Hi, What about the different tip shapes being used these days. Does that help in reducing the tip sound on props of bigger diameters?
I'm not sure of this question as well, I have heard of props that have multiple pitches set along the blades that work better at different RPM's. I understand that most fixed pitch propellers have a constant pitch along the blade. Thank you Brian Bundaberg Aust. ----- Original Message ----- From: <phill.h...@gmail.com> To: "KRnet" <kr...@mylist.net> Sent: Monday, August 06, 2012 12:53 AM Subject: Re: KR> RE: 2300 Propellor Here in lies a paradox of sorts. An air propeller's tip speed limit is about 900 ft/s (speed of sound). The rule is to keep max tip speed below 900ft/s. The prop is at its most efficient tip speed at just below 700 ft/s (above which compressibility starts to degrade efficiency). So lets aim for cruising at an engine speed that gives us a tip speed of just under 700 ft/s. Typical GP VW...max cont rpm about 3600, cruise range from 3000 up to 3400 Thrust line on the KR limits prop diameter to maybe 54in...KRs on original (short) gear legs maybe 52 might be the limit... According to my calculations a 54in prop turning at 3600rpm is turning at 847.7 ft/s, that's 94% of max allowable a 54in prop turning at 3000rpm is turning at 706.3 ft/s, that's 78% of max AND above the most efficient and quiet tip speed a 54in prop would have to turn at 2900 rpm to hit its most efficient tip speed A 57in prop turning at 3600rpm is turning at 894.7 ft/s, that's 99%!! of max A 57in prop turning at 3000rpm is turning at 745.6 ft/s, that's 83% of max AND still above it's most efficient tip speed A 57in Prop would have to turn at 2800 rpm to hit its most efficient tip speed a 52in prop turning at 3600rpm is turning at 816.2 ft/s, that's 91% of max a 52in prop turning at 3000rpm is turning at 680.2 that's 76% of max AND turning perfectly in it's most efficient tip speed Pitch determines AC speed, if you have the HP to back it up. It's a BIG compromise. You have to choose what you want more, better performance at take off or cruise On , robert7...@aol.com wrote: > Concur on calling Joe, and or Ed Sterba. I've got a Revmaster 2100, but I > don't know of anyone running the 2300 on a KR. I could be mistaken. My > prop > diameter and pitch is 54" x 54" using on a trigear. Prop by Ed Sterba. 52" > is common as well but not over 54 to keep tip speed below the magic > numbers. My cruse speed is 130 mph at 3000 rpm. I am happy with that but > I also > know others have done better. _______________________________________ Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. To UNsubscribe from KRnet, send a message to krnet-le...@mylist.net please see other KRnet info at http://www.krnet.org/info.html
