▁is ▁very ▁similar ▁in ▁make up ▁to ▁old - f ashion ed ▁gun pow der . ▁The ▁main ▁difference ▁is ▁the ▁presence ▁of ▁a ▁b inder , ▁usually ▁de xt rin . ▁The ▁commonly ▁used ▁Est es ▁model ▁ro cket ▁engines ▁are ▁made ▁with ▁black ▁pow der ▁prop ell ant . ▁Black ▁pow der ▁prop ell ant ▁must ▁be ▁pressed ▁very ▁tight ly ▁in ▁order ▁to ▁function ▁well . ▁Mot ors ▁designed ▁with ▁black ▁pow der ▁are ▁most ▁often ▁end - burn ers , ▁due ▁to ▁the ▁fast ▁burn ▁rate ▁of ▁this ▁prop ell ant . ▁A ▁simple ▁de xt rin - free ▁version ▁( the ▁most ▁commonly ▁used ▁form ulation ) ▁incorpor ates ▁ 7 5 % ▁pot ass ium ▁nit rate , ▁ 1 0 % ▁sul ph ur , ▁and ▁ 1 5 % ▁char co al . ▁De xt rin ▁may ▁be ▁added ▁as ▁desired ▁( us ually ▁between ▁ 0 ▁and ▁ 5 %). ▁Add itional ▁( co arse ) ▁char co al ▁or ▁metal ▁pow ders ▁( 5 ▁- ▁ 1 0 %) ▁may ▁be ▁added ▁to ▁obtain ▁an ▁interesting ▁spark ▁trail . ▁However , ▁this ▁may ▁alter ▁slightly ▁the ▁burn ▁rate ▁of ▁the ▁mixture . ▁ ▁Performance ▁ ▁The ▁imp ulse ▁( area ▁under ▁the ▁thrust - time ▁curve ) ▁of ▁a ▁black ▁pow der ▁motor ▁is ▁used ▁to ▁determine ▁its ▁class . ▁Mot ors ▁are ▁divided ▁into ▁classes ▁from ▁ 1 / 4 A ▁to ▁E , ▁which ▁covers ▁an ▁imp ulse ▁range ▁of ▁