AJS37 and Acceleration

I purchased this aircraft, about 2-3 years ago but didn't fly it much

Just one quick question, guys : does the AJS37 have a chance against the F16C or M2000C in a dogfight ( no missiles / rockets ) ??

Thank you

I purchased this aircraft, about 2-3 years ago but didn't fly it much Just one quick question, guys : does the AJS37 have a chance against the F16C or M2000C in a dogfight ( no missiles / rockets ) ??

Thank you

If you are good in making a good first turn and the other guy does something stupid or looses sight: YES

If not, you are dead :D

For me air-to-air is like described in the statement of the old Tornado Manual (from Digital Integration, 1991)... I try to translate:

"The Tornado (here Viggen) is - in the best case - not a good air-to-air fighter".

If you are good in making a good first turn and the other guy does something stupid or looses sight: YES

If not, you are dead :D

 

For me air-to-air is like described in the statement of the old Tornado Manual (from Digital Integration, 1991)... I try to translate:

"The Tornado (here Viggen) is - in the best case - not a good air-to-air fighter".

Going guns vs guns in the viggen is jumping in a cage filled with tigers and bears. It can only go south.

It's not awful but it's definitely at a disadvantage, like the F5 and Mig21 are. It has a pretty good instantaneous turn rate, and if you keep it at Mach 0.8-0.9ish sustained turn rate isn't too too bad. The main problem is that once you lose energy, it's tricky to gain it back.

It's not awful but it's definitely at a disadvantage, like the F5 and Mig21 are. It has a pretty good instantaneous turn rate, and if you keep it at Mach 0.8-0.9ish sustained turn rate isn't too too bad. The main problem is that once you lose energy, it's tricky to gain it back.

If you f*ck up, you are dead.

Well yes, but it's not like the F5 or Fishbed are more forgiving like that.

You can mix it up with F-5s and Mig-21 and if you are disciplined with your AOA and speed control stand a decent chance of shooting down your opponent,however you have to guesstimate lead as there is no lead computing gunsight in the Viggen.As TLTeo said, keep your speed up rather high for good turn performance or to take it vertical over the top.

Anything more modern than F-5/Mig-21 , well if you‘re not blowing though a furball taking shots of opportunity or ( as TOviper said )your opponent does a silly move , then it‘s most likely going to end ugly for the Viggen.

If you go for any turn fight keep a good look on your AOA indicator, otherwise be prepared to fight your engine stalls harder than the enemy jet. ;-)

Still,air to air combat is a fun challenge in the Viggen .

Regards,

Snappy

The thing is that even with max weight @30C, I should be able to rotate at 235kmph.

But my concern has to do with empty aircraft, 100% fuel, @15C I should be able to rotate at 180kmph.

Zone3

Hi outbaxx!

I went into this once more. A question rises while looking at what we have and what we got:

In the RC2 manual page 243, for take-off at mil-power a speed of 280km/h should be used for rotation. So far so good.

But to which mass does this setting belong?

And: Is this at 0 ft @15°C?

The more I try and the more I fly, the more I come to the conclusion that the spring, holding the boogie of the main landing gear in the neutral position, might be "a bit" too strong, thus giving too much resistance for a rotation around the axis of the boogie.

What do you say?

Hi outbaxx!

 

 

 

I went into this once more. A question rises while looking at what we have and what we got:

 

In the RC2 manual page 243, for take-off at mil-power a speed of 280km/h should be used for rotation. So far so good.

 

But to which mass does this setting belong?

 

And: Is this at 0 ft @15°C?

 

 

 

The more I try and the more I fly, the more I come to the conclusion that the spring, holding the boogie of the main landing gear in the neutral position, might be "a bit" too strong, thus giving too much resistance for a rotation around the axis of the boogie.

 

 

 

What do you say?

Hi

@15°C, mil power

15000kg ~ 280km/h

16000kg ~ 290km/h

17000kg ~ 295km/h

I’ve had thoughts like you about the main gears but I’m not sure, been awhile but when taking off with Mil power I think has a smoother rotation than Z2 or 3, could be the low acceleration in Mil compared to afterburner but the resistance in the main gears would be the same?

Could be some some “ground handling” code that doesn’t transition smooth to “airborne”, I only have the AJS37 so I can’t compare to any other fast aircraft if they are the same during take off on different weights.

Why I say this about “ground vs air” is that when on landing with aerodynamic braking the loss of lift is also very sudden, but that is just a “feel” too, can’t say it’s wrong or just me doing something wrong.

Me: -This doesn’t “feel” right.

Truth: -Your “feel” probably suck.

Me: -Need to post a question/statement.

Truth: -Please don’t

Me: -posting anyway

;)

Regards

F

The more I try and the more I fly, the more I come to the conclusion that the spring, holding the boogie of the main landing gear in the neutral position, might be "a bit" too strong, thus giving too much resistance for a rotation around the axis of the boogie.

I’ve had thoughts like you about the main gears but I’m not sure, been awhile but when taking off with Mil power I think has a smoother rotation than Z2 or 3, could be the low acceleration in Mil compared to afterburner but the resistance in the main gears would be the same?

Guys, first answer in this very thread:

Nice and thanks!

 

I believe the late rotation might have to be related to, again, the suspension. In DCS the suspension needs to be pretty stiff to handle the hard landings Viggen does. To rotate an aircraft with main landing gears behind the aerodynamic center the landing gears needs to be able to contract a little to create a little alpha while the aircraft still has all wheels on the ground. If not the aircraft needs to accelerate to enough high speed to be able to fly at 0 alpha. So again I believe it’s a tuning issue.

Even if Ragnar uses "I believe", he is one of the developers so he has a bit more insight than us.

Hi Holton!

Thanks for answering this interesting thread.

I have to ask back, just to make sure we are talking about the same thing.

The "suspension" of the main landing gear that I am talking about is the point where the boogie is hinged on the main landing gear strut, see red mark on the picture here:

What I (we) was (were) talking about is the spring system, that holds the boogie (the one carrying the two wheels) in a certain "neutral" position, which in fact seems - at the rear end - a little lower position when the aircraft is in flight.

I know that the RC2 says the following: "As the aircraft touches down, the bogie rotates slightly and removes a significant portion of the impact on hard landings."

I don't know where this sentence comes from (I really would love to know), but I think is overrated, sorry to say that.

Imagine, you are touching down with 4.5m/s, 14 tons are coming down. Now imagine the bogie rotating for a millisecond because the rear wheel is touching ground.

For this milisecond the spring should "remove a significant portion of the impact". No, not in my world. The main portion is eaten by the main suspension of the strut.

I think - RagnaDar please forgive me and get me right - overrated this sentence and programmed a massive spring with a high tension factor on the boogie.

If I was wrong now, another strawberry cake will make its way to HB. :)

Edit: To close the "loop", ... the spring in its current programming state seems to make rotation around this hinging point very hard, which why it is so hard to rotate during take-off.

I had the exact same thought one or two years ago and removed the boogey simulation but it had unfortunately no effect on rotation

I had the exact same thought one or two years ago and removed the boogey simulation but it had unfortunately no effect on rotation

LOL, DAMN. Ok ... hmm ... so ... then have to re-think everything from scratch.

Thanks for that info though!

Then we come into the field of the "coefficient of lift for a given alpha", which might be too low for low angles of attack.

Or the nose is too heavy. Or the forward wings don't produce enough lift at low speeds. Or the flaps don't produce enough downwash.

Or the elevons don't produce enough upwash. Or simply, the pilot is too heavy. Yes, that is the solution! :doh:

I had the exact same thought one or two years ago and removed the boogey simulation but it had unfortunately no effect on rotation

I think you were on to something when you talked about 0 alpha and speed.

I had time to do some take offs today and rotated at 280-ish km/h both with Mil and AB and i had a much smoother rotation. If I try to rotate at 240-250 with full AB, I almost always end up over rotating and get a high alpha warning.

The nose lift so fast perhaps due to a combination of acceleration, alpha and lift coefficients that I have no chance to stop it before I over rotate, even if I release the stick as soon as I see the rotation it will continue and I have to do stick fwd to compensate.

Perhaps the tweaking has to be done in the speed/alpha/lift section but that might have side effects on its own?

The nose lift so fast perhaps due to a combination of acceleration, alpha and lift coefficients that I have no chance to stop it before I over rotate, even if I release the stick as soon as I see the rotation it will continue and I have to do stick fwd to compensate.

This!

Perhaps the tweaking has to be done in the speed/alpha/lift section but that might have side effects on its own?

I assume it would!

What about the elevator/aileron effect? Could that be too small at lower speeds?

I often “feel” like the effect is exaggerated, that I get max G before I have the stick full aft for example. But perhaps it’s too small during the take off run?

I often “feel” like the effect is exaggerated, that I get max G before I have the stick full aft for example. But perhaps it’s too small during the take off run?

Stick movement does not correspond directly to G-loading in a non-FBW aircraft. Stick full aft just means fully after control surfaces, but you may reach peak G for a given speed with much lower control surface deflection.

That's how the Mig-21 and F-14 kill bad pilots; the Viggen behaves very similarly (you can pull ~12G at Mach 1.1-ish but the wings will strongly disagree with you and go their separate way).

Stick movement does not correspond directly to G-loading in a non-FBW aircraft. Stick full aft just means fully after control surfaces, but you may reach peak G for a given speed with much lower control surface deflection.

 

 

 

That's how the Mig-21 and F-14 kill bad pilots; the Viggen behaves very similarly (you can pull ~12G at Mach 1.1-ish but the wings will strongly disagree with you and go their separate way).

I was under the impression that using SPAK would eliminate such behavior, that when in SPAK if you let say pull 25% aft you will have the same amount of G regardless what speed or altitude you’re at, it’s called “stickforce per G”.

Why you can pull 12g is that the trim can’t keep up when you decelerate fast from supersonic, and that peak is around M0.8. So you shouldn’t be able to pull that high if you are accelerating through M0.8 if I understand it correctly, because the trim is still in subsonic.

At M1.1 the servos aren’t strong enough to pull that high so no, it can’t do that, not according to the Max G charts anyway.

As far as I understand, the pitch gearing and SPAK systems do that but only to a limited extent because, again, it's not a full FBW system.

As far as I understand, the pitch gearing and SPAK systems do that but only to a limited extent because, again, it's not a full FBW system.

What ive read it is working very good with the exception when decelerating fast from supersonic because the “series trim” take 15sec to go from high speed to low speed and the pitch gearing will give more elevator deflection than it “should”.

The pitch gearing at speed 0 give 22deg elevator but at 850km/h it will only give 8.7degress elevator with the stick full aft.

Above 850 we are in “high speed” and full aft will give 11.8deg. And those extra degrees is what is causing the high G when decelerating fast from supersonic to about M0.8.

On 12/21/2019 at 10:41 AM, TOViper said:

Just a side note about performance.

Yesterday I did a lot of Viggen sorties, and what I noticed is this:

 

.) Take-off with mil-thrust is now easily possible

.) The aircraft accelerates better until reaching 300km/h on ground (and until 400km/h during lift-off)

.) It "feels" better during take-off rotation and gains speed after lift-off

.) It lifts off like real Viggens in the videos that are around on Youtube

 

Payload was 100% internal fuel + XT + 4*Rb75 at an elevation of 1000m and ISA+7.

 

Edit: ALL I WROTE IS WRONG. This all is gone with the newest update. Don't know what happend, investigating.

 

Thanks HB for repairing an issue I noticed 1,5 years before, but wasn't able to figure out what it may have had caused (correct grammar/time??? )

Changelog of today:

DCS: AJS-37 Viggen by Heatblur Simulations

• Added SF37 F-21 Akktu Stakki livery by Wolfthrower (Livery challenge winner).
• Fixed negative weight on Rb75 family.
• Added Chinese localisation to Mjolnir Response and Wrath of Thunder campaigns. (Thank you!)