Sharrow MX-1: Tipless propeller (2020)
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Things are very different in the US because their GA culture is older, more powerful and protected by the FAA and pilots associations.
E.g., turbo prop (source https://www.quora.com/How-fast-is-the-tip-of-a-turboprop-bla...)
I double checked this math and got 474mph.
Meanwhile a Piper Arrow (4-seater piston, pretty comparable numbers to most Lycoming/Continental singles) takes off at 2700 rpm and has a 74” propeller, for a tip speed of 594mph. You can use a 3-blade propeller to reduce the diameter and cut noise somewhat (among other benefits).
Both of these are just the tip speed relative to the plane, I suppose you’d need to factor the airspeed too and use Pythagorean theorem but I’m no aerospace engineer.
As you noted, this is possible because the constant-speed prop on the turboprop allows it to take larger bites of air.
The Arrow needs that rpm to produce full takeoff power. However after takeoff it can be adjusted to a lower speed with minimal loss in power (e.g., 2500 rpm greatly reduces noise while losing 7-8% power). To reduce RPM like that in a fixed pitch you’d also need to reduce manifold pressure, causing more power loss.
If it had even a modest reduction drive, you could run the engine at a reasonable power setting while maintaining a more efficient tip speed but the prop and engine engineers had to meet in the middle resulting in a highly compromised solution.
Is it? I've always thought that while GA engines are in many ways stuck in the 1940'ies, they are actually quite efficient. Wikipedia seems to back that up at https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio... , with a couple of Lycoming engines producing BSFC numbers in the same ballpark as a modern car engine or Rotax.
Edit: A dyno graph from an late 1990's Corvette C5 engine (5.7L) shows about 170HP @ 2700 RPM. That's at the wheels, so probably close-ish to 195HP at the crank: https://cimg5.ibsrv.net/gimg/www.corvetteforum.com-vbulletin...
Sure there have been improvements in modern engines, but these primarily target efficiency across power outputs whereas (as sibling noted) planes tend to have stable power requirements.
Not sure what your point is about constant speed or gearing because I already said that.
The overall wisdom of this is a little questionable and crass of course, since there are also accidents that perhaps could have been recovered with more power.
Moving to a twin is a separate exam.
A big part of all those is the price of running the bigger plane/larger engine.
You could have a plane with constant-speed prop and fixed landing gear and it wouldn't be complex (unless it was a seaplane).
I used to do a lot of gliding and the most powerful aircraft routinely flown was a Piper Pawnee (175 kW / 235 hp engine, in contrast to say c. 120 kW / 160 hp for a Cessna 172), used as a glider aerotow – and even then most of the time we had [electric] winch launches. The pawnee once memorably broke a cylinder head while on tow out and had a sufficient power reserve to both get the glider to a safe altitude and fly the rest of the circuit without issue. At the rest of the field, all of the GA aircraft were highly fuel optimised and mostly run by "normal people" worried about the cost per hour more than anything else. Even the aerobatic aircraft – CAP 10s – had less powerful engines than that Pawnee. I didn't see a super- or turbocharger, and the only people flying twins at nearby airfields were entirely doing it for the point of [commercial] pilot training.
Yeah I mean that's a good encapsulation of what I'm saying: the working aircraft have more power, but the cheap ones are mopeds in comparison. I guess maybe it is mostly the fuel economy though but it generally seems like moonies and other high-performance aircraft probably have much higher insurance/etc. It's cheap to insure your honda accord, you're not going to get yourself in trouble with 1.8L. The FAA is probably happier too.
Diesel could reduce the costs a lot, the DA42 (twin) burns 8 gal/hr, around the same as a C-172, and loiters at 3.2 GPH. Runs on Jet A too (diesel can run on kerosene). I generally think having more modern more advanced aircraft in general could help, the GA fleet is obsolescent and there's no money to replace anything, it's just 70s era engine designs and airframes because that's when the world stopped turning (apart from like, aviation schools and military).
I think the noise is also an important issue for CPU cooling fans or electric fans for homes.
Would love to see such propeller made into everyday small fans.
If you're going to spend the space, simply use a bigger fan at lower RPMs.
Electric fans for homes are a more interesting question. I was going to suggest that a Vorando or Dyson already has a lot of elements of this, and gives more bang for the buck, but I think the two could be combined. A Vornado-style fan really reduces vortex shedding, but probably has some turbulence internally. A modified prop design could reduce that a lot.
So airplane propellers can have more push and lower rpm.
Some years since I last designed propellers and did run CFD-analysis on them. Could be fun to try it again. This was my last attempt: https://no.m.wikipedia.org/wiki/Sivilingeniør#Utdanning
Or move it to the back of the wing.
We do have better designs available, but very fast you end up with either very complex manufacture (and thus price) for special aeroelastic propeller, somewhat less expensive automatically adjustable props, better engines (hello recertification! the big cost killer and what made G100UL so important). I do not know if scimitar prop blades require adjustable mechanism, but wouldn't surprise me. And then there's how to fit scimitar blade on some airplanes.
So unfortunately non-trivial even when everyone involved is all for change, because change costs a lot.
https://en.m.wikipedia.org/wiki/Republic_XF-84H_Thunderscree...
Unsurprisingly it was noisy.
While I don't work in fluid dynamics anymore, it's cool to see people explore some of these ideas in the civilian world. Unfortunately, they may be solving the wrong problem for the vast majority of their users, for whom the cost doesn't justify any performance benefit.
Energy efficience on the other hand.. It is driven by a fairly average car battery, so every little Watt saved helps keep the drinks cooled.
To put it into perspective, 250Wh translates to 800~900 calories burned in a half hour[2]. That's not something most people around me can do.
[1] https://rowinglevel.com/rowing-times/10000m-times
250Wh = 900kJ = 215 kcal at 100% efficiency; humans are ~25% efficient at turning food into mechanical work so ~860 with error bars
During a bicycle race, an elite cyclist can produce close to 400 watts of mechanical power over an hour and in short bursts over double that—1000 to 1100 watts; modern racing bicycles have greater than 95% mechanical efficiency. An adult of good fitness is more likely to average between 50 and 150 watts for an hour of vigorous exercise.[clarification needed] Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain an output of around 75 watts of power.
Also see “How Much Electricity Can a Human Generate?” https://www.pedalpc.com/blog/how-much-electricity-can-human-....
What's interesting about this prop (to me, anyway) is that most of the sea-faring boats that need it the most will likely not use it because it doesn't feather or fold-away when not in use. For ocean-faring sailboats, that's critical, as the drag of trad props will cap their speeds by half a knot or so, which (over the span of a multi-week journey) might add meaningful amounts of time to a trip that you're just hoping to finish with.
But, here important, that electric engines have much better torque on low rpm, even exist electric engines which give high torque just from zero. Also it is typical, to overdrive electric engines for short time.
And other important thing, aging - electric engines could nearly not have aging at all, but gas engines have significant drop of power/torque at hundreds of hours of work, even if properly serviced.
Overall, You will really not see gas engine claimed power, but something much less, ~ 70-90% in good cases. But in case of electric engine, it will not only give claimed power, but could make up to 100% boost for limited time.
- From tutorial for auto engineers: "more than 90% of time, auto engine working at fast switching conditions, and extremely low load, near zero", vs marine (and air), where prop does near linear load-rpm function at working diapason.
This is because, turbine only eat power and does not give anything at low rpms, only effective on medium-high diapason.
For planes, turbine only gives an increase at significantly high altitudes, so, for example, typical light plane does not got improvement if flight on typical 1000-2000m, but got if go much higher, 5000m and more.
These are boat owners, remember.
I remember sitting in a class one day and hearing that there would always be wingtip vortices on planes, and wondered if that could be solved by looping the wing around (to where it almost looks like a biplane).
I wonder how many other ideas are being sat on because people don't realize its significance or have the resources (such as time or desire).
Another old option for eliminating such issues is to put the prop in a case, like a jet ski or most modern military submarines. Or just eliminate the concept of tips and turn the entire case.
We can't banish them, but you can do things to reduce them, the simplest of which is to move the tips further apart (i.e. lengthen the wings.) Everything about airplane design is a compromise, however.
https://en.wikipedia.org/wiki/Stipa-Caproni
Even newer patents should cite this research:
(For the record, it looks like the MIT LL patent was filed in 2017 [2]--not sure how that compares with the patents in the article.)
[1]: https://news.mit.edu/2022/lincoln-laboratory-inventions-win-...
Also, we’ve been eFoiling a lot and it is so calm compared to being on the water in an ICE propelled craft!
I'm just waiting for someone to make an RC scale injection moulded plastic version of it :P
I'm thinking of putting it on the Mini 2 and seeing what happens.
I'm considering this as well. I have an electrical outboard engine on my 24". 600W is way less stressing on the material than even small combustion engines.
I'll maybe try a 3D printed one next year. According to thingiverse, folks already successfully use printed props and the sharrow-design is there, as well, just need to adapt the mount and make sure the printer is up to it (i.e. convert from PLA to ABS, may have to get a new nozzle)
The tests were carried out on a 20ft Bayliner VR5 sportsboat fitted with a standard Mercury 150hp outboard engine, comparing Sharrow’s new tipless MX-1 against two market leading-competitors. Not only was it the fastest of the three (41.7 knots vs 40.8 knots and 39.0 knots) and the most efficient (4.6mpg @ 32 knots vs 4.2mpg and 4.1mph), it also planed earlier and outperformed them both at every 500rpm increment from idle speed to wide open throttle."
Seems like the title is incorrect? The article only claims 9-15% mileage improvements along with vibration reduction and handling improvements.
Really small boats with really huge engines can push quite a bit past hull speed at ultra low efficiency, and that's the only numerical stats they're providing in the article, which is interesting. I wonder if performance is just as high at low speeds, below hull speed, where most cargo ships operate and all the marketing greenwashing is occurring.
Hull speed is not "supersonic" but its a similar enough to rhyme concept, where the boat has a tough time pushing up or thru its own bow wave, sort of, so the max speed of a boat is mostly related to its length. Oddly enough the hydrodynamic variables all cancel out or whatever such that mostly all that matters is wetted hull length for hull speed. You'd superficially guess something like hull depth would matter or width or shape kind of like the stall speed of an airplane wing depends on its shape, but no, ships hull speed almost entirely depends on the wetted hull length. Just a weird hydrodynamics thing.
Maybe an air craft carrier with 10 times the power could go 5% faster, but it would take 100x the power to get an AC carrier up on plane like a ski boat.
However, I think there is a far less than 15% increase in thrust, and due to the super-linear loss of efficiency at the top end to get a 15% increase in efficiency for the same output level might only require a 3% or so increase in thrust at that output level.
They still seem to be around. Not rocking the world yet but I'm surprised that they haven't come out with a cheaper model. Might be harder to cast than expected.
Which is what i'm going to try next year - for my smol electrical harbour pusher.
If you have one of these fancy inconel printers that spacex uses, you could even print a steel version. And quite big ones, too.
In recreational marine these types of products tend to spread based on word-of-mouth and sell fairly low quantities but at higher price points. Related: Seakeeper (https://www.seakeeper.com/), a fairly crazy gyroscopic stabilization system, wildly popular but fairly quiet in the tech world.
A few problems that might show up with this type of prop/"screw" on a large ship:
- Ship propulsion uses a fairly large-diameter prop and runs at very low RPM (~100rpm vs 1000-6000rpm) compared to smaller planing vessels. The Sharrow prop advertises decreased cavitation at high speeds but this effect may be diminished at low RPM.
That said, cavitation is a different beast for ships than for recreational boats: In the recreational market few boat owners are concerned about propeller efficiency loss due to cavitation -- Concern is mostly around noise and vibration. In contrast, ships are very concerned with fuel and maintenance cost, so if the Sharrow blade successfully reduces both of these it may be helpful.
- Seems like they're currently machining these on a 5-axis CNC out of blocks of raw material which won't scale to larger sizes. The complicated shape may not lend itself as well to casting, and even if they casted the shape it would need to be finished and this would require expensive equipment.
- Might be more difficult for third-party repair [2] which is done manually or with 3-axis machines.
Generally the commercial maritime market is much slower to adopt new technology than recreational, and also much smaller by volume, so it may make sense for Sharrow to continue serving small outboard boats because margins + sale volume is much higher.
[1]: Incoming maritime emissions regulations: https://hbr.org/2022/10/climate-regulations-are-about-to-dis... [2]: Example of ship propeller repair: https://www.youtube.com/watch?v=RuV3AsKTQlM
So far though there has not been much in terms of real-world validation of the props on common boats. In some cases there are modest gains seen (<10%), but that is not enough to offset the increased upfront price of the Sharrow. If they could get the manufacturing cost down to that of a typical high performance propeller it might have more demand in the market.
[1]https://boattest.com/article/yamaha-cast-and-sell-sharrow-pr...
The marketing shows it outperforms at very high power level at very high speed.
Then the message veers off into ultra low speed modest power level applications like bulk cargo hauling, and fairly generic greenwashing, we can save the earth with this one nifty techno trick.
A better application would seem to be unlimited-class racing boat props or military-industrial complex torpedo propellers. They have infinite money, which makes the situation interesting.
There's an old joke that an engineer and an economist see a nickel on the ground and the economist tells the engineer not to bother trying to pick it up because the efficient marketplace theory proves there can't be nickels laying around ready to pick up, therefore it can't be there, must be an illusion. However, in the context of people with large amounts of money willing to pay anything for higher performance, it seems odd that a mere propeller shape could exist that nobody is already paying for, that nobody has been paying for over the last century.
My theory would be there's something about this prop that nobody is talking about. Most boats most of the time are not full throttle. WRT durability I wonder what its cavitation behavior is like.
If a "simple" innovation like that can move the needle juste by a few percent points on how much fuel we put into the transport industry, that's a very sizeable gain from a climate perspective.
Let's imagine 3% of improved efficiency (they announce between 9 and 15%, but let's be conservative) on the 3% of the world's emission, that's still almost 0.1% of the world's emission saved by only changing the propellers on cargo ships. It's still a massive improvement: 31 million tons of CO2 saved. At this scale, anything that moves the needle a little bit should be taken. But that's by plucking a number out of thin air, so I'd love to hear about it in the real world and at scale.
Regarding the rest of your message, I agree that the type of fuel that is burned is a big problem, but if changing a propeller means burning x% less of it, it's a no brainer to me!
Haven't checked the maths but energy use in buildings is a far bigger chunk of emissions than shipping.
"The Gossamer Albatross is a human-powered aircraft built by American aeronautical engineer Dr Paul B MacCready's company AeroVironment. On June 12, 1979, it completed a successful crossing of the English Channel to win the second Kremer prize worth £100,000 (equivalent to £538,000 in 2021)" ... "In still air, the required power was on the order of 300 W (0.40 hp), though even mild turbulence made this figure rise rapidly"
With the smol angry-pixie-driven (very quiet!) harbour pusher, i'm just looking at ways to not use up too many angry pixies. This one looks promising and can be 3D printed. Original props for that one come in plastic only, anyway, which is really good! Might've accidentally killed my rudder this year, otherwise.
I'm not in the industry I was just there to turn stuff off and on.
[1] - https://www.ll.mit.edu/sites/default/files/other/doc/2022-09...
Need big scientific research, with many other participants.
For example, it is wide known, that 6-blade prop give near same power as 3-blade but at half rpm, so tip speed is also half.
Curious people, could google quiet helicopter, there are few open publications. Overall, same conclusions - more blades, lower rpm, quiet tip techniques, and try to avoid turbulence from one blade by other blade.
("Aaaah, those ones! Yeah, sure!")
That doesn't mean it's bad, or that it won't work. It very well may have use cases that are not served by simpler propellers, and where the price is not a obstacle. For instance, I wonder about very large ships where a little bit of efficiency may pay off the purchase price.
- Turbine wheels noise is usually shielded by enclosure, and exists other powerful sources of noise, for example, intake. Yes, much noise of heli create intake air.
On civ subs, as I know, main driver of choose is just cost, so usually they use conventional cheap designs.
I wonder myself if it's small enough to use a laser-sintering print process to build.
Binder-jet printing of sand cores is pretty cool too.
a feathering/folding prop for a 35 foot sail boat is about 3 grand already, and it's certainly not a single piece of billet. The real exotic race-y stuff for that size boat is ~6 grand.
Yes, it sucks to ruin a prop -- but it's almost certainly user error 90% of the time; either sucking in boat lines (which will lead to a stall and engine mount damage/ prop-shaft damage in a majority of cases, not prop damage.), or running aground.
Btw.: Worst thing: ride backwards and you'll have to tighten the mounting screw or risk loss of prop. Best thing: Rudder survived hard prop contact with just a few scratches on the outer coat \o/
How Hard Can It Be...?