I have found a nifty free program that could do a flow simulation and show it graphically as a video clip in .avi format. It is called Flow Illustrator. It is not accurate to replace a full blown Computational Fluid Dynamics software but it is free. You will need to do your own model. This is simply done by using a side view of the model. You can do this by using an existing picture with non essential details such as background and people deleted. I use Microsoft paint to edit my picture. Please note that it is advisable for you to use the CUT function using SELECTION. Once the image you need is cut from the original, you crop the rest leaving with a totally white background. You can upload the picture and set three (3) variables; Reynolds number, time between frames and video length in seconds. I only change the setting for video length. If you want to do comparison of flow between two designs, you need to have the picture in the exact dimensions. The value of the Reynold’s number will be shown on the video.
You can see the comparison video on this link.
A screen capture of the comparison is shown below
Simulated flow on Satria Neon with Deflector
Simulated Flow over Satria Neo with Standard Spoiler
Notice I have cut out the wheels to indicate flow of air under the floorpan. Green coloured areas indicate high pressure/low velocity and Red indicates low pressure/high velocity. The comparison helps to show that the original design with standard spoiler has a bigger wake left in the trail of the car. The one with the deflector has a smaller wake as the height of the turbulence is reduced.
If you do another comparison with a sedan design, you would see that the wake is about the height of the boot. The deflector now looks like what we intended it to be. It is to reduce the wake by delaying air separation from the hatch. This partly answer the previous question of why the Fuel Consumption curve is not logarithmic. The deflector has therefore made the car more aerodynamic. It makes it easier to cut through the air. I would not be surprised if it has reduced the Cd value of the car.
Making the car aerodynamic has the added bonus of reducing drag and obtain faster acceleration and top speed.
It came as an afterthought. It was never my direct intention to have done what I made. I had initially made a Secondary Intake for reducing fuel consumption of this car. See my previous article. Then I wanted to make the spoiler adjustable so that it can actually be useful. This was on my previous thinking that the spoiler functioned as perceived. That it provided down force and that if I took it out, the handling would suffer.
This then changed somehow without any premeditated intentions. What I have right now is a combination of efficiency solutions. The secondary intake initially showed that I could save money in the movement of the throttle. That was fine. Then the aerodynamics were sorted. Never did I thought the two combined mods made significant fuel saving changes.
I did a test run yesterday for 230km in total. This was a return trip on the North South Highway. It was to test the Deflector at speeds above 90km/h. It performed admirably by registering an Indicated average Fuel Consumption (FC) of less than 5.0 l/100km. You can see the YouTube video here . Yes, this means I now have a YouTube account. Forgive me I am rather slow at 46 years old. I have only now found the use for it.
During the same journey I made similar tests for speeds of 100, 120 and inadvertently 130km/h. All of these test results were on solid straight roads with the AC switched on. I plotted the values which I had observed on a spreadsheet. I had expected a exponential curve from 100 to 130km/h. But I could not get it. The only time I observed a high FC is when the car was being driven at 100km/h up a 20 degree incline.
The table is now UPDATED on 9 November 2014.
The data is based on observed data from factory standard equipment. They are not absolute and the value is AVERAGE Fuel Consumption. The last data if drawn to scale should be closer but it should also be higher.
A few things floated in my mind. As engineers we are told that aerodynamic load is very much affected by speed of the object or vehicle. This aerodynamic load increases . Fuel consumption will increase dramatically as speed increases. Perhaps it is too early and too easy to say that somehow with the combination of both modification, we have come to a point where the world is no longer flat. I might need to spend more day trips to Melaka to do more tests. One might say that these values at these speeds are insignificant as the speeds are low. But these speeds are what normal people are driving at. This is the whole point of doing these modifications. It is so normal people could save money driving normally.
Should anyone ask about performance degradation; I simply did not see any. The maximum top speed is still attainable.
Just a quick one as I do not want to give away too much. Finally managed to do up the fibre glass work with Chooped Mat and Roving. The Roving is better suited to hold the surface on the edges as it is stronger.
Needed to brace this securely on this working design. I would not need to get a really solid grip on the production model as it will totally be fibre glass. As it is now, wood is used as the main structural material. I would only need this working design to make some sets of mould. The finished product would therefore be much lighter and look nice.
Deflector mounted on car
Had a spin around Putrajaya. About 45km distance. First round registered 4.3 l/100km while the second registered 4.5l/100km. Will keep doing test and maybe try to add more surface area on the bottom. I am very happy as it is, there was little effort to try and clean it up. Not even fillers and it still meets the target. Probably I might get better results with the extension.
Posted in Aerodynamics, Fuel Economy, Spoilers
- Tagged Aerodynamics, Composite, Deflector, DIY, Fuel Consumption, Prototype, scratch buiding, spoilers, Woodwork
It has been a few weeks of browsing through my den of broken things to put together a test rig. The reason being to please my self doubt about what I am trying to do. A lot of times I have questions floating in my head if I could actually pull this off. I have been messing around on the internet and trying to find something that could show that my half baked ideas is actually worth the time. Time is on my side. I have stopped working for the moment. I ended my previous job as a Manager for Fire and Gas Detection system with Draeger Safety with a small compensation package. That bit of kit would probably last me a few months before I actually need to find a job. At 45 years of age, that is not going to be easy.
I have taken a piece of wood from my hoardings and bought a cheap set of planer. The last time I used this was in Secondary School in the early 80’s where we learned woodworking. I therefore whittled down this piece of wood for two days to come as close as possible to the profile that I needed. I also used my dremel and coarse grit sandpaper to give a good smooth finish. Woodworking is very addictive I must say. I find myself constantly reshaping the profile untul it looked satisfying to my eyes. I was not looking for an effective aerodynamic profile. I wanted it to look good. I had to force myself to stop because I needed to do this rig and reassure myself.
I took the finished piece of wood and proceeded to find the center of gravity. This is crucial as this would help to reduce the torque demand on the servo motor. Placing the servo in line with the axis of rotation means reducing the weight that had to be moved around the axis. I simply held the spoiler by the side of both hands. I slide both hands to the center of the piece. Where the tilted, the weight has gone the other way. I slid the hand which had no resistance because of this shift. I put the wood on a pen and tried to balance it as much as possible. This way, I found the center of gravity and marked with a pen. I then used the grain of the wood to show me the pivot point at each end of the piece.
Then I looked inside the cabin again to find unused TV stands meant for my 42 in plasma TV. I drilled both at an approximate height. The undriven pivot side was held by a simple screw. The driven side had a servo hub which was nailed. The hub has a 24T spline which would normally be attached to the servo shaft and screwed in place. This is another issue that I would need to address. I would need to cut an approximate width of 20mm to enable the screw to tighten the sawn wooden piece against the servo. Once that servo is tightened, it would then be screwed to the main piece.
Finished Test Rig
I have been trawling the pages of Servo City for a few weeks now and have ordered some bits and pieces. I will tell why I need those a few paragraphs later. I have made a test rig to show myself that the small servo could turn the wooden spoiler. A video of which can be found on my facebook link here
Close up of Hitec HS-425BB RC Servo
What I have realized after playing with the test rig is that the weak link lies in the connection to the HITEC Servo. This HITEC HS 425BB was bought from a local Arduino authorised agent at MyDuino.com. It was the biggest RC Servo that they had. I could see that at a speed of 200km/h and with a surface area of 7,500mm2, the wind load on the spoiler would only be contained by the servo hub and the swivel joint. Even though this HS 425BB is a model with bearings, I would think that it would not be sufficient to handle the load. Therefore I decided a redesign is in order. Part of the items I hard ordered online was an aluminium arm to connect to the spoiler. But because the spoiler would have a different pivot point and than the servo, the hole on the arm must be modified to a slot.
Having two support on the driven side would increase load capability. This also means is that the torque demand on the servo would be increased. I am prepared to make the spoiler lighter by hollowing; making more holes where necessary.
I have mentioned in some random postings on the internet of the need to have malleable aerodynamic surfaces to reduce drag in different driving conditions. In fact Autospeed.com has mentioned this as a stumbling block in automotive design advances. Articles such as this one has given me ideas about changing the effect of rear roof spoilers from just providing small down-force and drag to actually help reducing wakes.
Spoilers to reduce wake meant for big profile vehicles such as MPVs and SUVs
Since I mentioned about Arduino in my last post, I have actually bought one from RS Online Catalog. I have the Starter Kit for Arduino Uno which comes with lots of bits and pieces. I have mentioned that I had never dealt with electronics before. The most I have done is fondled with DC circuitry. Hence an order was given and the money was pumped into the Open Source community. I hope they use it well. I received the box and was amazed at the amount of things Malaysian Ringgit could buy. When I say ‘the amount of things’ it is not about the quantity of odds and ends. Its about reusable components. This Starter Kit is amazing in terms of what things you can make with it.
It took me yet a few more days before I started fiddling with it. I blame it on my age. A child would rummage through it without a second thought. A teenager would plug it in first and jump for joy to see the yellow LED lit up. A twenty year old would skip all the pages and build it up with the first drawing. I am 45 years of age. I read every single page of the manual and tutorial first. Even then, I went to the website Arduino.cc to have a look at the specifications of the blue thingy that i a permanent resident at the side of my bed. Its entirely ok. My wife has her TV/Android phone/ Android Tablet as companion.
I have this.
It started with this
What that thing does is move the servo using a potentiometer. The LCD shows the angle in degrees from the readout of the servo. The LCD is meant as part of the development of what I intend to build. I would use it to adjust the angle while doing testing. I will adjust the angle of deflection and see the effect on the fuel consumption via the on board FC computer.
Yes that servo is tiny and has a stall torque in oz-in. It came with the starter kit. About mid of March I bought a bigger servo from MyDuino.com and its a markedly bigger in size and now I have something that pulls in kg-cm. The intention is to move a piece of aerodynamic surface as part of my car’s rear spoiler. I have calculated that for a 1m span, the wind force acting on it at 200km/h would total 1.4Nm2.
A discussion on these sort of spoiler is well documented. I have to admit that it does not contribute much on the actual down-force required for a front engined front drive car. In fact, when looking at the profile, it would also provide less drag. Quite simply when the designers made this, it was never meant to provide much effect other than cosmetics and form rather than function. Proton now understands to sell it, it need to look nice. Unfortunately. In essence, the design and flow of the spoiler is very fluid. This suggest a high amount of design work was invested in this one piece of fiber. There is no argument that this part actually sells more of the car than any other body kit. It is therefore wise to preserve the design as much as I possibly can.