|Stack of Ribs
|Ace Spar Varnish - part
#16375 - was used
throughout the airframe
|After wing construction was complete,
and all fittings were pre-fit, and drilled,
Ailerons were cut free with a hack saw
|I used these Balsa Fillets, to
stiffen up the Rib to Spar joint.
|Left Aileron Closeout.
|Right Front Cabane Strut Fitting.
|Right Rear Cabane Strut Fitting,
and Aileron Cable Pulley.
|Fuel Tank Bay, before the 1/16"
Plywood Leading Edge was
|The fuel tank was built using a
two piece mould that Doug
Bryant used on his Pietenpol. I
used 4 to 6 layers of fiberglass,
and Polyester Resin. The filler
neck was from a mid 80's Ford
Pickup Truck saddle tank.
|Fuel Tank install complete. The forward edge of the tank is retained between two 3/4" X 3/4" spruce that
is glued to the back of the forward spar. The aft edge of the tank has 2 screws and large washers, that
thread down into two blocks that are glued to the forward edge of the aft spar.
|Right Outboard Aileron Pulleys,
that line up the cables to the
Aileron Horns. This location also
has a clear Lexan cover, which
doubles as the Cable Fairlead.
|Left side of Aft Spar, in the
Center Section, where the
Aileron Pulley turns the cable
down into the Cockpit.
|Another view of the Right Wing Tip.
Note the Balsa Gussets on each side of
the 1/2" X 1/2" wing tip braces, where
they glue to the spars.
|Left Forward Lift Strut Fitting.
These Fittings are built to the
|Right Forward Lift Strut Fitting. You can also see the Drag / Anti-Drag
cables, and the Compression Struts.
|Bottom view of the Wing,
showing the Left Aileron
|Covering is complete through
heat shrink, and 500 rib stitches,
ready for Paint.
|With the covering installed, you
can see how I repositioned the
support jig, to suspend the wing
from the hard points.
|Rustoleum #7715 Aluminum Oil Base Enamel Paint, was brushed on to prevent UV rays from deteriorating
the Dacron Fabric, and lock the fibers together. Red Devil # Chinese Red color was used for the trim
|We determined the length of the lift struts, using
1X4 firing strips, and adjusting the length until
there was No Dihedral with about 1/16" to 1/8" of
|Jury Struts and brackets are pre-cut.
|Looking up along the Right Rear
Cabane strut, showing the pulley
inspection hole, Aileron cable,
Cabane rigging cables, as well as
the Fuel Valve handle.
|Looking up at the bottom of the
wing, above the passenger's head.
This is the fuel outlet, fuel valve
and line, and the torque tube
handle that controls the fuel valve.
|Pilots Eye View of the Wing
Tank Fuel Shut Off Valve.
The black pillow block that
supports the torque tube has
2 screws that thread up into
the 1/4" plywood center
| Terms associated with a WING :
MEAN AERODYNAMIC CHORD - The Imaginary Line that extends from the center of the radius of the
leading edge, to the center of the tip of the trailing edge.
ANGLE OF INCIDENCE - The angle between the Fuselage Longitude Line and the Mean Aerodynamic
Chord of the Wing.
ANGLE OF ATTACK - In Flight, this is the angle between the Mean Aerodynamic Chord and the
CRITICAL ANGLE OF ATTACK - The Angle of Attack at which the wing Begins to Stall. This angle
varies with the type of airfoil, but is generally between 12º and 18º.
WASHOUT - is a twist in the wing, where the leading edge of the outboard portion of the wing is twisted
to a lower angle of incidence than the inboard portion, causing the inboard portion to reach it's Critical
Angle of Attack before the outboard portion. Angle of incidence is the angle between the Mean
Aerodynamic Chord (MAC) of the wing, and the longitude 0 of the fuselage - on the Piet it's the top of the
longerons at the cockpits. On the Pietenpol the angle of incidence is set with the difference in length of
the cabane struts - the front ones are 1" longer than the back ones, making about a 3 angle of positive
incidence. The purpose of washout is to ensure the inboard portion of the wing is location where the
stall begins, leaving the outboard aileron portion to be the last part of the wing to stall, thus maintaining
aileron control until the entire wing is stalled. Now comes the kicker: On a hershey bar wing - constant
chord, straight wing -, the stall naturally occurs at the inboard portion of the wing, therefore washout is
not really required. Just rig the entire wing at the same angle of incidence as the inboard portion, where
the cabane struts are, by the length of the lift struts. Although, it could be recommended to err the tips
toward a lower angle of incidence. The wing twists easily, till the lift struts & cables are installed. On
wings where the leading edge is swept, or the trailing edge is swept forward (tapered wings), or the
entire wing is swept (like on jets) is where washout really is needed, because sweeping the wing back
causes the tips to stall first. Washout reduces Total Lift.
To conclude, I have about 1/16" to 1/8" washout in my wingtips, which probably is about 1º or so. The
wing is rigged straight (no dihedral), and just slightly err towards washout. Now, instead of testing the
'Runway Hardness', I try to land as softly as a butterfly with sore feet !!
|Middle of Center Section, Trailing
Edge, clamp is used to hold
alignment till adhesive sets.
|Twine was used to position
the Aileron Cable location,
|Wingtip fittings serve duel purpose in that they retain the wing tip bows, and the Drag / Anti-Drag cables.
They are a very tight fit, and required me to use my Grandpap's hand crank drill to get the holes close
enough to the corner.
|Right side of Aft Spar in the
Center Section. A small hole in
the 1/4" Plywood is the Fairlead
that also supports the Lexan
|Right Forward Lift Strut Fitting.
|Looking down on Center Section,
behind the Rear Spar, where the
Aileron pulleys, and inspection
|Here you see the inspection
hole at the right rear cabane
strut fitting, which is one of the
hard points that was employed
to support the wing with the jig.
|Right Aileron Cutout.
|Complete, and ready for first flight - Received the Airworthiness Certificate on Jan 8 '02.
Once the weather cooperated, and everything was finally ready, we were out of excuses, and Doug
Bryant did the first flight on March 28 '02. He also did the second and third flight.
I did my first flight on May 4 '02 !! What a momentous occasion !!
|Begin Fabric Install, using 2.7 oz Dacron Homebuilders Fabric, from
Aircraft Spruce & Speciality Co.
|Bottom view of Port side Aileron control. The clear Lexan inspection
cover is also the cable guide, to prevent the cable from stepping out
of the pulley.
| The Wing of a Pietenpol is one of it's most unique features. It is designed
to with the ability to move for & aft, in order to maintain a safe Center of
Gravity. It makes good sense to move the wing, as opposed to adding
Ballast. This is one of the primary reasons the airframe is known to have had
a wider variety of engines installed, than any other airframe in Aviation
The airfoil is such that it produces a LOT of lift at slower airspeeds, with
High Drag as the trade off. It's like flying with a notch of flaps always in. The
High Drag also helps prevent airspeeds past Vne, thus reducing the
possibility of Control Surface Flutter. None of the Control Surfaces of the
Pietenpol are Mass Balanced. For this reason, you must pay close attention
for any possible flutter.
Hard landings in a Pietenpol are because as you round out for landing
and increase the angle of attack, the Induced Drag (drag associated with Lift)
increases dramatically and rapidly decreases the airspeed...as opposed to a
sharp stall break. The sharp stall break just isn't there in the Pietenpol wing, it
is more like a mush straight ahead.
Bernard Harold Pietenpol listed the safe Center of Gravity Range as
between 1/4 and 1/3 wing chord. The wing has a 60" chord, hence the safe C.
of G. range is between 15" and 20" of the Chord. The Aft C.G. limit of 1/3 of
the chord, is among the farthest aft limits of any Hershey Bar wing. The
Pietenpol Airfoil has a lot of Negative Pitching Moment, which essentially
means if the tail would fall off, the nose would pitch sharply down. This
Negative Pitching Moment is why the Pietenpol Airfoil can get away with such
an aft C.G. limit. This Negative Pitching Moment also increases the Trim
Drag, which is how much down force the tail must induce, in order to achieve
Level Flight. Maintaining the C. of G. as far aft as possible, without going
past the aft limit, will give a more efficient flight, and causes more sensitivity in
the Pitch Axis, however, if the aft limit is surpassed (very dangerous), the
wing probably will NOT come out of a stalled flight condition.
|In House Construction - Due to a lack of room, I had no choice but to build the wing with leading edge
down, and initially support it with 4 jigs under the spars. As construction progressed, and covering
material was installed, I re-located the jigs to support the wing at the hard points - Cabane Strut Fittings,
and Lift Strut Fittings.
Complete, and ready for
|A Lazar beam pen was used to
keep the spars straight
|The wing is built, complete with
ailerons, control horns, and
hinges, BEFORE the cap strips at
the ailerons are cut, to remove
|Right Front Cabane Strut, and
Right side of Radiator.
|2' wide, 1/4" Aspenite was used to protect
|Left Rear Jury Strut Fitting. Note
how the vertical jury strut can pivot
for & aft, in order to move the
position of the wing.
|Left side view of Radiator
support, before the radiator
|Milestone: After one year of construction, the day finally came to move the wing to Benton Airpark.
|Looking up at the inspection hole
for the Left Hand Aileron pulley.
The Lexan cover doubles as the
|Left Aileron Pulley inspection
hole. Lexax cover will be Flush
Mounted - not yet installed.
|Moving the wing out of the house.
|Building the Jig, to Mount the Wing to the Trailer
|We Made it to Benton Airpark in a light drizzle,
with NO DAMAGE to the wing !!!
|Wing and Fuselage are Finally Married !!!
|Left bottom wing tip.
|This is the Left Front Lift Strut location.
|Bottom of left wing, ready for
|Left Outboard Trailing Edge.
|Left top of wing, ready for covering.
|Here you can see the Right Front
Spar Scarf Splice.
|Before fittings are permanently
installed, varnish must be applied
in the holes, and under the fitting.
|Bottom of Center Section, under the
Fuel Tank Bay. Note the Plywood
Doubler, which supports the Clamp
that retains the Fuel Valve.
|1/16" Plywood Leading Edge
installed, you can see half of the
hole where the Radiator Filler
Neck will protrude.
|Left Rear Jury Strut Fitting, made
from 1/2" X 1/2" extruded
Aluminum. Cable Fairleads are
made from Oak Hardwood.
|Here is the nuts and washers on the
other side of the spar. This is one
of the few locations where holes
were drilled through the spars.
|Right Rear Jury Strut Fitting.
Cable Fairleads are made from
Oak Hardwood, screwed into 1/4"
Plywood that is glued to the spar.
|Radiator Cavity pieces.
|Bottom of the Right Wing Tip.
|Drag / Anti-Drag, Anti Chafe
method is a small piece of
1/16" Plywood with two
holes, that is retained with a
Zip Tie. I should have used
Rib Stitch Chord to retain
the plywood, instead of the
|Leading Edge. Also see how I
built the wing support jigs.
|Bottom of Left Wing, after the 1/16"
Plywood was installed. Also note the
Lift Strut Fitting, and the
|Left Front Lift Strut Fitting.
|Stits Covering Method, using Poly
Brush, Poly Tak, and Poly-Fiber
|Here you can see looking up into the cavity which the
top radiator tank will be recessed into. The radiator is as
wide as between the Cabane Struts. The hole in the
middle is for the filler neck, and the hole at the far end,
is for the top radiator hose fitting.
|Front Cockpit Cover, is a Sheet Metal Butterfly
type cover, and is very useful during cold weather
|The Top Radiator Tank sits up into a Cavity behind the Leading Edge.
| It is said that Bernard used a French Curve to draw the airfoil, and it took about ten minutes to
draw, hence he called it a 'FC-10' airfoil. However, if you loft the coordinates of the plans to
paper, there is evidently an error in one of the ordinates on the top about 2/3 way back on the
airfoil - solution is to just blend out that little dip in the top line.
If you're building a Pietenpol, I suggest keeping it the Pietenpol airfoil for several reasons:
1. It works.
2. It allows slower take off and landing speeds.
3. It allows you to use drag to advantage, especially in emergency landing, to do a precise short
4. It's part of Aviation History.
|To retain the front cover, six homemade clips were made from #10 Phillips head machine screws & nuts,
drilled through the center, and use a welding rod through the hole, bent to form the latch / handle.
|This is a view of the plans type 'Barn Door' hinges. The original aluminum hinge pin was discarded, and
replaced with an AN screw, with the shank long enough to go all the way through, cut the threads off, and
drilled for a cotter pin with a washer under the pin. Motorcycle Master Links are used at the cable attach.
|Due in large part of this front cockpit cover, a great
deal of the wind is kept out of the cockpit, and can
be flown in some colder temps down to about 50º.
It also helps in the aerodynamic aspect, and gives
it a unique look. It can be removed in about ten
minutes with a screwdriver.