Literally feeling the aerodynamic drag of vehicles

Posted on September 23rd, 2008 in Aerodynamics,Driving Emotion,Economy,Electric vehicles,pedal power by Julian Edgar

As we covered in Analysing Road Car Drag, most aerodynamic drag of current vehicles is created by separation pressure drag. Put simply, this is reflected in the size of the wake – the cross-sectional area of the disturbed air dragged along behind the car.

The most slippery vehicles in the world – the solar race cars – have reduced separation pressure drag to the extent that the other types of drag (eg viscous drag, induced drag and interference drag) become more important.

But in all conventional cars, it’s separation drag that remains the big one.

Now this gives rise to a rather interesting idea. Imagine you’re standing alongside an empty road. The day is a still one – there’s not much wind blowing. A car is rocketing towards you along the road, travelling at perhaps 100 km/h. It will pass close by to you. It grows in size and then roars past.

Now – what do you feel?

Clearly, you will be able to feel the wake – the eddies and turbulent air indicative of the aerodynamic disturbance of the car. This disturbance will take into account the separation pressure drag and the frontal area of the car – the two when multiplied form the vast majority of the actual aero drag that’s experienced by the car.

And, equally clearly, the smaller the air disturbance that you can feel, the greater the slipperiness of the vehicle.

For the Greater Good?

Posted on September 11th, 2008 in Driving Emotion,Economy,Electric vehicles,Global Warming,pedal power by Julian Edgar

Here in Queensland the State Government has issued a discussion paper entitled Improving Sustainable Housing in Queensland.

The paper canvases a range of requirements the government is considering implementing for the construction of new houses and units.

I think it astonishing how little government regulation has been applied to the energy efficiency of housing. Especially in the context of the media attention given to fuel-efficient cars, there seems to have been a deathly silence on what is surely the far more important area of housing.

After all, a typical house is going to be consuming energy for something in the order of five to ten times as long as a car, and will be doing so most hours of the day and night.

Finding the Shortcomings

Posted on May 15th, 2008 in Driving Emotion,pedal power by Julian Edgar

As I canvassed in this blog, my wife Georgina and I have been thinking of going pedal touring. Carrying 3½-year-old son Alexander in a Burley child trailer, we originally were going to use recumbent trikes, machines that are stable and have a very wide range of gearing.

But getting the trikes to any distant location is an expensive exercise, so we reluctantly decided to instead ride Brompton folding bikes. (Disclaimer: Georgina’s business sells Burley trailers, Brompton bikes and Greenspeed recumbent trikes.)

The advantage of the Bromptons is that they can be folded into such a small package that on an airline flight they cost nothing at all to take with us. In fact, flying within Australia on Virgin Blue, we can take along two bike trailers, two bikes and all our camping gear – and pay not one cent extra over the three fares!


Posted on May 1st, 2008 in Handling,pedal power,Suspension by Julian Edgar

georgina-on-laden-trike.jpgAs many of you will know, on my recumbent pedal trike I use a Firestone airbag for rear springing. This air spring has major advantages over other springing approaches but as it has little intrinsic damping, external damping is needed.

The rear damper is an ex-R1 Yamaha motorcycle steering damper. This is an unusual design for a motorbike steering damper in that it runs an external passage connecting the sides of the piston. The piston is a loose fit in the bore. The damping action in standard form is provided by the oil passing through the bypass passage, and also making its way past the loose piston. (I assume that the steering damper can be tuned in its action by placing restrictors in the bypass passage.)

To make the steering damper suitable for use as a suspension damper, I modify a plug in the external passage and insert in this passage a one-way valve. This allows free-er flow of oil on bump and more restriction to flow on rebound. Bump damping is therefore provided by the oil flowing in the bypass passage around the open valve and also around the piston, and rebound damping by the oil flow past the piston only.

This gives the desired asymmetric bump/rebound damping.

Bikes, bikes…

Posted on March 25th, 2008 in Driving Emotion,pedal power by Julian Edgar

gt3trailersmall.jpgMy wife’s business Speed Pedal sells recumbent trikes, folding bikes and bike trailers. Through her work, she often gets to meet people who collect unusual pedal-powered machines. So there’s the man with something like 100 bikes – everything from historic to current, from tandem to single to well… you name it! And another bloke who rides just weird looking machines. Complete with his long flowing beard, on the road he looks an amazing eccentric.

I always figured that was all a bit bizarre, but I now think I am heading in the same direction.

You see, I’ve recently bought two new bikes. And both of them are pretty strange. However, the difference that I have to a collector is that I am buying them only to use, and if I don’t like the machine, I’ll sell it.

To people reared on the traditional diamond framed bike, the fact that other bike designs even exist is a source of surprise. I have previously covered (both in this blog and AutoSpeed) the design and development of my favourite pedal-powered machine – a full suspension recumbent trike.

However, while I love the machine, it has a major disadvantage – it is large and unwieldy to send to distant places.

Broadening test horizons…

Posted on February 26th, 2008 in Driving Emotion,pedal power by Julian Edgar

I’ve just returned from an interstate holiday. Originally from South Australia, my wife and I recently flew back to that state for ten days.

In addition to catching up with family and friends, I also wanted to do some riding. I broke-down my self-built, recumbent, full suspension, pedal trike so that it could be placed in a box for freighting the thousands of kilometres. Because I didn’t want to spend a lot of time reassembling, the box was pretty bloody large.  The cost of interstate freighting was not inconsiderable – but I am still very glad I took the trike.

My home Queensland terrain comprises steep and fairly rough bitumen roads. Most of the roads have no gutters – they’re rural and semi-rural roads. I might be inching my way up a 15 per cent grade one moment, pedalling in bottom gear – and then barrelling down the other side in 81st gear the next. I think the roads are very demanding of recumbent trikes: in fact, it was unhappiness with a commercial non-suspension trike that caused me to start to build my own machines.

Thank you all

Posted on November 26th, 2007 in Driving Emotion,Opinion,pedal power by Julian Edgar

dsc_0034.jpgThank you.

Thanks to all of you; but to especially those who have been reading my material for a long time.

By your praise, and by your criticism, and by your demands that I produce the best for you that I can, you have all made me a far better self-taught engineer than I would ever otherwise have become.

Because I know that if I say something like: “This performance mod makes the car go faster” there will be a chorus of “Prove it!”, or “How much faster?”

I know if I write something about (say) how an anti-roll bar works, and I get it wrong, there will immediately be people happy and ready to correct me.

Doing this job for nearly ten years has taught me, in a way that I’d not realised before today, that in mechanical things I constantly internally justify what I do and how I am doing it, and that in everything I do I need to cite evidence that it works.

So thank you all.

And can I also say, you’re equally all responsible for my being today thrown off a discussion group!

Ah, the swings and roundabouts…

Touring plans…

Posted on October 18th, 2007 in Automotive News,Driving Emotion,pedal power by Julian Edgar

Regular readers will know that when it comes to shopping, I am happiest digging through the junk at a tip shop, foraging at garage sales or even – if this can be called ‘shopping’ – picking up stuff that others have dumped by the side of the road. In short, glittering neon’d shops and my version of fun don’t go together. (Except, it needs to be said, when buying cameras or watches…)

So today was very unusual. I spent nearly all day with my wife Georgina and 3-year-old son Alexander shopping for brand new items: assessing and evaluating; picking up things, weight being felt in hand; turning products over and over while assessing quality; even putting some things down on the ground and lying on them. Yes, right there in the shop.

And when the day was finished, we’d spent something like AUD$700.

So what were we buying? Camping gear!

After doing a long drive in a diesel Hyundai i30 fell through, both Georgina and I felt all psyched-up for a tour. The Hyundai trip was going to have been a very long one, but when I was mulling-over its cancellation, I realised that the distance travelled wasn’t of that much importance. In fact, in my view, neither was the fact that it was to be done in a car.

Then, almost of its own volition, the thought popped into my head: why not go touring on our trikes?

Both Georgina and I are enormous fans of recumbent pedal trikes. These vehicles, which are simply nothing like a bicycle to pedal, incorporate stability and cornering fun in a way impossible to imagine if you’ve not experienced it. (In Georgina’s trike-selling business, over three-quarters of those who book a test ride buy a trike.)