
Ask HN: How to make lightweight flight armor like Iron Man's? - ghosthamlet
Can we make this nowaday? Why no man made this? It is 100 times more useful and cool than airplane.
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FiatLuxDave
I'm going to write a more extensive answer than I normally would, just because
I love seeing a question like this on HN. It's nice to see someone thinking
about something more interesting than ReactJS for ads.

Because you won't be using aerodynamics for lift, the issue is all about
thrust. The thrust can be used directly for lift; contrary to aurizon's post,
you don't need a 3500:1 thrust ratio - that's only if you are trying to get
lift from the aerodynamics of the suit.

Thrust is about force. To get force in flight you need to react against a
reaction mass. The more reaction mass used, the less energy needed. If you are
able to react against the mass of the earth itself, you only need to spend
energy to change your velocity or altitude. This is the same situation as
being on the ground. You could achieve this if you could react directly with
the ground instead of using air as an intermediate medium. An example of this
would be a magnetic drive that used the earth's magnetic field. Trust me,
that's not easy - the earth's B-field has almost no gradient on a human scale,
and most magnetic machinery operates via gradients.

Using the atmosphere to react against, you get more thrust per unit power the
more air flow you interact with. If you have a means of pulling in a lot of
air to push against, like with a fanjet or helicopter blades, you can get
decent efficiency. This is the strategy used by the Martin JetPack. The extra
machinery gets away from the Iron Man suit idea, though - at a certain point
you are a suit attached to a flying machine.

With enough power, you can get usable amounts of thrust from even small
amounts of reaction mass. Rockets get great thrust, but only for short time
periods. People have made rocket packs, and for short duration flight, we can
build something. Note that Tony Stark's suit is powered by nuclear fusion (the
arc reactor) which gives millions of times more energy per unit mass than
chemical fuels.

You may be interested in www.gravity.co , I think they are using the "short
duration" option I described above.

~~~
aurizon
I can not see where I suggested a 3500:1 ratio. With plot devices - anything
can be done. I do not know if we will ever be able to produce 'reaction-less
thrust', as some people say it has been done, others say no.
[https://www.google.ca/search?q=reactionless+thrust&oq=reacti...](https://www.google.ca/search?q=reactionless+thrust&oq=reactionless+thrust&aqs=chrome..69i57.5565j0j8&sourceid=chrome&ie=UTF-8)

Gravity manipulation? The small tethered water jets are interesting, but power
and range are limited.

[https://www.google.ca/search?ei=qzt2WrfGMpCasQWX3pK4BA&q=wat...](https://www.google.ca/search?ei=qzt2WrfGMpCasQWX3pK4BA&q=water+jet+flight&oq=water+jet+flight&gs_l=psy-
ab.3..0i22i30k1l3.40957.45784.0.46084.16.16.0.0.0.0.113.1560.10j6.16.0....0...1.1.64.psy-
ab..0.16.1555...0j0i131k1j35i39k1j0i67k1j0i8i13i10i30k1.0.-OpDIWXjAek)

~~~
FiatLuxDave
A 10 metric ton safe needs a minimum of 9.8 kilonewtons of thrust to fly (this
being downward-directed thrust). The first stage of a Saturn V rocket provided
35100 kilonewtons of thrust. This is where I came up with the 3500:1 ratio.

~~~
aurizon
Ah, I was speaking figuratively, not precisely

------
aurizon
In our dreams we can make this, we can also use it in plots for action movies
- but we can not now make the real stuff. With enough thrust you can make a 10
ton safe fly, and you would be OK in it, but you would need the thrust of a
Saturn 5.

In the future?? I suspect we will get stronger and lighter armor, and we will
get more efficient thrusters - who knows if we will ever make something like
Iron Man, we will try, and we might get there one day

