AFAIK the only production airplanes with thrust vectoring are military fighter jets.
Tiltrotors such as the V-22 are arguably “thrust vectoring”. They certainly have mechanisms to alter the vector of engine power delivery.
There are doubtless more oddball cases in the range of homebuilts, prototypes, proof of concept subscale models, etc.
The F-22, F-35B, and AV-8 (Harrier) all have thrust vectoring capability as standard equipment.
TV provides STOVL capability for the F-35B and Harrier, and increased pitch authority for the F-22.
Good point. Sorta.
As I almost said about the V-22, if the term “thrust vectoring” is to have any meaning, we need to keep it fairly narrow. After all, any ordinary airplane can alter the thrust vector versus the horizon simply by raising or lowering the nose. The thrust vector remains aligned with the aircraft, but not the horizon.
In the case of powered parachutes, my reading of the FAA’s piloting manual for them (http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/powered_parachute_handbook.pdf (60MB PDF)) says that they fly at a fixed AOA and hence fixed speed. From steady state cruise, increasing power produces first a pendulum motion of the car forward hence nose up. Which a moment later translates into increased AOA & lift. Which a moment later translates into upward motion of the whole vehicle, a reduction in AOA back to steady state and a hence a re-alignment of the car with the overall vehicle motion. So thrust “vectors” instantaneously as a means of control but very quickly washes out and amounts to the same thing as an ordinary airplane: you can alter the thrust line versus the horizon, but not versus the vehicle.
So I choose to define “thrust vectoring” narrowly: The ability to alter the thrust line versus the vehicle to a material degree for purposes of control or direct lift. In fact we could (should?) make pretty strong decision to separate that into the narrower enhanced control class, e.g. F-22, and the wider direct lift class, e.g. AV-8 & F-35B.
I’d also argue against including rotorcraft in the “vectored thrust” category. Even the V-22. Also for reasons of not muddying the definition into uselessness. A rotor in any forward flight has a more complex interaction with the airstream than simply being a fan pushing air parallel to its rotational axis.
To each his/her own; I’m certainly not the Minister of Definitions on this one.
Aside: Yesterday was the first time I saw a V-22 ‘in the wild’. It was taking off from Boeing Field.
That’s why they have the HV diagram, and why we’re trained to remain within the envelope. But we’re also trained to operate outside of the HV envelope with the understanding that it is a calculated risk, because there are situations where operating within the ‘dead man’s curve’ is necessary. Yes, hovering OGE at low altitude puts you in a risky situation; but the likelihood of a total engine failure is remote.
So how do you supply power to the rotor on the failed motor? You’re going to want that, unless you have redundant rotors in every position.
It’s not quite in production yet but the civilian AgustaWestland AW609 should reach certification next year:
Hence my “such as”. The current V-22 is neither the first, last, nor only tiltrotor in history.
Nope.
If you have enough rotors spread appropriately then any one can stop turning and you make up the control difference with differential power on the others. And you make up the difference in total power required by bumping the output of all of them.
Think cyclic and collective. But cyclic control is achieved by altering the thrust of the various other lift rotors, not by tilting their thrust plane.
Then what is the minimum number of rotors needed, such that the failure of one or more of them may be compensated for by the remaining rotors, and what layout would allow the failure of one or more rotors, such that the aircraft can be held in a hover?
Let me give an example. Suppose you have a hexagonal platform with motor 1 at 11:00, motor 2 at 1:00, and the others at 3:00, 5:00, 7:00, and 9:00. Motor 1 fails. You’d need to cut motor 2, or else the 11:00 corner would descend. So now you’re flying on four motors, but the aircraft is balanced. What happens if you lose another motor?
Additionally, what happens when (not if) you lose all power? You can’t autorotate with fixed-pitch propellers. Even if you can vary the pitch, I think they would be too small for autorotation. Of course the aircraft could be (or would have to be) equipped with a full aircraft recovery ballistic parachute system. But that’s a last resort in fixed wing aircraft, which can glide without power, and not an option on helicopters, which can autorotate.
Motors at 1:00 and 9:00 increase power, motor at 5:00 decreases, all relatively. Average motor is boosted by 20%. The goal is not to finish the flight, but to get to the ground in one piece.
Johnny: As **Chisquirrel **says. All that matters is the centroid of lift be in the middle and the total be enough.
Naturally there are failure modes that can overwhelm any redundant system. The certification FARs say you have to achieve 1:1 million or whatever odds of a catastrophic failure. You can do that with redundancy, reliability, or some of each. A twin-pac turbine engine is an example of the former. A very strong and carefully inspected “Jesus nut” is an example of the latter.
The goal is not to design a vehicle that can’t possibly catastrophically fail. Every vehicle we’ve ever built fails at that standard. The goal is one that catastrophically fails rarely enough that the risk is acceptable. Just as you said about hovering within the no-autorotate zone: it’s safe *enough *when done infrequently enough.
The more you install redundancy the less reliable the individual parts need to be. A twin engine aircraft needs highly reliable engines. An aircraft with 1000 engines that can stay airborne with just 800 running could have individual engines that are far less reliable than the twin and still work.
The entire debate about all this stuff is how much redundancy is enough and how much faith do we put in calculations about non-interdependence between failure modes given that we don’t yet have the millions of hours of real world experience we already have with existing tech.
One of the challenges here is social. And applies to many other things, including self-driving cars and solar power. The public and society and legal precedent has very high expectations based on the current highly mature state of highly mature tech. We are therefore far less tolerant of the teething pains inherent in revolutionary new tech.
So our new, new tech must burst on the scene as safe as, and cheaper than, the current state of the art in current tech. Imagine that early aircraft had had to be safer than trains before they were accepted under the safety regs and also had to be both roomier and cheaper than trains before they were accepted in the marketplace. That’s a very tall order that early aircraft utterly failed at.
It’ll be interesting to see how this effort at distributed propulsion rotorcraft goes.
NASA is working on a X-airplane with 18 propellers, 9 on each wing. See http://aviationweek.com/commercial-aviation/nasa-plans-tests-distributed-electric-propulsion (maybe paywalled) and NASA X-57 Maxwell - Wikipedia.
See also NASA GL-10 Greased Lightning - Wikipedia for an X-rotocraft with 10 prop-rotors.
With current computing we see thousands of small computers harnessed together instead of one big powerful one. Will we one day see aircraft with dozens or hundreds of power sources and thrust units? Perhaps.
In response to this DARPA project VTOL X-Plane - Wikipedia these guys Aurora Flight Sciences - Wikipedia have been working on some novel inventions.
Like this: http://www.aurora.aero/evtol/. This is a vid of what they’re working on that starts out with CGI of a full-scale product then transitions to real vid of real, albeit sub-scale experiments: Aurora Flight Sciences' Electric VTOL Aircraft - YouTube
This: Programs - Aurora Flight Sciences is a different idea. Here’s a year old vid of it hovering: The Aurora Flight Sciences VTOL Plane | Inverse - YouTube
The trade press now says they’ve just successfully flown it from hover to forward flight and back to a hover. AFAIK there’s no public vid of this latest test yet.
This stuff is coming. It will blend a lot of ideas we’ve seen in hobbyist drones into what will be full-scale cargo and people-carrying aircraft
