John wrote:
Bill Daniels wrote:

There 30lb thrust model specs at 5.5 gal/hour (350ml/min) which isn't
horrible for a jet. At speed 30lb is roughly 30hp so it takes 3.3 times
to get 100hp so 18 gal/hour which is about 3 times more fuel than a ricip
but it sure could be a lot of fun ;-)
John
If I recall correctly, one pound of thrust = one HP at around 325 knots.
That's quite a bit of 'at speed'.

That sounds about right, I didn't have the figures in front of me. Even so
if you slowed it down to 150-200 you'd still have a fairly potent engine
for the weight. And it still would be a blast!

Yep, 375mph (or 325 knots). If you factor in propeller efficiency, it's
lower. The math is pretty simple if you know the prop efficiency
(usually about 80% or so), you multiply the two, so in reality the magic
number is about 300mph or between about 250-275 knots.

In other words, a 100hp engine makes 200 pounds of thrust at about
150mph, 100 lbf at 300mph, 50 lbf at 600mph (and so on, putting it
simply). Or, a 30 lb thrust engine is equivalent to a 15hp prop job at
150mph, 30hp at 300mph...

Quite a bit of "at speed."

Static thrust comparisons are a little more complicated, that depends a
lot on the propeller.