JAS 39 Gripen Park Jet - RC Groups
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Dec 11, 2004, 03:07 PM
Park Jet Guru
jetset44's Avatar
Build Log

JAS 39 Gripen Park Jet


Hereís the latest member of the Park Jet series, the Saab JAS 39 Gripen. This design is very similar in concept to the F-18 and F-15 Park Jets, and uses the same construction methods and power setups. Like the other jets, itís intended to be a park flyer built using simple construction methods and inexpensive and readily available components. Itís designed to be built almost entirely from either 6mm Depron or BlueCore foam. Here are the specs:

Wing area: 258 sq in
Span: 23.9 in
Length: 42.3 in
Weight RTF: 16.6 oz as shown unpainted (estimate 17.5 oz painted)
Wing loading: 9.8 oz/ft2
Motor: Himax 2015-4100 with 4.4 gearing
Battery: Etec 11.1V 1200 mAh Lipo
Prop: APC 9x6 SF
Current draw: 11.5 amps static
Power loading: 139 watts/lb
Radio equipment: Berg 5 receiver, GWS Pico and Hitec HS-55 servos, Phoenix 10 speed control
Flight controls: Wing elevons, full-flying canard, rudder

The flight performance of this model is excellent! The Gripen has the same wide speed range and excellent handling characteristics as the F-18 and F-15 Park Jets, and is surprisingly easy to fly. The biggest difference is that the Gripen is slightly less stable than either the F-18 or F-15 and is more maneuverable and quicker on the controls. Just like I suspected, the Gripen loves high alpha slow flight and is rock solid at sustained 30-40 deg alpha. Iíve been able to hold full aft stick and 1/4 throttle and watch the model crawl rock solid at very high alpha only a foot or so off the ground. The model can also do incredibly tight low-level turns with no hint of stalling by holding full aft stick and full throttle, just like a 3D ship. And of course it also flies well at high speed and easily flies as fast as I'm comfortable flying a foam airplane (about 50 mph). Just like the other Park Jets, the Gripen performs best with a power setup that provides 15-20 oz static thrust and 45-50 mph pitch speed.

But the best part about flying the Gripen is that the double delta planform looks just awesome in the air--almost like a spaceship. SINISTER is the best word to describe it! Itís just a thrill to watch this model fly. Iím hoping to get some flight video shot and posted soon (if the weather cooperates).

Currently, I recommend flying the Gripen with mixed canard/elevon flight controls for pitch. My model is set up so that full aft stick deflects the canard trailing edge down 3/4" and the wing elevons trailing edge up 3/8Ē. This setup provides excellent pitch control at both high speed and low speed and good stall characteristics. However, I do intend to test other mixing combinations to see if anything else works better. My model also has rudder control, which is optional but invaluable for providing directional control during high alpha flight.

For those of you that donít have easy access to Depron or want to save time printing plans and cutting out parts, this design will soon be available as a laser-cut kit from www.3dfoamy.com. Levi puts out excellent quality kits that will save you a lot of time relative to scratch building! Kits should be available in a few weeks.

Enjoy, and as always, post pictures if you build it!

Steve
Last edited by jetset44; May 04, 2006 at 07:51 PM. Reason: Added pictures of the painted model
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Dec 11, 2004, 03:08 PM
Park Jet Guru
jetset44's Avatar
Here are some more pics of the prototype, including close-ups of the canard installation and the motor installation and a family shot showing the Gripen along with the F-18 and F-15 Park Jets.

Steve
Dec 11, 2004, 03:10 PM
Park Jet Guru
jetset44's Avatar
Here are some pics taken during construction of the Gripen that show the internals. Iíll post more construction info soon.

Steve
Dec 11, 2004, 03:11 PM
Park Jet Guru
jetset44's Avatar

Plans


Here are the plans for the Gripen Park Jet. As usual, these plans consist of two filesóa scaled assembly drawing that shows how everything fits together and a full-scale parts template. The parts template is posted in both tiled and non-tiled formats. Previews are posted below to show how the plans should look when assembled. Enjoy!

EDIT: Here's a link to an illustrated construction guide for this model:

http://www.parkjets.com/JAS_39_Park_...ion_Manual.pdf

Steve
Last edited by jetset44; Jun 15, 2008 at 01:11 AM. Reason: Added link to construction guide
Dec 11, 2004, 03:19 PM
Registered User
TBolt's Avatar
All I can say is WOW! All of your designs fly so awsome. The only problem I have with your airplanes, is that I am all out of electronics to install in any more planes.
You are the MAN!
Dec 11, 2004, 03:20 PM
Experimentor
WOW STEVE! These plans looks great! here's the markings used at the Gripen
Dec 11, 2004, 03:40 PM
FLY FREE!!!!!!
Yes Yes Yes!!!!!HeeHaw Whoooooooiieeee!!!
Thanx!!!Great Fantastic !!!!
Let Construction commence!!
Dec 11, 2004, 03:49 PM
Registered User
Rane's Avatar
WOW STEVE! impossible beautiful plane.
-rane
Dec 11, 2004, 04:12 PM
Watch This !!!
edkoz's Avatar
Steve:

Thank you.

Oh well .... I've got the extra depron. I'm off to Kinkos for some full size plans. I'm going to be on a first name basis with the people at Kinkos if you keep this up.

Ed
Dec 11, 2004, 04:17 PM
Registered User
Damn!! And I already started the T-38....

Dec 11, 2004, 04:23 PM
Registered User
fuelsguy's Avatar
Steve,
Another great model.
With this construction technique becoming popular can we keep track of how many people are designing different airplanes?
I'm half way though an F-4 build and then found the thread of the Finnish F-4 plans.
How about having people post "Designs in progress" on one of these threads, maybe the F-18 one, and maybe "Designs wanted" as well.
Just a thought,
Ivor
Dec 11, 2004, 04:50 PM
Semper Fi, Do or Die
kscbob1's Avatar
Steve:

I've noticed that the gears on your HiMax gearbox are opposite the way they come from the factory. The factory has the 6.66 ratio set up initially. Did you reverse them because this is a pusher?

Bob
Dec 11, 2004, 06:26 PM
Registered User
Micronics's Avatar
Nice Job Steve!
very cool jets!
thanks for the plans.

Allen
Dec 11, 2004, 07:12 PM
Registered User
trondb's Avatar
Well ,another nice one ! I`m out of words..
Steve, you keep ezoner`s busy
Last edited by trondb; Dec 11, 2004 at 07:19 PM.
Dec 11, 2004, 08:03 PM
Park Jet Guru
jetset44's Avatar
Thanks for all the compliments. I'm looking forward to seeing how everyone else's Gripens come out! I'm sure happy with mine.

kscbob - Yes, I swapped the Himax gears from the 6.6 to 4.4 set since that gearing matches the speed and thrust range needed for this model better. Or did you mean that I've mounted the gears pointed the other way on the shaft? If I did, I guess I hadn't noticed that...

fuelsguy - Yes, there has been a virtual explosion of Depron jets lately, hasn't there. Isn't it great?!? And I don't see an end to this anytime soon since there are some many cool airplanes out there to be modeled and so many different ways you can size these jets (indoor micro, "pocket" size for small motors, "Park Jet" size for 100W motors, and scaled up 150% size for 150W+ motors). The possibilities seem almost endless! This is such a great time to be in this hobby.

Iswald - Wow, I can't tell if you're excited about this model or not from your post...

Steve


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