The Powerplant

Which One?

The problem of which powerplant we select to power our SST is a rather difficult one. In principle, the requirements are relatively simple;

  • The powerplant must be an afterburning turbojet.

  • The powerplant must be capable of ‘supercruise’.

    • This means, the engine needs to be able to ‘breathe’ at supersonic speeds, necessitating a variable geometry inlet ramp, and the ability to function with minimal high speed fuel burn.
  • No more than two of the powerplant should be needed to sustain ‘supercruise’.

    • The pair of engines alone must be able to exert sufficient ‘dry thrust’ to sustain supersonic cruise.

The number of civilian afterburning turbojets we have to choose from, complete with variable geometry inlet ramps to facilitate ‘supercruise’, perhaps also with variable aperture propelling nozzles, is rather minimal.

Strictly speaking, we are limited to just one – the Rolls Royce/SNECMA Olympus 593 – that’s it in the banner above in our logo ^^^

The Olympus 593 is what powered Concorde, however it’s no longer in production, there are no spares for the few complete engines which still exist(in museums, mostly) it’s maybe a bit too large for our needs, and having originally been developed for the Vulcan and TSR2 it stretches the definition of a civilian powerplant somewhat anyway.

That Olympus won’t work – we’re going to need a military derived engine.

Thrust SSC

It’s worth noting that when Richard Noble faced almost this very same problem during the development of the Thrust SSC Supersonic car (which served no practical purpose other than to go very fast indeed without flying), he managed to source two Rolls Royce Spey Engines from an RAF spec F-4 Phantom. (The American ones used General Electric J-79s)

 

Thrust SSC

Thrust SSC at speed

The RR Speys make about 54kN of dry thrust, 91.2kN wet.

For comparison, the Olympus 593 makes 139.4kN dry, and 169.2kN wet, but is only slightly larger in diameter.

For the goal of achieving Mach 1 at ground level the RR Speys for Thrust SSC were actually rather good – the Thrust SSC was able to run the engines at full reheat for the entirety of each speed run, and the sprint-distance range they needed to cover on the test track was small enough that they didn’t need to carry much fuel, let alone passengers, bags and potable water.

Noble’s more recent effort, the Bloodhound, uses the Eurojet EJ200 engine and a rocket motor (akin to the Saunders-Roe SR53 cold war interceptor concept) which is intended to theoretically push it to 1,000mph – but that hasn’t happened yet.

Bloodhound SSC

Bloodhound SSC at speed

By the way, the Bloodhound propulsion set-up is detailed here; http://www.bloodhoundssc.com/project/car/engines

Let’s continue…

 

The Possibles

Knowing that our prerequisites are that we need a pair of supercruise capable afterburning turbojets, and that we will not find that in the civilian realm, it is to the various air superiority fighters and attack aircraft we must turn to source our engine off-the-shelf, so to speak.

Starting with the American hardware, some of our engine source options are;

  • F-15 Eagle

  • F-14 Tomcat

  • F-18 Hornet

  • F-16 Falcon

The Euro-Franco-British Options;

  • Panavia MRCA Tornado

  • Eurofighter Typhoon

  • Dassault Rafale

The Russian Options;

  • Mig-29

  • Su-27

There are more I know, but this will do to start with.

All of the American fighters listed use a variation of only two core engine designs, the GE F110 and the P&W F100, which make 131-142kN and 79-129.7kN dry and wet thrust respectively.

The EJ-200 engine from the Typhoon makes 60-90kN dry and wet thrust, it’s French step-sister the Rafale uses the Snecma M88 powerplant, which makes 50-75kN dry and wet thrust.

The Panavia Tornado used Turbo Union RB-199 engines which make 40-73kN dry and wet thrust.

The Mig-29 uses Klimov RD-33 engines which make 50-81.3kN dry and wet thrust, and finally the Su-27s Saturn AL-31 makes 74.5-122.58kN dry and wet.

(I will make a summary table of the above once I get the wordpress plugin working!)

Based on the above list, the US made engines are the most attractive powerplants still in production, or a pair of Saturn AL-31 ‘s would be pretty good.

The EJ-200 appears to be roughly equivalent to the old RR Spey’s – I wonder how much they actually differ?

Finally, the Turbo-Union RB-199’s, the Snecma M88’s and the Klimov RD-33’s are a little low on thrust it seems, so they should probably be discarded.

Dual Use Limitations and Military Import Embargoes

 

Depending on where we set-up shop to build our SST, and how many politicians we make friends with, our luck may vary considerably when we come to source our engines.

Let’s presume for the time being, for arguments sake, that we’ll be building in the US or the UK – we automatically run into problems trying to import any Russian-made engines or even French engines, so these become a less probable likelihood of success – although there are some privately owned Mig-29’s in the US which must have gotten the OK from the state department somehow.

Next, let’s consider the GE and P&W powerplants – these would be ideal, and very probably would have the best (but most expensive) technical support in terms of engineering and spare parts, however the F110 and F100 engines are very obviously used in basically just all of the US air superiority fleet, so although it’s not unheard of to win dual-use permission from the US state department to equip a civilian aircraft, getting those permissions take literally years so it would seem to be a pretty futile endeavour.

Let’s go back to Richard Noble’s example – he managed to get both a pair of Speys and his latest EJ-200 from Rolls Royce without significant issues, so perhaps let’s follow in his footsteps since he has kindly trailblazed the path for use of ex-military jet engines on civilian engineering projects.

Government approval of such purchases also comes willingly when, like the SST initiatives, they are used as an educational ‘STEM’ advocacy vehicle, being shown off in schools and museums etc. – this fits perfectly with the mission of ‘The Mach Barrier’.

 

Actual Engines for Sale Now

Switching back for a moment to our ‘Donor Airframe’ options (see the info about the Citation X being used as the basis for our SST on the other page), it should be noted that occasionally ex-military jets can and do pass into civilian hands, and with them all of their hardware and systems.

Although the Turbo-Union RB-199 engines from the Tornado were not the most powerful of the options discussed in this page, if they were included with the purchase of a complete Tornado donor aircraft, they would very well make a cost-effective starting point for our SST to use.

The exact minimum thrust we will need to clear ‘the mach hump’ is not known at this early stage – nor is the minimum fuel burn needed to achieve our desired range, but you shouldn’t look a gift-horse in the mouth, they say.

 Actual stand-alone engines that can be bought with cash money, can be found – though some may only be good enough for museum exhibits and may not have been airworthy for a very long time. Here, for instance is an Olympus engine from Concorde’s predecessor, the TSR-2, which ultimately formed the basis for the RR/Snecma 593 Olympus.

 And another;

This one is sold, apparently, advertised at http://www.jetartaviation.co.uk/ but this is the same type of engine used to power the Thrust SSC, and is broadly equivalent to the Eurojet EJ-200.

We need two of these, to make one Supersonic Citation.