Ten minutes to read, and it will save you an hour of guessing. What the sheets are for, the order to work them in, and how to read what they tell you.
Start with what you know
A design from scratch usually starts at Sheet 06, the Constraint Diagram: say how slow it must land, how fast it must climb and turn, and it tells you how big the wing and the motor have to be. Sheet 05 then builds up the weight that follows from that, and only then does Sheet 01 draw a wing that delivers it.
If you already have an aeroplane in mind, with a weight and a span, start at Sheet 01 instead: type in the all-up weight, the span and the two chords, and read the stall speed. If you do not know the weight yet, guess. The point of the set is that a guess gets corrected by the sheets that follow.
Every field already holds a sensible model, so you can open any sheet and see a complete answer before you change anything. Change one field at a time at first and watch what moves.
The order a study is worked
The Sheets menu at the top of every page groups the sheets by stage, in the order a design is worked:
- Sizing. Wing Sizing (01), Weight Budget (05) and the Constraint Diagram (06). These three are a loop: the requirements set the wing, the wing sets the weight, and the weight changes the wing. Go round it until the weight you assumed on Sheet 01 and the weight Sheet 05 builds up agree.
- Aerodynamics. The Airfoil Matrix (02) and the Drag Build-Up (07).
- Stability and control. Balance and Tail (03), Controls and Servos (11), Lateral Stability (12).
- Propulsion. Propeller Matching (08) and the Battery System (09).
- Structures. Structures (10) and Landing Gear (15).
- Performance. Power and Endurance (04), Field Performance (13), the Glide Polar (14) and Mission Energy (16).
Under the header on every sheet are links to the one before and the one after it in that order, so you can walk the whole study without going back to a menu. The worked studies show four complete aeroplanes taken through every sheet this way, which is the quickest way to see what a finished study looks like. The design checklist puts the same order on one page you can print and tick off.
Your figures travel with you
When you follow a link from one sheet to another, from the menu, from the previous and next links, or from the strip at the foot of a sheet, the figures you have already worked out go with you and fill the boxes that need them. Nothing is sent anywhere: they ride in the address of the page, which is also why the address bar is a complete record of your design.
Three ways to keep a design, all of them yours rather than ours:
- Copy link puts the page's address, with every figure in it, on your clipboard. Bookmark it or send it to someone.
- Save this design downloads a small file. Load it on any sheet with Load a design, and it fills the fields that sheet uses.
- The design report reads that file back as one document: the aeroplane, what each sheet said about it, and the warnings.
Reset opens the sheet again with its own defaults and nothing carried in.
Reading what a sheet tells you
The row of large figures is the answer. Under each one is a short verdict, and a figure in red is one the sheet thinks you should look at again. Below the figures:
- The notes say what the numbers mean for your aeroplane, in sentences. Read them; they are where the sheet explains itself.
- Where this stops being valid lists the range each method behind the sheet was built for, and where your design sits in it. A figure outside its range is a guess, however many decimal places it has.
- What moves it shows which of your inputs the chosen answer depends on most. Spend your effort on the top of that list.
- Two at a time sweeps two inputs across a grid, for when one field alone does not tell the story.
- Where people go wrong collects the mistakes that particular method invites.
Units
The sheets work in metric. Wing Sizing and the atmosphere tool also have an Imperial switch in the title bar, and whatever you type there, figures travel between sheets in metric, so switching units never changes a design. The unit converter carries every pair the sheets use, including the two everybody gets wrong: ounces per square foot, and kilogram-centimetres of servo torque.
At the flying field
After your first visit the sheets work with no signal at all. On a phone, use your browser's Add to Home Screen and the set opens like an app. Nothing you type is stored on the device or sent to us.
How far to trust the numbers
These are preliminary design methods: good for choosing between options and for catching mistakes before you cut balsa, not a substitute for flight testing. The methods page gives every formula and its source, and the glossary defines every term. Build in stages, keep a margin on every number, and test-fly carefully.
If a number looks wrong, it may be. Send a correction with your source and it goes into the next revision, credited.
Questions people ask
- Where should the balance point be?
- Ahead of the neutral point by a margin, measured from the leading edge of the mean aerodynamic chord. A conventional sport model is usually set at a static margin of 12 to 15% of that chord, and a flying wing at 3 to 8%. Sheet 03 works out the neutral point and the safe band; Sheet 01 says where the mean aerodynamic chord starts on a tapered or swept wing.
- What wing loading should my model have?
- Compare models by wing cube loading rather than wing loading, because it does not change with size. Below 4 is a floater, 4 to 7 a trainer, 7 to 11 a sport model, 11 to 15 scale or a warbird, and above 15 a racer. Sheet 01 gives both figures and the band yours falls in.
- What Reynolds number is my aeroplane flying at?
- There is no single one. Reynolds number belongs to a length and a speed, so the wing, the tail, the fuselage and the propeller blade each have their own, and the tail is nearly always lower than the wing. The Reynolds tool works out every part at once.
- Do the sheets cost anything, or need an account?
- No. Every sheet is free, there is no account, and nothing you type is sent anywhere: the figures stay in your browser and in the page's address. Once a page has been opened, the site keeps working without a signal, which is what it is like at most flying fields.
- Which sheet do I start with?
- With a set of requirements and no aeroplane yet, Sheet 06. With an aeroplane in mind, a weight and a span, Sheet 01. The design checklist lists what each stage should settle.