To follow up, if my simple arithmetic is correct, a 94 inch propeller
spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.Â*
According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a
typical summer density altitude of, say, 8,800' MSL, the CalAir's prop
tips are supersonic.

But I may have screwed up the math...

On 10/17/2020 10:09 AM, Dan Marotta wrote:
The CalAir A-9b, for instance...

On 10/16/2020 8:50 PM, 2G wrote:
On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
Take-off performance looks impressive. I was surprised by the
amount of noise - sounded not unlike a petrol engined aircraft as
it passed the camera, although presumably it is actually much less
loud.

Any idea what the endurance is of that aircraft?

As the owner of a petrol self-launcher, I like to know that I have
enough endurance for a launch to 2,100 feet (700 m), a relight if
necessary, and a reasonable self-retrieve later if necessary. I
will stick to petrol until batteries can cope with at least that.
Much of the noise you hear from any propeller-driven aircraft comes
from the tips of the propeller breaking the sound barrier.Â*Â* That
won't change between an electric vs petrol engine.Â* The longer the
propeller, the faster the tips move.
My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500.
If you do the math, this works out to 454 mph, well below the speed
of sound. Few GA aircraft have props that go supersonic, and you can
really tell those few that can.

Tom


--
Dan, 5J