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JAS-39 Gripen Owners/Build Thread

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JAS-39 Gripen Owners/Build Thread

Old 09-22-2008, 02:58 AM
  #51  
rcjets_63
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Default RE: JAS-39 Gripen Owners/Build Thread

All "tarted" up with Monokote trim sheets in preparation for the maiden flight. Have a few details and checks to wrap up this week but she'll be ready to go this coming weekend. Can't wait!

The CamLex cockpit is delayed a bit so I installed a sport scale cockpit using a B-ARF tub and dash sticker.

Regards,

Jim
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Old 09-24-2008, 09:46 AM
  #52  
Ray Davis
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Default RE: JAS-39 Gripen Owners/Build Thread

I've the only SM ARF-Plus Gripen w/ bad hinges?!

Ray
Old 09-24-2008, 10:23 AM
  #53  
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Default RE: JAS-39 Gripen Owners/Build Thread

Ray,

After seeing your post, I immediately checked out my hinges and they look fine. Mind you, the elevon hinges hadn't received much flexing (yet) but the rudder has seen a bit of action from taxi tests. I will continue to keep a very close eye on them. Sorry to hear that you had a problem. Nice of SM to offer to replace the wings.

Regards,

Jim
Old 09-25-2008, 01:16 AM
  #54  
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Default RE: JAS-39 Gripen Owners/Build Thread

Build – Electrical Power System

This was probably the most challenging part of the build (at least for me). When I was building my last jet, NiMH batteries had just arrived on the scene. A lot has changed in the past ten years or so (what’s a LiPo, what’s an A123, what’s a Powerbox, etc) and I want to thank Wayne, Spencer, & Todd for bringing me up to speed.

I went with [link=http://duralitebatteries.com/flight/batteries-mg.php]Duralite Lithium-Manganese[/link] packs because 1) they don’t catch on fire when you charge them, 2) Duralite’s product line included everything needed besides the batteries (chargers, regulators, switches, load testers), and 3) I watched Ron pull out a Duralite equipped BVM Bandit that he had charged and flown about a month earlier and the battery ignited the kero-start immediately. Ron gets about a half dozen flights on a charge and it’s hard to argue with success. So here’s the way it all fits together (refer to the wiring diagram below)

A 3800mah pack feeds the Rx. Another 3800mah pack drives the ECU and smoke pump. A 1500mah pack runs the lights and AB ring. With LiMn, you need a voltage regulator and a PowerBox or SmartFly seemed to be overkill for the Gripen so I went with the [link=http://duralitebatteries.com/flight/accessories4.php]High Current Voltage Regulator with Heavy Duty Switch, 7.5 amp w/16ga wire, deans connectors (6V)[/link] which includes a Y-harness that splits from a Deans connector to dual JR connectors each plugging into a port on the Rx. Since I’ve installed digital servos, I was concerned about voltage drop to the Rx if attempting to pull more than 3A through a JR connector so the dual connectors are a simple solution to the problem. The Jetcat ECU is internally switched and is connected directly to the ECU pack. Tamjets suggests tapping power for their smoke system off the ECU battery so I made a little adaptor using an old switch harness. The light system is split as the position/strobe/landing lights need regulated power, but the AB ring works better with full power (per Todd/Dreamworks recommendation). I modified a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=105_107&products_id=679]JR Heavy Duty Deluxe Switch Harness[/link] to produce a switched Y-harness. For the lights, a non-switched [link=http://duralitebatteries.com/flight/accessories4.php]Voltage Regulator, 7.5 amp w/standard 22ga wire[/link] is shown in the diagram but I used a switched regulator because that’s what got shipped in error.

With the JetCat P120SE in the back of the plane, I wanted to put the batteries as far forward as practical. I made little lite ply holders for each battery that are glued into the nose just forward of the hatch. The batteries are held in place with velcro straps and the regulators are strapped to the batteries.
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Old 09-25-2008, 01:39 AM
  #55  
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Default RE: JAS-39 Gripen Owners/Build Thread

Build - Front Equipment Bay

Once again, there are about a million different possible combinations and we all have our favorite equipment. I used an UltraPrecision [link=http://www.up-1.com/uptwo.html]UP-2 valve[/link] for the retracts/doors and a [link=http://www.up-1.com/upsix.html]UP-6 valve[/link] for the proportional brakes since I had them already and they’d always worked superbly. I added a [link=http://www.tamjets.com/gearfailsafe.php]Tamjets Gear Failsafe[/link] for the retracts just in case (besides, it’s cool and has a blinking light and pushbutton). A couple of [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=46_173&products_id=602]Robart Fill Valves[/link] and an [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=46_173&products_id=990]Air Gauge Set[/link] round out the bay and are connected to twin tanks in the nose. The components are mounted on a [link=http://www.dreamworksrc.com/catalog/product_info.php?products_id=67]Carbon Fiber Simulated ABS[/link] sheet (cuz it looks sharp) which extends about 2” forward from the rearward nose gear former. The light and AB modules are velro'd to the fuselage sides.

I felt there was too much flex in both the SM lite ply component tray and in the ABS tray to safely mount the canard servo so I installed a couple of 3/8” hardwood rails running across the fuselage to serve as the servo mounts. I also ran a couple of ¼” rails along each side of the fuselage to better support the ABS tray. Note: Don’t raise the component tray above the “stock” level or put thick components at the front of the tray to avoid interfering with the bottom of the cockpit tub.

Servos
I went with Joeflyer’s recommendation (once again, hard to argue with success) of a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=126_127_131&products_id=475]DS168 Thin Wing Servo[/link] for the rudder, [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=126_127_131&products_id=368]DS8411[/link] servos for the elevons but upgraded to a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=126_127_131&products_id=1093]DS8711[/link] for the canards since I plan to mix in full down canard for aerodynamic braking and wanted to make sure the servo was up to the task. The nose wheel steering uses a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=126_127_131&products_id=1126]JR 4131[/link] servo, and a pair of [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=126_127_131&products_id=535]JR 331[/link] servos drive the retract and brake valves.
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Old 09-25-2008, 01:40 AM
  #56  
quist
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Default RE: JAS-39 Gripen Owners/Build Thread

Jim,
Make sure that you unplug your batteries when the plane is in storage. The failsafe switch draws power when shut off.

Are you going to maiden the plane on Saturday?
Old 09-25-2008, 01:46 AM
  #57  
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Default RE: JAS-39 Gripen Owners/Build Thread

Tony,

Thanks for the tip; I didn't know that. Fortunately, the Deans connector between the Rx pack and the Regulator is very accessible. (I'd rather be lucky than smart). As for the maiden, this weekend is definitely the plan though I don't know if it will be Sat or Sun.

Regards,

Jim
Old 09-25-2008, 02:14 AM
  #58  
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Default RE: JAS-39 Gripen Owners/Build Thread

Build - Lights

Both an [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1240]Afterburner Light Ring[/link] and position/strobe/landing lights are installed. The AB light ring installation was handled in Post #22 so I'll focus on the remaining lights in this post. The Gripen features red and green position lights on the inlet sides, a strobe light on the tail, landing lights on each main landing gear strut, and another landing light on the forward nose wheel door. Initially I chose the [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1370]Beacon EVO 5[/link] light module. It has five separate output pairs (the MLG lights are fed off the same contacts) and a single internal electronic switch (activated by the the Rx). A switch tripped by the nose strut was used to turn the landing lights off when the gear was up. However, the EVO 5 didn’t seem up to the demands I was placing upon it and appeared to be overheating. As such, I upgraded to the [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1144]Multilight Mini Module[/link] (eight separate outputs and two electronic switches) and the nose strut switch was eliminated.

The position lights are [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1153]25mm x 10mm Drop Style[/link] lights and a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1167]11mm Luxeon Headlight[/link] is installed in the nose gear door. These products are pre-built and include heat sinks which are required since the lights are on for an extended period. They were Hysol’d in place through holes cut in the fuselage and gear door. The strobe light doesn’t require a heat sink and is simply a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1150]1W white Luxeon Emittor[/link] soldered to the wire leads running through the fin/fuselage. A Deans Micro Plug connector installed in the leads allows the fin to be removed for transport. Note: when soldering the emitter to the leads, make sure you correctly identify and connect the anode and cathode (which have a subtle difference in their pins). If you get it backwards, the light won't come on but neither the emitter or module appear to get damaged by the error.

The MLG lights were the most difficult since there wasn’t a pre-built product that seemed to fit. Each light is a 1 W white Luxeon emitter attached to a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1157]Tube Cooler[/link] (heat sink) using [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=51&products_id=1158]Thermally Conductive Adhesive[/link]. A pair of holes was drilled in the tube cooler and 4-40 button head screws mount the tube cooler to a [link=http://www.dreamworksrc.com/catalog/product_info.php?cPath=41_136&products_id=1357]9/16" Door Collar[/link] which was reamed out to fit the 15mm gear strut. The cone shaped reflector used in the nose gear headlight really focuses the light well but unfortunately is not available separately. I’ll have to make something similar from scratch (maybe from a toothpaste cap) one day. In the mean time, the lights really spice up the plane and I got a few oohs and ahhs from the guys when I brought the Gripen out to the field to get a few programming tips from a JR rep.

Regards,

Jim
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Old 09-25-2008, 09:54 PM
  #59  
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Default RE: JAS-39 Gripen Owners/Build Thread

Build - Balancing/C.G.

The SM manual shows to balance the model between a range of 110mm (trainer) to 140mm (normal) aft of the wing leading edge at the root. The concensus seems to be to use the aft end of this range and Joeflyer has moved his C.G. back to 145mm and reported in other threads that his Gripen flies well and doesn't tuck in the turns.

I made a balancing jig made from 1/8" lite ply that engages the front wing pin and the carbon spar. Simply sandwich the two jigs between the fuselage and each wing and hang the model from the ceiling (or garage door opener brackets) with light rope & hooks through the balancing holes (drilled at 110 thru 140mm). It took 3 oz of lead just forward of the nozzle to balance at 140mm (gear down, UAT full, tanks empty, smoke pump/tanks removed). This method was quite sensitive and adding/subtracting a 1/2 oz of lead had the model hang noticeably off-level.

Regards,

Jim
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Old 09-26-2008, 07:13 AM
  #60  
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Default RE: JAS-39 Gripen Owners/Build Thread

Good luck with the maiden Big Jim!! She looks great. Nick
Old 09-27-2008, 09:50 PM
  #61  
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Default RE: JAS-39 Gripen Owners/Build Thread

Well the Gripen had it's maiden flight today so I'm very pleased.

Highlights:
1) Flew straight as an arrow. Total trimming required was 1 click of down. Didn't tuck in the turns at all.
2) Awesome power in the Jetcat P120. Most of the flight was 1/2 throttle. A couple of 3/4 throttle passes looked at the 200mph mark according to the onlookers.
3) Very responsive and fun to fly.

Lowlights:
1) Incredibly sensitive in roll (even at +/-11mm throw and 45% expo). Fed in some aileron after takeoff to turn slightly away and went knife edge at about 6 feet of altitude. That was a real "Pampers" moment!
2) Forgot to turn off the canards for landing to reduce pitch sensitivity. Did a medium intensity bounce landing.
3) Snapped the nose gear strut pin on the bounce. The pin was a total POS; it snapped clean in two and the fracture section shows it to be case-hardened to a depth of about 1/64" rather than completely through. Will replace with a pin made from a 6mm hardened steel cap screw.

Will download some photos and video ASAP - having some tech problems with the new camera. Many thanks to Big Balls Ron for spotting.

Regards,

Jim
Old 09-28-2008, 08:23 AM
  #62  
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Default RE: JAS-39 Gripen Owners/Build Thread

Jim,

Congratulations on your maiden. Glad it went well.

Joe
Old 09-28-2008, 08:44 AM
  #63  
RonLongAZ
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Default RE: JAS-39 Gripen Owners/Build Thread

Any time Jim, Now lets go out anf land her without the bounce. Remember FLAIR!!!!!!!!!!!!!!!!




Ron
Old 09-28-2008, 10:02 AM
  #64  
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Default RE: JAS-39 Gripen Owners/Build Thread

The Gripen slows right down when you pull the nose up. Just get the nose up on your approach and bring it in under power. It will do a nice carrier type landing. This is the best way to land if you have a short runway. If you're not use to landing this way you should practice a few slow nose up fly-bys at a safe altitude.

If you have plenty of runway you can come in faster then gradually pull the nose up. The landings do take a little bit of practice to get right. If you're use to flying a delta wing then it will come easier.

Joe
Old 09-28-2008, 03:13 PM
  #65  
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Default RE: JAS-39 Gripen Owners/Build Thread

CONGRATS! now that the maiden is done.. lets see some paint!!
Old 09-29-2008, 05:11 AM
  #66  
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Default RE: JAS-39 Gripen Owners/Build Thread

Here are some photos of the maiden. The resolution isn't the greatest, but that's life. Unclejoe, where were you when I needed you??????

Regards,

Jim
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Old 09-29-2008, 01:58 PM
  #67  
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Default RE: JAS-39 Gripen Owners/Build Thread

thanks to all info posted it all been great help. i'm a new owner of a nice sm gripen w/amt. i have a dumb question on the canards with elevator up in which direction should the canard go? i have two jet owner arguing over the direction in which they should go. please help.
Old 09-29-2008, 02:23 PM
  #68  
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Default RE: JAS-39 Gripen Owners/Build Thread

trocks,

I'm glad the info has been a help to you and best of luck with your Gripen.

To answer your question, the canards move in an opposite direction as the elevons. When the elevons go up, the front of the canards go up and the rear of the canards go down. This is because the canards are ahead of the C.G. and act like little wings. To pitch up, canards increase their angle of attack, giving more lift, and helping to raise the nose.

Which amt engine are you using and what is your color scheme? Feel free to post any photos of your build.

Incidentally, do not forget to turn off the canards for landing. It is too pitch sensitive (even with the revised throws posted earlier) even at half canard for landing.

Regards,

Jim
Old 10-06-2008, 10:54 PM
  #69  
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Default RE: JAS-39 Gripen Owners/Build Thread

I finished the video of the test and maiden flights. Here's a link if you'd like to see it.

[link=http://www.youtube.com/watch?v=y_tXVrL9H4I]http://www.youtube.com/watch?v=y_tXVrL9H4I[/link]

The video quality on the maiden isn't the greatest, but stay with it as it gets better with some high resolution footage from a subsequent flight.

The test flights are going well and I'm getting the bugs worked out. With the narrow gear, the model will wobble and whack a wingtip if you get on the NWS or brakes too much. There is too much travel in the main struts so I'll add some 3000 weight transmission oil to take out about half of the travel. Also, the lower clamp for the oleo link can rotate on the strut and needs to be pinned in place (eg. set screw with a flat on the strut shaft).

Burnt off 6-7 gallons of kero this weekend and had a great time. I need to find the right power setting for those nose high approaches per joeflyer. Something to practice (as well as remembering to turn off the $%^&*@ canards for landing).

Thanks to all who helped me get this bird built and in the air. It is one awesome "ride".

Regards,

Jim
Old 10-07-2008, 05:27 AM
  #70  
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Default RE: JAS-39 Gripen Owners/Build Thread

Hello guys,

A buddy of mine is flying a JetLegend JAS-39 Gripen.

On the gripen, the canards come with a built in angle into their shaft that holds them. this means they could be installed in either an anhedral or dihedral angle.

Anyway, since there was no manual with the model - he installed them in an anhedral position and this is how it was flying until now. Note: model flys fine, but it does have a slight instability on the roll axis, which we contributed to the rather short wing span.

He found lately that the original full scale gripen uses dihedral angle in the canards, and changed his over as well.

My question is - what kind of change in flight characteristics could we anticipate when going from anhedral to dihedral on the canards ?

thanks.
Old 10-07-2008, 06:05 PM
  #71  
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Default RE: JAS-39 Gripen Owners/Build Thread

The Gripen does tend to rock back and forth a bit in roll (just like the F-16 "hunts" in yaw). I would doubt that you will notice any difference with the flipped canards though. If I recall all those subsonic aerodynamics courses accurately, in theory you should get slightly better high AOA performance with them corrected.

Regards,

Jim
Old 10-08-2008, 01:32 PM
  #72  
NickC5FE
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Default RE: JAS-39 Gripen Owners/Build Thread

Dude, Jim....i just checked the vid! Nice man, looks like it has a shiznit ton of vertical.......Glad she is treating you good. Nice video. Nick
Old 10-13-2008, 02:45 AM
  #73  
rcjets_63
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Default RE: JAS-39 Gripen Owners/Build Thread

Hey Nick,

Nick, thanks. Yup, it's got lots of vertical. Rotates with authority on take off and blasts off with the 120 even with a full load of fuel and smoke juice. Its a slick airframe and also really maintains the speed out of a dive. Throttling back to near idle at the top of a split-S and applying power only once you pull out will still give a very fast pass. Maintaining throttle in the dive will easily take you over the 200mph

Gripen owners/builders....In an effort to improve ground handling, I cut down on the travel of the main oleos to 7/16" and it did the trick quite nicely. Just disassemble the scissor link at the mid-point by removing the small nut/bolt. Slide out the lower strut, spring and piston, and add some oil (differential oil - 3000 weight recommended, I used After run oil since it was handy). Reassemble and check the travel. Repeat if necessary until you have the same amount of travel on each side.

Here's a short (30 sec) video of a take-off, split-S, & fly-by: [link=http://www.youtube.com/watch?v=VUFXsopte50]http://www.youtube.com/watch?v=VUFXsopte50[/link]
Here's the video of the maiden & test flights: [link=http://www.youtube.com/watch?v=y_tXVrL9H4I&NR=1]http://www.youtube.com/watch?v=y_tXVrL9H4I&NR=1[/link]

Regards,

Jim

Old 10-26-2008, 08:12 PM
  #74  
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Default RE: JAS-39 Gripen Owners/Build Thread

I picked up an older JL Gripen and the guy I bought it from suggested I modify the canard control horn to better grip the aluminum tubes from each canard.
I drilled and tapped a 4-40 thread to further help keep the canards from shifting.
I filed a flat spot on each canard tube for the 4-40 screw to seat tightly.
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Old 10-26-2008, 08:27 PM
  #75  
leelevinson
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Default RE: JAS-39 Gripen Owners/Build Thread

I have an older JL Gripen and have a question regarding the CG point.
On the sheet plans that came with mine it shows the CG point at 175 mm behind the leading edge at the wing root.
On this thread and other threads it seems that most Gripen builders (mostly SM) have been setting the CG at 140 - 145 mm behind the leading edge.

Anyone have any experience with setting the CG point at 175 mm behind the Leading Edge ??
Getting ready to fly it and am not sure where to set the CG.

Thanks

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