When my military specialty comes up in conversation, there is one question that’s always asked. It’s not “Have you been in combat?” (No.) It’s not, “What’s it like?” (Exciting, fun, fulfilling, terrifying, painful, exhilarating. Have you got all night?). No, the question that is asked 100% of the time is “What’s the fastest you’ve ever been?”
The answer to “How fast is the aircraft going” is best answered “relative to what”? According to Sarge’s Official Source, there are 6 measurements of airspeed. Indicated Airspeed, Calibrated Airspeed, True Airspeed, Equivalent Airspeed, Density Airspeed and Groundspeed. #4 and 5, I’ve either never heard of, or flushed them from my mind in an attempt to reclaim unused memory. So, in this abbreviated session of Aeronautical Engineering 101, we will discuss the official definitions of the 4 remaining measurements and what they actually mean.
According to Wikipedia, “Indicated airspeed (IAS) is the airspeed indicator reading (ASIR) uncorrected for instrument, position, and other errors. From current EASA definitions: Indicated airspeed means the speed of an aircraft as shown on its pitot static airspeed indicator calibrated to reflect standard atmosphere adiabatic compressible flow at sea level uncorrected for airspeed system errors.” Huh?
Indicated Airspeed is the speed the air hits the hole in the Pitot tube. It is also the speed the air hits the wings and since the air flowing over the wings keeps you airborne; this is a good number to know.
Again according to Wikipedia, “Calibrated airspeed (CAS) is indicated airspeed corrected for instrument errors, position error (due to incorrect pressure at the static port) and installation errors.” In other words (yes, please!), indicated airspeed isn’t the exact speed of the air hitting the Pitot tube, it has to be corrected for position errors of the static port. OK, Mr. Test Pilot, is there air flowing across my wings or not? Most modern aircraft display Calibrated Airspeed on the Airspeed Indicator.
“True airspeed is the speed of the aircraft relative to the atmosphere. The true airspeed and heading of an aircraft constitute its velocity relative to the atmosphere.” Because the air gets thinner as the aircraft goes higher, there’s less pressure on the Pitot tube for a given speed. This is typically expressed as a percentage of the Speed of Sound AKA Mach Number (661.4788Knots at sea level on a standard day (59 degrees F).
“Ok, Mr Test Pilot, How long is it going to take us to get from Point A to Point B?” Ahh, you mean ground speed! Ground Speed is essentially True Airspeed adjusted for Wind. A True Airspeed of 500 knots flying into a direct headwind of 80 knots results in a groundspeed of 420 knots or 7 nautical miles per minute. (A nautical mile is 6000’, it’s easier to compute), so a 700 mile journey is going to take 100 minutes. Same airplane flying with a 100 mile tail wind will complete the 700 mile journey in 70 minutes. Which explains why it take a lot more time to fly from New York to Seattle than Seattle to New York in the winter. In the northern hemisphere, the jet stream tends to flow West to East.
We’re done with definitions. (BTW it could have been much worse, Wikipedia provided formulas to calculate all those different airspeeds! Didn’t want any heads exploding out there.)
So, Juvat, what’s the fastest you’ve ever been? (800 knots fastest speed on my airspeed indicator and 1600 knots fastest ground speed.) Why did you go that fast? And the answer to any question related to flying beginning with “Why” is always “Because I couldn’t” …pull harder, land quicker, fly higher or in this case, go faster!
So….There I was*
FAST!
Flying the F-4E at Moody. Reagan is in the White House and the military buildup that would eventually cause the fall of the Soviet Union has begun. Where at Kunsan, under the second worst President ever, flying time per month was in single digits, we’re now flying 25-30. It was glorious, so much easier to maintain proficiency in your skillset when you actually use your skillset. But I digress…
One of the other benefits of the buildup was the emphasis on realistic training. We deployed to Red Flag frequently, to the tune of 2-3 times a year. On one particular deployment, I was leading a two ship on a pre-exercise warm up ride. The Red Flag rules required crews to fly two sorties with practice ordinance before they were allowed to drop live ordinance. The first ride was with BDU-33s, a 25 lb practice bomb, and the second ride was with full sized inert weapons. This took care of a few things. First, it familiarized the crews with launch and recovery procedures. It also familiarized the crews with the airspace and targets. (It’s “poor form” to drop a 2000 lb live laser guided bomb on some Rancher’s cattle trough because it looks vaguely like the SAM site you were searching for.) And since all crews did them, it got the crews into the visual lookout habit.
We’d been there several times, but had to “bomb up” every time. Today’s target was a SAM site that was comparatively close to the range entry spot. We had hit the tanker before entering, so gas was not going to be a factor. The range was cleared supersonic at all altitudes and minimum altitude was 300’ AGL. We’ve popped up, acquired the target (the real one, thanks for asking!), had a successful release (thank you BB stackers), and watched the bomb track right into the abandoned Bread Truck that was the SAM “Radar Van”.
Feeling very enthused, we are egressing the area, in formation and I decide to see how fast an F-4E with two tanks and a jamming pod and a Pave Spike (laser) pod will go at 300’ above the ground. Gas is not a factor. Stroke up the AB and let the Rhino run! Through the Mach with no real problem, but that’s about as fast as the old girl will run.
We’re in good formation, I’m on the right, visual look out is set. Front seaters have front vector and outside the formation. Back seaters have rear vector and inside the formation. A quick glance up, and I see a Canadian F-104 a couple thousand feet above me passing left to right. Maybe he doesn’t see me. Just as we pass under him, I see him start a right turn. Perfect! It’ll be 180 degrees before he starts having a converging vector to our flight path. The 104 doesn’t turn very fast, so I should be well away before he gets turned around.
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| F-104 affectionately known as the "Zipper" Source: aereimilitari.org |
We’re roaring along and rapidly coming up on the edge of the airspace when I sense a presence. I look out the right side and there, in fingertip formation with me is the F-104! He waves, THEN lights the AB and accelerates away from me. Ok, note to self. First, supersonic at 300’ above the ground in a desert will raise a dust cloud visible for miles pointed right at you. Second, an F-104 is a Mach 2 capable fighter.
FASTER!
I’m at Cope Thunder in the Philippines (the Pacific Air Force’s version of Red Flag) flying the F-15. Today’s mission is an Offensive Counter Air mission and we’ve got responsibility for the post-strike egress. Comparatively, the Pre-strike guys have it easier. Everybody on their radar screen is bad. Not so for post-strike. We’ve made it to the target area and made the turn to the egress route, make out the F-16s about 10 miles in front of us. We’re too far back to help them if needed. I push it up, but unlike Nellis, there’s a very strict restriction against supersonic in the Philippines. I can only get to about 600-625 without risking a boom. I’m gaining on them, but not very quickly.
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| F-5E Source: mnd-nara.tistory.com |
Finally we get to feet wet where supersonic is authorized. In with the burners, and as I accelerate, I see an Aggressor F-5 starting to convert. While in range right now, when he completes the conversion, any missile shot I take now will time out unsuccessfully. I call for the F-16s to break, but they don’t. Above the Mach now, I glance inside and see 800 on the HUD. For a second I think that’s an altitude, then realize that’s speed. I’m closing on the F-5 quite nicely and the F-16s seem to have stagnated him outside of range in trail. I’m in range, take the shots, watch them time out and call the kill.
The F-5 pulls off and heads to the regenerate point (he has to “touch base” to get a new life, adds realism to the exercise). I keep an eye on him for a minute and notice that my canopy is kind of rippling. Betty tells me I’m at Bingo, so I pull it out of burner and pull it into a fairly steep climb, top out in the high 40s, proceed to the airspace exit point, then back down to Clark, pitch out and land. I ask the maintenance chief about the canopy. He said that was normal at very high speed and was caused by the friction of the air against it.
FASTEST!
We’re at a different Cope Thunder and this time the Red Air is provided by a squadron of RAAF Mirages. This will be their last big exercise in the Mirage before they outfit their squadron with FA-18s (Fay-Deens in their lingo). We will assist in their transition but that’s a future story.
I am leading a flight of 4 F-15s in a pre-strike sweep, our shoot ROE is everybody out front is most likely bad, but we have to have a positive ID before shooting. There are a lot of ways this can be accomplished, most of which can’t be talked about. Suffice it to say, this ROE tended to make sure there were huge swirling engagements. I’ve got a contact out front coming down the scope. He’s approaching range for the shot and I’ve got an ID. It’s a Mirage.
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| Mirage IIID and Mirage IIIE Source: es.wikipedia.org |
“ Fox 1”.
He starts a turn to slow down the closure, increasing time of flight of my missile. That turn is taking him away from the strike package, so I turn slightly away from him back toward the package. The missile times out as a miss, meanwhile this guy is right at the edge of the scope 60 degrees at about 20 miles. I’m starting to get too far away from the strike package to support them and turning any further towards the package will cause the Mirage to drop off my radar. I hand him off to the AWACS to keep track of and turn hard to get pointed back at the package and push it up.
AWACS calls and tells me the Mirage has turned hot and is 20 miles in trail closing. The package speed is planned at 540 (9 miles a minute), I’m doing 600 (10). If he’s at the Mach, it’ll take him 10 minutes to close. TOT for the package is 4 minutes. He’s not going to be a factor for ingress, but I file him away to watch out for on egress.
About a minute later, AWACS calls and says Bandit is at our 6 for 10 miles closing. Holy Crap, how fast is he going? She barely finishes that call and she updates it to 5 miles and closing.
I call the flight to hard turn 180 degrees (Hard turn, as opposed to break turn, is an energy conserving turn of typically 6-7 gs, Break turn is everything she’s got). We come around and in the turn descend to put him with a blue sky background and us in the ground clutter. Chaff and Flares just because. Get a radar lock and a visual inside min range for either missile.
But there are four Eagles and only one of him.
The turn, chaff and flares had broken his radar and missile locks, so no friendly losses. Did I mention the Mirage is a Mach 2 capable fighter? So, if I was doing Mach 1 and he’s doing Mach 2, at sea level on a standard day, effectively, I’m doing 0 and he’s doing 661.4788 knots (11 miles/minute and change).
There’s an old fighter pilot adage that goes “Speed is life, keep your Mach up.” But there’s also “It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles; if you do not know your enemies but do know yourself, you will win one and lose one; if you do not know your enemies nor yourself, you will be imperiled in every single battle.”**
Oh, and the 1600 knot ground speed? Had a wingman abort on takeoff for a 1v1 BFM ride. All alone in an F-15 with a bunch of gas, thought I'd see how fast she'd go at 50,000'. Airspace was 250 miles long. I got across it fairly fast, but the perception of speed wasn't there. Kind of boring actually.
Oh, and the 1600 knot ground speed? Had a wingman abort on takeoff for a 1v1 BFM ride. All alone in an F-15 with a bunch of gas, thought I'd see how fast she'd go at 50,000'. Airspace was 250 miles long. I got across it fairly fast, but the perception of speed wasn't there. Kind of boring actually.
*What’s the difference between a Fairy Tale and a War Story? A Fairy Tale begins with Once upon a time and a War Story begins So, there I was.
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