1/8" ply to the side of the wood structure to bring the edge even with the 5/8" hole. A 1-1/2" long piece of dowel was prepped by sanding a slight flat spot and a some short holes (to give more contact area for the glue). I installed the small eye screw (that comes with the BVM hanger) near the edge of the dowel. The eye screw acts as a handle to hold the dowel when gluing it in place. The dowel can then be drilled for the big eye screw.
Although the tank can now be attached to the pylon, a second support is required to keep the tank pointed forward. Basically, you need to add a pin or plywood tab elsewhere on the top center of the tank to engage feature on the pylon. The Rafale tank had 1/2" wide piece of 1/8" ply glued near the back of the tank. The ply tab fit into a slot in the bottom of the pylon. The Reaction/Phantom tank had a small vertical fin near the rear of the tank. The two little tabs at the aft end of the pylon (as seen in the first photo of this post) capture the fin and keep the tank straight. The method you use is up to you; just make sure that there is a bit of play so that it doesn't bind. You want your tank to release cleanly.
Continued on next post.....
Last edited by rcjets_63; 03-02-2015 at 02:27 PM.
01-11-2015, 10:32 PM
#1054
Drop Tanks - Continued
For the Gripen, I wanted to install an anti-rotation feature that wouldn't screw up the scale look of the pylon or the tank. The painted tanks will likely weigh about a pound each and will put me over the 20Kg (44 lb dry) weight limit of the Jet World Masters so I will likely not have the tanks installed during static judging of the underside. A non-scale hole or slot in the bottom of the pylon didn't sound very good, so I checked a high resolution bottom view photo of the full scale to see if there were any possibilities......BINGO!
The front release mechanism has a circular feature that would suggest using the pin method. I simply installed some old BVM hatch pins I have from back in the ducted fan days. The pin was glued into the tank per the method used for the dowel.
With the structural part done, I fitted the tanks to the pylons, and took the bird outside for some overall pictures. I think the drop tanks really add to the overall look of the plane.
The pneumatic control for the tanks is very simple. I use the BVM button valve installed next to my brake servo. A mix is used to make the servo rotate backwards just a bit to bump the button valve when I press a push-button on my Jeti DC-16 radio. Here's a pic of the setup in the Reaction-Phantom.
Regards,
Jim
For the Gripen, I wanted to install an anti-rotation feature that wouldn't screw up the scale look of the pylon or the tank. The painted tanks will likely weigh about a pound each and will put me over the 20Kg (44 lb dry) weight limit of the Jet World Masters so I will likely not have the tanks installed during static judging of the underside. A non-scale hole or slot in the bottom of the pylon didn't sound very good, so I checked a high resolution bottom view photo of the full scale to see if there were any possibilities......BINGO!
The front release mechanism has a circular feature that would suggest using the pin method. I simply installed some old BVM hatch pins I have from back in the ducted fan days. The pin was glued into the tank per the method used for the dowel.
With the structural part done, I fitted the tanks to the pylons, and took the bird outside for some overall pictures. I think the drop tanks really add to the overall look of the plane.
The pneumatic control for the tanks is very simple. I use the BVM button valve installed next to my brake servo. A mix is used to make the servo rotate backwards just a bit to bump the button valve when I press a push-button on my Jeti DC-16 radio. Here's a pic of the setup in the Reaction-Phantom.
Regards,
Jim
Last edited by rcjets_63; 03-02-2015 at 02:30 PM.
01-12-2015, 09:03 AM
#1057
LOL, I'm afraid not. That AW Gripen was built by Radek Suk (www.jety.cz) of the Czech Republic.. Obviously he has some friends at 211 Squadron at Caslav Airbase where Czech Gripens are based. I heard that he sold the model and it is now decorating some airport lobby.
Regards,
Jim
Regards,
Jim
01-13-2015, 08:58 AM
#1058
A bit of progress in multiple areas. I have the size of the graphics files to within less than 1%. Now I just need to tune the printer settings so that the white areas match a bit better to the full scale.
I had the pitot tubes made and picked them up last night. They really add some zing to the model. Now I just need to trim/sand the adjoining fiberglass so they blend in perfectly.
Regards,
Jim
I had the pitot tubes made and picked them up last night. They really add some zing to the model. Now I just need to trim/sand the adjoining fiberglass so they blend in perfectly.
Regards,
Jim
01-13-2015, 10:32 PM
#1063
So today I did the gear doors with the piano hinge just like Jim he is my big inspiration to finishe my gripen .so after the nose gear doors I'm waiting for new retracts going to use regular robart 635 with long main struts non rotating and the same for the front ,the canard it's fixed and painted for now I'm going to kept this colors on the jet maybe adding some digital camo in the white spots only ,there so more sending and bondo work to the model and it's cold so long waiting before sanding and painting .
01-15-2015, 10:05 PM
#1070
So today I finly finished the nose body work ,it's not perfect but I'm ok with ,so I did black window seal did some black and gray painting the canopy polishing with head light polish kit some decals and flat clear cote I hope this looks ok and matching the rest oh a jet and I did little weathering to show the panel lines and rivets.
01-18-2015, 08:44 PM
#1074
Ok some more work on the gripen new fuel lines ,removing the old retracts and planning for the new struts length with wooden 1/2" stick cuting off more of the main gear doors and adding the section to make one bigger ,I might actually make new nose gear doors to match the scale length ,
The last picture show the old and new fuel pickup line.
01-18-2015, 08:45 PM
#1075
Ok some more work on the gripen new fuel lines ,removing the old retracts and planning for the new struts length with wooden 1/2" stick cuting off more of the main gear doors and adding the section to make one bigger ,I might actually make new nose gear doors to match the scale length ,The last picture show the old and new fuel pickup line.