Citroplane metamorphosis
Final year in the aviation institute is as overloaded as a train in India: final assignments, state exams, flying practice, 14 license exams and the Master thesis.
In order to graduate with dignity, this train not only has to move like the Shinkansen Hayabusa but all of its passengers have to reach their destination as well. Among them Master thesis being the passenger with the splendid turban and a retinue. Wishing that this job would have a tangible result, that theoretical knowledge would be escorted and verified with as much practice as possible led to “Body aerodynamic modification design and research” idea being born.
No start? No problem
Continuing with the train metaphor. First stop had to be buying a potential and salable car. This meant that it was necessary to go into the depths of car ads websites, where car buyer-ups fight for fresh metal like pigeons for bread crumbs. But it seems that these spoiled birds are not interested in French croissant, which the 1997 Citroen ZX is. All in all buying this car was not a mistake, it has fuel injection, some roof camber and a pretty comfortable ride for long tests.
A car for the price of champagne – what can go wrong? When arrived at the outskirts of some village to see the car, first thing that had to be done was to get it out of a snow bank. When the car was out, it revealed no signs of rust, but the onset of optimism was not enough to start it – the starter motor was inoperative. So the buying-selling personnel gave it a push, yet the vehicle showed the same reaction as a senior enjoying his deep afternoon sleep privileges – a short snore and the sleep was continued. Suspicion fell on the fuel index which if it could, would point to the center of the earth. The seller poured some fuel in and after a second push the Citroen woke up, started to react to the accelerator and almost instantly began blowing buyer revivifying warm air through the vents. This was not caused by a fire it was due to the car being French. Of course one should expect surprises from a car, where the battery terminal is connected by a self-drilling screw. Only three of the four wheels were usable and each of them was held only by two screws out of four. After solving these problems, sorting out the brakes and a few other minor things a unique verdict was given from the roadworthiness inspector “the car looks awful but I don’t have any remarks”. I am not sure what kind of reply he was hoping for, maybe “you’re not the most handsome inspector but you did your job ok”? The important thing is that a roadworthiness certificate was given and the tests could be continued.
Dumb and dumber
Firstly we had to verify the CFD results: is airflow really the same in real and virtual worlds. Since there is nothing more real than black wool tufts, they were used to cover the Citroen’s body. This tuft testing method is old yet still quite common in aviation and can be seen on many gliders. Straight and neat tufts indicate goodness, dangling and swinging ones show evil forces being present. So after a few hours of decorating, and the car looking like a bad Dumb and Dumber’s van replica, it was time to hit the road. Sitting in the following car cameraman position and seeing how the tufts perfectly replicate the results gotten from the CFD tests, as well as the ones described in literature, provided inspiration to slave days and nights to create a more aerodynamic body or as it later became known “The car with the rear attached”. But the Citroplane also has enclosed rear wheel arches, smooth wheel covers, side skirts and a belly pan attached, which also demanded a load of work. Everything had to be light, reliable and stiff. It also had to make use of existing holes under the car and be as cheap as a decently driving young man’s car insurance.
At first the whole kammback design was imagined a lot less complicated and should’ve only lasted a few tests until it was dismantled. But in the end me and my colleague from aviation mechanics decided to make our lives harder by fabricating a 1.4m (4.6ft) long wooden frame which replaced the car’s rear door and bumper using their original mounts – this is how to the first version of Citroplane was born. Interesting fact for all rusty boot door owners: Citroen ZX had this part made from fiberglass.
With the second version, gracefully named the V2, it was being attempted to make the Citroplane more practical with the least aerodynamic losses. So the kammback got under the blade of an angle grinder and its geometry was respectively changed. Since the V2 was being modified after defending the Master thesis, it meant that there was an undefined time limit, and all of the little imperfections could be sorted out. In the end the whole car was wrapped in a white slippery layer of patience, in a form of vinyl wrap. The expectations were not met – they were exceeded. Roots of aircraft modelling and paying attention in university lectures helped to make the kammback so that it was a rigid part of the car and could be relatively easily installed/uninstalled. That “relatively” could be compared to the transformation from coupe to roadster of the sunken into oblivion Citroen Pluriel.
For the fuel efficiency tests same sections of roads were being used when there was minimal traffic. Not that the modifications seemed unreliable but so no one would hamper the average speed and not to interfere with those who don’t obey the speed limit. In sum the amount of variables was always being reduced as much as possible. Always two people in the car and a full tank of petrol. Of course this does increase the fuel consumption, however it was the decrease in percentage that was analyzed. Since dependability of the modifications was mentioned: at first there were a few mounts that needed adjustment, so they were modified along with the car to a point where the discomfort to ride in it was very small.
Other subjective observations of the modified car are: less pressure requiring accelerator pedal and a longer slowing-down time when you lift your foot off it, less wind noise when a window is opened and a significant increase in attention on the streets. Although the attention decreased with the second version. Probably due to the car looking a little more stock. Nevertheless, during the time on the streets the same amount of thumbs up as the Facebook page is showing now was collected, so I can answer this question like a generously gifted female “Yes, they are real”. Other advantages of the modified car include its cleanliness – despite it is possible to wash Citroplane in a self-service car wash it is not vital to do it often because an aerodynamically clean car prevents dirt from sticking. When washing your car I suggest paying attention to those parts where the biggest amount of dirt has accumulated – it is quite a good turbulent flow indicator. But I believe that attention will not be paid so I will forestall: boot doors, especially those which protect the cargo of hatchback and estate cars collect dust as well as an Audra* vacuum cleaner.
Practical value of the modifications is not revolutionary: the original consumption of 6-7l/100km (39-34 US MPG) was decreased depending on the conditions to 4.3-5l/100km (54.7-47 US MPG) (17-39%) but it is a difference, which would not be shameful to mention in a manly barbeque talk. Also this difference would increase with speed.
FAQ
Is it electrical? – No.
Is it difficult to drive? – No.
So when are you going to take-off? – No.
Does the police give you trouble? – Not really.
It’s not very good in the city with that rear is it? – Yes, not very good – there are no benefits due to low speeds.
What is the theoretical coefficient of drag? According to the calculation of the empirical method the Cd is 0.28 while the computers calculated it to be 0.23.
* Translates to ‘Storm’ – an old soviet vacuum cleaner.
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