Official Freewing JAS 39 Gripen 80mm EDF Jet

[rms]

Are doing som small maintenance on my Gripen. So I fly the Mirage. Almost as good as the Gripen in hige alpha ;-)

[radfordc]

That is so.

[Airguardian]

That is not so.

[radfordc]

Forcing an aircraft to yaw means the inner wing flying slightly slower than the outer wing, which in turn means the inner wing generating less lift than the outer one. Which in turn means that the yaw you commanded also causes roll in the same direction.

The effect you describe is not the primary reason that yaw/roll coupling occurs...in fact it's nearly negligible. The reason a plane rolls when yawed is almost all due to dihedral effect. An aircraft with positive dihedral will roll in the same direction that the rudder is moved. An aircraft with negative dihedral (anhedral) will roll opposite the direction that the rudder is moved. Zero effective dihedral often results in no roll coupling at all (as Kallend pointed out with finely tuned pattern ships).

[kallend]

Been waiting for Gripen to come back in stock in the European Warehouse since November. Not Freewing or Motion RC fault just one of those things. While I have been waiting for the Gripen to come back in stock it has got me thinking. The FMS Rafle is due out soon and this has a more powerful motor in the model. Mmmm should I go for that. I do not think anyone has one yet because they are not avaliable yet. But it got me thinking 🤔

I put the FMS motor/fan in my Gripen. Very easy modification and not too expensive.

[Evan D]

I did add, and then removed, that the one big thing I personally don't like is that it's FMS and distributed for us in the US by HH. In general I like FMS (and EFlite) but there are certain design things I think FW does better. I do hold a grudge about HH and their marketing department and to some extent customer service. The grudge is mostly that they used to be so awesome and now just aren't.

Since Hobby Zone sells it, I'll probably buy one from them.

But that said FW and Motion aren't perfect either. As some say it's a first world problem.

[Captain Moron]

Just been study the Rafale and like Evan D states, there are thinks that are good about the Rafale and some that are not so good. The one thing the Rafale does not have is the Motion RC Customer Service and that is a big factor to me. So I think I wait until the Gripen is back in stock.Looks like we are going to be in this Lockdown until the spring so there is no hurry and I am sure the Gripen will back in stock by the spring 😊

[Evan D]

The aircraft are sufficiently different that, to me, one does not substitute for the other. That said there are things about this specific rendition of the Rafale I like (there are others I don't). As far as the more powerful motor, I think you have to look big picture and think about the aircrafts weight and the ducting losses of a bifurcated exhaust versus the Gripens clean single. But it's a good thing to be thinking about.

[Captain Moron]

Been waiting for Gripen to come back in stock in the European Warehouse since November. Not Freewing or Motion RC fault just one of those things. While I have been waiting for the Gripen to come back in stock it has got me thinking. The FMS Rafle is due out soon and this has a more powerful motor in the model. Mmmm should I go for that. I do not think anyone has one yet because they are not avaliable yet. But it got me thinking 🤔

[Evan D]

When I stated that yaw really effects roll in my earlier post I want to clarify that I meant during high alpha or very low/ zero airspeed Using the yaw TV really effects roll. And not necessarily in a bad way, you can do some neat things with it.

I also said way back after my first TV flights with the Gripen to be careful using a lot of yaw TV input because the plane will do a quick corkscrew and end up pointed straight down and to play with it at altitude.

Before the TVs my Gripen was flying awesome. After I put them on it was still awesome. I did turn the pitch mix down a slight bit but it tracked perfect and had no change in pitch with or off throttle. The only down side was I was going through the battery much faster.

Later last week I went back and cut the nozzle foam and put on the plastic nozzle from the old rear fuselage. I also redid the centering of the TV servos and up’ed the yaw rate.

When I flew it Sunday it was horrible. Flew very nervous and would come out of a pitch flip tilted. Also it dove on throttle and pitched up off. A turn of the ball link fixed the pitch issue and moving the CG forward 3mm calmed the twitching.

Lookin at the TV on the bench maybe glueing the plastic nozzle may have changed the exit just a little. I re centered as best I could and have 8 sets of batteries for today.

Mo better. A tweak here a tweak there and pushed the battery back to the more tail heavy spot and all’s well. Surprisingly even one turn of the yaw ball link on the TV makes a lot of difference in feel. As I’ve said before the new TV ball has a lot more authority than previous FW TVs.

And yaw really effects roll...

[janmb]

I'm curious as to how the Su-57 would react in that regard, since the way the vertical stabs are canted means they must geometrically generate a fair amount of 'opposite-roll' moment when applying yaw, potentially compensating part of the aerodynamically-coupled, yaw-induced roll. :)

Yup, that may very well be one of the exceptions

[HaroldAnderson]

The viking jet is at it again!

Nice flights. You are having too much fun performing Gripen ballet !! I can rip around with any of my jets but this one is so much fun to fly slow and graceful. A high alpha slow pass at 70% throttle coming within a few feet of you sounds so cool too...

[Airguardian]

It is hard to imagine an aircraft with a geometry that has none of that coupling, nor have I ever encountered one yet.

I'm curious as to how the Su-57 would react in that regard, since the way the vertical stabs are canted means they must geometrically generate a fair amount of 'opposite-roll' moment when applying yaw, potentially compensating part of the aerodynamically-coupled, yaw-induced roll. :)

[Evan D]

Flew 8 sets of batteries today dialing it in a bit better. Had a great time with it. Really a special airplane.

[janmb]

Perhaps you've not flown a competition level pattern plane.

I have.

In general you wouldn't notice it much there at all since F3A and similar are flown in the vertical only plane, so you don't do any yawing in wings level orientation at all anyway. But if you try, you will learn that these models follow the laws of physics too.

[kallend]

Obviously neither have I, but it is a matter of fairly basic physics causing this.

Forcing an aircraft to yaw means the inner wing flying slightly slower than the outer wing, which in turn means the inner wing generating less lift than the outer one. Which in turn means that the yaw you commanded also causes roll in the same direction.

It is hard to imagine an aircraft with a geometry that has none of that coupling, nor have I ever encountered one yet.

Perhaps you've not flown a competition level pattern plane.

[janmb]

Well, I haven't flown all aircraft, or even 99% of them, but I think that may be an overestimate based on my experience, both full size and model.

Obviously neither have I, but it is a matter of fairly basic physics causing this.

Forcing an aircraft to yaw means the inner wing flying slightly slower than the outer wing, which in turn means the inner wing generating less lift than the outer one. Which in turn means that the yaw you commanded also causes roll in the same direction.

It is hard to imagine an aircraft with a geometry that has none of that coupling, nor have I ever encountered one yet.

[kallend]

Originally posted by Evan D View Post

"And yaw really effects roll..."

As it does on 99% of all aircraft.

Well, I haven't flown all aircraft, or even 99% of them, but I think that may be an overestimate based on my experience, both full size and model.

[janmb]

As I’ve said before the new TV ball has a lot more authority than previous FW TVs.

Strongly doubt that. The ball itself, and the angles it can produce, is not significantly different from the older 70mm balls.

A perceived experience of this VT having more authority, if at all correct, is probably more down to the rest of the airframe than the VT unit itself.

And yaw really effects roll...

As it does on 99% of all aircraft.

[Evan D]

Before the TVs my Gripen was flying awesome. After I put them on it was still awesome. I did turn the pitch mix down a slight bit but it tracked perfect and had no change in pitch with or off throttle. The only down side was I was going through the battery much faster.

Later last week I went back and cut the nozzle foam and put on the plastic nozzle from the old rear fuselage. I also redid the centering of the TV servos and up’ed the yaw rate.

When I flew it Sunday it was horrible. Flew very nervous and would come out of a pitch flip tilted. Also it dove on throttle and pitched up off. A turn of the ball link fixed the pitch issue and moving the CG forward 3mm calmed the twitching.

Lookin at the TV on the bench maybe glueing the plastic nozzle may have changed the exit just a little. I re centered as best I could and have 8 sets of batteries for today.

Mo better. A tweak here a tweak there and pushed the battery back to the more tail heavy spot and all’s well. Surprisingly even one turn of the yaw ball link on the TV makes a lot of difference in feel. As I’ve said before the new TV ball has a lot more authority than previous FW TVs.

And yaw really effects roll...