Among the many interesting things that can be found in the hangar of my university’s aviation department, the “engine gallery” as I call it always catches my attention. While not extensive or comprehensive in any way, it does have two very interesting exhibits – neither of which have any application whatsoever to the department’s small fleet of Skyhawks and a single Seminole 😀 (though I sometimes hope they could have). Dusty and pretty much ignored, they are two of the probably most famous Soviet turbines ever produced – the Klimov TV2 turboshaft and the Tumansky R-11/13/25 afterburning turbojet…
First up is the Klimov TV2-117A, powering the most popular medium-lift helicopter ever made - the Mil Mi-8 :). A surprisingly small package, the TV2-117 produces 1500 SHP for takeoff, and weighs - who would have thought - about 330 kg. More than 16,000 have been produced, clocking over 100.000.000 flight hours since 1964... the donor of this particular engine was probably one of the Croatian Air Force's Mi-8MTV-1s (and sorry for the poor lighting, it was a bright day outside. And don't ask about the Skyhawk in the back, long story 😀 )Essentially a large turboprop turning a very large propeller, the turboshaft engine needs a relatively low mass flow of air and can make do with a small intake. The pipes and casings on top of the intake are the engine accessories - the generator, starter, oil reservoir, pumps etc - which normally sit inside the fuselage; however, for practical reasons, this engine was mounted on the frame upside down Out back is the part that gives this engine type its name, the main power shaft. This connects to the gearbox, which then transmits the power to both the main and the tail rotorsThe TV2 in its natural environment - on an Mi-8 :). Note how little space the engines themselves take up... the caps on the intakes up front, a distinctive feature on many helicopters, are air filters - on the Mi-8 specific to later military and some civil models - which permit operations in dusty environmentsThe second gem is the quite small, but also quite loud, Tumansky R-13 turbojet that powers the two-seat Mikoyan-Gurevich MiG-21UM. Rated at 63,7 kN with reheat, the R-13 (right) is just one part of the MiG-21's powerplant, which also includes the intake and the exhaust (left)...
This though requires a bit of a winded explanation that would not really fit into the photo description box :D. Far from being a simple pipe, the exhaust has a vital role to play as part of the reheat system. Normally, for a fire to burn – and reheat is, in a fashion, just that – oxygen is required. On a turbofan, where there is a substantial amount of air being ducted around the engine core, it is a straightforward matter to divert some of it into the exhaust to aid the combustion of the additional fuel being injected. On a turbojet however, you have to get creative :). The solution adopted for the R-11/13/25 family – and I believe for other turbojets as well – was to duct a small amount of air around the core, just enough to sustain the reheat. The more astute will have noticed that in the above photo, the exhaust has another pipe inside, perforated in the front by a series of small holes. When this assembly is mounted on the back of the engine, air – forced between the two pipes by the low pressure compressor – is blown through the holes, supplying the reheat with oxygen.
A handy size comparison, with a note: unlike the two-seat MiG-21UM, the single-seat 21bis pictured here uses a more powerful 69,6 kN R-25, itself a development of the R-13 - however, externally they look the same and are the same size, so it'll do :). Note also that the nose cone - part of the intake system - is in the fully extended position for supersonic flight. As such, it keeps the shockwave from entering - and damaging - the engine, as well as slowing the air down to subsonic speeds before it reaches the compressorsA rear view of the R-13 showing the flame stabilizers, an integral part of the reheat systemA rear view down the tailpipe of an operational 21bis, showing the R-25's different (circular) flame stabilizers. Note how far the engine itself is deep within the airframe...And to finish it all off, an artsy view of the first low pressure compresor stages of the R-13... took me a good half hour to get this right 🙂
Achtung, Skyhawk! 
ne želim biti dosadan, ali – bravo, bravo… gušt čitati.