Stack of Ribs

House Preparations

Ace Spar Varnish - part #16375 - was used throughout the airframe construction.

After wing construction was complete, and all fittings were pre-fit, and drilled, Ailerons were cut free with a hack saw blade.

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 installed.

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 Plans Dimensions.

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 cutout.

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 paint.

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 Washout.

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 section bottom.

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 Relative Wind. 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, and Fairleads.

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 cover.

Right Forward Lift Strut Fitting.

Looking down on Center Section, behind the Rear Spar, where the Aileron pulleys, and inspection holes are.

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 History !!      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.

Wood Construction Complete, and ready for Spar Varnish

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 the ailerons.

Right Front Cabane Strut, and Right side of Radiator.

2' wide, 1/4" Aspenite was used to protect the carpet.

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 was installed.

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 cable Fairlead.

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 !!!

Billy

Dale

Dave

Dave

Wing and Fuselage are Finally Married !!!

Left bottom wing tip. Varnish Complete

This is the Left Front Lift Strut location.

Bottom of left wing, ready for Covering.

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 Zip Tie.

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 Compression Struts.

Left Front Lift Strut Fitting.

Stits Covering Method, using Poly Brush, Poly Tak, and Poly-Fiber   Reducer.

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 operations.

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 field landing. 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.