Official Freewing JAS 39 Gripen 80mm EDF Jet

[Sam78EDMO]

Hi, I'm thinking of getting the Gripen as ARF version. Ideally I want an EDF to get a thrust to weight ratio above 1. With the EDFs I checked it seems to be a very close call to get there. My question, how heavy is the ARF Version? Motionrc states 2350g for both Version PNP and ARF. How much extra weight would the thrust vectoring set add?

Thank You and best regards

[Evan D]

I have all this info in the RCG thread.

The TV unit weighs 164g. The stock back part weighs 74g. Extensions are 17g.

The TV unit robs about 10% of the thrust you have with a non TV'ed Gripen.

In my opinion if you want more than 1:1 you need to go 8S.

[Sam78EDMO]

I have all this info in the RCG thread.

The TV unit weighs 164g. The stock back part weighs 74g. Extensions are 17g.

The TV unit robs about 10% of the thrust you have with a non TV'ed Gripen.

In my opinion if you want more than 1:1 you need to go 8S.

That thrust reduction kills it otherwise it could work. A rough calculation.

2350g (pnp without lipo according to motion)
- 354g EDF (according to rccastle)
- 80g PNP ESC (rough estimation)
- 50g removing some scale parts like antennas and pilot, (rough estimation)

That would be 1866g

+ 90g TV nozzle
+ 320g FMS 80mm EDF
+ 92g Flyfun 120A ESC
+ 833g light SLS 6s/7000ma/h lipo
+ 50g receiver/telemetry/gyro etc.

That would add up to 3251g with the FMS having 3550g of thrust - 10% = 3195 of thrust
Close call maybe there is a little bit more to remove or to replace with lighter parts.

[Evan D]

I think your biggest mistake there is assuming that the FMS EDF unit makes 3550g of thrust. Most spec'ed thrust numbers are either theoretical or if actual it's with the unit not in a plane.

[xviper]

The main reason to have more thrust than weight is so the plane can hover in a vertical attitude and with only one VT nozzle, there is no roll control when there is no air going over the control surfaces. The one jet that I know of (single TV nozzle) that claims to have such a thrust/weight ratio is the Flex Innovation FlexJet TV. It flies on 8s and has just over 1:1 T/W. It can't hover for long before it starts to roll uncontrollably. It needs just a little bit of forward speed for the control surfaces to work. If you're not going to hover, you don't need more than 1:1 T/W. At or near 1:1 is plenty for all kinds of 3D tricks. Even the stock Gripen can do weird and crazy things with TV. But then, with these things, it's not always a matter of "need". If you want it and gotta have it, that's another story.

[Airguardian]

Technically, a jet may still be able to roll without 'VT-roll' because the air gets dragged around the exhaust and flows over the wings, so some deltawing jets with large control surfaces close enough to the nozzle still retain some roll authority in hover. That said, the FW Gripen with the 'handicapped elevons' that FW designed this jet with (rather small in chord and not full span), plus the fact that the Gripen nozzle sits further aft from the wings on the Gripen... I wouldn't expect it to have that sort of redeeming feature ;)

[kallend]

Hi, I'm thinking of getting the Gripen as ARF version. Ideally I want an EDF to get a thrust to weight ratio above 1. With the EDFs I checked it seems to be a very close call to get there. My question, how heavy is the ARF Version? Motionrc states 2350g for both Version PNP and ARF. How much extra weight would the thrust vectoring set add?

Thank You and best regards

Gripen is not the way to go for reasons described above.

Get a Sukhoi 35 ARF Plus with FMS PRO fans, T/W >1, full 3d vectored thrust. Inexpensive (everything being relative, of course).

[SanExup]

I wish motion sold the Su35 as an ARF plus...

[paulrkytek]

I wish motion sold the Su35 as an ARF plus...

San I just bought the airframe and suspension bits from the spares catalogue then just bought the servos, escs, fms 1900kv fans separate becs wiring etc etc elsewhere, you will then get a true more than 1:1 thrust to weight ratio which if you have the skills ( which I do not) you can vertical hover as per Air Guardian videos . The question is do you have both the time and the inclination to do it ?

Freewing SU35. 1080mm ws, 1610 long. 2 number FMS70mm 3060 1900kv 12blade in-runners 2.6-2.7kg, 2xHobbywing skywalker 80amp escs.
5000mah Turnigy 60-120c 6s 825g flight time 3 to 3.5 mins. 50% expo on everything. Separate rx bec and 2s battery, 10ch rx. Horizontal stab servos Turnigy DMC809 19.5gm 3.8kgf .07 sec digital metal gear ball bearing servos . rudders ,3 vector thrusts 13.5g 2.0KGF Racerstar MG90. Flaperons Corona DS939 13.5g MG 2.5kgKGF. Total completed all up flying weight 3450gms. Thrust 5.4kg ( static FMS figures ) or 1.5 to 1. Assume actual thrust at 70% static =3.78kg which is 1.1 to 1 actual thrust

[Airguardian]

FWIW, hovering the jet is easy enough to pull at some altitude with a good, well set-up gyro on... The tricky part is to do that just a few meters from the ground, THAT is indeed tricky and you may crash if you attempt it without practicing a lot first at higher altitudes and getting a good hang of how the jet behaves in hover and the kind of inputs it takes to control it there.

[SanExup]

The Su35 is one of those planes I find myself hovering over the buy button. It haunts me in a way, I've seen the model fly in person and it looks so good. And it seems really fun to fly once you grok the flight characteristics. I also have a few projects going already. Hopefully they will keep offering it for some time and I can eventually add it to my collection. For now I'll have to settle for Airguardian's entertaining flying.

[kallend]

The Su35 is one of those planes I find myself hovering over the buy button. It haunts me in a way, I've seen the model fly in person and it looks so good. And it seems really fun to fly once you grok the flight characteristics. I also have a few projects going already. Hopefully they will keep offering it for some time and I can eventually add it to my collection. For now I'll have to settle for Airguardian's entertaining flying.

So many other planes are announced, sold for a year or two, and then discontinued.

There's a good reason this Sukhoi is still selling after what, ten years?

[PawPaw]

Just curious…anyone flying the Gripen with canards and TV programmed with Futaba? I watched the canard mixing video for Futaba but I’m thinking adding the TV would exceed the allowable 6 mixes in the T10J? Thanks for your input!

[Sam78EDMO]

Thanks for all your comments and suggestions. For the moment I will scrap the idea completely. I thought as the Gripen is labeled as "intermediate" it would be a good EDF to start with and to go with a custom EDF initially to slowly increase the flying abilities and skill. In reality I would most likely just brutalize it very quickly. I will come back to this once I feel save flying EDFs.

Apart from that I found some videos testing the thrust with varying results. Whats interesting about the FMS EDFs, if you look closely the 3.5kg thrust is for 7S (They just write 25v) which is not even in the recommended specs of the system.
https://www.fmsmodel.com/product/fms...-motor-pro/41/
One the other hand this test comes to exactly 3.5 kg with just 6S

https://www.youtube.com/watch?v=0Fz0lQG1lFs

This test only gets up to 3.1 kg thrust

https://www.youtube.com/watch?v=-1WqIuzTf-k

and another one come sto 3.35kg thrust

https://www.youtube.com/watch?v=0GZmPr904_w

Here is an interesting comparison of FMS and Freewing EDFs. So the timing seems seems to change a lot in terms of thrust.
https://www.rcgroups.com/forums/show...its-comparison

[Evan D]

Welcome to the world of EDFs. I suggest a good flying sport jet first and then work your way up. Something like an Avanti. Use it out of the box and figure out where you want to go from there.

Usually jumping into a higher performing EDF leads to "future disappointment and regret".

[kallend]

Thanks for all your comments and suggestions. For the moment I will scrap the idea completely. I thought as the Gripen is labeled as "intermediate" it would be a good EDF to start with and to go with a custom EDF initially to slowly increase the flying abilities and skill. In reality I would most likely just brutalize it very quickly. I will come back to this once I feel save flying EDFs.

Apart from that I found some videos testing the thrust with varying results. Whats interesting about the FMS EDFs, if you look closely the 3.5kg thrust is for 7S (They just write 25v) which is not even in the recommended specs of the system.

1. The "official" thrust values are generally obtained with bench power supplies, not battery packs, so there is no voltage sag.

2. The "official" thrust values are on open test stands, so there are no losses associated with ducting, turbulence from cheaters, etc.

3. So the only values that really matter are installed values in your specific plane, which may be as much as 15% (or even more) below the "official" values.

4. When comparing thrust values from different sources, it is important to know things like the brand, capacity and age of the battery pack, the air temperature (this makes a difference), the pack temperature (makes a huge difference).

5. I hesitate to specify "C" values of the pack, since these are mostly mythical numbers anyway.

6. The links to tests that you provided were not using laboratory grade measuring equipment - so take their accuracy with a small grain of salt.

[kallend]

Thanks for all your comments and suggestions. For the moment I will scrap the idea completely. I thought as the Gripen is labeled as "intermediate" it would be a good EDF to start with and to go with a custom EDF initially to slowly increase the flying abilities and skill. In reality I would most likely just brutalize it very quickly. I will come back to this once I feel save flying EDFs.

Apart from that I found some videos testing the thrust with varying results. Whats interesting about the FMS EDFs, if you look closely the 3.5kg thrust is for 7S (They just write 25v) which is not even in the recommended specs of the system.
https://www.fmsmodel.com/product/fms...-motor-pro/41/
One the other hand this test comes to exactly 3.5 kg with just 6S

https://www.youtube.com/watch?v=0Fz0lQG1lFs

This test only gets up to 3.1 kg thrust

https://www.youtube.com/watch?v=-1WqIuzTf-k

and another one come sto 3.35kg thrust

https://www.youtube.com/watch?v=0GZmPr904_w

Here is an interesting comparison of FMS and Freewing EDFs. So the timing seems seems to change a lot in terms of thrust.
https://www.rcgroups.com/forums/show...its-comparison

From your original post it was not clear that this is your first EDF.

In that case I retract my Sukhoi 35 suggestion and agree with Evan. Get a simple sport jet first, preferably an inexpensive one.

[Airguardian]

Avanti is a good recommendation.

[PawPaw]

Found my solution with Futaba: My Gripen now has canard/aileron, canard/elevator, TV mixing, and A3L gyro on elevons only with my T10J. Took all 10 channels with the gyro mode switch, 9 without. Used all 6 mixes available in the T10J and a SBD-1 SBus decoder added to my R3008SB but it all worked out. Just need some decent maiden weather!

[HockeyMac!]

I did quite a bit of work to keep the weight down, but also shift the CG further back. As you can see below, I flipped the nose gear around, ty airguardian for walking me through this, added the light burner, cut two holes in the battery compartment so the battery sits further aft, and finally moved the ESC about 1 inch back from its present position. The ESC was by far the easiest here to do.

It's got 6 coats of minwax and I'm waiting for the paint to arrive and then will add the ordinance.