On mass and aerodynamics

Is there a trade off between mass and aerodynamics? A streamlined velomobile may reach a higher speed at the same power input because of the decreased aerodynamic drag but the fairing adds extra mass to the vehicle. Is there a speed penalty in adding mass? The rolling resistance of the wheels will increases but also the time and energy needed to accelerate the vehicle. While setting a new hour record only the first minutes are used for increasing the speed. But in normal every day traffic we may have to stop every km...
I calculated the total trip time for a 5 km trip and varied the number of starts. In the next diagram you find the total trip time and the maximum speed for different vehicles. The coefficient of rolling resistance was held constant at 0.005. The QuestSL is a Quest with the mass of an MTB. For the calculation of the plywood velomobile I estimated the effective area to be equal to that of the Versatile. The mass of the Plywood Velomobile was very optimistic chosen to be 18 kg (The current proto is 23 kg).

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I assumed a cyclist that delivers 75 W power. At that level the MTB would reach ~20 km/h which is more that the most of us do... We can conclude that at 7 starts in 5 km the Quest and the Plywood Velomobile perform equal. The mass reduction compensates for the compromised aerodynamic quality. At an increased cyclist power the break even point moves to the right. 7 starts in a 5 km trip is quite high but not unrealistic for an urban trip. 

All in all we can conclude the most apparent difference exists between the MTB and the other vehicles. The differences between the velomobiles are small. It would be interesting to see what happens when a small slope is taken into account. Another interesting thing is recuperative breaking and start assist.

On second thougth: After a 5 km trip in a Quest with one start only the total work done is 48.2 kJ. The Quest reaches a maximal speed of ~42 km/h after 3.5 minutes. The kinetic energy of the vehicle and rider at 42 km/h is ~7 kJ. Now it becomes very clear what happens when we have to stop and accelerate again: we loose the kinetic energy of 7 kJ which is 7/48=15 % of the energy needed with one start only. Would we have to stop 7 times our energy usage more than doubles ! The MTB uses 104 kJ for the 5 km trip with one start only.  His kinetic energy reaches 2 kJ only (2/104= ~ 2%). An extra stop doesn't bother him to much... 
Depending on the number of starts in our trip, recuperative breaking and start assist would give a significant increase in performance of the Quest...

Remark: decreasing the mass of the velomobile is not helping much as it is dominated by de rider.