- Messages
- 10,063
- Reaction score
- 24,715
- Location
- TENNESSEEESSEEEEEE
- Arrma RC's
- Limitless
- Mojave
- Typhon 6s
This is my last RC car I’ll build I promise…. Famous last words I know.
I have one more project in me. I had said the 200+ build was my last one, but I have this one last car that I cannot get out of my head. It will be Typhon 6s / Senton 6s based.
This is a bit of a long read and parts may not make sense unless you read all of it. Bear with me here as this is 5 years of mind dump LOL. (Don't worry there are lots of colorful pictures and shiny things)
About 5 years ago I had started on a high-speed build that required some advanced aerodynamics using ground effect. Here is an image of that Slash 4x4 when I was attempting to build it. Ultimately, I gave up due to the body construction challenges, and concerns about ride height.
I struggled to make the body work by sculpting it out of foam and plaster. I decided to scrap the project. Fast forward to today with easy access to 3D printers and CAD design, and new 1/5 scale parts, now I am finally ready to finish up this project and get the idea out of my head!!!! This time Arrma Typhon/Senton 6s based.
First a little lesson on ground effect and what makes this car work.
In very basic terms ground effect is the interaction of a wing and its related airflow near the ground. Most college level documentation you will find on ground effect relates to airplane use and many over the water (so they can get close to the ground plane without crashing)
Borrowing this explanation from Wiki Ground effect (aerodynamics) - Wikipedia
A wing generates lift by deflecting the oncoming airmass (relative wind) downward. The deflected or "turned" flow of air creates a resultant force on the wing in the opposite direction (Newton's 3rd law). The resultant force is identified as lift. Flying close to a surface increases air pressure on the lower wing surface, nicknamed the "ram" or "cushion" effect, and thereby improves the aircraft lift-to-drag ratio. The lower/nearer the wing is with regards to the ground, the more pronounced the ground effect becomes. While in the ground effect, the wing requires a lower angle of attack to produce the same amount of lift.
The other thing that normally occurs on a wing is that high and low-pressure zones mix. This is often referred to as wing tip vortices. The ground partially blocks those vortices normal circular travel and allows the wing to be more efficient. More on this later related to my car design…
In the case of a car we use an airfoil that is flipped upside down to instead accelerate the airflow under creating a low pressure zone which generates negative lift or downforce. The diffuser does much of this function on our RC cars.
Most people who research automotive applications will come across Colling Chapmans application from the golden era of Formula 1 in the late 70’s and early 80’s. His design had an air channel under the car, but with the addition of floating side skirts that sealed to the ground. This created a powerful venturi under the car that would suck it to the ground. The seal kept the high and low-pressure zones from interacting with each other. The cars were going faster than ever, and his cars won!
Like all things there are some drawbacks. Racing drivers have a racing line through the turns that takes them across the rumble strips/curbs on the racetracks. As the car would hit those and raise on one side the skirt’s seal was broken (low-pressure zone under the car is lost and mixed with outside high-pressure zones), and in some cases the car would lose it’s downforce and go wildly off the track. It was not long before racing governing bodies banned the technology/idea.
Fast forward to today, 2022 rules for Formula 1 are allowing them to utilize ground effect again!!! This decision was made as the air is less disturbed for the following car with ground effects than if they generate their downforce via a large rear wing or other top side mounted aero devices. Thus, making it safer for the trailing cars in less turbulent airflow. Thanks to advanced airflow simulation and computer analysis aerodynamics engineers can create the sealed sides with purposely created vortices. (Not using skirts that touch the ground like the 1978-1982 cars). It is very clear all the F1 teams raised their front wings for 2022 designs in order to let more air pass through to the center section of the car where the ground effect takes place.
Another example of this being done with JGTC race cars. Notice the raised center section of the front splitter? They are purposely driving air under the car for ground effect.
Now moving on to applying this to an RC car.
One of the things most people struggle to wrap their heads around is that RC cars are scaled size, but nothing else is scaled down. The air molecules are the same. This means that the minimum clearance to the ground applies to the RC car as it would a real car or airplane. This is where the design gets interesting!
It was difficult to find solid data on airfoils near the ground, but I was able to find some general data related to the chord length of an airfoil in relation to the ground. Essentially what I found is that I need the airfoil chord to be as short as possible as the longer chord would require a higher distance off the ground. I wanted to use strong 6s parts in the build. This meant a 1/8 Typhon type of wheelbase instead of using a 1/7 long wheelbase like the Limitless!
College groups did some high quality wind tunnel tests collecting data points and both that I had found net the same conclusions.
As the H/C or height to cord length reaches to the far right the negative lift is lost. (Simplified if the wing is too far from the ground it will have reduced downforce). Too far to the left (close to the ground) and the negative lift or downforce can be lost if beyond 0.1 ratio and the downforce may stall and create extreme drag. In all I found the sweet spot looked to be around 0.15 – 0.2 which was my target height and chord length range.
Another study with similar data
I played with the wheelbase of a Typhon and looked at what extra length the airfoil would have to have a nice diffuser/pointed tail. I was coming up with something around 540mm for the airfoil. I’ll attempt to package the front leading edge a little smaller.
This meant that I would need a height somewhere around 80 mm to 100mm off the ground to be in that ideal sweet spot I was looking for with the H/C ratio of around 0.15 to 0.2
Given GRP tires are around 98mm diameter and BSR foams at full height are around 103mm I was going to need something different or a unique car design!
Thanks to Losi and the 5ive B model I had an option for a flat faced 140mm wheel. (plus foam of 5mm I could be looking at a final diameter of 150mm)
GRP tires in front for size comparison:
This would provide me the extra height needed to get the ground clearance where I need it. (or at least close to it)
The wheels will be cut down to a 40mm width to match the 1/8 scale BSR’s as I don’t need the full width. I’ll be reaching out to Gone Bananas soon to get them “skinned”.
These wheels are 24mm hex, so I have ordered from Just Bash it RC the Arrma 6s adapter for 24mm hex wheels.
I had mentioned before how wing tip vortices can cause issues. This design is much like a catamaran boat and will nearly eliminate those issues as the side pontoons containing the wheels and batteries will block/seal the sides. The design is in its early stages and needs lots of revision. I want to get most of the parts on the chassis and confirm dimensions before doing a final form of the body. It will be modular/ bolt on as I’ll need access to the sides where the batteries go and the top center where the rest of the guts live.
Steering angle is limited to around 10 degrees much like any of my streamliner bodies:
Same as above with some color added to help you see how a final version might look. The images make it look small, but it will actually be a tall car. It is pretty easy to see how this design would slice through the air very nicely!
I cannot wait to see how the car works as the ground effect should create excellent downforce and reduce drag at the same time. In theory this car should work very well!!!!!!!!!!!!!
If you wondered how I come up with these crazy ideas. This one was semi borrowed. It has not been done in a high-speed application before. College solar car teams use this design with some lift in their design to attempt a neutral lift/drag for top efficiencies. This layout is the most efficient aerodynamically in a square 4-wheel configuration. (Obviously most land speed cars are often shaped like a rocket and would be more efficient like my 200+ project.)
Assembly began yesterday!
Just Bash it 24mm hex with 24mm hex nut setup with Arrma wheel nuts on there.
These are +10mm so I used Senton 6s arms and CVDs all around to help bring the width back in.
Initial mock up, still need some links to lock the suspension in the place I want it.
I also still need to trim the wheels width down to 40mm as they are way too big in full size:
I have one more project in me. I had said the 200+ build was my last one, but I have this one last car that I cannot get out of my head. It will be Typhon 6s / Senton 6s based.
This is a bit of a long read and parts may not make sense unless you read all of it. Bear with me here as this is 5 years of mind dump LOL. (Don't worry there are lots of colorful pictures and shiny things)
About 5 years ago I had started on a high-speed build that required some advanced aerodynamics using ground effect. Here is an image of that Slash 4x4 when I was attempting to build it. Ultimately, I gave up due to the body construction challenges, and concerns about ride height.
I struggled to make the body work by sculpting it out of foam and plaster. I decided to scrap the project. Fast forward to today with easy access to 3D printers and CAD design, and new 1/5 scale parts, now I am finally ready to finish up this project and get the idea out of my head!!!! This time Arrma Typhon/Senton 6s based.
First a little lesson on ground effect and what makes this car work.
In very basic terms ground effect is the interaction of a wing and its related airflow near the ground. Most college level documentation you will find on ground effect relates to airplane use and many over the water (so they can get close to the ground plane without crashing)
Borrowing this explanation from Wiki Ground effect (aerodynamics) - Wikipedia
A wing generates lift by deflecting the oncoming airmass (relative wind) downward. The deflected or "turned" flow of air creates a resultant force on the wing in the opposite direction (Newton's 3rd law). The resultant force is identified as lift. Flying close to a surface increases air pressure on the lower wing surface, nicknamed the "ram" or "cushion" effect, and thereby improves the aircraft lift-to-drag ratio. The lower/nearer the wing is with regards to the ground, the more pronounced the ground effect becomes. While in the ground effect, the wing requires a lower angle of attack to produce the same amount of lift.
The other thing that normally occurs on a wing is that high and low-pressure zones mix. This is often referred to as wing tip vortices. The ground partially blocks those vortices normal circular travel and allows the wing to be more efficient. More on this later related to my car design…
In the case of a car we use an airfoil that is flipped upside down to instead accelerate the airflow under creating a low pressure zone which generates negative lift or downforce. The diffuser does much of this function on our RC cars.
Most people who research automotive applications will come across Colling Chapmans application from the golden era of Formula 1 in the late 70’s and early 80’s. His design had an air channel under the car, but with the addition of floating side skirts that sealed to the ground. This created a powerful venturi under the car that would suck it to the ground. The seal kept the high and low-pressure zones from interacting with each other. The cars were going faster than ever, and his cars won!
Like all things there are some drawbacks. Racing drivers have a racing line through the turns that takes them across the rumble strips/curbs on the racetracks. As the car would hit those and raise on one side the skirt’s seal was broken (low-pressure zone under the car is lost and mixed with outside high-pressure zones), and in some cases the car would lose it’s downforce and go wildly off the track. It was not long before racing governing bodies banned the technology/idea.
Fast forward to today, 2022 rules for Formula 1 are allowing them to utilize ground effect again!!! This decision was made as the air is less disturbed for the following car with ground effects than if they generate their downforce via a large rear wing or other top side mounted aero devices. Thus, making it safer for the trailing cars in less turbulent airflow. Thanks to advanced airflow simulation and computer analysis aerodynamics engineers can create the sealed sides with purposely created vortices. (Not using skirts that touch the ground like the 1978-1982 cars). It is very clear all the F1 teams raised their front wings for 2022 designs in order to let more air pass through to the center section of the car where the ground effect takes place.
Another example of this being done with JGTC race cars. Notice the raised center section of the front splitter? They are purposely driving air under the car for ground effect.
Now moving on to applying this to an RC car.
One of the things most people struggle to wrap their heads around is that RC cars are scaled size, but nothing else is scaled down. The air molecules are the same. This means that the minimum clearance to the ground applies to the RC car as it would a real car or airplane. This is where the design gets interesting!
It was difficult to find solid data on airfoils near the ground, but I was able to find some general data related to the chord length of an airfoil in relation to the ground. Essentially what I found is that I need the airfoil chord to be as short as possible as the longer chord would require a higher distance off the ground. I wanted to use strong 6s parts in the build. This meant a 1/8 Typhon type of wheelbase instead of using a 1/7 long wheelbase like the Limitless!
College groups did some high quality wind tunnel tests collecting data points and both that I had found net the same conclusions.
As the H/C or height to cord length reaches to the far right the negative lift is lost. (Simplified if the wing is too far from the ground it will have reduced downforce). Too far to the left (close to the ground) and the negative lift or downforce can be lost if beyond 0.1 ratio and the downforce may stall and create extreme drag. In all I found the sweet spot looked to be around 0.15 – 0.2 which was my target height and chord length range.
Another study with similar data
I played with the wheelbase of a Typhon and looked at what extra length the airfoil would have to have a nice diffuser/pointed tail. I was coming up with something around 540mm for the airfoil. I’ll attempt to package the front leading edge a little smaller.
This meant that I would need a height somewhere around 80 mm to 100mm off the ground to be in that ideal sweet spot I was looking for with the H/C ratio of around 0.15 to 0.2
Given GRP tires are around 98mm diameter and BSR foams at full height are around 103mm I was going to need something different or a unique car design!
Thanks to Losi and the 5ive B model I had an option for a flat faced 140mm wheel. (plus foam of 5mm I could be looking at a final diameter of 150mm)
GRP tires in front for size comparison:
This would provide me the extra height needed to get the ground clearance where I need it. (or at least close to it)
The wheels will be cut down to a 40mm width to match the 1/8 scale BSR’s as I don’t need the full width. I’ll be reaching out to Gone Bananas soon to get them “skinned”.
These wheels are 24mm hex, so I have ordered from Just Bash it RC the Arrma 6s adapter for 24mm hex wheels.
I had mentioned before how wing tip vortices can cause issues. This design is much like a catamaran boat and will nearly eliminate those issues as the side pontoons containing the wheels and batteries will block/seal the sides. The design is in its early stages and needs lots of revision. I want to get most of the parts on the chassis and confirm dimensions before doing a final form of the body. It will be modular/ bolt on as I’ll need access to the sides where the batteries go and the top center where the rest of the guts live.
Steering angle is limited to around 10 degrees much like any of my streamliner bodies:
Same as above with some color added to help you see how a final version might look. The images make it look small, but it will actually be a tall car. It is pretty easy to see how this design would slice through the air very nicely!
I cannot wait to see how the car works as the ground effect should create excellent downforce and reduce drag at the same time. In theory this car should work very well!!!!!!!!!!!!!
If you wondered how I come up with these crazy ideas. This one was semi borrowed. It has not been done in a high-speed application before. College solar car teams use this design with some lift in their design to attempt a neutral lift/drag for top efficiencies. This layout is the most efficient aerodynamically in a square 4-wheel configuration. (Obviously most land speed cars are often shaped like a rocket and would be more efficient like my 200+ project.)
Assembly began yesterday!
Just Bash it 24mm hex with 24mm hex nut setup with Arrma wheel nuts on there.
These are +10mm so I used Senton 6s arms and CVDs all around to help bring the width back in.
Initial mock up, still need some links to lock the suspension in the place I want it.
I also still need to trim the wheels width down to 40mm as they are way too big in full size:
Last edited:
