Static thrust for Sonex with 54" prop

[Mel]

The Aero-Vee engines seem to be working out okay, but since they weigh
at least 160lbs, they might seem a bit heavy for the thrust produced.

They supposedly make 80hp at 3400 rpm. It matters little how much HP
they make, what matters is how much thrust is applied to the aircraft.

You could have a 200hp engine on a Sonex, but trying to dump it into a
54" prop turning 3400rpm would give you very little more thrust. IOW,
the props are less and less efficient as they turn faster, get smaller,
and use pitch to load up the motor.

Another downside is that when props turn much more than 2600 rpm they
start getting noisy.

How much static thrust does a Sonex built according to plans have with
either an Aero-Vee or a Jabiru 2200? With a 72" prop turning at 2600
rpm, I would think 80 hp would make 500-600 lbs. I wonder what 80 hp
into 54" at 3400 rpm would make?

[[email protected]]

Mel wrote:
> ...
> How much static thrust ...



I can't imagine any answer that would be of any value to any purpose
unless your goal is to lock the brakes and use the prop blast to sweep
out your hangar. Thrust while static is of no practical use. I'd
think that thrust while in motion might be more enlightening.

Daniel

[Bill Daniels]

> wrote in message
ps.com...
>
> Mel wrote:
> > ...
> > How much static thrust ...
>
>
>
> I can't imagine any answer that would be of any value to any purpose
> unless your goal is to lock the brakes and use the prop blast to sweep
> out your hangar. Thrust while static is of no practical use. I'd
> think that thrust while in motion might be more enlightening.
>
> Daniel
>

The one place that static thrust is of interest is a glider tug - you need
to get things moving before the glider wing drops.

Bildan

[Mel]

wrote
>
> I can't imagine any answer that would be of any value to any purpose
> unless your goal is to lock the brakes and use the prop blast to sweep
> out your hangar. Thrust while static is of no practical use. I'd
> think that thrust while in motion might be more enlightening.>
> Daniel

Daniel, I can't imagine any answer that would be of any value to any
purpose in your reply.

Static thrust, while not much of an indicator of cruise performance,
does at least give something easily measureable to compare one system
to another.

And, as was mentioned by another post, static thrust is used for
comparison purposes in aircraft that fly slowly with lots of drag or
that tow other aircraft. I guess this doesn't apply much to the Sonex,
but still, if one engine/prop combo makes twice as much static thrust
as the other, I'll bet it climbs better than the other, anyway.

If the Aero-vee produces 400 pounds while tied down, it might mean
something because a 65 hp Rotax 2-stroke with a 72" prop makes about
that much because the prop is turning so slowly.

To carry this to the other extreme, I have a motorcycle that makes 145
hp at 9,000 rpm. The engine probably weighs 150 to 180 lbs. I could
fit a direct drive prop to that thing that would soak up 145 hp. It
would probably be about 14" in diameter with 10 blades and 45 degrees
of pitch. It would sound like it was making LOTS of thrust, but I bet
the Rotax would make more.

Is the 54" usually used for the Sonex an airframe requirement? Do the
Sonexes with aircraft motors (optimized for 2500 rpm or so) turn larger
props, or do they also have to use the little prop?

All silliness aside, I was just wondering what the typical Sonex set-up
generated thrustwise.