Offline stability bench: Barrowman-style center of pressure, a mass-budget CG, caliber band, rail-exit, recovery descent, and a fin-flutter note — then share a PDF or PNG build card.
FinCaliber Rocket is an Android bench for stacking a nose, body tubes, optional transition and boat-tail, and a fin set, then reading stability against a selected motor. Four tabs: Fleet, Bench, Motors, Pad. Intro pages cover stacking the airframe, watching CP and CG, and leaving with a build card. The fleet subtitle calls it an offline stability bench; motor cards are stored offline; the intro says the card is fully offline and ready for the pad.
The home list shows each card with a caliber chip. Filter All / Under / Sport / Over. Search covers rockets and motors and can also filter by band. Open a card to edit on the bench, duplicate (name gets “copy”, callsign gets “-X”), delete, or jump to recovery and rail helpers. Create starts a blank “New airframe” (NEW-18, 18 mm sport card, B6) and opens Bench. Restore starter fleet puts the seed set back.
| Card | Callsign | Seeded motor |
|---|---|---|
| Schoolyard Alpha — 18 mm STEM first flight | SA-18 | B6-4 |
| Dual-Bay Courier — payload / egg-loft look | DBC-24 | D12-5 |
| Fin-Can Sprint — 29 mm four-fin sport | FCS-29 | F15-6 |
| Campus Mini-A — 13 mm park flyer, streamer | CM-13 | A10-3T |
| Night Range Trainer — LED-sled payload | NRT-18 | C6-5 |
| STEM Club Lifter — long 24 mm, D12 or E9 | SCL-24 | E9-4 |
| Backyard Balsa Bird | BBB-18 | B4-4 |
| Troop Tube Trainer | TTT-18 | C6-5 |
| Ellipse Nose Cruiser | ENC-24 | E12-6 |
| Boat-Tail Arrow — streamer sprint | BTA-18 | C6-7 |
| Egg-Loft Widebody — 41→29 mm transition | ELW-29 | D12-7 |
| Swept Wind Rider | SWR-24 | C6-5 |
| Cardboard Classic | CC-18 | A8-3 |
| Payload Stacker — G12 long-burn option | PLS-29 | G12-7 |
Nose profiles: conical, ogive, elliptical, parabolic (each has a Barrowman factor). Materials for nose, body, and fins: balsa, basswood, cardboard, lite-ply, PLA print, PETG print — each with a density, wall thickness, and flutter factor. Optional transition and boat-tail. Fin count 3–6 in the engine. Undo / redo (40 steps), snap, z-order on mass points.
Kinds: payload, ballast, recovery pack. Station along the stack. CG is the wet mass budget: tube and nose estimates from density, fin planform, those points, plus the selected motor casing treated as wet mass near the tail.
Share PDF (A4-style page) or PNG (1080×1600). Header reads “FINCALIBER ROCKET · BUILD CARD” with name and callsign. The sheet includes motor, caliber margin, rail-exit, and recovery descent. Android share sheet only when you tap share. Rockets and motors live in a local Room database; units, default stock, and onboarding live in DataStore (fincaliber_prefs).
Library lists designation, impulse class, average thrust, burn, propellant and total mass, casing length, diameter, delay, notes. Favorite toggle. Assign a motor onto an open airframe. Create a custom motor (impulse, thrust, casing) stored offline. Filter the list; delete is available on the detail screen.
1/2A3-2T · A8-3 · A10-3T · B4-4 · B6-4 · C6-3 · C6-5 · C6-7 · D12-5 · D12-7 · E9-4 · E12-6 · F15-6 · F30-4 · G12-7 · G40-7
1/2A through G. Notes in the seed set call out schoolyard, 13 mm mini, 24 mm sport D, 29 mm F/G, long-burn vs fast F, and rail or flutter checks on the larger impulses.
Counts how many cards sit Under / Sport / Over. Coaching assumes light wind. Flags stacks short on the rod and fin sets that want thicker root stock. Watch list is the five lowest-caliber cards.
Exit speed from average thrust minus axial weight (pad angle 0–25° on the helper; model allows 0–30°), over rail length (helper slider 300 display-units up to 3200 mm equivalent). Clear means ≥ 13 m/s. If shy: lengthen the rail, drop wet mass, or step up impulse.
Parachute (Cd 0.75) or streamer (Cd 0.55). Descent from mass, air density 1.225, and canopy or streamer area. Notes: soft school-field (< 4.5 m/s), sport soccer-field (< 6.5), brisk (< 9), or hot (size up the chute or leave the streamer).
Score from span/thickness, material flutter factor, and motor average thrust. Calm / watch (add ~0.4 mm root or clip the tip before a windy F/G hop) / risk (thicken the root or shorten the span). Tune span, root, thickness, and stock on that screen.
CP combines nose, transition, boat-tail, and fins. Nose factors: conical 0.666, ogive 0.466, elliptical 0.500, parabolic 0.511. Calibers = (CP − CG) / body diameter. Under < 1.0 cal: add aft ballast, grow fin area, or pick a milder motor. Sport 1.0–2.2 cal: the settings text calls this the sport band for a calm NAR/TRA school field. Over 2.2 cal: weathercock risk; shift payload forward or shrink fin span. Settings: metric mm/g or in/oz; default fin and nose stock for new cards; restore fleet; replay intro.
Questions about a caliber band, a rail-exit that stays short of 13 m/s, recovery notes, a flutter advisory, or a build card that did not share: roslynhugheyyw3365@gmail.com. Include airframe name, callsign, motor designation, body diameter, CP/CG or caliber shown, rail length, and pad angle. Mail is answered in the order it arrives, usually within a few business days.
Yes. The intro and fleet copy describe an offline bench. Rockets and motors are in Room; preferences are in DataStore. A PDF or PNG leaves the app only when you share a build card through the system sheet.
Under-stable below 1.0 caliber, sport band from 1.0 through 2.2, over-stable above 2.2. The chip on each card uses those same cutoffs. Coaching text for each band is shown in the app (aft ballast / sport field / weathercock).
Clear requires at least 13 m/s at the end of the rod. The helper uses average motor thrust, wet mass, rail length, and pad tilt. Lengthen the rail, reduce wet mass, or choose a motor with more average thrust.
A mass budget: estimated nose and tube mass from material density and wall, fin volume from planform and thickness, plus payload, ballast, and recovery points you place, plus the selected motor’s total mass near the tail. CG is the wet weighted station.
No. Settings describe a Barrowman-style nose/transition/fin stack. There is no 6-DOF sim, no wind field, and no certification stamp in the app — the Pad tab labels notes as calm-day sport notes.
Yes. Motors → create. Fill impulse class, average thrust, burn, masses, casing, diameter, delay, and notes. It is stored on the device like the seed motors.
DANYLYTSKYI_DEVELOPER — roslynhugheyyw3365@gmail.com. Send the numbers on the open card (caliber, rail-exit, descent, flutter note) so the reply can match what you see.