Realistic AAR (and other) Orbits

Discussion related to development of realistic carrier-based combat missions.
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Rhino
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Realistic AAR (and other) Orbits

Post by Rhino » Thu Feb 10, 2022 7:22 pm

Getting the speeds of tankers and other orbiting aircraft like AWACS correct in the mission editor can be difficult because the airspeed setting in the DCS Mission Editor is set for either ground speed, or True Airspeed (I've seen it listed both ways) as opposed to indicated air speed (KIAS), which is obviously more useful for us in the air. For this I'm assuming True Airspeed (TAS) There's a relatively simple math equation to get this input correctly. It is:

TAS = (KIAS x 0.018 x altitude in thousands of feet) + KIAS

So for instance, say you want the tanker at 20,000 feet with an indicated speed of 275 knots it would be: TAS = (275 x 0.018 x 20) + 275; solved TAS = 374, so that's what you put in the speed box for the tanker in the mission editor and then also making sure it's in correctly in the orbit advanced waypoint criteria. This formula will allow you to put any aircraft at any particular indicated airspeed and altitude you want, within the performance capabilities of the aircraft of course.

The following is some real world info about the two main big wing tankers we use in DCS.

KC-135 MPRS-
Standard orbit speed: 275 KIAS or .78 mach, which ever is lower
MPRS refueling altitude band: 5,000-35,000 feet
MPRS refueling speed band: 220-300 KIAS
A/A TACAN is DME only, no bearing info (correctly modeled in DCS in the Y band)
In a standard 4-hour refueling sortie, KC-135 can offload on average up to 135,000 lbs of fuel

KC-130-
Standard orbit speed: 240 KIAS
Refueling height band: 500 feet up to service ceiling (approx. 28,000 feet)
Refueling speed band: 120-250 KIAS
A/A TACAN is capable of both DME and bearing info (currently only modeled with the X band in DCS AFAIK)
In a standard 4-hour refueling sortie, KC-130 can offload on average up to 28,000 lbs of fuel

Source: https://www.japcc.org/aar
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Trim
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Re: Realistic AAR (and other) Orbits

Post by Trim » Mon Feb 14, 2022 1:00 pm

Curious where you got that formula. Is that something from ED? I don't know how they calculate TAS, but in the real world, it is based on pressure altitude and air temp. Neither of which are in that formula. So, is it just something to get you in the ballpark, or is that how ED calculates TAS?

Lion
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Re: Realistic AAR (and other) Orbits

Post by Lion » Mon Feb 14, 2022 1:19 pm

any info on what altitudes recovery tankers should fly at?

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Rhino
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Re: Realistic AAR (and other) Orbits

Post by Rhino » Mon Feb 14, 2022 3:07 pm

I pulled the formula out of a Discord discussion on the Hoggit server awhile back, so I think it’s got to be relatively specific to DCS behavior. I’m by no means a math or physics guy, so I certainly didn’t come up with it on my own. I’m of the belief that the speed you input into the mission editor is always ground speed, as opposed to TAS. That makes the most sense to me because the ground units are also done in knots through the same interface and I doubt there is different programming between air and ground units as far as the mission editor is concerned.

That said, the formula seems to work in so far as you do the calculation and the indicated airspeed you’ll see in the cockpit is what you wanted given the input inside the mission editor. However, I have not experimented with substantial changes in temperature or barometric pressure within the sim to see if that changes the outcome.

Lion, I’ve not found any official documentation for overhead recovery tanking with the S-3. However, from what I’ve read, recovery Marshal stacks for the air wing started at 2,000 feet and went up every 1,000 feet for each squadron in fuel priority order. So for an air wing circa late 90’s, early 2000’s I would assume 3 hornet squadrons at 2,3 & 4 thousand feet, a tomcat squadron at 5K, Prowler at 6K, S3 at 7 and E2 at 8, thus the recovery tanker would probably be orbiting at no lower than 9,000 feet. But I don’t know if a squadron was just always assigned a specific altitude for use on every recovery, or if altitudes were assigned by the marshal controller based on what aircraft were actually flying in that particular cycle. Again, that’s mostly speculation on my part. Surely Mr. Bean will have much better real world knowledge of the marshal altitudes and recovery tanker altitudes.
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Trim
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Re: Realistic AAR (and other) Orbits

Post by Trim » Mon Feb 14, 2022 3:59 pm

Yeah, the way they do airspeeds in the ME is definitely not straight forward. If it was a ground speed though, the indicated speed should change depending on where in the orbit it was, assuming the wind is not set to zero.

I'm all for whatever gets us a tanker going at a decent speed. If that formula works, great.

The biggest issue with setting up the tankers in the ME is that IRL, they will come to you and fly at whatever speed you want them to, for the most part. That's my understanding anyway. They can't so that in the sim, so we have to set them on a racetrack pattern and we have to go to them. If they just started flying away from us in their pattern we may have to fly really fast to catch them, or flying slow and plan on waiting until they come back. Either is not great for fuel efficiency.

I'm pretty sure that IRL if an aircraft is having fuel issues while recovering, the recovery tanker would get themselves in a position so that if the landing aircraft bolters, they can already be in a position to just drop down to them and hook up. That's why real world they can let their fuel get a lot lower than we can before they have to get fuel. That's why I'm okay with landing a bit heavy. If we are bringing ordnance back, sometimes we might need to dump so much fuel to get below trap weight that we might only get one pass.

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Rhino
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Re: Realistic AAR (and other) Orbits

Post by Rhino » Mon Feb 14, 2022 4:20 pm

I believe that is for the most part true regarding IRL tankers. I’m also pretty confident that they generally fly their orbits at a much faster (and more efficient) cruising speed until they’re requested for a rejoin, at which point they slow to the more acceptable speeds for fuel transfer, which obviously we can’t set up in DCS.

I’ve been reading a couple books about the Hornets and Tomcats use in Iraqi Freedom and they mention that the tankers would do their best to change altitudes and airspeeds to compensate for weather and turbulence. Not sure how often they would stray from an established tanker track however, except to support a SAR or other emergency.

Seems to me so far our mission builders have pretty accurate tanker tracks/speeds. I think our Marianas range KC-135 is pretty consistently in the 250-270 KAIS range and if I recall correctly, the tanker in the campaign two missions back was right in the 260-270 range.
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