Just to hang there, it takes half
Parking upside down only needs 1 G, the car's own weight. That halves the grip: about 110 plungers, 125 octopus suckers or 15 geckos, and about half a pound per square inch. With tight seals, it takes about 30 Shop-Vacs running at once to keep up with the leaks.
So why does it need big fans?
Leaks. A car isn't sealed to the ceiling like a jar lid. Tesla says the Roadster has seals along the bottom edges, called "ground sealing," a bit like a mini hovercraft skirt (Electrek, Drive Tesla). But no seal is perfect, and at full 2 G suction, air rushes through any gap at about 240 mph.
The suction itself stays the same. What grows is how much air the fans must pump out to keep it, and it grows fast. At the full 2 G:
| Gap around the edges |
Air the fans must move |
In bounce-house blowers |
Fan power |
| 2 mm (tight seal) |
~2,800 cubic feet a minute |
~2 |
~19 kW |
| 5 mm |
~7,000 |
~5 |
~46 kW |
| 1 cm |
~14,000 |
~11 |
~93 kW |
| 2 cm |
~28,000 |
~22 |
~185 kW |
| 10 cm, no seals at all |
~140,000 |
~108 |
~930 kW |
With no seals, that's close to a megawatt, so the seals are the whole trick.
What about parking overnight? Hanging there only takes 1 G. According to our calculations, with a tight 2 mm seal that's about 7 kW, or about 52 kWh for 8 hours upside down. With a 1 cm gap it's about 260 kWh. Tesla hasn't said how big the battery is; it promised 200 kWh back in 2017 (Wikipedia). Park on the ceiling for the selfie, not for the night.
Could you really do it with plungers?
In theory, yes: about 110 plungers stuck to a perfectly smooth ceiling to hang it, or 220 to match the full 2 G, with the car's weight shared evenly. In practice, plungers slowly leak, one pops, and then everybody pops. Glass installers use the same idea every day, carrying windshields with hand-held suction cups. Just don't try it with a car.
Show our math
Our assumptions. Tesla hasn't published the car's weight or how big the sealed area is underneath, so we guessed carefully:
- Car weight: 2,000 kg (about 4,400 lb). Marques Brownlee quoted Tesla calling it a "4000+ pound car" (TechCrunch).
- Sealed floor area: 5.6 m² (3.5 m × 1.6 m), our estimate for a low two-seater.
- A smooth, flat surface. Seal edge 10.2 m long; gaps from 2 mm to 10 cm.
Weight (1 G): 2,000 kg × 9.81 = 19,620 newtons (about 4,400 lb of force). 2 G: 39,240 N (about 8,800 lb).
Suction needed: force ÷ area. 1 G: 19,620 ÷ 5.6 = 3,500 Pa = 0.51 psi = 3.5% of air pressure = 14 inches of water = 36 cm of water. 2 G: 7,000 Pa = 1.02 psi = 7% = 28 inches = 71.5 cm of water.
Air already pushing on the floor: 101,325 Pa × 5.6 m² ≈ 567,000 N ≈ 58 tonnes of force.
Plungers: about 40 lb each (University of Kentucky): 8,800 ÷ 40 ≈ 220 (2 G), 4,400 ÷ 40 ≈ 110 (1 G). A perfect vacuum on a 15 in² cup gives 14.7 × 15 ≈ 220 lb each: 40 (2 G), 20 (1 G).
Octopus suckers: 16 kg each: 4,000 kg-force ÷ 16 = 250 (2 G), 125 (1 G). Geckos: 133 kg each: 30 (2 G), 15 (1 G).
Shop-Vacs: a 6-gallon Shop-Vac moves at most about 85 cubic feet of air a minute with nothing blocking it, and less as the suction rises; its full sealed suction is about 55–60 inches of water (Shop-Vac). At 2 G's 28 inches it's roughly halfway, so about 40 cubic feet a minute (our estimate): 2,800 ÷ 40 ≈ 70 Shop-Vacs with a 2 mm gap, 140,000 ÷ 40 ≈ 3,500 with no seals. At 1 G (14 inches) about 64 cubic feet a minute each: 2,000 ÷ 64 ≈ 30. A Shop-Vac can reach the suction level, but only over its hose opening; the car needs it over 5.6 m² while air leaks in.
Leaks: speed of air through a gap = √(2 × pressure ÷ 1.2): 108 m/s (240 mph) at 2 G, 76 m/s (170 mph) at 1 G. Flow = 0.6 × 10.2 m × gap × speed. At 2 G: 2 mm → 1.3 m³/s (2,800 cubic feet a minute); 10 cm → 66 m³/s (140,000). A bounce-house blower moves about 1,290 cubic feet a minute.
Power: pressure × flow ÷ 50% fan efficiency. 2 G: 18.5 kW (2 mm) up to 930 kW (10 cm). 1 G: 6.6 kW (2 mm), 33 kW (1 cm), 330 kW (10 cm); 8 hours = 52, 260 and 2,600 kWh.
These are our own estimates from the assumptions above, not Tesla figures. How the fans and the moving wing work.
Sources:
Roadster Flies is an independent fan site, not affiliated with Tesla. Tesla's numbers are marked as Tesla's claims until someone tests them. Spot a mistake? Tell us.
