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xanthraxoid t1_j6mhqlg wrote

The figure for what constitutes a "short runway" is given as "1,5000ft" which is obviously a typo. I assume it was supposed to be 1,500 rather than 15,000 as the latter is a ~3 mile runway and probably not what would be considered "short" :-P

The idea of changing airflow around an aerodynamic surface using forced air isn't exactly new. There were experiments with "coanda effect wings" for propulsion as well as control at least as far back as the 1950s.

There are also devices (NOTAR) using the coanda effect as an alternative to the tail rotor on some helicopters.

Applying the concept more broadly seems like a fairly obvious possibility to consider. I'm sure there are plenty of engineering challenges ahead on that path, though, so it may turn out to be a dead end for some reason.

The most obvious potential challenge that occurs to me is the "fun" of keeping the various nozzles needed operating evenly, given that they're generally very long thin slits that need to be kept un-clogged. If you get a bit of dirt wedged in one, or bend the edge somehow, the airflow will be absent where the blockage is and faster in other places. Obviously, you'll want ways to avoid that happening altogether, but you have to assume it'll manage to happen anyway, so you'd want the avionics to be able to at detect / adapt to that kind of condition.

Fun stuff! :-D


Working_Sundae t1_j6nqwh0 wrote

Can this design be scaled upto large aircraft or does it only work for small flying aircraft like the one pictured above


xanthraxoid t1_j6nuokq wrote

AFAIK the largest vehicles made with the "UFO" design were of a scale similar to the one in the pictures. IIRC (I did read up on it a while back) the main problem was difficulty with stability and control, so they shelved the plans.

These days, with computer control, reacting to changes in dynamics hundreds of times per second would be perfectly feasible, though, so perhaps those challenges are ready to be taken on.

Some modern aircraft are deliberately designed to be inherently unstable and require constant active control from an onboard computer to remain pointy-end-first. The advantage is that when you do want to change direction, it can be done very quickly indeed. With that and thrust vectoring, you can also make a plane that will function in states where a more traditional design would turn into a billion dollar brick (see Relaxed Stability and Supermanoeuverability)

In terms of scaling it up to larger sizes, I expect they'd scale reasonably to a point, but as you get larger, the sheer volume of air you'd need to huff around starts to be an issue. The density of air doesn't go up as your aircraft size goes up, so it's not just a matter of doing the same thing but bigger.

The article linked to by OP was only talking about using these kinds of techniques for control surfaces, though, not for directly generating lift, so we're only talking about a pretty small fraction of the required oomph compared to the flying saucer.


Racer-Rick t1_j6oqmxy wrote

1500 feet is still longer then the 1092 foot long super carrier runway… Odd. Where are they planning on launching them from?


xanthraxoid t1_j6pdqy6 wrote

I'm no DARPA-ologist, but I would hypothesise that this spec is for an initial phase to develop / demonstrate the technology, to be potentially followed by a more demanding spec aimed at a potential deployable asset.

Also, bear in mind that by far the majority of aeroplanes don't have to take off from a carrier. While being able to take off from a carrier is definitely a useful feature, being able to take off from a 1500ft runway still opens up a lot of potential places to fly from - old WWII aerodromes, for example. If you have a friendly airport nearby, there's less need to rely on using a carrier (though you'll still have to arrange fuel supply and other support stuff)


Independent-Deer422 t1_j6pfemd wrote

Carrier capability is not a design factor for anything other than carrier aircraft. Everything else operates off a normal airfield.