LightShip Systems Review - Aerodynamic Enhancement System

[Rory (Lightship Team)]

Any available info (or informed estimates) on how the drag of the Lightship compares to Bowlus trailers?

www.bowlus.com

Hi Josh - curious the feedback of others with real world experience. @turbopilot ? I can reach out to a contact I have who is considering a swap to a Lightship.

From our engineering teams here, the key differentiating features:
- blunt shape at front of bowlus is not as good at reattaching the air coming off the tow vehicle (compared to tapered like lightship)
- frontal area is much bigger than lightship
- camm tail shape (lightship) is better than wedge to detach air cleanly

we have some estimates here internally at the difference in drag, but wouldn't want to share those publicly as not validated/proven.

 

[turbopilot]

Hi Josh - curious the feedback of others with real world experience. @turbopilot ?

I have no experience with the Bowlus. But given LightShip has a very refined force sensor (on the hitch of the LightShip) and associated hardware/software, there is no reason a "Portable Force Sensor" could not be easily fabricated and placed between the tow vehicle and any brand of trailer for a tow test. The force sensor can read the force necessary to pull the trailer (in Newtons). Once you have the force required to pull the trailer you can back into the hardest number to calculate without a wind tunnel: the Coefficient of Drag.

So there is no reason LightShip could not easily calculate the Coefficient of Drag for every make and model towable RV on the market with very little effort. Could even offer a service to anyone with some other brand of towable to come to the factory and get your Coefficient of Drag measured (along with a sales pitch )

The drag equation is simple to calculate once you know the Coefficient of Drag for a trailer.

The drag force (F_d) is calculated using the standard aerodynamic drag equation:F_d = ½ × ρ × v² × C_d × AWhere:

• ρ = air density
• v = velocity
• C_d = coefficient of drag
• A = frontal area

I also think it would make sense to display the real time force measurements from the force sensor on the LightShip in tow on the Atlas tablet. There are so many variables impacting drag force (speed, wind, cross wind angle, temperature, altitude, tire pressure, rain, snow etc), displaying the force actually experienced in real time, at the hitch, towing a LightShip would be valuable information for the driver because that directly impacts range.

 

[Holdmybeer]

In conclusion Gemini AI's verdict is the Lighship totally wins on total drag force at hwy speeds because its lower frontal area displaces less air at hwy speeds.
However, the Bowlus likely has a lower pure drag coefficient because its permanent fixed shape is more purely raindrop and lacks the mechanical seams of a telescoping roof. Furthermore, the boat tail design of the Bowlus is more aggressive than the tail design of the Lightship at minimizing drag at hwy speeds
* Lighship's stated goal was to achieve a drag coefficient comparable to a Tesla model 3 which is ~0.23, however this is an aspirational benchmark rather than a confirmed figure for the trailer itself.

 

[turbopilot]

Lighship's stated goal was to achieve a drag coefficient comparable to a Tesla model 3 which is ~0.23, however this is an aspirational benchmark rather than a confirmed figure for the trailer itself.

Your premise is wrong. No such claim was made by LightShip. The claim is that the output of the drag equation, in newtons, is the same for a LightShip in tow and a Tesla Model 3 rolling down the highway at 62 MPH. Obviously the coefficient of drag and the cross sectional flat plate area of the Model 3 and LightShip are different.

But all this has been proven empirically, not by wind tunnel tests. The towing tests have repeatedly confirmed that the LightShip requires 250 watts per mile delivered to the trailer wheels by the electric motor, at highway speeds, in tow, to cancel forces measured at the force sensor on the hitch. This is exactly the same power needed to propel the Tesla Model 3 down the highway. So the output of the drag equation has to be the same for the Tesla Model 3 and LightShip. The key variables in that equation are frontal area and drag coefficient which are obviously different between the LightShip and the Tesla Model 3. But the output of the equation (in Newtons) has to be the same, ie 250 watts required for every mile.

But the bottom line is that the same amount of energy is required to move a Model 3 and a LightShip (in tow behind a tow vehicle) down the road at 62 MPH.

As to the Bowlus, a rough comparison could quickly be made by towing a Bowlus (or any conventional towable RV) with an EV tow vehicle. Take the EV tow vehicle over a measured course alone without towing and determine the watts per mile consumed. Then immediately tow the Bowlus over the same course and get the kilowatts consumed. Then convert the difference into watts per mile for each situation.

This has been done by several owners of the Pebble Flow EV trailer which has an aerodynamic shape but high frontal area. The reports I have seen suggest the Pebble Flow requires watts per mile somewhere between the LightShip and an Airstream. I suspect it would be close to the same power consumption required by the Bowlus.

 

[Holdmybeer]

Your premise is wrong. No such claim was made by LightShip. The claim is that the output of the drag equation, in newtons, is the same for a LightShip in tow and a Tesla Model 3 rolling down the highway at 62 MPH. Obviously the coefficient of drag and the cross sectional flat plate area of the Model 3 and LightShip are different.

But all this has been proven empirically, not by wind tunnel tests. The towing tests have repeatedly confirmed that the LightShip requires 250 watts per mile delivered to the trailer wheels by the electric motor, at highway speeds, in tow, to cancel forces measured at the force sensor on the hitch. This is exactly the same power needed to propel the Tesla Model 3 down the highway. So the output of the drag equation has to be the same for the Tesla Model 3 and LightShip. The key variables in that equation are frontal area and drag coefficient which are obviously different between the LightShip and the Tesla Model 3. But the output of the equation (in Newtons) has to be the same, ie 250 watts required for every mile.

But the bottom line is that the same amount of energy is required to move a Model 3 and a LightShip (in tow behind a tow vehicle) down the road at 62 MPH.

As to the Bowlus, a rough comparison could quickly be made by towing a Bowlus (or any conventional towable RV) with an EV tow vehicle. Take the EV tow vehicle over a measured course alone without towing and determine the watts per mile consumed. Then immediately tow the Bowlus over the same course and get the kilowatts consumed. Then convert the difference into watts per mile for each situation.

This has been done by several owners of the Pebble Flow EV trailer which has an aerodynamic shape but high frontal area. The reports I have seen suggest the Pebble Flow requires watts per mile somewhere between the LightShip and an Airstream. I suspect it would be close to the same power consumption required by the Bowlus.

It’s not a premise and Ben Parker said it at SxSW. He didn’t say it has the same coefficient of drag as the Tesla or that it would but that it is the aspirational goal as is in your reach should exceed your grasp. In 2023, however he did say that in computational fluid dynamics simulations the L1 was at the same 0.23 coefficient as the Tesla model 3.

 

[turbopilot]

In 2023, however he did say that in computational fluid dynamics simulations the L1 was at the same 0.23 coefficient as the Tesla model 3.

The trouble with this issue of a constant like the Coefficient of Drag is that there are really two different trailer CD's. One CD is the computed value in a wind tunnel in free air for the LightShip (or any trailer). Of course this CD is entirely fictional since a trailer cannot move at highway speeds in free air because it has to be towed.

The second CD for a trailer is the calculated value when the trailer is running in the wake of a tow vehicle, because the tow vehicle is now enhancing the aerodynamics of the trailer plowing through the air. And to complicate it more that "towed CD" will be different for every tow vehicle type pulling a LightShip.

This whole analogy was started to demonstrate that a LightShip behind a pickup tow vehicle required the same amount of additional energy from that tow vehicle as did a Tesla Model 3 moving in free air. And that was without TrekDrive ON. With the electric motor engaged it delivered just enough energy to cancel that 250 watt per mile demand on the tow vehicle, returning the tow vehicle to the same efficiency as it had not towing at the expense of the electricity needed by the LightShip.

So the computational fluid dynamics simulation back in 2023 is interesting but that was all done when LightShip was a concept, not a reality actually being towed on the highway. Now we know with actual towed data that the simulations were near perfect in terms of the predicting outcome, the energy required to move the LightShip behind a tow vehicle. The individual variables leading to finding are complicated and not directly comparable.

 

[Holdmybeer]

Any available info (or informed estimates) on how the drag of the Lightship compares to Bowlus trailers?

www.bowlus.com

In other words, no.