▁with ▁the ▁surface ▁area . ▁For ▁a ▁given ▁aer od ynamic ▁form , ▁the ▁area ▁in ▁turn ▁increases ▁with ▁the ▁square ▁of ▁the ▁wing ▁span . ▁If ▁struct ural ▁efficiency ▁can ▁be ▁maintained , ▁the ▁struct ural ▁weight ▁of ▁the ▁air frame ▁also ▁increases ▁with ▁its ▁surface ▁area ▁and ▁the ▁square ▁of ▁the ▁span . ▁But ▁the ▁internal ▁volume ▁increases ▁with ▁the ▁cube ▁of ▁the ▁span . ▁ ▁For ▁example , ▁if ▁the ▁dimensions ▁are ▁all ▁double d ▁in ▁size , ▁then ▁the ▁area ▁and ▁lif ting ▁capacity ▁increase ▁ 2 ▁× ▁ 2 ▁= ▁ 4 ▁times , ▁while ▁the ▁volume ▁increases ▁ 2 ▁× ▁ 2 ▁× ▁ 2 ▁= ▁ 8 ▁times . ▁ ▁For ▁a ▁passenger ▁aircraft , ▁this ▁dou bling ▁in ▁size ▁allows ▁up ▁to ▁twice ▁the ▁cabin ▁space ▁per ▁passenger . ▁Alternatively , ▁for ▁a ▁transport ▁it ▁allows ▁up ▁to ▁twice ▁the ▁space ▁to ▁fit ▁in ▁bul ky ▁but ▁light ▁cargo . ▁Thus , ▁large ▁aircraft ▁are ▁both ▁more ▁comfortable ▁and ▁operation ally ▁flexible ▁in ▁use ▁than ▁smaller ▁types . ▁ ▁Str ucture ▁Although ▁a ▁larger ▁wing ▁car ries ▁larger ▁forces , ▁it ▁is ▁also ▁th icker . ▁The ▁main ▁sp ar ▁in ▁the ▁wing ▁approxim ates ▁an ▁I - be am , ▁whose ▁depth ▁equals ▁the ▁wing ▁thick ness . ▁For ▁a ▁given ▁overall ▁load ▁to ▁be ▁carried , ▁the ▁forces ▁in ▁the ▁beam ▁decrease ▁with ▁the ▁square ▁of ▁its ▁depth . ▁If ▁a ▁wing ▁is ▁double d ▁in ▁span ▁it ▁is ▁also ▁double d ▁in