# Theoretical question about wingless flight with a flight pack

## Main Question or Discussion Point

What is the power to weight ratio required from a wingless augmented portable flight pack (jetpack) so that it can enable flight horizontally?

Assume that the jetpack and the user both weigh 300 pounds combined.

## Answers and Replies

Related Mechanical Engineering News on Phys.org
Anachronist
Gold Member
Well, if the power to weight ratio is above 1.0, it can fly horizontally. How fast horizontally depends on the ratio.

The horizontal component of thrust that is possible is given by the Pythagorean theorem, where the total thrust is the hypotenuse and the weight is one vertical side:
$$F = \sqrt{T^2-W^2}$$
where ##F## is the horizontal thrust, ##T## is the total thrust, and ##W## is the total weight.

So if the jet pack thrusted just 301 pounds, it could be tilted ever so slightly to impart a slight horizontal force to propel the wearer horizontally, but slowly.

CWatters
Homework Helper
Gold Member
I doubt humans make very good "lifting bodies" so +1 to what Anachronist said.

I doubt humans make very good "lifting bodies" so +1 to what Anachronist said.
I guess it depends on what you mean by very good. A skydiver can reach horizontal speeds of 19 m/s while vertical speed is about 72 m/s, is that bad, good? Not good enough to land I suppose :-(

Cheers

CWatters
Homework Helper
Gold Member
Any glide slope less than 1:1 isn't even bad.

cosmik debris
Anachronist
Gold Member
Any glide slope less than 1:1 isn't even bad.
That depends on the speed at which you hit the ground. :)