Find out whether it will fly before you cut anything.
Saqr Consulting publishes sixteen free calculation sheets for people designing model aircraft and small unmanned aircraft. Put in the dimensions you are considering; get back the numbers that decide whether the aircraft is pleasant, marginal or dangerous — in plain English, with the traps called out, and with every assumption written down where you can check it.
All sixteen sheets are free and open. No account, nothing to install, works on a phone at the field.
New here? How to use the sheets, in ten minutes.
Sheet 01 draws your wing to scale as you enter dimensions,
then tells you how it will behave.
What this site is for
The gap
Plenty of free calculators will hand you a wing loading. Almost none will tell you that the airfoil you picked stops working at your Reynolds number, or that your balance point is a centimetre from unflyable.
Numbers with consequences
Every figure here comes with what it means for the aircraft on your bench — how it will land, what the tail has to carry, how much of the pack you will actually use.
Including the bad news
Where a choice has a known trap, the sheet says so plainly. Seventeen of the twenty-seven airfoils on Sheet 02 carry a "watch out" of their own. That is the part a spec table leaves out.
New Revision E: the site around the sheets
Sheet Index
Sixteen sheets, numbered in the order you meet them rather than the order you use them. A design usually starts at 06, where the requirements decide how big the wing and the motor have to be, goes to 05 for the weight that follows, and only then to 01 to draw a wing that delivers it. Any sheet also works on its own.
There is also a standalone atmosphere calculator. It is not a sheet — it is the block of code every sheet uses to work out the air, put behind its own inputs, so you can see density, density altitude, the speed of sound and viscosity for the day you are actually flying on. Set the conditions there and they travel to every sheet.
And a Reynolds number calculator, which answers the question the airfoil sheet keeps asking. There is no single Reynolds number for an aeroplane: the wing, the tail, the fuselage and the propeller blade are four different flows at the same moment, and the tool shows all four at once — including the propeller, which does not see the aircraft's speed at all.
And a unit converter covering every pair the sheets use, with the exact factors listed so you can check the arithmetic rather than trust it. It includes the two that are got wrong most often: wing loading, where one ounce per square foot is 3.05 g/dm², and servo torque, where one kg·cm is 13.89 oz·in.
Wing Sizing Sheet
Enter weight, span and chords. Get wing loading, wing cube loading, stall speed, aspect ratio and Reynolds number, with a scale drawing of the wing and a plain reading of each number. Metric and imperial.
Airfoil Selection Matrix
Twenty-seven curated sections filtered by Reynolds number, mission and build method. Every section's usable range is drawn as a bar against yours — if it does not cross your line, it is the wrong tool whatever its polar says.
Balance & Tail Sheet
Neutral point, safe centre of gravity band and tail volume coefficients — given as a millimetre measurement at a named station on the wing, because that is how a model actually gets balanced. Handles flying wings and their sweep offset.
Power & Endurance Sheet
Drag polar, power required against airspeed, motor sizing, pack mass and endurance. Shows why a two and a half kilo trainer cruises on sixty watts and still needs three hundred from the pack to climb.
Weight Budget Sheet
Build the all-up weight group by group: structure from wing area and build method, propulsion, pack, avionics, payload and the contingency everyone forgets. Turns the first number every other sheet depends on from a guess into an estimate.
Constraint Diagram & Design Point
Every requirement drawn as a boundary on one chart: stall, cruise, climb, launch and turn. What survives all of them is the feasible region, and its corner is the wing area and the motor the brief actually demands. Shows which single requirement sized the aeroplane.
Parasite Drag Build-Up
Where the drag actually comes from, component by component, at the Reynolds number each part really sees. Replaces a guessed drag coefficient with one you can argue with, and shows why the landing gear is usually a fifth of it.
Propeller Matching
Advance ratio, pitch speed and slip, tip Mach number, static thrust, and the efficiency the propeller actually reaches at cruise and in the climb — which are not the same number, and the other sheets have been assuming they were.
Battery & Electrical System
What the pack really delivers: current, C rate, voltage sag under load, the energy lost as heat inside the cells, usable capacity and speed controller headroom. There is a power no pack can exceed, and this shows how far from it you are.
Structures & Spar Sheet
The flight envelope as a chart: how fast you can pull hard before the wing reaches its limit rather than stalling first. Then the bending moment that arrives at the root, and the spar caps that carry it in eight materials. On a light model a gust can load the wing harder than you can.
Control Surfaces & Servo Torque
What the air does to an aileron, elevator or rudder, and what that asks of the servo behind it. Torque goes as the square of airspeed, and as the square of the surface chord, so the two decisions people make casually are the two that matter. Also how fast the ailerons will actually roll it.
Lateral & Directional Stability
Whether it tracks straight, and whether it picks a dropped wing up. The fin makes weathercock stability and the fuselage spends it; the dihedral makes roll stability and the wing position quietly adds or removes three degrees of it. Neither number is good on its own — the ratio decides how it flies.
Take-Off, Landing & Field Performance
Whether the strip you actually have is long enough. The ground roll is worked out step by step from the thrust you measured and the surface you are standing on, and the obstacle at the end is cleared at the climb angle the aeroplane can really hold. A headwind is the cheapest runway there is; long grass takes off badly and lands well.
Glide & Sink Polar
What it does with the motor off. The speed that goes furthest and the speed that stays up longest are two different speeds, and the second is 24% slower than the first on every aeroplane ever built. Into wind you fly faster, not slower. Weight changes neither the glide ratio nor your mind about it.
Landing Gear & Ground Handling
Where the wheels go, what they carry, and whether it tips over. A tricycle is stable on the ground and a taildragger is not, and every other difference follows from that. Drawn to your dimensions in side view and plan, with the propeller clearance and the wheel size the surface actually needs.
Mission Profile & Energy Budget
Does the flight fit in the pack, segment by segment, in watt-hours. Climb, cruise, loiter and the reserve you choose to hold back — and the curve that says what every gram of payload costs you in loiter, which is the question most small-UAV studies exist to answer.
Why these sheets and not a spreadsheet off a forum
Four things a downloaded spreadsheet almost never gives you.
It tells you when you are wrong
Aggressive taper without washout, a fin too small to track straight, a battery heavier than the airframe you claimed, a tail already working so hard it will stall before the wing does — each one is caught and explained rather than silently returned as a number.
It names the traps
Some choices are popular and wrong. Sheet 02 flags them by name.
NACA 23012 is chosen by scale builders copying full-size drawings, and its stall is famously abrupt — worse at model scale than its full-size reputation suggests. Standard tables list it without comment.
It is honest about precision
Every lift coefficient, pitching moment and Reynolds band in the set has been checked against published tunnel and computational sources by Fayssal B., and revised where the evidence disagreed. Most maximum lift figures came down.
Each airfoil now states whether its pitching moment was measured or computed — twelve of the twenty-seven rest on computation, and the sheet says so rather than presenting all twenty-seven as equally solid.
It works where you build
One file per sheet, no account, no install, no network once loaded. Everything recalculates as you type, on a phone in the workshop or at the flying field.
Found something wrong?
These sheets carry indicative figures for lift coefficient, pitching moment and parasite drag. A measurement you have taken, or a published polar showing that a figure here is wrong at the Reynolds number it claims, beats a compiled table every time.
Send it with your source and it goes into the next revision, credited. Same for a calculation you think is off — show the working and it gets checked properly.
Send a correctionEvery sheet carries a revision letter so you can see what changed.
Who works these out
The sheets were compiled by Fayssal B., using standard preliminary design methods — tail volume and lifting-line stability, the parabolic drag polar, ISA atmosphere — applied at the scale and Reynolds numbers models actually fly at, which is where most textbook figures quietly stop being true.
Saqr Consulting publishes these as design aids: shortlisting and sizing tools for hobby and student work. They are not airworthiness determinations, and nothing here is offered as licensed engineering advice.
Found something wrong? Say so — corrections go straight into the next revision, and everybody gets it, because there is no other kind of reader.