Original hardware brass screws from my door and locks, plus one of the stainless screw that I used as a replacement.
I just replaced the door knob assembly on my home and found that it was held in place by a faceplate that was attached by two, 5/8″, brass screws. These screws, shown at right with their replacement, would not have been able to withstand a criminal, I think. Our door is metal, foam filled, and reasonably strong. I figure it would have withstood a beating, but the brass screws would not, especially since only 1/4″ of the screw is designed to catch foam. Look closely at the screws, and you will see there are two sizes of pitch, each 1/4 long. Only the last 1/4″ looks like it was ever engaged. The top 1/4″ may have been designed to catch metal, but the holes in the door were not tapped to match. The bottom 1/4″ held everything. Even without a criminal attack, the screw at right was bent and beginning to go.
Instead of reusing these awful screws or buying similar ones, I replaced them with stainless screws, 1 3/4″ long, like the one shown in the picture above. But then I had a thought — what were the other locks on my door attached with? I checked and found my deadbolt lock was held in by two of the same type of sorry, 5/8″ brass screws. So I replaced these too, using two more, 1.75″ stainless steel. Then, in my disgust, I thought to write this post. Perhaps the screws holding your door hardware is as lousy as was holding mine. Take a look.
I’ve gone sailing a few times this summer, and once again was struck by the great difference between sailing and boating, as well as by the mystery of the hull speed.
Sailors are distinct from boaters in that they power their boats by sails in the wind. Sailing turns out to be a fairly pleasant way to spend an afternoon. At least as I did it, it was social, pleasant, and not much work, but the speeds were depressingly slow. I went on two boats (neither were my own), each roughly 20 feet long, with winds running about 10-15 knots (about 13 mph). We travelled at about 3 knots, about 3.5 mph. That’s walking speed. At that speed it would take about 7 hours to cross Lake St. Clair (25 miles wide). To go across and back would take a full day.
Based on the length of the boats, they should have been able to go a lot faster, at about 5.8 knots (6 mph). This target speed is called the hull speed; it’s the speed where the wave caused by the bow provides a resonance at the back of the boat giving it a slight surfing action, see drawing.
This speed can be calculated from the relationship between wave speed and wavelength, so that Vhull = √gλ/2π where g is the gravitational constant and λ is the water line length of the boat. For Vhull in knots, it’s calculated as the square-root of the length in feet, multiplied by 1.34. For a 20 foot boat, then,
While power boats routinely go much faster than this, as do racing skulls and Americas cup sailboats, most normal sailboats are designed for this speed. One advantage is that it leads to a relatively comfortable ride. There is just enough ballast and sail so that the boat runs out of wind at this speed while tipping no more than 15°. Sailors claim there is a big increase in drag at this speed, but a look at the drag profile of some ocean kayaks (12 to 18 feet, see below) shows only a very slight increase around this magical speed. More important is weight; the lowest drag in the figure below is found for the shortest kyack that is also the lightest. I suspect that the sailboats I was on could have gone at 6 knots or faster, even with our current wind, if we’d unrolled the spinnaker, and used a ‘screecher’ (a very large jib), and hung over the edge to keep the boat upright. But the owner chose to travel in relative comfort, and the result is that we had a pleasant afternoon going nowhere.
Data from Vaclav Stejskal of “oneoceankyacks.com”
And this brings me to my problem with power boating. Th boats are about the same length as the sailboats I was in, and the weight is similar too. You travel a lot faster, 20 to 25 knots, and you get somewhere, but the boats smell, and provide a jarring ride, and I felt they burn gas too fast for my comfort. The boats exceed hull speed and hydroplane, somewhat. That is, they ride up one wave, fly a bit, and crash down the other side, sending annoying wakes to the sailboaters. We crossed lake St. Clair and rode a way down the Detroit river. This was nice, but it left me thinking there was room for power -assisted sailing at an intermediate speed, power sailing.
Both sailboats I was on had outboard motors, 3 hp, as it happened, and both moved nicely at 1 hp into and out of the harbor, even without the sail up. Some simple calculations suggest that, with I could power a 15 to 20 foot sailboat or canoe at a decent speed – hull speed – by use of a small sail and an electric motor drawing less than 1 hp, ~400 W, powered by one or two car batteries.
Consider the drag for the largest, heaviest kayak in the chart a move, the Cape Ann Double, going at 6.5 knots. At 6 knots, the resistance is seen to be 15 lbs. To calculate the power demand, convert this speed to 10 fps and multiply by the force:
Power for 6 knot cruising = 10 fps x 15 lbs = 150 ft lbs/s = 202 W or 0.27 hp.
Outboard motors are not 100% efficient, so let’s assume that you need to draw more like 250 W at the motor, and you will need to add power by a sail. How big a battery is needed for the 250 W? I’ll aim for powering a 4 hour trip, and find the battery size by multiplying the 250 W by 4 hours: that’s 1250 Hrs, or 1.25 kWh. A regular, lithium car battery is all that’s needed. In terms of the sail, I’m inclined to get really invovative, and use a Flettner sail, as discussed here.
It seems to me that adding this would be a really fun way to sail. I’d expect to be able to go somewhere, without the smell, or the cost, or being jarred to badly. Now, all I need is a good outboard motor, and a willing companion to try this with.
Heat exchange is a key part of most chemical process designs. Heat exchangers save money because they’re generally cheaper than heaters and the continuing cost of fuel or electricity to run the heaters. They also usually provide free, fast cooling for the product; often the product is made hot, and needs to be cooled. Hot products are usually undesirable. Free, fast cooling is good.
So how do you design a heat exchanger? A common design is to weld the right amount of tubes inside a shell, so it looks like the drawing below. The the hot fluid might be made to go through the tubes, and the cold in the shell, as shown, or the hot can flow through the shell. In either case, the flows are usually in the opposite direction so there is a hot end and a cold end as shown. In this essay, I’d like to discuss how I design our counter current heat exchangers beginning a common case (for us) where the two flows have the same thermal inertia, e.g. the same mass flow rates and the same heat capacities. That’s the situation with our hydrogen purifiers: impure hydrogen goes in cold, and is heated to 400°C for purification. Virtually all of this hot hydrogen exits the purifier in the “pure out” stream and needs to be cooled to room temperature or nearly.
Typical shell and tube heat exchanger design, Black Hills inc.
For our typical designs the hot flows in one direction, and an equal cold flow is opposite, I will show the temperature difference is constant all along the heat exchanger. As a first pass rule of thumb, I design so that this constant temperature difference is 30°C. That is ∆THX =~ 30°C at every point along the heat exchanger. More specifically, in our Mr Hydrogen® purifiers, the impure, feed hydrogen enters at 20°C typically, and is heated by the heat exchanger to 370°C. That is 30°C cooler than the final process temperature. The hydrogen must be heated this last 30°C with electricity. After purification, the hot, pure hydrogen, at 400°C, enters the heat exchanger leaving at 30°C above the input temperature, that is at 50°C. It’s hot, but not scalding. The last 30°C of cooling is done with air blown by a fan.
The power demand of the external heat source, the electric heater, is calculated as: Wheater = flow (mols/second)*heat capacity (J/°C – mol)* (∆Theater= ∆THX = 30°C).
The smaller the value of ∆THX, the less electric draw you need for steady state operation, but the more you have to pay for the heat exchanger. For small flows, I often use a higher value of ∆THX = 30°C, and for large flows smaller, but 30°C is a good place to start.
Now to size the heat exchanger. Because the flow rate of hot fluid (purified hydrogen) is virtually the same as for cold fluid (impure hydrogen), the heat capacity per mol of product coming out is the same as for mol of feed going in. Since enthalpy change equals heat capacity time temperature change, ∆H= Cp∆T, with effectiveCp the same for both fluids, and any rise in H in the cool fluid coming at the hot fluid, we can draw a temperature vs enthalpy diagram that will look like this:
The heat exchanger heats the feed from 20°C to 370°C. ∆T = 350°C. It also cools the product 350°C, that is from 400 to 50°C. In each case the enthalpy exchanged per mol of feed (or product is ∆H= Cp*∆T = 7*350 =2450 calories.
Since most heaters work in Watts, not calories, at some point it’s worthwhile to switch to Watts. 1 Cal = 4.174 J, 1 Cal/sec = 4.174 W. I tend to do calculations in mixed units (English and SI) because the heat capacity per mole of most things are simple numbers in English units. Cp (water) for example = 1 cal/g = 18 cal/mol. Cp (hydrogen) = 7 cal/mol. In SI units, the heat rate, WHX, is:
The flow rate in mols per second is the flow rate in slpm divided by 22.4 x 60. Since the driving force for transfer is 30°C, the area of the heat exchanger is WHX times the resistance divided by ∆THX:
A = WHX * R / 30°C.
Here, R is the average resistance to heat transfer, m2*∆T/Watt. It equals the sum of all the resistances, essentially the sum of the resistance of the steel of the heat exchanger plus that of the two gas phases:
R= δm/km + h1+ h2
Here, δm is the thickness of the metal, km is the thermal conductivity of the metal, and h1 and h2 are the gas-phase heat transfer parameters in the feed and product flow respectively. You can often estimate these as δ1/k1 and δ2/k2 respectively, with k1 and k2 as the thermal conductivity of the feed and product, both hydrogen in my case. As for, δ, the effective gas-layer thickness, I generally estimate this as 1/3 the thickness of the flow channel, for example:
h1 = δ1/k1 = 1/3 D1/k1.
Because δ is smaller the smaller the diameter of the tubes, h is smaller too. Also small tubes tend to be cheaper than big ones, and more compact. I thus prefer to use small diameter tubes and small diameter gaps. in my heat exchangers, the tubes are often 1/4″ or bigger, but the gap sizes are targeted to 1/8″ or less. If the gap size gets too low, you get excessive pressure drops and non-uniform flow, so you have to check that the pressure drop isn’t too large. I tend to stick to normal tube sizes, and tweak the design a few times within those parameters, considering customer needs. Only after the numbers look good to my aesthetics, do I make the product. Aesthetics plays a role here: you have to have a sense of what a well-designed exchanger should look like.
The above calculations are fine for the simple case where ∆THX is constant. But what happens if it is not. Let’s say the feed is impure, so some hot product has to be vented, leaving les hot fluid in the heat exchanger than feed. I show this in the plot at right for the case of 14% impurities. Sine there is no phase change, the lines are still straight, but they are no longer parallel. Because more thermal mass enters than leaves, the hot gas is cooled completely, that is to 50°C, 30°C above room temperature, but the cool gas is heated at only 7/8 the rate that the hot gas is cooled. The hot gas gives off 2450 cal as before, but this is now only enough to heat the cold fluid by 2450/8 = 306.5°. The cool gas thus leave the heat exchanger at 20°C+ 306.8° = 326.5°C.
The simple way to size the heat exchanger now is to use an average value for ∆THX. In the diagram, ∆THX is seen to vary between 30°C at the entrance and and 97.5°C at the exit. As a conservative average, I’ll assume that ∆THX = 40°C, though 50 to 60°C might be more accurate. This results in a small heat exchanger design that’s 3/4 the size of before, and is still overdesigned by 25%. There is no great down-side to this overdesign. With over-design, the hot fluid leaves at a lower ∆THX, that is, at a temperature below 50°C. The cold fluid will be heated to a bit more than to the 326.5°C predicted, perhaps to 330°C. We save more energy, and waste a bit on materials cost. There is a “correct approach”, of course, and it involves the use of calculous. A = ∫dA = ∫R/∆THX dWHX using an analytic function for ∆THX as a function of WHX. Calculating this way takes lots of time for little benefit. My time is worth more than a few ounces of metal.
The only times that I do the correct analysis is with flame boilers, with major mismatches between the hot and cold flows, or when the government requires calculations. Otherwise, I make an H Vs T diagram and account for the fact that ∆T varies with H is by averaging. I doubt most people do any more than that. It’s not like ∆THX = 30°C is etched in stone somewhere, either, it’s a rule of thumb, nothing more. It’s there to make your life easier, not to be worshiped.
The glory of American screws and bolts is their low cost ubiquity, especially in our coarse thread (UNC = United National Coarse) sizes. Between 1/4 inch and 5/8″, they are sized in 1/16″ steps, and after that in 1/8″ steps. Below 3/16″, they are sized by wire gauges, and generally they have unique pitch sizes. All US screws and bolts are measured by their diameter and threads per inch. Thus, the 3/8-16 (UNC) has an outer diameter (major diameter) of 3/8″ with 16 threads per inch (tpi). 16 tpi is an ideal thread number for overall hold strength. No other bolt has 16 threads per inch so it is impossible to use the wrong bolt in a hole tapped for 3/8-16. The same is true for basically every course thread with a very few exceptions, mainly found between 3/16″ and 1/4″ where the wire gauges transition to fractional sizes. Because of this, if you stick to UTC you are unlikely to screw up, as it were. You are also less-likely to cross-thread.
I own one of these. It’s a tread pitch gauge.
US fine threads come in a variety of standards, most notably UNF = United National Fine. No version of fine thread is as strong as coarse because while there are more threads per inch, each root is considerably weaker. The advantage of fine treads is for use with very thin material, or where vibration is a serious concern. The problem is that screwups are far more likely and this diminishes the strength even further. Consider the 7/16″ – 24 (UNF). This bolt will fit into a nut or flange tapped for 1/2″- 24. The fit will be a little loose, but you might not notice. You will be able to wrench it down so everything looks solid, but only the ends of the threads are holding. This is a accident waiting to happen. To prevent such mistakes you can try to never allow a 7/6″-24 bolt into your shop, but this is uncomfortably difficult. If you ever let a 7/6″-24 bolt in, some day someone will grab it and use it, in all likelihood with a 1/2″ -24 nut or flange, since these are super-common. Under stress, the connection will fail in the worst possible moment.
Other UNF bolts and nuts present the same screwup risk. For example, between the 3/8″-24 and 5/16″-24 (UNF), or the #10-32 (UNF) and also with the 3/16″- 32, and the latter with the #8-32 (UNC). There is also a French metric with 0.9mm — this turns out to be identical to -32 pitch. The problem appears with any bolt pair where with identical pitch and the major diameter of the smaller bolt has a larger outer diameter (major diameter) than the inner diameter (minor diameter) of the larger bolt. If these are matched, the bolts will seem to hold when tightened, but they will fail in use. You well sometimes have to use these sizes because they match with some purchased flange. If you have to use them, be careful to use the largest bolt diameter that will fit into the threaded hole.
Where I have the option, my preference is to stick to UNC as much as possible, even where vibration is an issue. In vibration situations, I prefer to add a lock nut or sometimes, an anti-vibration glue, locktite, available in different release temperatures. Locktite is also helpful to prevent gas leaks. In our hydrogen purifiers, I use lock washers on the ground connection from the power cord, for example.
I try to avoid metric, by the way. They less readily available in the US, and more expensive. The other problem with metric is that there are two varieties (Standard and French — God love the French engineering) and there are so many sizes and pitches that screwups are common. Metric bolts come in every mm diameter, and often fractional mm too. There is a 2mm, a 2.3mm, a 2.5mm, and a 2.6mm, often with overlapping pitches. The pitch of metric screws and bolts is measured by their spacing, by the way, so a 1mm metric pitch means there is 1mm between threads, the the equivalent of a 24.5 pitch in the US, and a 0.9mm pitch = US-32. Thread confusion possibilities are endless. A M6x1 (6mm OD x 1mm pitch) is easily confused with a M5x1 or a M7x1, and the latter with the M7.5×1. A M8x1.25 is easily confused with a M9x1.25, and a M14x2 with an M16x2. And then there is confusion with US bolts: a 2.5mm metric pitch is nearly identical to a US 10tpi pitch. I can not rid myself of US threads, so I avoid metric where I can. As above, problems arise if you use a smaller diameter bolt in a larger diameter nut.
For those who have to use metric, I suggest you always use the largest bolt that will fit (assuming you can find it). I try to avoid bringing odd-size bolts into their shop, that is, stick to M6, M8, M10. It’s not always possible, but it’s a suggestion. I get equipment with odd-size metric bolts too. My preference is to stick to UNC and to avoid odd numbers.
Robert Buxbaum, January 23, 2024. Note: I’ve only really discussed bolt sizes between about #4 and 1″, and I didn’t consider UNRC or UNJF or other, odd options. You can figure these issues out yourself from the above, I think.
Leading up to the Cybertruck launch 4 weeks ago, the expert opinion was that it was a failure. Morgan Stanley, here dubbed it as one, as did Rolling Stone here. Without having driven the vehicle, the experts at Motor trend, here, declared it was worse than you thought, “a novelty” car. I’d like to differ. The experts point out that the design is fundamentally different from what we’ve made for years. They claim it’s ugly, undesirable, and hard to build. Ford’s F-150 trucks are the standard, the top selling vehicle in the US, and Cybertruck looks nothing like an F-150. I suspect that, because of the differences, the Cybertruck can hardly fail to be a success in both profit and market share.
Cybertruck pulls a flat-bed trailer at Starbase.
Start with profit. Profit is the main measure of company success. High profit is achieved by selling significant numbers at a significant profit margin. Any decent profit is a success. This vehicle could trail the F-150 sales forever and Musk could be the stupidest human on the planet, so long as Tesla sells at a profit, and does so legally, the company will succeed. Tesla already has some 2 million pre-orders, and so far they show no immediate sign of leaving despite the current price of about $80,000. Unless you think they are all lying or that Musk has horribly mispriced the product, he should make a very decent profit. My guess is he’s priced to make over $10,000 per vehicle, or $20B on 2 million vehicles. Meanwhile, no other eV company seems to be making a profit.
The largest competing electric pickup company is Rivian. They sold 16,000 electric trucks in Q3 2023, but the profit margin is -100%. This is to say, they lose $1 for every $1 worth of sales –and that’s unsustainable. Despite claims to the contrary, a money-losing business is a failure. The other main competitors are losing too. Ford is reported to lose about $50,00 per eV. According to Automotive News, here, last week, Ford decided to cut production of its electric F-150, the Lightning, by 50%. This makes sense, but provides Cybertruck a market fairly clear of US e-competition.
2024 BYD, Chinese pickup truck
Perhaps the most serious competitor is BYD, a Chinese company backed by the communist government, and Warren Buffet. They are entering the US market this month with a new pickup. It might be profitable, but BYD is relatively immune to profitability. The Chinese want dominance of the eV market and are willing to lose money for years until they get it. Fortunately for Tesla, the BYD truck looks like Rivian’s. Tesla’s trucks should exceed them in range, towing, and safety. BYD, it seems, is aiming for a lower price point and a different market, Rivian’s.
A video, here, shows the skin of a Cybertruck is bulletproof to 9mm, shotgun, and 45 caliber machine gun fire. Experts scoff at the significance of bulletproof skin — good for folks working among Mexican drug lords, or politicians, or Israelis. Tesla is aiming currently for a more upscale customer, someone who might buy a Hummer or an F-250. This is more usable and cheaper.
Don’t try this with other trucks.
Another way Cybertruck could fail is through criminal activity. Musk could be caught paying off politicians or cheating on taxes or if the trucks fail their safety tests. So far, Cybertruck seems to meet Federal Motor Vehicle Safety Standards by a good margin. In a video comparison, here, it appears to take front end collisions as well as an F-150, and appears better in side collisions.
This leaves production difficulty. This could prevent the cybertruck from being a big success, and the experts have all harped on this. The vehicle body is a proprietary stainless steel, 0.07″ thick. Admittedly it’s is hard to form, but Tesla seems to manage it. VIN number records indicate that Tesla had delivered 448 cybertrucks as Friday last week, many of them to showrooms, but some to customers. Drone surveys of the Gigafactory lot show that about 19 are made per day. That’s a lot more than you’d see if assembly was by hand. Assuming a typical learning curve, it’s reasonable to expect some 600 will be delivered by December 31, and that production should reach 6000 per month in mid 2024. At that rate, they’ll be making and selling at the same rate as Rivian or Ford, and making real money doing it. The stainless body might even be a plus, deterring copycat competition. Other pluses are the add-ons, like the base-camp tent option, a battery extension, a ramp, and (it’s claimed) some degree of sea worthiness. Add-ons add profit and deter direct copying (for a time).
Basecamp, tent option.
So why do I think the experts are so wrong? My sense is that these people are experts because of long experience at other companies — the competitors. They know what was tried, and that innovation failed. They know that their companies chose not to make anything like a Cybertruck, and not to provide the add-ons. They know that the big boys avoid “novelty cars” and add-ons. There is an affinity among experts for consensus and sure success, the success that comes from Chinese companies, government support and international banking. If the Cybertruck success is an insult to them and their expertise. Nonetheless, if Cybertruck succeeds, they will push their companies towards a more angular design plus add-ons. And they will claim cybertruck is no way novel, but that government support is needed to copy it.
Franklin’s walking stick, willed to General Washington. Now in the Smithsonian.
Many famous people carried walking sticks Washington, Churchill, Moses, Dali. Until quite recently, it was “a thing”. Benjamin Franklin willed one, now in the Smithsonian, to George Washington, to act as a sort of scepter: “My fine crab-tree walking stick, with a gold head curiously wrought in the form of the cap of liberty, I give to my friend, and the friend of mankind, General Washington. If it were a Scepter, he has merited it, and would become it. It was a present to me from that excellent woman, Madame de Forbach, the dowager Duchess of Deux-Ponts”. A peculiarity of this particular stick is that the stick is uncommonly tall, 46 1/2″. This is too tall for casual, walking use, and it’s too fancy to use as a hiking stick. Franklin himself, used a more-normal size walking stick, 36 3/8″ tall, currently in the collection of the NY Historical Society. Washington too seems to have favored a stick of more normal length.
Washington with walking stick
Walking sticks project a sort of elegance, as well as providing personal protection. Shown below is President Andrew Jackson defending himself against an assassin using his walking stick to beat off an assassin. He went on to give souvenir walking sticks to friends and political supporters. Sticks remained a common political gift for 100 years, at least through the election of Calvin Coolidge.
Andrew Jackson defends himself.
I started making walking sticks a few years back, originally for my own use, and then for others when I noticed that many folks who needed canes didn’t carry them. It was vanity, as best I could tell: the normal, “old age” cane is relatively short, about 32″. Walking with it makes you bend over; you look old and decrepit. Some of the folks who needed canes, carried hiking sticks, I noticed, about 48″. These are too tall to provide any significant support, as the only way to grasp one was from the side. Some of my canes are shown below. They are about 36″ tall, typically with a 2″ wooden ball as a head. They look good, you stand straight, and they provides support and balance when going down stairs.
Some of my walking sticks.
I typically make my sticks of American Beech, a wood of light weight, with good strength, and a high elastic modulus of elasticity, about 1.85 x106 psi. Oak, hickory, and ash are good options, but they are denser, and thus more suited to self-defense. Wood is better than metal for many applications, IMHO, as I’ve discussed elsewhere. The mathematician Euler showed the the effective strength of a walking stick does not depend on the compressive strength but rather on elastic constant via “the Euler buckling equation”, one of many tremendously useful equations developed by Leonhard Euler (1707-1783).
For a cylindrical stick, the maximum force supported by a stick is: F = π3Er4/4L2, where F is the force, r is the radius, L is the length, and E is the elastic modulus. I typically pick a diameter of 3/4″ or 7/8″, and fit the length to the customer. For a 36″ beech stick, the buckling strength is calculated to be 221 or 409 pounds respectively. I add a rubber bottom to make it non–scuff and less slip-prone. I sometimes add a rope thong, too. Here is a video of Fred Astaire dancing with this style of stick. It’s called “a pin stick”, in case you are interested because it looks like a giant pin.
Country Irishmen are sometimes depicted with a heavy walking stick called a Shillelagh. It’s used for heavier self-defense than available with a pin-stick, and is generally seen being used as a cudgel. There are Japanese versions of self defense using a lighter, 36″ stick, called a Han-bo, as shown here. There is also the wand, as seen for example in Harry Potter. It focuses magical power. Similar to this is Moses’s staff that he used in front of Pharaoh, a combination wand and hiking stick as it’s typically pictured. It might have been repurposed for the snake-on-a-stick that protects against dark forces. Dancing with a stick, Astaire style, can drive away emotional forces, while the more normal use is elegance, and avoiding slips.
Sailing ships are wonderfully economic and non-polluting. They have unlimited range because they use virtually no fuel, but they tend to be slow, about 5-12 knots, about half as fast as Diesel-powered ships, and they can be stranded for weeks if the wind dies. Classic sailing ships also require a lot of manpower: many skilled sailors to adjust the sails. What’s wanted is an easily manned, economical, hybrid ship: one that’s powered by Diesel when the wind is light, and by a simple sail system when the wind blows. Anton Flettner invented an easily manned sail and built two ships with it. The Barbara above used a 530 hp Diesel and got additional thrust, about an additional 500 hp worth, from three, rotating, cylindrical sails. The rotating sales produced thrust via the same, Magnus force that makes a curve ball curve. Barbara went at 9 knots without the wind, or about 12.5 knots when the wind blew. Einstein thought it one of the most brilliant ideas he’d seen.
Force diagram of Flettner rotor (Lele & Rao, 2017)
The source of the force can be understood with help of the figure at left and the graph below. When a simple cylinder sits in the wind, with no spin, α=0, the wind force is essentially drag, and is 1/2 the wind speed squared, times the cross-sectional area of the cylinder, Dxh, and the density of air. Multiply this by a drag coefficient, CD, that is about 1 for a non-spinning cylinder, and about 2 for a fast spinning cylinder. FD= CDDhρv2/2.
A spinning cylinder has lift force too. FL= CLDhρv2/2.
Numerical lift coefficients versus time, seconds for different ratios of surface speed to wind speed, a. (Mittal & Kumar 2003), Journal of Fluid Mechanics.
As graphed in the figure at right, CL is effectively zero with sustained vibrations at zero spin, α=0. Vibrations are useless for propulsion, and can be damaging to the sail, though they are helpful in baseball pitching, producing the erratic flight of knuckle balls. If you spin a cylindrical mast at more than α=2.1 the vibrations disappear, and you get significant lift, CL= 6. At this rotation speed the fast surface moves with the wind at 2.1 times the wind speed. That is it moves significantly faster than the wind. The other side of the rotor moves opposite the wind, 1.1 times as fast as the wind. The coefficient of lift lift, CL= 6, is more than twice that found with a typical, triangular, non-rotating sail. Rotation increases the drag too, but not as much. The lift is about 4 times the drag, far better than in a typical sail. Another plus is that the ship can be propelled forward or backward -just reverse the spin direction. This is very good for close-in sailing.
The sail lift, and lift to drag ratio, increases with rotation speed reaching very values of 10 to 18 at α values of 3 to 4. Flettner considered α=3.5. optimal. At this α you get far more thrust than with a normal sail, and you can go faster than the wind, and far closer to the wind than with any normal sail. You don’t want α values above 4.2 because you start seeing vibrations again. Also more rotation power is needed (rotation power goes as ω2); unless the wind is strong, you might as well use a normal propeller.
The driving force is always at right angles to the perceived wind, called the “fair wind”, and the fair wind moves towards the front as the ship speed increases. Controlling the rotation speed is somewhat difficult but important. Flettner sails were no longer used by the 1930s because fuel became cheaper and control was difficult. Normal sails weren’t being used either for the same reasons.
In the early 1980s, there was a return to the romantic. Famous underwater explorer, Jacques Cousteau, revived a version of the Flettner sail for his exploratory ship, the Alcyone. He used aluminum sails, and an electric motor for rotation. He claimed that the ship drew more than half of its power from the wind, and claimed that, because of computer control, it could sail with no crew. This claim was likely bragging, but he bragged a lot. Even with today’s computer systems, people are needed to steer and manage things in case something goes wrong. The energy savings were impressive, though, enough so that some have begun to put Flettner sails on cargo ships, as a right. This is an ideal use since cargo ships go about as fast as a typical wind, 10- 20 knots. It’s reported that, Flettner- powered cargo ships get about 20% of their propulsion from wind power, not an insignificant amount.
And this gets us to the reason your curve ball does not curve: it’s likely you’re not spinning it fast enough. To get a good curve, you want the ball to spin at α =3, or about 1.5 times the rate you’d get by rolling the ball off your fingers. You have to snap your wrist hard to get it to spin this fast. As another approach, you can aim for α=0, a knuckle ball, achieved with zero rotation. At α=0, the ball will oscillate. It’s hard to do, but your pitch will be nearly impossible to hit or catch. Good luck.
Robert Buxbaum, March 22, 2023. There are also Flettner airplane designs where horizontal, cylindrical “wings” rotate to provide high lift with short wings and a relatively low power draw. So-far, these planes are less efficient and slower than a normal helicopter. The idea could bear more development work, IMHO. Einstein had an eye for good ideas.
The Dead Sea in Israel is a popular tourist attraction and health resort-area. It is also the lowest point on the planet, with a surface about 430m below sea level. Its water is saturated with an alkaline salt, and quite devoid of life, and it’s shrinking fast, loosing about 1 m in height every year. The Jordan river water that feeds the sea is increasingly drawn off for agriculture, and is now about 10% of what it was in the 1800s. The Dead Sea is disappearing fast, a story that is repeated with other inland seas: the Aral Sea, the Great Salt Lake, etc. In theory, one could reverse the loss using sea water. In theory, you could generate power dong this too: 430m is seven times the drop-height of Niagara Falls. The problem is the route and the price.
Five (or six) semi-attractive routes have been mapped out to bring water to the Dead Sea, as shown on the map at right. The shortest, and least expensive is route “A”. Here, water from the Mediterranean enters a 12 km channel near Haifa; it is pumped up 50m and travels in a pipe for about 52 km over the Galilean foothills, exiting to a power station as shown on the elevation map below. In the original plan the sea water feeds into the Jordan river, a drop of about 300m. The project had been estimated to cost $3 B. Unfortunately, it would make much of the Jordan river salty. It was thus deemed unacceptable. A variation of this would run the seawater along the Jordan in a pipe or an open channel. This would add to the cost, and would likely diminish the power that could be extracted, but you would not contaminate the Jordan.
A more expensive route, “B”, is shorter but it requires extensive tunneling under Jerusalem. Assuming 20 mies of tunnel at $500 MM/mile, this would cost $10B. It also requires the sea water to flow through the Palestinian West Bank on its way to the sea. This is politically sensitive and is unlikely to be acceptable to the West Bank Palestinians.
Vertical demand of the northern route
Two other routes, labeled “C” and “D” are likely even more expensive than route B. They require the water to be pumped over the Judaean hills near Bethlehem, south of Jerusalem. That’s perhaps 600m up. The seawater would flow from Ashkalon or Gaza and would enter the Dead Sea at Sodom, near Masada. Version C is the most politically acceptable, since it’s short and does not go through Palestinian land. Also, water enters the dead sea at its saltiest point so there is no disruption of the environment. Route D is similar to C, somewhat cheaper, but a lot more political. It goes through Gaza.
The longest route, “E” would go through Jordan taking water from the Red Sea. Its price tag is said to be $10 B. It’s a relatively flat route, but still arduous, rising 210m. As a result it’s not clear that any power would be generated. A version of this route could send the water entirely through Israel. It’s not clear that this would be better than Route C. Looking things over, it was decided that only routes that made sense are those that avoided Palestinian land. An agreement was struck with Jordan to go ahead with route D, with construction to begin in 2021. The project has been on hold though because of cost, COVID, and governmental inertia.
In order to make a $5-10B project worthwhile, you’ll have to generate $500MM to $1B/year. Some of this will come from tourism, but the rest must come from electrical power generation. As an estimate of power generation, let’s assume that that the flow is 65 m3/s, just enough to balance the evaporation rate. Assuming a 400 m power drop and an 80% efficient turbine, we should generate 80% of 255 MWe = about 204 MWe on average. Assuming a value of electricity of 10¢/kWh, that translates to $20,000/ hour, or $179 million per year. This is something, but not enough to justify the cost. We might increase the value of the power by including an inland pond for water storage. This would allow power production to be regulated to times of peak load, or it could be used for recreation, fish-farming, or cooling a thermal power station up to 1000 MWe. These options almost make sense, but with the tunnel prices quoted, the project is still too expensive to make sense. It is “on hold” for now.
It’s not like the sea will disappear if nothing is done. With 10% of the original in-flow of water to the Dead Sea, it will shrink to 10% its original size, and then stop shrinking. At that point evaporation will match in-flow. One could add more fresh water by increasing the flow from the sea of Galilee, but that water is needed. When more water is available, more is taken out for farming. This is what’s happened to the Arial Sea — it’s now about 10% the original size, and quite salty.
Elon Musk besides the prototype 12 foot diameter tunnel.
There’s a now a new tunnel option though and perhaps these routes deserve a second look: Elon Musk claims his “Boring company” can bore long tunnels of 12 foot diameter, for $10-20 MM/mile. This should be an OK size for this project. Assuming he’s right about the price, or close to right, the Dead Sea could be raised for $1B or so. At that price-point, it makes financial sense. It would even make sense if one built multiple seapools, perhaps one for swimming and one for energy storage, to be located before the energy-generating drop, and another for fish after. There might even be a pool that would serve as coolant for a thermal power plant. Water in the desert is welcome, even if it’s salt water.
Sharrow Marine introduced a new ship propeller design two years ago, at the Miami International Boat show. Unlike traditional propellers, there are no ends on the blades. Instead, each blade is a connecting ribbon with the outer edge behaving like a connecting winglet. The blade pairs provide low-speed lift-efficiency gains, as seen on a biplane, while the winglets provide high speed gains. The efficiency gain is 9-30% over a wide range of speeds, as shown below, a tremendous improvement. I suspect that this design will become standard over the next 10-20 years, as winglets have become standard on airplanes today.
A Sharrow propeller, MX-1
The high speed efficiency advantage of the closed ends of the blades, and of the curved up winglets on modern airplanes is based on avoiding losses from air (or water) going around the end from the high pressure bottom to the low-pressure top. Between the biplane advantage and the wingtip advantage, Sharrow propellers provide improved miles per gallon at every speed except the highest, 32+ mph, plus a drastic decrease in vibration and noise, see photo.
The propeller design was developed with paid research at the University of Michigan. It was clearly innovative and granted design patent protection in most of the developed world. To the extent that the patents are respected and protected by law, Sharrow should be able to recoup the cost of their research and development. They should make a profit too. As an inventor myself, I believe they deserve to recoup their costs and make a profit. Not all inventions lead to a great product. Besides, I don’t think they charge too much. The current price is $2000-$5000 per propeller for standard sizes, a price that seems reasonable, based on the price of a boat and the advantage of more speed, more range, plus less fuel use and less vibration. This year Sharrow formed an agreement with Yamaha to manufacture the propellers under license, so supply should not be an issue.
Vastly less turbulence follows the Sharrow propeller.
China tends to copy our best products, and often steals the technology to make them, employing engineers and academics as spys. Obama/Biden have typically allowed China to benefit for the sales of copies and the theft of intellectual property, allowing the import of fakes to the US with little or no interference. Would you like a fake Rolex or Fendi, you can buy on-line from China. Would you like fake Disney, ditto. So far, I have not seen Chinese copies of the Sharrow in the US, but I expect to see them soon. Perhaps Biden’s Justice Department will do something this time, but I doubt it. By our justice department turning a blind eye to copies, they rob our innovators, and rob American workers. His protectionism is one thing I liked about Donald Trump.
The Sharrow Propeller gives improved mpg values at every speed except the very highest.
When I began college in 1972, the majority of engineering students and business students were male. They from the top of their high school classes, and from stable homes mostly; they went on to high paying jobs. Boys also dominated at the bottom of society. They were the majority of the criminals, drug addicts, and high-school dropouts. Many went off to Vietnam. Some, those who were handy, went to trade schools and a reasonable life, productive life. Society did not seem bothered by the destruction of boys in prison, or Vietnam, or by drugs, but there was an outcry that so few women achieved high academic levels. A famous presentation of the problem was called “for every 100 girls.” An updated version appears below showing the status as of October, 2021. A more detailed version appears further down.
From the table above, you can see that women are now the majority of those in college, the majority of those with a bachelors degree or higher, and a majority of those with advanced degrees. Colleges added special tutoring, special grants, and special programs. Each college had a Society of Women Engineers office, and similar programs in law and math. All of these explicitly excluded men or highly discouraged their presence. The curriculum was changed too; made more female-friendly. Dirty, and physical experiments were removed, replaced with group analysis of the social interactions — important aspects of engineers that boys were far-less adept at doing well. Perhaps society and engineering is better off now, but boys (men) are far worse off. This is particularly seem by the following chart, looking at the bottom. Boys/men provide the vast majority of the prison population, of those diagnosed as learning disabled, of those expelled, or overdosed, and among the war dead.
I’ve previously noted that a majority of boys in school are considered disruptive, and that these boys are routinely diagnosed as ADHD and drugged. It is not at all clear that this is a good thing, or that the drugs help anyone but the teacher. I’ve also noted that artwork and attitudes that were considered normal for boys are now considered disturbing and criminal like saying I wish the school was blown up. The cure here, perhaps is worse than the disease. I’m not saying that we should encourage boys to say such things, but that we should acknowledge a difference between an active and a passive wish. And we should find a way to educate boys/men so they don’t end up unemployed, addicted, or dead. Currently boy, particularly those at the bottom are on the scrap-heap of society.
Here is some source material for the above:
For every 100 women enrolled in US colleges (degree-granting postsecondary institutions) at all levels there are 75 men enrolled. Source: National Center for Education Statistics
For every 100 women enrolled in US graduate schools there are 68 men. Source: Council for Graduate Schools (2020)
For every 100 women who earn bachelor’s degrees from US colleges and universities, there are 73 men. Source: National Center for Education Statistics (2021-2022)
For every 100 females in local jails in the US, there are 614 males. Source: Department of Justice via Wikipedia
For every 100 females in state and federal prisons, there are 1,225 males. Source: Department of Justice
For every 100 females in federal prison, there are 1,331 male prisoners. Source: Federal Bureau of Prisons
For every 100 female military personnel who have been wounded in action during Operation Enduring Freedom, 5,098 men have. Source: Congressional Research Service
For every 100 female military personnel who have been wounded in action during Operation Iraqi Freedom, 4,982 menhave. Source: Congressional Research Service
