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davidb

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Even with zero aircraft speed, the airfoils and control surfaces must have considerable airflow from the props. How they tie that all together with computers is well beyond my simple mind.
 

davidb

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I guess its safe to assume it has some sort of accelerometer based stabilization as part of the control system? I’d guess anyone who buys one for toying will want to fly it low in hills and mountains (I would). The rate of climb would be enough for light winds in such an environment but I wouldn’t want to be like a bat flitting around in the swirlies.
 

cheapracer

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I guess its safe to assume it has some sort of accelerometer based stabilization as part of the control system?
Millions of cars have them, and have had for years.

Obviously not the same, just pointing out the basic tech is very common and well sorted.
 

pictsidhe

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Static margin is very relevant when you are trying to program FBW. With +ve margin, FBW is a simple autopilot. With -ve margin, the FBW needs to dynamically stabilise the thing too. The more -ve the margin, the harder that is to pull off. There will be some limit beyond which the motors and actuators are incapable of responding fast enough.
 

Hot Wings

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There will be some limit beyond which the motors and actuators are incapable of responding fast enough.
Quite true. And the X-29 engineers discovered this pretty quickly.

But for something like the BF the electronics are up to the task. In HZ flight and the ailerons can be moved pretty quickly without exotic hardware. Besides I don't think there is any reason to consider negative static margin. This thing is already responsive enough. In vertical mode the BF is probably both dynamically and statically neutral and depends on artificial stability. In this mode the inertia of the motors/props doesn't seem to be a limitation. So why not take advantage of augmented or artificial stability in the HZ mode as well?
 

Topaz

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Given that the operator's head is about mid-ship, his/her CG (about at the navel) is forward of the mid-point of the vehicle. Means the overall CG is probably slightly forward as well, giving it a small positive static margin.
 

BBerson

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I stumbled upon this book yesterday at the library, oddly coincidental. About the history and disappointment of the "individual lift device" industry up to 2013. He decribes the Martin Jet Pack flight at Airventure 2008 that I watched. It got all of 12" high with two assistants holding it steady (at least it flew).
Many of these devices actually worked but didn't sell a single unit, as far as I know. Might change with eVTOL.
First 50 pages:
https://books.google.com/books/about/The_Great_American_Jet_Pack.html?id=ycr1HSRzRuIC&printsec=frontcover&source=kp_read_button
 

pictsidhe

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Given that the operator's head is about mid-ship, his/her CG (about at the navel) is forward of the mid-point of the vehicle. Means the overall CG is probably slightly forward as well, giving it a small positive static margin.
Neutral point is near 1/4 chord. For a biplane like this with equal? size wings, it's 1/4 of the way between the 1/4 chords of the wings.
Blackfly seems to have it somewhere manageable at any rate. Once you are into -ve margin, whatever is adding dynamix stability needs to be correctly tuned. The more negative, the more accurate it needs to be. The upshot of this is that changing the aircrafts properties, such as different payload weight and or position, changes the tuning. The payload is the 'pilot'. Get the margin -ve enough, he can't scratch his head without upsetting things. So, -ve margin greatly complicates the FBW task, more so with nearly 1/2 the weight a human. Thinking this is easy underestimates the task...
 

markaeric

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It had a typical joystick for pitch and roll that was normal. It had sort of a coulee hat button on top of the stick that controlled throttle/altitude. Normally that would be pitch trim, so my helicopter experience prevented me from operating it correctly in the 60 seconds of sim time I had. (long line of kids waiting).
Hence my "designed by industry outsiders" comment.
Seems a bit awkward. I know you have very limited experience so you might not be able to elaborate more.

Vertical takeoff consists of pressing up on the hat switch. Pressings down makes it go down. How does one transition between vertical and horizontal flight? How is horizontal flight controlled?
 

BBerson

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Push the switch up with thumb to lift off and then push joystick forward to transition to forward flight.
The switch was actually near the top on the stick backside where a thumb could push it.
 

BBerson

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I found this wiki entry that says the Martin JetPack is light enough for FAR 103 but doesn't qualify because it can't meet the stall speed requirement. May explain why it did not fly untethered at Airventure 2008.


"The Martin Jetpack is a small VTOL device with two ducted fans that provide lift and a 2.0-litre V4 piston 200-horsepower gasoline engine.[4] Although its pilot straps onto it and does not sit, the device cannot be classed as a backpack device because it is too large to be worn while walking. However, the Martin Jetpack does not meet the Federal Aviation Administration's classification of an ultralight aircraft: it meets weight and fuel restrictions, but it cannot meet the power-off stall speed requirement. The intention is to create a specific classification for the jetpack - it uses the same petrol used in cars, is relatively easy to fly, and is cheaper to maintain and operate than other ultralight aircraft. Most helicopters require a tail rotor to counteract the rotor torque, which, along with the articulated head complicate flying, construction, and maintenance enormously. The Martin Jetpack is designed to be torque neutral – it has no tail rotor, no collective, no articulating or foot pedals – and this design simplifies flying dramatically. Pitch, roll and yaw are controlled by one hand, height by the other.[5]"
https://en.m.wikipedia.org/wiki/Martin_Jetpack

Edit, I see the empty weight reported is higher than 254, so comments on the wiki are interesting but unreliable. The book I linked said the Martin Jetpack was "classified as an experimental ultralight airplane". (also unreliable and confusing)
 
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Hot Wings

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Horizontal flight control should also be pretty easy to duplicate but how do they handle the transition?
Had a chance this evening to sit in a quiet room with a cup of very good Darjeeling. Realized this is kind of a dumb question. All six degrees of freedom use the craft as reference except altitude/vertical. It's the only one that needs to use earth as the reference?

Based on my viewing of the videos and BBersons simulation observations it appears it has no rudder/yaw control (Z axis rotation in HZ flight)?

The other thing that I noticed from this video:
[video=youtube;l53JKod9yfA]https://www.youtube.com/watch?v=l53JKod9yfA[/video]

Its a lot larger than I had expected based on the raw dimensions+.
 
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BBerson

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Yes, it looked very large at first sight. That's why I suggested a bit more wing area would qualify for 103.
 

cheapracer

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Its a lot larger than I had expected based on the raw dimensions+.
Yup, surprisingly sizey, see how small their heads are in the videos.

I would like to see someone get in and out of it, doesn't look so easy.


Oh, and 103, because we can't have a post without those 3 numbers in it, it's the law.
 

davidb

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I have another can of worms. BF can operate at 50 feet agl and below for an entire flight. It could even follow terrain while maintaining less than 50 feet agl. Think WIG but not limited to relatively flat terrain or water.

In class B or C airspace that starts at the “surface” with the surface in some parts of said airspace being navigable waters, can a WIG legally operate? Watercraft of sizable height can operate within a few hundred feet of the runways at KSFO. What I’m wondering is does the FAA care about vehicles that don’t “protrude” above 50 feet agl.
 

Aerowerx

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Millions of cars have them, and have had for years.

Obviously not the same, just pointing out the basic tech is very common and well sorted.
Are you thinking of Accelerometer or Accelerator? An accelerometer measures the rate and direction of acceleration, including the force of gravity. An accelerator is a control that makes you go faster.
 

BBerson

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I have another can of worms. BF can operate at 50 feet agl and below for an entire flight. It could even follow terrain while maintaining less than 50 feet agl. Think WIG but not limited to relatively flat terrain or water.

In class B or C airspace that starts at the “surface” with the surface in some parts of said airspace being navigable waters, can a WIG legally operate? Watercraft of sizable height can operate within a few hundred feet of the runways at KSFO. What I’m wondering is does the FAA care about vehicles that don’t “protrude” above 50 feet agl.
Any airplane or seaplane or ultralight or helicopter could operate below 50 feet if allowed. I haven't heard of any 50 ft rule.
 

davidb

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Any airplane or seaplane or ultralight or helicopter could operate below 50 feet if allowed. I haven't heard of any 50 ft rule.
I haven’t either. Supposedly WIGs are regulated under maritime laws because they operate on and within (50 feet?) of the water? Supposedly the FAA hasn’t ruled on WIGs operating over land because no one has tried to register one? I am just wondering if airspace designated as starting at the “surface” means the actual surface or is there a buffer of say 50 feet.

I can’t find any precedence on this.
 
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