Iskra Jet Passes 50 Sparkling Years In Service
Poland’s TS-11 Iskra is a training aircraft that was produced by PZL Mielec (Poland’s State Aircraft Works located in the city of Mielec) during the height of the Cold War. The design has been operational for half a century with the Polish Air Force, primarily as the country’s initial jet and armament trainer. There are few military aircraft designs around the world that have given 50 years of service; the Iskra stands in good company with designs like the Lockheed C-130 Hercules and Northrop T-38 Talon.
The design of Poland’s first jet trainer began in 1957 by Tadeusz Soltyk, thus the “TS” designation. Poland’s trainer design was entered in a 1959 competition for a multi-use jet trainer that would equip all Warsaw Pact countries. Powered by an early export version of the British Armstrong Siddeley Viper jet engine, the first Iskra (the English translation means “spark”) prototype flew in early 1960; Polish-produced copies of the Viper engine powered the next two prototypes in 1961. A total of four pre-production airframes were built.
PZL’s TS-11 entry ultimately lost the Pact-wide competition to the Czechoslovakian-designed L-29 Delfin. Sources give varying reasons for its dismissal in the competition. One cites a politically motivated outcome, another mentions that the Polish aircraft industry was directed towards agricultural aircraft, and another noted that the Iskra couldn’t operate from a grass airfield, a possible requirement. In the end, Poland ordered the TS-11 into production for itself anyway.
The first production Iskra was delivered to the Polish Air Force in 1963. A TS-11 broke four FAI world aviation records for aircraft in its weight class in 1964, three for speed and one for distance. The aircraft drew attention, but no export orders, until serial production was almost complete. Ultimately, over 400 airframes were produced in three main versions, including the final series for eventual export. Initially, the jet was produced as a pure trainer. The more numerous intermediate version incorporated equipment for armament training, including under wing pylons and avionics. The final large batch was produced in part to fill the type’s only export order which came in 1975; the final all-new TS-11 airframe came off the assembly line in 1979. Along the way, small numbers of special-use aircraft have been produced; the Air Force received camera-equipped reconnaissance versions in single and twin-seat models, and the Polish Navy ordered six radar equipped Iskras (the only radar-equipped variant) for reconnaissance use in the 1990s.
Initial production Iskras incorporated license built engines, but in 1966, the Polish-designed and produced WSK SO-1 engine was introduced. In 1969 the more powerful WSK SO-3 engine was incorporated. The latest engine version, known as the SO-3W, was introduced in 1981 and retrofitted on those remaining airframes. The latest engine variant produces greater than 600 pounds more thrust than the earlier SO-1 engine, and improves on the length of time between overhauls too.
Today, Poland’s Air Force operates fewer than 60 Iskras, both as trainers and as the mount of the Biało-Czerwone Iskry, or “White and Red Sparks”, the Polish Air Force’s 7-aircraft jet aerobatic team. The airframe has been retrofitted with modernized avionics to meet the needs of the Air Force, but today’s fourth and fifth generation aircraft would require an extensive upgrade to the Iskra’s electronic capability. Indeed, several programs have been launched that would replace these Iskras with a small number of lead in fighter-trainer aircraft, but they were cancelled before reaching general production.
The Indian Air Force was the only country to import Iskra trainers. They initially ordered 50 of the trainer aircraft, and then received 26 more remanufactured jets over a 29-year span. One source states some Indian Iskras were employed flying anti-UAV patrols against Pakistan during the Kargil conflict in 1999, where their slow speed maneuverability was important in the mountainous terrain. Only one complaint about the jet during Indian operations has come to light… test pilots reported it could enter a flat spin under certain conditions, and a restriction of no more than a one spin revolution was imposed on Indian pilots. The last Indian Air Force TS-11s were retired in 2004.
The Iskra has found favor in the civilian aviation community as a jet warbird; it has been exported to Australia, the U.K., and the U.S.. The fourth prototype is privately owned and operated in Poland too. As of August 2013, there were 32 actively registered TS-11s in the U.S.; undoubtedly not all of these are airworthy. Iskras have raced at the National Air Races at Reno NV since 2010, starting with Neubert Aero Corp’s #3 Pole Dancer, which was flown by Thom Richard. Lately, racer #1 Hot Section (owned by Thom Richard) has been flown by Lachie Onslow.
Thom highlighted some characteristics that distinguish the TS-11 from many other jet trainers. “It’s a thin wing, which means high approach speeds; it uses a lot of runway. Also, being a turbojet, it won’t get out of its own way on takeoff. A 4,000 foot runway is comfortable at sea level, but it gets marginal on shorter strips. It stalls surprisingly abruptly and snap rolls really easy.” Thom notes that there are “no limits on spins… I’ve heard from the [Polish pilots] that there’s never been a flame out during a spin. Not verified, but received from several sources”. And, he notes that “120KIAS over the fence on landing is a bit fast for a straight wing airplane”.
About racing at Reno, he adds: “It’s very light on the controls, having hydraulic aileron boost. Absolutely delightful running on the course. It even has a force simulator on the elevator to keep you from pulling too hard on it… +8 [and] -4G’s. The other jets from the era, and later, are much heavier. Not much need for rudder at speed. What it lacks compared to the L-39 is the flashy looks and air conditioning. Also the L-39 out climbs the Iskra significantly. It [Iskra] only does 3,150 feet per minute at 200 knots airspeed with a stock motor. Not very impressive for a jet. We do however have a solution for that by installing a different engine. The airplane is underpowered (though technically, all airplanes are…); with an extra 1,000 pounds of thrust, the airplane would probably be impossible to beat in Reno, and would end up with better fuel specifics for higher cruise altitudes and a much faster climb.” Since racing Pole Dancer at Reno, Thom has piloted the modified P-51 Mustang Precious Metal in the Unlimited class. How does the Iskra jet’s performance compare with the Unlimited racer? “Infinitely better. [Precious Metal] is a stick in concrete, heavy, and rolls like a Stearman.”
According to Thom, when he raced in Hot Section, the Iskra could go “… faster than all other stock L-39’s, which was a great surprise to everyone. Other than lightening the aircraft, throwing out old radios, seats, gun equipment, etc, we had no [modifications] to the airframe or the engine.” “…if you look at 2010 videos, you’ll see that the little jet that could (ours) pretty much took every start and was later passed due to lack of power. He added “The smaller, thinner wing also handles turbulence beautifully. I would hear all kinds of complaints from the L-29/39 guys after a heat about turbulence, but I always had a very good ride. Love the airplane… it’s a very slick aircraft. Great design.”
Were there any difficulties transitioning from a “Western” to an “Eastern” design when training to fly the Iskra? Thom said “Not really. All jets are easy. The methodology in the eastern block machines are all the same [from] TS-11s through high end MiGs. Surprisingly standardized. Good reliable systems and excellent redundancy. The original gyros tend to mess with Western pilots initially, but you get used to it very quickly”.
Besides operating as a warbird and racer, there’s still a possibility for a remanufactured and re-engined TS-11 variant that could be built for the Polish Air Force as its new-generation fighter lead-in jet trainer. A current program to acquire a new advanced trainer is experiencing some turbulence. Conceivably, the Iskra’s legacy could stretch well into the 2020 timeframe… or 60 years! Whether this new “re-invention” occurs hasn’t been decided yet, but the usefulness and adaptability of Tadeusz Solytk’s jet trainer design isn’t in question half a century after he designed it.
Thanks to Thom Richard for his insight and pilot report. Photos by the author except where noted.
Gallery by Joe Kates..