Official Freewing JAS 39 Gripen 80mm EDF Jet

[kallend]

The Gripen flys very good. I realy like how it flys. Its very predictable i slowflight high alpha. + good topspeed 180kmt level flight.
The Mirage is a smaler plane and now delivered with the same motor.
My Gripen is 2362gram with some telemetry+ battery. Was 2350g in ad. And the Mirage is advertised to 2200g+ bat.

How did you manage that? My Gripen is 2500 without battery and without tailweight, and all that's added to the stock PNP is a 20g receiver and a 25g afterburner. The Mirage is 2,200 complete with battery,

[janmb]

Bloody hell there must be someone with some good comments on the Gripen out there. The Gripen surely is not that bad
Is it!!!!!!!!!!!!

It's not bad at all. Has anyone claimed that it is?

[janmb]

I am going to 8s on mine, but its fun to fly stock. True its not fast and must run with over 50% power most of the time witch is unusual compared to my other edf's. It lands great looks awesome and is a worthy addition to any fleet, in my opinion. Also I have found and still testing, so no conclusion, that trimming the leading edge of the canards down a few mm seems to increase stability. (Jury still out on that one but so far so good).

That is indeed the case, and showcases the main purpose of the canards in the first place: Form the airflow over the main wing.

Having a look at just about any air show, landing sequence or similar will easily demonstrate that the full size uses the canards in a pitch down attitude almost exclusively, and especially in any high alpha scenario (which for deltas equals pretty much all the time as long as we're talking sub-sonic)

And that is my gripe with the default configuration - poor CG makes the jet need to use canards for up pitch or even lift - neither of which should be the case. Pretty much the only case where you will see significant pitch up canards is during takeoff to help rotation.

[TangoVector]

That is indeed the case, and showcases the main purpose of the canards in the first place: Form the airflow over the main wing.

According to the guys at SAAB the Gripen uses its leading edge flaps to get best airflow over the wing, the canards are for faster reaction in pitch and keeping the hydraulic system smaller. Some good links about that awhile ago.

The fixed canard with trailing edge flap on the Viggen on the other hand, are almost only for the airflow over the main wing.

[janmb]

According to the guys at SAAB the Gripen uses its leading edge flaps to get best airflow over the wing, the canards are for faster reaction in pitch and keeping the hydraulic system smaller. Some good links about that awhile ago.

The fixed canard with trailing edge flap on the Viggen on the other hand, are almost only for the airflow over the main wing.

The Viggen is a completely different case. It doesn't really have canards in the traditional sense at all.

The Gripen uses canards very much like the other modern deltas - which means they are pitch down 98% of the time.

All modern jets, including canard deltas, use slats to shape the main wing - that is a completely separate topic. What the canards do is change the relative alpha of the airflow actually hitting the main wing.

A fine example here, by "our" full size version from Cosford. This is a 9 minute display, including lots and lots of examples of high G positive pulls. Have a close look at the how often you see canards above neutral (or even at neutral). (spoiler: 0)

[Gary S.]

According to the guys at SAAB the Gripen uses its leading edge flaps to get best airflow over the wing, the canards are for faster reaction in pitch and keeping the hydraulic system smaller. Some good links about that awhile ago.

The fixed canard with trailing edge flap on the Viggen on the other hand, are almost only for the airflow over the main wing.

The whole idea of airflow stability is why my neutral position for the canards is down on the leading edge several mm. Shout out to Airguardian as well for bringing it up. If you consider the plane being a delta will easily go into an alpha position with the slightest touch, that spoils the airflow for efficient level flight. Which in my opinion it leads to the " wing rock" as the alpha turbulence try's to set up to soon in a low angle of attack. With the canards edge down it conditions the airflow to be more balanced and less prone to unbalanced turbulences.

[xviper]

Bloody hell there must be someone with some good comments on the Gripen out there. The Gripen surely is not that bad
Is it!!!!!!!!!!!!

As I had implied before, you are way over-thinking this and reading stuff into peoples' posts that they really are not saying.

[Airguardian]

"Technically" you do see the Gripen and Rafale using canards 'pitch-up' as trim compensation for elevon-flaps, but that is very specific to reduce angle of attack during landings to facilitate pilot view of the runway and have more clearance to prevent tail strikes. BUT THAT'S IT! You don't see them using canards 'pitch up' in any other type of 'normal' flight conditions. Particularly not in high alpha!


BTW, don't expect SAAB to tell you about all the exact details of their flagship aircraft.
The canards are very obsiously used for so much more than 'increased pitch authority'.

[janmb]

"Technically" you do see the Gripen and Rafale using canards 'pitch-up' as trim compensation for elevon-flaps, but that is very specific to reduce angle of attack during landings to facilitate pilot view of the runway and have more clearance to prevent tail strikes. BUT THAT'S IT! You don't see them using canards 'pitch up' in any other type of 'normal' flight conditions. Particularly not in high alpha!


BTW, don't expect SAAB to tell you about all the exact details of their flagship aircraft.
The canards are very obsiously used for so much more than 'increased pitch authority'.

Definitely.

As can be seen very clearly in the video I linked, the canards contribute very little to pitch up authority at all. Sure, they do probably move the CoL forward a little bit, but not a whole lot. The the control surfaces commanding the pitch maneuver are exclusively the elevons.

[rms]

The Mirage is 2200 flying weight, so a difference of at least 600g.

Ohhh....I bought the wrong plane ;-)
Just kidding...The Gripen is very nice.

[rms]

I think somewhere out there there's a light, high voltage setup that strikes the balance between optimum CG, thrust and weight. Evan may already be close with his (I think) light batteries. When I find it this plane should be a lot of fun. I thought my 8S Jetfan setup flew poorly given the very nose heavy CG, even with 3500 watts on tap. Fixing the CG on mine with heavy batteries adds a lot of weight which creates a vicious circle.

Honestly, my opinion is this is a plane where its performance is primarily kneecapped by it's nose heavy CG. Fixing that requires lots of weight and that has all kinds of negative effects on an already heavy for the size plane.

We need a weight reduction program for the front of the plane as rms was indicating, then perhaps things will start moving in the right direction.

If using 8s with 2 batteries like 4s 3000 in serie = 6s 4000 in Wh. And put one in the middle of the plane somewhere where its space. This might be a solution :-)

[xviper]

If using 8s with 2 batteries like 4s 3000= 6s 4000 in Wh.

Scratching my head on this one.

[Evan D]

8x3 = 6x4

Scratching my head on this one.

[Mizer67]

I really think 8S shines on this plane. The JF/ HET 1738 or 1865 just work well. The 1738 has a little less power but gets a easy 4:30 on 5000mAh while the 1865 gets you that vertical at 4:00. I really like the Hobby King Plush 120HV. Cheap, small, light, works perfect and good for 8S.

I prefer 6+2 for 8S and can't find any that I really like. The PowerHobby 5000mAh 100C 8S pack is the best I can find for this and is 765g and fits great flat on the battery tray or upright moved back a tad more. There may be a 4+4 option but I have very limited use for 4S 5000 packs.

I agree the #1 thing is weight and balance on this plane. We need a way to get rid of the tail weight we are putting in it. Going to lighter 3500-4000mAh 8s is NOT an option.

I could barely eek out 3:00 with ~15% left in the pack with 8S 4000's.

I agree it needs ~5000s for the flight time too, but can't find any that are significantly less that my 4000's are in weight. Everything 8S is around 850 grams that I can piece together for 5000's. 4500's run around 800 grams best case. I think it needs to fly with maybe 750 grams of batteries at most. 700 would be better but seems out of reach. What's the Powerhobby 8S weigh? I couldn't locate a weight.

Aside from removing the pilot, there's not much else in the nose that can come out either. Perhaps one of the single wheel nose gears from another plane (F-15 perhaps?) might help slightly to make this more like an "E" model at the same time.

[HockeyMac!]

I'll take a look tonight, but with some foam shaving is it possible to move the fan unit back some? I haven't really touched mine sans for 3d printing ordinance, but I feel like the weight savings in the front and CG adjustment are the way to go. I remember one person cutting foam to move their battery back, that seems like a good place to start. I'm sure there's more we can do!

[Evan D]

The PowerHobby 5000mAh 100C 8S pack is 765g. They also have a 5000 50C 8S but it's bigger and heavier. You'll need a 8S charger for these.

I could barely eek out 3:00 with ~15% left in the pack with 8S 4000's.

I agree it needs ~5000s for the flight time too, but can't find any that are significantly less that my 4000's are in weight. Everything 8S is around 850 grams that I can piece together for 5000's. 4500's run around 800 grams best case. I think it needs to fly with maybe 750 grams of batteries at most. 700 would be better but seems out of reach. What's the Powerhobby 8S weigh? I couldn't locate a weight.

Aside from removing the pilot, there's not much else in the nose that can come out either. Perhaps one of the single wheel nose gears from another plane (F-15 perhaps?) might help slightly to make this more like an "E" model at the same time.

[xviper]

8x3 = 6x4

Thanks. Didn't know that's how it's done. Too simple, I guess.

[xviper]

I'll take a look tonight, but with some foam shaving is it possible to move the unit back some? I haven't really touched mine sans for 3d printing ordinance, but I feel like the weight savings in the front and CG adjustment are the way to go. I remember one person cutting foam to move their battery back, that seems like a good place to start. I'm sure there's more we can do!

Looking at the part at the rear of the compartment where it narrows, that part looks quite thin and you could easily cut right through to the intake channel. I suppose if you cut through, the battery could actually plug the hole.

[rms]

Scratching my head on this one.

8s= 29,6Volt x 3000mAh( 3Ah) = 88,8 watthour wh
6s= 22,2Volt x 4000mah( 4Ah) = 88,8watthour
But with higer performance on the 8s will give less flight time.

[HockeyMac!]

I can't recall who did this, a few pages back.