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BJC

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That's not my understanding of the situation at all. It was not an intentional crash. However the situation came about, the operators were trying to save the vehicle, but were unable to recover from the spin.
At 14 seconds, it looks to have pro-spin control deflections.


BJC
 

gtae07

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At 14 seconds, it looks to have pro-spin control deflections.
The "flight termination system" works by deliberately putting the aircraft into a spin. I assume it works this way to avoid the hassle of explosives (as used on rockets), to ensure the aircraft comes down in a small predictable area, and to minimize the kinetic energy on impact (as opposed to, say, a straight-down dive or spiral descent at Vne). I also assume that there is no override to that signal once it is enacted, for operational security reasons.

From a Flightglobal article:
Northrop Grumman says the crash on 29 March of a Ryan Aeronautical RQ-4A Global Hawk unmanned air vehicle (UAV) was caused by an abort signal from another remotely operated vehicle which was being tested more than 250km (140nm) away. The signal accidentally triggered the Ryan UAV's flight termination system.

"We had problems associated with a flight termination signal and frequency management," says Northrop Grumman Ryan Aeronautical Systems Global Hawk programme manager Bob Ettinger. "Someone else was testing their flight termination signal and we were high enough that we received their signal," he says. The UAV was operating around 75km from its Edwards AFB launch site in California and is believed to have received the erroneous termination signal from the source.

Transmission of the termination signal coincided with a banking manoeuvre by the RQ-4A. The movement temporarily caused the UAV to lose a crucial carrier signal that prevents the termination system from becoming activated.

This is one of three tones: the first is a constant monitor tone which, if dropped, will cause the UAV to return automatically to land. The second tone arms the flight termination system, which is then prevented from activating by the third signal.
 

BJC

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That's good to know. I was concerned that the "pilot" had not had adequate instruction in spin recovery.


BJC





Your challenge, should you choose to accept it, is to discern the sreious from the tongue-in-cheek comments.
 
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gtae07

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That's good to know. I was concerned that the "pilot" had not had adequate instruction in spin recovery.
I don't know that the Global Hawk even has direct "standard" pilot controls. As far as I can tell, there is no "manual" flight mode; the deepest a ground operator can get is to the level of inputting FMS or autopilot commands. It's flown on full-time autopilot.

I found a PDF on the FAA website that confirms this; it's a USAF presentation that (I assume) is intended to familiarize the FAA and others with what they can and can't do with the aircraft in flight. If I could get a link to copy properly I'd post it, but it's on the first page of results if you search "global hawk direct pilot control".

Of note:
Unusual Attitude Recovery
* Since the global hawk was designed to operate autonomously and avoid unusual attitudes, there is no unusual attitude recovery capability.
* If an unusual attitude were experienced the only course of action would be to wait and see if the aircraft recovers on its own or terminate the flight.
 

Toobuilder

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It was being flown from Edwards, and received a 'die' command from nellis. I dont know why nellis sent that command.
A former colleague of mine was in the control room at EDW for this event, and thats my understanding as well.

The latest CLAW will not allow departure from controlled flight. An F-35 pilot cant do anthing with the controls which will over -g, stall, spin, or otherwise depart the aircraft. Let that sink in for a minute. We are creating a generation of pilots that can ham fist the controls in the pattern without any fear of an aerodynamic stall. Im sure this is going to significantly improve safety, but will these pilots even be able to fly an airplane with direct linkage control architecture? We have enjoyed anti lock brakes on cars for years now, and have learned that maximum shopping = stomp on brake as hard as possible and the car will figure out the rest. Safety improves, yes, but how do these same drivers do when you drop them behind the wheel of a 69 Chevelle on an icy road?
 

Toobuilder

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The "flight termination system" works by deliberately putting the aircraft into a spin. I assume it works this way to avoid the hassle of explosives (as used on rockets), to ensure the aircraft comes down in a small predictable area, and to minimize the kinetic energy on impact (as opposed to, say, a straight-down dive or spiral descent at Vne). I also assume that there is no override to that signal once it is enacted, for operational security reasons....
The above is spot on, with the addition that in the case of the GH and other long wing aircraft, theres really no recovery possible once the fuel migrates out to the wingtips as the spin wraps up. The MMOI is just way too much to overcome aerodynamically.
 

gtae07

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The latest CLAW will not allow departure from controlled flight. An F-35 pilot cant do anthing with the controls which will over -g, stall, spin, or otherwise depart the aircraft. Let that sink in for a minute.
To be fair:
* Meeting the performance requirements for that aircraft (or any modern fighter since the 80s) pretty much mandates a statically-unstable design. Fly-by-wire is therefore a necessity from the beginning.
* Aircraft like the F-35 are intended to be flown right at the limits of achievable performance, while the pilot is very much occupied doing other things like trying not to get shot. The less of the pilot's brain that needs to be occupied trying not to exceed performance limits and remembering which combination of controls to use in this situation vs. that one, the more can be devoted to situational awareness, weapons employment, etc.

Also note that the biggest deal with the F-35 is the sensor integration and networking. It's all designed to give the pilot the best information possible in an easy-to-understand format, to maximize his chances of successfully completing the mission and getting back home. The less of his finite mental processing ability he has to devote to playing sensor integrator and control limiter, the more he has available to do the higher-order stuff.

They don't give a hoot about purity of the mechanics of flight or raw man-over-machine skill. It's all about getting the job done.

This is much the same reason for the increasing prevalence of FBW and advanced glass in airliners and other passenger aircraft. The most feasible means of improving safety for the general public is what's going to get used, and the numbers say that's the solution.


Now, bear in mind that pretty much all of these pilots (commercial and military) are still training in aircraft with direct mechanical/hydraulic controls. I suspect that will continue to be the case for a while longer. Perhaps the training needs some changes, but the basics should be there form the beginning. The trick is probably maintaining those skills over the long term with periodic refreshers.

We are creating a generation of pilots that can ham fist the controls in the pattern without any fear of an aerodynamic stall. Im sure this is going to significantly improve safety, but will these pilots even be able to fly an airplane with direct linkage control architecture? We have enjoyed anti lock brakes on cars for years now, and have learned that maximum shopping = stomp on brake as hard as possible and the car will figure out the rest. Safety improves, yes, but how do these same drivers do when you drop them behind the wheel of a 69 Chevelle on an icy road?
With the car example, at least, it's almost irrelevant. The vast majority of cars on the road today have ABS. We're nearly to the point that anyone driving an older car without ABS, electronic engine controls, etc. is doing so by choice, and therefore will learn how to handle that car. And most likely, a collector car like that isn't going to be driven on an icy road anyway. It's like worrying about people not knowing how to use slide rules and trig tables any more. As long as you can do basic hand arithmetic, even a dirt-cheap calculator can do the complex stuff.

With aircraft it's a little different; the bulk of the GA fleet (and a substantial portion of the airliner and non-fighter military fleet) is still mechanical controls, and that'll remain the case for a long time.


I know we (pilot community) grouse a lot about people who blindly follow a GPS and don't know what to do if it breaks or isn't there... but the common knee-jerk reaction of teaching pilots "paper charts, only paper charts, and nothing but paper charts" and pretending that GPS doesn't exist isn't going to solve that problem--it mistakes the messenger for the message. I'd argue the better solution in this case is to teach responsible GPS usage, with the paper navigation as fundamentals and as a fallback. Emphasize situational awareness, planning, and being able to recognize bad data or a failure with sanity checks (after all, that's the important part... right?). Fussing over the paper chart minutae of calculating ground speeds and course corrections "on the fly" with an E6B doesn't buy you much. There are more important lessons to be learned.
 

BBerson

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I searched "raked wing tips". Didn't find any mention of spin resistance.
Installed on the 787 and others for less drag. https://en.m.wikipedia.org/wiki/Wingtip_device

The 21 page proposal Revan posted was a very good description of the problem. But I didn't see any reference (NACA, wind tunnel, etc) about raked tips for spin resistance.
 

BBerson

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I have a R/C model that can fly either on autopilot mode or full control. It won't spin or depart from controlled flight on autopilot mode. I suspect future personal aircraft will have full autopilot mode with automatic interaction with ATC and navigation.
Perhaps if the pilot could only choose full control mode from above say 200 feet or something. So crashing from pilot error would be eliminated. The autopilot would automatically take over below 200 feet agl or prevent a blind canyon entry, or stall after engine failure, for example.

There are now R/C models with a button that will make it return and land at your feet automatically.
The additional cost is around $75.
 

Hot Wings

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but how do these same drivers do when you drop them behind the wheel of a 69 Chevelle on an icy road?
The value of the remaining Chevelles goes up - and so does their insurance rate!

I see a good analogy for this whole discussion in cooking. From a Chef's point of view the only way to cook is over a flame. but that is too dangerous, or messy for some. The next step in safety up the safety ladder is the electric glass top. One more rung brings us to the induction cook top. Another and the "chef" uses a microwave. The ultimate safe method - FBW - (Food By Wire) AKA order it.

Some people just don't have the kinesthetic sense to feel what many of us take for granted. I had a semi hard time transitioning from the drum brakes on that 69 Chevelle to disk brakes when driving on those icy roads. I could feel the little hydraulic pulse in the brake pedal when the self energizing drum brake locked up and that helped me evaluate the road condition. I can't feel that with disk brakes. ABS chatter to me is the same as having to apply power to make the runway - 'I screwed up. Do better next time.'

Interesting debate but it all boils down to those of us that want to fly planes that will perform well and will spend the time to safely prepare tasty food, those that just want to eat, and those that want both. The last group keeps the restaurants busy. GA FBW is unavoidable - if we survive long enough.
 

Dan Thomas

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Can't just add five feet tips onto a Glastar wing. To modify an existing wing (to add five feet to the span) would require splicing a stronger section at the strut attach point (The highest stress point). And some beef up of the root.
Beefing up some areas just moves the extra loads to the edges of the strengthened spots. The whole thing needs beefup if you're going to add that much.

I flew a Glastar that I had put a Subaru in. It never struck me as motorglider material. It handled like a small 185, which is to say that it doesn't glide all that well. An old Champ has a lower sink rate, and they're pretty draggy.
 

Toobuilder

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To be fair...
I am acutely aware of the difference between the “romance” of flying skills and the need to produce an effective weapon system. The more we can ease the modern combat pilots from the minutiae of flying the aircraft so that they can focus on neutralizing threats, the better. But this and the anti lock braking example were used only to illustrate that skills we once were able to cope with as a fact of life can atrophy to the point of extinction. Yes, “dumb” fighters and ‘dumb” cars are gone, but “dumb” GA airplanes are going to be in the fleet for a long time, so the need to train effectively remains with us.

And yes, pilots would stall, spin and die back when a Cub was the standard trainer, but can there be any argument that the standards of stick and rudder skills have diminished since then? I admit that humans are horrible at predictably executing “biological” control laws, but we are not doing ourselves any favors by allowing instructors to teach the fundamentals of flying when they don’t even know how to use the rudder pedals in flight.

And for the record, I’m not against making things easier when it’s a fundamental change. I’m not giving up my Ipad, GPS or ADS-B products without a fight. Some may argue, but these products have revolutionized navigation and pilot SA, and there’s no going back. The same cannot be said (today) for the aerodynamic behavior of a GA airplane at the limits of the envelope. Every design is different, and in some cases every example within the design series is unique. Until there is a “FBW app” that universally cures this behavior, there is going to have to be a certain level of motor skills required. In this area, I prefer to remain sharp, and though it may be unpopular to say, those who can’t or won’t should not be flying.

So in short, I think we should keep figuring out ways to make flying safer (without restricting freedom of movement), but in the meantime we need to suck it up and train to effectively control these unwieldy, unpredictable and skill intensive machines.
 
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BBerson

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Beefing up some areas just moves the extra loads to the edges of the strengthened spots. The whole thing needs beefup if you're going to add that much.

I flew a Glastar that I had put a Subaru in. It never struck me as motorglider material. It handled like a small 185, which is to say that it doesn't glide all that well. An old Champ has a lower sink rate, and they're pretty draggy.
Yes, my intended point was actually that modifying an existing wing to that extent is not practical. A whole new wing or new airplane is needed.
I only hinted at what sort of changes to evolve to the new wing would be.
 

jedi

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from [url said:
http://smithaerospace.us/images/WIT_...tion_Paper.pdf][/url]

We propose development of a longer span and lower powered motor-glider version of the carbon fiber fuselage Sportsman using a 125 hp Gemini turbo Diesel and a reduced gross weight to account for the lighter empty weight of using the smaller, lighter engine. The 125 hp Gemini turbo Diesel installation is anticipated to be 200 pounds lighter than the Centurion Diesel. With a conservative 100 pound allowance for the two 5 foot wingtip extensions we plan a 1400 pound empty weight. Below, specifications are given for two gross weights, one that retains the 1000 pound useful load and another that is a more typical 500 pound two seat trainer useful load. The Centurion Diesel powered Sportsman specifications are included for reference.

We believe this would make an excellent two seat trainer for both airplane and glider flight training. The improved airframe efficiencies would make up for the reduced power and the turbo diesel engine would be an economical consumer of diesel or Jet-A fuel. On cross country flights, this aircraft could be capable of 1500 NM between fuel stops if needed.

Build a GlaStar, rather than the more expensive Sportsman, as a proof of concept, and show us the real world benefits. Use a 160 HP IO-320, keep the same gross weight, and replicate the C.A.F.E. testing for performance. (Note the the yaw stability was not judged to be favorable by the C.A.F.E. test pilot.)

Doing that would allow a reasonable measure of the basic performance of the two configurations at a much lower cost than building a more expensive airframe with a different wing, engine and gross weight.

Good luck. I eagerly await the results.


BJC
Without detracting from the suggestion to modify a GlaStar I would like to review the reasoning for selecting the Sportsman Diesel for the baseline in the design study.

The carbon fiber fuselage Sportsman is lighter than the fiberglass standard Sportsman. Rather than convert this weight savings into reduced empty weight the weight savings is reinvested in stronger wing structure and increased gross weight. The motor glider uses this tail cone weight savings to offset the lighter and less powerful Gemini diesel which has the same power output as the first three Sportsman built. This increased gross weight is not needed in the motor glider version with the strengthened wing structure. The gross weight is therefore reduced to that of the glass fiber Sportsman and the additional strength is applied to the increased wing bending moment due to the increased span of the crescent wing tips. The allows the easily constructed Hershey bar (zero twist) Sportsman to benefit from BSLD characteristics.

I believe this increased performance qualifies this Sportsman to be registered as a motorglider with many additional operational benefits. It is not intended to be a soaring machine in the modern sailplane sense. It is a motor glider with performance comparable to a primary glider. The manual can have a specified procedure for inflight engine shutdown and relight to allow students to train for engine out flight. There is no requirement for a medical certificate so the aircraft retains that light sport pilot benefit without the 1320# weight limitation. It allows heavy pilots to obtain a glider rating that is otherwise unavailable too them because of a lack of high useful load two place training gliders. It would make a very economical training platform. There are additional benefits I chose not to include here. The shorter length and associated smaller aerodynamic tail volume of the GlaStar compared with the Sportsman is perceived to be a disadvantage when the span is increased with the addition of the raked tips.

Cost was not the driving factor in the design study. However, I would hope the proposed design would compare very favorably with a new Cessna Skylane. Note that Glasair is in the process of certifying the Sportsman as a primary aircraft that could be used by flight schools.
 
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REVAN

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I believe this increased performance qualifies this Sportsman to be registered as a motorglider with many additional operational benefits. It is not intended to be a soaring machine in the modern sailplane sense. It is a motor glider with performance comparable to a primary glider. The manual can have a specified procedure for inflight engine shutdown and relight to allow students to train for engine out flight. There is no requirement for a medical certificate so the aircraft retains that light sport pilot benefit without the 1320# weight limitation. It allows heavy pilots to obtain a glider rating that is otherwise unavailable too them because of a lack of high useful load two place training gliders. It would make a very economical training platform. There are additional benefits I chose not to include here. The shorter length and associated smaller aerodynamic tail volume of the GlaStar compared with the Sportsman is perceived to be a disadvantage when the span is increased with the addition of the raked tips.
As a motor Glider, it also would not be limited to 10,000 feet altitude like an LSA. This is a big benefit to a plane with a turbocharged engine and a big wing.
 

Victor Bravo

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Raked tips are not there to improve spin behavior to the best of my knowledge. They are there to reduce drag at the wingtip by reducing the lift curve to zero in a more controlled manner, with the hope of reducing the energy lost to a tip vortex.

Certain outer wing taper planforms (often similar to raked tips ) have also been shown to rearrange the pressure distribution on the top of the wing, so that there is less "motivational force" in the pressure field to power the vortex. This was named the "Scheumann Wing Planform", after Wil Scheumann, who published an article in a 1984 Soaring Magazine explaining how this principle works. He modified the outer wings of his AS-W12 sailplane, and demonstrated positive performance gains at slow speed/climb. Scheumann's ideas were adopted and developed by Klaus Holighaus of Schempp-Hirth Segelflugzeugbau, which introduced the first Discus sailplane with the "cranked" wing leading edge. The competition performance of the Discus using this planform was improved and it became the leading Standard Class sailplane in the world. The "Discus Planform" as it eventually became known, is now seen on the majority of high performance sailplanes.

And Wil Scheumann, who is usually the smartest man in the room, got the idea for this wing planform from the smartest woman in the room, some chick named Mother Nature.

il_570xN.249905861.jpg
 

REVAN

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Raked tips are not there to improve spin behavior to the best of my knowledge. They are there to reduce drag at the wingtip by reducing the lift curve to zero in a more controlled manner, with the hope of reducing the energy lost to a tip vortex.
They do reduce drag. That's the big attraction. We all know that almost no one will change the airplane to make it safer. But, many will jump at the chance to lower drag and get better performance. When better stability and handling comes with it, that's progress.
 

REVAN

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To get the real benefits of a BSLD with the raked tip, I think it is important to get the crescent shape in the trailing edge of the rake. One of the best performing aircraft in a stall is the Kasperwing ultralight. Take a look at the trailing edge. Then note the line I drew to modify the leading edge out at the tip. It's a small change to the wing design to get from the Kasperwing to the proposed raked wing.

kasperwing-top_mod.jpg

In my monofin, I use a pretty deep crescent, and it works well even though I'm using a flat plate without any built in reflex or twist. This is a bi-directional application of the tech. With wing twist and reflex in the raked tip, the rake could probably be reduced from what I'm using and get a similar benefit in the designed lifting direction, but not when the wing is lifting inverted.

Worlds_Orca_France.jpg
 
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henryk

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"raked wing."-another words?(I dont understand)...

BTW=Kaspers wing-tip rudders are working effective in deep stal regime

and are the "winglets",

see=BKB1-A L/D=30 with only AR=10
or BEKAS L/D=44 with AR=15 !
 

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