Posted for "Giffen Marr" <GAMarr@Charter.Net>:

Marv
I have seen both. My guess is that the single fin has the least drag, but
requires the greatest ground clearance. the V fin has more drag, but allows
for a higher pitch angle for both take-off and landing.
Giff Marr
LIV-P/Mistral

[If you put a single ventral fin on the bottom of a typical LIVP it would have to be a couple feet+ deep before it ever came anywhere near to having a ground clearance issue. Considering a typical critical AOA of about 15-16 degrees and that there is already a positive angle of incidence in the wings, there is no chance of impacting a typical ventral fin during either takeoff or landing as you would have to rotate well beyond the stall point to close that gap. IMHO that would have to take some really ham-fisted stick handling and a tail strike would likely be the least of one's worries <G>. (We installed a 12" deep one on Ted Noel's IVP and checked ground clearance by raising the nose so the fuselage was 10 degrees nose up (to simulate a 35-40% below critical AOA) and we still had almost 2 feet of clearance, if memory serves.) But that wasn't really my question... I'm still wondering if there are any actual reports comparing the two styles? Furthermore, how does one go about determining what the included angle should be between the legs of the "V" and the optimal area required on an inverted-V style fin in order to maximize the desired yaw effect with the least amount of drag? Some years ago Curt Longo was going to do the aero work on an inverted-V fin designed specifically for the IV but he became detached from that project before bringing it to completion. <Marv> ]

_____

From: marv@lancair.net [mailto:marv@lancair.net]
Sent: Sunday, April 29, 2007 5:19 PM
To: Lancair Mailing List
Subject: Re: [LML] Re: Lancair IV turbine yaw solutions?

I'm curious if there are any NACA/NASA/other reports out there regarding the
inverted-V style of ventral fin vs a single vertically-oriented ventral
fin... anybody ever see one? As mentioned countless times here, anecdotal
evidence ("He developed it for the garrett conversion and said it was quite
effective") is nice but a well-documented aerodynamic test series would be
better. Not casting aspersions or throwing stones, just curious.

<Marv>

"Colyn Case on earthlink" <colyncase@earthlink.net wrote>:

Berni,
I have not converted to a turbine. However, you can buy a ventral fin
kit from Mike Custard at www.advancedaviationinc.com . He developed it for
the garrett conversion and said it was quite effective.

Colyn