AI Viggen roll angle

[Leviathan667]

Hi, I'm designing a mission where I'd like an AI Viggen to make a 180° turn on a 3 km radius (6 km diameter).

The issue is the plane will invariably make 78° rolls. It seems unable to make a sustained turn with any other value of roll. Is there a way to instruct the AI otherwise. E.g. turn with a 20° roll?

 

[Machalot]

At what airspeed?  Turn radius and airspeed uniquely determine G's and bank angle.  This is from the mechanics of flight, completely independent of airframe.

Edited August 9, 2022 by Machalot

[Machalot]

I made this chart quickly and didn't really check it for errors, but it hopefully gets the point across.  (If it turns out to have an error I'll correct it.)

Update: I checked it by reversing all the calculations and they are correct.

Edited August 9, 2022 by Machalot
verified correct

[Leviathan667]

1 hour ago, Machalot said:

At what airspeed?  Turn radius and airspeed uniquely determine G's and bank angle. 

 

The airspeed was mach 0.6 (730 kph) at 500m ASL.

When you say: 

Quote

This is from the mechanics of flight, completely independent of airframe.

I understand what you mean. There's a max number of Gs given a certain speed and turn radius. But what I'm looking for is to make the AI make a a turn that is well below it's max G for a given airspeed and turn radius. A very loose turn.

 

 

 

[Machalot]

25 minutes ago, Leviathan667 said:

The airspeed was mach 0.6 (730 kph) at 500m ASL.

When you say: 

I understand what you mean. There's a max number of Gs given a certain speed and turn radius. But what I'm looking for is to make the AI make a a turn that is well below it's max G for a given airspeed and turn radius. A very loose turn.

 

 

 

It's not a max number of G's. For a level, steady turn, there is exactly one specific number of G's and one specific bank angle for each pairing of airspeed and turn radius.  Independent of altitude, by the way.

It looks like 20 deg bank angle occurs at about 370 km/h TAS and 3 km radius.  

Having said all that, I can't account for the AI behavior. Are they making unsteady turns? 

[Leviathan667]

I made a video to show what happens when I try to make an AI Viggen make a turn around a large radius.

 

[MYSE1234]

14 minutes ago, Leviathan667 said:

I made a video to show what happens when I try to make an AI Viggen make a turn around a large radius.

 

Looks about what I would expect it to do with that setup tbh. It's trying to fly leveled between the waypoints, and have to make sharp turns to get to the next one due to the short distance between them.

[Leviathan667]

I'd like the AI to make a turn with a diameter of 3 km (it may be 2.5 or 6 km, it does not matter) at mach 0.6. I made a drawing to explain what I'm trying to do and what the AI actually does.

 

[Machalot]

That picture helps a lot. I posted your question on the HB testers discord and I'll let you know what they say. 

[Leviathan667]

Thanks.

[Machalot]

So far the suggestions are:

1. command a circular orbit and end it after a half orbit. 

2. maybe there's an aerobatics task that will do it.

Doesn't sound promising.

[Leviathan667]

Thanks Machalot! I did try the aerobatics task. It works provided the following is done:

• Set a 180° turn
• Empirically find out the roll angle for a 3 km turn given the aircraft's speed (I'd very much like to find out how you mathematically make this kind of calculation)

My finding was: 

	Speed					ASL altitude
Turn radius	IAS1	TAS1	IAS2	TAS2	Mach	Alt1	Alt2	G load	Roll
3 000 meters	398 mph	396 mph	736 kph	734 kph	.60 mach	500 meters	1 645 '	1.74	55 °

• Set an area where the turn ends
• Make a triggered action (switch to WP2) and it works.

 

See imagenull

 

 

[Machalot]

18 minutes ago, Leviathan667 said:

Empirically find out the roll angle for a 3 km turn given the aircraft's speed (I'd very much like to find out how you mathematically make this kind of calculation)

For 3 km turns you can use the plot I made above.  If you want a general capability for any radius I can give you the equations.

[Leviathan667]

18 minutes ago, Machalot said:

For 3 km turns you can use the plot I made above.  If you want a general capability for any radius I can give you the equations.

I'd like to have the equations please.

Also, unfortunately the aerobatics task won't work when the main task is anti-ship. It does not work with AFAC, pinpoint strike, etc. also. But it does work with ground attack, intercept, CAS, etc. How strange!

24 minutes ago, Machalot said:

For 3 km turns you can use the plot I made above.  If you want a general capability for any radius I can give you the equations.

Yes indeed. It is very useful!

[Machalot]

1 hour ago, Leviathan667 said:

I'd like to have the equations please.

You can make a copy of my spreadsheet. 

https://docs.google.com/spreadsheets/d/1UO-FqLKl_dQl50_dzuHEvxhtSyU5kxsMvIvesEfPFMY/copy#gid=0