"Jet" pack

Viv
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Re: "Jet" pack

Post by Viv » Tue Apr 05, 2011 12:37 am

Hi Metiz

As a long time biker I have crashed at a variety of speeds, I can only assume doing it in a vertical orientation is going to hurt just as much or if not more ;-)

Any way isn't a half scale RC model for pussies too? have it full scale and write your own page in history ;-)

Viv
"Sometimes the lies you tell are less frightening than the loneliness you might feel if you stopped telling them" Brock Clarke

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Monsieur le commentaire

Jutte
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Re: "Jet" pack

Post by Jutte » Tue Apr 05, 2011 1:01 am

"...assume doing it in a vertical orientation is going to hurt just as much or if not more."
Yep take it from me... vertical sucks real bad!

metiz
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Re: "Jet" pack

Post by metiz » Thu Apr 07, 2011 12:37 pm

Here's a small article on a "jet pack" testflight with a dummy. http://www.physorg.com/news/2011-04-jet ... video.html

If these guys can do it with half a car strapped to their backs then how hard can it be to make a PROPER jetpack! :lol:

I realy want to build a scalemodel
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Jutte
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Re: "Jet" pack

Post by Jutte » Fri Apr 08, 2011 9:17 pm

Have you ever seen the "Johnny Jetpack" Vids?
http://www.johnnyjetpack.com/
Fly Johnny... fly....erm....

marksteamnz
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Re: "Jet" pack

Post by marksteamnz » Sun Jun 05, 2011 9:22 pm

The Martin Jet pack has just flown to 5000ft and been parachute recovered
http://martinjetpack.com/Jolly good but this whole jet pack flying belt thing has me well exercised.
First up I'd love to fly one I'd sign any waver / disclaimer and have at it.
BUT
There are a number of problems.
Where are you going to fly it?
If it's flying high say 5000ft you need a pilots license, air traffic control etc etc and you will need to land at a designated airport etc. If you fly low you say 20 ft you are only ever going to be flying over your own land or land you have permission to fly over. After the third 20 ft up pass by some wealthy muppet flying uninvited over our farm I'd be looking for rocks to throw. I'm not well pleased by neighbors with 2 stroke trail bikes running race pipes down doing laps on their patch the valley on a Saturday morning, imagine an unmuffled 200hp 2 stroke, buzzing over head. The gee whiz factor only lasts so long.
The oh shit factor.
When the noise stops 50 feet up their current rocket deployed chute won't save you, it might make a nice shroud. If they spend a LOT OF MONEY on development so a rocket pulls the pilot via their harness up and away from the crippled jet pack to a suitable height before deploying a personal parachute (sort of a light weight ejection system) there may be a solution.
Payload
I've never seen a 96kg lard arse like me flying the thing and I'm pretty sure as they never talk thrust or weigh of the manikins that the recent 5000ft trip was probably done with a very light load.

Enough to be going on with
Cheers

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Re: "Jet" pack

Post by marksteamnz » Thu Jun 16, 2011 8:26 am

Of course there's always the newly invented Hover bike
http://www.gizmag.com/hoverbike/18813/picture/135528/

Newly invented? Yeah right.
Nothing like this http://en.wikipedia.org/wiki/Piasecki_VZ-8_Airgeep

sockmonkey
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Re: "Jet" pack

Post by sockmonkey » Mon Jul 25, 2011 3:28 am

PyroJoe wrote:Replacement landing gear can be expensive at times. :D
This. Untill you can shrink it down to less than 50 kilos there is no point in configuring it as a jet-pack that you're strapped to rather than say, a flying motorcycle that you ride on.

Dan211
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Re: "Jet" pack

Post by Dan211 » Mon Jul 25, 2011 8:26 am

Hi Metiz,

Just thought I would clear up some common misconceptions about Jetpack dynamics. Jetpacks are naturally unstable. There is no correcting force that will stabilise a Jetpack at hover, not matter where the pilot is positioned. This is because the thrust vector intersects the CoG and thus cannot provide a correcting moment.

This does not mean a Jetpack cannot be flown manually - it just means doing so takes practice and it will not naturally right itself when the pilot takes their hands off the controls as a fixed wing aircraft would. Because of this, the Martin Jetpack utilises a full fly-by-wire system which greatly simplifies its operation. Any joystick input is basically telling the fly-by-wire system that the pilot would like 10 degrees pitch forward or 2 m/s vertical velocity etc, the rest is handled by the state estimation and control algorithms.

Hope this helps.

Dan

metiz
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Re: "Jet" pack

Post by metiz » Mon Jul 25, 2011 9:43 am

It would if I had a big sack of money to burn :P but thanks for the info. I'm just saying that it could be done simpler i.e., fly by wire, but with less "wires" :lol:
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Re: "Jet" pack

Post by marksteamnz » Mon Jul 25, 2011 10:59 am

If the lift point ie nozzles are high above the COG won't that stabilize a flying whatever? Ruins the maneuverability of course.
Dan211 wrote:Hi Metiz,

Just thought I would clear up some common misconceptions about Jetpack dynamics. Jetpacks are naturally unstable. There is no correcting force that will stabilise a Jetpack at hover, not matter where the pilot is positioned. This is because the thrust vector intersects the CoG and thus cannot provide a correcting moment.

This does not mean a Jetpack cannot be flown manually - it just means doing so takes practice and it will not naturally right itself when the pilot takes their hands off the controls as a fixed wing aircraft would. Because of this, the Martin Jetpack utilises a full fly-by-wire system which greatly simplifies its operation. Any joystick input is basically telling the fly-by-wire system that the pilot would like 10 degrees pitch forward or 2 m/s vertical velocity etc, the rest is handled by the state estimation and control algorithms.

Hope this helps.

Dan

Dan211
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Re: "Jet" pack

Post by Dan211 » Mon Jul 25, 2011 12:02 pm

marksteamnz wrote:If the lift point ie nozzles are high above the COG won't that stabilize a flying whatever? Ruins the maneuverability of course.
Dan211 wrote:Hi Metiz,

Just thought I would clear up some common misconceptions about Jetpack dynamics. Jetpacks are naturally unstable. There is no correcting force that will stabilise a Jetpack at hover, not matter where the pilot is positioned. This is because the thrust vector intersects the CoG and thus cannot provide a correcting moment.

This does not mean a Jetpack cannot be flown manually - it just means doing so takes practice and it will not naturally right itself when the pilot takes their hands off the controls as a fixed wing aircraft would. Because of this, the Martin Jetpack utilises a full fly-by-wire system which greatly simplifies its operation. Any joystick input is basically telling the fly-by-wire system that the pilot would like 10 degrees pitch forward or 2 m/s vertical velocity etc, the rest is handled by the state estimation and control algorithms.

Hope this helps.

Dan
Here's a picture that may help:

Image

In diagram A the device is hovering with zero attitude with the lifting point some distance above the CoG. In diagram B, the device has tilted over. Because of the horizontal distance, d between the thrust and the CoG, a correcting torque, m is created (thrust x d) which attempts to correct the tilt - this device would have natural stability. The problem with this diagram though is that the thrust direction is always down whereas on an actual Jetpack type device the direction of thrust would change with the tilt and intersect the CoG as in diagram C. There is no horizontal distance between the thrust vector and the CoG so there is no correcting torque. Hope this helps.

Dan

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Re: "Jet" pack

Post by marksteamnz » Mon Jul 25, 2011 7:29 pm

Thanks for your patience Dan, got it. I kept getting aerodynamic effects ie tail feathers on rockets confusing me. If hovering everything rotates round the COG quite happily. Light bulb on. The clever bit if you were DIYing a jet pack would be to integrate the laser ring gyro type auto stability from large RC helicopters into a fly by wire system. Not trivial if the work Armadillo Aerospace has done to stabilize their hovering rockets is anything to go by.

Dan211 wrote:
marksteamnz wrote:If the lift point ie nozzles are high above the COG won't that stabilize a flying whatever? Ruins the maneuverability of course.
Dan211 wrote:Hi Metiz,

Just thought I would clear up some common misconceptions about Jetpack dynamics. Jetpacks are naturally unstable. There is no correcting force that will stabilise a Jetpack at hover, not matter where the pilot is positioned. This is because the thrust vector intersects the CoG and thus cannot provide a correcting moment.

This does not mean a Jetpack cannot be flown manually - it just means doing so takes practice and it will not naturally right itself when the pilot takes their hands off the controls as a fixed wing aircraft would. Because of this, the Martin Jetpack utilises a full fly-by-wire system which greatly simplifies its operation. Any joystick input is basically telling the fly-by-wire system that the pilot would like 10 degrees pitch forward or 2 m/s vertical velocity etc, the rest is handled by the state estimation and control algorithms.

Hope this helps.

Dan
Here's a picture that may help:

Image

In diagram A the device is hovering with zero attitude with the lifting point some distance above the CoG. In diagram B, the device has tilted over. Because of the horizontal distance, d between the thrust and the CoG, a correcting torque, m is created (thrust x d) which attempts to correct the tilt - this device would have natural stability. The problem with this diagram though is that the thrust direction is always down whereas on an actual Jetpack type device the direction of thrust would change with the tilt and intersect the CoG as in diagram C. There is no horizontal distance between the thrust vector and the CoG so there is no correcting torque. Hope this helps.

Dan

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Re: "Jet" pack

Post by Dan211 » Tue Jul 26, 2011 12:02 am

No problem Mark. The Martin Jetpack actually does employ a full Inertial Navigation System for its stabilisation which does include 3 axis gyros (not ring laser, most likely MEMS) among a suite of other sensors. Such systems are becoming fairly common these days, even in the DIY community particularly for quadrotor platforms. Check out a recent quadrotor stabilisation system (using low cost gyros) from Hobby King - http://www.hobbyking.com/hobbyking/stor ... duct=17537.

Dan

sockmonkey
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Re: "Jet" pack

Post by sockmonkey » Tue Aug 02, 2011 8:26 am

I think the aussie guy with the hoverbike would be beter off with adjustable-pitch fans that can autorotate rather than parachutes since this thing is almost never gonna fly high enough for a chute to deploy. Ideally it would have some kind of emergency power like a CO2 canister or something that would give you 10-20 seconds worth of power to the props. Adjustable pitch props also mean they can be rigidly coupled to each other to always turn at the same speed so the gyroscopic forces are always balanced

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Re: "Jet" pack

Post by ethanehunt » Thu Nov 10, 2011 6:21 am

Not likely with today's technology.

In the '50s and '60s we tried something similar with various versions of the flying platform. Ultimately, they were too noisy, too maintenance intensive, too much a target, and the Soldier could not actually fight from it - all problems that are still inherent with jet packs.

By the time you work out all the problems with a combat jet pack, you suddenly have a helicopter-like system on your hands, and it is just easier to build helicopters.

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