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To:  lml@lancaironline.net
Date: Sun, 16 Nov 2008 18:04:28 -0500
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From: "Bill Wade" <super_chipmunk@roadrunner.com>
References: <list-3301419@logan.com>
In-Reply-To: <list-3301419@logan.com>
Subject: Re: [LML] Prop Length for 360
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  As a followup to the general question on length I found this webpage:
 http://www.mh-aerotools.de/airfoils/jp_propeller_design.htm . Also, "Design 
for Flying" by Dave Thurston is a good book that covers the considerations 
in aircraft design- I've found it to be very helpful. He has a section on 
propeller design and what I get from it is that large diameter is preferable 
but is restricted by the need to keep the tip speed subsonic and by ground 
clearance. "For example, study of a recent 250-hp constant-speed 
installation indicated that a three-blade 76-in diameter propeller was 
slightly more efficient than a 76-in diameter two-blade, and much more 
efficient than a 74-in diameter two-blade one, particulary at climb speed. 
However, an 80-in diameter two-bladed design was the most efficient of all 
throughout the entire flight range, provided such a large diameter could be 
used."

 It may be that Hartzell doesn't recommend a 70" blade due to an interaction 
with the IO-360. Shorter or longer might change the propeller's resonant 
frequencies so it wouldn't be excited by the engine pulses. I'm not sure 
that the engine counterweights would dampen the prop- I believe they're 
tuned for crankshaft frequencies. Since you're midway through the overhaul I 
don't know what your options might be. Your best sources might be Lancair 
and other builder/owners who could tell you what has worked for them.  -Bill 
Wade


----- Original Message ----- 
From: <mmcmanus@grandecom.net>
To: <lml@lancaironline.net>
Sent: Saturday, November 15, 2008 7:36 AM
Subject: [LML] Prop Length for 360


> I'm in the middle of getting my Hartzell 2 blade prop overhauled for my 
> Lancair
> 360.  I got a new hub at 50% discount from Hartzell to eliminate the 
> recurring
> eddy current inspection. The prop shop doing the overhaul has issues with 
> the
> blades and they will not issue the formal 8131 (I think) paperwork for the
> overhaul.  The problem is the blade length.
>
> I bought the airplane 3 years ago and it had an overhauled "0" time prop 
> when
> the airplane was built in 2002. The blades are 70" long according to the 
> prop
> shop.  They also say that the Hartzell recommends a 72" blade. But 
> Hartzell
> also allows a 68" blade for the Lyc 360.  They do not however, recommend a 
> 70"
> blade.
>
> The question is, since I've had no problems or vibration issues with my 
> 70"
> blades - should I be concerned? I guess Hartzell's recommendation is based 
> on
> some harmonic resonance or some other vibration related things (which are
> outside my knowledge).  Does my 70" blade length provide cruise or climb
> capabilities that are greater or lesser than a 68" prop.
>
> I'm planning to have the 70" blades reinstalled on the new hub, and the 
> log
> entry will just say the standard overhaul stuff (except the IAW stuff), 
> and it
> will specify "experimental A/C usage only."
>
> Any thoughts?
>
> Thanks,
> Matt McManus
> lnc2 360
> 408 hours total time airplane.
>
>
>
>
> --
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