Questions about velomobile design
I'm chipping away at developing a velomobile design. Some understanding of applied aerodynamics for aircraft with near zero flow separation helps (sailplanes). Lack of skills and resources to formally model such separated flows with CFD, as applied to velomobiles...this held me back...maybe we can discuss on the Applied Aero... or CFD flow modeling for velo... threads.
For the other design/engineering issues I am a bit unfamiliar with bicycle design and there are no velomobiles available to interrogate/reverse engineer. So there are several questions, if anyone has thoughts.
1) Suspension/steering geometry.
- Camber
- Caster
- King pin inclination
- Toe in/out.
Are there common opinions about ideal geometry for velomobiles?
At looks like there are some similar values. The strut drawing that velomobeil.nl sent me, the axel looks to be angled up at 4deg. A lot of velo' photos show what looks like vertical struts and camber of -4deg.
If that strut is vertical, drawing a line from the top pivot down to the bottom pivot on the steering plate, looks like kingpin inclination is 5deg and caster is about 4deg.
The proximity to the wheel means that bottom pivot point can't shift much (dy) to increase kingpin inclination. The strut could be angled inwards at the top if the cost in cockpit width was acceptable. The castor does look it could be increased by shifting the pivot point forward, but I ignoring for now the kinematics of the system which includes the front linkage.
So are there opinions on ideal geometry? Caster and king pin inclination are much less than on a tadpole trike. Any opinions about that?
There are a couple of variations in strut design with different axel inclinations..that I know of. I assumed there might be more. Does anyone know what those variations are..? (length, axel position, axel angle, angle of steering plate mount area).
If we get past these ones we can look at Akerman angle and scrub angle....
A while ago I found a summary of the geometry ideas for velomobiles by an engineer at a symposium some years ago, but now cannot find it.....
2) Structural load cases for velomobiles...
Can anyone share a list of load cases and some ideas on the methodologies used? Applying loads to some of the complex composite shapes I can do, but I am starting from scratch on load cases.
I had a quick look and found some sources for references for bicycle load cases......
An Assessment of Bicycle Frame Behavior under Various Load Conditions Using Numerical Simulations
Derek Covilla,*, Philippe Allardb, Jean-Marc Drouetb, Nicholas Emerson
It's on ScienceDirect.com. Google the title, the link was huge, sorry.
One or two of their references may be useful.
INTERNATIONAL STANDARD ISO 4210-6
Cycles — Safety requirements for bicycles —
Part 6: Frame and fork test methods
One can also make/find a short list of critical load cases, rather than doing every single possible load case.
3) What are typical Q values in velomobiles?
4) Are velomobiles sensitive to pitch oscillations (squat/anti squat) from the pedal forces (pedal bob)? Do designers sometimes add an extra idler pulley to align the chain to the swingarm hinge point?
5) What are typical body shell GRP/CRP laminate stacks? The overall laminate, not at the locally reinforced areas.
6) Are velos with sandwich core quieter (urethane, klegecell/Devinicell/honeycomb)
7) What size rear wheel do most Evo-Rs have? How is it removed? I had a plan for the wheel to be removable to the front, which needed the swingarm to be morphed so the wheel fitted over it. But I'm thinking it might be easier to remove the swingarm with wheel.
8) Are there some long cage derailleurs that take up less space sideways ( Y axis)? Available space is limited for me and I do not have a flat floor running the length of the body. Maybe I can discuss the body in the applied aero thread.
More later...
Gregg
I'm chipping away at developing a velomobile design. Some understanding of applied aerodynamics for aircraft with near zero flow separation helps (sailplanes). Lack of skills and resources to formally model such separated flows with CFD, as applied to velomobiles...this held me back...maybe we can discuss on the Applied Aero... or CFD flow modeling for velo... threads.
For the other design/engineering issues I am a bit unfamiliar with bicycle design and there are no velomobiles available to interrogate/reverse engineer. So there are several questions, if anyone has thoughts.
1) Suspension/steering geometry.
- Camber
- Caster
- King pin inclination
- Toe in/out.
Are there common opinions about ideal geometry for velomobiles?
At looks like there are some similar values. The strut drawing that velomobeil.nl sent me, the axel looks to be angled up at 4deg. A lot of velo' photos show what looks like vertical struts and camber of -4deg.
If that strut is vertical, drawing a line from the top pivot down to the bottom pivot on the steering plate, looks like kingpin inclination is 5deg and caster is about 4deg.
The proximity to the wheel means that bottom pivot point can't shift much (dy) to increase kingpin inclination. The strut could be angled inwards at the top if the cost in cockpit width was acceptable. The castor does look it could be increased by shifting the pivot point forward, but I ignoring for now the kinematics of the system which includes the front linkage.
So are there opinions on ideal geometry? Caster and king pin inclination are much less than on a tadpole trike. Any opinions about that?
There are a couple of variations in strut design with different axel inclinations..that I know of. I assumed there might be more. Does anyone know what those variations are..? (length, axel position, axel angle, angle of steering plate mount area).
If we get past these ones we can look at Akerman angle and scrub angle....
A while ago I found a summary of the geometry ideas for velomobiles by an engineer at a symposium some years ago, but now cannot find it.....
2) Structural load cases for velomobiles...
Can anyone share a list of load cases and some ideas on the methodologies used? Applying loads to some of the complex composite shapes I can do, but I am starting from scratch on load cases.
I had a quick look and found some sources for references for bicycle load cases......
An Assessment of Bicycle Frame Behavior under Various Load Conditions Using Numerical Simulations
Derek Covilla,*, Philippe Allardb, Jean-Marc Drouetb, Nicholas Emerson
It's on ScienceDirect.com. Google the title, the link was huge, sorry.
One or two of their references may be useful.
INTERNATIONAL STANDARD ISO 4210-6
Cycles — Safety requirements for bicycles —
Part 6: Frame and fork test methods
One can also make/find a short list of critical load cases, rather than doing every single possible load case.
3) What are typical Q values in velomobiles?
4) Are velomobiles sensitive to pitch oscillations (squat/anti squat) from the pedal forces (pedal bob)? Do designers sometimes add an extra idler pulley to align the chain to the swingarm hinge point?
5) What are typical body shell GRP/CRP laminate stacks? The overall laminate, not at the locally reinforced areas.
6) Are velos with sandwich core quieter (urethane, klegecell/Devinicell/honeycomb)
7) What size rear wheel do most Evo-Rs have? How is it removed? I had a plan for the wheel to be removable to the front, which needed the swingarm to be morphed so the wheel fitted over it. But I'm thinking it might be easier to remove the swingarm with wheel.
8) Are there some long cage derailleurs that take up less space sideways ( Y axis)? Available space is limited for me and I do not have a flat floor running the length of the body. Maybe I can discuss the body in the applied aero thread.
More later...
Gregg