Why Flight Time Matters More Than the Battery Spec

Pressure, flow, software, and accessories all matter. Flight time and working height come first because they decide whether the aircraft can remain on the work face and whether it can reach the scope from the planned setup.

Apellix publishes a 32-minute battery maximum and 195-foot maximum working height for the B2. Lucid publishes 19 minutes and 150 feet for the Sherpa. The arithmetic is direct: (32 - 19) / 19 = 68.4%, reasonably stated as approximately 70% higher flight time. For height, (195 - 150) / 150 = 30% more published reach.

These are manufacturer specifications under different unpublished test conditions. They do not prove a matching increase in square-foot production. They do define materially different operating envelopes.

AirTrace can automate a selected cleaning grid under active pilot supervision, but software does not erase the physical battery cycle. Once the aircraft must leave the work face, cleaning pauses until it lands, changes batteries, relaunches, and returns to position.

A battery change is not a two-minute hand movement. Cleaning stops while the pilot backs away from the surface, descends with the hose, lands, secures the aircraft, changes the batteries, completes checks, relaunches, climbs, and finds the exact restart point. The crew may also have to reset hose slack and reopen a controlled work area.

To make that visible, the planning model below applies the same assumptions to both aircraft: a 15% reserve, 45 seconds to land, two minutes to change batteries, 45 seconds to take off, 90 seconds to return to position, and one minute of ordinary interruption per cycle. The result is modeled time availability, not observed field performance.

Hillcrest Tower at 12720 Hillcrest Drive in Dallas is a useful public example. The property page describes a 10-story, 168,189-square-foot office building with a 16,818-square-foot typical floor. Gross floor area is not facade area, so the next step is an explicit model, not a property claim.

Assume a roughly square 16,818-square-foot footprint, about 130 feet per side, 12 feet per story, and 20% deductions for areas outside the cleaning scope. That produces approximately 50,000 square feet of modeled cleanable vertical surface. Hold application speed constant at Apellix's published 5,000-square-foot-per-hour maximum solely to isolate endurance. The model then requires 600 airborne cleaning-clock minutes.

At 24.2 usable cleaning minutes per B2 sortie, the scope requires 25 modeled sorties and 24 battery transitions. At 13.15 minutes per Sherpa sortie, it requires 46 modeled sorties and 45 transitions. Under the shared transition assumptions, the longer-flight case produces 48.1 cleaning-clock minutes per elapsed hour versus 41.2, turning the same modeled cleaning clock into approximately 12.5 versus 14.6 elapsed hours.

That is a difference of roughly 2.1 crew-hours before any platform-specific production, quality, weather, or site-access difference is assumed. The point is not that every Dallas tower takes those hours. The point is that each landing multiplies fixed overhead across a large facade.

A 45-foot difference is not cosmetic. At an assumed 12 feet per story, it represents about 3.75 story-equivalents. A 10-story property like Hillcrest Tower may fit inside both published height envelopes from a suitable ground setup. On a taller building, 195 feet may keep additional elevations inside the drone scope before a separate launch point or access method becomes necessary.

The FAA's general altitude rule is not the cleaning system's working-height claim. Hose mass, fluid, wind, facade geometry, standoff, obstacles, people, vehicles, airspace, and the complete operating plan can all reduce practical reach. Height still belongs beside flight time at the top of the hardware decision because it controls addressable scope.

The right buying questions are practical: What reserve will the pilot use? How long is the complete land-change-relaunch cycle? How many cleaning minutes does the scope require? What height remains with the actual hose and fluid load? Does one approved setup reach the surface?

Flight time and height do not replace a field demonstration. They tell you where the demonstration starts. When the published difference is 32 versus 19 minutes and 195 versus 150 feet, SkyPSI treats both as first-order constraints, not brochure footnotes.