Thailand picks Swedish fighters over Russia's

Post by **Vympel** » 2004-10-09 09:32am

Umm, not too fair unless you also compare the weight.

Even so, the JAS 39 does not have a thrust to weight ratio in excess of unity when using afterburner. So even taking into account weight, it is a fair point. In basic fighter configuration, it weighs 8.5 tonnes. That would require 83.4kN to even reach unity. The RM12 engine of the Gripen (a modified F404) can't do it. It needs an upgrade.

Mange · Post by **Mange** » 2004-10-09 11:16am

Precisely Vympel.

Kazuaki, I went down to the local library, but I didn't find exactly what I was looking for. I did however find out that the maximum sustained turn rate (is that the correct expression in English?) is 20 degrees per second for JAS-39 Gripen in a publication.

Kazuaki Shimazaki · Post by **Kazuaki Shimazaki** » 2004-10-09 11:25am

Vympel wrote:Even so, the JAS 39 does not have a thrust to weight ratio in excess of unity when using afterburner. So even taking into account weight, it is a fair point. In basic fighter configuration, it weighs 8.5 tonnes. That would require 83.4kN to even reach unity. The RM12 engine of the Gripen (a modified F404) can't do it. It needs an upgrade.

Oh, I knew the Gripen's empty weight (6.6t or so), but I didn't know what they considered its "basic fighter configuration."

I wonder how long it could stay in the air in that kind of configuration. Figure the AAMs are at least 500kg between them. That means the plane's going up on 1500kg or less of fuel.

Ma Deuce · Post by **Ma Deuce** » 2004-10-09 11:31am

Mange the Swede wrote:You are aware of course Sea Skimmer, that JAS Gripen is totally dependent on its electronic flight control system. It has been shown time and again that when it fails, the pilot can't control the aircraft.

Only with the canard fins attached. If they are removed, the plane is stable enough to fly without computer assistance, though with rather limited maneuverability. The exlposive bolts on the canards were not part of the Grippen's design from the beginning, they incorporated later during development, probably due in part to those famous flight computer failures which resulted in the loss of at least one prototype...

Mange · Post by **Mange** » 2004-10-09 11:41am

Ma Deuce wrote:
Mange the Swede wrote:You are aware of course Sea Skimmer, that JAS Gripen is totally dependent on its electronic flight control system. It has been shown time and again that when it fails, the pilot can't control the aircraft.
Only with the canard fins attached. If they are removed, the plane is stable enough to fly without computer assistance, though with rather limited maneuverability. The exlposive bolts on the canards were not part of the Grippen's design from the beginning, they incorporated later during development, probably due in part to those famous flight computer failures which resulted in the loss of at least one prototype...

And not to forget the one that crashed in Stockholm during an airshow ten years ago during the (then) annual Waterfestival. Man, that really was scary. Lucky that noone was hurt, though.

CJvR · Post by **CJvR** » 2004-10-09 12:29pm

Mange the Swede wrote:And not to forget the one that crashed in Stockholm during an airshow ten years ago during the (then) annual Waterfestival. Man, that really was scary. Lucky that noone was hurt, though.

There were two crashes during the test phase, unfortunately they were both very public spectacles that caused far more political problems than technical ones.
The previous design JA37 had 7 crashes but none on live TV. Also during the previous fighter programs the international tension kept a lid on the worst peaceniks crackpots, JAS39 had no such luck.
The instability is hardly an issue all new modern fighters and quite a few strike aircrafts as well are instable.

Howedar · Post by **Howedar** » 2004-10-10 03:19am

Mange the Swede wrote:You are aware of course Sea Skimmer, that JAS Gripen is totally dependent on its electronic flight control system. It has been shown time and again that when it fails, the pilot can't control the aircraft.

You are apparently unaware that this is true of every fighter designed in the last two decades.

Post by **Beowulf** » 2004-10-10 03:36am

Howedar wrote:
Mange the Swede wrote:You are aware of course Sea Skimmer, that JAS Gripen is totally dependent on its electronic flight control system. It has been shown time and again that when it fails, the pilot can't control the aircraft.
You are apparently unaware that this is true of every fighter designed in the last two decades.

Three decades. The F-16 is aerodynamically unstable and first flew in the early 70's.

Mange · Post by **Mange** » 2004-10-10 03:38am

Howedar wrote:
Mange the Swede wrote:You are aware of course Sea Skimmer, that JAS Gripen is totally dependent on its electronic flight control system. It has been shown time and again that when it fails, the pilot can't control the aircraft.
You are apparently unaware that this is true of every fighter designed in the last two decades.

No, I'm fully aware of this, but the back-up computers on JAS has, until recently, been prone to failure.

Post by **Sea Skimmer** » 2004-10-11 03:25am

Beowulf wrote:
Howedar wrote:You are apparently unaware that this is true of every fighter designed in the last two decades.
Three decades. The F-16 is aerodynamically unstable and first flew in the early 70's.

Not every fighter in the last two or three decades has been unstable, the MiG-29 and Su-27 notably.

Howedar · Post by **Howedar** » 2004-10-11 03:33am

Yes, I was exaggerating. Of course, the point is that an aerodynamically unstable fighter is not exactly untested territory.

Kazuaki Shimazaki · Post by **Kazuaki Shimazaki** » 2004-10-11 12:55pm

Sea Skimmer wrote:Not every fighter in the last two or three decades has been unstable, the MiG-29 and Su-27 notably.

The MiG-29 is definitely stable, but as I understand it, the Su-27 is not stable in pitch. It can handle short periods without the FBW system, but IIRC it will become increasingly hard to control the pitch as you go on.

Post by **Sea Skimmer** » 2004-10-11 01:30pm

Kazuaki Shimazaki wrote:[
The MiG-29 is definitely stable, but as I understand it, the Su-27 is not stable in pitch. It can handle short periods without the FBW system, but IIRC it will become increasingly hard to control the pitch as you go on.

Perhaps that true, but it was my understanding that only the very recent developments of the aircraft like the Su-35 where unstable.

Kazuaki Shimazaki · Post by **Kazuaki Shimazaki** » 2004-10-11 01:46pm

Sea Skimmer wrote:Perhaps that true, but it was my understanding that only the very recent developments of the aircraft like the Su-35 where unstable.

The canards really increased the instability, supposedly by a "factor of three to five times". But even the Su-27 has to employ "electronic stability" in the pictch control circuit. And the SDU-27 FBW system is supposed to "control the statically unstable aircraft in the pitch channel." (Gordon, 1999).

And yes, I'm aware that there is some dispute to that fact. However, I've also seen archives of old NG posts with the same notion. Besides, it makes sense - most fighters in the 80s have to turn to instability to get greater maneuverability, with the MiG-29 being the exception. And analog FBW systems and instable aircraft are hardly new by then - even if Soviet avionics tend to be ten years behind, by the time the Flanker was in service, the F-16 already had analog FBW for like ten years, and even the F-15A has a "Control Augmentation System." Plenty of time for them to catch on.