Official Freewing JAS 39 Gripen 80mm EDF Jet

[Sekhet]

Just for what it's worth, I have and fly a BVM Chengdu J-10, which is similar to the SAAB JAS 39 Gripen, and I have it set up on two Bavarian Demon Cortex Pro gyros. One is for the canards only and the other for elevons, rudder and nose gear.
We tried to do it with one but when the gyro was set so it would have any damping effect it would cause the canards to fight the elevons setting off a feedback loop that, if left on, could destroy the aircraft. With two gyros that have been properly programed and controlled by their own switch, all of the control surfaces work with each other with the added bonus of being able to do high alpha maneuvers like the cobra and still be in complete control. By the way this model does have thrust vectoring as well.

[Airguardian]

That's interesting...

Reducing gain on the gyro didn't solve it?
I don't see how they would be fighting each other...
If anything, they would be helping each other 'too much'.

Unless you mean you used high gain to achieve better control in low-speed and this messed up the high-speed envelope.

I'd like you to elaborate on this, please!
Valuable information!
I have been considering the Cortex Pro for other builds...

Basically the canards work exactly as the two elevon servos.[...]
So a single gyro probably will work.

With that setup and cross linking the canards and elevons, I think yes. But I don't think it's optimal.

[Sekhet]

That's interesting...

Reducing gain on the gyro didn't solve it?
I don't see how they would be fighting each other...
If anything, they would be helping each other 'too much'.

Unless you mean you used high gain to achieve better control in low-speed and this messed up the high-speed envelope.

I'd like you to elaborate on this, please!
Valuable information!
I have been considering the Cortex Pro for other builds...

First off, I trust all of my turbines to the Demon Cortex Pro. That being said, during the testing of the J-10, the gain was fully adjustable in flight so the optimum master gain for each flight mode could be determined and then later fine tuned for each axis via the pc program. This works well with most hobby grade gyros when the aircraft has dedicated control surfaces for each axis, pitch, roll and yaw. Most Hobby grade gyros can also handle elevons with out much trouble. When you throw canards into the mix is when it can become a little more complex. If you use the canards for pitch only and the elevons for roll and pitch then the gyro logic has to use more compute cycles to get the proper output for damping and in this example the elevons respond slower then the canards though only by a fraction of a sec. At a low gain this lag is not even noticed but nether is the wind damping effect. Now if you use the elevons and the canards for both pitch and roll control, like the J-10, then a single gyro will begin to "hunt" for the correct response and the oscillations will become more pronounced, even at lower gain settings, settings that don't do anything towards "turning off the wind". Isn't that what we are using the gyro for to begin with? With two gyros setup, as in my J-10, each one was tested on each axis one at a time for optimum usable gain in each flight mode and ultimately blended into three flight modes, "normal", "landing" and "high alpha", oh and of course "gyro off". I must state the the J-10 and the rest of my turbines fly very well without the gyros but I do go to many fly-ins and competitions where the wind isn't blowing straight down the runway or the wind a altitude pushes your figures around so using the gyro helps make a good maneuver look great and a crosswind landing look effortless.

To date I have never put a gyro in a fixed wing airframe without first flying it to make sure it was sound and setup correct.
I have also never put a gyro on any of my foamy jets, T-45 Goshawk, Stinger 90 Extreme, AL37 Airliner,T-33 Shooting Star or MiG-29 Fulcrum, and have no plans to put one on the Gripen.
Freewing and Alpha have designed these aircraft to be pilot friendly and they are! So I truly don't see the need for a gyro on any of them.

I know, I went off on a tangent, it's late here and I'm running on very little sleep.

[slumi]

Hi Airguardian,

so two gyros seem to be better.
Is it possible to do first flights leaving the canards in neutral position ?!?

[janmb]

Instead, I would use a separate gyro for elevons and canards.

Or simply using a sufficiently good gyro that easily deals with it all, such as the cortex pro. Expensive as hell, but best on the market by far.

I'm sure the top hobby eagle gyro would cope just fine with this setup as well, but no direct experience there so don't quote me on it


QUOTE=Airguardian;n276830]Transmitter just outputs pitch and roll. Mixing has to be made at gyro level when doing this.
Read the manual of your gyro. Everything should be detailed in there. If you are using a gyro you must read the instructions and familiarize with its operation. ;)[/QUOTE]

+1!

A gyro is not a free card out of having to study and learn. If anything, the exact opposite.

[kallend]

Or simply using a sufficiently good gyro that easily deals with it all, such as the cortex pro. Expensive as hell, but best on the market by far.

I'm sure the top hobby eagle gyro would cope just fine with this setup as well, but no direct experience there so don't quote me on it

Transmitter just outputs pitch and roll. Mixing has to be made at gyro level when doing this.
Read the manual of your gyro. Everything should be detailed in there. If you are using a gyro you must read the instructions and familiarize with its operation. ;)

+1!

A gyro is not a free card out of having to study and learn. If anything, the exact opposite.

Cortex Pro is listed at US$299 I'm sure it's very good.

I'd use two HobbyEagle gyros.

[Sekhet]

Hi Airguardian,

so two gyros seem to be better.
Is it possible to do first flights leaving the canards in neutral position ?!?

The best advice anyone can give you regarding the Freewing JAS-39 Gripen or any model, is to setup the aircraft per the manual, maiden it on conservative throws. Use the first flight to trim for your flight modes, and observe how it reacts to the wind. Then if you feel the need to use a gyro to smooth things out a bit, by all means go ahead. A gyro is not a bailout, autopilot or the magic reset button that some pilots seem to think it is. A gyro, when setup correctly, is there to make the small corrections so the pilot has a lighter workload.

And as for leaving the canards locked off in neutral, not having the model yet, but going on the information from those that have flown it, I wouldn't .

[Airguardian]

If you use the canards for pitch only and the elevons for roll and pitch then the gyro logic has to use more compute cycles to get the proper output for damping and in this example the elevons respond slower then the canards though only by a fraction of a sec. At a low gain this lag is not even noticed but nether is the wind damping effect. Now if you use the elevons and the canards for both pitch and roll control, like the J-10, then a single gyro will begin to "hunt" for the correct response and the oscillations will become more pronounced, even at lower gain settings,

Thanks for your reply, this is interesting.
I wouldn't have predicted that to be an issue, so it's good to know that it can be!

settings that don't do anything towards "turning off the wind". Isn't that what we are using the gyro for to begin with?

Not me. At least not as a primary concern.
My first priority with gyros is to make post stall maneuvering more predictable and eassier to handle, and to be able to use canards more as a 'flow control device' than as a pure pitching surface, which is not its role on the full scale aircraft.

Being able to make the jet feel locked in windy conditions is a nice and desireable 'secondary effect' for me personally. ;)

To date I have never put a gyro in a fixed wing airframe without first flying it to make sure it was sound and setup correct.

That's the way to go. One should trim the aircraft very well and get to know how it flies and what are its vices before masking them with a gyro.

A gyro is not a bailout, autopilot or the magic reset button that some pilots seem to think it is. A gyro, when setup correctly, is there to make the small corrections so the pilot has a lighter workload.

Absolutely! ;)

And as for leaving the canards locked off in neutral, not having the model yet, but going on the information from those that have flown it, I wouldn't .

Probably not a big deal, but then again, I wouldn't do that either.

[janmb]

Cortex Pro is listed at US$299 I'm sure it's very good.

I'd use two HobbyEagle gyros.

Yeah, they are expensive as hell

[kallend]

Transmitter just outputs pitch and roll. Mixing has to be made at gyro level when doing this.

That is true with every stand-alone gyro I know.

However, the latest SRXL2 AS3X receivers from Spektrum, such as the AR637T, specify to set up the plane first as if it had no gyro, so the elevon mixing is done in the Tx. Then after test flying, set up the gyro mode and gains from the transmitter by "forward programming" without changing the mixing at all. Presumably the receiver learns the type of wing during the bind and can interpret the mixed signal.

Disclaimer: I have not yet tried an elevon plane with the AR637T.

.
Read the manual of your gyro. Everything should be detailed in there. If you are using a gyro you must read the instructions and familiarize with its operation. ;)

Absolutely.

[janmb]

That is true with every stand-alone gyro I know.

It is common, but not the only way to go about it.

Gyros like the Cortex/Cortex Pro, as well as Jeti's rx built-in gyros operate by still letting the Tx do the various mixes, and let the gyros learn what's what during the teaching process.

While indeed many other gyro systems, such as Hobby Eagle, Admiral, Powerbox iGyro etc etc, both cheap and professional, require the gyro to do the actual mixing, and the tx to output single axis controls.

In either case, one fact remains the same regardless of approach: The gyro obviously needs to KNOW each single channel's involvement in each axis.

[xviper]

Well, let's see ........................... 2 simple HobbyEagles for about 40 bucks or 1 Cortex for 300.00. True the Cortex Pro can probably brush my teeth and sanitize my door handles, but do I need to have my teeth brushed and door knobs sanitized when the HobbyEagles will do what I need done on a Gripen? On the other hand, the HobbyEagle can do the mixing for me and that's as good as a self flushing toilet to me.

[Sekhet]

Well, let's see ........................... 2 simple HobbyEagles for about 40 bucks or 1 Cortex for 300.00. True the Cortex Pro can probably brush my teeth and sanitize my door handles, but do I need to have my teeth brushed and door knobs sanitized when the HobbyEagles will do what I need done on a Gripen? On the other hand, the HobbyEagle can do the mixing for me and that's as good as a self flushing toilet to me.

[Skosh25]

Will I be able to program TV with 8-channels? Will be using a Futaba R7008SB receiver.

[xviper]

Will I be able to program TV with 8-channels? Will be using a Futaba R7008SB receiver.

Don't know much about your Futaba but with TV, yes, 8-ch should do it. The VT should only take one more channel as the rudder portion can be Y'd to the actual rudder. Depending how you do the canards, you could eliminate one, maybe 2 more channels.

[janmb]

Well, let's see ........................... 2 simple HobbyEagles for about 40 bucks or 1 Cortex for 300.00. True the Cortex Pro can probably brush my teeth and sanitize my door handles, but do I need to have my teeth brushed and door knobs sanitized when the HobbyEagles will do what I need done on a Gripen? On the other hand, the HobbyEagle can do the mixing for me and that's as good as a self flushing toilet to me.

I never argued the Cortex being good value lol. Especially not in foamies.

It's a bit of a different story in larger, more expensive models though. First of all, the relative cost of the gyro becomes much less. And the amps you need to put through the gyro becomes a lot more (unless running satellite Rxes through the gyro and letting all the servo load go through a power box).

I have 100+ flights on HobbyEagle gyros too, and definitely think they are good value - decent performance at a far more sensible price point.

[Evan D]

Throttle
Elevon
Elevon
Rudder
Gear
Canards for pitch only
TV yaw
TV pitch

If you want canards for roll and pitch you need 9.

[janmb]

Will I be able to program TV with 8-channels? Will be using a Futaba R7008SB receiver.

2x Elevon, 1x Rudder, 1xCanard (pitch only), 2x vectoring, 1x gear, 1x throttle = 8. Requires Y-ed rudder vs nose steering.


One really hot tip if you are going R7008SB though, which I did in my Freewing Hawk with great success in order to gain more channels: Run a HobbyEagle gyro in SBUS mode.

R7008SB + SBUS gyro will give you a net of about 12-13 useful channels.

The trick is to set the Rx to have channels 1-8 as PWM outputs, and 9-16 as SBUS. Then you use the low range for anything NOT control surface related, such as throttle, gear, flaps, etc, and the upper SBUS range as your flight control inputs as well as gyro control and gyro gain channels, using the gyro as an SBUS to PWM converter.

Even if you don't even want a gyro at all, this is still a quite neat way of getting more channels out of a 7008

[Anders Boström]

Just send me the plane now!😛

[Skosh25]

2x Elevon, 1x Rudder, 1xCanard (pitch only), 2x vectoring, 1x gear, 1x throttle = 8. Requires Y-ed rudder vs nose steering.


One really hot tip if you are going R7008SB though, which I did in my Freewing Hawk with great success in order to gain more channels: Run a HobbyEagle gyro in SBUS mode.

R7008SB + SBUS gyro will give you a net of about 12-13 useful channels.

The trick is to set the Rx to have channels 1-8 as PWM outputs, and 9-16 as SBUS. Then you use the low range for anything NOT control surface related, such as throttle, gear, flaps, etc, and the upper SBUS range as your flight control inputs as well as gyro control and gyro gain channels, using the gyro as an SBUS to PWM converter.

Even if you don't even want a gyro at all, this is still a quite neat way of getting more channels out of a 7008

Great idea! Yes, planning to put a hobby eagle A3 Super in this as well so I think that’s what I’ll do. Thanks.