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JAS-39 Gripen Owners/Build Thread

Old 08-29-2008, 05:37 PM
  #1  
rcjets_63
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Default JAS-39 Gripen Owners/Build Thread

This thread is intended for use by JAS-39 Gripen owners and builders and potential owners and builders to share information, tips, questions, and experiences with models of this amazing 4th generation jet fighter aircraft. With some luck, we can use this as a primary reference to quickly find such info as recommended control throws (especially for the canards), suggested cockpit parts (since there is no specific cockpit kit), C.G range, recommended engines, engine mounting, instruction manual, and a variety of other info (some of which may have been previously posted in other threads but is hard to find).

I'm aware of three Gripen kits currently available. There is the 1/7th scale Skymaster ARF Plus Gripen (available in three paint schemes), the 1/7th scale Jetlegend Gripen (available in ARF or kit), and the Airworld 1/5th Gripen kit. Paul Gray also produced a Gripen kit but I believe the molds are currently owned by PJP.

I purchased a Skymaster Gripen (all white gelcoat scheme). SM also has the prototype paint scheme and a full camo scheme. Photos of the three SM Gripens are given below.

Regards,

Jim
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Old 08-29-2008, 06:18 PM
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Default RE: JAS-39 Gripen Owners/Build Thread

I bought the SM white gelcoat version since I wanted to do a sport paint scheme. I also purchased all the SM options including the air kit, gear door cylinders, fiberglass (not kevlar) fuel tanks, hardware kit, landing gear, brakes, and the tailpipe. My initial excitement upon receiving the kit was quickly damped when I discovered that the model had been damaged in transport. While the box was lined with wood panel reinforcing, the fuselage, right wing, canopy, and tailpipe had been damaged either by the parts shifting around during transport, or by customs inspectors, or some combination of the two. I took some photos of the damage and sent them off to SM to see what they wanted to do about the damaged kit.

My first impressions were that the plane fit together quite well. The main spar slid in place, the wing alignment pins engaged the fuselage with just a bit of encouragement, the fin slid into place, and there were minimum gaps between the fuselage/hatch and the nose/canopy. The gelcoat looked good (other than where the plane was damaged). The landing gear looked very solid. Overall, I was quite impressed with the plane.
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Old 08-30-2008, 12:16 AM
  #3  
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Default RE: JAS-39 Gripen Owners/Build Thread

hi rcjets_63
the sm gripen is very good plane for beginer, i have one and i love the gripen fly.
maybe i will go to airworld gripen,see this video for my gripen:
http://video.yahoo.com/watch/1394669/4809792
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Old 08-30-2008, 04:59 AM
  #4  
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Default RE: JAS-39 Gripen Owners/Build Thread

faisalx21, thanks for posting the video link. The flight looked great, particularly the first landing (nice and slow with minimum rollout). Just a tip for your camera man, next time turn off the autofocus (just set it at infinity and leave it there).

Landing Gear/Gear Doors

Although I'm doing a sport paint scheme, I wanted to add a few scale touches including the landing gear doors. The full scale Gripen has an inner and an out door for each main while the nose gear has a forward and twin rear doors. The kit comes with one piece gear doors and typically this is how they are installed (if at all). The doors are quite stiff since there is an inner and outer fiberglass layer. Fortunately, the main doors come with the cut line and pockets for the offset hinges already molded in. The gap between the skins is filled with epoxy & milled fibre. The outer gear door will be driven with an air cylinder while the inner door will have a linkage to the strut. The nose door is a bit more straightforward though I had to cut pockets for the hinges. I'll later whip up a linkage to drive the twin doors from a single air cylinder. The forward door will have a linkage to the strut.

I had a bit of a problem with the landing gear mounts in that when the wheels didn't retract deep enough into the fuselage to allow the doors to fully close. I compensated for this by cutting an [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXE952&P=7]Ernst thrust plate[/link] and mounting it under each side of the gear. The nose gear mounting rails needed to be notched slightly to provide clearance for the steering arms. The left nose door was a bit of a challenge due to the nearby groove for the gun port which didn't leave much room for the offset hinges. You can see the landing lights on the main gear struts and nose door; more about them later.

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Old 08-30-2008, 10:01 AM
  #5  
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Default RE: JAS-39 Gripen Owners/Build Thread

I have a JL Gripen and got a cockpit from Dante @ Camlex Ent.
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Old 08-31-2008, 08:34 PM
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

As requested, here is the instruction manual. For some reason, it is no longer posted on the Skymaster site.

The manual is in Word format and far exceeds the 200K max and RCU only supports JPG/GIF/TXT so I've divided it up into individual steps.

Page 1 - Step 1: install the 3 pcs fuel tanks.

Comments: The photo shows the "old" style plastic tanks. Current tanks became shorter/smaller when the main landing gear was relocated approximately 1-1/2" forward (which was done to help rotation during takeoff).

Page 2 - Illustration of fuel system

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Old 08-31-2008, 08:45 PM
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 3 - Step 2: Take out the front servos mount,

Page 3 - Step 3: Connect nose cone to fuselage by 6 screws

Page 3 - Step 4: Canards shafts and servo arm must be installed first (make sure that there is a minimal lateral movement)
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Old 08-31-2008, 08:57 PM
  #8  
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 4 - Step 5: Take out the Engine cover then setup the two screws for rudder fin. When you place the rudder fin in the fuselage, please make sure you use thread lock or a spring washer to set the screw in tightly. Also, make sure you check the screw regularly to ensure that the rudder does not come loose. Please keep in mind, if the rudder is even slightly loose, it could cause flutter and serious damage on the plane.

Page 4 - Step 6: Glue the 6 Hinges for the Wings

Comment: This step was applicable to the eariler version. The ARF+ version has the wingskin hinged.

Page 4 - Step 7: Install the two servos for the Elevons

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Old 08-31-2008, 09:02 PM
  #9  
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 5 - Step 7 continued from page 4: We suggest use of the Futaba # 9204. (#9151) or JR # 8425 (#8511 or 8611) servos for the elevons

Page 5 - Step 8: Glue the servo mounts for the elevon servos and cut the hole then glue for Rod Horns. Note: Please make sure the servo is secured to the mount. The servo mount base should have enough surface area to hold it. If you only glue the servo mount directly to the wing surface without additional support may cause the whole thing to rip off in extreme conditions. This will cause serious damage to your plane such as fluttering. We suggest you use a thin plywood or layer of fiberglass to increase the base surface space before you glue the servo mount.

Page 5 - Step 9: Connect both push-pull rods for Elevon servo control (the ARF Gripen kit includes 2 rods for Elevons).
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Old 08-31-2008, 09:12 PM
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 6 - Step 10: Install both with main Fuel Tank

Comment: The photo shows the third fuel tank installed between the cutout for the landing gear. This is the old style of tanks and has been changed. The new version features a smaller tank installed between the inlet ducts (and under the canard axle).

Page 6 - Step 11: Make the bulkheads holes to fasten the dual wall tail pipe.

Page 6 - Step 12: The tail flange has two brackets. Mark and drill holes in the brackets so they line-up with the holes in the right / left bulkheads holes.
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Old 08-31-2008, 09:16 PM
  #11  
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Default RE: JAS-39 Gripen Owners/Build Thread

Just some video's of Gripens I watched before I purchased. Was always looking for and install video but guess I'll have to do that now myself. ;-)
Thanks for your video faisalx21 is was one I hadn't seen before

Good video of a red and white sports version. http://www.youtube.com/watch?v=ibFUQz5oztk
This is a nice scale colour scheme with missiles and smoke, looks good. http://www.youtube.com/watch?v=jCK5rDkl4Ms
Video of a retracts up hard landing, listen for the noise as it hits, ouch. http://www.youtube.com/watch?v=NaRx25FuX6U
Video of a blue sport gripen like mine. Have to wait till the 5:28 mark to see it in a long video. http://www.youtube.com/watch?v=vfqKla5R49s
Another video with a smattering of a red gripen, take off, inflight and landing. http://rcuvideos.com/video/Jets-in-Chile
Just a takeoff of a blue sport. http://www.youtube.com/watch?v=RGl-0uErijg
On board video of rc gripen, if you ever wanted to know what it would be like. http://www.youtube.com/watch?v=G_sKgbKDChw
couple of video's from the skymaster site. http://www.jetsrc.com/videos/JetsRC_Aeropicnic2006.wmv
http://www.jetsrc.com/videos/Gripen02.wmv
http://www.jetsrc.com/videos/JAS39.wmv
Good video from hawaii of a red sports http://www.hawaiijets.com/aircraft/G...Tim-Gripen.wmv
and another of a blue with a p-70 http://www.hawaiijets.com/aircraft/G...n-p70title.wmv

Now all I have to do is get the video of mine off the camera and onto here.
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Old 08-31-2008, 09:17 PM
  #12  
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 7 - Step 13: Make the holes for install the Landing gear

Page 7 - Step 14: Install main gear with setup air pipes for air breaks for the main gear

Page 7 - Step 15: If you use the Jet Cat Engine you must add glued two (2) engine mounts
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Old 08-31-2008, 09:26 PM
  #13  
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 8 - Step 15 continued from page 7: Notice: Because the engine mounts are not placed in the usual position, the gravitation from landing and the turbine weight could cause a lot tension to the engine mount to detach. Please check the engine mounts regularly for properly maintain and prevent detaching that can cause great damage to the plane. In case there has been a heavy landing, checking at this time is absolutely necessary. The extra tension on the engine mount could increase the chances of damage to your plane. In the case that you find a loose engine mound, we recommend using tension epoxy such as Hysol to reinforce the mount.

Page 8 - Step 16: Make sure the engine is on the center line and adjust the engine position fore and aft as necessary

Page 8 - Step 17: Install the servos for the Canard (the ARF Gripen kit includes a rod for Canard)

Comment: Correction, the ARF Gripen kit includes a METAL CONTROL HORN for the canard

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Old 08-31-2008, 09:32 PM
  #14  
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 9 - Step 18: setup the front servo and make two piano wires control to the nose gear

Page 9 - Step 19: install the retracts control servo with break control servo, install two (2) valves for jet engine with the fuel pump
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Old 08-31-2008, 09:36 PM
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 10 - Step 20: Install two batteries into nose cone for CG balance

Page 10 - Step 21: Set-up elevator function for up / down movement for each to between 25 mm ~ 30 mm

Comment: The C.G. location, control throws, and canard set-up recommendations from Gripen owners will be discussed in later posts
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Old 08-31-2008, 09:43 PM
  #16  
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Default RE: JAS-39 Gripen Owners/Build Thread

Skymaster ARF Saab Jas-39 Gripen Instruction Manual

Page 11 - Step 22: Set-up ailerons function for up / down movement for each to between 8 mm ~ 10 mm

Page 11 - Step 23: Set-up Canards function for up / down movement for up ( 50 mm / down 35mm). A rudder is not used on this ARF Gripen, if you wish or need to use the rudder function, you need to do the following: the fins include all wood material needed for the optional rudder function, if you need to use rudder, you must cut the rudder yourself.

Comment: The C.G. location, control throws, and canard set-up recommendations from Gripen owners will be discussed in later posts

Page 12 - Tip: For those that are not familiar with the delta wing and the canard, we recommend setting up your radio with 2 or 3 flight mode. One for regular flight, one for landing, and another option for 3D flight maneuvers. Please refer to the set-up diagram in the manual for range of regular flight mode. For landing mode, we recommend reducing the canard range by 50% or more. For 3D flight maneuvers, you may want to set up another flight mode with the range of the card and aileron to its maximum.

End of Instruction Manual
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Old 08-31-2008, 10:24 PM
  #17  
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Default RE: JAS-39 Gripen Owners/Build Thread

Build - Removable Fin Modification

When gas prices started to rise, I traded in my SUV for something a bit smaller. While I suspect that I might be able to shoehorn the Gripen into the car, transporting my BVM Bandit was a lot easier thanks to the removable fin. The SM Gripen has a similar fin mounting structure so I decided to also make it's fin removeable. It's pretty simple:

- drill and tap two 6-32UNF holes in the right side of the fuselage (since the rudder servo/cutout is on the right) in line with the tubes that receive the carbon fibre rods. I drilled the holes about 3/8" below the fuselage fin joint.
- counterbore the holes using a Dremel to accomodate the head of a 6-32 cap screw
- grind a notch in the fin's carbon fibre tubes for the cap screw to engage.
- cut a couple of 6-32 cap screws to the right length so the heads are flush with the fuselage skin when the fin is installed and the screws are tight.




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Old 09-01-2008, 08:59 AM
  #18  
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Default RE: JAS-39 Gripen Owners/Build Thread

Good going, Jim. I've built two of these, one original SM (same as the Jet Legend one) and one SM ARF+. Some comments on the build instructions:

Step 1 - The ARF+ tanks hold only 72 oz. (I measured them) which is not enough if you are installing anything bigger than an 18# engine. I found a 15 oz. tank that fits under the duct bringing my capacity to 87 oz. My Falcon is a thirsty engine. I would like more since i'm limited to 6 minute flights. If anyone has found something larger that fits please let me know.

Steps 7 & 8 - Make sure that you do not mount your servos directly to the wing skin. I epoxied a couple of pieces of thin ply to the inner skin and made them long enough to tie them to the adjoining wing ribs. Also I used JR 8411's for elevons and canard, which work fine.

Step 15 - I made some small plywood supports for the rear of the engine mounts. This is a poor design and needs support from the bottom. See pictures, viewed from the bottom.

Step 16 - Install your engine as far forward as possible to minimize added nose weight for balance.

Steps 21 - 23 - The recommended canard throw is way too much. Here are the settings I'm using:

Canard: + 15mm/-10mm (measured at the front root point)
Elevator: +/- 22mm w/ 45% expo (measured at the root/inboard next to fuse root)
Aileron: +/- 11mm w/ 45% expo (measured same as above)
Rudder: +/- 25mm w/ 50% expo (measured at bottom)
CG: 145mm behind wing root front tip)

I have my canard on a three position switch for normal, half travel, or off. I use normal all the time except for landing, when I switch to half (about + 8/-5 mm.). I've also tried turning canards off for landing, but find that half throw works fine.

The above is a good place to start, then you can modify the settings to suit your flying style.

Joe


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Old 09-02-2008, 09:46 AM
  #19  
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Default RE: JAS-39 Gripen Owners/Build Thread

Here's a couple of pictures of my installation. The turbine is a Jet Central Falcon.

Joe
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Old 09-02-2008, 09:48 AM
  #20  
joeflyer
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Default RE: JAS-39 Gripen Owners/Build Thread

Here;s a few pictures of my Gripen in action. Since these were taken I've added gear doors and a smoke system.

Joe
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Old 09-03-2008, 01:09 AM
  #21  
rcjets_63
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Default RE: JAS-39 Gripen Owners/Build Thread

Build – Engine Bay

The bolting flanges on the Jetcat aluminum bracket are slightly above the engine centerline so it is necessary to install the two additional engine mount blocks per page 7 step 15 of the instructions. I’m using a Jetcat 120SE turbine so I also wanted to mount it as far forward as possible. The wooden mounting rail needs to be better supported at the aft bulkhead so I installed a couple of 1/8” ply supports back-to-back to engage the bulkhead, additional block, and mounting rail. The rails as installed in the kit extend rearwards from the aft bulkhead and can be cut off as needed.

The engine bay is thermally protected using a ceramic blanket RTV’d into place and sealed with aluminum tape to reflect any radiant heat. The rudder servo cable and tail strobe wire were routed under the blanket as high in the fin base as possible. I extended the metal tape forward to the back of the hatch cutout to seal off the fin base (and preventing any airflow from pealing off the tape in-flight) and to keep the wires in place.

A similar layup of blanket/tape was used on the engine hatch.
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Old 09-03-2008, 01:17 AM
  #22  
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Default RE: JAS-39 Gripen Owners/Build Thread

Build - Exhaust Duct

A couple of hardwood blocks are mounted on the back side of the rear bulkhead and allen head screws hold the “ears” of the exhaust duct in place at the front. A jig which engages the back of the turbine nozzle and the front of the bell-mouth (and keeps them spaced 1” apart) was very handy to get the alignment right.

Supporting the exhaust duct at the rear was a bit more problematic. The fiberglass nozzle as furnished has the rear duct support (“flower petal” type) already installed. However, it is too small since SM is now furnishing a 96mm diameter duct with this kit. The support can be ground away to make the pipe fit but I wanted to install an afterburner light ring and it all but blocked the spaces between the petals. At first, made a larger support and installed it a couple of inches forward in the nozzle. However, the exhaust duct isn’t centered in the nozzle at this point. I also noted that the nozzle (as supplied) points down about 5 degrees (very unscale-like). I sanded the front of the nozzle and shortened it slightly to get it to point straight back. The problem was eventually solved by using a series 1/16” ply strips glued fore/aft inside of the nozzle to support the duct. The afterburner light ring fits around the duct and is prevented from being blown rearwards by the ply strips. Metal tape on the inside of the nozzle also helps reflect the light for better visibility.

The tailpipe was cut to length with the outer pipe ending about 3/8” short of the fiberglass nozzle and the inner pipe ending about 3/8” short than the outer. This should keep the air moving between the pipes as well as keep the air flowing through the rear fuselage. The “zig-zag” spacer between the pipes was in the cutoff portion of the pipe and needed to be reinstalled. This was made a lot easier but cutting a few notches in the inner and outer ring around the spacer and flattening it slightly to get it to slide in place.
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Old 09-04-2008, 01:33 PM
  #23  
NickC5FE
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Default RE: JAS-39 Gripen Owners/Build Thread

Looks great Jim, I forgot I can check on my iphone. Nick
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Old 09-04-2008, 02:06 PM
  #24  
ianober
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Default RE: JAS-39 Gripen Owners/Build Thread

Be careful with those lights, they are very close to the cone and if left on too long they could heat up and melt it.
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Old 09-04-2008, 09:45 PM
  #25  
Spencer K
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Default RE: JAS-39 Gripen Owners/Build Thread

Ian, Todd and the entire jet community would have to disagree...

[link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1240]Afterburner Lights[/link]
read the description: "These rings do not generate ANY noticeable heat."
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