General view IT3 engine

Due to recent job change and house moving, I have not been able to put as many hours in the workshop as I would have liked. This will stay the same for a few months so I will concentrate on getting the main scheme of the car under way and start with the actual car design. This means the IT3 engine will be finished later but still on time to gather relevant info before the important design decisions on the V8 engine are made.

Some screenshots on the engine design almost finished. At this point it is missing spark plug and ignition hall effect sensor, and other sensors (Temp, Engine speed, Inlet pressure, EGT), carburettor, exhaust and engine stand.

The image below shows a cross section of the engine assembly. It clearly shows the main section of con rod, crank shaft and piston, on the lower part; and the exhaust valves and cam shaft on the upper part, behind the rocker carries section. Note the minimal cross section of the piston, quite innovative on an model engine of this size. The bore is Ø35 mm and stroke is 20 mm. Not quite to scale, but this allows for bigger engine capacity and thus more power, without significantly affecting overall engine envelope. Obviously the big flywheel will not be used on the V8 engine. On this test engine it will be used to, first provide enough inertia for the engine to not stall at low revs, and secondly to allow measuring the rough power of the engine.

Below is the entire engine, showing mainly the distribution system. On the V8, this will be different as only gears will be used. The depicted arrangement was chosen to test the gear system, but a chain is used to keep cost and complexity down.

I do not intend to bring into the CAD assembly all the fixings and other mechanical elements to reduce amount of time on design. Since this engine assembly is not too complex, it is worth taking the risk of not playing around with hundreds of fixings in CAD.

Overall very excited to start with the scheming of the car. I might start doing some 1:1 plots to start sketching by hand on it. Even perhaps a cardboard mock-up. This is always a good practice as it is the only way of getting a feeling on the size and helps a lot with packaging (engine, cooling system, control systems, batteries, etc).

More progress with IT3 engine

After a few months without doing much work, I have been putting in some hours in the last weeks at the workshop. It is nice to start seeing the parts in real live that I have been designing for some time, although it has been quite painfull in some instances. Camshafts, cranshaft and valves are all quite triky to machine for its geometry, tolerances and material of choice.

I have been doing external parts of the engine first, then internals that require turning and will finish with internals that are mainly milled. It is intersting to see the nice learinign curve from the IT1 to the IT3 at all levels: resources, cost, materials, design techniques.

Every component requires a lot more time to manufacture, and uses the equipment´s capabilities more extensibely. One noticeable example is the engine head. On IT1 it was made with 3 axis machining, with two main ops. On IT3 it has to be done with 4 axis machining, and it takes 13 ops, aproximatelly 10 times as much machining time, and 6 times as much cost in cutting tools. This is true for most of the parts and will have a big impact on final cost of the V8 engine and time required to manufacture.

On the design side of things, although it is more complex, it is more enjoyable. The better I learn how to use my equipment, the freer design becomes. On the other side, there is still a limit of resource and times available, although this will be enhanced with the use of DMLS and rapid casting techniques I am planning to use for most of the engine external and structural parts. I am considering outsourcing some components of the internals as cost would not be that high compared with the amount of time and tooling costs it would take me.

See some components that I have made so far, although not fully finished:

I have made now the 4 valves that will be used on the IT3 (2 exhaust valves and 2 inlet valves). The one on the picture below is a inlet valve. The stem has Ø3mm on its sliding surface, and Ø2 mm on the wet section. The valve head is Ø14 mm. On the image, the valve still has some material to be removed at the top. I will do that on a secondary op, as the top needs to be grinded to achive a high level of flatness and height tolerance. Material is stainless steel AISI316L for both types, and was not too hard to machine.

 Cam shafts. there are two camshafts, that operate the inlet and outlet valves separatelly. They are slighly different, as the pitch between the IN valves is different to the pitch ont he EX valves. This arrangement allows the maximum valve surface with a given cylinder diameter. The material for the cam shafts is EN24T and is quite hard to machine. At the stage shown, the cams have not been milled yet. For the IT3 engine I will mill the valves, with interpolation as the tests I have made are quite good. See the next picture below. The cam profile was calculated in Excel, then transferred in Catia using a macro, and then into Visual mill. The profile is different from EX valves to IN valves. I will post more pictures after the cams have been milled. The millign of the front flange is also missing, and it will accomodate the features to connect the timming gears. Both cam shafts, have a Ø8 mm diameter on the main shaft, and are bored to Ø6 mm, making it quite light. I will try to keep this arrangement on the V8 engine, although it will be a challenge to drill such a lenght in this steel.

Below is the sequence of pictures of the crankshaft machining. It is also made in EN24T, and is quite hard to machine. The nice thing is that it is turned using this arrangement, rather than with the chuck. This is to allow the turning of two differnet axis of the main and rod journal. I started with a billed of Ø30 mm in diameter. See the bracket on the left to spin the part that I made. 

Below is the first op finished. This is basically the turning of the main journal, which consists of different diameters, that will be used to fit the timing sproket and the fly wheel. On this engine I have not added any feature to spin the engine. I will rather use a friction wheel on against the fly wheel as it is quite a big one (for what I am used to). The main journal is Ø10mm and the rod journal is Ø12 mm.

 The next op consists of milling the material around the rod journal, rather than turning it. I just did it like that because it is much safer. See as well, that the cranshaft now is fixed on the secondary axis, ready to turn the rod journal. The next picture shows the rod journal being finished.

The next steps are to mill the camshaft to form the counterweight area, and key groves for the timming sproket and flywheel. There will not be any oil passages on this one, to simplify the component, it will use a splash type of crank case. 

Below is a picture of my workshop being busy on a late dinner time. Many more to come.

Test engine IT3

After a while of not wrinting any post I finally found a minute to show some pictures of the engine I am working on. This is a single cylinder test engine, which will be used to test the design of the V8 cylinders. The design is almost 100% complete but I have already made some of the main parts.

I will be posting more often from now on. The next two pictures are from the engine head - quite a lot of machining!

These is the engine head rockers bracket. There are two per cylinder. It is quite an original design but I do not think they will make it to the final V8 engine design.

This is the main engine parts put together. The cam cover is missing.

 This is one of the split bearings. It is quite hard to machine due to the tang for locking the position in rotation. It is all made on the milling machine, using a rotary table.It is accurate to 0.01 mm in all dimensions, which is quite an achievement bearing in mind my equipment.
You can see I also do drawings for every single part to keep all the details for when I start designing the V8 engine in a few months.

Dynamic Vehicle Simulation

The last step of the preliminary design is to find out the actual overall performance of the vehicle. For this purpose, I use a MatLab coded 4 corner vehicle simulation, which I developed as my dissertation.

I will not get into much details about the model. In short, it can simulate the forces, accelerations, speeds and travels of each corner of the car, including sprung and unsprung masses. Additionally, it simulates engine and gearbox functions, as well as aerodynamic effects.

After completing the weight estimation and aerodynamic study, the data was input to the MatLab code to simulate a series of maneuvers: pure acceleration, 180º corner and chicane.

Basically, I wanted to find out how the car would perform and if this would be equivalent to the real F1 car.  Let´s take 5g as maximum lateral acceleration of the 1:1 car. At 1:3 scale, this acceleration would be 3 times smaller. Not the force, since there is mass involved, but it would be the acceleration. This is considering, the car has a turn radius of also 3 times less, and speed 3 times less as well. Therfore, the Lat Acc we are looking at is 1,67 g.

In order to run the model, many parameters have to be introduced: polar moment of inertia, masses, inertia of the wheels, engine torque curves, aero parameters, suspension stiffness, and a few more. The CoG is calculated on a quick estimation from the DMU, assuming some masses. The mass is estimated at 12,5 kg, which would be excellent to achieve.

The Tyre model used is a simplified version of Pacejka. The maximum mu coefficient is 2,2, similar to a good racing tyre. I might have gone a bit optimistic here, but the actual values should not be too far. In order to properly find out, I will perform testing on the R26 tyres at 1/5 scale. The tyre construction for this car will be similar.

The simulation is run by a series of driving inputs, that control steering and throttle/brake inputs, as a function of time. After the simulation is run, the results pop up like this:

Therefore, the important results are:
Max Lat Acc: 2,6 g at 120km/h.
Max Long Acc (from a simulation not shown):1,2 g, but average from 15 to 100km/h is 0.56.
Max Speed: 130 ish km/h.

Considering that some of the assumptions might be a bit optimistic, but that there is also room for improvement on the aero side, this results are quite satisfactory. The car will perform slightly better than a scale 1/3 F1 car and will look fast.

Interesting to see from the tyre slip values, is that the handling is very understeering. This is due to the CoP position, which is way too far on the back. I expect to be able to correct this by improving the front wing performance. Testing the simulation with a CoP just 50 mm behind the CoG, an increase of 15% in Lat Acc is obtained.

Next steps is to complete the DMU more components, and perform composite test coupons to gather material data for FEA.

Preliminary design CFD

CFD stands for Computational Fluid Dynamics. To put it in short, CFD are numerical models that are used to study the behavior of fluids within a set of boundary conditions.

As I am building a car at 1/3 scale, it will translate to 1,64 m vehicle in which aerodynamics will play an important role, as it does with the real F1 cars. This is why, for first time in all my cars I have decided to use CFD to improve the aerodynamic efficiency of my car. At this stage, only a preliminary study has been conducted but some valuable data has been obtained. This data will be used in the detail design later on in the project.

The process starts with meshing the geometry to study. The model is the same that was made for the DMU in CATIA, with the difference that I only study the front and rear sections, not the full car. This split is made to save modelling and CPU time.

The model was imported in COSMOS FlowWorks 2007 in iges format. After cleaning the geometry and fixing some defects on the surface, these is what is obtained:

The boundary conditions are stablished as 20 or 30 m/s flow, symetry on the XZ plane and symetry on the XY plane. The latter is used to simulate the road, as a big simplification. I did not want to use rolling floors since it is the preliminary stage only. A real F1 car has about 1500 kg downforce, which translate to 18,5 kg at 1/3 scale. This design is therefore not too far away, considering it still has plenty of room for optimization (assuming a maximum speed of 120km/h which would be 360 km/h on the 1:1 car).

The results were as follows:

FRONT

20m/s: 12.1 N

30m/s: 28.2 N

REAR

20 m/s: 22.7 N

30 m/s: 52.4 N

As you can see, there is flow detachment, especially on the diffuser and front wing airfoils. I am aware this is not correct and should be further developed, but it is just the starting point and a preliminary design.

Drag values were really high, and I assume it is due to not having the full body, rolling floor, and main simplifications on the cooling outlets on the rear section. For the dynamic simulation, a 1/3 of the downforce coefficient is used accounting for the drag.

The rear section, was optimized during several iterations using a NACA profile airfoil. This increased the initial downforce values by around 50%. Further refinements were made to remove airflow separation close to the trailing edge of the RUMP (rear upper main plane) and rear flap.

On the other hand, the front section was not refined, and thus a low downforce value is obtained. Additionally, the front wing is closer to the floor. Therefore the influence of not having a non-rolling floor is more acute than for the rear wing.

The Center of Pressure (CoP) is located -223 mm behind the CoG. This is too far behind, but is the result of the poor front downforce at the moment. The downforce value, might seem low but in fact, comparing it to what should be at 1/3 is not that low. Making some numbers, we find that the downforce is not scaled by 3 times, but by 81 times (F=1/2*p*A*Cz*V^2, area is 3^2 and speed is 3^2, hence 3^4=81). Reynolds number is way within the laminar flow and so turbulent flow is not a concern. 

Car preliminary design study

After completing the wing test project, I started a preliminary design of the car to overview the estimated performance of the vehicle. I though it was important to make this study at that point, since will indicate me if the car will deliver scale able F1 performance and find out if any other test is necessary on engine, clutch or other areas.

A first iteration of the surface was modeled in CATIA to be used as a DMU (digital mockup). The RB model created is a combined version of the 2010-2013 cars. They all have followed a rather steady evolution, than a revolution. This is why the outer surface has not changed significantly  As always  it is on the details that one can notice the differences.

I started the modelling with the legality box, based on the FIA F1 rules. This model is used to check that the car is within the constrains of the FIA. I used different colors depending on the section of the car.
The next step was to create the surface model of the car body, which means just the outer surface. Only the left section of the car is modeled to save CAD time. The model is then closed to create a solid which is used for the CFD analysis.

 The solid model was split for the front and rear sections. Each model is then independent and transferred into the CFD software.This model is used as well as a digital mock-up. It is used to locate the main components of the car, i.e. chassis, engine, radiators, rc servos, electronics and so on.

Using the generative surface design tools from CATIA the different car sections can be extracted to create separate assemblies. Each assembly is linked to the surface model and any changes to the surface or trimming features are associative to the assemblies.

At this point, the DMU was left on hold, in order to make the CFD analysis, weight estimation and dynamic simulations. With this three steps, an estimation of the performance has been obtained.

Layup and curing Wing component (wing test)

The component is produced with wet layup in a similar fashion as the molds  The difficulty with wet layup is that the low resin viscosity and low tack makes it hard to preform and assemble. The plies were cut using paper templates created directly from CATIA v5. A drappability analysis was conducted on each layer to define the cutting kits.

Standard 2x2T 200 gsm was used with 5 layers on each wall. The spars have 4 layers each of the same material. Resin is Axson Epolam 2022, and was cured at 60ºC. This cure cycle was selected since this is a test wing to validate the processing, not the structural performance of the wing itself. The Epolam 2022 resin system can be postcured at 100ºC to obtain a higher Tg.

To create the assembly, the material is layup on each upper and lower moulds, including cores. After that, the spar preforms are layup on the mandrels and foam cores. Each preform is bagged and debulked separatelly before being assembled.

The end result was quite good and showed that wet layup could be used for the entire car. However, weight is such a big concern that it will have to be studied a bit further with different parts and perhaps compare that with a prepreg-alike made. For a wet layup I expect a 20% more RW than for the prepreg, but on the other hand is so much cheaper.

I am planning on making a simple sample test plan to obtain material characteristics for the FEA. Even though I do not have FEA software to compute dedicated composite elements, a shell analysis with a definition of the orthotropic properties for each type of laminate area would do. I will use the rule of mixtures to combine the different layups and materials.