Cessna 172 correction comments (Arii 1/72, long)
Tjepke Heeringa
I'm currently working on a 1/72 scale Airfix Bird Dog, and my thoughts
wandered to its sister, the Arii Cessna 172. After dredging up some
previous threads on Deja (notably one by Vesa Halme) I decided to do
some checking myself. And while it certainly isn't a good kit, imho it's
not so bad as it was made out to be either.
As 172 post seem to come up fairly regularly, I decided to post my own
observations here. I hope I can get some feedback from other 'spam can'
builders, and offer some help on building one.
Anyway, what I used as basis for my measurements were several drawings
in the book 'Complete guid to single-engine Cessna's' by Joe Christy.
They seem to be copies of original Cessna drawings. I've scaled these up
to 1/72 to be able to use them. I also have some pictures I took of a
Cutlass RG, for some detail things.
Regarding those and some basic measurements, I came to the following
conclusions:
- Wing:
I've found two values for 172 wingspan: 36 feet (old wing) and 35 feet
10 inches (new wing). This works out to 152,40 mm and 151,69 mm
respectively. Arii's 172 wing is in fact 147,75 mm in span, and the
Airfix Birddog (same wing) has a span of 151,30 mm.
This means the Arii wing is indeed short in span, by about 4,5 mm. By
comparing both wings to the drawings, I found that the Arii outer wing
sections including the ailerons are actually pretty good, it's the flaps
that are too short. So if you want to lengthen the wing, it has to be
done on the inner sections. The inner part of the wing is a
constant-chord section so this shouldn't be a problem. Trailing edges of
the wing are acceptable, but could use thinning down. Also the
characteristic stiffeners on the flaps and ailerons must be added. The
stiffeners are triangular in cross scetion, and should be 0.1 mm in
diameter. They can be made from stretched sprue. (The cross section of
stretched sprue will remain the same, so if a sprue is triangular before
stretching it will be triangular after stretching!)
The Bird Dog wing is much better dimensionally, but still a little bit
short. However, the trailing edges are horribly thick, so they can't
really be used as a replacement... Also, the rooftop windows of the 'Dog
and the 172 are radically different.
- Fuselage:
The shape of the fuselage is quite wrong. It is too short and the
contour near the engine cowling is wrong (in side view).
According to my measurements the fuselage is about 2 mm short. The
easiest way to solve this (if you want to) is to cut off the tailfin and
glue it back on 2 mm further back. The rear fuselage should then be
trimmed on the rudder hinge line (so both the fin and the fuselage end
along a straight line). The rear fuselage must be thinned down (it is
too wide at the rear) and a new rudder added.
Where the fuselage really goes wrong is in the shape of the bottom
fuselage, in the cabin area. In the kit, the bottom fuselage slopes
continuously from the rear of the engine cowling to the tip of the tail.
In fact, there should be a flat part (roughly parallel to the ground)
and then a slope towards the tail. This produces a definite kink in the
side profile. The kink is about where the wing struts attach to the
fuselage.
This is fairly easy to fix, however. The height of the fuselage where it
meets the cowling is okay. Glue a strip of card to the bottom fuselage,
near the wing struts to build up the height there. Then use Milliput to
fill in the rest of the shape. Sand to the correct cross section, and
you're done.
The panel lines for the door are wrong, this makes the door frames too
thick and the windows too small. The windows should be as high as the
top line around the door. Enlarge the window and rescribe the door. The
rear windows look funny and do not agree with my drawings, but I believe
they were changed somewhere in the 172's history. The windhield and rear
window aren't too clear and don't fit well, it's probably better to make
replacements.
- Cowling:
The cowling has a 'bump' on top that's characteristic of the Cessna
175/Hawk XP. For a regular 172 sand the top of the cowling flat. The
cooling intakes wrap around below the spinner, but this is wrong. There
should be two seperate, rectangular openings. Some 172's have the
landing and taxi lights in the cowling instead of in the leading edge of
the wing, so check which one you want to build. For early 172s the front
cap of the Airfix Bird Dog can be used, this has a more correct
configuration.
The sides of the cowling in the kit are rounded, they bulge outwards.
They should be flat, so sand flat. If the shape of the fuselage is
altered as above, the cowling needs to be changed so it will fit again.
The spinner is way too blunt (for later 172s) or way too large in
diameter (for early versions). The prop seems okay, so remove the prop
blades, correct the spinner, and stick the blades back on.
- Tail surfaces:
Vertical tail looks quite good. I have some doubts about the 'box' on
top of the vertical tail, I suspects this should be much thinner. Later
model 172's have dorsal fin that's larger than the one in the kit.
The horizontal tails are good. The elevator outline however isn't
correct. The balance areas in front of the hinge line are triangular in
the kit, whereas they should be rectangular. This can be rescribed.
Again, add stiffeners from sprue.
- Landing gear:
Landing gear is a bit basic. The wheel pants are much too thin (they can
be fattened using card), and the wheels don't have a lot of detail. The
nosewheel strut is a bit crude, the torque link could use replacing. The
shape of the fairings varies enormously between model years, from pointy
(like in the kit) to round.
Many 172s have the wheel pants removed, in which case the spares box
should yield some wheels.
- Interior:
The interior could use some attention, though very little of it will be
visible (unless you open the doors or add the top windows). The floor
should be lowered so it sits level with the lower edges of the doors.
Kit seats can be used if mounted on new supports, they're quite nice.
The kit instrument panel can be used, or make your own using your
favorite technique. The kit control wheels are nice and can be used as
they are (you might want to add a Cessna logo in the center...)
A lot of interior pictures can be found in online sources (particularly
sites where aircraft for sale are shown), use them to check out some
furnishing options and panel layouts.
Whew, that's quite a lot there. I hope someone (besides me) actually
finds this useful or interesting. If so, comments please!
Tjepke