Construction of 1/9 Grumman Goose by Scale Dynamics
Copyright 1995,1999 by Jeffrey E. Perkins
Wing construction is not conventional. You may note that both left and right wing panels have been provided. The reason is that the wings must be constructed upside down. The left wing is depicted on drawing sheet 1. Use this view to construct the right wing, that is, upside down. Also, use the drawing sheet 2 to build the lift wing, again, upside down. Note that the wing ribs each has a reference line, which should be parallel with you’re your building board during construction. When joining the wing halves, be sure to secure them so that you can ensure for proper dihedral. Although the full size aircraft has 0 degrees dihedral, 1 or 2 degrees would not hurt the model. My preference on dihedral is scale appearance. Due to not anchoring the wings, my model has several degrees of anhedral. Oops!
Wing joining is also done upside down. Warning… do not install WP1 before joining wing halves since the top of the main spar is used as a reference line. Use a flat table to join the wing halves. Mine apparently wasn’t. This gives a dihedral of zero degrees on the top surface of the wing. And 3 degrees of built in dihedral on the bottom surface on each wing. The CG is located at 25% chord but it also should be actually below the wing to ensure stability. The CG was not given on the information supplied by Grumman. The weight of the fuselage on the real Goose helps somewhat with stability wanting to level the wings. If the model’s wing weighs more than the fuselage, some ballast may be added to the fuse help roll stability. The wing tip floats will tend to dig into the water with a top-heavy flying boat. Therefore, install the servos low in the fuse.
Wing ribs are on drawing sheet 3. The wingtip floats sections upper right is 1/8 balsa with 1/32 ply for extra strength.
This is the most tedious method to construct the wings. Build the wings using complete ribs. Cut out the ribs as shown on drawing sheet 3 except, include the slot on W1-W7 and proceed as follows. This method will ensure the trailing edge lines up with each rib without undue attention from the builder. The down side is that the centers of W1-W7 must be cut out in place, which is very tedious. The main spar insert must then be slid in, test fitted, removed and replaced after adding glue. I built one half a wing in this manner and devised wing method II.
The benefit of this improved method is that installation of the main spar insert and the tedious cutting of the ribs while in place are eliminated. The only down side is that the trailing edges are harder to line up. The addition of the forward and aft ¼ square balsa runners was added to ensure alignment. The other deviation from a normal wing construction method is that the ¼ inch hardwood outer spar runners are laid flat on the table and the main spar insert is added and allowed to dry. W1-W7 is added with the main spar assembly laying flat. After drying, lay the assembly down, upside down on the wing plan sheet in the usual normal wing construction manner. The forward part of the ribs through W1 & W2 are not used as shown on the plans. You must remove 1/8 inch of W3 & W4 (I made W3 [forward] of ¼ inch balsa) forward of the main spar to account for WP-1 thickness (1/8 inch). Note that I used ¼ inch dowels as opposed to what is shown on the plans. In addition to what is shown on the plans, I added two 1/8-inch runners at the corners of forward part of the wing ribs so that I could put off adding the ½ thick leading edge until after the wing is sheeted. The main purpose of the extra runners was to allow sheeting the wing without the leading edge in place, later making it easier to blend the leading edge with the sheeting on the wing. See the printout called Addendum.cad for a one piece WP-1.
As best I can tell the Goose had spit flaps. This is the reason for the dashed lines on
the plans. A scale deviation would be
to make STD flaps perhaps with a smaller area.
These flaps look very large in area for a model. The flap angle should be kept small for the
model. Deflection for the real Goose was two notches: 30 & 60 degrees. I consider flaps a necessity. My nine
(now 9+) twin Long John (similar to Ugly Stick) slows it down on those
hot Texas humid days. The landing
performance with flaps down is very noticeable, slowing the model
significantly. Once you have flaps on a model, you will always prefer any model to
have them.
Construct using 1/16 balsa making ribs of appropriate size to fit proper contour. The real Goose had movement both up and down of 20 degrees. Modern aircraft such as the Piper Cherokee have less down aileron than up, which reduces adverse yaw.
The float is angled outboard 3 degrees using the top surface of the main spar as a reference line. The floats are 90 degrees to the bottom surface of the wing. Note webbing parts on sheets 1 & 2. The webbing at the float has some plywood, the thickness of which is designed for an exact fit. In practice, the fit may not come out exactly correct. Mine did on one but not the other. The main purpose of the plywood is to have a good surface to mount the aft float strut to. Not shown on the plans is a cross member to the float struts, which is about 1/8 inch thick. The shape of the scale strut is elliptical. This part was designed was thought to not be necessary. However, the strut is not stiff enough as shown on the plans. You can find this part on Addendum.cad. My model has brass brackets and wires for the floats (at scale locations). It is advisable to add the stiffener. You should consider stubbing the float, attaching them with bolts and nuts which will prevent damage to the wing. I saw a neat attachment scheme, which consisted of slots in the wing. The floats strut ends simply slide in and brace wires hold them in place. Should a hard landing occur, the idea is to prevent damage to both the wing and float.
The float is designed to be built in a top and bottom a half. The construction order is given in reverse order in these instructions versus the actual assembly order. The skin flat patterns are shown on sheet 3. The skin thickness was wrongly designed for 1/16 but the balsa cannot bend around the curves. So, 1/16 skin was used on the hull of the float and 1/32 elsewhere. Cut all skins slightly oversized. Start by mounting the bottom skins first; trim when dry. Next, add the sides and work up. The floats are tedious to sheet but their final weight was about 1.5 oz without glass and paint. You can use an inside coat of Titebond all over the inside of the skins for warping and added strength on thin balsa after dryad.
Back to the typical construction sequence. Frame up the float in both a top and bottom half. The two struts are added just prior to sheeting. The float formers shown top right on drawing sheet 3 are stiffened with 1/32 plywood. This also gives the struts a better surface to glue to. Good contact cement should do the job but warping should be avoided. Old college books are a good tool to use a pressing tool to prevent warping while drying. The plywood on these parts all face forward on assembly. If you like, save a step by making the strut formers out of 1/8-inch plywood. The float side rails have no designation on them. You need 4 side rails per float. The float keel is made of 1/8 plywood and is designed to fit exactly with all the former slots (why did I bother with this). You may need to soften the stringers with water, pre warping them if necessary. Hard balsa stringers are preferred but softer balsas will maker your job easier. Assemble the two float halves. Next install the forward strut and allow drying. Add the aft strut using the TOOL_1 provided on sheet 3; align aft strut with forward strut-eyeball it. Sheet the float completely.
It is also built in a top and a bottom half. The formers are not exactly identical so you
should mark each of them top and bottom.
However, the cowling formers top and bottom is identical. This nacelle shape was very strange but this
is what was on the minimum drawing from Grumman. The “Top View” on sheet 4 is used to lie out the formers onto the
side rails (1/16 plywood). I pinned
these parts by bending T pins around them while gluing NA2 through NA5. A note on designations: N=nacelle,
A=aft of firewall. Add all “half”
formers. Epoxy the two nacelle halves
together. Add the end pieces, NA1 forward, and NA6 aft; epoxy. It would be
a good idea to coat all parts with a thin coating of epoxy thinned with acetone
before sheeting or assembly of nacelle halves.
Add 1/8-inch square hardwood stringers two at a time to prevent
warping. Hold in place with rubber
bands. Sheet with 1/16 balsa (basswood
might be ok). Make each panel to cover
through ½ of two of the stringers.
There are six separate panels.
Glue in place onto wing assembly with epoxy. I get #6 screws from Wall Mart to use for plain hatch
covers. Use one of these or similar to
hold in place onto WP-1 while epoxy
is curing. Don’t bother trying to
remove the screw later. The screw will
help make sure you get a solid bond with no air in between. Note:
it is easier to install the blind nuts in NA1 prior to gluing it onto the end
of the Nacelle.
Note on sheet 4 (top right of page) that CWL1 is shown located on NA1A (removable firewall). This is for reference only. It is not glued to NA1A and must fit around NA1A. Make a copy for all the cowl parts since only enough are shown for one cowling. Glue the four CWL3 parts together using the view marked “CWL3” found on the left side of sheet 4. Glue the cowing in 2 separate decks. This part is Very light when finished. A cowling cut from balsa or foam blocks might be easier to make.
A left side view is shown on sheet 5. It is ½ scale. The tail wheel is not shown but is located aft of F29, from balsa edge to 2.01 inches.
The boat section is built upside down. Use the layout on sheet 6. Layout Boat-1 through Boat-5, reinforcing butt joints with scrap 1/8 balsa. Locate balsa “spine” (1/4 x ½ stock) on centerline allowing excess on ends. The overhanging ends are pinned to help prevent the boat from warping after adding balsa skin. Glue in place F1L-F29L (L=lower), Wing_Fwd and Wing_Aft. Glue in N1 & N2 (orient approximately 45 degrees) as shown on sheet 5. Shape and sand to shape. Add 1/8 square balsa stringers. Add balsa keels. The keel on the forward boat section is in two pieces. The “straight” piece is not straight but curved, dished out. This is per the Grumman drawing. This part, with the arrow & fwd, installs on the model one way. The shape probably helps the Goose get off the water easier but will have no noticeable affect on how the model handles. Add aft balsa sheeting (1/8) over F17-F29. Sheet the forward section using two layers of 1/6 balsa. It is rather tricky going around the curves on the just aft of the nose. You might consider blocking this in with balsa.
To aid in construction I made a boat stand. Its base is 25& ½ inches long using F4 & WING_AFT as a guide. Glue
on formers F1T-F8T. Add stiffener and 1/8 square balsa stringers
and 1/16 sheeting. Orient the sheeting
at about 30 degrees to slip around the curves.
Note: Add sheeting after building
cabin section. Suggestion: extend cabin
section forward as a hatch, giving access to the forward part of the fuse.
See sheet 7 for pictorial, parts ad construction sequence. Note: No allowance has been made for gasket clearance of the cabin section to the fuselage. A friend from Canada modified this and made it extend farther to the nose to allow access to the fuse where a battery pack can be located. It is also handy to add nose ballast weight in this location. Recently I discovered an error in the design. The diagonal cross member WIN-X is not correct. Instead, after building the frame, shape a part that will follow the curve of WIN-2 flowing evenly down to the windshield. The real goose had 3 pieces formed to shape on each side above the pilot.
Assemble the cabin by working from forward to aft. Place wax paper over the exposed boat section since it needs to be built to fit. You may prefer to use balsa for the two forward formers but backing them up with 1/8 balsa but modifying other parts such as WIN-2 is required. Follow the sequence as shown on the plans. Be sure to align the two side pieces with F13T. So far I have only built one of these cabin assemblies but I intend to build one more. The problem of warping of the two sides. WIN-1A, occurred during painting. I would suggest sheeting with 1/32 ply at least on the outside with the side pilot’s window cut oversized around the 3 open edges. The gap will allow space to place the side window; mounted inside. The flat pattern for the main window, WIN-FP1C.cad is drawn to the exact size to fit around the front window with no overlap. I believe it can be installed as is drawn. Work from forward to aft by first gluing in F9 & F10; use cloths pins to hold thin ply F9 against 1/8 balsa top former F8. Now add 1/16 skin to forward top section (not part of cabin section). Add 1/8 stringers to cabin section. Add cabin sides, WIN-2. Simplification: It may be simpler to replace the too numerous parts WIN-11 (-1, -2, -3, & no dash) with solid balsa blocks sanding to shape. I am including several photocopies of color photos to clarify this shape.
Add the remaining fuse formers to the top section if you have not done so. Add 1/8 square balsa stringers and sheet with 1/16 balsa. This was delayed until now to aid in constructing the cabin section.
This part is impractical to build as shown but the formers are the correct shape; OUTSIDE MOLD LINE. It would be better to solid this in with balsa. I offer this part with the nacelle fairing for a reasonable price. To make a solid part, glue or contact cement 1/16 plywood with an appropriate thickness of balsa wood. Glue all this mess together and sand the inside to fit the contour of the wing. Shape the top surface to that of the plywood sandwiched formers. The formers have the inside shape predefined for you and are correct.
This was the most difficult to design. This was my opinion when the instructions were first written but actually this would be difficult to build as shown with sheeting; impractical. Please do not cutout the parts shown on the blue line drawing since new parts are defined in the extra printout (aft0.cad). I will leave it to you to figure out the assembly procedure of the old aft section (don’t bother). The new (summer 98) design is build in two halves on the vertical cut line (plane). Assemble as shown on the print out. Glue the two halves together. Be sure to check that F29 matches that of the fuselage. Add stringers a pair at a time (opposite sides of the fuse) to avoid warping. The old aft section was very rigid. Add balsa scrap blocks about the horizontal stab saddle. Shape the leading edge of the aft section and the saddle. Add 1/16 sheeting all around the assembly.
This part is much easier to build. It fits together like a jig saw puzzle. Mine went together easily and sheeted nicely with 1/16 balsa, angling the grain at about 45 degrees. You can build it in “abstract vector space” or without use of the plans as long as the parts are cut out accurate enough.
Perhaps you have already guessed that the rudder is not built in a typical manner. Use the construction guide on the drawing. The ribs are glued at a right angle to the building board. Locate the ribs R3-R8 onto R9. R2 ‘s top edge fits at the edge of the slot in R9. Notice the indentations in R11. R14 goes between R7 & R8 on the center- line of R9. Use R11 to check the fit of R3-R8 but do not glue in place yet. You can add R13 now or after removing the rudder assembly from the worktable. Remove the assembly from the work surface after dried and add R10 to the slot in R9. Also add R11, R1 and R2. Finally add R12 and R13 wooden blocks. I found R13, as a foam block was not worth the trouble; wood is easier to shape. Sheet the ruder with 1/16 balsa. The real goose had a fabric-covered rudder. I always seal the sheeting with a coat of clear dope when using plastic covering. There are always some loose balsa fibers after sanding and these somewhat prevents the heat shrink covering from sticking. However, I covered my rudder with ¾ oz cloth and water based floor covering which is a non-toxic material. This water base covering caused the panels to warp or bow inward, giving the typical drooping affect of real fabric covering. Note: Sheet with the grain parallel to the ribs.
The Horizontal stab and elevator are constructed in a similar fashion as the rudder described above, they are both built with the ribs point up 90 degrees from your building board. The horizontal stab is built in two pieces and later joined, with zero dihedral. The elevator is built in one piece and separated at the center section after adding the music wire. I sheeted the stab with 1/32 basswood and the elevator with 1/16 balsa wood sheeting. The results were light and strong but the bass wood warped slightly after using water based coating over the ¾ oz clothe.
Construct the horizontal stab with the construction guide
given on sheet 10 of the drawing set.
Glue H1 on to S1, adding H2 through H6. Check alignment of each
rib as you go to the previous one.
Allow to dry and reinforce all joints with a waterproof glue (I use
Titebond). Add the hardwood
stringers. Add wingtips. The wingtip ribs are too small to be
practical so the use of thick sheeting works better. Cover with 1/16 balsa sheeting but as noted before, I found 1/32
basswood took the compound curves well without warping the internal structure. If you like, try bonding the 1/32 balsa to
1/32 basswood for better finishing results, putting the balsa on the
outside. I always give it a coat of
clear butyrate dope before covering.
This will seal the balsa skin and tack down any loose balsa dust before
covering with plastic heat shrink types.
If you use ¾ oz cloth and the water based “floor sealant” I would use two coats of clear dope. For
simpler construction, build the horizontal section in two parts and join
together, which makes it easier to add the stringers and sheeting later.
Build the elevator in one piece starting with S2 pinned to the construction guide. I made S2 a little wider than shown on the plan set, you can sand it down later. S2 is slightly too narrow but this part was not revised. Glue in E2A, which is the most current part. Add S3A to the centerline of S2, also with E2A. The old part, E2 should not be used since the rudder throw will be too limited. The unrevised part, E2, was based on the full-scale aircraft. Install the piano wire with epoxy and small diameter brass wire typically used to solder landing gear wire together. The assembly will not fail. Continue adding ribs through E6, making sure the airfoil lines line up with each of the other ribs. Add the WT-2 end pieces. Add S4A. Add trailing edge balsa and sand to shape. Again, like H7, E7 is a bit of a waste of time but add it if you like. You can glue a piece of scrape wood in place of E7 and sand to shape, allowing for the sheeting to be added later. I sheeted my elevator with 1/16 balsa and covered it with ¾ oz cloth. It was light and strong. Install your control horn before sheeting. For strength, angle the sheeting to be parallel with S4A.