CH701 STOL
This site has no affiliation with Zenair or The Zenith Aircraft Company...
Disclaimer:
The use of information from this web site is experimental
in nature, for educational purposes and is USED AT YOUR OWN RISK!
Click to join
AirVWEngBuilders
Click to join
FlyFloatBuilders
Metric Converter
Note:
1 in = 25.4 mm
1 ft = 304.8 mm
1 ft = 12 in




Page 3

CH701 Float Design:
Previous...
1 
2  3 
4
Next...




Now On To The Float Design Process!
In the design process when developing a part from scratch... I like to first
start with a pattern, on paper first to scale... then build a model mockup in
wood if possible. If you can make the part in wood... then no sweat when it
comes to making in metal. It's easy to correct any mistakes on paper first then
on to the next step of trying to make a mockup of the part, especially when it
comes to... complex parts for the Nose Wheels and Main Wheels Retract Mechanisms.
It may take a couple of trys to get it right... if your lucky, take your time, you
can get it done on paper first, then there is not much left to do, but make the part...



Basic Bulkhead Development  Patterns!
There are a total of 15 Bulkheads... all of various sizes. The main Bulkhead
F9[just before the step]... which all of the other Bulkheads are based on... is the
largest Bulkhead and establishes the beam[box] width  W and height  H of the
floats[box]. Keep in mind that... dimension  H is unique for each Bulkhead... as it
depends on its location or position along the length of the float! You cannot design
any of the other Bulkheads until F9 is done and  "H"[height]... MUST be determined
for each Bulkhead!!!
After all... IT ALL BEGINS AT THE STEP!
Now there are some common points that are very important in the design. You must
establish... the basic configuration first[box] ie. width[beam] and height, then the
side & bottom "V" angles... for the float profile[ie. they are 25° for both],
then the width of the top and determine the radius... keeping it simple.
NOTE: All of the bulkheads follow the same profile... so that part is very easy. Keep
in mind you have to have a good grasp on your high school math. To confirm your
design... do the design with math and then back it up graphically... you can do this
when its time to draw up the patterns... Below are the basic steps to developing your
patterns!
All of the dimensions for the bulkheads are in a
Bulkheads Dimensions Table(pdf)... and
are the full scale size Bulkhead patterns[dimensions] for a 1200lb max. aircraft!
A heavier aircraft in the 1500lb range will require a wider beam width of 27"... and next
larger[stronger] size main wheels[5"] and nose wheels... [These are
PDF files]!


June 14, 2010
Basic Bulkhead Pattern:
Start by drawing a box using the width[beam] and height dimensions of the LARGEST specific
Bulkhead, ie. the widest and highest at the step... F9, and ALWAYS... work from the top
down, since all of the bulkheads
have the same common upper levels. Draw in the center vertical line[H] which is the
center of the float... then establish side slope rise  H1 of the "V" at the center
which is based on the angles [25° in this case]of the float profile. This in turn
establishes the flat top dimension  W2... and locate this dimension on each side of
the center vertical[H]. In this case these dimensions are W2 = 117mm... each side for a
total 234[W2 X 2] across the top. This establishes the basic float profile and...
it is really that simple!


June 14, 2010
F1  Bulkhead  0.032:
What you see here is the completed pattern of the Bulkhead started in the previous
photo above! This pattern is for the nose of the floats... the F1 Bulkhead!
You must next establish the rise of the "V"... from the center to the side slope rise
I call, height = H1. You can do this with math[you need to know W/2 and Tan 25°]
or use a protractor and measure up 25°... [I do both to confirm my numbers] from
this point... draw the float "V" slope lines and side slope lines. This establishes
the flat top width  "W2"... which is important in the final configuration shape of
the float! In my design for a width  W = 383mm and height  H = 249mm and 25°
angles... H1 = 89mm, H2 = 160mm, W1 = 74mm, and W2 x 2 = 117mm[flat top width] x
2[= 234mm]. Using a CAD program is really the best way to do the basic drawing... no chance of errors there
and very fast!
Not to difficult if you follow that procedure for each bulkhead. The round top design is simple and very easy to develop!
To complete the round top design... add the radius for the round top. The radius for this design is 184mm, and from there it
gets easy and basically done.
One good feature with the round top is the exterior skin is applied in two pieces and built upside down in a nice
cradle setup and is very easy to build once the top skin profile is established!
I like one other major feature with the round top floats that can be added, is that you can add a walkway to the top the
full length of the float which... it adds extra weight, but is stronger(adds a backbone) and would have to be at least 8"
wide or more to be
effective... ever try walking on a 2" x 8", it can be a little difficult... Sooooo


June 14, 2010
F9  Bulkhead Design  0.032:
SPECIAL NOTE:
This has to be the FIRST Bulkhead[profile] to be designed... it has the widest
beam W[width] and H[height], and the rest of the Bulkhead designs, are based on this
main Bulkhead[F9], all 15 of them... NO EXCEPTIONS!!!!
This is a full scale pattern of the largest main Bulkhead[F9} in the floats...
[the last Bulkhead just before the step]. It's complete and ready to use to cut the
plywood forming blocks. Maximum beam width[W] of the floats... W = 610mm and
maximum height[H] at the center H = 546mm, then... H1 = 142mm, H2 = 404mm, W1 = 188mm,
and W2 = 117mm... only 14 more to go! Once the basic Bulkhead profile is established,
the dimensions H2 and W1 are no longer of any use and not needed!


June 18, 2010
F9  Finished Bulkhead Pattern at the Step  0.032: It should be noted here that Bulkheads F7 and F8 are the
same size as The F9 Bulkhead but are  0.025 material!
Now it all happens on the Step. The Step is 32mm[1.25"]... so H = 546mm & W = 610mm
on these floats... side slopes and "V" slope is 25°... and the aft portion from the step rises 7° to
F15 Bulkhead(rudder end)!
Note: the nice round top design!


June 18, 2010
F15  Aft Bulkhead  0.032:
The design ia a round top design in it's simplest form. This is the rear Bulkhead
where the Float Rudder is attached.
Float design Update:
I started designing floats by doing all of the math calculations by hand... and is a very tedious process. Float designs
can be developed using a spreadsheet simply by knowing the buoyancy required, then deciding on the width and height based on
the buoyancy. The basic float profile can be developed in about 1/2 hour as opposed to a couple of days... and super
efficient and accurate(no errors)! I have developed float profiles for 1700 lb to 2200 lb floats. This amounts about 50% of the
Bulkhead design process... the rest is all straight forward!




Page 3

CH701 Float Design:
Previous...
1 
2  3 
4
Next...



