Comet
Sailplane Project
This report
is dedicate to documenting the
characteristics of the Comet Sailplane configuration.
The specifications for Comet Sailplane that I
am currently building for the 2009 SAM champs are listed in the
Specification Block shown below on Comet plan Plate No.3, which has a
copyright date of 1946 in the lower left corner.
For the past few of days Alfredo Herbon, Jim
O'Reilly, Gene Wallock, and myself have been involved in correlating and
validating dimensions and areas of the Sailplane configuration
geometry drawn on the Comet plan with the numbers in the Specification
block. A summary of our collective findings are presented below, which
will then be discussed further below.
Flat Plan Wing Span...........80-1/2
in.
Flat Plan Wing Area.................890 sq.in.
Projected Wing Span..................78 in.
Projected Wing Area...............864 sq.in.
Stab Span.....................................36 in.
Stab Area..................................294 sq.in.
Rudder Span...................................8 in.
Rudder Area................................47 sq.in.
Fuselage Sub Rudder Span....1.32 in.
Fuselage Sub Rudder Area...5.55 sq.in.
Stab Sub Rudder
Span..........2.77 in.
Stab Sub Rudder Area..........6.32 sq.in.
Fuselage Length............................51 in.
Wing Discussion
Alfredo developed the wing planform below with
his AutoCad program. All measurements of the wing dimensions shown were
taken from my copy of the Sailplane Comet plan. Alfredo use AutoCad to
determining the flat plan wing of 890.69 sq.in. Jim O'Reilly independently
came up with a flat plate wing area of 889.7 sq.in., both of which are
very close to 890 sq.in.
Using 10 degrees for the wing's inner panel
dihedral angle, 28 degrees for wing's tip panel polyhedral angle, Alfredo
calculated the projected wing semi-span to be 38.29". This was close
enough to the specification value (78/2) = 39", considering paper
shrinkage and measurement inaccuracies, to conclude that the Specification
Block 78" span and 834 sq.in. area are
"PROJECTED" values.
Stab Discussion
Alfredo developed the stab planform below with
his AutoCad program and determined the area to be 294.17 sq.in. based on a
stab span of 36 in.
Rudder Discussion
Alfredo developed the rudder planform below
with his AutoCad program and determined the area to be 47.02 sq.in. based
on a rudder span of 7.96 in.
Sub Rudder Discussion
Alfredo developed the fuselage sub rudder
planform below with his AutoCad program and determined the area to be 5.55
sq.in. based on a rudder span of 1.32 in.
Alfredo developed the stab sub rudder
planform below with his AutoCad program and determined the area to
be 6.32 sq.in. based on a sub rudder span of 2.77 in.
Small Rudder Discussion
In the latest issue of SAM Speaks, Gene
identified two Sailplane configurations, on with a large rudder and one
with a small rudder. The one with the small rudder is seldom seen, but
Alfredo was aware of it and actually had seen one fly. He said it was
literally uncontrollable under full power due to a violent Dutch Roll
tendency. This Sailplane with the small rudder was built from a Sailplane
plan that appeared in the excellent Argentine magazine "Aeromodelismo",
published during late 1940's and early 1950's in Buenos Aires. Alfredo was
able to developed the "small rudder" planform below with his AutoCad
program and determined the area to be 24.68 sq.in. based on a rudder span
of 4.71 in.
Fuselage Length Discussion
I measured from the Bulkhead No. 1 aft to rear
tip of the stab platform to be 47-1/8". I then measured the cowl (shown on
a different place on the plan) from the Bulkhead No. 1 forward to the
front face of the cowl to be 3-7/8". The measured length from the
front face of the cowl to the rear tip of the stab platform is therefore
51". Gene Wallock indicates that total length is generally measured from
the prop back to the tail, which would account for most of the 3/4"
difference in the specification value of 51-3/4" value.
I want to extend my personal thanks and
gratitude for all of support in this effort, but especially to Alfredo
Herbon who responded so generously with his time and his
interest........................Tandy