SAPAC SAAB JAS-39 Gripen

Dec 28, 2009 No Comments by

By Mark Ronge

See Photos Below

The JAS Gripen is an aircraft not commonly modeled, which makes SAPAC’s version all the more enjoyable to own. A Swedish-developed aircraft, the Gripen was designed in place of purchasing popular American F-16 and F-16 fighters. The Gripen is still being improved to this day; in fact, last year, a new, improved model of the Gripen began testing. The Gripen utilizes the delta wing shape with front canards, giving it a unique appearance and amazing maneuverability. The JAS 39 is a supersonic fighter, capable of super cruise speeds of Mach 1.1 (Mach 1.2 with the newer version). One of the coolest things about this jet is that it was designed to take off and land on common public roads! This was to be useful if the operators did not have bases of operation. It even could land (on the roads), be refueled and back up in the air under 10 minutes. SAPAC has a full line of awesome EDF jets, made of both composite and foam. Their version of the Gripen is a very large foam model, capable of both a 70mm fan and 90mm with some modification. The ARF setup with the fan includes the brushless motor and 70mm fan. Measuring 59 inches in length, this is the largest foam EDF jet I’ve ever seen. With the foam comes incredibly light wing loading, which allows for high alpha maneuvers and in general, more forgiving flight characteristics than an all-composite model.

Unique Features

I still can’t get over how large this model is! I immediately knew that this was going to be a favorite at the flying field. Once built, the 5-foot long model looks fantastic just sitting there, and looks even better flying by. Hardware is included, along with the brushless motor and fan in this version (it costs only five dollars more than the ARF, so you might as well get the motor and fan unit). Water slide decals (tricky to install) are included as well; however, once they’re installed they look great. After various flights, the decals did begin to peel slightly, but in general, held up to the abuse I put the model through.

The instruction manual is not as complete as some other models I’ve built, but since this model is intended for expert pilots only, I wouldn’t be surprised if most people don’t even bother to look at the manual. The build process is pretty straightforward. Everything is epoxied together for strong connections, and at the speeds that this model will fly, no reinforcements are needed above the stock setup. Working with the epoxy on such a large model can be somewhat hard; you cannot rub the model with alcohol as the paint will come off, and using masking tape ends up with the same result.

Plenty of armament is included, and once added makes the model look absolutely stunning. This is the best-looking foamie EDF jet that I’ve ever put together, and I just love looking at it before I fly. Landing gear is sufficient for paved surfaces, anything else you may want to hand launch, or more preferably use a bungee for his model. Unfortunately, the decorative missiles must be removed if you go this route.

In order to complete the Gripen (assuming you purchased the model with the fan and motor), you will need an 80 amp brushless ESC, 3-4 micro servos and your radio equipment of choice. The model utilizes elevon mixing, so be sure you have a 4-channel radio capable of this. The recommended battery is a 3300, 4-cell LiPo with at least a 25c discharge; however, if you can spring for it, I would recommend a 3800-4000mAh battery, 25-30c discharge. I also found out that a 5-cell battery does work on this motor, if you need the extra performance, just do some bench tests with your speed control and five-cell battery setup first (measure amps/watts) to make sure that the combination will be reliable in flight. There is so much room for batteries; I’d imagine you could fit a 10-cell 4000mAh setup, so there are no space limitations with this model. Fit and finish was pretty good, a pretty simple overall build—the hardest part was trying to handle the epoxy with such large wing surfaces, if you have an extra hand laying around, be sure to ask for help. I recommend you install the motor and fan unit towards the rear of the exhaust (you can see grooves were to install), as opposed to the location stated in the manual. This helps achieve proper CG without adding any weight.

In The Air

Control Throws

Aileron: +/-3/4 in., 25% expo

Elevator +/-3/4 in., 25% expo

Rudder: +/-1 in., 25% expo

I tried using the landing gear on our local rough grassy flying fields for the first flight or so. I couldn’t get the model off the ground, so I ended up having to hand launch the model from there on out. I notice that the wheels sit cambered in at an awkward angle, and this possibly may produce some extra drag. But even if they were spinning freely, I can never take off the ground with any of my EDF jets in the types of fields we have around here, most EDF landing gear is designed for paved surfaces, and I know that the gear will perform on a paved runway. I removed the gear for subsequent flights (along with the armament) and just landed on the belly. After multiple flights, I’ve had no problems thus far.

Stability

In general, the Gripen is behaves well under windy conditions. The jet is very sensitive in the axial direction; it does want to roll when the wind is pushing on it. I recommend higher expo (40-50%) for the first couple of flights and make adjustments as you get more experience flying the model. Under windy conditions, I do find myself trying to keep the jet straight, but not overly so that it becomes a chore. Just be careful when flying far out—if a wind gust hits the Gripen, it can be difficult to distinguish which way she rolled initially, especially with the light gray paint scheme.

Tracking

The model flies as straight as an arrow, even under windy conditions. Aside from the aileron controls, hardly any input is required to keep the model straight. It turns predictably and keeps it heading throughout the entire course of the turn easily.

Aerobatics

Delta wing EDF jet designs lend themselves to blazingly fast roll rates. If you had the desire, you can make this thing roll five times in a row in a flash. The only problem is orientation becomes an issue as it can be a little difficult to determine if the model is upright or inverted after some quick rolls. Keep it up a few mistakes high and you’ll be able to figure out the orientation. Keep up speed to complete a level loop, and after a speed run, the Gripen seems to carry its speed and have decent vertical performance. Since the Gripen has a fully functional rudder, pretty much anything a sport plane can do, this jet can do. One unique feature about this model is since it has a fairly light wing loading for its weight, you can glide across the sky in a high alpha angle of attack. You can harrier it across the sky, almost like a 3D plane.

Glide and stall performance

Using the stock motor and a 4-cell LiPo, the Gripen will fly at about 50 mph as a top speed. This does not leave much room for error in keeping your speed up; I found it takes full power to make turns without losing too much altitude. I prefer the 5-cell setup, and have been using a 4000mAh 5-cell LiPo with the stock motor with great success. However, it is forgiving and will not stall nearly as easily as other composite EDFs of the same size, so it is a more relaxing flight experience.

Pilot debriefing

I recommend this model to any expert pilots looking to get into larger-size EDF jets. This is the perfect stepping stone from smaller foamies, and gives a much more exhilarating flight experience. In fact, due to the exhaust design, the Gripen sounds much more like a real jet than other EDF models I have flown. Everyone at the field loves this jet, and even though it is not a screamer, it looks fantastic cru
ising around and moves at a very scale-like speed.

Highlights

· Huge scale looks

· Extremely reasonable price

· Included motor and fan unit work great

· Foam is easy to repair

Gear Used

Radio: Spektrum DX7 transmitter, Spektrum AR500 receiver (spektrumrc.com), 4 Hitec HS-65 servos (horizonhobby.com, hitecrcd.com)

Motor: Included brushless inrunner w/ 80A Castle Creations Phoenix ESC (castlecreations.com) w/ included 5-blade EDF unit

Battery: Thunder Power RC Pro Power 30C 3850mAh 4-cell LiPo (thunderpowerrc.com)

Specifications:

Model: SAAB JAS-39 Gripen

Distributor: Sapac America (sapacamerica.com)

Type: Scale EDF

Wingspan: 35.4 in.

Wing Area: 356.5 sq. in.

Length: 59 in.

Weight: 3 lb., 9 oz.

Wing loading: 23.024 oz./sq.ft.

Power Req’d: Electric inrunner and 70mm EDF unit

Radio Req’d: 4-channel

Price:$129

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