Aerodynamic drag and why a coupe is better

[Anonymous]

Recent conversations about various owners fuel consumptions got me thinking about aerodynamic drag..as I'm sure you often think about it..

I was discussing some performance profiles in aircraft and recollect that my kit plane I built in the 1990's would do 155 knots (about 178 mph) on a Rotax 921 engine rated at 100 bhp..

Obviously a whole bunch of aerodynamic related factors figure in that equation..

I then pondered about various Z4 fuel consumption figures..about 95%+ of the time I drive with the roof down..whereas..I ususally see most other Z4s with their roofs up!

So I wonder how much extra fuel I'm burning compared to those top up guys and the coupes?

Interesting article here http://sersol.weebly.com/workshop/convertible-aerodynamics# about some modelling top up and down and the effect of a rear spoiler on affairs..and also the wind deflector effect..


Since drag force goes up with the square of the speed at 70mph I must be burning quite a bit more fuel?

Enjoy!

 

[enuff_zed]

[ref]Pbondar[/ref], you are missing the one vital part though.

Life is a drag with the roof up

 

[tintoverano]

Life is a drag with the roof up

:rofl:

 

[Anonymous]

[ref]Pbondar[/ref], you are missing the one vital part though.

Life is a drag with the roof up

Thank you for that detailed, reflective analysis!

 

[Chris_D]

Don't even get started on bike-racks!

I'd be interested to see the CFD model of adding my bikerack and sometimes 2 bikes on the back of the zed, top down averaging 100kmh (new Dutch speed limit. s'okay).
I swear I can feel the drag sometimes, especially in a headwind.
What a drag. :lol:

 

[enuff_zed]

[ref]Pbondar[/ref], you are missing the one vital part though.

Life is a drag with the roof up

Thank you for that detailed, reflective analysis!

My pleasure.
Can't just let you get away with slack fact-finding.

 

[flybobbie]

3 and 4 looks a bit draughty in the back seats.
What kit plane did you get 155kts on 100hp, Pulsar by any chance.

I'm still waiting to try out a Glasair in the hanger.

 

[Anonymous]

3 and 4 looks a bit draughty in the back seats.
What kit plane did you get 155kts on 100hp, Pulsar by any chance.

I'm still waiting to try out a Glasair in the hanger.

Dyn Aero Banbi MCR01

 

[Chris_D]

That reg no.
:rofl:

 

[Anonymous]

That reg no.
:rofl:

I had to formally write to the UK CAA explaining why it was OK, they refused to grant my original application..

I had to explain that Toad of Toad Hall and Pooh Bear where my role models.. :tumbleweed:

Notice the yellow theme there too? :rofl:

 

[enuff_zed]

Hell, it's so small it looks like you have spats on your feet!

 

[Anonymous]

Hell, it's so small it looks like you have spats on your feet!

That's why it was so speedy..0-10,000 ft in 6min 45 secs..not bad for a kit plane..bloody vicous handling..snap roll on stall..roll rate greater than 90 degrees per sec..

The ex Empire Test School check pilot loved it!

Just like a little jet fighter he mused..couldn't get the buggar out of it!

 

[buzyg]

[ref]Pbondar[/ref], you are missing the one vital part though.

Life is a drag with the roof up

:driving:

Spot on, stuff the techno babble. :lol:

 

[buzyg]

Dyn Aero Banbi MCR01

I have shoes bigger than that.

Looks and sounds like amazing fun. 8)

Enjoy play time in your very own PooP.

Oh and if you get the chance, put the roof down. :wink:

 

[MACK]

Getting back on top kinda.
I was always told using the air con had a detrimental effect on fuel economy. Obviously driving top down isn't as efficient as top up, but I do wonder how top down and air con off compares with top up and air con on.

 

[Smartbear]

Getting back on top kinda.
I was always told using the air con had a detrimental effect on fuel economy. Obviously driving top down isn't as efficient as top up, but I do wonder how top down and air con off compares with top up and air con on.

I read that driving with the windows down was worse for economy than driving with the ac on, I should think that top down driving’s far worse than just windows down :?
Rob

 

[Anonymous]

At least 23% plus more drag according to this ..ish..

 

[flybobbie]

I have driven everyday with the roof down, still get 29-30 mpg, half town and country. Same as roof up winter.
I would say quality of fuel is a factor, i noticed my car and bike didn't like the cheap £1.01 litre petrol from Asda..
I'm sticking to Shell unleaded and that runs better than the super.

(Looks like that instrument panel cost more than the aircraft, i'm just trying to solve a climb power problem on a Tomahawk).

 

[Anonymous]

I get about 28mpg measured over 3,000 miles..and generally that’s a pretty rapid pace...with lots of acceleration and braking due to the nature of the roads where I potter ... :driving:

I probably spent around £25k avionics on a £66k build back in late 1990s on G-POOP.. IFR GPS..two other GPS plus 2 axis auto pilot didn’t help... :tumbleweed:

 

[BadgerDog]

I get... less mpg. The larger engine loves to chug gas if you are on and off the throttle. Not too bad cruising down a highway on cruise control, but whats the fun in that?