written up on http://www.recumbents.com/mars/pages/proj/tetz/TFVM/TFVMp1.html
by John Tetz
I built the trike in 2004 which was my first trike project and I learned a lot. The shell for the Velomobile was built early 2005 (both were designed together – a must). I wrote some first impressions after completing it. This is a write up of new impressions now that I have around 3,000 miles of trike/VM riding.
Trike View
written up on http://www.recumbents.com/mars/pages/proj/tetz/TFVM/TFVMp1.html
Foamshell VM
written up on http://www.recumbents.com/mars/pages/proj/tetz/manual/0intro.html
NEW IMPRESSIONS:
Noise - I originally said the Foamshell is very quiet, and there is no need to change this statement. I have gone to two Velomobile events in North America - September and October 2006. At each, several people rode my VM. The first impression reported after coming back from a short ride was the utter quietness inside the vehicle - practically no drive train noise – and only a slight rumble from road noise. The sound from the tires is a wind up sound as speed increases. I have been told it’s stealthy quieter than even unfaired bikes as it passes by.
Size of vehicle - I originally felt the vehicle to be huge and fat (in relationship to a narrow streamliners and unfaired vehicles).
Since then I have gotten used to its size. It’s actually smaller overall than many other Velomobiles, and is designed to fit inside my 1989 Honda Civic. It also has to fit on my porch where I park it.
I have come to find the extra room inside is quite nice. Getting into a narrow streamliner now seems very tight and confining (but the advantage is, it really does fly).
I wrote that the trike takes up more room on the road so slinking between cars and a curb can’t be done. I have learned that I can squeeze thru tight spaces more readily then I really thought I could.
As fat as this vehicle seems, the tail end is relatively narrow. It’s narrow because of the tail contraction giving decent aerodynamics. What this means is there is less room for the cargo. And because a cargo load cannot be hung directly on the shell I use a luggage rack to hang the panniers (typical bike principle) and to support the tail. Here the turtle deck behind the rider's head is opened showing the carbon luggage rack and tail support.
Getting the panniers in/out is a little tight, particularly when they are fat with cargo. Sometimes I have to remove a part of the cargo, then inset the panniers in the vehicle and place the cargo back in. However a large percentage of my cargo is simply tossed into a simple foam carrier. Because I ride essentially every day mainly to run errands I do not need large cargo capacity.
Here is a view of the white carrier (Zote foam of course).
Slower speed - I originally complained that it took more rider effort than a streamliner (however much less than an unfaired vehicle). The CdA on the VM is around 1.3 sq ft while the streamliner is around 0.73 That’s a 3 mph difference at around 20 mph. The extra effort (or less speed) over a streamliner is true, but I find the VM so comfortable that I don’t care as much about the extra effort required (as long as it’s only a reasonable increase).
I originally said a Trike/VM is wonderful at busy intersections. I have gotten to really truly appreciate this advantage. I find I will more often take the Trike/VM up town to run errands because it’s so relaxing.
The tension at intersections in a streamliner is very noticeable and becomes annoying. When I have been riding the trike/velomobile for weeks at a time and then get on a bike I notice I wiggle a bit for awhile. A bike actually takes effort to balance which goes un-noticed after you have been riding it for some time. But the effort is there all of the time.
I also had made a statement that the rolling resistance of trikes seem to be much higher than bikes. That was totally wrong. I bought a small datalogger from Kit Wolf from the UK which seriously improved my data taking ability for coastdown measurements. It turns out that for a series of reasons my toe settings on the front end was off. My longer than normal trike cross tube was bending more that I realized resulting in toe out with rider weight. By setting up more correct tie rod angles this weight induced error can be reduced to where toe change is minimal. I also wrapped some carbon on top of the steel to reduce bending.
I found this error by making Toe vs Crr measurements and was able to make the optimum setting. It turns out the Crr on a trike is similar to bikes. Whew! <BR>
Note how steep the toe-out curve is vs how much slower the toe-in changes. This suggests that the toe settings should be biased towards toe-in to be on the safe side.
I talked about how the VM got blown around in crosswinds. I believe a good part of that problem was the error in toe settings. The toe was more out than toe-in at the time. Not good for stability. By making the corrections mentioned above the crosswind stability improved dramatically. That sort of high turtle deck behind the rider’s head helps counteract the nose being pushed around.
I also believe the direct above seat handlebars have a lot to do with the feeling of stability. Tiny micro adjustments can be instantly made with the fingers for directional control. I can feel crosswinds tugging on the handlebars and make almost effortless instant corrections for directional control. Without wind the vehicle tracks exactly where I want it. Rider comments I have received is extremely favorable. Solid, predictable, dial right in, a highlight of the vehicle.
I have come to love the above seat handle bars even more as I used them. My out-stretched arms feel more natural - easier to make those micro adjustments with the fingers. There is no alternate left right steering from the weight of the legs rotating when pedaling at all – the arms could be acting like a damper. And on an unfaired trike those out stretched arms also give a lower CdA over under seat steering due to the reduced frontal area. CdA measurements I have made give 2.8 sq ft for my trike vs 3.5 for typical under seat steering trikes. That’s a 1 mph difference around 15 mph.
It’s easier to walk along side the trike/VM to both control and push it along. On one occasion the jockey pulley machine screw backed out and I lost the pulley. I easily walked up the hills by pushing on the handlebars and coasted down the hills. I got close to home before a friend picked me up.
The vehicle is easier to lift by grabbing the handlebar and the hand hold at the back of the seat (of course it has to be light enough to do that - it weighs 43 pounds). I find there are many times I have to lift the vehicle up over curbs to park it in front of a store or to turn it 180 degrees around again to head off in another direction. I pick it up and spin it around. I seem to do this a lot.
At these VM meetings there were quite a wide range of riders trying out my VM. Getting in just about all the VMs require some amount of contortions including mine. Getting the feet up and over the cross bar on my VM was clumsy for some – and simple for most. The riders with larger diameter legs had more trouble. Long legged riders had no problem. I can easily move the BB to give reasonable leg length adjustment. Clearance to the handlebars was surprisingly less of a problem even for the long legged. The handlebars can be adjusted up and down a small amount for fine tuning. I need to come up with a way to adjust for different arm lengths.
Many of these initial feelings of cramped quarters go away after a few weeks. The muscles' memory takes over and you seem to have plenty of room. Tighter clearances can give better aerodynamics resulting in less wear and tear on the legs, lugs and heart of the rider over the years they will be riding it.
When riders came back from a test ride in my VM they have big grins and immediately say this thing moves !! They are amazed how it jumps when they push on the pedals. Acceleration of a weighty vehicle costs the rider dearly – and acceleration occurs over and over during a ride.
Very few people have actually have had the experience of a truly light weight, aerodynamic vehicle so when they experience one this becomes a brand new thrill. I could not let inexperienced people try my streamliners. They are more like flying an airplane, but with the VM just about anyone can ride it and feel the thrill.
Here is an aerodynamic foil view. Fat but clean lines particularly for the forward section. The rather blunt nose is designed to reduce nose overhang and to allow a fair amount of cross wind angle without creating detachment on the lee side.
But speed with a trike/VM is more nerve-wracking on hard cornering. Although I have gotten more used to the limits of cornering I still feel much more concerned in a VM than I do on a bike or streamliner. If you do go over it’s a high sider – not nice. The lightness of the Foamshell helps by not raising the Cg.
Some experimental VMs have very large frontal areas and poor if any foil shape along the sides resulting in very poor air foil flow. And lots of disturbed air up front from various peturbances. Given that average humans can only put out 75 to 100 watts these vehicles wear out the rider unless they go very slowly. However I did ride one in the rain in my street clothes and it was very cozy inside. Hmmmm, maybe I need to investigate an enclosed vehicle.
This is an example of the design compromises one is faced with. I have chosen head out to get a lighter vehicle, better aerodynamics, and to be able to hear traffic. If it rains a lot I use my car which sits in the driveway weeks at a time. No one human powered vehicle design can handle all requirements. My trike can be taken out of the shell in a relatively short period of time and used as an unfaired vehicle which I run thru most of the summer. I like the simplicity and the open air feeling of an unfaired vehicle. And when you put it back in the shell the increase in speed along with low effort restores the thrill of shelled vehicles.
I have yet to add a head light, LED push button directionals and three NACA ducts for cooling. Two for the hand area and one in front of the windshield. The effect of the foot holes behind the cross tube is there’s not much air coming up into the cockpit. This keeps that bottom air cleaner longer and keeps the turbulent layers from growing, lowering drag but a new problem in terms of getting adequate cooling.
When climbing long hills I flip the canopy open to get more air. My windshield is removable but I would like to come up with a windshield that can be moved down during the ride to get more head cooling. The rest of the time I like having a windshield. – particularly in the cold. That windshield needs to be narrow enough to see around it when it gets too fogged.
In terms of ride quality, a bike essentially has one track that can sneak thru a small slot. A trike has three tracks – you’re bound to hit those bumps. Plus trikes will shake left/right as each wheel hits various bumps. And because of their lightness a foamshell will shake left/right (streamliners do not shake left/right ). This shaking gives the impression the bumps are worse. A front suspension is a must in terms of reducing this shake (not needed on a unfaired trike).
Conclusion:
The fact that average humans can only produce 75 to 100 watts is what drives my designs. I built the VM based on what I have learned from years of streamliner experience. It’s quite obviously seen in my VM.
I have always been attracted to the concept of small and light weight and minimalism. Another factor is my work shop is on the second floor, up a rather steep narrow stair case so the vehicles have to be small and light, and come apart in sections. Also I’m at an age where I cannot put out lots of power.
The HPV community is doing wonderful pioneer work in developing alternate transportation vehicles.
This is one solution to our VM exploration, an exciting one, but is not necessary the answer for all needs.
John Tetz