NEW DARPA VTOL X-Prize

Not sure i understand. The goals of the program were to get a VTOL aircraft flying at 300-400 kts at twice the efficiency of a helicopter with comparable hover efficiency, and better useful load fraction. Also, the PM was pretty specific about wanting something not found on the wheel of VSTOL misfortune.

Do you think these were not useful goals, or did you not like the concepts Lockheed/Sikorsky, Phantomworks, Karem, and Aurora submitted?
In the latter case, what would you have proposed?
 
AeroFranz said:
Not sure i understand. The goals of the program were to get a VTOL aircraft flying at 300-400 kts at twice the efficiency of a helicopter with comparable hover efficiency, and better useful load fraction. Also, the PM was pretty specific about wanting something not found on the wheel of VSTOL misfortune.

Do you think these were not useful goals, or did you not like the concepts Lockheed/Sikorsky, Phantomworks, Karem, and Aurora submitted?
In the latter case, what would you have proposed?
Click to expand...

Only fans w/o rudders make sense. Fan storage units obviously don't as explained earlier.
Fans which fill large portions of the fuselage are likewise lazy designs which do not take into account current CFD research.
As for a proposal. Why would one do that here?
 
Sorry, i still don't understand.

"Only fans w/o rudders make sense"

The LightningStrike concept has no rudders (and by rudder i mean a vertical surface designated for yaw control). Yaw control is effected through differential thrust of fans on opposite sides of the vertical plane.

"Fan storage units obviously don't as explained earlier."
What do you mean by "Fan storage units"? you mean the distributed fans along the span? The distributed part comes with the need to provide engine out redundancy. It has been a feature of VTOL aircraft since the dawn of VSTOL flight. X-22 has FOUR turboshafts with all the fans interconnected, for example. Definitely not simple or lightweight, but that's what you gotta do to cope with the OEI case. Or you can have a single engine only, and your only way out of a pickle is the bang seat (Harrier, F-35).

"As for a proposal. Why would one do that here?"
I'm not actually suggesting you do that and that DARPA would pick it up, it's more for my own curiosity. If you're bashing concepts proposed by the largest aerospace corporations in the world, i would like to hear what more efficient concepts you have in mind.
 
AeroFranz said:
Sorry, i still don't understand.

"Only fans w/o rudders make sense"

The LightningStrike concept has no rudders (and by rudder i mean a vertical surface designated for yaw control). Yaw control is effected through differential thrust of fans on opposite sides of the vertical plane.

"Fan storage units obviously don't as explained earlier."
What do you mean by "Fan storage units"? you mean the distributed fans along the span? The distributed part comes with the need to provide engine out redundancy. It has been a feature of VTOL aircraft since the dawn of VSTOL flight. X-22 has FOUR turboshafts with all the fans interconnected, for example. Definitely not simple or lightweight, but that's what you gotta do to cope with the OEI case. Or you can have a single engine only, and your only way out of a pickle is the bang seat (Harrier, F-35).

"As for a proposal. Why would one do that here?"
I'm not actually suggesting you do that and that DARPA would pick it up, it's more for my own curiosity. If you're bashing concepts proposed by the largest aerospace corporations in the world, i would like to hear what more efficient concepts you have in mind.
Click to expand...

Any obstruction to direct fan flow reduces that flow.

Large numbers of in serial fans adding weight and complexity while reducing reliability are an engineering lark. Four or even five sounds fine. The less the better. One is likely insufficient even for UAS, but that may be in question as it is possible only small quasi disposables make sense in extreme operational environments.

These designs push no envelopes but are easily demonstrated which is all that is truly sought. Career moves. Not DARPA hard. They have no survivability yet are high cost if they are transitioned.
Small companies are wasting their limited time and resource even proposing against the innovatively flaccid LSIs in this risk adverse, politically stacked environment. Seeing no sign of a third offset yet.
 
ok, thanks.

"Any obstruction to direct fan flow reduces that flow."
agreed. The LS design has stators behind the fan, required to hold the centerbody with the electric motor. Beyond those, there aren't other obstructions. I think all ducted fans to date have had stators, unless they're rim motors.

"Large numbers of in serial fans adding weight and complexity while reducing reliability are an engineering lark. Four or even five sounds fine. The less the better."

It's a tradeoff. The goal is to maintain a trimmed T/W slightly greater than one in the event of one, or worse two engine/motor failures. With two motors only, in an emergency each has to be sized to provide twice the nominal hover power. So you're lugging around engines twice as big as they need to be. It's actually worse than that, because unless both motors are located at the cg, they will induce a turning moment along one of the axes. If you have four independent motors on a wing, you start being able to cope with the problem by overspeeding the good motor on the side of the failure and cutting down the power of the two motors on the other side, and each motor must provide "only" 4/3 of the nominal hover thrust. As you increase the number of motors this gets better. There's the old joke of the frustrated Cessna 152 pilot who's out of fuel, waiting to land and is told to wait because an eight-engined B-52 has lost one engine. Yeah, if you've got eight, engine out is a non-event.
I think what is missed here is that while with gas turbine or ICE engines, more units of smaller power are heavier than a single large unit of equivalent total power, with electric machines the disadvantage is not quite as bad, so you pay less of a penalty for distributed propulsion. You can also try to recoup some of the weight penalty by using the thrust differentially and getting rid of rudders, for example.

"These designs push no envelopes but are easily demonstrated which is all that is truly sought"

I'll respectfully disagree. I don't think there's anything easy in the aerodynamics and control laws of a distributed propulsion VTOL unlike any in the wheel of VTOL misfortune. If you look at the wing/duct units, it looks nothing like older ducted fan vehicles like, say, X-22 or Doak.
Building and flying the XV-24 will require working out the practical aspects of megaWatt class power systems on airplanes. What's the most electric power flown on aircraft today? it might be the 787, which is at least an order of magnitude less. What's learned there can be applied to increasingly electrified aviation, regardless of whether it's VTOL, commercial or military. Rolls Royce Libertyworks is one of the partners, and they're already using what they're learning in commercial offerings. Honeywell's MW flight-rated lightweight generator will come in handy as soon as the air force gets serious about lasers.
 
AeroFranz said:
ok, thanks.

"Any obstruction to direct fan flow reduces that flow."
agreed. The LS design has stators behind the fan, required to hold the centerbody with the electric motor. Beyond those, there aren't other obstructions. I think all ducted fans to date have had stators, unless they're rim motors.

"Large numbers of in serial fans adding weight and complexity while reducing reliability are an engineering lark. Four or even five sounds fine. The less the better."

It's a tradeoff. The goal is to maintain a trimmed T/W slightly greater than one in the event of one, or worse two engine/motor failures. With two motors only, in an emergency each has to be sized to provide twice the nominal hover power. So you're lugging around engines twice as big as they need to be. It's actually worse than that, because unless both motors are located at the cg, they will induce a turning moment along one of the axes. If you have four independent motors on a wing, you start being able to cope with the problem by overspeeding the good motor on the side of the failure and cutting down the power of the two motors on the other side, and each motor must provide "only" 4/3 of the nominal hover thrust. As you increase the number of motors this gets better. There's the old joke of the frustrated Cessna 152 pilot who's out of fuel, waiting to land and is told to wait because an eight-engined B-52 has lost one engine. Yeah, if you've got eight, engine out is a non-event.
I think what is missed here is that while with gas turbine or ICE engines, more units of smaller power are heavier than a single large unit of equivalent total power, with electric machines the disadvantage is not quite as bad, so you pay less of a penalty for distributed propulsion. You can also try to recoup some of the weight penalty by using the thrust differentially and getting rid of rudders, for example.

"These designs push no envelopes but are easily demonstrated which is all that is truly sought"

I'll respectfully disagree. I don't think there's anything easy in the aerodynamics and control laws of a distributed propulsion VTOL unlike any in the wheel of VTOL misfortune. If you look at the wing/duct units, it looks nothing like older ducted fan vehicles like, say, X-22 or Doak.
Building and flying the XV-24 will require working out the practical aspects of megaWatt class power systems on airplanes. What's the most electric power flown on aircraft today? it might be the 787, which is at least an order of magnitude less. What's learned there can be applied to increasingly electrified aviation, regardless of whether it's VTOL, commercial or military. Rolls Royce Libertyworks is one of the partners, and they're already using what they're learning in commercial offerings. Honeywell's MW flight-rated lightweight generator will come in handy as soon as the air force gets serious about lasers.
Click to expand...
..Would argue no loss ridden open prop design escapes the wheel.
IMHO two issues need be pursued for some time before any transitionable VTOL were built.
First is fuel to lift thrust. IARPA's sought to crack the fuel to electricity efficiency w/no VTOL and that should be pursued for future application but for right now for VTOL lets just get fuel efficient combustion (non-jet) high T/W fan. Thermal and acoustic can be handled by modern material science later. Higher energy density fuel beats electricity and thus lower weight w/o electrical complication. Many more iterations are affordable.
Second get the aerodynamics of the airfoil using research apparently not being used so far. So far blunt T/W solutions w/ no aerodynamics research. Get the fan characteristics finalized including placement right and a finally flyable and quite subscale (w/diesel power) proto. Way back Aurora had a proto which approached something that looked like an airplane. Since then...
 
I see what you mean, and agree to some extent. There are unfortunately certain things that don't become apparent (or inevitable) until you get into the nitty-gritty details of design.
The open prop certainly gives you larger diameter (and lower discloading) but at the same time a ducted fan has no wake contraction and thus has better hover figure of merit. It also doesn't lend itself as well to distributed propulsion, because you would need much larger spans.
FWIW, i know Aurora tested several airfoil/ducted fans combinations during four wind tunnel tests. The current configuration is the result of trying to keep the flow attached at extreme wing tilt angles and reduced power settings, something older ducted fan vehicles didn't manage too well (X-22 was limited in that regard). I believe that is a significant invention in itself.
Anyway, there is more than one way to skin the cat, as shown by the vastly different configurations that were entered. Lockheed/Sikorsky and Karem had open props, Aurora and Boeing ducts. Some missions might favor a particular type over another, it just turned out that DARPA thought the distributed electric was the better one for the ground rules they had established.
 
AeroFranz said:
I see what you mean, and agree to some extent. There are unfortunately certain things that don't become apparent (or inevitable) until you get into the nitty-gritty details of design.
The open prop certainly gives you larger diameter (and lower discloading) but at the same time a ducted fan has no wake contraction and thus has better hover figure of merit. It also doesn't lend itself as well to distributed propulsion, because you would need much larger spans.
FWIW, i know Aurora tested several airfoil/ducted fans combinations during four wind tunnel tests. The current configuration is the result of trying to keep the flow attached at extreme wing tilt angles and reduced power settings, something older ducted fan vehicles didn't manage too well (X-22 was limited in that regard). I believe that is a significant invention in itself.
Anyway, there is more than one way to skin the cat, as shown by the vastly different configurations that were entered. Lockheed/Sikorsky and Karem had open props, Aurora and Boeing ducts. Some missions might favor a particular type over another, it just turned out that DARPA thought the distributed electric was the better one for the ground rules they had established.
Click to expand...
They have a too weighty a design they have to sling along. makes one wonder it they really have anything in handling extreme wing tilt angles. Hard to not see ham fistedness in the design.

No mission favors open props from the loss which detracts from endurance/performance to the large RCS. Props beat the air into submission. Airplanes fly. Prop wash over wings is not efficient lift. Only pusher props don't interfere w/ the wing.

USG should commit to subcomponent developments before any vehicle. Again they are listening the risk adverse and not demanding slower but risky.

PS repeating- L/W requires an efficient propulsor which only fuels provide. Power storage is where this unfortunately begins. Distributed Electric is neither robustly uncomplicated nor weight efficient in the end. Until again subcomponents prove otherwise. Certainly non is seen here.
 
Experimental aircraft tend to be overweight. For example, of necessity you are using COTS engines which may not be optimum for the design.
It's not necessary to demonstrate the "objective" performance if you can show that you are carrying penalties related to COTS components that wouldn't be there if you had a custom engine, such that a production vehicle would have. To keep costs down, this is always acceptable. Remember, the total money being spent for this program, including multiple awards in Phase I, is the equivalent of buying three Super Hornets more or less.

"makes one wonder it they really have anything in handling extreme wing tilt angles"

I don't know where you got that impression. I can only repeat that there were several wind tunnel campaigns and several thousand hours of CFD cluster time that resulted in the evolution of the wing/duct shape. All the competitors did that.

"No mission favors open props from the loss which detracts from endurance/performance to the large RCS. Airplanes fly. Prop wash over wings is not efficient lift. Only pusher props don't interfere w/ the wing."

Range and endurance depend on three things: specific fuel consumption (SFC), lift to drag ratio (L/D), and empty weight fraction. Both piston engines and turboprops have lower SFC than turbofans. L/D of prop planes can be as good as jets, and so can the empty weight fraction.
As for pusher props, they ingest the wake of the wing, which also incurs a loss. If they were superior, you'd find them in more airplanes. The fact that they're the exception rather than the rule tells me that's not the case.

Low observables were never a goal of the program. At any rate, lots of air vehicles in US inventory are not LO, and i don't get the sense that the services are going to an all-LO fleet any time soon.

I will grant you that there are a lot of weight penalties to accept for a hybrid system. I don't think you agree that there is value in advancing the state of the art by actually building hardware.
 
AeroFranz said:
Experimental aircraft tend to be overweight. For example, of necessity you are using COTS engines which may not be optimum for the design.
It's not necessary to demonstrate the "objective" performance if you can show that you are carrying penalties related to COTS components that wouldn't be there if you had a custom engine, such that a production vehicle would have. To keep costs down, this is always acceptable. Remember, the total money being spent for this program, including multiple awards in Phase I, is the equivalent of buying three Super Hornets more or less.

"makes one wonder it they really have anything in handling extreme wing tilt angles"

I don't know where you got that impression. I can only repeat that there were several wind tunnel campaigns and several thousand hours of CFD cluster time that resulted in the evolution of the wing/duct shape. All the competitors did that.

"No mission favors open props from the loss which detracts from endurance/performance to the large RCS. Airplanes fly. Prop wash over wings is not efficient lift. Only pusher props don't interfere w/ the wing."

Range and endurance depend on three things: specific fuel consumption (SFC), lift to drag ratio (L/D), and empty weight fraction. Both piston engines and turboprops have lower SFC than turbofans. L/D of prop planes can be as good as jets, and so can the empty weight fraction.
As for pusher props, they ingest the wake of the wing, which also incurs a loss. If they were superior, you'd find them in more airplanes. The fact that they're the exception rather than the rule tells me that's not the case.

Low observables were never a goal of the program. At any rate, lots of air vehicles in US inventory are not LO, and i don't get the sense that the services are going to an all-LO fleet any time soon.

I will grant you that there are a lot of weight penalties to accept for a hybrid system. I don't think you agree that there is value in advancing the state of the art by actually building hardware.
Click to expand...

Your final point may be closest to correct. See no advancement of the state of the art. Build manned versions these things for the commercial market. That should not be DARPA's job.
There is not a COTS engine, fan, airfoil solution ready to build but for a DARPA PM's career.. Subscales and an appreciation of diverse aerodynamics research clearly not being utilized in this program would be a start. Adding more fans to assure transition to forward because you have weight problems is not a performance strategy. (my apologies). DARPA wants hard. A few fanned performance military VTOL is hard and it won't come from COTS.

Can't see mentioning Props outperforming jets on L/D has anything whatsoever to do w/ this discussion. Never mentioned turbofans nor would... Not an SFC solution by any means.

If the whole creature is designed right, modern material science renders weight a non issue.

Only an airplane can minimize drag.

A prop sufficiently spaced behind a wing gets clean flow. so.. Understand that pushers are unforgiving to pilots so not common. we are talking UAS and no need for loss ridden props.

Hybrid need only be added w/ all it's penalties after all else were perfected.

No LO, no high dynamic maneuver = no military application. What is DARPA doing it for?
 
jsport said:
If the whole creature is designed right, modern material science renders weight a non issue.
Click to expand...

Where is that material that has negative mass?
 
And why are we worried at all about "inefficient lift" if weight is a "non issue"?
If we're worried about only "minimizing drag" for performance reasons, why wouldn't you want the prop in front of the wing producing more thrust ( Fex= T-D) as opposed to behind the wing where it experiences losses?
 
_Del_ said:
And why are we worried at all about "inefficient lift" if weight is a "non issue"?
If we're worried about only "minimizing drag" for performance reasons, why wouldn't you want the prop in front of the wing producing more thrust ( Fex= T-D) as opposed to behind the wing where it experiences losses?
Click to expand...
Not sure who your asking but all props produce loss. Frontal prop more loss as turbulence over the wing/ fuselage.
 
quellish said:
jsport said:
If the whole creature is designed right, modern material science renders weight a non issue.
Click to expand...

Where is that material that has negative mass?
Click to expand...
Funny not funny.
 
Jsport,
frontal prop = "tractor".
What you are saying about propellers does not match with what I have been taught/read, not to mention 99% of what production aircraft look like. Can you give me references that support your assertions?
 
AeroFranz said:
Jsport,
frontal prop = "tractor".
What you are saying about propellers does not match with what I have been taught/read, not to mention 99% of what production aircraft look like. Can you give me references that support your assertions?
Click to expand...
Not sure of the question. Front mounted Prop clearly effects flow over the wing. Slip steam from puller props even apply force to vertical tail surfaces of an conventional airplane. all bad

https://www.youtube.com/watch?v=PzvVPaP6Afw
 
You have a small increase in drag with a tractor configuration. It also frequently provides higher control-authority as it bathes the control surfaces, so it is frequently considered a "wash".

On the other hand, there are well-documented disadvantages of the pusher configuration. Chief among those is the propeller inefficiency compared to a tractor installment which is generally substantial.
 
_Del_ said:
You have a small increase in drag with a tractor configuration. It also frequently provides higher control-authority as it bathes the control surfaces, so it is frequently considered a "wash".

On the other hand, there are well-documented disadvantages of the pusher configuration. Chief among those is the propeller inefficiency compared to a tractor installment which is generally substantial.
Click to expand...
If the proper point of force is selected not even pusher prop based control is better than puller.
Clean flow over the top of the wing adding to lift is superior to puller disturbed lift.

w/o seeing CFD otherwise pushers are better....

duct fans pushers best
 
Jsport,
there are only handfuls of pusher production aircraft. It is reasonable to assume that established aircraft manufacturers think tractor propellers have greater merit in most applications. The choice of tractor vs pusher has to be made in the context of system level performance, meaning you have to consider what happens to propulsive efficiency as well as aerodynamics, structures, weight and balance, stability and control, overall layout, etc.

Tractors just integrate more nicely. Just to name an example, if you have a pusher prop on a fuselage, your landing gear length grows in order to deal with prop strike. Most pushers also need an extension shaft to preserve the fineness ratio of the fuselage or to keep the engine near the cg, and those tend to be mechanical design nightmares. If you put pusher engine nacelles on the wing, it moves the cg aft, and designers don't like that a whole lot.
Also, because of wake ingestion, pusher props tend to be noisy. Have you ever heard a Piaggio Avanti flying overhead? It's very distinctive and loud.

But you don't have to take it from me. I am positive there are several NACA reports from the thirties on the NTRS dealing with the topic. I invite you to look them up and see for yourself their conclusions.
 
AeroFranz said:
Jsport,
there are only handfuls of pusher production aircraft. It is reasonable to assume that established aircraft manufacturers think tractor propellers have greater merit in most applications. The choice of tractor vs pusher has to be made in the context of system level performance, meaning you have to consider what happens to propulsive efficiency as well as aerodynamics, structures, weight and balance, stability and control, overall layout, etc.

Tractors just integrate more nicely. Just to name an example, if you have a pusher prop on a fuselage, your landing gear length grows in order to deal with prop strike. Most pushers also need an extension shaft to preserve the fineness ratio of the fuselage or to keep the engine near the cg, and those tend to be mechanical design nightmares. If you put pusher engine nacelles on the wing, it moves the cg aft, and designers don't like that a whole lot.
Also, because of wake ingestion, pusher props tend to be noisy. Have you ever heard a Piaggio Avanti flying overhead? It's very distinctive and loud.

But you don't have to take it from me. I am positive there are several NACA reports from the thirties on the NTRS dealing with the topic. I invite you to look them up and see for yourself their conclusions.
Click to expand...
Aerofranz,
not a fan of props any way as you have seen, yep know about the CG, landing gear, noise. control, but thank you for further info.
 
jsport,

Could you provide us examples of pusher propellor configurations that demonstrate your views of their performance advantages over similarly sized and powered tractor propellor aircraft?

Richard
 
Richard N said:
jsport,

Could you provide us examples of pusher propellor configurations that demonstrate your views of their performance advantages over similarly sized and powered tractor propellor aircraft?

Richard
Click to expand...
Richard,
with all due respect sir, any very quick search renders a CFD displaying pusher prop displaying unfettered free flow until it hits a wing. Pullers flow immediately hit a disrupting wing. Not sure why this is any argument.
https://www.youtube.com/watch?v=WLvP6Pjy0E8

jsport
 
It's not unfettered. It's ingesting the wake of the fuselage. The inflow is anything but uniform.
Pushers have been around since before the Wrights. Why is it not the predominant layout if it is obviously superior?
For the minority of vehicles that do use the pusher layout, the reasons are often found in areas that have nothing to do with propulsive efficiency.

CFD, as helpful as it is, has nothing on a wind tunnel test of the thirties performed by NACA.
 
AeroFranz said:
It's not unfettered. It's ingesting the wake of the fuselage. The inflow is anything but uniform.
Pushers have been around since before the Wrights. Why is it not the predominant layout if it is obviously superior?
For the minority of vehicles that do use the pusher layout, the reasons are often found in areas that have nothing to do with propulsive efficiency.

CFD, as helpful as it is, has nothing on a wind tunnel test of the thirties performed by NACA.
Click to expand...
Not arguing anything you state it is your biz, but to reinforce over a wing into and then out of a prop is cleaner in CFD.
 
To reiterate what AeroFranz says,because it's true.

Pusher props: CG problems, usually leading to long drive shafts (more weight), or rear mounted engines, which don't help, unless you're using a canard, which limits the useful trim envelope and hence landing and take-off speeds. This is also a result of avoiding a ground strike, which limits alpha and tends to require taller landing gear(more weight). Of course, there is also the problem of prop FOD due to it being placed behind the landing gear. It lacks the efficiency of a tractor engine, however, the thrust wake doesn't impede the fuselage or flight control surfaces behind it (Pluses and minuses there). It does have the benefit of lower cabin/cockpit noise if it's in the tail.

The simple fact is that a tractor configuration tends to be the lower weight, lower cost solution for the majority of mission profiles, where propeller driven aircraft are concerned. If that wasn't the case, there would have been more pusher configurations throughout history. Overall, it simply isn't a very successful strategy for most mission profiles.

Aeronautical engineers don't choose pusher or tractor configurations because it's what they're used to, it's because the minimum weight, and hence cost, is what drives the design for most mission profiles. Pusher configurations have only really been used successfully in designs that a) want twin engines on the center line to negate the penalty of the engine out situation and or frontal area for high speed or b) because they want a canard to prevent the stall/spin scenario. All of these designs tend to pay a penalty when compared to the more conventional tractor designs in their class; higher landing speeds, lower payload fraction to name but a couple. I know I'm a broken record on this and I intend to stay that way, but the mission profile drives the design, not the other way around.

I should qualify this line of argument; what I posted is as it relates to internal combustion engines with direct drive. Electric propulsion will change some of these paradigms due to the ability to distribute propulsion around the airframe and away from the power generator, as shown in the winning design in this contest.
 
Hey jsport,

Your CFD video is missing the flow coming off the trailing edge of the wing and the interference that would occur when it hits the prop. Why don't you include examples of real world conditions like crossflow from sideslip, turbulence caused by the deflection of a leading edge device or trailing edge flap, or the garbage a pusher prop would be spitting out behind a stalled wing. How about an example of showing us an existing real airplane carrying people and not just a generic picture from a screen?

The configuration you have shown probably has nothing to do with flow into the prop and everything to do with giving an unobstructed view from the nose for sensors and cameras.
 
jsport said:
Not arguing anything you state it is your biz, but to reinforce over a wing into and then out of a prop is cleaner in CFD.
Click to expand...

No, not even close. If you have some data to back this assertion it would be revolutionary.
 
quellish said:
jsport said:
Not arguing anything you state it is your biz, but to reinforce over a wing into and then out of a prop is cleaner in CFD.
Click to expand...

No, not even close. If you have some data to back this assertion it would be revolutionary.
Click to expand...
The operative word is 'cleaner' based on spacing (simple 5th grade stuff) than prop in front of wing which was clearly shown in the previous CFD posting. Props disturb plenty when they are in the front. Which universe are we living in here.

Let us please return to the original title of this tread. This DARPA program as no military relevance since there is no LO, no high dynamic maneuver or efficient VTOL fans or reasonable endurance provided by only fuels not hybrid system. Again bureaucracy/ academics distraction rather operational relevance.
 

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Aurora, DARPA Subscale XV-24A Completes Flight Test Program
By S.L. Fuller | April 4, 2017

Aurora Flight Sciences’ XV-24A LightningStrike subscale vehicle demonstrator has completed its planned flight test program, Aurora said Tuesday during Navy League’s Sea Air Space. Tests included outbound and inbound transition fight. The full-scale demonstrator is currently in production, with the flight test program slated for late 2018.

http://www.rotorandwing.com/2017/04/04/aurora-darpa-subscale-xv-24a-completes-flight-test-program/
 
Some more on subscale flight tests incl. new video:

http://www.darpa.mil/news-events/2017-04-04

Unfortunately no full transition is shown in the vid. However "Four of the test flights featured an expanded flight envelope in which the vehicle experimented with increases in air speed until the wing generated most of the lift."

I hope the full-scale version will be capable of softer landings ;)
 
Via Aurora's website

Sentinel
 

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She's not pretty but she's certainly turning heads.
 
VTOLicious said:
Patent related to Sikorsky's proposal: US20160304196A1 Engine installation of vertical take-off and landing (vtol) aircraft

https://patents.google.com/patent/US20160304196A1/en?q=B64C29%2f00&after=20151231&page=1

EDIT: ...and another one: US20160311553A1 Tail sitter vehicle with aerial and ground refueling system

https://patents.google.com/patent/US20160311553A1/en?q=B64C29%2f00&after=20151231&page=2
Click to expand...

That second patent look similar to the TX design propulsion unit with prop rotor instead of ducted fan, and some sort of freewing outer wing panel like a Karem tiltrotor? Hows the TX related work these days?
 
That thing certainly did get a double helping of ugly. It just looks like it ought to be incredibly draggy with all those separate fan cowls and so forth.
 
I wonder if hybrid-electric distributed fan propulsion will finally achieve the necessary efficiency to enable the long delayed "air car" of science fiction. I would think all those electric motors required to spin the fans would weigh enough to offset the increased efficiency from the enhanced "disc area" but maybe not. This architecture came too late for Pratt to have considered it to drive the ultra high bypass fan rather than using a mechanical gearbox but I don't see any indication GE is thinking about it either. It isn't directly related but electric boosted turbo compressors are also being introduced in cars. In this case, the electric motor is simply used to spin up the compressor to eliminate turbo lag.
 
LightningStrike patent. Exiting to see one of SPF members name among authors.
 

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