Postings about the DaSH Human Powered Airplane project. Our goal is to have fun and learn while building an HPA on a budget of no more than the price of a new car by keeping the design simple and the build time to a minimum.
Completed biscuits for Main Wing Spars and Tail Boom
We've completed manufacturing all the biscuits for the Main Wing Spar (including an extra set of standard Outer Wing Spar and a set of Longer Outer Wing Spar), and for the Tail Boom (tail boom biscuits are in the foreground in the above photo).
We also built the 24 foot long biscuiting tool that is necessary to use in all the tapered wing spar segments where the biscuits can only be assembled from one end of the spar. The old tool used on the fuselage frame was 12 feet long and is not long enough for the 6.7 m (22 ft) long tapered outer wing spars, or for the 4.5 m long tail boom.
We'll start biscuiting the main wing spars and tail boom this week ("Biscuiting" = gluing the biscuits, designed to prevent buckling of the thin-walled tubes under load, inside the carbon fiber tubes at designated intervals of 4 X tube diameter or less).
Finishing the biscuits for Main Wing Spar and Tail Boom
Side 1 of Tail Boom and Wing Spar biscuits glued to foam
Biscuits with Side 1 glued on, separated out in preparation for gluing Side 2 of the balsa faces
Gluing Side 2 of the balsa face to a biscuit
Completed biscuits glued, clamped and taped, drying before finishing
A bunch of biscuits with both sides glued, awaiting final sanding and drilling
Sanding the foam flush on a biscuit
Inspecting a biscuit after sanding
Video of final sanding and removal of side tabs on a main wing spar biscuit.
All the finished biscuits (plus spares) -- 273 total biscuits
Biscuiting Tool
The long biscuiting tool is made of two 12 foot long ( X 1 1/4" OD) aluminum tubes
Cleaning the inside of the larger diameter splint section prior to gluing
Long biscuiting tool spliced together with larger diameter splint in center (attached with epoxy)
Creating a marking tool for the long biscuiting tool
Marking tool for the long biscuiting tool
Marking the base line for the long biscuiting tool
Marking the distance marks on the long biscuiting tool
Marking both ends of the long biscuiting tool
Marking the center of the long biscuiting tool
Support for tape measure used in marking the long biscuiting tool
Syringe plunger stopper glued in place near end of biscuiting tool
The biscuiting tool was held at an angle on this stairway, and the string was fished through the pole and past the stopper with a heavy wire weight
The strings in place and yoke for gluing syringe attached
Marking the biscuit locations with tape on the outside of the main wing center spar
Main wing center spar section marked with tape showing biscuit positions
The biscuit positions are marked on the outside of the of the wing spar tubes so that the tube can be squeezed there and the biscuit held in place when the biscuiting tool is withdrawn after gluing the biscuit in place (but before the glue has dried).
Tail bearing brackets and control horns
Completed Horizontal and Vertical Tail bearing brackets and control horns, ready to glue onto the tail spars.
This past week and a half we've been making the anti-buckling biscuits for the main wing spar and tail boom. We take balsawood sheets made of 2 sheets of 1/16" balsa, with grain rotated approximately 20 degrees from each other (we laminated those sheets a couple of weeks ago), and then laser out the biscuit doublers for the straight part of the spar, and also the tapered part of the spar and tail boom.
Then we glue one biscuit doubler side to a large 1/2" thick EPS foam sheet, then drill out the holes, and cut each biscuit apart from the sheet. Then we glue and clamp the second side biscuit doubler (using a center 5/16" bolt, and tape on the edges).
The final step, not yet completed, will be to sand off the excess foam around the edges to make a completed biscuit.
Laser cutting biscuit doublers
A sheet of completed laser cut biscuit doublers
Box 'o laser cut biscuit doublers, waiting to be glued into biscuits
Arranging biscuit doublers on 48" X 8" X 1/2" EPS sheet prior to gluing
Applying polyurethane glue to biscuit doubler face
Spreading glue on biscuit doubler. Spread the glue thin and off the end tabs
Gluing biscuit doublers to an EPS sheet
Glued biscuit doubler sheets clamped under steel weights
Drilling out foam and excess glue from biscuit doubler holes
Separate side 1 of biscuit doublers from sheet
Gluing second side of biscuit doubler to main wing biscuits
Test fitting the Lift Wire Clamp model onto the main wing spar
Andy built a 3-D model of the lift wire clamp, so we could test fit the clamp to the wing spar, and the sailing thimble that is the wire termination to the clamp. Grant built a model of just the ring part of the clamp for a slightly different sized clamp back in December (see the 6-Dec-2013 blog post for a photo of that). We'll choose which ring size to use based on the FEA results. The real part will be machined out of 7075 aluminum once we pick the exact size and configuration.
Lift Wire Clamp model, with sailing thimble test fit. The actual aluminum part will have 'wings' that are about twice as long as shown. Kevlar lashing around the wings will hold the part onto the wing spar.
Wes has now machined all the parts for propeller shaft part of the drivetrain. This includes titanium bearing seats that glue into the prop shaft, an aluminum spider to hold the top chainring, and mandrels for alignment to the prop shaft during gluing.
Thrust bearing, titanium bearing set, aluminum spider and chainring for DaSH drivetrain
