Excerpt from March 2009 STARS Newsletter
Walt H. suggested the club once again have an airplane project similar to what the club once did in the past with the Bristol Scout biplanes.
Dick S. presented a possible Russian Yak-6 twin electric motor plan which club members could build. This plane would have a wingspan of 73.75, wing area of 5.75 sq/ft, weight approx. 6 lbs., producing a wing loading of 16 oz. Cost for two electric motors and ESCs would be approximately $90. 90 oz of thrust would be produced with a 7.4 volt battery pack which equates to 45 oz/motor. This is a high lift airfoil design. Suggest we use two - 2 cell 7.4 volt lipos at 2300 to 2500ma for a cost of $35 each. All together cost would be approximately $200.
Gary F. suggested looking into hobbyking.com for batteries as well. Walt thought if 5 to 6 members were interested, it could lead to more media about STARS and possible new members. We may even be able to build kits to make it easier for others to build.
Dick has compiled Material Lists for the Yak 6.
Click on images or links below to view.
The first assemblies to be constructed are the
wing center section(s) and the forward fuselage. I like to begin with a "kit" of the sub assemblies I am building. The first step for me is to make patterns. In the process of making patterns I will make some corrections which I will then be able to incorporate into the instructions with the
construction photos.
To make the patterns, which will be used to trace the shapes onto the wood, I do the following, using the Staples Plan Copy, a red ink pen, carbon paper and poster board:
Using a red pen (so I know where I have traced), I make carbon copies of elements of the drawing
onto thin poster board. I make notes on the
drawing at the same time which are carboned
onto the parts being copied. Next I will cut these
parts out of the poster board and trace them onto the wood. Then I will make the sub assembly "kit" and start putting parts together. This is only a suggestion. If you prefer to do it a different way, please do.
Shown here are the patterns for the forward
fuselage module sides, the center section ribs,
the forward fuselage crutch cross pieces and the
forward fuselage bulkheads.
Some corrections were necessary on the rib
pattern.
Ribs for wing center section traced onto 3/32"
med/hard balsa from (corrected) rib pattern(s).
If you are building a 2 piece wing which separates in the middle, R1 should be 1/8" lite ply or ply. If you are building a one piece wing R1 may be 3/32" or 1/8" balsa.
Shown here is 99% of the wing center section parts. Not shown is the 1/16" wing center section
sheeting. Remember, the center section is built in 2 halves. At the top of the photo are the
hardwood landing gear blocks. You can make these or buy commercially available blocks and modify them to fit.
After the landing gear blocks are the 5/16" Balsa spars. I cut mine from 3/8" square stock. The spar webbing is not shown. It will be 1/16" sheet balsa with the grain running vertically. I may
use thinner ply webbing - haven't decided. Next are the 1" sheet balsa leading edge pieces. They are I" X 2" X correct length.
Between the L.E. pieces are the ply pieces which will hold the dowels for wing/fuselage attachment. Some bracing will have to be added to this joint.
Next is the 1/4" ply wing joiner brace. It will have a 1/16" sheet balsa laminated to one side to make sanding to a slip fit easier. The wing joiner will be glued into the right wing half only and will "slip fit" in/out of the left wing half when assembling/disassembling at the field.
The ribs are shown on either side of the center section.
The aluminum tubing shown is installed at the rear of the wing ribs at the indicated locations. The
smaller diameter / longer tube will be glued into the right wing half to half the tube's length. The
larger diameter shorter tube will be glued into the left wing half. The tubes will telescope
together/apart when assembly/disassembly takes place at the field.
At the rear of the photo are shown 1/2" X 1 1/2" Trailing edge stock pieces that will be installed
between the wing sheeting as well as the 1/16" ply pieces which will go on the bottom. This is where the wing hold down bolts will pass through.
If you think of any improvements to this construction please let us know about your ideas.
The next photos will be during construction.
Shown above and to the left is the wing center
section left side with the spar webs added.
Next will be the top sheeting.
After the top sheet has been added, the rib trailing edge taper at bottom can be sanded to a
point intersecting the top balsa wing sheeting as shown. The center section trailing edge
stock has been added and the slotted landing gear block has been slid into place from the
center and epoxied into place. Note that the ribs supporting the L.G. block were reinforced
with 3/16" square balsa stubs to give more support and glue area to the L.G. block. A ply
doubler will be added to the landing gear where it is to be drilled through for the 3/16" landing
gear wire stub.
In the next photos, the wing bottom will be
sheeted, the leading edge will be shaped and
the 1/16" reinforcing plate for the wing
attachment bolt will be added. As always -- as long as the correct angles are maintained, if you have a preferred way of doing these steps of construction, please do so and advise us of any improvements you think could be made.
To the right are photos of the completed
left side wing center section - Top view
then the bottom.
I'll start on the right side assembly next
Wing center sections as one unit
The forward fuselage upper and lower fuselage sides. The upper sides are built on a crutch first, and then the assembly is turned over and the lower fuselage is built onto the upper assembly.
The two pieces that comprise the wing center section
Shows all the upper bulkheads assembled and ready to be installed on the crutch
Shows all the lower bulkheads assembled and ready to install on the crutch
Shows the 3/16" balsa crutch cross pieces. The sides of the crutch are simply 3/16" square balsa strip.
These 4 photos are of the forward upper fuselage being built on the crutch
Assembling roof framework of upper front half of
fuselage. Also building in the framework for the
top hatch, using plastic wrap to separate the
hatch from the rest of the structure.
The same structure shown 3/4 rear view
Shows the hatch framework removed
Showing the roof has been sheeted.
Photos showing preparation prior to sheeting the top of the hatch
Photo showing hatch has been sheeted and in place. Roof sheeting is all 1/16" balsa
These photos show construction of the removable (eventually) nose structure.
The entire nose from the front to bulkhead #3 will be a removable unit. It will be done with a simple "twist lock" mechanism built into the structure.
These photos show drilling bulkhead #3 for the "twist lock" mechanism
This photo and the next show the nose ready to
be planked with 1/8" sheet balsa.
Because the nose will later be made removable, there is plastic wrap between bulkheads 3B and 3C so as not to glue them together
Photo showing the 1/8" nose planking completed.
Photo showing the planked nose section with a
piece of paper inserted between bulkheads 3B
and 3C to show that they are not glued together.
At this point they are held together only by the
fuselage crutch. The nose section will later be
made removable as the battery access hatch.
These three photos show the forward fuselage bottom half being assembled onto the crutch and upper
half of forward fuselage.
The cross members of the crutch between bulkheads #3-4-5 will eventually be cut away to allow installation of the batter box.
Bottom view of forward fuselage, showing crutch cross members removed @ bulkheads 3-4-5 to allow battery box to be built into fuselage.
Sheeting has begun.
Photo above shows the front of the forward
fuselage module all sheeted and the nose block added and shaped.
Photo showing the chin sheeted , the air scoop added and the nose block shaped
Photo showing the removable battery hatch
(nose) at 1/8 turn for removal
Battery box hatch removed. Battery box can now be built into fuselage
Photo shows 3 sides of the battery box installed in the front of the fuselage. The bottom of the box is plywood and has holes drilled in it to accept airflow from the chin scoop and will help to keep the batteries cool
Photo shows the battery box completed.
The sides and top are 1/8 inch balsa
Photo shows the battery box installed and the
removable nose cone attached. The battery box extends from bulkhead 3 to bulkhead 5 and also serves to stiffen the nose area.
Photos showing the rear fuselage sides (only) attached to the front fuselage module.
View of the top of the rear fuselage
Photo showing the fuselage relatively complete
View of the bottom of the rear fuselage with all longerons, bracing, stringers etc. At this stage of
construction the wing center section and fuselage combined weight is 32.2 ounces.
A 3/4 front view of the completed fuselage.
A 3/4 rear view of the completed fuselage
Above shows the nacelle being built onto the
wing. As per the plans, it shows the 1" square
post epoxied to the wing bottom. Formers N1
through N4 are installed on the post and the top
and bottom keels are added.
This shows the top of the wing center section with the nacelle framework installed. Note that the nacelle center post side view on the plan shows
This photo shows the relationship of the entire nacelle framework to the wing center section.
The next photos will show the firewalls and landing gear attached.
This view and the next show the landing gear
installed into the nacelle. Working with what I had "on hand" I cold formed the main landing gear legs from 5/32" steel wire. The trailing legs are formed from soft 3/32" wire and attached to the main gear with carpet thread and cyanoacrylate.
This view and the next show the landing gear installed into the nacelle. Working with what I had "on hand" I cold formed the main landing gear legs from 5/32" steel wire. The trailing legs are formed from soft 3/32" wire and attached to the main gear with carpet thread and cyanoacrylate.
This photo shows an overall view of the wing
bottom with nacelles framed up, firewalls added
and landing gear installed.
Above is a drawing of the dummy M11
Radial engine for the Yak 6. It looks more
difficult than it actually is to construct.
Click on photo to enlarge.
The crankcases with the 2" motor hole drilled
using a forstner bit, and the five 1/2" cylinder
holes also drilled using a forstner bit. The
forstner bit will give you a lot less tearing in the
balsa than a brad point or any other type of bit.
Here is photo of crankcase painted grey with 1/2" thin wall aluminum tube cores for cylinders inserted and painted black
Here is the engine with the o-rings and washers
installed on the aluminum tube cylinder cores.
The balsa plugs were die cut with a piece of the
1/2" aluminum tube sharpened on one end.
Head fins and rocker arms are next.
This is obviously "generic" rather than scale.
Nonetheless it is a relatively easy way to make a simulated radial engine that will fit over an electric motor.
Cylinders with head/fins added.
This is the simulated 5 cylinder engine with
rocker arms, pushrods and mounting tabs
installed.
As shown in this photo and the next, I made
some changes to the finished 5 cylinder dummy
radial engine as follows: I shortened the rocker
arms, raked the pushrods back and installed stub exhausts.
Doing this as you build will be easier than
modifying the cylinders after you have finished
them. From a few feet away this should create
an acceptable "illusion" on the aircraft.
