Forty centimetres of real estate.
Measure before you dream. The standard glider instrument is the 57 mm round; older panels carry 80 mm legacy holes; and every hole needs more than its diameter — bezels, mounting screws and your fingers demand about 70 mm between 57-mm centres. The panel is not a plane, either: it curves with the fuselage, loses its corners to the canopy frame, and shares its lower edge with the stick at full deflection.
The arithmetic is brutally simple: usable width minus margins, divided by centre spacing, times two rows if the panel height allows. That number — the tool below computes it — is the entire negotiating space. Everything else in panel design is deciding which instruments deserve to be in it, and which move to a remote box behind the panel where they never needed a hole at all.
The scan is the job.
A panel exists to be read in half-second glances between scans of the sky. The layout rule follows: the instruments read most often sit nearest the sightline over the nose — vario and airspeed first — grouped by flight phase, with anything that must be read in turbulence given the largest digits. Audio is the best panel space you own: a vario you can hear buys back whole minutes of eyes-outside time per hour.
Depth is the forgotten dimension. Behind every instrument live a connector, a fuse and often two pneumatic lines with their minimum bend radius — 40 millimetres of air that the panel drawing never shows. The instrument that fits the hole but not the space behind it is a classic Saturday discovery.
Build the panel, mind the amps.
Typical draws: 120 mA per 57 mm instrument, 450 mA for a 57 mm EFIS, 700 mA for a large display, 300 mA for a transponder, plus a 100 mA hum of radio and bus. The panel usually runs out of millimetres before it runs out of milliamps — until the transponder arrives, when both go at once. A soaring day is long: plan for eight hours, not five.
Sunlight is the acceptance test.
A canopy is a greenhouse with glare. A display that looked brilliant on the workbench competes in flight with direct sun, canopy reflections and your polarized sunglasses — which can black out an LCD at exactly the wrong angle. The numbers that matter: transflective or ~1000 cd/m²-class brightness, a matte face, and a viewing angle that survives being mounted thirty degrees off your sightline.
The test that matters is not a datasheet: it is the instrument in the actual panel position, under the actual canopy, at noon, wearing the sunglasses you actually fly in. Do it with a cardboard mockup and a borrowed unit before cutting anything. Ten minutes in the sun answers questions no brochure will.
Behind the face: one bus, one budget.
The modern panel's secret is that most of it is not on the panel. Sensors, FLARM, the transponder body and logger live as boxes on a shelf behind, joined by the CAN spine — two wires, terminated at both ends — with only displays and controls claiming holes, the transponder's control head among them. That is what makes the small panel possible: the hole budget spends on what you look at, not on what computes.
The power side deserves the same drawing: fused branches from a master, wire gauged for the run length, and the current budget from the tool above compared honestly against the battery. Label both ends of every wire. The panel you can troubleshoot in a hangar in October is the one that was documented in March.
In your cockpit.
Start from the scan, not from the shopping list: decide what you must see in a half-second glance, give those the prime holes, move everything else to the bus. One EFIS in a 57 mm hole now carries what four holes used to; a dedicated traffic display earns its place the first time it saves you a radio call. And keep the drawing — the next owner of the glider inherits your panel logic, or the absence of it.
The two wires that make the small panel possible have their own article: one cable behind the panel.