Official Freewing JAS 39 Gripen 80mm EDF Jet

[Airguardian]

Some more Gripen fun:

[Gary S.]

Great flight!
Is that the 90mm EDF conversion?

Its the 80mm jetfan 1758 HET 8s SMC 4500 packs. I am considering 90mm and have done some prototyping on an old fuse, but it just flys so good right now its hard for me to justify doing it.

[TangoVector]

Its the 80mm jetfan 1758 HET 8s SMC 4500 packs. I am considering 90mm and have done some prototyping on an old fuse, but it just flys so good right now its hard for me to justify doing it.

I have flown my 90mm a few times and didn't get the thrust-line just right when I carved it out and glued the liner in. I was ready for that, so the plan was to fix it with some shims between the tail section and the fuselage, and maybe put a 90mm TV-unit that I have during winter. If I was to do it again, I would use a hole-saw to get the thrust-tube enlarged accurately. The performance is definitely there and the low-speed acceleration is vey nice. For me it was fun but I think I would probably just go with an XFLY 80mm and get the TV-tail from MRC if I would buy a Gripen today. So with your setup, the performance-gain might not be that big going 90mm, but it's always fun to try.

Airguardian told me to put the TV in straight away, so that's what I'm doing. It won't be pretty, but I hope there will be beauty in the performance.

[Airguardian]

Thanks for the feedback guys!

Can make the nozzle look better by adding the plastic cover back in it as I did! ;)
(It's available as a spare part!)

[flightaddict]

My forward pitot tube kept breaking off at the point of the nose cone so I rebuilt it with a few bits of triangle shaped plywood and a control rod pushed into the a hole drilled in the stump of the factory tube. Then I put a piece of 2mm shrink tubing filled with MinWax polyurethane on the rod to form a rubber ducky pitot that bends instead of breaking.

[kallend]

My forward pitot tube kept breaking off at the point of the nose cone so I rebuilt it with a few bits of triangle shaped plywood and a control rod pushed into the a hole drilled in the stump of the factory tube. Then I put a piece of 2mm shrink tubing filled with MinWax polyurethane on the rod to form a rubber ducky pitot that bends instead of breaking.

I just 3D printed a bunch:

https://www.thingiverse.com/thing:4654706

[TangoVector]

My 90mm Gripen with Thrustvectoring looks like Pingu! Still some finishing touches, so it will be better, but not by much.


NOOT NOOT!

[Airguardian]

Oh hell...
That's pingu nightmare stuff!

If such a nozzle shows up during my sleep it may legit give me PTSD, I swear...

[Airguardian]

Nose LG moved to the aft of the battery compartment, CG now 40mm behind factory molded underwing-marks... plane has never flown better!

Feels like even wind turbulence tolerance has somewhat improved a bit!

[kallend]

Nose LG moved to the aft of the battery compartment, CG now 40mm behind factory molded underwing-marks... plane has never flown better!

Feels like even wind turbulence tolerance has somewhat improved a bit!

Interesting to watch your flat spin exits. My Su35 will fly right out of a flat spin like that but my Gripen always drops its nose and exits nose down. I wonder if the CG is the reason - my Gripen CG is only about 25mm behind the marks.

[Airguardian]

CG is part of the deal.
I still find the Su-35 better suited for flat spins though because you can easily control yaw rate with the differential stabs (roll input) regardless of VT nozzles and thrust.
So when I want out of the spin with the Su-35 I give a brief opposite roll input to arrest the spin, then neutralize the roll input and the spin dampens pretty fast.

For high alpha exit though, the better option is to spin with yaw + pitch input WITH throttle, which is not quite my preferred method otherwise.
So when you want out, you neutralize yaw, the jet rotation dampens and you control high alpha exit with pitch and thrust.

On the Gripen instead, I find there is very little yaw damping so once the jet starts spinning it barely needs encouragement to continue.
When I want to exit I first need to arrest the rotation, and since the elevons are not as efficient for this purpose as the Su-35 FFSs, I instead need to feed counter yaw and add throttle.
This makes the recovery process slower and the jet often 'unstabilizes' when it stops and skids around a bit until you get it back under control. (5:50 on the video)

I will test more the pure yaw+pitch and throttle method to see if I can make high alpha exits as easy as with the Su-35 but so far that hasn't been something I've really tried, so will withhold conclusions for the time being.

In any case, the further aft you set CG, the easier it should be to achieve. Right now I'm not even keeping back pressure on the stick to maintain the spin :)

[TangoVector]

Looks very nice with the nose-gear reversed But the flying looks even better

[Airguardian]

Thanks!
Gonna blush!

[kallend]

CG is part of the deal.
I still find the Su-35 better suited for flat spins though because you can easily control yaw rate with the differential stabs (roll input) regardless of VT nozzles and thrust.
So when I want out of the spin with the Su-35 I give a brief opposite roll input to arrest the spin, then neutralize the roll input and the spin dampens pretty fast.

For high alpha exit though, the better option is to spin with yaw + pitch input WITH throttle, which is not quite my preferred method otherwise.
So when you want out, you neutralize yaw, the jet rotation dampens and you control high alpha exit with pitch and thrust.

On the Gripen instead, I find there is very little yaw damping so once the jet starts spinning it barely needs encouragement to continue.
When I want to exit I first need to arrest the rotation, and since the elevons are not as efficient for this purpose as the Su-35 FFSs, I instead need to feed counter yaw and add throttle.
This makes the recovery process slower and the jet often 'unstabilizes' when it stops and skids around a bit until you get it back under control. (5:50 on the video)

I will test more the pure yaw+pitch and throttle method to see if I can make high alpha exits as easy as with the Su-35 but so far that hasn't been something I've really tried, so will withhold conclusions for the time being.

In any case, the further aft you set CG, the easier it should be to achieve. Right now I'm not even keeping back pressure on the stick to maintain the spin :)

Tried it today. I managed to get to 40mm by moving the pack as far back as it would go.

Agree it flies better, and the flat spin exit was definitely improved.

[Airguardian]

Come all join in on the #churchofbestCG !!

[TangoVector]

I'm a believer! So are there any detailed pictures taken of reversing the nose-gear? This will be a winter mod for me, if it happens.

[Airguardian]

There are now!


You need to perform some minor foam carving so that the wheels fit in place and the steering arm doesn't rub with the side wall, all pretty easy though laborious.

Notice I also had to cut the stock wooden piece with the square gap to install the steering servo in place. Measure well the distances so it will work as expected.

I use Tx programming to make sure that the steering servo doesn't clip or bind when retracted and limit throws to about 15% in retracted gear position. I still want it to be able to move a bit to 'break free of locks' so that the servo doesn't fry if it got stuck in a bad position.

You can use the stock plastic mounting block by relocating it, but it is designed to slide into the foam and mounting it now that the airplane is glued together would take quite some forcing of the foam and I wasn't happy with that, so I used instead some inventive on my end and made a new mounting block made of 2mm plywood planck, a couple of plywood square rods and some additional balsa rods to keep the weight down. Everything is covered in epoxy to prevent wood delaminations when possible. The wooden mounting block itself, I glued to the foam with the 'Kingboxer' contact glue that comes with FW kits. There is plenty of contact area so it should do a great job. So far so good!

[flightaddict]

After about a year of messing around with this bird and finding it too heavy and underpowered to get off my clubs poorly groomed grass strip, I stumbled on a solution. I had this fan that I bought about a year ago to put in my T33 but wound up not using it in favor of the stock fan. It is a Freewing 3658-1875 kv M10336582 12 blade system with the unpainted aluminum can. The Gripen used to take about 250 feet to get off if it ever did and it was a best a 50/50 proposition. Now it gets up in as little as 50 ft with an HRB4000mah and has way more vertical and straight line speed. All this and only about 3 more amps draw and 0.4 lbs more thrust. Flys about the same with a HRB-5000mah, just an extra minute of flight. It still comes down at 3.70 volts after 3.5 minutes with the 4000 and 4 minutes with the 5000. As an extra bonus, this fan weighs 60 grams more so it shifts the CG back a bit. If you want to stay with 6S, this setup is a winner. It's a different plane altogether. Another bonus, I think it sounds better. Here's a first flight video with a HRB4000 and the CG about 1 cm aft. I still had about an inch and half more rearward space on that battery with this system so I could go back a lot on CG. I didn't get off the throttle much as I was having too much fun with higher speed.

https://1drv.ms/v/s!AgyRWjrzvkdorzKS...vy-yt?e=WAHjBK


https://1drv.ms/v/s!AgyRWjrzvkdorzM6pr4MbmtTp4jo?e=xYDbGf

[Airguardian]

I really think the stock fan choice for this bird is really not great. FW should work harder on that aspect of their models IMO.
Still a fantastic jet though, made three flights just the other day in absolute 0-wind conditions and I had an absolute blast!

[Evan D]

Still my favorite. I agree the stock set up is lacking when you add the TV due to about 10% loss of thrust. But left stock without TV it's just right.