Archie's Archery Depot

More Info On Blade Mechanical:

Wiper Blade Technology

Wiper blades are a small yet important part of a car. It usually goes unnoticed and is sometimes even neglected. But windshield wipers are very important part of not just a car, but any vehicle as they are installed on every motor vehicle from cars to trains to aircrafts and water crafts. Usually they are also a required by law, why you ask? Because windshield wipers or flat wiper blades help make driving safer as they remove water and dirt from the windshield that may block the driver?s view.

Flat wiper blades consist of a swinging arm pivoting from one end. The side of the blade that touches the glass has a long rubber attached to it so when the arm swings back and forth water and dirt is pushed away making sure that the view of the driver is clear and unhampered. The main purpose of this mechanism is for safety; so that the windshield would always be free from anything that can block the driver?s view.

Also, windshield wipers are usually coupled with a washer or a sprayer. When activated, the sprayer would squirt water into the windshield and then the blades would swing. The purpose of this is so that the driver can clean the windshield anytime, anywhere.

Mary Anderson is given credit for inventing the windshield wiper swinging arm because she was able to patent it in the United States in 1903. However, it was J.H. Apjohn who was able to come up with the method of having two brushes going up and down on a piece of glass of the same year. Whichever the case may be the windshield wiper became standard on all American cars 13 years after Mary Anderson patented it. And in 1919, William Folberth was able to invent the first ever automatic windshield wiper and the patent was granted by 1922. Then, the feature of having an adjustable delay between wipes was introduced in 1969 by Robert Kearns. Then, the first rain sensitive wiper was introduced by Citroen in 1970 and was used on their SM model. The wipers would swing once and check to see if the glass was wet or dry. If it was dry, the motor would draw a higher current and delay was created. If the glass was wet, the motor would draw a lower current and would swing faster with less delay. Ever since the year 2006, rain sensing and rain sensitive windshield wipers are common among Cadillacs and are available by request from other motor dealers like Honda, Toyota, Chrysler, Jeep, Mercedes and others.

Flat blade wipers have come a long way since 1903. Not only are they automatic nowadays, but they have a variety of uses as well. Some cars are fitted with smaller wipers at their headlights to ensure adequate and unaltered lighting from them. Other models like mini vans, sports utility vehicles or SUVs and station wagons have windshield wipers at the back window so that they can make sure that their rear view is also free from any mud and dirt.

About the Author

Sam is the owner of Modified Car Parts. You can find more information on Flat Wiper Blades on Turborevs website.

Mechanical engineers out there...Why do wind turbines have 3 blades?

Most wind turbines I see have 3 blades, so I assume that's the most efficient design, but why? Common sense tells me that more blades should be better, and that a lot of wind is being wasted going through all that open space.

Thinking about "wasted" wind energy is the wrong idea. In a typical wind farm probably 99.999% of the total wind energy the blows over the farm is wasted, because it doesn't even go near the turbines, if goes between them or over them. But that doesn't matter, because the wind costs nothing. What matters is that you extract the amount of power you want for the minimum cost of turbine.

More blades are not necessarily better. If you went to the extreme of say hundreds of blades, there would be so little space between them that the wind would just be blocked by the turbine and blow round it (doing no work) rather than through it.

Also, the largest forces in each blade, caused by the wind bending the blade and the centripetal forces in the rotating turbine, are at the blade roots. If you have many blades, either the roots have to be small because there isn't any room for big ones (so they can't take the high stress levels without breaking), or you have to make the hub of the turbine a bigger radius to make room for the blade roots. The bigger hub blocks off more wind, and adds to the total weight and cost.

There is an optimum linear speed for the blades to travel to get the maximum energy from the wind. So there is a tradeoff between long blade rotating slowly or short blades rotating quickly. The centripetal stresses increase proportional to the square of the turbine RPM so for a given power of turbine it is usually better to make a big diameter turbine that rotates slowly.

The number of blades is chosen to produce the cheapest design (which usually means the lightest weight) taking into account all the constraints on the design. It turns out that for large turbimes, the best option is for a small number of large blades. In fact 2 blades would often be better than 3, but 2-bladed turbines have an intrinsic problem with stability that limits the maximum speed they can run safely, and this can mean that they have to be shut down in strong winds when the wind power would be greatest. (I don't know any easy way to explain the reason for the stability problem without going into the maths of how gyroscopes work etc, but simplest way to fix the problem is to have 3 or more blades).

Some very small turbines do have more than 3 blades. 6 or 8 blades seem to be popular numbers in the UK for small turbines that power road signs in remote locations, etc.

It turns out that there is a fairly narrow range for the "best" number of blades for many types of rotating machinery. For example the number of fan blades on large jet engines is usually very close to 25. It isn't a coincidence that the different engine companies use similar numbers of blades on all the diffferent engines they design. They all have to work with the same laws of physics.

Leucaena-grass balance a management priority
TO avoid the frequent problem of denuded grass pasture between flourishing rows of leucaena, cattle producers need to widen the row spacing to balance out the leucaena to grass utilisation.

Thanks for visiting!