Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

mt-propeller.com

Post reply on HN
Print view View original

31–40 of 104 posts

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

#31

Post by polishdude20 »

dmoy wrote: post #23
tus666 wrote: post #17

At what point does a prop become a fan? A 777 engine has 22 fan blades, twice this thing.

> At what point does a prop become a fan? Linguistically, a prop becomes a fan when you anchor it to something immovable, or attach it to something movable but without any intention of propelling it using the prop. Fan - try to move the air around, but not the thing it's attached to. Prop - try to propel the thing it's attached to Edit: I realize that might sound ambiguous given terms like "turboprop" and "turbofan"…

That's not true about a turbofan. A large part of the thrust is actually from the fan itself. The bypass air that never goes into the combustion chamber produces most of the thrust.

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

#32

Post by jonsen »

dmoy wrote: post #23
tus666 wrote: post #17

At what point does a prop become a fan? A 777 engine has 22 fan blades, twice this thing.

> At what point does a prop become a fan? Linguistically, a prop becomes a fan when you anchor it to something immovable, or attach it to something movable but without any intention of propelling it using the prop. Fan - try to move the air around, but not the thing it's attached to. Prop - try to propel the thing it's attached to Edit: I realize that might sound ambiguous given terms like "turboprop" and "turbofan"…

"A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.":

https://en.m.wikipedia.org/wiki/Turbofan

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

#33

Post by stevehawk »

AmVess wrote: post #28
Scene_Cast2 wrote: post #6

I'd imagine that, just like in other industries, there are tons of metrics (or counter-metrics) that are also important. Some that come to mind are efficiency, noise, vibration, cost, maintenance, stall characteristics, RPM requirements, weight, etc etc. From some fiddling with RC quads, I remember that increasing the number of blades does increase thrust, but at the cost of efficiency and several other parameters.

The cost of this blade setup means no one will buy it. Very high cost to purchase and equally high cost to maintain for such a tiny benefit. I had a laugh at the noise reduction claim. Sure, it will reduce noise, but the open exhausts on planes are the loudest part unless some nitwit is screwing around with the pitch.

I can't say I have the numbers to dispute this. But the loudest thing on my Cessna is not the open, 1970s era exhaust. It is definitely the prop whipping through the wind.

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

#34

Post by JumpCrisscross »

mhb wrote: post #19
JumpCrisscross wrote: post #8

Earlier quoted context omitted.

Easier to balance; if everything is even, you need to balance two blades to counter one misbehaviour, and do so perfectly to avoid introducing new misbehaviours. (They’re prime for resonance reasons. I don’t remember what, specifically.)

Why would they be easier to balance? The hand-waving about resonance also pervades that reddit "explanation" thread which doesn't explain anything about what prime or odd numbers of blades have to do with resonance in a single propeller.

> Why would they be easier to balance?

Have you balanced a fan? The wobbles aren’t solely at the blade points. Having a blade opposed by nothing helps avoid a problem where one blade balancing throws another off.

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

#35

Post by mhb »

lazide wrote: post #27
mhb wrote: post #19

Earlier quoted context omitted.

Why would they be easier to balance? The hand-waving about resonance also pervades that reddit "explanation" thread which doesn't explain anything about what prime or odd numbers of blades have to do with resonance in a single propeller.

“Prime numbers are generally used to reduce the magnitude of resonances. These occur in a non-linear multi-frequency system when two of the frequencies ω1:ω2 match at a ratio p:q, where p,q are comprime integers.” Per https://physics.stackexchange.com/questions/484288/why-choos... It’s also matched by practical experience - engines which have simple low integer multiple resonances in moving parts (like opposing 2 cyl…

Thanks. The explanation there makes sense. Still, this must be a secondary effect since there are plenty of examples of even-bladed and non-prime bladed propellers.

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

#36

Post by imnotreallynew »

buildbot wrote: post #30
dmoy wrote: post #23

Earlier quoted context omitted.

> At what point does a prop become a fan? Linguistically, a prop becomes a fan when you anchor it to something immovable, or attach it to something movable but without any intention of propelling it using the prop. Fan - try to move the air around, but not the thing it's attached to. Prop - try to propel the thing it's attached to Edit: I realize that might sound ambiguous given terms like "turboprop" and "turbofan"…

I am not sure this is really correct - turbojets (as in fighter jets) sound more like what you describe, turbofans if I remember correctly, get most of the thrust (>70%?) from bypass air around the combustion, and very little from actual combustion thrust. It just also feeds it's own combustion chamber air to keep the fan part going. Perhaps it is a fan if enclosed? Vs. a prop if not?

Most modern fighter jets have turbofan engines as well.

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

#37

Post by stevehawk »

Scene_Cast2 wrote: post #6

I'd imagine that, just like in other industries, there are tons of metrics (or counter-metrics) that are also important. Some that come to mind are efficiency, noise, vibration, cost, maintenance, stall characteristics, RPM requirements, weight, etc etc. From some fiddling with RC quads, I remember that increasing the number of blades does increase thrust, but at the cost of efficiency and several other parameters.

The big wins here are likely the increase in thrust and ultimately cruise speed, which makes twin props more competitive with very light jets, and the decrease in noise which may make more airports accessible to the aircraft in question due to local noise limitations.

The big loss here is purchase price and maintenance price. But that's on a scale that's probably not bothering a person who can afford a brand new Beechcraft King Air or to completely refurbished a used version of the plane in the video (they quit making the Piper Navajo 30 years ago).

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

#38

Post by mhb »

JumpCrisscross wrote: post #34
mhb wrote: post #19

Earlier quoted context omitted.

Why would they be easier to balance? The hand-waving about resonance also pervades that reddit "explanation" thread which doesn't explain anything about what prime or odd numbers of blades have to do with resonance in a single propeller.

> Why would they be easier to balance? Have you balanced a fan? The wobbles aren’t solely at the blade points. Having a blade opposed by nothing helps avoid a problem where one blade balancing throws another off.

It's still not obvious why this would be different for even vs. odd blade numbers or why changing one blade throws the others "off". If you have two blades and change one, you need to be concerned with the other blade. If you have three blades and change one, you need to be concerned with the other two blades.

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

#39

Post by colechristensen »

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.

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

#40

Post by TaylorAlexander »

post_break wrote: post #13
samwillis wrote: post #11

Somewhat related thread [0] from last month about the "tipless" Sharrow MX-1 prop [1] which achieves efficiency gains of between 9-15% over comparable 3-blade propeller designs. They started out working on an aircraft propeller but pivoted to a watercraft prop. 0: https://news.ycombinator.com/item?id=33949895 1: https://www.mby.com/gear/sharrow-mx-1-tipless-propeller-1101...

I immediately questioned cavitation and that link delivered. That's INCREDIBLE. The only issue is the price of course. That looks like a perfect candidate for 3D printing and then machining the final part vs billet.

> That looks like a perfect candidate for 3D printing and then machining the final part vs billet.

Now you need two expensive machines, not just one. Billet is not that expensive. I've seen people suggest this before and I looked on their site. They show a multi axis CNC machine making the parts. You would need exactly the same machine to post machine the 3D printed part, but now you have a second expensive and slow process to manage (the metal 3D printing). With billet a huge bar of material shows up, you slice each piece in a few minutes, mount it in your CNC and go. 3D printing feed powders have their own expensive processes they need to go through, so they probably cost much more than billet, reducing any potential cost savings on the material side. And the second expensive machine and process adds a lot of new expenses. Plus, you have to validate the product all over again instead of just selling them.

I bet the high price is mostly due to patents and lack of competition. It is probably not inherently super expensive to make, beyond the need for a high end multi axis CNC machine.

Post reply on HN