Lub npe ntawm helical iav feem ntau txawv ntawm spur iav. Raws li lub npe qhia, nws yog "iav nrog inclined hniav". Cov hniav nto ntawm hom iav no tsis yog sib npaug rau cov kev taw qhia axial, tab sis muaj qee qhov suav nrog lub kaum ntse ntse. Nws yog qhov tseeb vim qhov no suav nrog lub kaum ntse ntse uas helical iav muaj ntau yam ntxwv txawv ntawm cov iav spur.
Nyob rau hauv cov nqe lus ntawm kev txhim kho kev ua tau zoo, helical iav muaj ntau dua coincidence degree tshaj spur iav (nce nrog qhov nce ntawm iav dav thiab helix lub kaum ntse ntse), uas coj muaj zog bearing peev xwm rau lub tsheb thiab ntau dua qhov kawg torque uas yuav tsum tau loaded. Yog li ntawd, nws muaj cuab kev zoo nyob rau hauv lub tshav pob ntawm high-ceev thiab hnyav load.
