Every once in a while, I like to go wading in the "Radical New Aircraft Design" bin that is the United States Patent and Trademark Office. Occasionally I come out with something written in patent speak that only a rocket scientist can decipher and I just stare blankly at, however, this time I came out with a real gem.
I give you Patent Number 20080099633, which was published yesterday, called Aircraft airframe architectures, a wholly innocuous title. An engineer at Pratt & Whitney came up with a radical new design to improve the fuel efficiency of a shorthaul aircraft. Rather than have two engines, the design calls for a "single gas generator core including a forward compressor driven by a rearward turbine about a core axis and configured to remotely drive multiple bladed propulsion elements."
Now in English. What the designer describes here is one main gas core mounted in the tail of the aircraft that drives two fans or turboprops which are mounted to the sides of the aft fuselage.
The benefits :
-Improves fuel efficiency by adding a gearbox to the core which optimizes the speed of the core and fans.
-Improves fuel efficiency further by providing a significantly higher bypass ratio. That is to say the ratio of air that passes through the fans is significantly greater than the air that goes through the engine's core. Having two fans and a single core the thrust generated from the fans improves fuel burn.
-Reduces noise by evening the gases exiting the rear nozzle.
-There is also additional fuel and weight savings by only having a "single gas generator core" that drives the fans.
I put together a rendering of how the engines are mounted on the rear fuselage of an aircraft, based off of the diagrams enclosed in the patent application.
That is pretty sweet wonder if it will see it on any airplane soon.
Great idea until the gearbox, or indeed any part of the central engine, goes kaflooey, resulting in one of those embarassing silences.
Looks like a twin-turbine heli design in reverse (with fans rather than a rotor, of course).
Ducting would be quite complicated. Why not provide each of the fans with it's own nacelle and an inlet scoop for the core under the aircraft? Wouldn't that provide more design flexibility?
LowObservable raises a point I neglected to make. Fundamentally, it is a single engine aircraft. Probably not commercially viable. Yet, still a very imaginative idea.
Jon
Seems interesting. As said above, it probably has limited application for airliner type roles. Could be interesting for smaller aircraft (PiperJet, D-Jet etc), or in particular UAVs...
This appears to be more useful for very small, long range UAVs than commercial aircraft.
I agree with T. Varadaraj. Those curves in the nacelle look like trouble, as they could cause all sorts of shock and pressure waves. You could use straight nacelles and create a variable scoop inlet in those nacelles for the core, which should let you optimize the actual flow through the core for different flight conditions.
That's an old hat - not only VERY questionable from a mechanical standpoint - overall fuel efficiency is certainly worse than conventional tail-mounted turbofan engines.
Looking forward to seeing all the 'radical' concepts of the past 60 years being re-invented now that the eco-hype is on - very entertaining! :)
...UMMMM if the hot turbines are in the tail, why do your geared fans show cute little flames inside 'em?
Several Blended Wing Body concept designs use similar ideas. You would have three engines (say) along the back of the plane, and drive nine fans with them -- three from each turbine -- to maxmize efficiency. The BWB have interesting boundary layer issues, of course, which other planes don't have.
From the number, this looks like a patent application rather than a patent. There have been quite a number of designs published over the years which featured various forms of this idea, including the first draft of what eventually became the Harrier. It will be interesting to see if this form of it is deemed novel enough to be issued a patent.
Also see US20080098719 to see details of the propulsion system.
Not radical enough. Let's get really eco-radical...
Primary propulsion: turbofans, pick your favorite, either high-bypass or open-rotor.
Secondary propulsion, used only in takeoff, initial climb-out and landing, when flaps are configured for low-speed flight: propellers, driven by cold-flow tip jets using compressed bleed air from the engines (a concept proven in the Sud-Ouest Djinn helicopter of the 50s). Propellers fold into fairings for low drag during high speed flight.
Benefits: excellent short-field performance, high power at low speeds for climb, high speed cruise using just the turbofan(s), much lower total engine weight than a design that must perform takeoff using turbofans only. The cold-flow tip jets eliminate the need for an engine at each prop that would be just dead weight during cruise.
What do you think, should I file a patent?? :-)
I seem to remember hearing the Lear Fan couldn't meet certification due to a similar design. Whereas if something happened to the central gearbox, bot engines would be taken offline.