Zipping at FL 730 - Flying the "hottest" 104

by Walt BJ, retired USAF F-86, F-102, F-104 and F-4 pilot

Hokay. Sit down, lean back, open a cool one, and here it comes.

It was in 1967 and Paul Da San Martino and I were sent up to Tyndall AFB in the Florida Panhandle to do some fighter affiliation with a U-2 to test its new self-protection device. We got to fly the missions because we both had full pressure suits, a USAF modified version of the Navy Mark IV. Very comfortable compared to the old partial pressure MC3 and MC4s, even comfortable enough to perform air combat wearing them, something that was not true of the MC3/4 suits. Anyway the U2 was up at his operational altitude for the tests and we made numerous intercepts, playing the enemy for him. His device didn't particularly bother us and we deduced from what we could see on our radar scopes that our ASG14 radars were not sophisticated enough to be bothered. I don't know how familiar you are with the ASG14 but it's a modern analog to the RAF AI 10 used in WW2. Basically, it is a spiral scan search radar with no angle track capability. Just find him on the scope, turn toward him to fly him to the center and go get him. You know when he's dead ahead (on boresight) because then he paints as a circle around the center of the scope - the circle's radius is his range. The set can, however, lock on and track a target in range from 10 miles on in. The pilot has to keep the target directly ahead, as I said, since there is no angle track capability at all. It can, when locked on, feed range to the computing gunsight; effectively, too, I might add. Range shows up on the sight; miles when missiles are selected, feet when guns are selected.

A side comment on intercepting U2s. We had been doing this from some time in our F104As with the original J79-3B engine. The mission was fuel-critical; a five minute delay meant every thing had to go just right or we'd be low on fuel for the required IMC approach. The installation of the J79-19 engine (a slightly modified -17 engine) increased our excess thrust about 25%, so we expected an improvement but were uncertain as to how much. We were pleasantly surprised.
The first time we ran an intercept on a U2 at his operational height in the Dash 19 bird, we had no data to plan from nor did the FSQ7 SAGE computer. To make things simple and sure I had the controller roll me out 35 miles behind the U2 at 38000 (tropopause that day). Catching the U2 would be no problem since the overtake at attack speed would be in excess of M1.2. I went to max AB and followed the controller's steering. I was mostly looking out for him since often the U2 emitted a wisp of a contrail. Then at 18 miles I saw a contact at 12:00 on the radar. (20 miles was the only range selection in search) and glanced at the gauges. I was now doing M1.8 at 58000, and I was most impressed since the old 3B would have still been way below that struggling to get to M2.0. I completed the intercept, getting a tallyho at about 2 miles, and pulled off the target with about 1000 pounds more fuel than I'd ever had left with that old engine. One caveat I should add - we frequently had much colder than standard OAT over Homestead (HST) at 25N latitude - as cold as -75 Celsius. That does help even the Dash-19's performance. I remember seeing the E/M diagram for the -19 bird - can't find out who's got one nowadays but I do remember the -19 Zipper peaked at 1300 Ps.

SAGE is 'Semi Automatic Ground Environment' - a giant dinosaur of a dual computer that could calculate 600 intercepts simultaneously. Each SAGE system covered roughly a 600 mile square. Many ground radars transmitted data to it - it integrated the inputs and solved each intercept every two seconds. The commands were transmitted to the interceptors by data link. There were two dials, one target altitude, the other commanded altitude, and a data-link command steering dot on the scope. A small circle was positioned on the scope where the computer thought the target would be. It was accurate enough even for the 104A's 'spinscan' radar. I liked SAGE and data link after the bugs were gone - it was nice and quiet; the only voice communications were for safety. It even worked pretty good! Never as good, though, as an expert GCI controller who knew the ropes of fighter v fighter combat. For example: "BJ, Dave here - he's 20 port 15, turning hard into you.....hard port 140; he'll be 12 o'clock for 10, 10,000 high..."- But to compare SAGE with what we have now - well, the core RAM was 100 Kilobytes! It was vacuum tube design, using a lot! of twin triode tubes, and used ferrite core memory. The beast required 15 tons of air conditioning to keep it from overheating. I think NADGE is a son of SAGE. The SAGE building was five stories high and almost a perfect cube of grey cement. It looked like Stalinist architecture minus windows.

E/M is Energy Maneuverability, a concept developed in the early 60s by John Bond, a fighter expert who was also one of my 86 instructors at Nellis. P/S - a combination of kinetic (velocity) and potential (altitude) energies. The units are in feet per second - 1300 Ps means that theoretically the airplane can generate a climb rate of 1300 fps or about 78000 fpm/400 mps. One uses the aerodynamic and other limits of the airplane under consideration to generate lines of equal P/S. Left margin is stall speed, top line is combat ceiling, right margin is redline or if you're game enough absolute speed attainable. Now superimposing one aircraft over a dissimilar one immediately reveals the good and bad zones of each with respect to the other. Naturally we carefully examined the 104 and the F4 against the MiG17/19/21 and 23. Since the 104A could exceed the 710 CAS redline speed by a very wide margin I don't doubt the bird could reach that 1300 state - I seem to remember that was below 30,000 but at M 2.0. I never exceeded the 710 limit by much-saw 750 a couple times (once at about 100 feet above sea level) and have had friends without kids reach 850 plus. I, on the other hand, being married with two daughters, had a modicum of discretion. I have zoomed many times from 38-42000 and M 2.0 and seen the altimeter stop while still going up. (Our standard 3-needle altimeter had a mechanical stop at 86000). I estimate we were topping out at between 90-95000 depending on how slow one arced over the top. I always floated over the top with about a tenth of a G max on the airplane and the IAS down around 125 or so. I always handled the controls delicately in that situation so I never had a problem. Sometimes I would go to zero G and release a pencil in front of me and use that indicator to maintain a true parabolic flight path. Since the pencil was in free flight, just keeping it apparently motionless in front of me let me maintain the same ballistic flight path - no lift being generated meant no stall was possible, no stall meant no problem. Come to think of it I was flying formation 'around' that pencil.

Climb profiles - we normally used standard profiles because of the programming of the SAGE computer. Military - 350/.9; AB 450/.9. Once at commanded altitude we flew at the speed commanded by SAGE. Profile 1 - AB climb, AB cruise to target. Profile 2 - AB climb, military cruise. Profile 3 (normal one) Mil climb, 'liner' (max range) cruise - normally about .87.
I have flown a max energy climb a couple times. Attaining 600 KIAS ASAP after TO then maintaining 600 to crossover to M 2.0. This 'profile' was devised by us to get a fighter to a place in space in minimum time for intercept or to provide cover for an asset under attack/harassment. Our environment there in S. Florida had a need for that option. But we never had to use it.

Time to go home back up at Tyndall when the U2 system test was over it was time to go home. I looked at Paul and suggested "Let's wear our p-suits and go home at high altitude." He was all for it and so we filed for Homestead, doglegging south into Warning Area 168 to avoid civvie traffic and incidentally not boom anyone. I did a little dash-one research and fiddled with my E6B a bit and came to the conclusion FL730 was attainable at M2.0 and would give us an IAS we could comfortably fly at. I filed the IMC clearance for a TAS of 1150 TAS which certainly raised the eyebrows of a C119 aircraft commander standing next to me at the clearance desk. We suited up, got our clearance, and took off. We climbed in military to the tropopause. There I called Miami Center and got clearance to accelerate for the M2.0 climb on up to FL730. We went into afterburner, my throttle back a shade from full, to give Paul a little slack out there in loose wing. Arriving at 2.0 fairly quickly I started the climb, maintaining 2.0. We leveled at 73000 on the altimeter and eased back to about 3/4 AB to maintain 315 IAS, on the good side of max L/D. I called "Level Flight Level 730" to Miami Center and he came right back with "And you weren't lying about your true airspeed, either!" I chuckled to myself, envisioning the vector arrow simply jumping across his radar scope at 20 miles a minute. It was a standard Florida day, bright sun, some towering cumulo-nimbus scattered about, the tops well below us, lots of puffy white cumulus, even further below. The sky overhead was noticeably darker than down on the deck, yet not as dark as it got at the apex of a zoom climb. Our motion across the dark blue Gulf of Mexico was perceptible. We were burning about 100 pounds of fuel a minute and covering 20 miles a minute and the TACAN mile-meter was really counting down, a tenth of a mile (smallest division) clicking past every third of a second. Coming up on the coast, still about 275 miles from Homestead AFB (HST), I raised my fist, jerked it back to signal to Paul 'out of AB', nodded my head for execution, and eased the throttle slowly back to idle. Paul was out in loose wing, staying right with me. (He was an ex-TAC F-100 type with lots of fighter time and a skilled and aggressive pilot). We held 315 KIAS all the way down the descent and hit the initial for runway 05 about 10 miles out of Homestead. I think we burned less than 200 pounds or so of fuel all the way down to 1500 AGL. What a great flight and what a great view of the world from up there. Not as different as the view is up around 90000 on a zoom climb but still visibly darker overhead with more white haze on the horizon than at 35-40000. The curvature of the horizon was faint but discernable. It was odd to look way down and see contrails along the airways.
Oh, yes, we did have the J79-19 engines installed - that made the U2 intercepts and the XC really pieces of cake! To my present-day sorrow I threw away the clearance sheet and my navigation card and then compounded that error by turning in my full pressure suit when I transferred from ADC to TAC - it was on a hand receipt and I realized later I could have kept it and no one would have been the wiser. It was tailored personally to me and would fit no one else and would have made a damn fine souvenir of some awesome flights. But I will always remember the great times flying the Zipper - and the rare flights like the ones I just described.

Thanks for listening - Walt "BJ" Bjorneby - 104ever!

Walt BJ (Bjorneby, Walter): Was born in Alaska, was always interested in flying, enlisted in the USAF in August 1951, went through airborne radio school, applied for Aviation Cadets, made corporal working on aircraft radios, and was finally accepted, starting class in January 53. Flew Piper Cub (108 hp), T6, T28 and T33. I got my wings on April 28 1954. Then off to F-86F school at Nellis AFB - great challenge as there were no 2-seaters. First flight was solo chase and then they turned us loose for 8 solo unsupervised flights! I had gun camera film of 3 Sabres (all classmates) ahead of me as we flew in trail along the bottom of the Grand Canyon - unfortunately during one of many moves I lost it. Nowadays such a case of 'flying indecency' would result in a noisy court-martial! I was fortunate enough to spend all but four years of my officer career flying fighters. (Those four years were spent at desks in USAFE and Germany!) I flew in nine fighter squadrons, which is rather rare, spurning three higher headquarters assignments to stay in the cockpit. I valued flying fighters more than promotion. Every now and then I buy a lottery ticket (whenever the dollar amount at chance exceeds the odds against winning) hoping to win enough to buy my own 104.
So far - no dice. Hals und Beinbruch!

Walt "BJ" Bjorneby

Weight: zero fuel
12,562 lbs
12,562 lbs
14,760 lbs
14,900 lbs
Weight: take-off clean
20,000 lbs
20,600 lbs
21,700 lbs
21,700 lbs
Thrust: Military
9,600 lbs
11,870 lbs
10,000 lbs
11,870 lbs
Thrust: Afterburner
14,800 lbs
17.900 lbs
15,600 lbs
17.900 lbs
Thrust/Weight Ratio:
That means that the F-104A with the J79-GE-19 engine was by far the hottest F-104!

Note: those are average numbers from various references.

The -19 engine is visually slightly longer with a more complex nozzle than the -3B. A nozzle lock system was installed. Two extra suck-in cooling air doors were added. The trunnion mounts are a stronger steel alloy. The trunnion mounts are the horizontal mounts roughly at the engine's center of balance, they are short cylinders sticking out right and left just like the trunnion mounts (elevation pivots) on black powder muzzle-loading cannon. In fact, they serve the same purpose and look very similar. They take the thrust and weight/gravity loads and transfer them to the airframe. There's another mount at the top front of the compressor to stabilize the engine and another still to take torque loads, but the trunnion mounts are the strongest by far. BTW my big Webster's 3rd dictionary says it's from the French, "trognon", meaning stump (what's left of a tree after it's cut down).