[HN Gopher] MT-Propeller 11 blade propeller delivers 15% increas... ___________________________________________________________________ MT-Propeller 11 blade propeller delivers 15% increase in static thrust Author : voidmain0001 Score : 71 points Date : 2023-01-06 19:29 UTC (3 hours ago) (HTM) web link (www.mt-propeller.com) (TXT) w3m dump (www.mt-propeller.com) | [deleted] | WalterBright wrote: | The Wright Bros achieved 90% efficiency with their propellers. | Adding 15% to that gives 103.5% efficiency, which I'm not buying. | vasco wrote: | 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. | rbanffy wrote: | > 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. ;-) | WalterBright wrote: | 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% | rootusrootus wrote: | 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... | TylerE wrote: | Due to much higher rpm, balance is imporant, and your diameter | is constrained (you want the propellor as small as possible | because you want to A: keep the whole thing underwater and B: | Not bang the tips on the bottom. | colechristensen wrote: | With aircraft you can't just say "efficient" you have to point | out what you're trying to optimize. | Hendrikto wrote: | Seems like 1 blade would theoretically be optimal, but due to | requiring a counterweight, a two blade design is superior. [0] | | [0]: https://aviation.stackexchange.com/questions/23009/what- | are-... | swayvil wrote: | Prime number so no harmonics? Therefore no... vampiric eddys or | vacuum bubbles...? Just my first guess. | | How's 13? 17? | rbanffy wrote: | Obviously 13 would optimize for luck. | travisgriggs wrote: | For reference on more or less blades, aviation stack exchange has | some great discussions on this subject. One of my favorites | | https://aviation.stackexchange.com/questions/23009/what-are-... | emptysea wrote: | Interesting so basically the more blades, the less efficient it | gets but you get more thrust | | Sort of makes sense why drones have a couple blades so they can | putter along for hours | spullara wrote: | Ok, how much better is 13 blades? | buildsjets wrote: | 2 better than a prop that only goes to 11. | rbanffy wrote: | It's luckier as well. | [deleted] | samwillis wrote: | 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... | post_break wrote: | 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. | TaylorAlexander wrote: | > 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. | TylerE wrote: | That makes it a great candidate for near-net casting. That | way you save the 80% of tre billet you'd be turning into | chips, and your fancy CNC gets more parts per shift. | samwillis wrote: | Ultimately I suspect if they wanted to make these in | significant volume, die casting or loss wax casting then | machining would be correct route forward. 3D printing metal | is _expensive_ and the parts are likely to not be as strong. | Most 3D printing (sintering) processes for metal result in a | slightly porous part that needs sealing, those small gaps | produce imperfections. | | https://en.m.wikipedia.org/wiki/Die_casting | | https://en.m.wikipedia.org/wiki/Lost-wax_casting | | Take a look at turbine blades in jet engines, they are | incredibly complex with tiny air holes. They are made using a | loss wax then machining process. | foobarian wrote: | I love how the stroboscopic effects in the video recording makes | it look like the blade is spinning slowly like in videogame or | anime show airships. | hindsightbias wrote: | What's the weight? | stevehawk wrote: | their 7 blade is ~225lbs.. so I'd guess at a minimum it's ~265# | johntb86 wrote: | Why are they only using odd numbers of blades? | Cerium wrote: | Generally odd numbers of blades are better for vibration. | | I know that in wind turbines they are favored because it | reduces the effect of the blade crossing the tower. When one of | the blades in a three blade wind turbine crosses over the tower | the force on it is reduced (since the wind is already slowed by | the presence of the tower). The other two blades are in maximum | loading, but balance much of their forces against each other | reducing the bending moment on the turbine shaft. | JumpCrisscross wrote: | 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.) | mannykannot wrote: | Four years ago they were using a nine-bladed propeller, so | while having a prime number may be desirable, it does not | seem to be necessary. | mhb wrote: | 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. | lazide wrote: | "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 o1:o2 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 cylinders, or inline 4 cylinder) tend to | have large vibrations/ + resonances that need special care | and work to handle, or require running at much lower speeds | to avoid self destruction. | | Most propellers and fans have 3 blades because of this, | plus additional tradeoffs efficiency wise. | | More blades will move more air/media per rpm but with more | friction (reduced efficiency). | | Fewer blades (2 or the absolute worst, 1) causes more | vibration and requires more work to balance + cancel | resonances. | mhb wrote: | 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. | lazide wrote: | Sometimes, the constraints make the extra work | worthwhile. It's an engineering problem. | | Typically, you'll see more blades when you have a limited | area you can cover with the blades (aka, low wings or | stubby wings, or lots of engines relative to the wing | size) and need more power/thrust. Adding more engine | power is easy enough, if the decrease in overall | efficiency and stronger airframe required are ok. It's | not a super common trade off, but it's not that uncommon. | | If the 'more blades' math means it's an even number, then | so be it. Balancing them more carefully, strengthening | the airframe in problems areas more, etc. is all part of | the equation. It is more work though. | | You'll see similar tradeoffs between something like a jet | ski water impeller and a cargo ship prop. | | Jet engines have similar type of trade offs - max power | vs overall efficiency, or efficiency at cruise vs | efficiency during variable condition use. Or noise vs | power. | | The type of engine used in a fighter jet makes very | different tradeoffs than in an airliner. | | Adding ducting around a prop or fan also allows much | higher total thrust for the given real estate, at the | cost of weight and a bit of efficiency. | | 3 is usually the cheap and easy answer. Sometimes it's | even the exhaustive and time consuming answer too! | JumpCrisscross wrote: | > _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. | mhb wrote: | 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. | tus666 wrote: | At what point does a prop become a fan? | | A 777 engine has 22 fan blades, twice this thing. | mcarmichael wrote: | The relevant conceptual distinction seems to be whether the | aerodynamics of the blade(s) are conceptually independent, or | interdependent. Better explained here: | https://en.wikipedia.org/wiki/Propeller_(aeronautics)#Aircra... | dmoy wrote: | > 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" both of which are on planes. | | The turboprop uses air to speed up propellers to move the | plane. A turbofan uses just accelerated exhaust from the | engine, and the fans are just a means of feeding the engine | combustion material (air) | buildbot wrote: | 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? | justsomehnguy wrote: | >Perhaps it is a fan if enclosed? Vs. a prop if not? | | Stipa Caproni | rbanffy wrote: | Dear Lord! Half of the lift is due to the repulsion Earth | feels from it. | imnotreallynew wrote: | Most modern fighter jets have turbofan engines as well. | polishdude20 wrote: | 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. | jonsen wrote: | "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 | bitwize wrote: | Back in the 80s there were experiments run with propfans -- | propellers with many stubby blades that offered near jet-like | performance while consuming half the fuel. They never got | anywhere because propfan engines were large and noisy and the | dropping price of oil made the fuel economy concerns less | urgent. | rbanffy wrote: | A think a lot of the noise was because the blades were | counter-rotating. | netr0ute wrote: | > what point does a prop become a fan | | I don't know, because I think the whole purpose of a prop is to | be a fan. | lazide wrote: | No quite. Fans == move air, relative to the thing the fan is | mounted to. | | So a jet engine has fans, because it is moving air into and | around the engine, but not using them to move itself around | directly (It uses the jet of air created by the thermal | expansion from the burning fuel and compressed intake air to | do that, mostly). | | Propeller == moves something through air (or another media | like water) directly. | | Semantics, mostly. | hnburnsy wrote: | for those wondering... | | https://www.reddit.com/r/AskEngineers/comments/g39s6s/is_the... | mhb wrote: | I read 80% of it and I'm still wondering. | Scene_Cast2 wrote: | 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. | Ekaros wrote: | My understanding as well. You increase on metric and make some | other one worse. In the end it is complex process of finding | some balance between these. | | Not that there isn't some improvements that can be made like | have been done with improved materials(less weight), computer | design and so on in more complex engines. | AmVess wrote: | 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. | stevehawk wrote: | 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. | vlovich123 wrote: | Would that change when using an electric motor? | rbanffy wrote: | 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 and two | auxiliary ones on the wingtips for use during takeoff). | stevehawk wrote: | 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). | MonkeyMalarky wrote: | If you trade efficiency for faster cruise speed, is your trip | being shorter a net win for fuel costs? | TylerE wrote: | No, because drag scales with v^2. Going 10% faster requires | 21% more power (and thus fuel), but only reduces trip time | by 9%. | jcims wrote: | Props with high blade count substantially reduce noise for drones | as well | | https://youtu.be/1nk74KEIc2c?t=138s | buildsjets wrote: | I'm really not a big "fan" of MT's cheezy wooden propellers. They | call them "Natural Composite" but it's really just | densified/compressed wood with a thin fiberglass wrapping. Here's | an example of what you can expect from in-service damage, a | Jetstream 41 recently hit a bird, shed a blade, and it shot right | through the passenger cabin. The hilarious thing is that the | government investigation called it a "survivable accident" | because no one happened to be seated in the row that it shot | through. https://avherald.com/h?article=4f2a35e6 | | I was involved in the evaluation of proposed repairs to a | Beechcraft Bonanza with a 3 bladed MT prop that taxied into a | vinyl traffic cone at idle speed. The Beech shed two prop blades, | bent the engine mount and firewall. There was a slight cut in the | traffic cone, but it was returned directly to revenue service. | FullyFunctional wrote: | Are the wooden construction essential to the new blade design? | What are the Beechcraft Bonanza props made of? | | (As a complete layman, not even a pilot, I love the sound | profile of the proposed props) | buildsjets wrote: | Normally, the prop on a Bonanza is made of aluminum. Based on | observation of prior incidents, I would expect no or | negligible damage to an aluminum propeller in the same | circumstance. However, even if no external damage is seen, | some engine manufacturers (and insurers) require a complete | engine teardown and inspection in the event the propeller | contacts an object while the engine is running. | [deleted] ___________________________________________________________________ (page generated 2023-01-06 23:00 UTC)