Ken Powell wrote:

Hi Everyone,
   In the interests of sharing information, I decided to share the CG
calcs I have done in preparation of installing a 13b in a RV-4.  I am
doing a firewall forward mockup at this time and will have some pictures
in the next month.  If you find errors in either the results or the
assumptions, please let me know.  Possible errors in the assumptions are
the estimated firewall forward weight of the 13b or the Lycoming (345
lb) or the location of the CG of either the Lycoming or the 13B.
   In this exercise, I followed the methodology of Alan Tolle and
'removed' the Lycoming and 'installed' the 13b at various locations.
Note that engine CG was the variable for these calculations, not the
prop flange.
   Here are some interesting observations on RV-4 CG (these measurements
were taken using page 26 of the RV-4 plans set as a template):

1.  If the Lyc and 13B are prop flange to prop flange, then the CG of
the engine moves aft 3.00".

2.  If the CG's of the Lyc and the 13b are equal, the prop flange of the
13b moves forward 2.125".

3.  If the 13b CG is moved forward of the Lyc CG by 4", the prop flange
(for the psru) is 6.125" forward of the Lync prop flange (with a 4'
extension).

4.  If the 13b CG is moved forward of the Lyc CG by 5", the prop flange
(for the psru) is 7.125" forward of the Lync prop flange (with a 4'
extension).

5.  If the 13b CG is moved forward of the Lyc CG by 6", the prop flange
(for the psru) is 7.125" forward of the Lync prop flange (with a 4'
extension).

Assumptions:

1.  The CG of the Lyc is 10" aft of the crankshaft flange (without the
prop extension).

2.  The CG of the 13b is 21" aft of the psru/prop flange (this does mean
the psru prop flange) - the Ross drive is 14.51" long and Tracy's drive
is 14.625" long

3.  That both engines with all systems weigh 345 lbs (this is Tracy's
estimate).  These calcs do not recalculate the CG of the 13b based on
the weight of the radiators, coolant and oil being located in different
configurations. The CG is in the middle of the mass, i.e., 21"  from the
prop flange.

4.  That both engines with all systems weigh 345 lbs (this is from
Tracy's Conversion Guide).

NOTE: The CG locations are the positions quoted by Alan Tolle in March
of 1999 on Paul's Newsletter.  Alan stated that the Lycoming CG is 14"
from the prop flange and I interpreted this to mean 10" behind the
crankshaft prop flange / without the extension.  He also estimated the
13b with Ross redrive at 21.1" which I rounded to 21".

ASSUMPTIONS:
-- PLANE IS A RV-4 --  THIS IS THE MOST FORWARD ALLOWED CG!!!!!!
192 lb = FULL FUEL (32 GALS)
170 LB PILOT
NO PASSENGER
NO REAR BAGGAGE
12 LB'S FRONT BAGGAGE
12 lb oil (7 qt instead of 8 qt)
345 LB engine weight for both the lycoming and the 13B 950 lb aircraft
total weight
Lycoming CG = 16" in aft of datum / 14" aft of the prop flange (the CG
distance from the datum for the Lycoming was the biggest guesstimate)
13B CG = 21" aft of prop flange

Ken Powell

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