Official Freewing JAS 39 Gripen 80mm EDF Jet

[T-CAT]

Hey guys, posted 3 more vids today.

Assembly:

Canard Mixing (on Spektrum):

CG and Rates:

TV Mixing Video is coming next week (but really simple).

Nice job guys. I watched them this morning. The drone chase of the Gripen at the end of the Canard Mixing video was fantastic.

[James]

Thanks T-CAT - Alex is a beast on those sticks when it comes to that stuff. We have some more of that footage to show off tomorrow on our Live show. We are going live tomorrow rather than Friday with Friday being 9/11, just doesn't feel right to go live that day.

[T-CAT]

I'll be there tomorrow for sure, James.

Alex is most definitely going beast-mode with the drone footage.

[Airguardian]

You know this for a fact, or is it guesswork? airflow doesn't get "stalled", the wing does.

We could say that I do.
It's not like I have run wind tunnel tests myself, but others have.
And it's otherwise known stuff and aerodynamic phenomena if you have the time and willingness to research it.

Will try my best at a 'short' explanation of what goes on.

Assuming you are familiar with the concept of boundary layer and airflow separation, in subsonic flight, as the wings keep increasing angle of attack, the flow tends to separate from the wing, causing a loss of lift and an increase of drag. That's essentially the wing stalling. This can happen in many different ways depending on wing design and particular flow/surface conditions.

For the most part, aero-engineers have traditionally loved laminar flow (aka-smooth flows) over surfaces as turbulence is associated with losses.
It just so happens that, in fact, laminar flow is usually not really good at sticking to the wing once you start changing AoA and so on, and discoveries were made and researched.
In particular, high sweep, sharp edges, wing leading edge root extensions and canard devices can produce VORTICES that help the airflow over a wing stick to it along a wider flight envelope. Of course this adds some penalties but the overal output is dramatically for the better. A good design of LERX/canards can improve lift by as much as 50% during maneuvering flight and delay boundary layer separation (and thus, wing stall).

Wing rocking is a dynamic phenomena that originates from detached flow causing asymmetric loads on the wings in a periodic fashion.
Thus, to get rid of it, you want to make the flow field around the jet as stable as possible, and limit airflow separation. Vortices are very energetic flow patterns that infuse 'energy' or 'momentum' to the flow next to the wing surface, essentially reinvigorating it and delaying the boundary layer separation by mixing it with air that is more separated from the wing surface by means of these vortices.

Going back to the Gripen (or any Eurocanard, for that matter), what you want to achieve is to reproduce those vortice flows over the wings. Mind that a jet without canards may well produce its own vortices just by having a good amount of leading edge sweep (example: Mirage) or LERX (F-16/18, Su-35, MiG-29...). But canards improve the airflow performance much further.

To produce powerful vortices, you want the canards to have a slight positive angle of attack with respect to the airflow. If the canards are in-line with the flow and have a symmetrical airfoil, they do nothing really, other than produce drag. Deflecting them so they are no longer in line with the flow will produce a number of vortices on the top or the bottom of the canard surface, and on the wingtip. In the case of the jet flying in a turn, these vortices propagate over the wing, changing the properties of the flow downstream from the canards and modifying lift distribution. Vortices will typically form on the high-sweep leading edges and merge with those of the canard wingtip. Depending on the wing-canard design, the root of the canard may produce yet another vortice, and the fence immediately aft of the canard also produces its own vortice. Even if a vortice doesn't quite form, the canards change the entire flow field before and behind them and change the effective angle of attack for the wing. When deflected at the appropriate angles, this means that the wing sees a smaller effective AoA than it actually flies at.

That's a lot of vortices that the guys who designed the jets thoroughly researched and calculated in order to boost the jet performance. Flow conditions and geometry are not identical for the fullscale jet and for our models so the effect won't be the exact same (of course) but the principle and concept/idea still applies all the same.

And here comes why I don't like to see those canards being deflected up too much... there comes a point where continuing to increase angle of attack will start detracting from these 'stable' vortices and just produce outright detached (stalled) flow. Such flow is totally deprived of energy/momentum and will destroy the entire flow field aft of it. Instead of helping the airflow keep attached to wing surface you are generating a high pressure zone on top of the wing. You do kill lift, increase drag very badly and worse of all, you encourage 'asymmetry' in the dynamics of those flows, making them unstable and back to producing oscillations.

So, the cure: you want the canards to move 'almost' aligned with the flow... but keeping a slight positive angle with respect to them. This will produce more or less the 'right' flow patterns and improve your aircraft handling. No, this is not just theory, I actively use this to improve flight performance on my Eurofighter.
And the beauty of it is that it may sound so very complex, but it is SO EASY to implement.
Just drop a gyro on canards, get a neutral CG.
Bam.
Done.

You have made the best possible upgrade to your eurocanard in my extremely biased point of view.

Test it out, fine tune to your own likings, enjoy the power of vortices, thank me later! ;)

[nuts-n-volts]

You had to poke him!

[Airguardian]

Reminder: 'slight pitch up angle on canards' actually translates to pitch-down deflection when the jet is turning or flying high alpha.

Say, if the plane's angle of attack is 20º, a 15º pitch-down deflection still produces a positive 5º AoA for the canards and thus, the canard is still lifting up, not pitching down.

On the other hand, if the jet is at 20º AoA and you further deflect canards pitch-up by an amount of 15º, the AoA of the canards will be 35º. This only mounts up with further deflection and increasing angle of attack, so sustained extreme high alpha with pitching-up canards is indeed less than ideal, and yes, that's pretty much a fact and not just guesswork.

Made this drawing some time ago to try and explain more visually what I was talking about.
The 3rd figure would be the 'ideal' condition you want to achieve.

[Evan D]

James, in the throws video (12min) your Canards are backwards for pitch. You have up elevons (TE go's up) with down canards (TE go's up). The canard TE should go down.

When I do canards I don't activate trim in the mixes for them. I do all trimming with the main surfaces. I also have an activation switch.

[Sekhet]

We could say that I do.
It's not like I have run wind tunnel tests myself, but others have.
And it's otherwise known stuff and aerodynamic phenomena if you have the time and willingness to research it.

Will try my best at a 'short' explanation of what goes on.

Assuming you are familiar with the concept of boundary layer and airflow separation, in subsonic flight, as the wings keep increasing angle of attack, the flow tends to separate from the wing, causing a loss of lift and an increase of drag. That's essentially the wing stalling. This can happen in many different ways depending on wing design and particular flow/surface conditions.

For the most part, aero-engineers have traditionally loved laminar flow (aka-smooth flows) over surfaces as turbulence is associated with losses.
It just so happens that, in fact, laminar flow is usually not really good at sticking to the wing once you start changing AoA and so on, and discoveries were made and researched.
In particular, high sweep, sharp edges, wing leading edge root extensions and canard devices can produce VORTICES that help the airflow over a wing stick to it along a wider flight envelope. Of course this adds some penalties but the overal output is dramatically for the better. A good design of LERX/canards can improve lift by as much as 50% during maneuvering flight and delay boundary layer separation (and thus, wing stall).

Wing rocking is a dynamic phenomena that originates from detached flow causing asymmetric loads on the wings in a periodic fashion.
Thus, to get rid of it, you want to make the flow field around the jet as stable as possible, and limit airflow separation. Vortices are very energetic flow patterns that infuse 'energy' or 'momentum' to the flow next to the wing surface, essentially reinvigorating it and delaying the boundary layer separation by mixing it with air that is more separated from the wing surface by means of these vortices.

Going back to the Gripen (or any Eurocanard, for that matter), what you want to achieve is to reproduce those vortice flows over the wings. Mind that a jet without canards may well produce its own vortices just by having a good amount of leading edge sweep (example: Mirage) or LERX (F-16/18, Su-35, MiG-29...). But canards improve the airflow performance much further.

To produce powerful vortices, you want the canards to have a slight positive angle of attack with respect to the airflow. If the canards are in-line with the flow and have a symmetrical airfoil, they do nothing really, other than produce drag. Deflecting them so they are no longer in line with the flow will produce a number of vortices on the top or the bottom of the canard surface, and on the wingtip. In the case of the jet flying in a turn, these vortices propagate over the wing, changing the properties of the flow downstream from the canards and modifying lift distribution. Vortices will typically form on the high-sweep leading edges and merge with those of the canard wingtip. Depending on the wing-canard design, the root of the canard may produce yet another vortice, and the fence immediately aft of the canard also produces its own vortice. Even if a vortice doesn't quite form, the canards change the entire flow field before and behind them and change the effective angle of attack for the wing. When deflected at the appropriate angles, this means that the wing sees a smaller effective AoA than it actually flies at.

That's a lot of vortices that the guys who designed the jets thoroughly researched and calculated in order to boost the jet performance. Flow conditions and geometry are not identical for the fullscale jet and for our models so the effect won't be the exact same (of course) but the principle and concept/idea still applies all the same.

And here comes why I don't like to see those canards being deflected up too much... there comes a point where continuing to increase angle of attack will start detracting from the these 'stable' vortices and just produce outright detached (stalled) flow. Such flow is totally deprived of energy/momentum and will destroy the entire flow field aft of it. Instead of helping the airflow keep attacched to wing surface you are generating a high pressure zone on top of the wing. You do kill lift, increase drag very badly and worse of all, you encourage 'asymmetry' in the dynamics of those flows, making them unstable and back to producing oscillations.

So, the cure: you want the canards to move 'almost' aligned with the flow... but keeping a slight positive angle with respect to them. This will produce more or less the 'right' flow patterns and improve your aircraft handling. No this is not just theory, I actively use this to improve flight performance on my Eurofighter.
And the beauty of it is that it may sound so very complex, but it is SO EASY to implement.
Just drop a gyro on canards, get a neutral CG.
Bam.
Done.

You have made the best possible upgrade to your eurocanard in my extremely biased point of view.

Test it out, fine tune to your own likings, enjoy the power of vortices, thank me later! ;)

It looks like someone was paying attention to my lectures in Advanced Aerodynamics class.
The one thing you have to remember is models are moving through the same air as the full scale aircraft and not everything scales down.

[James]

James, in the throws video (12min) your Canards are backwards for pitch. You have up elevons (TE go's up) with down canards (TE go's up). The canard TE should go down.

When I do canards I don't activate trim in the mixes for them. I do all trimming with the main surfaces. I also have an activation switch.

Noticed that after I made live, I think I had swapped receivers and accidentally plugged the canards into different ports. But at least it is right in the mixing video. I will reshoot that portion and reupload as soon as I can.

[Airguardian]

The one thing you have to remember is models are moving through the same air as the full scale aircraft and not everything scales down.

So I said.

Flow conditions and geometry are not identical for the fullscale jet and for our models so the effect won't be the exact same (of course) but the principle and concept/idea still applies all the same.

You still want a smooth airflow over the wing and delaying flow separation... using the canards properly still helps in that regard, be it model or fullscale.

[Sekhet]

So I said.



You still want a smooth airflow over the wing and delaying flow separation... using the canards properly still helps in that regard, be it model or fullscale.

OK, I guess I have to be more direct. When a wrote, "It looks like someone was paying attention to my lectures in Advanced Aerodynamics class." It was a nice way of stating, Thank you for reading the text books I co-authored or for being one of my students and paying attention in class. A large amount of your post #326 was ether a direct quote or slightly reworded from the text book, my published papers or my lectures. I hold no ill will and again thank you for paying attention.

[Airguardian]

Oh, gotcha... still, I have not undergone my engineering studies in the US and I doubt the books I've read were the same as the ones you co-authored.
I definitely didn't make a copy paste for my previous post, I just wrote it as it came to mind!

FWIW, I'm reading 'Design for Air Combat' right now by Ray Whitford. I'm halfway through, a really good read!

I plan on going back to my books of fundamentals after I'm done with it as I am trying to get a more in-depth knowledge of subjects that escaped me during my studies, such as supersonic flight. My teachers went straight into the math and sadly I didn't get a thing, so I'm slowly doing that as a hobby now, haha!

[TangoVector]

I plan on going back to my books of fundamentals after I'm done with it as I am trying to get a more in-depth knowledge of subjects that escaped me during my studies, such as supersonic flight.

Fun fact about the Gripen: Everybody knows it is unstable in the full scale version, but that's only mostly true. When going supersonic the center of pressure, since it moves backwards when supersonic, is behind the CoG and makes the aircraft stable-ish.

[Sekhet]

FWIW, I'm reading 'Design for Air Combat' right now by Ray Whitford. I'm halfway through, a really good read!

Professor Whitford was a wonderful Aeronautical Engineer and had the ability to pass on his knowledge in a way that most could understand.
I met Ray in 1993 when he was a Visiting Professor at the U.S. Air Force Academy. We would occasionally "tag-team lecture" an aerodynamics class in such a way as to make the information being passed on more fun and less dry.
Ray and I stayed in touch up until his passing in 2018.

[JLambCWU]

Going live in :10 min!

Friday’s normal time slot has been moved to 12pm EST TODAY to reflect our respect for Sept 11th tomorrow.

http://youtu.be/GxoW1Ov9D9A

[Airguardian]

Professor Whitford was a wonderful Aeronautical Engineer and had the ability to pass on his knowledge in a way that most could understand.
I met Ray in 1993 when he was a Visiting Professor at the U.S. Air Force Academy. We would occasionally "tag-team lecture" an aerodynamics class in such a way as to make the information being passed on more fun and less dry.
Ray and I stayed in touch up until his passing in 2018.

Now that is amazing!

But I didn't know he had passed away, sad news, may he rest in peace. :'(

I am really enjoying his book. As you say, he made complex topics very 'affordable' for people with a basic background knowledge on the topic.
I wish there were more like this!

Speaking of... (and sorry for the off-topic) do you know by any chance, any good book that goes more in-depth in terms of vortice-calculation?
For the most part I have only seen them being simulated with CFD and/or tested in wind tunnels.
Are there any known 'more rudimentary' empirical or analytical methods to make starting approximations for these?
I have not been able to find any, and my professors didn't have this information either so I would appreciate any reference that I can further investigate, thank you!

[janmb]

You know this for a fact, or is it guesswork? airflow doesn't get "stalled", the wing does.

Prepare to get owned lol.

[Sekhet]

Now that is amazing!

But I didn't know he had passed away, sad news, may he rest in peace. :'(

I am really enjoying his book. As you say, he made complex topics very 'affordable' for people with a basic background knowledge on the topic.
I wish there were more like this!

Speaking of... (and sorry for the off-topic) do you know by any chance, any good book that goes more in-depth in terms of vortice-calculation?
For the most part I have only seen them being simulated with CFD and/or tested in wind tunnels.
Are there any known 'more rudimentary' empirical or analytical methods to make starting approximations for these?
I have not been able to find any, and my professors didn't have this information either so I would appreciate any reference that I can further investigate, thank you!

Check out the works of D.F. Abzalilov, R.F. Mardanov, P.K. Chang, G.Yu. Stepanov and D.V. Makakov to name a few.
I must warn you, the information can be very dry and a deep dive into your math skills.

[Airguardian]

Thanks for the reference... will dive in at own risk!

Edit: I would also be interested in your books, I will appreciate if you send me a DM with a few references!

[Quickstop]

Prepare to get owned lol.

It’s ok, no problem being wrong, always want to learn something new!