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Title: Need a little doubt clarification on prop pitch Post by: Imperial fire on July 08, 2017, 02:13:45 PM I have a 900 kV motor...
So i plan to make a plane that is meant to carry weight as priority and isn't meant to go fast... Should I use a 11*5 prop or a 10*7 prop. Am I right in assuming that a high pitch prop isn't good at low speeds?? Or is it the other way ... Am a little confused.. Any help appreciated.. Tnx. Title: Re: Need a little doubt clarification on prop pitch Post by: rajjames on July 08, 2017, 03:15:58 PM Not sure about the right propeller. But for the second question, a higher pitched propeller gives more control at lower kv as compared to an identical(same material, profile, length, etc) lighter pitched one. The reason being that a high pitch prop can scoop out more air and hence more thrust for a given rpm at the cost of more current.
Title: Re: Need a little doubt clarification on prop pitch Post by: Imperial fire on July 08, 2017, 05:45:38 PM I thought it was more related to speed of airplane??
I mean won't a high pitch prop stall at low speed of airplane?? And if it stalls it won't give that punchy thrust ...isn't that so.. God I've mixed up so many simple things in my head..can't think straight.. Title: Re: Need a little doubt clarification on prop pitch Post by: sanjayrai55 on July 08, 2017, 06:21:40 PM Not sure about the right propeller. But for the second question, a higher pitched propeller gives more control at lower kv as compared to an identical(same material, profile, length, etc) lighter pitched one. The reason being that a high pitch prop can scoop out more air and hence more thrust for a given rpm at the cost of more current. This is wrong Title: Re: Need a little doubt clarification on prop pitch Post by: sanjayrai55 on July 08, 2017, 06:26:53 PM A prop is basically specified by 2 sizes : Diameter and pitch eg 9 X 6
The diameter determines torque, ie Thrust The pitch determines speed - by definition the distance the prop would travel (for 9 X 6 would be 6") in one revolution, if the medium it was moving in is incompressible. Air being very compressible, this is not absolute A higher diameter prop would yield higher torque. a 9X6 would give almost the same thrust as a 9 X 8, but the speed of the 9 X 8 would be about 20% more An increase in say 10% of diameter, would lead to a disproportionately higher thrust, and power requirement (read current) Title: Re: Need a little doubt clarification on prop pitch Post by: sanjayrai55 on July 08, 2017, 06:29:06 PM Play around with some numbers on this to get an idea
http://rcplanes.000webhostapp.com/calc_thrust.htm or download RC Tools app on your phone Title: Re: Need a little doubt clarification on prop pitch Post by: Imperial fire on July 08, 2017, 08:19:22 PM Hey Sanjay..so ummm.
The thing is I have to make a thick wing...and it's slightly undercambered...to get lots of lift...yes it will be slow I suppose... What I am essentially worried about is ... At low speeds will a high pitch prop give reasonable thrust?? Or will it simply consume lots of current and drop my bird out of the sky... I understand the best way to know is playing with bnumbers or even better to actually try and find out.. But I was wondering if anyone had tried... I somewhere read something about real life turboprop airplanes changing prop pitch of blade mid air to get max efficiency... I mean yeah not all rules of large airplanes apply to model aircraft ... I think it's time to get a power meter ...but even that can measure only ' static' thrust. |