Tool · First-estimate sizing

Sizing Calculator

The whole method of this module in one page: pick a class, enter the crew and payload, describe the sketch and the engine, set the mission, and watch the takeoff weight converge. Every intermediate number is shown, so you can check a hand calculation step by step, or size your own design.

Inputs

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Result

Figure T.1 Left choice: the empty-weight fraction the trend predicts (blue) and the one the design can afford (violet), crossing at the solution; with a payload drop, the affordable curve is computed from the weights segment by segment. Right choice: takeoff weight against the first cruise distance, a trade study around your design point.

Mission at the converged takeoff weight
\(i\)	Segment	\(L/D\)	\(C\) (1/h)	\(W_i/W_{i-1}\)	\(W_i\) (kg)

Iterations
Step	Guess (kg)	\(\We/\Wo\)	\(\Wf\) (kg)	New \(\Wo\) (kg)

How it is calculated

Empty weight: \(\We/\Wo = A\,\Wo^{\,C}K_{vs}K_{\text{tech}}\), Raymer's Table 3.1 (Lesson 2).
\(\LDmax\) from the sketch, \(\tfrac12\sqrt{\pi e A_{\text{wet}}/C_{fe}}\) with \(A_{\text{wet}} = A/(\Swet/\Sref)\), or entered directly (Lesson 3). Jets cruise at \(0.866\,\LDmax\) and loiter at \(\LDmax\); propeller aircraft the other way round.
Propeller \(C = c_PgV/(1000\,\eta_p)\) at the segment's speed (Lesson 4).
Segments (Lesson 5): takeoff 0.970, climb 0.985, cruise and loiter by Breguet, combat \(1 - C_{\text{combat}}(\TW)t\), landing 0.995. An optional drop subtracts a fixed weight after the first cruise.
Each iteration follows the weights through the mission from the guessed \(\Wo\), takes \(\Wf = 1.06(\Wo - W_{\text{drop}} - W_x)\), and computes the new \(\Wo = (W_{\text{crew}} + W_{\text{payload}} + \Wf)/(1 - \We/\Wo)\) (Lesson 6). Without a drop this is exactly the sizing equation.

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