Official Freewing JAS 39 Gripen 80mm EDF Jet

[Mizer67]

The stock CG is pretty nose heavy (the lines molded into the fuse). I'm fairly certain that unless you have a "unicorn" of a plane Marktur that any 6S pack you shove in it as far back as you can physically manage you'll be fine w/the CG unless you carve foam or are adding significant tail weight.

I've flown it at 140mm and I'd like to get it a little further back (albeit I'm using a gyro). I'm going for a neutral CG if I can manage it without adding too much more weight. I think it'll help with its performance.

[Mtpisgah99]

i think, if you added this Gripen Thrust Vector Upgrade Set from Freewing - FJ21811011 my be it won't be nose heavy any more with the stock CG measurement.

BRAND: FREEWING / SKU: FJ21811011

https://cdn.shopify.com/s/files/1/1052/4162/products/freewing-80mm-edf-gripen-thrust-vector-upgrade-set-motion-rc-15541834350705.jpg?v=1600718606

[Evan D]

What? Wow where’d you find that?

[HaroldAnderson]

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?

Either use a razor or some of the small blue wire cutters to cut the tail cone at the back of the plane. Then just peel it off the foam. It comes off really easy.

[xviper]

i think, if you added this Gripen Thrust Vector Upgrade Set from Freewing - FJ21811011 my be it won't be nose heavy any more with the stock CG measurement.

BRAND: FREEWING / SKU: FJ21811011

https://cdn.shopify.com/s/files/1/1052/4162/products/freewing-80mm-edf-gripen-thrust-vector-upgrade-set-motion-rc-15541834350705.jpg?v=1600718606

So, does anyone know what the weight difference is between the stock butt end and the VT end?

[RudyD54]

So, does anyone know what the weight difference is between the stock butt end and the VT end?

I recall James saying 80 grams on the video about it.

[xviper]

I recall James saying 80 grams on the video about it.

Not sure if 80g would be enough to offset the weight of a 5000mah battery. Well, at least it'll require less additional tail weight to be added.

[RudyD54]

Not sure if 80g would be enough to offset the weight of a 5000mah battery. Well, at least it'll require less additional tail weight to be added.

It really depends on how much your battery weighs. I’m using rather light 4000s (~590g) and I could get as far back as 147mm by adding 80 grams to the tail to simulate the addition of the VT if I’m recalling correctly (I mentioned it a few pages back) while not adding any other additional weight

[xviper]

I'll only use 5000's in mine. The lightest being just over 700g (Gens Ace @~725g). My heaviest being 850+g, so those will be way too heavy to work in this plane.

[rms]

It really depends on how much your battery weighs. I’m using rather light 4000s (~590g) and I could get as far back as 147mm by adding 80 grams to the tail to simulate the addition of the VT if I’m recalling correctly (I mentioned it a few pages back) while not adding any other additional weight

How did it fly with CG at 147mm? Was it getting neutral inverted?

[Mizer67]

I've been 15mm back of the molded marks in the wings and it's still nose slightly nose heavy there.

It's getting closer to neutral there but still needs some down stick inverted.

[Mtpisgah99]

I'll only use 5000's in mine. The lightest being just over 700g (Gens Ace @~725g). My heaviest being 850+g, so those will be way too heavy to work in this plane.

reasoning of getting this jas39 gripen for me is to do hovering with high alpha and doing it with lighter wt. is ideal for my aircraft. nose heavy is good also if im doing straight forward flight.

VT, 80g additional wt. to tail from CG might work for my 4k or 5k amps batt.

[kallend]

reasoning of getting this jas39 gripen for me is to do hovering with high alpha and doing it with lighter wt. is ideal for my aircraft. nose heavy is good also if im doing straight forward flight.

VT, 80g additional wt. to tail from CG might work for my 4k or 5k amps batt.

You'll need a lot more thrust if you want to hover the Gripen, and you would have no roll control even with the VT unit. You'd be better off with a Sukhoi 35 which is hardly any heavier, has much better T/W, and roll control from the VT.

[Evan D]

I thought the same, 8S for decent power (stock 6S will not hover it) and TVs. With the JF/ HET and 850g of 8S batteries I had to add I think 80g to the tail which IF THE TVS EVER GET IN STOCK should work out well.

BTW, just so you know, "4K or 5K amps" is wrong in many ways. K is kelvin, k is kilo. 4k is 4000 and a 4000 Amp would be huge. 4000 mAh is the right way, milli Amp hour. Amp has a capital A since its a persons name.

[Marktur]

without adding the printed tail cone, with the HRB 6000 6s EC5 connector, pushed all the way to the back, with the missiles attached, if I put my fingers behind but not covering the printed line, I’m at Neutral, slightly nose down balancing point. No cutting of foam yet, just flush against the rear wall. I would guess thats about 10mm further back. I will maiden like this, then make my adjustments after I see it in the air. Hope we will get together and fly later....waiting to hear from the crew...

[xviper]

reasoning of getting this jas39 gripen for me is to do hovering with high alpha and doing it with lighter wt. is ideal for my aircraft. nose heavy is good also if im doing straight forward flight.

VT, 80g additional wt. to tail from CG might work for my 4k or 5k amps batt.

You may to put much more thrust into it to hover or reduce the weight of it considerably. You'll be able to do high, high alpha more easily but a vertical hover may be difficult. Perhaps removing the landing gear may help with the weight but then, you'd be hand launching and belly landing exclusively. The SebArt Mig 29 have thrust to weight ratio of 1.1:1 it just has enough to launch vertically out of my hand. As said by someone else, you need dual nozzles for roll control when there's no airflow over the wings. Otherwise, it'll corkscrew and be hard to control.

[Airguardian]

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?

I'd rather disable trim for canards entirely and set their neutral offset point mechanically.
When you trim the aircraft in flight, you don't really want canards moving with the trim, only elevons.

[kallend]

I'd rather disable trim for canards entirely and set their neutral offset point mechanically.
When you trim the aircraft in flight, you don't really want canards moving with the trim, only elevons.

Much as it grieves me to admit it, I agree with Jandro.

[kallend]

Of all the scale EDFs I have from various manufacturers, the FW Gripen is the only one without ejection seat warnings. I thought maybe the Czech Air Force was unusual in this respect.

Turns out that FW just didn't bother. You can see the warning in this photo of 9234.

[janmb]

'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 ;)

Agreed, it requires surprisingly large amounts of pitch. Improved CG will likely help that (and avoid using positive pitch canards that much).

As usual though, this model is roll sensitive as hell, so definitely don't need a lot there.