Official Freewing JAS 39 Gripen 80mm EDF Jet

[Marktur]

HAPPY THANKSGIVING! Hope everyone is going to have a good dinner tonight, and go flying tomorrow!

I think we're ready to maiden tomorrow!!! Really excited!

I cut away some foam on the horizontal detail on each side of the tail section (on the bottom), and glued in about 3 oz of lead. I didn't want to put anything in the duct, and wanted to use as little as possible, so as far back as made sense. I am balancing on the CG now with the HRB 6s 6000. I don't think 3oz is going to affect the flight characteristics that much at all...and it is a jet, afterall..

Found these missiles (below) in my piles of "extra stuff", and asked my buddy to print me a few of the connectors so I can slide them off an on as I like...but I really do appreciate the additional contrast from them for visibility too. There were foam standoffs on the shafts of the missles I removed, and you can see where I glued the attachment parts on. I think they're from Freewing, made of foam and paper, so no weight added, really. My buddy also printed missiles for me too, so I can use them if I need a bit more weight towards the back.

After all the reading, I'm thinking I need to be about 10mm behind the printed CG for best performance, but I'll maiden as is and then do some fine tuning once I get used to it. I have a Lemon RX/gyro with satellite (tested in another jet, so I know it's solid), but I'm leaving the gyro OFF until I know it is flying right by itself. Then I may turn it on for wing-rock and high-alpha stuff...but we'll see. I really don't use gyros in airplanes that often - mostly drones and helis.

I set my "high" rates to the low rate settings in the book, like Mike? did in the Motion videos, with mid at 90% and low at 75%. We can always add more, but I want to make sure the first flights are successful.

I watched a lot of the full-scale videos posted here, and suggested by YouTube...wow, it is agile! Possibly tighter turning than our own F-16? Pretty nice jet - and very cool that it stays "in the box" the entire time at airshows. Wow.

Canards: how many MM's of down should we be at in the relaxed position? Videos look like maybe 1-2 degrees?

[Marktur]

PS. My buddy printed a tailcone for me. Told him to go heavy on the fill, and it is solid. Just wanted to find out how you guys attached it...it looks like I need to cut off the original tailcone, but leave about 1" to slip inside the new plastic one? It also has holes in it for more weight, and I figured I can pour in some epoxy to add more weight if necessary. I'm going to fly it as stock with my lead weights first because I'm thinking I may want to add more after reading all 55 pages here! :)

[Evan D]

I’m not using any canard reflex, where did you hear to do that? You’ll probably like it balanced a bit behind the marks but on the marks works for the maiden. The missiles look good. I have sidewinders on mine. Good luck with the maiden.

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[kallend]

PS. My buddy printed a tailcone for me. Told him to go heavy on the fill, and it is solid. Just wanted to find out how you guys attached it...it looks like I need to cut off the original tailcone, but leave about 1" to slip inside the new plastic one? It also has holes in it for more weight, and I figured I can pour in some epoxy to add more weight if necessary. I'm going to fly it as stock with my lead weights first because I'm thinking I may want to add more after reading all 55 pages here! :)

That sounds like the tailcone I designed. https://www.thingiverse.com/thing:4650359

Yes, it needs a stub of foam (about 13mm) to locate it and to glue to. The holes can hold up to 60g of additional lead.

I also have Sidewinders to the correct scale (1:9) with lugs that fit the Gripen rails. https://www.thingiverse.com/thing:4653284

Several of us have found that about 2 - 3 mm down at the front of the canards improves the stability.

[4923crew]

I combined two video's into one that were recorded on my 3d printed and designed wing tip mounts for my GoPro session cameras. Enjoy.

[jkallend]

. . . . . .. I did remove the louvers from the cheater duct on the bottom of the plane to improve air flow into the fan.

Did you make before and after thrust measurements to see if it made a difference?

[radfordc]

Did you make before and after thrust measurements to see if it made a difference?

I don't have a way to measure thrust accurately.

[radfordc]

You can buy two A3 Pro gyros (one for the elevons and rudder, one for the canards and nosewheel) for the price of an Aura and still have $$ left over.

Good idea. I will say that I'm happy with how the Eagle A3 Pro is working. I'm not seeing the wing rock that some complain about. Plane flys stable and solid.

[Evan D]

While mine does rock, especially in windy weather, I don't fly with gyros and most deltas rock. Not a complaint, more an observation. I can see how gyros would help with it.

[kallend]

Good idea. I will say that I'm happy with how the Eagle A3 Pro is working. I'm not seeing the wing rock that some complain about. Plane flys stable and solid.

Yes, I've had good results with the A3 Pro.

(Not using it in the Gripen though since I have a stabilized RX on the elevons. I *may* add one on the canards and VT later, when the VT finally arrives.)

[Airguardian]

If Cortex Pro or iGyro is the way to go, coupled with high-end servos, my interest in making it unstable just vanished. I think I rather buy another plane of some sort and enjoy that, there are many to chose from! Back to the thinking cave!

There may be other cheaper options. The Guardian was capable of handling 333Hz refresh rates for example and it was just 60$, plus the control algorithm was decent. (Dangit ET, why did you have to close???) :'(

So maybe just do some research to see what other options are there?

[Airguardian]

After all the reading, I'm thinking I need to be about 10mm behind the printed CG for best performance

'Best' performance is certainly much more aft than that. But 130mm (10 behind factory marks on the wings) is flyable. Okay-ish for a maiden. If you can't get it further aft, even better.

I set my "high" rates to the low rate settings in the book, like Mike? did in the Motion videos, with mid at 90% and low at 75%. We can always add more, but I want to make sure the first flights are successful.

Not a great idea IMO. For roll, maybe, but this plane is not pitch sensitive AT ALL (with stock CG at least). Limiting throws actually makes it more dangerous to fly IMO as you lack controllability and/or may not even be able to rotate from the ground if you don't have enough pitch authority.

Go for the max throws you can get and drop in a good amount of expo (40-60%), and that will do it ;)

[KevinMar]

Motor wires have an enamel coating you have to remove.

That makes a lot of sense. I've soaked the wires in IPA, but that hasn't worked. How should I go about removing the coating?

[kallend]

There may be other cheaper options. The Guardian was capable of handling 333Hz refresh rates for example and it was just 60$, plus the control algorithm was decent. (Dangit ET, why did you have to close???) :'(

So maybe just do some research to see what other options are there?

The HobbyEagle A3 pro and A3 Super can go to 333Hz too (if the servos can handle it).

[kallend]

'Best' performance is certainly much more aft than that. But 130mm (10 behind factory marks on the wings) is flyable. Okay-ish for a maiden. If you can't get it further aft, even better.



Not a great idea IMO. For roll, maybe, but this plane is not pitch sensitive AT ALL (with stock CG at least). Limiting throws actually makes it more dangerous to fly IMO as you lack controllability and/or may not even be able to rotate from the ground if you don't have enough pitch authority.

Go for the max throws you can get and drop in a good amount of expo (40-60%), and that will do it ;)

I did my maiden at 130mm and immediately moved to 135 for the second flight. I have flown it at 140mm and it was quite OK but required a smaller pack.

FWIW I have my pitch rate at 100% and roll at 80% (Spektrum units) with 50% expo. Roll at 100% was way too fast.

[Marktur]

That sounds like the tailcone I designed. https://www.thingiverse.com/thing:4650359

Yes, it needs a stub of foam (about 13mm) to locate it and to glue to. The holes can hold up to 60g of additional lead.

I also have Sidewinders to the correct scale (1:9) with lugs that fit the Gripen rails. https://www.thingiverse.com/thing:4653284

Several of us have found that about 2 - 3 mm down at the front of the canards improves the stability.

Thanks for the Thingiverse designs...yup, saw the link and sent to my buddy before it even arrived!

Canards: yeah, I’ll do that too. Does this then require a bit of up elevon to compensate?

Where is your Cg?

[kallend]

Thanks for the Thingiverse designs...yup, saw the link and sent to my buddy before it even arrived!

Canards: yeah, I’ll do that too. Does this then require a bit of up elevon to compensate?

Where is your Cg?

CG at 135mm

About 5 clicks of elevon trim was all that was needed.

[Marktur]

Thanks guys...

I’m going to Take your advice and start with full rates and 50% expo. I trust you guys both after watching your videos! I will pop on the tail cone, then cut some foam inside to get it to 135mm at least. Just to be sure, where do you start your measurement, or how many mm’s from the printed line? Before I glue, I will cg it, and if I still need more weight I’ll fill the holes with 5 min epoxy.

Lol...better not eat too much or I’m gonna pass out and not wrench!

Any recommendations on the best method to cut the tail cone off?

[Marktur]

CG at 135mm

About 5 clicks of elevon trim was all that was needed.

ok, I need to turn off elevon trim in the mixes, then I can trim them separate from the canards. Hmmm, never used the “other” trim controls at the top of the radio..for the canards...is that the best way to handle this, or just measure 2mm down and don’t allow the mix to trim and call it a day?


LOL Sorry for all the questions- first canard for me.

[Evan D]

The line is 122. I'm happy at 15mm behind that or 137. That said I feel that at that point it is starting to be tail heavy-ish and recommend a little more forward for your maiden.