Cumic Build 18/ 2019

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Updated Apr 13

Updated Apr 16

Update Apr 19

The 100 inch Cumic

“V-Tail ” was one of Lee Renauds prototypes that was never kitted, apparently there were some Prototype Kits handed out back in the day.

The Plans show full flying articulating V-Tail surfaces

The wing is two panel, plug in style like the Aquila’s and Sagitta, the pod form, more reminisant of the Aquila’s though

The inner panel is constant chord and the outer is swept the complete wing has a straight trailing edge

The fuse is a thinner Aquila style, wood and ply pod and boom style.

Cumic designed in 1972 and updated in 1973.

From the Plans

Airtronics Design, July 20, 1972

Revised Mar 12, 1973

100 Inch Wing Span Standard Class

620 Sq In

16:1 Aspect Ratio

For Comparison, other Vintage Airtronics Sailplane Info

Super Questor

WS 80 Inch (projected Flat)

Airfoil   E 385 Flat bottom                           (Questor is E 385 Flat bottom)

Aspect Ratio 12.1: 1

Wing Area Tapered Tips 500 Sq In

Aquila Grande
WS 123 Inch
Airfoil LR51510
Aspect Ratio 15.1 : 1
Wing Area 1000 Sq In

Grand Esprit

WS 134 Inch
Airfoil Eppler E385 f b
Aspect Ratio 16.6 : 1
Wing Area 1100 Sq In

WS 99 Inch
Airfoil  12% flat bottom
Aspect Ratio 12.3 : 1
Wing Area 810 Sq In

Sagitta 900

WS 99 Inch
Airfoil Eppler E205
Aspect Ratio 11.1: 1
Wing Area 900 Sq In


Well onward and upward

There will be some changes, from some of the Detail shown on the PDF file

  • the stab set will be fixed
  • the trailing edges will be done with some 3/16 wide spruce
  • the wing rods, I believe they are shown as .187 dia, will be changed to a single 1/4 inch rod
  • the poly hedral, and dihedral angles will be increased
  • the canopy will be a little shorter, Aquila canopy, as near as I can tell shows a Canopy app. 3/4 inch longer more like what was used on the Grand Esprit, though perhaps the Cumic fuselage is narrower
  • spoilers will be added, dial cord actuated
  • I never had any good luck printing a PDF file for a plane build and being happy with the results, so I have made some assumptions, gathered some dimensions, and recreated the Cumic in Auto Cad. As I go along I can pick up size info from the plans and Build this Beauty

Some more rib detail as well as Trailing edge notches

the ribs get cut one at a time with a single edge razor blade, and later get cleaned up with sandpaper, and have the notches cleared correctly

the inner panel ribs are in the forward stack

I had previously marked the trailing edges for the rib notches and use a stop and eyes, to control the width. The original plans did not have these notches

checking for fit, the outline of the wing panels are on a piece of Kraft paper, I do that work with some dimensions and a Mechanical Drafting arm, the good ole days

the tip panel ribs two of each, and the notches are cleaned at a bit of an angle to suite the spar

Jan 27 2017

leading edge, trailing edge, trailing edge caps, spars

Just like building a kit, getting all the long lumber together and cut to dimension

More lumber , the spars are 3/32 x 1/4 Inch

Trailing edge notches were previously added to suit the rib tails

tip panel, lower spar trailing edge and 7 ribs. Want both panels the same, measure and precut spars and mark the rib location, never fails

Feb 01

cut outs for the spoilers, the original Cumic did not have any spoilers

looks like the inboard end of an inner Panel

lower spar ribs and rear trailing edge

set to glue down some more ribs, I have a Mark on the lower spar, and there’s a line going back to the TE to align the ribs

Feb 02

Ribs are modded from original plans to suite capped trailing edges and notches at ends

tip up, match panels at polyhedral join

gussets at root corners

leading edge top to match rib top for later upper d tube sheet overlap

Panel stack

3/32 square diagonals glued in three places

Feb 11

tip panel build continues, diagonals are proud of the bottom surface over the wing and run over the lower spar

diagonal lumber ripped to dimension

shear webbing gets diagonal notches added to suit each rib bay

something like this, the height of the shear web still needs some adjustment

I like to thin use thinner material for the shear webs as I proceed out the tip

Mar 20

leading edge needs some work

fuselage forward template, aft is tapered 1/8 balsa

top spar set down with level

small drag spar, perhaps unnecessary, but was shown on the original plans


inner panel roots

1/16 doublers on tip panels

tip panel spar set

forward fuse lite ply

dial cord tubing

inner panel set

wing rod tube box ply doublers

rear ply doubler

rear ply doubler clamped

fuse forward sides cut

upper d box sheet. no lower sheet on this model

cap strips




oops, no order here, back to fuselage pieces I see

3 nose blocks, need a Cumic?

checking the fit

lower corner stock

April 01

Fuselage formers with control rod holes and servo wire pass thrus
I ,like to get the locations for all formers indicated accurately
more prep work, wing rod tube hole
a level comes in handy to check the sides from tail end forward to in front of the wing leading edge
a ply doubler is used where the lite ply sides join with the aft balsa
wing rod tube thru here, fillets at corners
former to fuse side fillets cut from tri stock
fillets cut to length and angled at the bottom for clearance
canopy opening doubler in place
nose block and formers in place, keep an eye on shape here to get symetry on both side
lower aft fuselage
crosspieces for servo tray
v tail block notch in fuse, I want some freedom here to make adjustmentsdd
just a piece of 1/8 lite ply
stab set, with some aluminum tubes, no offset, didn’t want that complication
parts and pieces for the stabs
square jig in place helps with alignment later
a few diagonal ribs
and some support for the aluminum tubes
this should work
from the forward side
both stab sets
v tail mount build up
both fuses with notches
fuse forward

April 07

fuse rear top 1/4 balsa sheet
hardwood block for around the wing rod tube
epoxy and a couple clamps
from the underside
V-tail setup, square to the board
a little time spent here
set along the lines as well
back side or down, against a straight edge
bits for the tail mount
tail set into fuse, a couple screws will hold this down
underside of the tail mount
looking a lot better

April 19

Fuselage detail, with a hollowed out aft canopy block so I can get at the wing retainer spring
Underside, rough, will clean up to suit
Tail feathers set in at fuse rear, angles everywhere 🙂
stuff to secure wing to fuse, gets added at wing root
4 x 1/8 ply wing root fillets, this will clean up the wing to fuselage transition nicely
This hand held coping saw goes back to the early 70’s real quite as well
here we are holes added, I think I have them all , can open them up later if needed
back to the stab set with the moveable part ready for some shaping
V Tail aft