SR-71 Blackbirds playing chicken, what do the pilots see?

Factual Questions
1

Inspired by a scene in a story I recently read (in that only one plane was a Blackbird but this simplifies things)

The scenario is both planes are approaching head on at operational altitude and Mach 3 (for a closing speed of Mach 6) and the question is, what would the pilots see?

Given clear conditions how far away could they reasonably spot the other plane and what would it look like as the other aircraft approached?* Would it seem to grow gradually from a dot or would the closing speed be so fast the pilot wouldn’t really be able to see much at all?

…and how big would the boom be when they hit? (I’m joking with that one but I’m sure it would be pretty impressive)

*In the story the sun angle is low and it reflects off an unpainted panel on one of the aircraft letting the other pilot spot it further away than he would have otherwise.

2

I think it would depend on whether the planes were leaving contrails. A contrail is far more visible than the plane itself, so in this case you would see the trail approaching from a reasonable distance. Once you actually saw the plane, it would be on you very quickly. You could work out the distance at which you’d be able to see it under optimum conditions if you knew the diameter and the visual acuity of the eye.

This video has some “head on” passes of airliners, filmed from the cockpit. The closing speed here would only be about Mach 1.6, and you can see the planes are gone pretty fast from when they are first visible, but because of the contrails you can see them approaching from quite a way before that: Air-to-air traffic: aircraft, fly-by's, contrails - YouTube

3

At that speed, it’s all plaid.

4

Well, even if the planes aren’t closing perfectly head-on to each other, and even accounting for the curvature of the Earth, would even visible contrails be enough to warn the two pilots that, “Hey, there’s something up ahead of me, and it’s coming at me really fast?”
The wiki on the SR-71 lists its top speed as Mach 3.3 at 80,000 feet, which is 2,200+ mph/3,540+ kph (~3,227 feet/sec or ~983 meters/sec). Not sure if Blackbirds tool around at Top Speed all the time, so the “Cruising Speed” could be considerably less, although I do recall reading somewhere that the Blackbird’s engines work best at higher speeds; something about Ramjet airflow versus regular jet turbine engines.
Doubling that (best closing speed, head-on to each other) is ~6,400+ feet/sec or ~1,900+ meters/sec; at those speeds, it seems to me that it’s kind of a “blink-and-you’ll-miss-it” situation.
IIRC, at that altitude, the sky is more black than blue, so a Blackbird might be hard to spot.
Maybe LSLGuy or Johnny L.A. can weigh in for some pilot’s perspective on this.

5

So take, for example, the nice example at 0:36 in that video. 6 Mach/1.6 Mach is 3.75. Imagine that segment of video speed up 3.75 times. Instead of lasting 18 seconds it lasts 4.8 seconds.

One thing people forget is the square law on visual area vs. distance. Things are quite small and not increasing all that fast and then when near zoom! They get big faster and faster.

6

GOL flight 1907 hit a private jet very nearly head-on, and it doesn’t seem that the pilots of either flight ever saw the other plane approaching. The smaller plane was landed successfully, and while the pilots knew they had hit something they had no idea what it was until several hours after they landed.

7

Wikipedia says that normal visual acuity, if I understand the entry correctly, means that you can discern an object that occupies an angle of 1 arc-minute of your field of view. The SR-71’s wingspan is 55 feet, so when it occupies 1 arc-minute of your field of view, it’s at a distance of 35 miles. But the wings are so thin that this would require that it approaches you in an impossible attitude (i.e. with its yaw axis pointed directly at you). Consider instead that it’s actually approaching you nose-first, and the relevant dimension for the angle calculation is much less than 55 feet. We should instead use something like engine nacelle diameter, or fuselage height, which appears to be more like 6 feet; this reduces the distance of first discrimination to 3.9 miles. The time required to close that gap is just 3.2 seconds.

So if the pilot of one of the planes happens to spot the other at the first possible moment, he’ll have just enough time to think “hey, I think that’s headed toward me” before generating a shower of titanium and meat-mist.

8

The closest thing to this happened many times during the cold war when SR-71s were over the Barents Sea (north of Scandinavia), skirting the Russian coast, and they were intercepted head-on by Mig-25s or Mig-31s. Initial vectoring was ground-based, then within about 60-75 miles the Mig-31 IR scanning could pick up the hot SR-71 against the cold sky. Other onboard detectors on the Mig gave approximate distance to target via triangulation, which allowed planning the required zoom climb to reach 62,000 ft, which was within the engagement range of the R-33 missile. The R-33 was similar to the American AIM-54 Phoenix: R-33 (missile) - Wikipedia

This was extremely difficult and only possible because the SR-71s were flying the same route repetitively and the Soviets had good intelligence about the takeoff time, thus allowing over three hours to prep the Migs and them in position. These were non-hostile intercepts, viewed as practice for time of war. The SR-71s were not maneuvering or using their extensive ECM suite.

For the Barents Sea missions, the SR-71 was typically at about Mach 3.0 at 75,000 ft. As fuel burned off, it was capable of Mach 3.2 and about 85,000 ft, but the slower speed was chosen due to the required 32 degree bank angle to follow the coast, which reduced the chance of an engine “unstart”.

The Migs (although nominally capable of Mach 2.8 or so) had to trade speed for altitude, so by the time they reached about 62,000 ft, they were probably only going about Mach 1. The SR-71 passed overhead, head-on, 13,000 ft higher; the head-on closing rate was possibly around Mach 4.

A Mach 4 closing speed equates to about 1 mile per second, so under ideal conditions the SR-71 could be detected about 60 seconds out via IR. Due to the extreme closing velocity and thermal and fuel limits on the Mig, it had difficulty reaching that altitude then safely reaching the ground. So the pull-up maneuver had to be precisely timed.

Visually, the Mig pilots typically only saw the SR-71 as a contrail (in the rare conditions contrails existed at 75,000 ft) and/or a visual dot. Only once did any Mig pilot report visually seeing the aircraft as a small discernible outline. In published reports he did not give a subjective impression of the aircraft speed, but if some of the previously-posted airliner footage was played at 2x speed, that might roughly approximate it.

These were reported in the most detailed SR-71 book, “Lockheed Blackbird: Beyond the Secret Mission”, by Paul Crickmore. He even interviewed both Soviet and American pilots on both sides of the intercepts to get their personal accounts: Amazon.com: Lockheed Blackbird: Beyond the Secret Missions (Revised Edition) eBook : Crickmore, Paul F.: Kindle Store

9

Radar is your best friend here?

10

How far away would the other Blackbird have to be for you to have enough time to say that sentence, or even think it?

11

It took me 2.4 seconds to utter the sentence; at a closure rate of 1.21 miles per second, that’s 2.9 miles.

12

Which just shows that a simple “FUCK!!” might give you enough time to get out of the way.

13

Thanks for the answers everyone! That’s a really interesting read :slight_smile:

14

Absent contrails …

At airliner altitudes, armed with TCAS which is telling us an approximate azimuth and relative altitude, it’s rare to spot an opposite direction aircraft much outside 15 miles. 5 to 10 miles is more typical. If it’s hazy you may never see them at all despite them going by 1/2 mile away.

Back when I had younger eyes I could usually spot the speck of another fighter at about 8-10 miles. But that was looking through a box on the HUD telling me which tiny section of sky to scan. Absent radar info max practical spotting range is more like 4-5 miles.

Targets are easier to spot when they have some relative motion against the background. Targets you’re going to collide with will always have zero relative motion.

Absent relative motion, targets are easier to spot against a featureless sky than against a complex varying background of clouds and land. Conversely, with relative motion, targets stand out better against a mildly varying background. But not a real busy one. e.g. Looking down to spot a helicopter or light plane against a city background is very difficult.

As said by others, visual cross section is what matters. The side view of a 747 is much larger than the head-on view of the same aircraft. The head-on cross-section of an SR-71 is tiny.

Overall I’d expect that two SR-71s at cruise speed at cruise altitude doing a knowing head-on pass would spot each other just in time to start to think “oh …” before they collided. In an unknowing pas the odds are overwhelming they’d never notice, much less register seeing, the other aircraft before they collided.

15

I didn’t run the numbers on visible cross-section the way you did, but my intuition was telling me that, in this scenario, it wouldn’t matter much; yours and LSLGuy’s posts pretty much confirmed what I’d already suspected.

“…shower of titanium and meat-mist” indeed. :smiley:

16

Didn’t that vary according to size (F15/Su27 vF16/MiG29/Mirage series) and smokey engines (or not)?

17

Smoking engines mattered a lot, especially when looking up at them. Smoke trails are not as obvious against a ground background as against sky. Smoke trails don’t stand out as much as does dragging a contrail. Which case I dismissed in the first sentence. The F-4 had a standard tactic to close on the target with one engine in full afterburner and one in idle. Those two settings minimized the smoke versus the more conventional two engines at max power without AB which smoked like a coal-fired locomotive.

Size matters some. Absent an atmosphere it’d matter linearly. The max possible eyeball detection range would be strictly a matter of the angular size of the vehicle as seen from your aspect angle.

Head on or nearly so all these craft are pretty small. The head-on difference between the hulking F-14 and the tiny F-16 is 1 or 2x. Conversely in a maneuvering fight where you may be looking across the circle at the other guy’s planform, the difference between the F-16 and what we called the Rodans was significant. More like 5x or even 7x with the wings out.

Once you put some atmosphere with haze into the mix the differences based on size drop down a bunch. Often the haze reduces visibility such that you see an F-16 at 4 miles, a F-14 at 5 miles, and a 747 at 6 miles. Nothing, not even the broad side of a blimp, can be seen at 10 miles.

The higher the altitude, the less haze matters. But once you’re into the upper 20 thousands and above you often get cirrus clouds which have the same effect. Those altitudes are also the ones susceptible to contrails. I drove home yesterday at 39,000 in thin cirrostratus for all 3 hours enroute. We had a bright purple & orange 737 go by 1000 feet below and maybe 1/2 mile lateral offset. Never saw him despite knowing where and when to look.

18

Lucky you; I’m still holding out for the flying cars they promised us back in the 50’s, just so I can say the same.
Just out of curiosity, what were you “driving?”

19

Boeing 767-300ER