To quote John Oliver:
"Yemen, home to 26 million Yemeni people, and 27 million American drones."
While these numbers may be slightly exaggerated I started to wonder. As far as I know, military drones are used primarily for survaillance, meaning that they circle a potential target for hours on end to gather intelligence.
I immediately thought, that they would be spotted quickly, and any illegal activity would cease. Since they seem to be effective though, this can't really be true.
So my question is: Given typical operational parameters during survaillance, can military drones, like the Predator, be spotted with the naked eye if they are circling above you?
I tried to find an answer with some quick calculations of my own.
I can see quite a lot of airliners flying above me, and I can see their bodies quite easily. Airliners are larger though.
Some sizes I could gather are:
Length: 37.57m Wingspan: 34.1m Body width: 3.96m
Predator Drone Source
Length: 8.23m Wingspan: 14.84m Body width: 0.83m (estimated from picture)
When I look at just the length of the aircraft, I can calculate the angular size of the object in the sky if I know the altitude. I assume the A320 flies at around 32000 feet, or 9753m. For the drone I have no idea. But it can fly at 7620m and I would assume it stays a bit below, so I assume 6000m.
The angle of the object is then:
Angle = ArcTan(Length/Altitude)
The human eye has a resolution of 0.5-1 arc minutes, or 0.0125°.
For the given aircraft I come to these values:
A320: Angle = Atan(37.57/9753) = 0.22° Predator: Angle = Atan(8.23/6000) = 0.08°
So from the length, both aircraft should be visible. However, that doesn't seem to make sense, because they need to be wide enough as well. So for the body width's I get:
A320: Angle = Atan(3.96/9753) = 0.024° Predator: Angle = Atan(0.83/6000) = 0.008°
So the A320 should be visible quite comfortably, while the drone should be invisible to the naked eye.
This is all theoretical. I don't know the operation of the predator, especially how high it flies. I also don't know what really determines visibility. Does the wingspan alter the numbers?
Can anyone share any actual insight?