Books' NGAD concept

[books]

Hi all,

I'd like to request some feedback about a design idea I've been toying with this last year: taking the NGAP "third stream" of air to its logical extreme and actually having a dedicated inlet for it: that is, a two engine design with three inlets!

What I'm picturing is basically Rodrigo's Collins design, with essentially the same two underwing inlets, each feeding an NGAP engine's complete airflow needs for its lower bypass, higher performance mode, to include supercruise, max thrust and max G manuevers, etc. But then it would also have an overwing inlet positioned behind the canopy that, when desired, would feed extra air to the engines for more efficient cruise (and cooling and power generation) with a higher bypass ratio. I assume this over wing inlet would be much, much thinner than Boeing's recent concept images, probably more reminiscent of the X-47A in that respect.

Since this overwing, behind-the-canopy inlet would not be of any importance/criticality for low bypass mode dogfighting, it would not be a problem if it was blanked out during high AOA manuevers. If little internal doors closed off access from the overwing inlet to the engines for low bypass flight, there also would not be a problem with funky shockwaves from the third stream disrupting the normal operations of the engines during violent maneuvers. Instead, during low bypass flight, third stream airflow would be channeled over the engine compartments and selected avionics for cooling purposes, and exhausted in a manner separate from the main engine exhausts. (Obviously, what to do with unwanted third stream air during low bypass mode is a problem for any configuration -- but also an opportunity for any of them, in terms of cooling and power generation, whether the number of inlets equals the number of engines or not.).

I'm sure this concept would add weight, as well as complexity and risk in the area of Intake airflow combination for high bypass flight, as compared to just having larger mass-flow underwing inlets. But it also might have signature advantages in terms of keeping the maximum height and width of any given inlet down, while also using the structure of the aircraft wing, fuselage, and canopy to block a larger amount of the intake area from radar view than would be possible with an exclusively underwing inlet design. That is, it offers small inlet dimensions for a given mass flow, and also some of the signature advantages of over wing intakes, yet without the high AOA disadvantages that go along with a pure over wing inlet design.

 

[donnage99]

The stealth advantage of smaller inlet dimensions might be offset by additional breakage in its surface and the fact that it's 1 extra inlet. It's still 1 extra complex shape that is hard to manage signature wise.

 

[books]

Yeah, could be.

I can easily agree that the radar signature advantages I'm aiming for might not materialize, in which case I assume the whole idea would be pointless, since the hoped for signature reduction was the driving purpose.

That said, I can easily imagine the opposite too, that the third inlet might have net advantages for signature if done carefully. If so, I wonder how viable the idea might be in other aspects.

Personally, my major worry would be propulsion. The aircraft I can think of that combine airflow from different intakes, like the Republic Thunderflash and Thunderchief, tend to do it in ways that seem like symmetrical combinations of equal airflow volumes, whereas my idea might have to involve asymmetrical combination of dissimilar volumes. While I'm not proposing to direct the third stream air to the engines during fighter manueuvers , it still might be a pain to do, like one of those bold but slightly nutty 50s ideas...