Back to R/L visual detection of airborne targets for a moment.
After looking around the net I found a few interesting pdf's on BVR and WVR, etc.
Lt Col Patrick Higby, in
Promise and Reality: Beyond Visual Range (BVR) Air-To-Air Combat, presented to the Air War College, cited an USAF officer who evaluated missiles:
"Colonel James Burton selected five nautical miles—in daylight—as his BVR limit for evaluating air-to-air missiles."
footnoted: Burton, James G., “Letting Combat Results Shape the Next Air-to-Air Missile,” USAF Slide Presentation, 1985
So, evidently these two aviators have some lack of optimism on detecting enemy A/C at great distances.
The following citations are taken from a PhD thesis:
IMPROVING TARGET ORIENTATION DISCRIMINATION
PERFORMANCE IN AIR-TO-AIR FLIGHT SIMULATION
May 2003
"A total of 759 training engagements at the Naval Air Station Oceana Tactical Air Combat Training System (TACTS) range revealed that in 624 of the engagements the pilots first sighted the target as a dot against the background at an average distance of 5.67 nmi (Hamilton & Monaco, 1986; Monaco & Hamilton, 1985). In the remaining 135 engagements exhaust smoke, contrails and sun glint off the aircraft allowed the pilots to detect the aircraft at even greater distances. In the 122 engagements where exhaust smoke was the primary cue, detection distances averaged 7.64 nmi."
A dot at less than 6 miles for a jet fighter means a dot at
some closer distance for a WWII fighter. E.G. ME 109's are quite a bit smaller than modern combat jets.
"In 1983, Kress & Brictson studied 87 air-to-air engagements at the Yuma TACTS range. Average unaided detection distances for the target F-5 and F-4 aircraft were 3.1 nmi. When the pilots were aided with a head-up display (HUD) symbol that cued the pilot to the target’s location, the mean detection distance grew to 6.8 nmi."
F-5's are about the smallest jets around, around Mig-21 size, but they are still some amount larger than WWII fighters.
"Another study that investigated detection distances was Temme & Still (1991). They measured air-to-air target detection distances at the Naval Air Station Oceana TACTS range to see if there was a performance difference between those pilots who wore corrective eyeglasses and those who did not. Those with eyeglasses did not detect the targets until they were about 10% closer than those with unaided vision. Two very closely matched groups of eyeglass and non-eyeglass wearers had average detection ranges of 4.52 and 5.64 nmi respectively when using all detection means including aircraft sighting, target glint, contrails and exhaust smoke. When limiting subjects to aircraft-only detections, the corresponding distances were 4.35 and 5.54 nmi respectively."
"Another study by Hutchins in 1978 at the Air Combat Maneuvering Range (ACMR), which is the earlier name of the TACTS, involved 45 air combat training engagements. The mean detection distance of the A-4 targets was 3.09, with a range of 0.38 to 6.23 nmi.
"Other studies were done using observers on the ground. With visibility conditions spanning 7 to 10 miles over an 8-day testing period, O’Neal & Miller (1998) found detection distances for approaching T-38 aircraft to ranged from 4.77 to 6.73 nmi."
"Another ground observer study used 400 visual detections of a T-38 aircraft (Provines, Rahe, Block, Pena, & Tredici, 1983). The aircraft was approaching from a known direction and a distance of 9 miles and mean detection distance was 4.55 miles over the 400 trials."
So these studies put an outer limit on unaided detection of modern jets to a range of less than 6 miles. IMHO, during WWII in many combat situations where there was no CGI to guide pilots to the enemy, unaided visual detections of smaller WWII fighters are going to be less than the distances listed above.
IMHO, as I've mentioned before, for FSO or AvA there could be a parameter for a neutral icon color at greater distances that lets people see the "dot" as a
bogey with the descriptor - inline, radial, twin, multi, or something like that, and then depending on parameter settings, the closer it gets it suddenly reveals itself to be friend or foe.
Best.