Mailing List lml@lancaironline.net Message #65347
From: <Sky2high@aol.com>
Subject: Re: [LML] Re: Prop overspeed???
Date: Fri, 26 Apr 2013 19:26:05 -0400 (EDT)
To: <lml@lancaironline.net>
Also, sometimes people want to include the spiral speed (taking into account forward speed along with rotational speed - I leave that additional calculation as an exercise for the interested.
 
In a message dated 4/26/2013 6:22:45 P.M. Central Daylight Time, Sky2high@aol.com writes:
Angier,
 
For self interest purposes I upped the hi speed limit on the governor to 2770 and I routinely saw 2740 to 2770 on takeoff and climb to 700  AGL.  3000 RPM seems to have been a reasonable limit for certified props.  I xcntry raced at 2660 often with no debilitating results.
 
Calculate tip speed and anything over .8 Mach is troublesome.  Hmmmm   70 inches equal a radius of 35 inches - say 3 feet.  2800 rpm equal 3 x pi x 2800 = 26390 ft/min = 5 mpm = 300 mph = .394 Mach tip speed.  No Problem.
 
Prop balance is another story.
 
The "wing" chord and twist in a prop usually provides max lift abut 2/3 of the way towards the tip.  Additional speed on the designed prop has lift vs drag limits.  Oh, that's right - if you have a Hartzell prop on a 360 it is only 68 inches as a result of vibration analysis...............
 
Scott
 
In a message dated 4/26/2013 6:05:33 P.M. Central Daylight Time, N4ZQ@VERIZON.NET writes:
Scott, I think I may have acknowledged the warning and triggered a reset.

For an IO360 180hp, what high RPM would be a serious cause for concern?
I routinely see 2660/70 for sea level takeoff so not sure I need to tweak the gov.

Angier
N4ZQ



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