You don't add them up like this. I can make a car use 50% less fuel an infinite amount of times, not just twice.

Please rethink your statement. You cannot get more motive energy than the energy put into the propeller.

> I can make a car use 50% less fuel an infinite amount of times

No, you can't. Conservation of energy applies.

P.S. I didn't "add" them, either. 90% x 115% => 103.5%

That is not how it works.

1-((1-0.9)x0.85) = 0.915, 91.5%. 15% better.

(Your original point is not affected by this nitpicking, but:) A car, traveling any distance, between two points of constant height (in the gravity field), and neglecting work through friction (which is zero in the zero speed limit, albeit the movement is quite slow then, but a pumped out tunnel and mag lev gets you very close), requires no work, so no fuel. Technically.

> I can make a car use 50% less fuel an infinite amount of times,

At some point it'll be running on nuclear fission, as you won't be able to feed it a single whole atom. ;-)

Doesn't follow. One of the ways you can make a car use less fuel is by reducing drag and friction.

A propeller provides a certain thrust for a certain input power. If more power comes out than goes in, you can use it to construct a perpetual motion machine.

Your construction of what the number means doesn't make sense, and (therefore) you need to start over. It is generally a mistake to assume people quoting figures mean stupidly impossible things, even though sometimes they do.

Good luck with that.

> ...results in static thrust, 15% increase over the standard certified 5-bladed...

No mention of whether that higher static thrust is at some reference RPM, or when it's receiving some fixed X horsepower from the prop. shaft, or what.

From a quick search of the article, I see nothing connecting the 15% figure to efficiency.

Static thrust is plausibly measured with the airplane sitting still on the ground - which is helpful at the start of your take-off run, but probably not a metric that's worth any optimization.

They did not compare with the Wright Bros, but with their 5 blade prop. The Wright Brothers propeller was extremely inefficient at the speeds the test plane is flying, so don't take the 90% number at one speed and compare it blindly with a very different speed and behavior. Did the Wrights have cavitation or supersonic tip of the blade speeds?

No they did not. it was 66%