Fairing and aerodynamics on recumbents

opik_bidin
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Fairing and aerodynamics on recumbents

Postby opik_bidin » Thu Nov 15, 2018 4:27 pm

old article but still good, especially on aerodynamics

https://lonniemorse.wordpress.com/2013/ ... un-faired/

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The human body and the up-right bicycle are both aerodynamic disasters.

Yes – for this up-right rider – this is improvement – but there are better ways. I have come to realized there are two camps regarding the recumbent bicycle. Even major racing events now separate faired and un-faired bikes because faired bikes are aerodynamically more efficient.

Here is an example of the two categories.

Both of these bikes are of the same manufacture. The un-faired bike relies on high output wattage for speed while the faired bike can hold the same speed on less wattage.

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So why isn’t there more recumbent riders using fairings ? ?

Mostly because of the left over mind-set from the up-right bike whence we all grew up with. It also has to do with “the flock” the rider chooses to ride and race with.

Even though the faired bikes give more performance with less energy – your performance window could be a mis-match with the groupie your riding with.

Easy Racers recumbent bikes basically started the fairing movement years ago. The addition of a front fairing on a long wheel base “LWB” bike with low bottom bracket “BB”became a natural for noticeable improvement. It is now rare not to see a Tour Easy, Gold Rush, ti-Rush without a fairing or body sock.

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Here in the Great NW – the Oregon Human Powered Vehicles “OHPV” have had faired recreational riders for years. We fair our bikes not to go faster – but to ride a preferred speed easier.

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To better understand aerodynamics “in layman’s terms” lets take a look at a few pictures that perhaps will make it easier to understand the fundamentals of aerodynamics. One doesn’t have to be an expert in aero physics to understand that nature has already sorted it out for us.

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Notice that both – marine and air animals have one thing in common – Their body mass has a “the tear drop shape”

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From all dimensions – the tear drop shape is natures aero dynamic shape for high performance animals/mammals.

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This OWL is one of my favorite pictures of all time.

Now – lets take a look at some easy to understand illustrations.

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Notice when messing with natures shape the aerodynamic coefficient diminishes – or does it ? ? ?

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Even Moche knew how beneficial streamlining was back in the 1933

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Up-right bike aero dynamics most riders don’t know about. Think about wattage as horsepower. 746 watts = 1 horse power.

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Here is another chart that helps with understanding how much power = km/h for un-faired recumbents at race speeds. The speedo should help with conversion.

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One can only imagine what speeds could be obtained if fairings were used with these wattage outputs. Of course the amount of improvement would be in accordance to the application.

Notice the different Bottom Bracket “BB” heights in the pictures below. The lower the BB – the more need there is for a fairing.

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The higher the BB – riders tend to not use fairings because of the near horizontal body position.

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Here are some examples of fairings that have varied from mother natures tear drop shape. What is learned ? ? any fairing close to the aero shape of nature is better than nothing at all.

A closer look at the “aspect ratio”. Notice the first third of the shape is the nose cone.

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Below we can see a 3.5 – 1 aspect ratio. Meaning the widest part of the tear drop is approx. 1/3 the length of the shape. This is where the front wheels are on Velomobiles.

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The infamous Milan Velomobile that holds the “distance” world record 757.451 miles – 24 hours. Average speed 34 mph. I would say that is one refined tear drop.

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Ironically – the tear drop shape disappears when looking at from different angles. It is still there – but hard to see.

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The Quest is another record holding Velomobile. No doubt natures tear drop is working very well with a 3-1 aspect ratio.

For those of you that are thinking – what happens with the toe/knee box bumps on the Milan and WAW – if the body shape is reduced – the humps and bumps are minor influences. However, there is significant known drag when the wheels are exposed to the laminar flow.

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The WAW is almost 4-1 aspect ratio where as the blue Birk is example of a 3 – 1 aspect ratio tear drop. Notice the wheel fairings, which are 4-1.

Single Track Streamliner

Canadian rider Sam Whittingham rides the Varna Diablo III to a world record speed of 82.3 mph (132.5 km/h …

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Current World Record: September 18, 2009, 82.819 MPH

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Both of these World record holder share a similar feature – they both are of a narrower 5-1 aspect ratio.

See the 5-1 tear drop? This is the mpg world record holder of the World. Running on hydrogen, the PAC-Car II achieved a fuel economy of 12,665 miles per gallon gasoline equivalent (MPGe)!

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As bicycle riders – we all know that we are in cross winds most of the time. The lateral roundness of the tear drop shape it preferred to the flat sided designs. Refinement studies of cross winds are now being done with success.

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Trisleds “Completely Overzealous” World record holder for multi track Sept. 14, 2012 – Trisled’s trike powered by Gareth Hanks has set a record for three wheels of 71.79 mph.

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Another example of tear drop refinement.

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Note: – “with a bit of sarcasm” riding an up-right bicycle has the aero efficiency of a Humvee when exceeding the speed of 20 mph. It is the riders fitness that provides the horse power/wattage that make either of them go fast.

As I observe nature’s tear drop with relevance to a daily bike ride – I hopefully have illustrated the importance of aerodynamics. Human power is a fragile low power energy source when compared to our “feel the pain” of work vs performance. Aerodynamics is the most important element for human power over anything else. A simple fairing will give back more performance per dollar spent than a $2600. set of carbon disc wheels. The tear drop shape is only the beginning of establishing a successful model of aero efficiency. The ongoing refinement by World Record setting builders that go to Battle Mountain annually are at the cutting edge of human power.

This article hopefully titillates the rider to refine their existing recumbent bike as a faired bike “to feel it’s performance enhancement”. I encourage you to think more of the fairing 1st as a more efficient component to purchase in lieu of the “more expensive – less efficient components” that bike riders usually buy. How to set up a fairing properly with the many varied platforms of recumbents will come in a future blog.

Calvin27
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Re: Fairing and aerodynamics on recumbents

Postby Calvin27 » Thu Nov 15, 2018 4:55 pm

I remember seeing a product that was like a clip on fairing for road bikes. There was some analysis and it seemed that this $5 simple piece of plastic was basically cheat mode for cyclsts. I want to get one now - you've inspired me!
Fast light bike
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Workhorse bike
No brakes bike
Ebike :)

opik_bidin
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Re: Fairing and aerodynamics on recumbents

Postby opik_bidin » Thu Nov 15, 2018 4:58 pm

this is an old but I think very complete analysis on aerodynamics: shame it is just pictures and the text can't be copied, ill write it when i have time:

http://www.zzipper.com/documents/HPV_Paper.pdf

opik_bidin
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Re: Fairing and aerodynamics on recumbents

Postby opik_bidin » Sat Nov 17, 2018 10:48 am

The aerodynamics of human powered land vehicles

A bicycle and its rider are strongly impeded by their resistance to the flow of air. Aerodynamic stratagems have brought vehicles that can go 60 mph on a level road without assistance

by Albert C. Gross, Chester R. Kyle and Douglas J Malewicki

For decades the principles of aerodynamics have been applied with great success to improving the speed and efficiency of aircraft, automobiles motorcycles and even competitive skiers and skaters. Vehicles powered by human energy, however, were virtually ignored in view of the fact that air resistance is by far the major factor retarding force affecting them. With a bicycle, for example, it accounts for more than 80 percent of the total force acting to slow the vehicle at speeds higher than 18 mph. Here we undertake to explain this neglect and to show what attention to aerodynamics is beginning to do for the performance of human poered land vehicles.

Looking first at the bicycle, one sees that it has remained almost the same in form for nearly a century. The rover safety vehicle, which was introduced in England in 1884, could easily pass for a modern bicycle; it lacs only a seat brace, which wold have formed the modern diamond frae, and a few components such as brakes and multiple gears. Almost from the beginning the designers and users of bicycles recognized the importance of aerodynamics, but artificial constraints on design largely prevented the application of the necessary technology. It was as obviouse then as it is now that wind forces at the bicycle-racing speed from 20 to 30 mph are enormous.

Before 1900 the crouched posture of the bicycle racer had become common as a means of reducing air resistance. Another practive adopted before 1900 was to put a multiple rider bicycle ahead of a single racer to shield him from the wind. In 1895, The welsh wheelman Jimmy Micheal rode 28.6 miles in one hour behind a four man lead bicycle. In 1899 Charles ("Mile-a-minute")Murphy of the US gained international fame by pedaling one mile at 63.24 mph on a bicycle traveling behind a train of the long Island Rail Road on a board path built for the occasion.

In 1912 Etienne Bunau-Varilla of France patented a streamlined enclosure for a bicycle and its rider that was inspired by the shape of the first dirigible balloons. Versions of this bicycle and its descendants set speed records in Europe from 1912 to 1933. In 1993 Marcel Berthet of France covered 31.06 miles in one hour riding a streamlined rig named the Velodyne, his pace was more than 3 mph faster than anyone riding a standard bicycle had gone for one hour.

In the same year, the French inventor Charles Mochet built a supine recumbent bicycle (with the rider pedalling while laying on his back) that he later streamlined. With a professional race, francois Fare, this Velocar set a number of speed records between 1933 and 1938. Mochet and faure hoped the records would be recognized by UCI, the world governing body for bicycle racing. They were not.

In deed, in the 1938, the union banned the use of aerodynamic devices and recumbent bicycles in racing; the rule is still in force. The ban has been a serious deterrent to the development of high speed bicycles and is one of the two major reasons the bicycle has remained nearly unchanged for so long ( The other reason is that in the developed countries the shift to the automobiloe has made the bicycle less important for transportation than it once was.)

By its ruling the UCI essentially clasified improvements in the aerodynamics of bicycles and other technological changes as cheating (it is perhaps fortunate UCI wasnt active when a Scot-Irish veterinary surgeion, John Boyd Dunlop, developed the pneumatic tire for bicycles in 1887, otherwise people might now be riding bicycles and possibly automobiles with solid steel wheels. To its credit however UCI has gradually begun to relax its restrictions on changes in aerodynamics although recumbents are still forbidden. Since 1976 skintight one piece suit have been common in international bicycle racing. Streamlined helmet teardrop cross sections for frame tubing, streamlined brake levers and other aerodynamically improved components have been allowed. In fact, technological change in all forms of human powered vehicle is flourishing at a rate unmatched since the heyday of the bicycle in the 19th century.

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Alex Simmons/RST
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Re: Fairing and aerodynamics on recumbents

Postby Alex Simmons/RST » Sun Nov 18, 2018 6:05 pm

The CdA of the HPA record vehicle is of the order of 0.01m^2.
A slippery time trial rider in UCI specification competition will be of the order of 0.2m^2.

Use of NACA shapes at 5:1 is going to result in a very slippery object. In order to do it though, the rider has to sit facing the "wrong" way and use a mirror to guide their "forward" motion. This is because the wider part of the body is better placed closer to the front bulge and the legs are able to be enclosed within the tapered section. Sure you can have the same shape facing the "right" way as well, but to do so increases the size of the fairing, and CdA is directly proportional to frontal area.

Fairings are not always about improving performance, they are often used for comfort reasons, keeping wind and water away from the rider.

Joeblake
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Re: Fairing and aerodynamics on recumbents

Postby Joeblake » Sat Nov 24, 2018 10:25 am

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A late entry into the "soft" shell brigade.


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Joeblake
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Re: Fairing and aerodynamics on recumbents

Postby Joeblake » Sat Nov 24, 2018 10:46 am

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A fairing also gives more efficiency which saves power with an e-bike/trike, in both range and speed.
To acquire immunity to eloquence is of the utmost importance to the citizens of a democracy
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