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Zipper at FL 730

Posted by Jolly on April 25, 2012

Walt sent me this about flying the F-104 at FL 730 zipping along at Mach 2. Running a jet out to Mach 2 is hard enough, but doing it in less than 2 minutes is unreal!  All that and a gun too, how cool were those century series jets!  I'll include an F-104 video from the Italian AF for all you Zipper Alumni.  If any of our FU Alumni have other cool War stories like this, please send them to


Zipping along at FL 730 - Flying the "hottest" 104

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


            Ho-kay. Sit down, open a cool one, lean back and here it comes. And, gentlemen, this is the straight skinny. No B-S. This is about flying the 1956 F104A Starfighter with the new J79-19 engine, the modified F4E/S engine which replaced our old tired J79-3bs in 1967.  Those  -3b engines were about shot. They had cracked and warped frames - where the compressor meets the hot section and the hot section meets the turbine section and the afterburner bolts to the turbine section, whose meeting faces leaked hot air and gases. We had been using contractors to electron-beam weld these problems, but that could only do so much. If we got too slow at altitude, say under about 300 KIAS ( around .85M, close to max L/D) we would often get an aft overheat light. That could usually be extinguished by speeding up to about 320. Needless to say, this wasn't a practical solution nor anything we really  wanted to live with. But the F104s were needed in South Florida to keep an eye on Cuba's 125 MiG 21s . . .

            So - new engine time. The project was pushed by a fine gentleman, Col. David Rippetoe, up at ADC HQ. The latest model of the J-79 was the J79-17, used in the USAF's F4E and the US Navy's F4S and also in the single-engined Italian Air Force's F104S. The J79-17 needed a few changes to go into the F104A, so that version was labeled the J-79-19. The 104A got more changes but it didn't get a new designation. The biggest mechanical change, for us, was the provision to lock the nozzle at a setting that allowed flight in case of oil loss. Without nozzle locks the 104A even at full throttle lost so much thrust with the nozzle failed wide open that it couldn't sustain level flight. The lock was actuated upon discovery of oil loss by pulling out a T-handle located above one's right knee; unfortunately there was no place else to put it. A subsequent bailout would definitely bang that knee, but that is the way it was.  After the first flight we didn't care.

            The improvement in  performance with the Dash-19 engine was amazing. Our old -3b engines could get us to M2.0 in about 4 minutes 15 seconds, burn about 3000 pounds of fuel doing that, and cover about 100 miles. With the Dash 19 - 2 minutes in level flight, 1000 pounds of fuel, 27 miles. A 'Rutowsky' manuever involving a short dip to accel in zero G would trim 15 seconds off that 2 minutes; usually we didn't bother. Difference in thrust: military/AB: 9600/15000 vs 11870/17500. Thus there was about 2270 more in military, 2500 more in burner, increases in pounds of 'thrust available,' thrust actually exceeding that needed to maintain maximum level speed with the old 3b engine. Thus the added push went to added performance over and above what the original engine gave the 104A. I might add that the weight of the airplane minus 5800 pounds of fuel was a mere 14,500 pounds. Thus our thrust to weight ratio was better than 1:1 at half-fuel. 

            The 104A/Dash 19 could actually accelerate from .9M at 25000 feet to 1.05M in level flight in military power. At sea level, also in military, it could maintain .97M while its contemporaries had to go to afterburner to match it. From brake release to .94M took 42 seconds. Brake release to 45000 - 90 seconds. This all at a normal South Florida ambient temperature of 20C/85F with a standard armament load of 2 x AIM9B Sidewinder missiles and 750 rounds of 20 mm in an airplane right off the ramp. I did all of the above, feeling out the new performance levels. The Dash 19 engine had a more efficient compressor with a higher ratio and an 8% more efficient nozzle. But the nozzle's changed aerodynamics  had sacrificed the J79's memorable 'hoot' or moan for the better performance. We missed that unique characteristic but  then we were no longer bothered with the hot air leakage and resulting overheat-light problem. And we now had blazing performance!

            Now it was summer 1967 and Paul Da San Martino and I were sent up to Tyndall AFB in the Florida Panhandle to do some fighter affiliation training with a U-2 to test its new electronic self-protection devices. We were picked to fly the missions because we both had AN/APS22-3 full pressure suits, a USAF modified version of the Navy Mark IV. This suit was much more comfortable than the old partial pressure MC3 and MC4s, even flexible enough to perform air combat maneuvering wearing them, something that was not true of the MC3/4 suits. The U2 was up at the base of his operational altitude for the tests and we made numerous intercepts, playing the part of a typical enemy for him.

            His fancy electronic devices put a few flecks on our scopes but didn't particularly bother us and we deduced from what we could see that our 1956 ASG14 radars were not sophisticated enough to be bothered. I don't know how familiar you are with RCA's ASG14 but it's a modern analog to the RAF's AI Mk 8 used in WW2. Basically it is a spiral scan search radar with no angle track capability. Very simple in construction and operation; just find him on the 20-mile (max!) scope, turn toward him to fly him to the center and go get him. He'll show up as a small arc on the scope when he's 45 degrees off the nose in the turn. 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 (only!) range from 10 miles on in. Press a button on the stick grip and the antenna reverses direction and generates about a 10 degree conical scan. The pilot has to keep the target centered by flying the airplane, as I said, since there is no angle track capability at all. It does, when locked on, feed range to the computing gunsight; effectively, too. Range numbers show up on the sight; in miles when missiles are selected, feet when guns are selected. Handily, the Sidewinders look right along the same axis and will growl when they see the target. By the way, live harmonization proved the Zipper's M61 20mm Gatling gun had a meager dispersion of only 3 mils. It was electrically driven firing belted ammo so 'only' fired 67 rounds per second.

            A side comment on intercepting U2s. We had been doing this for some time in our F104As with the original engine. The mission was fuel-critical; a five minute delay meant every thing from then on had to go just right or we'd be low on fuel for the standard and oft-necessary instrument pattern approach. The installation of the J79-19 engine increased our excess thrust about 25%, so we expected an improvement but were uncertain as to how much. We were very pleasantly surprised. 

            The first time we ran an intercept on a U2 in his operational height zone using the Dash 19 bird we hadn't had the new engine long enough to get extreme high altitude performance data to plan from. Neither did the FSQ7 SAGE computer have any such data in its memory banks.  I was the squadron fighter weapons training officer then so I was designated to fly this first U2 mission in the improved aircraft.

            To make things simple and sure I had the controller roll me out 35 miles behind the U2 at an initial altitude of 38000 (tropopause that day). Catching the U2 would be no problem since the overtake at attack speed (M2.0) would be in excess of 700 knots. At rollout on the intercept heading I went to maximum afterburner setting (throttle all the way left and forward - joy!) and followed the controller's steering. I was mostly looking out ahead since often the U2 emitted a wisp of a contrail.

                      As the controller called "18 miles" I glanced down, saw a blip (contact) there at 12:00 on the radar scope, indicating the target was off-axis vertically, as I had expected. (20 miles was the only range selection in search mode) and glanced around the gauges. Surprise! 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 saw him 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. (+2% performance for every -10C)

            By the way, I liked SAGE and data link after the bugs were engineered out of it - 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 - he's 20 port 15, turning hard into you.....hard port 140; he'll be 12 o'clock for 10, 10,000 high..."

            I have a Lockheed-computed E/M graph of the Dash 19 104. I must say it is considerably understated. E/M refers to Energy Maneuverability Theory, a concept promulgated in the early 60s by John Boyd, a fighter expert who was also one of my F86 Sabre instructors at Nellis AFB. Its units are in PsubS - a combination of kinetic (velocity) and potential (altitude) energies. The units are in feet per second - 1300 PsubS means that theoretically the airplane can generate a vertical climb rate of 1300 fps or about 78000 fpm/400 mps. One uses the aerodynamic and other limits of the airplane under consideration to derive and plot lines of equal Ps on a graph with altitude on the Y-axis and speed on the X-axis.

            A warped trapezoid results; the curved left margin is the one-G stall speed, the curved top line is the absolute ceiling, the curved right margin is the limits redline or if you're game enough (dumb enough) the absolute speed attainable.

            Superimposing one aircraft's Ps chart  over a dissimilar one's Ps chart for comparison  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. (Guess which ones were blue and which ones were red.) 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 around 27,000 at 'only' 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 825 plus. I, on the other hand, being married with two young daughters, always exercised 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 USAF 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 my buttocks just touching the seat, less than a tenth of a G on the airplane max, trying for as close to zero AOA as I could get, with the IAS down around 125 or so, far below one-G stall speeds, especially with flaps full up, where stall speed would be about 190 or so.

            You can plainly see the curve of the horizon up there. And it is a long ways away, too, around 400 miles or so. And yes, the sky above is noticeably darker, but there is a whitish zone along the horizon.

             I always handled the controls delicately in that situation so I never had a problem. I would place my elbow on my thigh and fly by bending my wrist, my usual position when flying precise close formation as in a flyby. Sometimes I would  release a pencil in front of me and use that as an indicator to maintain a true parabolic flight path. Since the pencil was now 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. I did not spend much time at absolute zero-G, as that interferes with normal oil and fuel flows. Unfortunately I never got to chance to zoom the Dash 19 bird. I do not doubt it would exceed 100,000 feet starting from Vne. Zooming from Vmax (my guesstimate is at least M2.5) would probably establish a new world record for jets.

            Climb profiles - We normally used standard profiles because of the programming of the SAGE computer. Military - 350KIAS to .9; AB 450 to .95. Yes, we made formation climbs in afterburner even at night or in the weather - or both. Once at commanded altitude we flew at the speed commanded by SAGE. Profile 1 - AB climb, AB cruise to target, normally 1.7, could be 2.0. Profile 2 - AB climb, military cruise, .95. Profile 3 (normal one) Military power climb, 'liner' (max range) cruise - normally about .87.   I have flown a max energy climb a couple of times. I would reach 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. It was very impressive in the Dash 19 bird.

            Our environment there in S. Florida had a need for that option. But we never had to use it for real, although I did use it once during an exercise to hit a close-in target   that was about 60 miles away at 45000 when we got scrambled. We checked in with our controller. He said "Skip it - he's too close." I saw a contrail heading toward us about 50 miles away on the scramble vector. I replied "Negative - keep talking." He did that, and we did an Immelmann starting at Mach 2 and about 28000 up into the target's six and got him 35 miles out. Performance!

            Now up at Tyndall it was time to go home - the U2 system test was over. I doubt if they learned much from us, except that sometimes simple and unsophisticated works.  But we enjoyed the flying, a decided change from the usual missions. Since we had our p-suits with us I suggested to Paul that we go home at high altitude. He was all for it and so we filed IMC for Homestead, planning the route so as to dogleg south into Warning Area 168 to avoid civvie traffic and incidentally not boom anyone.

            I had done a little Flight Manual research and fiddled with my E6B calculator a bit and came to the conclusion that FL730 was attainable at M2.0 and would also give us an IAS a bit on the fast side of best L/D and one we could comfortably fly at, plus have enough fuel to get home with a decent reserve. I filed the IMC clearance for a TAS of 1150 knots and FL 730 via a step climb. By the way, the TAS 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 heading due south on a dog-leg into Warning Area 168 away from land (and telephone calls referencing double bangs). We climbed in military to the tropopause. Down south there it's usually around 38-39,000.  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 bit in AB to give Paul a little slack out there in loose wing. Arriving at 2.0 fairly quickly, about 2 minutes,  we began the climb, maintaining 2.0. We leveled at 73000 on the altimeter and eased back to about 3/4 AB to maintain 310 IAS, on the good side of max L/D during the 30 degree banked turn towards Homestead.

            I had 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 and alpha-numeric symbology 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. A little odd to see cumulo-nimbus anvils with cirrus toppings so far below. The sky overhead was a noticeably darker blue than down on the deck, yet not as dark as it got at the apex of a zoom climb. The horizon had a definite hazy whitish shroud to it. Our motion across the dark blue Gulf of Mexico was perceptible as the clouds and jet traffic contrails way down below  passed swiftly under us.

            We were burning about 100 pounds of fuel a minute (derived from fuel quantity readings 6 minutes apart) and covering 20 miles a minute and the TACAN mile-meter was really counting down, a tenth of a mile (smallest division) clicking past about every third of a second. Yet in the cockpit it was no different than cruising down at say 37,000 amd .87M. The aircraft was smooth and steady and gave no indication other than the Mach meter that we were really moving that fast. I didn't try any maneuvers but I could tell we were nowhere near our absolute ceiling, and not at maximum power, either.

            Maybe 50 miles out from Sarasota, still about 250 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 is an ex-TAC F-100 Vietnam vet with lots of fighter time, a skilled and aggressive pilot and a valued friend.) We held 310 KIAS, a little better than max L/D,  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. I believe we each had about 1400 pounds of fuel remaining as we pitched out to land. 

            What a great flight and what a great view of the world from up there. Not as different as the view is up above 90000 on a zoom climb but still visibly darker overhead with a thicker belt of 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 and the anvil tops of thunderstorms, also way below.  Oh, yes, we did have the J79-19 engines installed - that made the U2 intercepts and the high XC really pieces of cake!

            One thing I did notice exploring the Zipper's performance with its new mod engine. The normal fuel flow reading static on the runway before takeoff was about 8500 PPH. At 600 KIAS under 500 feet ASL right after T/O it read about 12500. Our GE Tech Rep affirmed that was factual and the standard engine/AB fuel proportion was still in effect. That meant that at that speed and altitude the Dash 19 was developing at least 25000 pounds of thrust. Zipper, indeed..

            To my present-day regret I misplaced  the DD175 flight clearance sheet and my annotated 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, and the lasting friendships made with my fellow Zipper pilots around the world.

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Posted by Frankn on
Awesome bar story!
I think you let a typo slip in though...the guy with the Ps charts was Boyd not Bond (if you haven't read his biography you should)
Posted by Jolly on
From CW:

Having flown only the German F104 at Luke AFB for 700 + hours I certainly enjoyed the great article " Zipper Jet at FL 730". Several times I made a 'fast' flight back to Luke but never anything that fast. And only at FL 55 for a few minutes. Super story by an exceptional pilot and aircraft. The Zipper was a super aircraft A great prodict of the "Skunk Works".

Thank you for the article.


C W Irvine
Posted by Jolly on
Thanks Frankin, fixed it. I've read the book and it's awesome. Ps diagrams were huge in the 80s when ever we talked about fighting another fighter. For me, Ps was never a big factor being a nose position fighter pilot. Those 450 knot 7-8G rate fights were just too painful!
Posted by Frankn on
Rate fighting is a young man's sport. By the time I moved to the viper I too became a nose position fighter...intimidation kills too. I've still got my cardboard Ps templates for the whiteboard, suppose I'll have to donate them to a museum.
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