DCS AJS-37 Viggen manual RC2.1

[TOViper]

Guys, I have read the section Roll during g-load on page 271 at least 150 times per day, and I still come to the conclusion that it needs a little rework.
I have a few versions (not only these 3) which could (!) maybe explain what the original author maybe had in mind:

Version 1:
During strong roll input during g-load at low airspeed (Vi < 350 km/h), high roll rates can only be achieved when reducing the g-load. This should not be confused with inverted spin.
On the other hand, if the roll input is neutralized, the roll ceases, and the g-load returns to normal values.

Vesion 2:

 During strong roll input during g-load at low airspeed (Vi < 350 km/h), high roll rates can be achieved as the g-load decreases. This should not be confused with a flicked roll.
If the roll input is neutralized, the roll ceases, and the g-load returns to normal values.

Vesion 3:

 During strong roll input during g-load at low airspeed (Vi < 350 km/h), high roll rates can be achieved as the g-load decreases. This is similar to a flicked roll.
If the roll input is neutralized, the roll ceases, and the g-load returns to normal values.

Another question came up for this:
Is this behaviour of the real aircraft and how is it modelled / does it behave in DCS?

Edited August 30, 2023 by TOViper

[widen76]

I would go for Version 2, but would replace "flicked roll" with "inverted plunging spiral" as this is the closest to the meaning of "störtspiral":

The original text is from SFI AJS37 Part 2, section 24.3.2 and reads in Swedish:

"Vid kraftiga skevroderutslag under lastfaktor med låg fart (Vi < 350 km/h) kan höga rollvinkelhastigheter uppstå samtidigt som lastfaktorn minskar. Detta ska inte förväxlas med inverterad störtspiral. Om skevrodren neutralställs upphör rollen och lastfaktorn återgår till normal."

Translated into english:

"In case of severe aileron deflection under low speed load factor (Vi < 350 km/h) high roll angle speeds may occur as the load factor decreases.
This should not be confused with an inverted plunging spiral. If the ailerons are neutralised, the roll ceases and the load factor returns to normal."

This is the technically correct description, but for general understanding "high roll rates", "roll input" and "g-load" might be more suitable, rather than the technical "high roll angle speeds" aileron deflection" and "load factor"...

Edited August 23, 2023 by widen76
roll changed to spiral

[Snappy]

2 hours ago, TOViper said:

Guys, I have read the section Roll during g-load on page 271 at least 150 times per day, and I still come to the conclusion that it needs a little rework.
I have a few versions (not only these 3) which could (!) maybe explain what the original author maybe had in mind:

Version 1:
During strong roll input during g-load at low airspeed (Vi < 350 km/h), high roll rates can only be achieved when reducing the g-load. This should not be confused with inverted spin.
On the other hand, if the roll input is neutralized, the roll ceases, and the g-load returns to normal values.

nullVesion 2:

 During strong roll input during g-load at low airspeed (Vi < 350 km/h), high roll rates can be achieved as the g-load decreases. This should not be confused with a flicked roll.
If the roll input is neutralized, the roll ceases, and the g-load returns to normal values.

null Vesion 3:

 During strong roll input during g-load at low airspeed (Vi < 350 km/h), high roll rates can be achieved as the g-load decreases. This is similar to a flicked roll.
If the roll input is neutralized, the roll ceases, and the g-load returns to normal values.

Another question came up for this:
Is this behaviour of the real aircraft and how is it modelled / does it behave in DCS?

 

Hi
My suggestion: 

"Large roll inputs during g-load at low airspeed (Vi < 350km/h) may result in high roll rates as the g-load reduces. However, this is not to be confused with an inverted spin. If the roll inputs are neutralized, the roll ceases and the g-load returns to normal values ".

Snappy.

edit:
While I was typing my reply Widen76's reply came in and had the original phrase translation. I agree with his suggestion to use slightly less technical expressions in the version for the manual.

Edited August 23, 2023 by Snappy

[renhanxue]

Regarding the inverted plunging spiral, the SFI defines it as different from an inverted spin (there is also an extremely rare non-inverted plunging spiral). A long time ago I translated the relevant part of the SFI, so I'll just paste that here.

 

24.4 Departure from controlled flight

24.4.1 Superstall and spin

If the angle of attack exceeds the permitted limits, some yaw disturbances appear around alpha 25-28°, and at alpha 28-30° there are weak pitch-up tendencies. If the stick is moved forward to counter the pitch-up, the aircraft returns to normal alpha, possibly after overshooting up to alpha ~50°. Note that the angle of attack instrument only shows the area -4° to +26°.

If the stick movement forward at the pitch-up is too small or is made too late, such that the angle of attack does not immediately decrease, the aircraft departs into superstall or spin.

Superstall is characterized by:

• indicated alpha 26° (actually around 60°)
• low rate of rotation (< 40°/s)
• stable or oscillating nose attitude

 

Two types of spin may be encountered:

Oscillating spin (most common)

• indicated alpha 26° (actually around 60°)
• moderate to high rate of rotation (> 40°/s)
• moderate to powerful oscillations in pitch and/or roll

Flat spin

• indicated alpha 26° (actually around 70°)
• high rate of rotation (up to 120°/s)
• weak or no oscillations in pitch and/or roll

The sink rate in a superstall or spin is around 100 m/s.

If the pitch-up occurs without aileron input, the departure usually results in superstall. If the pitch-up occurs with any aileron input active, the aircraft is affected by adverse yaw and the likelihood of a spin increases.

[...]

The oscillating spin may after ≥15 s diverge such that the aircraft rolls inverted, and from there it usually recovers to controlled flight on its own with control surfaces neutral (but see also the section on "inverted plunging spiral" below).

In superstall or spin the pitch authority is good, which eases recovery. Aileron input results in adverse yaw, that is to say rolling right gives a yaw to the left and vice versa. Rudder authority is negligible.

Recovery from superstall and oscillating spin is accomplished by moving the stick to a position somewhat forward of the neutral pitch position, with ailerons and rudder neutral.

To recover from a flat spin, the yawing rotation must be stopped first, which is accomplished with neutral pitch and full roll input in the direction of the rotation ("stick into the spin"). When the rotation has just about ceased, recovery is accomplished with neutral ailerons and the stick somewhat forward of neutral, just like when recovering from superstall and oscillating spin.

 

If the center of gravity is particularly far aft (aircraft with heavy loads on V7 (wing pylons) and no load on S7 (fuselage pylons)) the pitch-up tendency is more pronounced than with normal CoG positions. To return to a normal angle of attack a stronger pitch down input is required; the stick must be moved close to its fully forward position.

These characteristics are not affected to any significant degree by fuselage mounted loads. The characteristics with both fuselage and underwing loads are not known but are assumed to be the same as with only fuselage loads.

Stalled inverted attitudes have not been possible to achieve in flight tests. Moving the stick fully forward gives alpha about -30°, there are no pitch-up (pitch-down?) tendencies and when the stick is moved back to neutral the aircraft returns to a normal angle of attack.

 

24.4.2 Plunging spiral

In certain scenarios with a particular type of adverse dynamics, the aircraft can enter an uncontrolled attitude of the autorotating type, here called plunging spiral. The plunging spiral, which can be either right side up or inverted, is considered to be the potentially most dangerous form of uncontrolled flight that has been discovered during the spin tests of aircraft 37.

 

24.4.2.1 Inverted plunging spiral

The most common form of the plunging spiral is the inverted one. The following attitudes/maneuvers repeatably result in an inverted plunging spiral:

• Somersault into inverted position from oscillating spin (for example while attempting to recover from a spin with the stick fully forward)
• Stalling the tailfin through so-called "knife flying" (TN: knife edge?)

The inverted plunging spiral is characterized by the following:

• Negative load factor (-1 to -3)
• Low nose
• Very high rate of rotation in the roll axis (≥ 200°/s)
• High sink rate (≥ 150 m/s)

Moving the stick back and/or aileron input to either side tends to increase the rate of the roll rotation. The rotation can be stopped by moving the stick fully forward with no aileron input. When the rotation has ceased, the stick is moved back to neutral pitch, and the aircraft returns to controlled flight.

 

24.4.2.2 Non-inverted plunging spiral

The aircraft only departed into a non-inverted plunging spiral on a few occasions during the spin tests. It has not been possible to define any repeatable attitude or maneuver that results in a non-inverted plunging spiral.

During the spin tests the non-inverted plunging spiral only occurred on the following two occasions (not repeatable):

• When recovering from an inverted superstall
• When recovering from an oscillating non-inverted spin

The non-inverted plunging spiral is characterized by the following:

• Positive load factor (+1 to +3)
• Low nose
• Very high rate of rotation in the roll axiss (≥ 200°/s)
• High sink rate (≥ 150 m/s)

In a non-inverted plunging spiral, aileron inputs have no effect. Instead, the roll rotation must be stopped by pulling gently back on the stick until the rotation ceases. When the rotation has ceased, the stick is moved forward to the neutral pitch position and the aircraft recovers into controlled flight.

Edited August 24, 2023 by renhanxue

[TOViper]

Thank you guys for your answers. Maybe I will make something out of it for the next update ... cu soon!

Edited August 30, 2023 by TOViper

[TOViper]

Next update scheduled: August 31^st, 2023

[Machalot]

@TOViper Have you thought about incrementing the version number when you make updates?  There are many different files out there now called 2.1(beta).

[TOViper]

Guys, regarding the roll inputs, I have some news.
I tested this in DCS, and managed to see the fluctuating airspeed / g-load / roll angle speed. 2g, 350km/h, pull and roll > swinging around the longitudinal axis is clearly visible, and also swinging of the accelerometer is visible.

Therefore, I rephrased it:

Please  go through it and give me your feedback! THANKS!

Edited August 31, 2023 by TOViper

[TOViper]

19 hours ago, Machalot said:

@TOViper Have you thought about incrementing the version number when you make updates?  There are many different files out there now called 2.1(beta).

Hey Machalot! No, I initially had the plan that the RC2.1 stays in beta as long as it is not officially part of the module. Let's see when this changes...

[Machalot]

37 minutes ago, TOViper said:

Hey Machalot! No, I initially had the plan that the RC2.1 stays in beta as long as it is not officially part of the module. Let's see when this changes...

I'm only taking about the version number 2.1.  Typically one might increment a minor version number with each change, such as 2.1, 2.2, etc.  Or 2.1.0, 2.1.1, 2.1.2, just to make it easier to identify what version you are looking at. 

[TOViper]

Yeah, absolutely right. I hated to create more versions, since I wanted to measure the downloads. If the filename changes all the time, I have to collect all that data garbage.
In the credits section of the document you may find the release date and for which version of DCS the document is made (usually the latest OB which contained ANY update/change for the Viggen module).

Also, the PDF should contain META data about the document information block (which was entered into the source file before compiling to PDF)

Edited August 31, 2023 by TOViper

[TOViper]

Hey guys!

This time, RC2.1(beta) becomes RC2.1. Yes.

Hafe vun!

Update 2023-08-31:

- page 17: Replaced "The AJS37 Viggen was developed..." with "The Viggen (AJ37 version) was developed ..." (initially this was correct in RC2, but I messed it up during editing, sorry my fault!)
- page 32: Replaced "of the gas generator" with "of the engine"
- page 45: Added text for the red ELFEL warning light : ", or the ground power is applied."
- page 50: Replaced "Warning / Indicator table test" with "Indicator / Warning table test (KONTR LAMPTABLA)" according to the designation in the previous chapters, for better distinguishing of the two tests
- page 50: Replaced "Indicator system test" with "Indicator system test (KONTROLL)" for better distinguishing of the two tests
- page 56: Modified the engine limitations table slightly (thanks Machalot)
- page 159: Moved section "Backup approach" to page 158 for didactic reasons
- page 168: Moved section "Altitude hold warning" to page 167 for didactic reasons
- page 173: "LS" now reads "LS SKU"
- page 189: Moved section "Output of navigation data" to page 190 for didactic reasons
- page 233: Replaced "Before engine start-up checklist (with ground power on)" with "Before engine start checklist (with ground power on)"
- page 244: Moved section "Take-off on short runways" to page 243 for didactic reasons
- page 250: Added missing "L MÅL" in sentence "Cycle runway headings by pressing ___ once or multiple times until the desired runway heading is displayed."
- page 271: Rephrased section "Roll" slightly (let's see if it gets accepted ...)
- page 373: Reworked all emergency procedures slightly
- page 374: Reworked all emergency procedures slightly
- page 373: Added picture for OPTIONS > SPECIAL
- Chapter 5: removed words "checklist" or "procedure" from some headers (by definition, a procedure is something different than a checklist)
- Replaced "Cabin delta pressure" with "Cabin differential pressure" for all instances (hopefully I got all of them)
- Replaced "Master Caution" with "Master Warning" for all instances; Note: IMHO this was translated wrong from the beginning on, thus (sorry) I had to change it (HUVUDVARNING must be translated as MAIN WARNING; also, the color is red, which means "warning" and not "caution"; also, a Master Warning is triggered for flight safety relevant issues only > ergo this light comes on only when the shidd hits the fan ...).
- Added background picture (I pray it's not disturbing)
- Added date of update on the first page (thanks Machalot)
- Applied at least a half zillion small text corrections here and there (note: only a half zillion, last update there were more corrections to do ... )

 

Kind regards,
TOViper

Edited August 31, 2023 by TOViper

[Machalot]

On 8/30/2023 at 5:54 PM, TOViper said:

Yeah, absolutely right. I hated to create more versions, since I wanted to measure the downloads. If the filename changes all the time, I have to collect all that data garbage.
In the credits section of the document you may find the release date and for which version of DCS the document is made (usually the latest OB which contained ANY update/change for the Viggen module).

Also, the PDF should contain META data about the document information block (which was entered into the source file before compiling to PDF)

 

I'm grateful for all the work you've put into this, we owe you a debt.  It's a greatly improved document, and kudos for soliciting all this community input.

But I really don't understand the version numbering.  Ok, you want to keep download statistics on the January 2023 release of RC2.1.  But I don't see the logic behind "RC2.1" and "RC2.1 Updated August 2023" -- especially when the footer just says "Edition RC2.1" in all versions.  Why isn't the August 2023 release numbered RC2.2 or something?  Sorry for harping on this, but I have been bit by duplicated/non-unique version numbering at work too many times.

[Msiipola]

Thanks for your work with the manual!

But there should be a unique version number every time the document is updated. For example on the first page in the document. If you previously have downloaded the document, you never know if this is the latest update version or not.

[QuiGon]

I have to agree with the others in regards to the version numbering. It's quite odd and confusing. Apart from that your work on the manual is awesome!

[TOViper]

Hey folks, thanks for kudos!

Regarding the version numbering, the original idea was to create a new version with the RC2 as basis, so the decision was to cratee a RC2.1 (RC2 with just a few modifications according to the first updatelist). I didn't knew at that time if the manual would be accepted by Heatblur (to be put to the module officially).

The most important thing to understand is the following:
What you have now in hands is the manual RC2 in a state where I say: yeah, that's how I want my RC2.1 to be; having all repairs and changes implement.
That's why I never changed the number, because when you compare RC2 with RC2.1, there is no major change in structure and style; in fact it is basically the RC2, but a bit "better".

You can trash all versions you have downloaded so far, because ALL of them where BETA, this one now is not BETA anymore.
Why? Damnit, spoiler alert ...

 

P.S. Kodus to all of you who contributed in making this manual better!

Edited September 1, 2023 by TOViper

[renhanxue]

You're already keeping a change log of edits, clearly what you should do is just adopt the SFI's system where each page is dated individually and changes compared to the base version are highlighted with a black bar in the margin :V

[TOViper]

Oh you people ... if I had the time to do that, I would, but since I don't have ... the "Computer says NO".

[Machalot]

Just noticed something that could be improved.  On page 283 in the section about radar ranging, the terms DIVEBOMB and LEVEL BOMB are used as English translation of the weapon mode names, but everywhere else in the document they are given in the original Swedish as DYK or BOMB DYK, and PLAN or BOMB PLAN, respectively.  I think they should be in Swedish here too.

null

[TOViper]

Hey Machalot!

I agree and have already corrected it (besides many other things ...).

Thanks for the heads up!

Edited September 8, 2023 by TOViper

[TOViper]

Hey guys!

This time, I have just a small update of the RC2.1 for you.

Update 2023-09-30:

- page 283: Replaced "DIVEBOMB" with "BOMB DYK", thanks Machalot
- page 285: Added detailed description of HUD for figures 208 and 209.
- page 286: Added reference to "Fixed sight mode".
- page 329: Reworked description of BX6
- Repaired broken references to many figures (numbering didn't match anymore, if you see one, please report thank you!)
- Moved subchapter "Flight control system cockpit overview" from page 84 to page 80 (in RC2 Landing gear was a subchapter of flight controls, now it is a separate chapter).
- Applied about a quarter zillion small text corrections here and there (note: only a quarter zillion, last update there were more corrections to do ... :biggrin:)

Hafe vun and kind regards,
TOViper

Edited October 1, 2023 by TOViper

[Machalot]

Found a typo on p. 336; 80000 should be 800000.

null

 

I also have some formatting suggestions for this section.  The above bullet points could probably be better presented in a table.  The repitition of 0001 (800001), 0002 (800002), etc is kind of confusing.

The table immediately following, which presents all the detailed settings for the RB15, lacks a table number and a caption, it is just kind of floating there across two pages.

Also consider every place a CK37 memory address appears, set it in a different font, similar to how you've done with the enunciator lamps.  Maybe a fixed-width font like 800000.

Edited October 2, 2023 by Machalot

[widen76]

Found a few typos as well:

Page 117: “In Figure 94 there is a mountain about 5 km away” > Should be Figure 98 (the clickable link goes to figure 98, which is correct)

Page 261: Point 3, section “Automatic waypoint change” - “Press the fix trigger to the first detent (T0) and release” > T0 should be changed to T1

[Machalot]

8 minutes ago, widen76 said:

Page 261: Point 3, section “Automatic waypoint change” - “Press the fix trigger to the first detent (T0) and release” > T0 should be changed to T1

I also think the words "and release" should be deleted.  Releasing the trigger returns to the T0 state and would clear the fix, resuming automatic destination changes.  Unless I have misunderstood the visual fix procedure.

[TOViper]

6 hours ago, widen76 said:

Found a few typos as well:

Page 117: “In Figure 94 there is a mountain about 5 km away” > Should be Figure 98 (the clickable link goes to figure 98, which is correct)

Hey widen! Thanks for your input, but can you please doublecheck, because the newest version (September 30th) has already been corrected. Thanks!

6 hours ago, Machalot said:

Found a typo on p. 336; 80000 should be 800000.

null

 

I also have some formatting suggestions for this section.  The above bullet points could probably be better presented in a table.  The repitition of 0001 (800001), 0002 (800002), etc is kind of confusing.

The table immediately following, which presents all the detailed settings for the RB15, lacks a table number and a caption, it is just kind of floating there across two pages.

Also consider every place a CK37 memory address appears, set it in a different font, similar to how you've done with the enunciator lamps.  Maybe a fixed-width font like 800000.

 

Good input Machalot, thank you!
I think I am going to rework this section a bit for the next update.

6 hours ago, Machalot said:

I also think the words "and release" should be deleted.  Releasing the trigger returns to the T0 state and would clear the fix, resuming automatic destination changes.  Unless I have misunderstood the visual fix procedure.

Yup, thinking about the same as you.