Official Freewing JAS 39 Gripen 80mm EDF Jet

[Airguardian]

Ok, maiden done!

Just as expected, CG recommendation is overly nose heavy and first impression is that this jet is fast and doesn't quite fly like the Eurofighter.
At least not at the current CG setting and with my setup being rather on the heavy side... videos to follow soon, keep tuned!

[janmb]

Congrats Jandro!

Frode maidened his today as well - and while the model tracks like a knife and looks absolutely cooler than a snowman, it is indeed hard to balance with anything other than tiny batteries.

He used my gens ace 5000 45C packs, which are fairly light for their capacity, and still couldn't CG.

I think freewing is overdoing the conservative recommendations to the point of the design being difficult to cope with anymore. Always foam removal / tail weight needed, and that is so unnecessary.

[meadowhay]

Tyres kicked and fires lit ready for the maiden tomorrow.

https://youtu.be/-b6JAuAsWLU

[janmb]

Tyres kicked and fires lit ready for the maiden tomorrow.
https://youtu.be/-b6JAuAsWLU

GL!

[Radar-Guy]

I think freewing is overdoing the conservative recommendations to the point of the design being difficult to cope with anymore. Always foam removal / tail weight needed, and that is so unnecessary.

So maybe it’s a good thing that my 3DP nozzle came out a bit heavy...

[Airguardian]

Indeed it is... it will help you out!

So... Maiden video ready! :D

Copy-paste from video description on my initial thoughts:

Say hi to 'Jana', the new girl on my fleet! :D This is the new, just-released, Freewing JAS-39 Gripen (80mm EDF jet).
These were the maiden (1st) and 2nd flight, performed in a day with 'less than ideal' conditions... prettty windy and turbulent air!
So, even with the bad weather I decided to take-off with tail-wind due to field considerations... if anything were to go wrong, it's easier to rescue the plane from the open space to the right.
It also provides more 'obstacle-free' space to deal with any immediate issues. On the left side the jet would have to clear a treeline and if it goes down, it does so in the forest, where it's much more messy to handle the impact or to recover the jet afterwards if it gets stuck on a treetop... huge mess! Thankfully none of that happened of course, but taking off with cross-tail-wind with a new and untrimmed jet it's a bit challenging/scary.

Just as expected, factory CG is very nose heavy. The jet design doesn't quite help though, and I had to add 130g of ballast in the tail to even achieve factory recommended CG. Clearly my batteries are way too heavy for this jet (Panther 6S 5Ah, 870g), so if you are considering buying this jet and need to get new batts, definitely consider getting something lighter or you may run into a couple of nightmares. Despite the CG issue, the jet took the bad weather and survived it well enough. It exhibited quite some wing-rocking due to the turbulent conditions, made worse by nose-heavy CG. I tried to smooth it out by activating the S8R built-in gyro (controlling elevons and rudder) on the first flight but the roll gain was too high and the jet exhibited violent roll oscillations at high speed so I quickly turned it off and flew as-is. The separate gyro for canards (GWS PG-03) was left always on with a middle gain setting. I dismounted and resoldered the wires of one of the canard servos to reverse its direction and be able to use them Y-wired together for a pitch-only operation. I usually never get my gyros on for maiden flights (I consider the canard an exception), but then again, I usually maiden in better weather conditions so I had the S8R ready to help me in case of need... :p

After landing, before going for the second flight, I lowered the roll gain on the S8R built-in gyro and that improved things quite a bit, allowing the jet to tolerate the weather better. I think the plane will benefit massively from setting the CG further aft ...will do further testing in the coming flights, keep tuned! Achievable throws with stock gear are somewhat limited too and I think the jet's maneuverability would benefit from some 'further user work' on that end. ;) For now, here's my quick evaluation though. This jet is 'not the Eurofighter'. It is quite fast and likes to 'drift sideways' on moderate elevator pulls. Wing rocking is comparably worse (at least in current setup), although I think that will improve with better CG placement and more calm weather conditions. The JAS-39 does feel kinda mushy in pitch and yaw by comparison too. It has plenty of roll authority though. I'm liking the gyro on canards and the one on the elevons does help a lot with the bad weather. I really need to do more flying and try out lighter batts to really explore the full potential of this bird. Other than that, I find it pretty enjoyable and it tracks true at speed! :)

SPECS (Reflecting my setup):
Model Scale: 1/9th
Wingspan: 882mm
Length: 1613mm
Weight: 2350g (w/o batteries)
TOW: 3400g
CG: Factory recommended (molded into wings)
Material: EPO
Motor: Freewing 6S 3658-1920kV inrunner motor
EDF: Freewing 80mm 9-Blade EDF
ESC: Freewing 100A with 5A BEC (BEC deactivated by pulling red wire out)
Servos: All stock servos, 9g hybrid digital
Landing Gear: Electronic retractable w/ aluminum trailing link struts
Receiver: FrSky S8R gyro-stabilized receiver
Canards gyro: GWS PG-03 (added as a mod)
Separate UBEC: Freewing 8A (added as a mod)
Receiver battery: Rhino 2S 610mAh (added as a mod)
Main battery pack: Turnigy Panther 6S 5000mAh 75C

Congrats Jandro!
[...]
I think freewing is overdoing the conservative recommendations to the point of the design being difficult to cope with anymore. Always foam removal / tail weight needed, and that is so unnecessary.

Thanks, and very heavily agree... :'(

[janmb]

Dirty Dee Any chance of bugging you with cadding a Meteor and an IRIS-T for this bird? It deserves proper ordinance.

[kallend]

This jet is 'not the Eurofighter'.

Can you expand on what you mean by this?

Also I generally like to fly my EDFs with much the same CG as you use, so please keep us informed about where you end up with that.

I will not complete mine (which hasn't been shipped yet) until the VT arrives, so plenty of time to follow your adventures.

[kallend]

So maybe it’s a good thing that my 3DP nozzle came out a bit heavy...

Is that your original design?

[Airguardian]

Can you expand on what you mean by this?

Also I generally like to fly my EDFs with much the same CG as you use, so please keep us informed about where you end up with that.

I will not complete mine (which hasn't been shipped yet) until the VT arrives, so plenty of time to follow your adventures.

Sure!
The lateral-directional flight dynamics of this plane are pretty different to those of the Euro.

I mean, I can only gather so much from a couple of flights and further testing is due, but first impression is that the jet behaves very differently in a number of ways:

- Roll/yaw coupling doesn't work as smooth as on the Eurofighter, so while adding rudder on the EF to get wide drifted spirals is straightforward and barely requires pilot workload, the Gripen acts differently. It doesn't like sideslip as much, so to speak.
- Wing rock is much worse (probably due to the nose-heavy CG in good measure and worsened by turbulent air). For the most part I don't get much wing rocking with the euro even without a gyro on the elevons and the Gripen was wing-rocking a lot, even with gyro on.
- The Eurofighter is not a jet that feels really 'locked-in' or 'on-rails' compared to others (which for the most part, I like as it allows good maneuverability) but it reacts kinda predictable when putting it through its paces, keeping good lateral stability. The Gripen on the other hand drifts laterally (yaw/roll) when being pulled 'moderately' (not even hard by my standards).
Again, bad weather and CG very probably worsen that. Example: While on a looping, closing the radius too much at the beginning of the descent may cause the plane to 'snap' to the sides, making it harder to keep the maneuver looking 'clean'.
- JAS-39 does tolerate high alpha, at least better than the Hornet, even in nose-heavy configuration (which was to expect from a delta) but kinda feel like the EF had better handling while doing high alpha. Again, need to do more testing.
- The Eurofighter did react to pitch and yaw inputs much more agressively than the Gripen (which I love about the EF). Eurofighter is more similar to the Su-35 there, while Gripen felt more like the Hornet.
- I do a lot of rudder 'spirally' flying and no jet gets even close to the EF (maybe the Mirage? But I have not flown it). Not even the Su-35. Definitely not the Hornet and although the Gripen was better at this it still feels a bit 'off' when being pushed with rudder where the Eurofighter just feels natural.

Educated speculation:
Most of the behaviors described above are a result of nose-heavy CG on one hand, and different fuselage layout on the other. Particularly the way that the Gripen's nose and aft fuselage are designed, making the whole jet much longer than it is wide. The jet is kinda 'stretched out' in the longitudinal axis and this impairs some of the jet's lateral-directional capabilities. The vertical stab and rudder are also comparatively smaller, and very possibly blanked out at higher angles of attack compared with the EF. Analogies with the Hornet here come to mind.

Other than that, the jet tracks pretty straight and true at speed, guess also as a result of a longer fuselage.

And very important too, the total surface deflections on my Gripen control surfaces are rather limited compared to the Euro. That is most likely playing a big role, more so now that the nose-heavy CG impedes maneuverability. Plus, I'm obviously missing the vectored thrust. ;)

Will expand on these ideas as I do more testing.

[Radar-Guy]

Is that your original design?

Yes, it is. Exhaust diameter is 65mm (stock 67mm) as recommended for the Wemotec fan.

[slumi]

Hi Airguardian,

how did you wire your S8R gyro stabilized receiver ?
I am especially interested in the wiring of the canards and mixing from the transmitter.

[janmb]

This jet is 'not the Eurofighter'.

You may find it is closer than you think once dialed in. Frode flew his nickers off today, shifting the CG quite a lot.

[HockeyMac!]

Frode flew his nickers off today

Can you help with the translation :)

[kallend]

You may find it is closer than you think once dialed in. Frode flew his nickers off today, shifting the CG quite a lot.

It's "knickers".

[kallend]

Yes, it is. Exhaust diameter is 65mm (stock 67mm) as recommended for the Wemotec fan.

Nice.

[Airguardian]

You may find it is closer than you think once dialed in. Frode flew his nickers off today, shifting the CG quite a lot.

That's encouraging :)
Now just need good weather back again!

Yes, it is. Exhaust diameter is 65mm (stock 67mm) as recommended for the Wemotec fan.

I like the vane you made for the spar to reduce drag... any chance you share the STL? :D

Hi Airguardian,

how did you wire your S8R gyro stabilized receiver ?
I am especially interested in the wiring of the canards and mixing from the transmitter.

Sure, it's pretty straightforward, find diagram attached:

Canards are mixed for pitch only as if the gyro was not in there, simple! ;)

[slumi]

Thanks Airguardian for your quick reply.
So only one channel for the canards, that simplifies a lot.
I guess you use elevon mixing in the S8R gyro-receiver for Taileron L and Taileron R.
For the canards you use directly elevator.
Not clear for me is the function of PG-03 gyro, what for ?

[RudyD54]

She’s here in the states!!!!!!

[Gravythe clown]

Just got shipping notice. Nice.

Gravy