the past (and future) of turboprops
4 August 2006
Well, after ironing out some site issues and (hopefully) killing comment spam For All Time™, I figured it was probably worth writing something.
One of the last Tupolev Tu-114 airliners has been sent to the scrapyard, leaving the fastest propeller aircraft in history with a mere handful of survivors. Flight Global has some photos and a brief article on the matter. It’s unfortunate the aircraft couldn’t be saved, as it truly is one of the great technological breakthroughs of aviation.
What’s most amazing about the -114 is its performance. Based on the famous Tu-95 Bear bomber, it was one of the larger airliners of its day and could seat up to 220 passengers. It could reach 475 knots (880 km/h) and cruised at 415 knots (770 km/h) on the combined 60,000 shaft horsepower of its four gigantic Kuznetsov NK-12 turboprop engines. Maximum range was over 6,000 km, despite fuel burn figures that were probably marginal at best. That an airliner like this could be built in the late 1950s at a time when jet aircraft were viewed as the next best thing is remarkable.
The reason I mention this is the new generation of airliners that is currently under development. Efficient aircraft result in lower costs, a huge incentive for airlines to upgrade. Over 600 sets of blended winglets have been shipped for the Boeing 737, each saving over 100,000 gallons of fuel per year. If one aerodynamic change can save a significant amount of fuel, imagine what entirely new aircraft will do.
Even better, picture what a modern Tu-114 could do. Already extensive work has gone into propfan technology, basically the combination of a turboprop’s efficiency and turbofan’s high-speed performance. Modern composite materials could make the airframe strong, light, and aerodynamic. Bombardier’s Noise and Vibration Suppression system has made their Q series far more comfortable than past propeller-driven aircraft. Several of Boeing’s ‘Muppets’ designs, unveiled a few months ago, appear to incorporate this kind of technology. Turboprops have been experiencing something of a resurgence in sales lately – Airways had an article on Bombardier’s recent Dash 8 sales boom – with turboprop orders matching regional jets for the first time – and ATR has a much larger order backlog than usual.
Rising fuel costs are making high-frequency turboprop service a profitable alternative to regional jets in the short-haul sector. How long will it be until the same is true of domestic flights? Will the 737’s equivalent, 20 years from now, be running on propfans?
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Your blog makes me happy eric. A subtle place for plane geeks to unite.
Any idea what the noise level would be on these compared to a jet?
Well, it would almost certainly be a bit louder, but it depends on technology and engine placement. Rear mounting drops noise, as does the active suppression stuff.
Still, development on the 7J7 and MD-95X propjets stopped because of noise concerns, despite an estimated 30% reduction in fuel burn. Back then, though, fuel was cheaper than water (or something! ;).
Another strike against UDF back then was the fact that the fuselage designs didn’t allow for the possibility of the engine throwing a blade.
Look at any concept design with a UDF today, and you will see the fan assemblies placed far away from any airframe structure.
Considering that modern turbofan engines are designed so that a runaway blade doesn’t even pierce the nacelle, much less the fuselage, no company could justify the fuel savings at the risk of slicing the airplane apart.
Yeah, that’s an interesting (and certainly damning) point, one I hadn’t even considered. Guess I’ll have some questions for my Gas Turbine instructor this semester :). What’s the likelihood of that type of disaster occuring on a UDF engine compared with a turboprop? I’m assuming it’s much higher given the GE UDF engine’s huge number of blades.
Do the Russian types have less of that danger? It seems like their choice of a turboprop with high blade counts would be a little more reliable.
Eric, I’ve just been reading George Monbiot’s ‘Heat’ and he argues, somewhat impractically I had felt, that long distance propellor planes that fly slightly lower than mainstream jets, are a potential way to reduce CO2 emissions. The ‘should we fly so much in future’ issue has exploded over here in the UK in the media and in politics. Love to follow any further news you here on this front. Maybe the propeller plane might have a future.
That’s an interesting point, Mark – I’m not sure it applies to long-range stuff, but it makes sense with medium and shorter ranges. Jet engines actually produce more thrust as altitude increases (and temperature decreases) – and we also start hitting the jet streams, where groundspeeds really take off. I’m not sure propfans at lower altitudes would actually see efficiency gains when you factor that in.
The other challenge would be getting the engines powerful enough for larger aircraft… we could convert smaller jet airliners (the MD-80 series, for example), but larger might be a stretch. Propfan or unducted fan engines are much more practical for the short-to-medium ranges, and with smaller aircraft converted from jet engines there would be less congestion at higher altitudes.
On a related note, isn’t much of the environmental damage directly connected to flight at high altitudes? Would an equivalent amount of CO2 released at a lower altitude have a reduced impact?