by L. D. Alford
Did I say the T-39, Sabreliner, once provided the best heavy aircraft chase in the world? That included safety chase, photo chase, pace chase, and any other chase you want to do at normal jet and turboprop airspeeds and altitudes. The aircraft is fast, responsive, easy to fly, maneuverable, absolutely forgiving, stable, has great visibility, is inexpensive…what is there not to like.
The T-39 is literally the last of the German jet designs we “borrowed” when we conquered Hitler’s Germany. Like the F-86, if you dig deeply enough into the old German projects, you’ll find the predecessor of the T-39. The F-86 is a German follow-on to the Me-262. It is most likely a modification of Messerschmitt design P.1101. You can find the design almost to the exact rivet spacing in archives of old German blueprints. A variant actually was built.
The F-86 was so great a stretch of American technology after World War II that the wing slats, at first, could not be manufactured in U.S. factories. When the XP-86 went into testing at Edwards Air Force Base (AFB), the slats from the Me-262 had to be taken off the captured test aircraft at Wright-Patterson AFB, Ohio and shipped for installation on the XP-86 at Edwards. This should give you an idea of how close the design of the Me-262 was to the F-86. What the F-86 had that the Me-262 didn’t was a greatly improved engine (but only one), greater wing sweep, and eventually irreversible hydraulic flight controls. Like the Me-262, the F-86 could exceed the speed of sound in a dive.
The T-39 was a 1958 twin engine, trainer, small passenger jet design that just happened to use a variant of the F-86 wing. Its fuselage shape just happens to look a lot like a big Me-262 and the longerons and wing spars just kind of match those other two aircraft. They share many other characteristics, but I’ll save that for a future story. The T-39 had two pod mounted 3000 pound sea-level static thrust engines and weighed 18,650 pounds full takeoff load. The F-86E had a max gross weight of 17,100 pounds with a 7,500 pound afterburning turbojet engine. This means, under most conditions, the T-39 could match the performance of an F-86 if the F-86 stayed out of afterburner. This is why the T-39 one of the best heavy chase aircraft in the world.
Until the aircraft were dumped out of the Edwards inventory, we used them as testbeds, targets, and to chase heavy aircraft including the C-17s. This type of chase was great work and well suited to the T-39. With a max speed of 482 knots and a stall speed less than 100 knots, the T-39 could keep up with the C-17 in every phase of flight. The only place we ever had any trouble was during slow-down. When you airdrop a load out of an aircraft, following the turn to the drop run-in, the airdrop aircraft has to make a slowdown maneuver to get from infiltration speed (cruise speed) to the drop speed. Airdrop speed varies from 100 to about 130 knots depending on the type of load and the aircraft. The C-17 can slow down faster than any other aircraft in existence. It can go from a 300 knot cruise to 120 knot drop speed in seconds. When the C-17 pilot pulls back the power, the aircraft automatically throws out flaps, slots, spoilers, barn doors, etc., etc. Now try to keep up with that kind of deceleration in a slick aircraft, like the T-39, that flys like a fighter jet. The first couple of times we tired this, the C-17 spit us right out of formation. Finally, we came to a mutual agreement; the C-17 would give us a heads up well before they started their slow-down. That’s nice. I’m sure they were still laughing every time they pulled back the power to slow down. The moment the C-17 started slowing, we would throw everything out: speed brake, cross controls, power at idle, weaving all over the sky. Once you finally slowed down to the correct speed, you’d slip right back into position and try to act like nothing happened. I’m sure our photographer (photog) on the chase flights was not at all happy with our aviation hijinks. It’s bad enough for non-flying crew in high performance formation much less for the photog taking shots out the side window while all this hiacka stuff is going on. That’s known in the business as “barf-city.” But that’s what we were there to get—photographs and videos especially of the airdrop. We had a little help from the Sherpas.
A C-23 Short Brother’s Sherpa is the ugliest aircraft ever designed by man or God. It is a fat square airplane with a too thin wing and a twin tail. It looks like a recreational vehicle that a couple flat planks fell across, and it flys about like one too. A Sherpa at max power can make about 200 knots downhill and stalls around 85 to 90 knots. There is no way it could keep up with the C-17 or the T-39. Since the T-39 had a photog window (I was the program manager to modify the aircraft for this capability) on the copilot side (starboard side), and the Sherpa could open its back end to allow a photog a breezy, but clear view of the C-17, we teamed to do the airdrop photography for the C-17.
The Sherpa would hold 1000 feet above the C-17 drop altitude and wait for it to start the run in. A Sherpa at full speed going downhill could eventually catch up to the C-17. When they were in position, the Sherpa crew would throw open the back cargo door, the photog would stick his camera out the back, and they would get the pictures of the load going out the back of the C-17. They would also get the great pictures of the T-39 in safety and photo chase on the other side.
The T-39 would keep up with the C-17 for the entire flight usually making a formation chase pick up at takeoff and staying with the big beast until they were done with all the flight test points. Except for the excitement of rejoins, slowdowns, pickups, and safety chase work, the photog in the T-39 had it easy. He just lined up his cameras in the special window and shot video and pictures to his heart’s content.
Today, the T-39s and the Sherpas are all gone out of the Air Force inventory. I sometimes see the Edwards Sherpas when I fly into Destin, Florida and Willow Run, Michigan. One is still in its last orange and white flight test color scheme. All the T-39s are in the bone yard. They were pretty much completely used up and none of ours sported orange and white. The T-39s were a fantastic flight test asset—it was sad to see them go.
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Postscript: The T-39 was one of the best aircraft in the Edwards stable. It was cheap to operate, had some great snakes that would not kill you (like the awesome phugoid), and flew like an F-86. Because they were old, they became the golden watch offered at the budget altar every year. Eventually someone sacrificed them to the budget and ended an era, but that is another story.
The author is a retired Air Force test pilot. His other aviation, technical, and fiction writing can be referenced at www.ldalford.com.