Official Freewing JAS 39 Gripen 80mm EDF Jet

[xviper]

Yes, quite the conundrum.

The jet definitely needs the tail weigh of the TV, but also needs all the thrust it can get and then some. I'd hate to lose any thrust that I can get.

I'll likely tack on the TV like the existing nozzle and try them back to back.

Mind you, I bought the ARF and put the FMS 2100kv inrunner and matching FMS ESC in it, so there's that little extra bit of grunt already. As it sits right now, it balances right at the factory marks with the Gens Ace 5000. I'd like to get it back a few mm more.

[Mizer67]

That may be the only remaining reason for me to get the nozzle - extra weight on the tail end without having to add lead. On the other hand, lead weight may be more advantageous if the nozzle is less efficient at shoving thrust out the back.

Yes, quite the conundrum.

The jet definitely needs the tail weigh of the TV, but also needs all the thrust it can get and then some. I'd hate to lose any thrust that I can get.

I'll likely tack on the TV like the existing nozzle and try them back to back.

[JLambCWU]

I find the jet pretty lacking in control authority when AoA gets too high and speed drops (hence my recent crash shown in the previous video ensued) The jet has superb low-speed high-alpha handling but it has a limit, after which TV would provide the authority that current aerodynamic controls can't provide. But if you think installing the nozzle doesn't add any sort of value, you are indeed not flying the jet to its limits.

ANY aircraft will be lacking in control when the AoA gets too high. (hence the wing drop) A single TV nozel won’t change this.

Having flown both the TV and standard models, the TV doesn’t provided any measurable amount of deck angle above the stock aircraft in high AOA. It adds too much weight for any improvement in directional thrust.

The stock aircraft will comfortably hold the same or higher AOA in STABILIZED flight.

[HaroldAnderson]

4 more flights with smoke on the swedish queen, videos coming... soon enough ;)

I seriously wonder what went wrong at the factory... the jet was supposed to look like this:


Instead we got jets that we can't barely tell decal apart from fuselage grey... :'(

Oh wow!! If mine look liked that I wouldn't be considering painting it.... I guess they got their greys mixed up on the waterslide decals.

[Pogo]

Has anyone planned on extending the elevons inboard?

Yes, I've considered it but abandoned the idea for the reasons Airguardian mentioned. I'd want to use the inboard sections as flaps and the dimensions of the existing surfaces would make it a lot of work- doable but...
Tom

[Airguardian]

I thought about it but got discouraged by the fact that it is in the way of one of the wing's attachment points with screw.
If implementing full-span elevons like the fullscale jet, you'd need to 'disable' that joint, move it forward or something.

[TangoVector]

Has anyone planned on extending the elevons inboard?

[xviper]

I figure there won't be a weight penalty as I'll remove the lead I added and it should be the same weight more or less.

That may be the only remaining reason for me to get the nozzle - extra weight on the tail end without having to add lead. On the other hand, lead weight may be more advantageous if the nozzle is less efficient at shoving thrust out the back.

[Airguardian]

4 more flights with smoke on the swedish queen, videos coming... soon enough ;)

I seriously wonder what went wrong at the factory... the jet was supposed to look like this:


Instead we got jets that we can't barely tell decal apart from fuselage grey... :'(

In your experience, how should the gyro pitch gains be apportioned between the elevons and the canards?

I'd say set canards' gain as high as the gyro will take without oscillations, and then add some more on the elevons if you feel like it.

Canards tolerate being very sensitive as being close to CG they don't make as much pitching moment.
Also the stock actuation system quite limits their range and speed so you can abuse gain on them.

Ultimately I'd decide on what looks most scale for me. But I can't tell yet because I still need to get my CG aft to get proper scale results.

Too much gain could make the plane 'snap' too hard when finalizing maneuvers and overshooting so at that point I'd probably back off a bit.

It also depends on how much I shift CG aft. Usually the more 'tail-heavier' the higher gain you want to keep the plane in check.

That looked more like an unplanned landing than a crash. :-) I've got two of those right wing tip stalls on video I guess I should upload them to YouTube also. Mine were both with gear down. On one I was able to take off again. The other one was in a crosswind and required gluing the left retract back in place and straightening the landing gear where it bent at the notorious 4 hole weak point...

You know... it happens!
Not sure gear down is best option in case it does flop... besides ripping gear off it can also cause the jet to bounce and that has potential for more damage.
Glad to hear it wasn't bad anyway :)

Wish Freewing/Motion made a reissue of the LG struts with improved rigidity and getting rid of the unnecessary holes. It's quite an annoying aspect of this jet :'(

Having seen Harold's videos, I'm thinking I may forget the VT nozzle for this plane. The plane appears to be able to do stuff that one would have previously thought it could only do with VT. In its stock form, the Grip won't hover anyway, so it may be a pointless add-on. (The VT nozzles may serve a more valuable purpose with the big MiG, though.)

Disagree. After 38 flights with the Gripen I find the jet pretty lacking in control authority when AoA gets too high and speed drops (hence my recent crash shown in the previous video ensued), and clearly Harold agrees as he's had two more just like that. The jet has superb low-speed high-alpha handling but it has a limit, after which TV would provide the authority that current aerodynamic controls can't provide. Of course, TV will reduce Gripen performance in speed and thrust, so if you value that more, then don't install it. But if you think installing the nozzle doesn't add any sort of value, you are indeed not flying the jet to its limits.

[Evan D]

Good point. I'm planning on buying the TVs and if and when my spot gluing of the rear section comes loose installing it. The only hesitation is if the outlet is more inefficient in size and shape than the stock one, that is with the nozzle straight aft as It'll be less efficient with the nozzle deflected. I figure there won't be a weight penalty as I'll remove the lead I added and it should be the same weight more or less.

Having seen Harold's videos, I'm thinking I may forget the VT nozzle for this plane. The plane appears to be able to do stuff that one would have previously thought it could only do with VT. In its stock form, the Grip won't hover anyway, so it may be a pointless add-on. (The VT nozzles may serve a more valuable purpose with the big MiG, though.)

[janmb]

I plan to modify it myself.

I already did overlay nozzles for the Eurofighter TV. Been up on Thingiverse for a long time.

Yeah, the nozzles definitely need some love. The foam finish in the kit certainly doesn't look too impressive.

[xviper]

Having seen Harold's videos, I'm thinking I may forget the VT nozzle for this plane. The plane appears to be able to do stuff that one would have previously thought it could only do with VT. In its stock form, the Grip won't hover anyway, so it may be a pointless add-on. (The VT nozzles may serve a more valuable purpose with the big MiG, though.)

[janmb]

VT just showed up at RCC:

https://www.rc-castle.com/index.php?route=product/product&product_id=8964

Shouldn’t be long now before Motion gets them in.

Got mine in the main - will not wait. Currently doing my turbine conversion, so great boon to get it all done at once rather than having to pull it apart again later for VT retrofit.

[kallend]

Yes, it looks a lot like my old 90mm F-18E V2 that was made of EPS foam. If I get one I may have to modify your nozzle to fit it.

I plan to modify it myself.

I already did overlay nozzles for the Eurofighter TV. Been up on Thingiverse for a long time.

[HaroldAnderson]

Flying with smoke is terribly addicting.

You have been warned!

That looked more like an unplanned landing than a crash. :-) I've got two of those right wing tip stalls on video I guess I should upload them to YouTube also. Mine were both with gear down. On one I was able to take off again. The other one was in a crosswind and required gluing the left retract back in place and straightening the landing gear where it bent at the notorious 4 hole weak point...

[HaroldAnderson]

I don't like the job they did on the nozzle. It looks pretty cheesy.

Yes, it looks a lot like my old 90mm F-18E V2 that was made of EPS foam. If I get one I may have to modify your nozzle to fit it.

[Evan D]

Same picture that's been on Motions site for a long time. Like other TVs the outside of the nozzle is foam that can be easily peeled off and a better looking 3D printed part put there.

On yesterdays pod cast James said again the TVs are next year. I wish they would update the web site with more info and a better arrival date.

I don't like the job they did on the nozzle. It looks pretty cheesy.

[kallend]

No one said gyros were 'needed' as such, now, did any?

That said, if you want to make the best out of it, it is not a bad idea. The reasons have been covered quite in detail already.



Gyros helping with wind gusts (for me) is a nice second derivative of having them installed but not the main reason I do install them to begin with so... ;)

In your experience, how should the gyro pitch gains be apportioned between the elevons and the canards?

[kallend]

VT just showed up at RCC:

https://www.rc-castle.com/index.php?route=product/product&product_id=8964

Shouldn’t be long now before Motion gets them in.

I don't like the job they did on the nozzle. It looks pretty cheesy.

[Pogo]

I decided to go ahead with the LE flap modification I've been considering and got a good start on one wing, cutting out the shape and installing hinges, the servo etc. Nothing is finalized (glued) and it's very much a WIP but looking pretty good so far, I think. The LE drops about 25 degrees right now, which doesn't look like much, but as it's such a large surface span-wise, and on the front of the wing, I'm thinking it may be enough travel, but of course don't know. At the moment I'm trying to figure out a good way to cover the gap on the underside of the hinge line when the flap isn't deployed. Comments and ideas are more than welcome.
Christmas vacation started today so I'll be able to get some quality time in the aerospace facility uninterrupted by work.
Tom