Landing Gear

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The E-Hawk airframe employs a conventional landing gear configuration (tailwheel-type) which consists of two main wheels forward of the center of gravity and a small wheel to support the tail.  In this edition of the blog the E-Hawk team  fabricates the main gear structure and suspension struts.  We also install the wheels, rotors, and brake calipers.  The tail wheel assembly will be fabricated and installed at a later date as will the brake lever and hydraulic lines. 

The 4130 tubing for the gear leg is cut, coped, and placed into the welding jig.
The gear leg spreader is tack welded into place.
Both left and right gear legs partially welded.
Tabs that provide structural integrity to the landing leg attach point are tack welded into place. We will then heat the tab via oxy-acetylene torch and wrap it around the axle and finish welding the seams shut.
The wheel axle tube is temporarily slid into place to check the fit.
Aft gear attach tabs have been cut on the water jet are fit checked prior to welding.
Forward gear tabs will require some grinding to close the gap prior to welding.
The gear leg bottom mount will be the attach point for the strut. It's cut from 1/4" 4130 steel. It's clamped into place to ensure alignment with the upper gear strut mount.
Here is the upper gear strut mount clamped for alignment.
The strut mounts are now in position and will be permanently welded into place. Note the wheel axle runs all the way from the left leg to the right to ensure that the wheels will run parallel.
Right angle grinder is used to cut the wheel axle tube to the correct length.
Time to start working on the struts. These are spring holders.
Using the mill to cut slots into the strut spring tube.
One side is almost done. The tube will be flipped and a matching slot will be milled on the opposite side.
Checking to make sure that the slots were milled correctly and that the plunger slides freely.
We start to install the landing gear sub-assemblies onto the fuselage frame. The gear legs go on first.
The struts are temporarily compressed using clamps which makes it possible to attach both the top and bottom bolts through the strut mounts.
Left side gear is complete.
Front view of gear. Right side strut is up next.
Both sides are on with the gear supporting the fuselage frame for the first time.
Union break.

Rudder Control

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In this installment of the blog we work on fabricating and assembling all of the parts required for a working rudder.  We start with machining the rudder pedal bushings and finish with connecting the rudder cable.  See the pictures below for all of the steps in between.

Machining the rudder pedal bushings from 2024 aluminum round stock.
Drilling out the center to a size large enough to accept the cutting tool. Then we begin to enlarge the inner diameter to the correct dimension.
The bushing meets tolerance and is ready to be cutoff.
The 4 required bushings have been completed and are then test fit on the 4130 steel tube.
We created a CAD model of the EMG-6 designed rudder pedal with the bushings to ensure that everything would fit together.
We then 3D printed the rudder pedals and installed them on the fuselage frame to test their function.
Following the functional test of the originally designed rudder pedals we decided to make some modifications and designed a custom E-Hawk pedal that would later be fabricated from aluminum.
Engineering drawing for our custom pedal with bending parameters.
The flat panel of the rudder pedal cut on the waterjet from 1/8" 6061 aluminum. The part then gets annealed and sent to the hydraulic press for bending.
After bending is complete we polish the rudder pedals with fine grit sand paper and install onto aircraft.
Rudder cables are prepared by terminating the end with stainless steel cable thimbles and tin plated sleeves.
Once all the parts are aligned we swage the sleeve onto the cable.
The completed end of the cable is then attached to the forward rudder control horn via a shackle. A second sleeve will be swaged onto the cable for redundancy.
Time to route the cable from the control horn around the lower fuselage frame pulley, up through the tailboom pulley, and then down the length of the boom to the aft rudder control horn.
Rudder control cable routed along the lower pulley.
Rudder cable running along the upper pulley.
Rudder cable exiting the tail boom and making its way to the rudder.
Attaching the rudder control cable to the rudder control horn.
The control cable is temporarily secured to the rudder control horn. We will wait to permanently terminate via a swage.
For now we hold the cable in place using a 3D printed clamp that we can tighten with a wing nut.
Coiling up the excess of cable from the right side. Next we duplicate our efforts on the left.

Flight Controls

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In this installment of the blog we continue to work on the flight controls.  A number of tubes on standoffs are strategically located and fitted with nylon bushings to act as pivot points for the torque tubes.  We also weld up the control stick and add pulleys for the rudder cables to run on.

Fitting the torque tube standoffs into position just prior to welding.
Holding the parts in place for tacking.
Elevator control stick torque tube.
Aft bulkhead control mount standoffs are fitted and clamped into place for tack welding.
Checking the drawings for the control stick.
The wire brush will remove the burr from the control stick tube prior to welding.
Drilling holes in the control stick using a 3D printed drill fixture.
Locating holes to be drilled in control stick.
Aileron torque tube bearing being prepped for welding.
Completed aileron torque tube bearing with nylon bushings inserted.
Enlarging and deburring the holes in the elevator bellcrank.
Elevator control stick torque tube installed with control stick and elevator control horn attached. The 3D printed saddles are temporary until we machine the the real parts from aluminum.
Another view of the control stick mechanism.
We 3D printed a temporary u-joint from red TPU flexible filament to couple the control stick with the aileron torque tube. This way we can test the movement of the system.
The aft torque tube is shown here with elevator bellcrank and aileron bellcrank in place. The pulleys for the rudder cable are also installed. The red parts are temporary 3D printed shaft collars. The real collars will be machined from aluminum.

To The Paint Hangar

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The fuselage frame is at the stage where a coat of primer will help protect it from oxidation.  Although our shop is climate controlled during the day, the high humidity in the Hawaiian air will find a way to infiltrate.  So it’s off to the paint hanger to apply a coat of primer.  We will still have to do some welding (e.g. motor mount) in which case we will simply strip away the paint in the affected area.  

More Fuselage Frame

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In this blog we are able to finish most of the welding associated with the structural part of the fuselage frame.  We also fully attach both the upper and lower keel tube to the frame.  Coming up next will be flight controls.

Deburring some the bolt holes that will attach the nose skid to the fuselage frame.
Nose skid saddle being prepped for welding.
This is the rudder bar that the rudder pedals will pivot on. The lower keel tube is clamped into place so that we can drill through both parts for guaranteed alignment.
Rudder pedal bar is being positioned with respect to the lower keel tube.
The left-side seat to lower keel tube is positioned and tacked into place on the saddle. The right side is next to be installed.
The forward portion of the fuselage frame is mostly complete.
Final drilling to fully attach the keel tube to the fuselage frame.
Here we are taking some measurements for where the control stick will mount. With the basic structure of the fuselage frame mostly complete, it's time to start adding all of the structure for flight control actuation. In our next post we will cover the first part of the flight control system.

Building Egress Test #2

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With both upper and lower keel tubes now part of the fuselage frame the full length of the fuselage is known.  Bolting it to the tail boom and empennage gives the full length of the aircraft which now allows us to determine if the assembly can be removed from the building.  The partially assembled aircraft also allowed for a photo op.

Bolting the fuselage frame to the fuselage boom.
Preparing the assembly for transport.
It's not looking so good as we enter the first turn in the stairwell.

Here we attempt to get the fuselage out of the building.  Although we were unsuccessful here we may still have a shot if we have more people available help with the lifting and negotiating.

Forward Fuselage Frame

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Now that we have bent the lower keel tube and installed it we can proceed with fitting the rest of the forward fuselage tubes.  The keel pockets are located on the keel tube and clamped in place so that we can properly fit the Rudder Bar, Nose Skid Tube, Instrument Panel to Rudder Pedal Down Tube, and the Lower Instrument Panel to Rudder Pedal Down Tube prior to welding.

Completed forward section of the fuselage frame.
Rudder bar is clamped to keel pocket via standoff for welding.
Keel pockets located on lower keel tube.
Nose skid tube tacked into place.
Instrument panel to rudder pedal connection.
Clamping the instrument panel keel pocket to the upper keel tube for drilling.
Appears to be a perfect fit.
Now with the lower keel back in place we drill through the keel pocket into the keel tube for correct alignment.
Drilling the forward keel pocket.

Fabricating Wing Parts

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As we wait for the bulk of the wing parts (mostly aluminum tubing) to arrive, in-house fabrication has begun.  We can easily cut most of the 2.5D parts out of flat stock, be it aluminum or 4130 steel, on the waterjet.  We also produce our own CAD for the parts that are missing drawings within the EMG-6 builders database.

Here is a finished set of 20 Diagonal Attach Plates plus a spare. These will be used to reinforce the attachment of the diagonal struts to the leading and trailing edges of the wing.
Here we are using the provided PDF drawings to recreate the parts in Onshape, our CAD software of choice. From there we can generate the DXF files to be loaded in the OMAX layout program.
Here we have loaded the DXF file into the OMAX program and begin laying out the 20 copies of the part. Tabs are added, the cut quality specified, and the material parameters set prior to generating the machine path.
In this step the machine is homed and the z-height set.
Test firing the machine, first with water only followed by water and abrasive at high pressure.
What's left of the 0.125" 6061 aluminum sheet.
The tab remains and will have to be grinded flush.
The cut parts will be tumbled overnight to smooth out any sharp edges.
The next morning parts are removed from the tumbler and cleaned.
Although Hawaii does not have many fireplaces, this student has managed to find one. Please contact us for our chimney sweeping rates.

Bending the Lower Keel Tube

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After a long summer break, the E-Hawk Team is back at it again.  Today we manufactured the lower keel tube from a length of 6061 T6 aluminum tubing (1.0″ OD x .058″ WT).  This part requires two bends with a 9″ radius.  We do have a hydraulic pipe bender however we don’t have a die that will make the 9″ radius bend.  Instead we decided to design specific tooling that would allow us to make the correct radius bends.  For that we used Onshape to create a bending die comprised of two halves of 3/4″ plywood cut on the CNC router (Shopbot).  The two halves were then glued and screwed together and mounted to a larger piece of plywood.  The assembled jig was then clamped to a sturdy table.  The straight length of tube was measured and marked with the bending parameters and then filled with sand (actually waterjet abrasive) to prevent it from collapsing during the bending process.  It was then placed in the jig and clamped down on one end of the fixture with an aluminum strap.  The team then proceeded to manually bend the tube around the die up to the correct angle.  Following the first successful bend the tube was readjusted within the fixture and the process repeated for the second bend.

Lower Keel test fit.
Bend specification drawing.
CAD of the bending die to be routed from two layers of 3/4" plywood.
Cutting the tube bending die halves on the CNC router.
Assembled tooling fastened to a work table.
Closeup of the die wall showing the radius to match the 1" OD tubing.
The bend in progress.
Verifying the angle of the bend.
Emptying the sand after a successful bend.
Triming the end of the lower keel.
Installing the keel by clamping in place prior to drilling.
Pilot fit check.