Official Freewing JAS 39 Gripen 80mm EDF Jet

[kallend]

Hey Kallend,

Yes I did use your design! Many thanks for that and credits for a nice design ;) It worked like a charm.
So what I understand is that this extra weight is fine in the case of the Gripen. Not to worry too much about it.

Extra weight is never a good thing, but it's better than havng an out-of-balance plane.

[Ankor]

Hey Kallend,

Yes I did use your design! Many thanks for that and credits for a nice design ;) It worked like a charm.
So what I understand is that this extra weight is fine in the case of the Gripen. Not to worry too much about it.

[kallend]

Hey guys,

I maidened my Gripen a couple of days ago. It was a blast to fly and everything went well! I do have a question though. In order to balance it I had to replace the factory tail with a 3D printed one plus some extra lead weights. This added in total about 120gr to the plane. I am generally against adding dead weight to my planes but this one I couldn’t balance without it. I am balancing at 135mm btw. It’s a lot of extra weight though and I am curious how it is for your Gripens. I have read that it’s better to replace the EDF with a heavier one but I don’t want to do this right from the start. Please share how you balanced your models as well as any advice for that.

Cheers!

As the designer of a "Heavy Nozzle" (maybe you used my design) the farther back you add weight to balance the plane at the proper place, the less weight you need to add, which is why the nozzle is the best place to add weight,

https://www.thingiverse.com/thing:4650359

Just putting in a heavier fan unit requires more additional weight because it is closer to the CG, and as Evan stated, you need a LOT of additional power from the new unit to make up for that extra weight. Reversing the nosegear is an option but is a lot of work. With an even lighter pack than your 4000 you will be cutting into flight time.

Better to add 120g extra and have the correct CG than add nothing and have a nose heavy airplane,.

Even with a TV unit it can do with a little more weight in the tail: https://www.thingiverse.com/thing:4763795

[Evan D]

It flies great, even my heavier 8S does, but my favorite is my 6S on with TV.

[Ankor]

Thanks again mate. Then it doesn’t sound much different than you since I don’t have the missiles. Do you think that I should find ways to reduce that extra weight or do you thing that 120 grams are not that bad after all? (For this plane ofc)

[Evan D]

You have a heavier battery but you also are not balancing as far back. On the one I do not have TVs on, by memory, about 100g. Oh, and I fly with wing tip missiles that add tail weight.

[Ankor]

Thanks for the detailed reply! I indeed don’t have the tv unit and that’s why I opted for the 3D printed nozzle. It also adds weight. As for the batteries I am flying with the admiral 4000s pro which weigh 625g. I ll try some of your options but could you also tell me how much dead weight you added approximately? 120gr in my case feels a lot IMO.

[Evan D]

It's all how much weight how far forward or rearward. I assume you either do not have the TV unit (it adds tail weight) and/ or a heavy battery (nose weight).

Options,
Lighter battery. I use a 545-575g 5000mAh Power Hobby in my three Gripens (one is 8S and I add a 2S to that)
TV unit, even if you don't use it a lot it's a good way to add weight very far aft.
Remove weight up front, the pilot, the magnets in the nose, move the nose retract aft.
Dead weight, even with a light battery and TV I have had to add weight to all mine to get the balance around 30mm behind the CG marks. On the stock 6S with TV I added just a little but on my 8S and stock 6S without TV it was a lot more. Add it into the tail cone if possible, the further back the better.

Putting in a heavier EDF unit, unless it is much more powerful, to me isn't a good idea as the fan is not that far back. If you modify where the fan is to be further back that wold work but it's not easy to do.

[Ankor]

Hey guys,

I maidened my Gripen a couple of days ago. It was a blast to fly and everything went well! I do have a question though. In order to balance it I had to replace the factory tail with a 3D printed one plus some extra lead weights. This added in total about 120gr to the plane. I am generally against adding dead weight to my planes but this one I couldn’t balance without it. I am balancing at 135mm btw. It’s a lot of extra weight though and I am curious how it is for your Gripens. I have read that it’s better to replace the EDF with a heavier one but I don’t want to do this right from the start. Please share how you balanced your models as well as any advice for that.

Cheers!

[Airguardian]

Definitely move the CG back and max throws out.

[Evan D]

Sorry to hear that. Tall-ish grass? Wet? Maybe moving the CG back a little more (mine is 30-35mm aft of marks)...

[Yellowred]

Hi guys, planned maiden flight with the Gripen today, light winds and warm sunshine, c of g about 10mm rear, 5000mah Lipo, doesn't have Tv, we have a 65metre grass strip and it wouldn't rotate, tried a couple of times, Have it all mixed as per the Motion Recomendations, all that happened was the roll off strip into the long grass pulled a retract loose, disappointed

[paulrkytek]

Hi everyone, newbie here and just got my Grippen with Vector Thrust.

There was one comment on the Grippen VT motionrc comment that mentioned "Twitching servo fix" and the buyer mentioned that ".. The servo cables go right along the motor wires under the tail and we ended up having a twitching yaw servo on the thrust vectoring due to interference whenever we throttled up. Almost had a catastrophic crash on the first take of.."

Before assembling it with VT, is there any concern I should be aware of like placement or shielding it regarding this issue.
Thanks in advance for any comments and looking forward to flying the Grippen soon.

just check that all 3 servo wires are crimped tightly to the pins in case one has come loose as this also can cause a hit and miss signal

[kallend]

Actually you can have AS3X on elevons and also on canards/VT IF (and only if) your TX allows the elevon wing type AND also normal "tail" type. (the "tail" being the canard and/or VT pitch)

AFAIK only the iX14, iX20, DX18 and DX20 allow this.

The thing is, all flight surfaces declared in a wing or tail type will be set up for stabilization during forward programming, so you'll get pitch stabilization on the elevons and on the canards/VT.

I tried it but decided I wanted different rates on the VT from the elevons, which is why I ended up with the AS3X and the HobbyEagle.

Update: the new(ish) NX20 has elevons + canard as an option.

[Evan D]

And it's thrust vectoring. You're guilty of that one...

"Once is happenstance, twice is coincidence, three times is enemy action"; Goldfinger, in "Goldfinger" by Ian Fleming.

[kallend]

Hi everyone, newbie here and just got my Grippen with Vector Thrust.

There was one comment on the Grippen VT motionrc comment that mentioned "Twitching servo fix" and the buyer mentioned that ".. The servo cables go right along the motor wires under the tail and we ended up having a twitching yaw servo on the thrust vectoring due to interference whenever we throttled up. Almost had a catastrophic crash on the first take of.."

Before assembling it with VT, is there any concern I should be aware of like placement or shielding it regarding this issue.
Thanks in advance for any comments and looking forward to flying the Grippen soon.

"Once is happenstance, twice is coincidence, three times is enemy action"; Goldfinger, in "Goldfinger" by Ian Fleming.

[ArmorBolt]

Well... All the servo wires go aft along the top of the fuselage, on top of the ESC, along the motor and the wing servo wire then go outboard and the rudder and TV servos wires continue aft. If you were worried you should be concerned with all of them. That person probably had one bad servo or all the servos would show effect.

I found the review you are quoting which also says "I slightly changed the position of the extension plug under the tail and made sure the servo wire plugs were extra tight which resolved the issue.".

Sounds like he may not have plugged the servo in tightly.

Thanks, i will make sure extensions are plugged in tightly.

[Evan D]

Well... All the servo wires go aft along the top of the fuselage, on top of the ESC, along the motor and the wing servo wire then go outboard and the rudder and TV servos wires continue aft. If you were worried you should be concerned with all of them. That person probably had one bad servo or all the servos would show effect.

I found the review you are quoting which also says "I slightly changed the position of the extension plug under the tail and made sure the servo wire plugs were extra tight which resolved the issue.".

Sounds like he may not have plugged the servo in tightly.

[ArmorBolt]

Hi everyone, newbie here and just got my Grippen with Vector Thrust.

There was one comment on the Grippen VT motionrc comment that mentioned "Twitching servo fix" and the buyer mentioned that ".. The servo cables go right along the motor wires under the tail and we ended up having a twitching yaw servo on the thrust vectoring due to interference whenever we throttled up. Almost had a catastrophic crash on the first take of.."

Before assembling it with VT, is there any concern I should be aware of like placement or shielding it regarding this issue.
Thanks in advance for any comments and looking forward to flying the Grippen soon.

[Gravythe clown]

Raced a high performance Vulcan today. It’s was either a match or my Gripen was a bit faster. With the new EDF unit it’s really come alive.
I also did a unrestricted take off like I do with the mirage.
later a did a top end climb starting 20-40’. I made it to 832’ before she stalled out. I had just enough to nose her over.
still getting 4-5 minutes of flight off the 6000.

Gravy