10 ms·
MT-Propeller 11 blade propeller delivers 15% increase in static thrust
- peter_d_sherman 4y agoSeems like this 11 blade propeller -- might make a great rear propeller for the Celera 500L: https://ottoaviation.com/ https://ottoaviation.com/
- johntb86 4y agoWhy are they only using odd numbers of blades?
- JumpCrisscross 4y agoEasier 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.)
- mhb 4y agoWhy 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 4y ago“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-choosing-for-prime-numbers-eliminates-vibration 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 4y agoThanks. 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 4y agoSometimes, 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 4y ago> 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 4y agoIt'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.
- mannykannot 4y agoFour 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.
- Cerium 4y agoGenerally 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.
- steve_gh 4y agoOn wind turbines there are generally ground drag effects that reduce the wind speed closer to the ground. A 3 bladed setup minimises the wind speed (and therefore thrust) differences between blades, minimizing the off axis forces on the rotor bearings.
- spullara 4y agoOk, how much better is 13 blades?
- deleted 4y ago[deleted]
- buildsjets 4y ago2 better than a prop that only goes to 11.
- rbanffy 4y agoIt's luckier as well.
- hindsightbias 4y agoWhat’s the weight?
- stevehawk 4y agotheir 7 blade is ~225lbs.. so I'd guess at a minimum it's ~265#
- hnburnsy 4y agofor those wondering... https://www.reddit.com/r/AskEngineers/comments/g39s6s/is_there_a_reason_that_fans_always_have_an_odd/ https://www.reddit.com/r/AskEngineers/comments/g39s6s/is_the...
- mhb 4y agoI read 80% of it and I'm still wondering.
- Scene_Cast2 4y agoI'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 4y agoMy 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 4y agoThe 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.
- vlovich123 4y agoWould that change when using an electric motor?
- rbanffy 4y agoI'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).
- rootusrootus 4y agoKind 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...
- colechristensen 4y agoWith aircraft you can’t just say “efficient” you have to point out what you’re trying to optimize.
- carabiner 4y agoIn rotor design it's pretty clear. Thrust/power ratio here, or FM (Figure of Merit).
- colechristensen 4y agoIt’s not at all. How much does it weigh? How does it perform at different speeds? Thrust to weight ratio is very important to aircraft.
- TylerE 4y agoDue 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.
- Hendrikto 4y agoSeems 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-the-advantages-of-more-than-4-propeller-blades https://aviation.stackexchange.com/questions/23009/what-are-...
- carabiner 4y ago
- travisgriggs 4y agoFor 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-the-advantages-of-more-than-4-propeller-blades https://aviation.stackexchange.com/questions/23009/what-are-...
- emptysea 4y agoInteresting 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
- samwillis 4y agoSomewhat 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 https://news.ycombinator.com/item?id=33949895 1: https://www.mby.com/gear/sharrow-mx-1-tipless-propeller-110120 https://www.mby.com/gear/sharrow-mx-1-tipless-propeller-1101...
- post_break 4y agoI 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 4y ago> 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 4y agoThat 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.
- deleted 4y ago[deleted]
- foobarian 4y agoI 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.
- tus666 4y agoAt what point does a prop become a fan? A 777 engine has 22 fan blades, twice this thing.
- netr0ute 4y ago> 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 4y agoNo 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.
- dmoy 4y ago> 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 4y agoI 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?
- jcims 4y agoProps with high blade count substantially reduce noise for drones as well https://youtu.be/1nk74KEIc2c?t=138s https://youtu.be/1nk74KEIc2c?t=138s
- matthew-wegner 4y agoHuh! Thanks for posting this. I haven't seen 5" builds with props like this before. The opposite is definitely true for toothpick or smaller builds. Bi-blade is much quieter for something like a ~60g, 3" quad.
- buildsjets 4y agoI'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 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 4y agoAre 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 4y agoNormally, 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 4y ago[deleted]
- adolph 4y ago> 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. No, that’s not why. See FAA definition below. Survivable Accident - an accident in which the cockpit and/or structure remains relatively intact and the forces experienced by the occupants did not exceed or should not have exceeded the survivable limits of human G-tolerance. Such an accident is classified as survivable even if some or all occupants were fatally injured. (NOTE: the investigator makes his or her greatest contribution to air safety by documenting the reasons why aircraft occupants were fatally or seriously injured in survivable accidents.) https://www.faa.gov/documentlibrary/media/order/8020.11c_.pdf https://www.faa.gov/documentlibrary/media/order/8020.11c_.pd...
- WalterBright 4y agoThe Wright Bros achieved 90% efficiency with their propellers. Adding 15% to that gives 103.5% efficiency, which I'm not buying.
- vasco 4y agoYou don't add them up like this. I can make a car use 50% less fuel an infinite amount of times, not just twice.
- WalterBright 4y agoPlease 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%
- moloch-hai 4y agoThat is not how it works. 1-((1-0.9)x0.85) = 0.915, 91.5%. 15% better.
- deleted 4y ago[deleted]
- davrosthedalek 4y ago(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.
- rbanffy 4y ago> 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. ;-)
- swayvil 4y agoPrime number so no harmonics? Therefore no... vampiric eddys or vacuum bubbles...? Just my first guess. How's 13? 17?
- rbanffy 4y agoObviously 13 would optimize for luck.
- diskzero 4y agoAs a former aircraft owner, I immediately began to calculate the costs of doing on overhaul on those props. My three bladed props would need an overhaul at least every 2000 hours. There is also a time minimum as well if you don't reach the hours before the time interval. It seemed like the engines and the props would hit overhaul hours around the same time, usually hitting me with a bill well over $10,000. I wonder what the cost will be on dual, 11-blade adjustable pitch props? It makes my eyes water and feel thankful I am not the owner/operator of such an aircraft. Perhaps it all makes sense given the fuel consumption and speed improvements?
- eterevsky 4y ago> with an impressive noise and sound signature. Not sure whether it means that it was loud or quiet. /s
- JoeAltmaier 4y agoMore parts has a cost: the mtbf goes down geometrically.