Official Freewing JAS 39 Gripen 80mm EDF Jet

[haljennings]

I was told by by Motion January for the tv units.

[HaroldAnderson]

Geez. That looks like a 105mm stacked on top of that Gripen!! 😲

TangoVector I don’t think that it’s such a good idea to consider the FMS 90mm fan for the Gripen...

[Husafreak]

Glad to hear you guys are hard at work figuring out the optimum power system for this jet! Once I’ve flown mine with the stock fan I’ll have to see how I like it. The post that most concerned me was lack of acceleration after slow or high alpha flight. I hate that. Without buying anything I do have an 8s 80mm Stumax fan, remember them? Originally intended for a fiberglass Habu but sitting since 2013. I think it is a HET motor, can’t remember, says 1485 (or 1495) kv, end bell of motor color is OD green anodized. 11 blades Stumax fan. One of the first generation of fans to lose the dentist drill whine. That was designed for outright speed, the type of fan with no moldings, just a CF tube. I should wire it up and check amp draw and fish scale pull. But if that went into the Gripen I could put the stock 1920 into my (old out runner fan) MiG 21... The wheels are turning.

[Husafreak]

Oh...

Thank you!

Heck, just fly it like that

[radfordc]

Did measure the trust to 2,4kg with a fish weight with a SLS 6s 3500 30c, took of the inspection "lid" under got 2,7kg.

Wow, a 12% increase in thrust just by improving air flow to the fan. I will try it!

[kallend]

.
Got from 2,4kg to 2,7kg thrust took of the box/ lid under the fan.

OK, but what does that do to the performance in flight? It surely adds a lot of drag.

[Airguardian]

Not to mention 'scale appearance'

[Captain Moron]

Think I have been thinking to much on this Gripen and the power issue .Watch loads of videos on You Tube and the Gripen seems OK to me on the videos .I love the look of this Gripen and with working canards what is there not to like .All I need now is Motion RC Europe to get some back in stock before Christmas before the wife changers her mind and I will be one happy bunny .Come on Motion RC get them back on order .( I know there is not much Motion RC can do with the new stock .They will come when the container comes from China and not before ) but I canard wait 😜

[Pogo]

I maidened mine yesterday (2 flights then cold) and in my excitement forgot to screw down the EDF cover. It didn't budge actually, but I could have inadvertently experienced this thrust increase! I'm going to add a NACA duct to mine, probably between the gear bays.
Tom

[janmb]

I’m at 137mm and it drags it’s tail slightly in turns and needs the slightest push inverted. I like it more each time I fly it.

A well balanced model WILL drag its tail during bank and yank turns. It is perfectly normal, and a Good Thing. And it is not a drawback at all, once realizing all four control features should be used throughout flight, not just two of them...

[Evan D]

Thank you. I assume you are in the U.S.?

I hope they come on and verify that.

I was told by by Motion January for the tv units.

[Mizer67]

Thank you all for more knowledge, this forum is great! After looking at different fan-combos, the HET 1865kv mated with a JF or Wemotec seems to be the most 80mm thrust available at the moment, as you guys already have found out. I'm looking at the FMS 90mm metal 1500kv, wondering how much thrust will be lost in the tight space in the Gripen after it has been shoehorned in there. It claims 4.9kg thrust at 29.6V/108A, equalling 3.2kW. That thrust will not happen with not enough airflow, but if it is capable of giving >4kg thrust, that would be interesting. But a lot depends on the airflow and how smooth surfaces that can be achieved and if it doesn't work, I have a perfect excuse to get myself an F22 ARF...

I know I will like it as it is, but future mods are always being planned. I have the Su35 and the M2000 and have visions of this one being the perfect mix of both. There's a good chance I just get the TV and be happy with that... or maybe not!

3.5 kg of (installed) thrust from my "economy" version FW 1857kv motor and V2 Jetfan 80mm, if the numbers are accurate. That's more than my 6S 90mms. Down sides are the CG and flight times + the added weight. I'm pulling about 74 amps average over a slightly sub-3 min flight on that setup even when trying to economize on power.

Until I can fix the CG, it doesn't fly that well on 8S, in my opinion...with my example of one which seems to be even more nose heavy than most. Flies heavy and needs a lot of throttle. Good for straight line speed but not good all around.

[Gravythe clown]

Just maidened mine and got two addition flights. I’m not impressed. I flew it without turning on the stabilizer on my S8R (I had issues getting the stabilizer aileron function working right).
besides the power issue I also had a wing rock at times I knew was way above stall speed.
the power had two issues I noticed and I believe it’s been stated before here but under power and slow to regain power. I almost got into trouble on my first landing. Dropped gear and did a flyby to do gear check, peeled off on to down wind, throttled back to about 40% and she started to sink quick. So I eased in some more power, little more power, more power, damn back to 80% before I saw a increase in air speed. She definitely will get in front of you before you know it. At this point I just started my bank to get on to final. Of course at 80% she started to speed up now, so out of final on dropped the throttle again to about 30(needed to bleed speed). She bled it off quick and the started to drop again. So I started to easy in power again. This time I just sat with it until she started to respond more. I brought her in and she landed it in a high alpha and touch the skid plate.

next to flights I knew to add a little more power and let it sit for a second. So I stayed ahead of it the whole next two flights. But once I got at about 50% throttle she starts to rock. It’s not huge but it’s there.

I’m at about 130 on my CG with my pack all the way in the back and about 70G’s of lead in the backend.

I’ll think about trying the FMS unit to see if that helps.


Gravy

[kallend]

Just maidened mine and got two addition flights. I’m not impressed. I flew it without turning on the stabilizer on my S8R (I had issues getting the stabilizer aileron function working right).
besides the power issue I also had a wing rock at times I knew was way above stall speed.
the power had two issues I noticed and I believe it’s been stated before here but under power and slow to regain power. I almost got into trouble on my first landing. Dropped gear and did a flyby to do gear check, peeled off on to down wind, throttled back to about 40% and she started to sink quick. So I eased in some more power, little more power, more power, damn back to 80% before I saw a increase in air speed. She definitely will get in front of you before you know it. At this point I just started my bank to get on to final. Of course at 80% she started to speed up now, so out of final on dropped the throttle again to about 30(needed to bleed speed). She bled it off quick and the started to drop again. So I started to easy in power again. This time I just sat with it until she started to respond more. I brought her in and she landed it in a high alpha and touch the skid plate.

next to flights I knew to add a little more power and let it sit for a second. So I stayed ahead of it the whole next two flights. But once I got at about 50% throttle she starts to rock. It’s not huge but it’s there.

I’m at about 130 on my CG with my pack all the way in the back and about 70G’s of lead in the backend.

I’ll think about trying the FMS unit to see if that helps.


Gravy

The FMS is lighter than the stock FW unit.

Suggest you try my heavy nozzle. https://www.thingiverse.com/thing:4650359

[kallend]

I'm going to add a NACA duct to mine, probably between the gear bays.
Tom

Can you get some before and after thrust measurements?

[rms]

Wow, a 12% increase in thrust just by improving air flow to the fan. I will try it!

This is wrong, did a several test today, cold not get that difference. Was more around 2,4kg. But with a bigger fan/ motor you might need more air in.

But did another test several times, took of the rear,that increased the thrust from 2,4kg to 2,65kg but end diameter went up and the duct is very short...this is for testing purpose only ;-)
Did put the wire behind the fan in line and made a aerodynamic fearing aroud it. 2,4 kg thrust before and after. Will take it in the air and see if there is any difference.
If we want more thrust we need a bigger engine og fan that can move more air. Or go to bigger diameter fan.

[RudyD54]

Well, I finally got around to completing the setup on my Gripen. I went with a Spektrum AR637T, an RC Light Systems channel expander, and an SMC 6S 4000 battery. All flight surfaces are on channels 2-6 and the gear and nosewheel are on 7 and 8 through the expander. Thanks to @evand and kallend for sending me your radio files, they helped me understand the elevon setup. I was able to figure out how to setup the receiver to stabilize all the flight surfaces including the canards which I setup for pitch only. The only downside is I can’t trim the canards separately from the elevons but that’s no big deal. I’ll adjust them back to the neutral position after the maiden via the linkages. Once the vector unit is available I plan on upgrading to the AR8360T receiver which will give me two additional stabilized outputs for the pitch and yaw servos, and then I’ll just setup a couple of flight modes for the gain.

I was able to get the CG back to 130mm using the SMC 4000 which weighs 593 grams with no trimming of foam or extra weight. I’m going to see how I like it there before I make any modifications or add weight to the tail. I was curious so I temporarily added 80 grams of weight in the tail to simulate the addition of the vectoring unit and it brought the CG to 145mm. That’s probably further than I’ll personally be comfortable with but it’s nice to know I can get it there. My total ready to fly weight comes out to 2,999 grams and I measured my peak thrust on a full pack to be 2700 grams at around 2500 watts. It settles out around 2650 grams after a few seconds. I had previously measured 2400 grams of thrust but I realized I measured incorrectly. Oops... Those numbers would put me at .9 thrust to weight ratio. (Feel free to check my math).

I won’t be able to maiden until next weekend at the earliest but I’m excited to get her in the air now that she’s all ready and I’ll make sure to post some video.

[Evan D]

Sounds good Rudy. I’m at 137 and think it feels a tad tail heavy, try 130 as you are and adjust from there. 130 feels more locked in.

[Mizer67]

Good numbers RudyD54 . That SMC pack must really be a good one. I only get around low ~2400 grams and ~2400 watts out of the stock fan.

[RudyD54]

Good numbers RudyD54 . That SMC pack must really be a good one. I only get around low ~2400 grams and ~2400 watts out of the stock fan.

I had read a lot of good things about SMC on the battery testing thread over at rcgroups and I can confirm they are indeed impressive. I’m going to pick up a few more while they still have in stock. The only downside is they aren’t cheap, but they seem to be perfect for the Gripen.