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MT-Propeller 11 blade propeller delivers 15% increase in static thrust

mt-propeller.com

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Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#71

Post by recursive »

vasco wrote: post #52
WalterBright wrote: post #49

The Wright Bros achieved 90% efficiency with their propellers. Adding 15% to that gives 103.5% efficiency, which I'm not buying.

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.

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.

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#72

Post by carabiner »

rootusrootus wrote: post #9

Kind of related: Do the same efficiency dynamics that apply to wind turbines apply to a fan providing propulsion? I.e. if a one-bladed fan is the most efficient for capturing wind, would it also be the most efficient airplane propeller or boat propeller? Obviously efficiency isn't the only consideration, but I am curious and I expect there's going to be some fan experts in this thread...

Short answer is yes. But you have to compensate by making the rotor blades longer or spinning them faster to get the same thrust. You can't let the net velocity (vector sum of tip velocity + aircraft velocity) reach supersonic or bad things happen. So you have practical considerations that lead to tradeoffs that determine the number of blades.

The R22 and Cabri G2 are helicopters with basically the same mission, but one uses a 2-blade rotor, the other uses 3 blades. Different engineering choices, style, preferences.

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#73

Post by carabiner »

colechristensen wrote: post #39
rootusrootus wrote: post #9

Kind of related: Do the same efficiency dynamics that apply to wind turbines apply to a fan providing propulsion? I.e. if a one-bladed fan is the most efficient for capturing wind, would it also be the most efficient airplane propeller or boat propeller? Obviously efficiency isn't the only consideration, but I am curious and I expect there's going to be some fan experts in this thread...

With aircraft you can’t just say “efficient” you have to point out what you’re trying to optimize.

In rotor design it's pretty clear. Thrust/power ratio here, or FM (Figure of Merit).

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#74

Post by moloch-hai »

TylerE wrote: post #50
MonkeyMalarky wrote: post #45

Earlier quoted context omitted.

If you trade efficiency for faster cruise speed, is your trip being shorter a net win for fuel costs?

No, because drag scales with v^2. Going 10% faster requires 21% more power (and thus fuel), but only reduces trip time by 9%.

AIUI, drag scales as v³, the reason doubling horsepower adds only a trivial amount of speed.

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#75

Post by moloch-hai »

WalterBright wrote: post #54
vasco wrote: post #52

Earlier quoted context omitted.

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.

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#76

Post by moloch-hai »

recursive wrote: post #71
vasco wrote: post #52

Earlier quoted context omitted.

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.

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.

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#77

Post by [deleted] »

moloch-hai wrote: post #75
WalterBright wrote: post #54

Earlier quoted context omitted.

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.

[deleted]

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#78

Post by WalterBright »

moloch-hai wrote: post #76
recursive wrote: post #71

Earlier quoted context omitted.

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.

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#79

Post by rbanffy »

xplanephil wrote: post #70
rbanffy wrote: post #60

Earlier quoted context omitted.

I'd say the most favorable arrangement for noise would be a pusher configuration, with the engines close to the back of the plane instead of a tractor config on the front. This is done on the Piaggio Avanti. Not sure how well it works, but it looks like a spaceship. Eviation electrical plane recently changed their pusher design to a tractor, but kept the engines on the back (IIRC, they started with a central big one…

The problem with pusher configuration is that the prop operates in turbulent air, that has already ben disturbed by going around the rest of the airplane. Whereas in tractor configuration, the prop grabs "clean" air. This is traditionally cited as the reason why pusher prop planes are louder (from the outside). In fact, one of the noisiest GA planes is the Cessna 337, which is a pull-push twin configuration. The adva…

> Which makes for a very nice anti-ice system.

Didn’t know about that. Sadly, there isn’t much hot exhaust from electric motors.

Re: MT-Propeller 11 blade propeller delivers 15% increase in static thrust

#80

Post by aidenn0 »

moloch-hai wrote: post #74
TylerE wrote: post #50

Earlier quoted context omitted.

No, because drag scales with v^2. Going 10% faster requires 21% more power (and thus fuel), but only reduces trip time by 9%.

AIUI, drag scales as v³, the reason doubling horsepower adds only a trivial amount of speed.

You are both right, there are v^2 and v^3 effects, and depending on the speed regime, one or the other will dominate.
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