Is Horse Power an Outdated unit of Power !!?!!

Is Horse Power an Outdated unit of Power !!?!!

  15:03    Jimboyrulez

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I've never understood why we use the term Horsepower. We don't calculate a bulb's life in Candle Hours or an air plane's thrust in Eagle Power, so why do we calculate an engine's output in Horsepower? In order to understand how outdated and idiotic Horsepower as a unit is, we need to understand two things: first, the history of how horsepower as a unit came to be, and second, the definition and formula to calculate Horsepower. I learned the definition of Horsepower and the formula to calculate work and Horsepower while I was studying engineering at the University of Hertfordshire. In this article, we will analyze the work of James Watt, the inventor of Horsepower, and we will determine whether or not Horsepower is a good means of measuring how much power an automobile has. 

To understand this, we need to look into the history of the unit. Until the 18th Century, before machines became popular, the majority of laborious work was done by horses. With the invention of the steam engine, horses slowly started being replaced with machines. But, the steam engines at the time were not that efficient. In 1763, Scottish engineer, James Watt, took this as an opportunity to make a more efficient steam engine. During this era, some people were beginning to warm up to steam engines, whereas the vast majority still believed in horses. Watt started selling his more efficient steam engine to farmers and miners, but he needed a marketing strategy that proved that his steam engine was more efficient and powerful than other steam engines, as well as horses. To market his invention, Watt needed a unit that helped him do a measurement comparison that potential buyers could relate to the power of horses. But, instead of figuring out exactly how much power a horse really produced, he estimated. If he could successfully make this comparison, he could prove his invention was not only more efficient, but more powerful than the current means of producing energy. It didn't matter if his estimation was based on a pony, a weak horse, a race horse, or a super strong work horse. As long as his measurement was close enough to be believable, his strategy would be successful.
 

Now, before we go more in depth, it's important to understand horsepower and how it is calculated.

So then, what is Horsepower?

Horsepower is a unit of power. 

Well, then what is power? 

Power = work / time

So, then, what is work ?

Work = force x distance

So, 

Power = (force x distance) / time

Coming back to the question, "What is Horsepower?" 

As we learned in the above history lesson, Horsepower is a unit of power that was invented by James Watt. He invented Horsepower to market his steam engine. 

His sales pitch would be, "This steam engine replaces 2 horses." 

The American Journal of Physics 4, 120 (1936) claims to have derived the below photograph from the original James Watt notes. The photo has been digitally reconstructed for the sake of clarity.

It shows a horse mill with a 12ft radius and a horse churning it. The horse applies force to the mill, turns it around, and keeps going round and round. His notes talk about force and all his formulas. It claims that the horse applies 180 foot-pounds of force to turn the mill. But, here is an interesting fact: the journal doesn't explain how he derived the 180 foot-pounds number.

So, let's put his numbers in the formulas.

Power= (180 x 2π x 12 x 2.5)/minute

Power= 33,929 ft pound force/minute

However, in reality, this is the correct calculation: 2.5(2π x 12ft) = 188.5ft

In Watt's World: 2.5(2π x 12ft)= 180ft (60yds)

When we use his napkin math: Power = 32,400 ft lb force/minute.

In an absurd twist, he and his business partner, Matthew Boulton, standardized the figure at 33,000 ft lb force/minute. 

That is how we get our calculation of Horsepower today of one Horsepower equaling 33,000 ft lb force/minute, or 550 ft lb force/second. 

You might be asking yourself, what does this all actually mean? Well, it means that if there was a horse that was pulling a 550lb object with a pulley attached, it would pull that object 1ft per second. 

In the automobile industry, if there is a car with 200 Horsepower, it would pull the same load of 550lbs 200ft/second (or 110,000lbs 1ft/second). That being said, there are other things that need to be taken into consideration in terms of calculating a vehicle's top speed like aerodynamics, inertia by accelerating, rolling resistance, internal friction, etc. We won't be fully diving into all that in this article.

To further illustrate how ludicrous the concept of Horsepower is, we need to cover Metric Horsepower.

 

So in Society of Automotive Engineers (SAE) units, we are looking at ft lbs force/second.

In metric, it would be m kg force/second or kg force x meters/second.

1 Horsepower = 550 ft lb force/second. 

Or, 1 Metric Horsepower (1PS) = 75 kg force m/second 

 To explain why European, or metric, Horsepower numbers are different to American Horsepower, numbers we have to do some crazy math. 

Don't be scared, just take a deep breath. All we are doing is multiplying it with gravity. 

1HP = 550 x (lbs)(32.17ft/s²) = 17,694 lb ft²/s³ 

If we convert this to metric, we would get 745.6 kg m²/s³

Lets do the same calculation with metric numbers.

1PS= 75 x (1kg)(9.807m/s²)  

Then it's 735.5 kg m²/s³

As we can see, both the numbers are not the same despite it being the same thing. In fact, 1 Metric Horsepower = 98.6% of American Horsepower. That is why you will see the difference in Horsepower rating figures in America and Europe. 

For example, the Ferrari 812 Superfast is 800CV (Metric Horsepower) or 789HP (American Horsepower)

The McLaren 600LT is 600PS (Metric Horsepower) or 592HP (American Horsepower)

So, we learned that Horsepower, as a unit of power, was invented to market the steam engine. Math used in deriving Horsepower was inaccurate and approximate. The unit, if derived with metric values, is inconsistent. The idea of Horsepower is archaic. In today's world, we rarely get to see horses, so no one knows what the power of a horse is in order to compare it to the modern combustion engine. Moreover, in this day and age, where we plan to have commercialized space travel, do we want to rely on a unit with so many inaccuracies?

It's an error in basic math due to rounding up numbers. But, despite the Watt being a more accurate unit of power, the world is just comfortable with using the more barbaric unit of power- Horsepower. So, we will keep using Horsepower as a unit of power until we have combustion engines. If you want to use a more accurate, modern, and precise unit of power, use the Watt. It's not a huge change, neither is it difficult as we have been using Watt to measure power of bulbs and speakers since its inception. 

Do let me know if you enjoy these controversial technical articles and if you would like me to keep doing them. If there is a mistake in this article or if you disagree with this article please feel free to comment below. 

If you would like more detail here is the link to Horsepower's Wikipedia page.  https://en.wikipedia.org/wiki/Horsepower

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Carbon Fiber VS Fiber Glass VS Kevlar

Carbon Fiber VS Fiber Glass VS Kevlar

  14:25    Jimboyrulez

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 Carbon Fiber vs. Fiber Glass vs. Kevlar

In this article we are going to compare Carbon Fiber, Fiber Glass, and Kevlar. We are going to discuss key differences, and see which one is right for your particular application. I have some background in Motorsports Engineering, so I am going to explain this from the motorsports perspective.  However, the same fundamentals would apply to any application- be it motorcycles, airplanes, or boats. 

In talking to a lot of people about this, I have come to understand and realize that there are a lot of misconceptions and myths about these three materials, and most of the time people have it wrong. For example, people often argue that Carbon Fiber is stronger then Fiber Glass. That is a misconception. People often mistake strength for stiffness. I'll explain this a little bit more in detail. 

The definition of strength is the capacity of an object or substance to withstand great force or pressure. Whereas stiffness is an indicator of the tendency for an element to return to its original form after being subjected to a force. Strength measures how much stress can be applied to an element before it deforms permanently or fractures. Hardness measures a material's resistance to surface deformation. This is actually the key to understanding the differences between the three different materials in question. 

I am going to explain, once again, in a simpler way. If you take an object and apply pressure, pulling two ends of it in opposite directions, the point at which it breaks indicates its tensile strength. If you apply force that is larger than the strength of the material, the material would break. This is known as the ultimate tensile strength. Strength has nothing to do with how far the material can flex or deform. It is only defined by when it breaks. I hope this clears up any confusion around the concept of strength. 

Stiffness is calculated by how far something stretches. The stiffness of a material is the ability of a material to resist deflection or deformation. It is important to understand that stiffness and strength are not related. You can has a very stiff material that is not very strong, or you can have a very strong material that is not very stiff. This brings us to elongation. The definition of elongation is the amount of extension an object has while under stress. This is usually expressed as a percentage of the original length. Elongation is basically how far the material will stretch before it breaks. So, if you have more elongation, you can essentially get a tougher material because it would stretch more before it breaks. 

Imagine a plastic that is not very strong but stretches a long way. You hit it with a hammer, and the hammer would just bounce back or deform it. It's not going to snap it or shatter it. Now, imagine you do the same thing to the same size piece of glass. This may not be lot stronger than plastic, but it's a lot stiffer, so it doesn't deform as much. So, when you hit it with a hammer it will shatter in to thousand pieces. 

Lastly, density is basically just how much a material weighs per unit area. Since we have established the basic definitions of what constitutes our material properties that we're interested, we can now actually start to have a look at the differences between the materials we are comparing.

Composite materials always have fibers sitting within a resin matrix. This basically means that we have a whole bunch of straight aligned fibers being held together by some sort of epoxy resin. We are not going to go much in depth on the epoxy resin for this article. 

Let's take a look at the tensile strengths of different materials. First, let's bust some myths here by noticing that fiber glass is stronger then Carbon fiber. Ultimate tensile strength is defined by force over area, and glass is stronger than carbon fiber and Kevlar both. S-Glass is stronger than E-Glass, but it's a much more expensive grade of Fiber Glass.

In reference to the above graph, Carbon Fiber is stronger than High Strength Steel, but Kevlar and Fiber Glass are both stronger than Carbon Fiber. 

So, the question is: why do so many people have the misconception that Carbon Fiber is stronger? Carbon Fiber is incredibly stiff and it is low density. The main problem is that people tend to confuse themselves between stiffness and strength. 

If you check out this stiffness graph here, you will notice that Carbon Fiber is incredibly stiff, but don't confuse that with strength. 

The second reason for this confusion is density. As you can see from this graph, Fiber Glass has more density than Carbon Fiber and Kevlar. Kevlar is the least dense because it's like a regular polymer.

Now, let's look at this as horsepower and weight. A lot of horsepower and a lot of weight on a car doesn't help go fast. To go fast you need a healthy power to weight ratio. Similarly, what you need to understand is the strength/weight ratio and stiffness/weight ratio. 

Let's look at relative strength to weight ratio in comparison to the stiffness to weight ratio.

As we can see over here in terms of relative strength to weight, Kevlar is strongest in tension. It's an awesome material- it's very strong but it does have its drawbacks. 

S-Glass is also stronger in strength to weight when compared to Carbon Fiber. S-Glass is a high quality material- it's very expensive, but it's not weaker than Carbon Fiber. 

Generally, when people deal with E-Glass, people think that Carbon Fiber is stronger than Fiber Glass because they have E-Glass in mind. However, it's important to realize that the difference in terms of percentage is not all that different when looking at carbon fiber, E-Glass, and S-Glass. They are all pretty similar. 

What I am trying to say here is that if your use or if your structure is only strength critical, then Fiber Glass might be the way to go as it's comparatively a lot cheaper. And, even if you go with E-Glass, it is not comparatively that much weaker. 

That being said, the minute you put stiffness in the picture, it's a whole different story. If you see the same graph and look at the stiffness to weight ratio, there is a huge difference. Compared to S-Glass & E-Glass, Carbon Fiber is a lot stiffer. Compared to E-Glass, Carbon Fiber is five times stiffer. In fact, Carbon Fiber is stiffer than everything else by a lot more. Yes, even Kevlar!

If we were to reverse the direction of our loading and put the material in compression, all the other materials do quiet well except Kevlar. 

When you look at this graph what you'll notice is that Kevlar looses by a considerable amount when you put it under compression. 

So, if you are considering a material for a composite structure that might bare aerodynamic load, like a rear wing for a lot of downforce, then considering S-Glass or Carbon Fiber might be the best way to go. You might be able to get away with E-Glass depending on your particular structure and use, but you definitely should not risk it with Kevlar. 

Let's take elongation into consideration. What catches your eye is that carbon has almost no elongation what-so-ever. This creates a problem with material toughness.

If you look at a stress/strain line graph you would understand it better. The stress/strain curve line means how much a material would move for a given amount of stress. 

If you look at S-Glass, it has a really high tensile strength, and it has a really high elongation as well. This makes it the toughest material. 

So, if you need a material with the best load bearing strength, S-Glass might be the way to go. 

Kevlar is not bad either, coming in at second best place in the graph. It has really good abrasive qualities, and that is why it's used in bullet proof vests. It is a very good quality material for under body or skid plates of race cars.

So, the question is, what material body kit should you order for non competitive race or street cars. I would recommend Fiber Glass because it's the strongest, it has flex, and it's a seventh of the cost of Carbon Fiber. Additionally, it's not that much heavier.

Now, if you compare the weight of Carbon Fiber vs. Fiber Glass without Epoxy resin, Carbon Fiber is 30% lighter. But, once you make it into the structure, there is hardly a noticeable difference. This is because Fiber Glass needs a much thinner layer of Epoxy resin. In reality, it's only a 15% weight savings when compared to Fiber Glass. 

The question you need to ask yourself while comparing Carbon Fiber and Fiber Glass is if a 15% weight difference is worth seven times the cost for your application. For most applications, it isn't worth it, and that money can be well spent elsewhere. 

The reason why I am not addressing Kevlar here is because, for most applications, you would not need Kevlar considering Carbon Fiber and Fiber Glass would be the two best options for the most part. Fiber Glass is best used in areas where you need flex and strength. For structural parts, the underbody of the car, or tubing that requires strength, you don't want to have any flex. Carbon Fiber would be best for these areas. 

I hope this article was useful. Leave a comment below, and let me know what you agree/disagree with, or if you would like me to write more informative stuff like this one. 

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