DaSH PA -- Dead Simple Human Powered Airplane: 2014

Load test of the 40 m version of the wing (v6-WE) on Day 2

We did load testing of the DaSH wing on Sunday 10/26 and Monday 10/27 at the Hiller Aviation Museum in San Carlos, CA. The folks at Hiller were very generous to let us do our testing there, and it was fun because we ended up being a kind of 'live exhibit' over the weekend. We were fortunate that the space was available, as we found it is very difficult to find a place large enough to assemble a 40 m (130 foot) wing indoors!

The goal of the testing was to first get the lift wire length dialed in with a 1 g loading to give the proper dihedral angle, then test to 1.5 g to make sure there was adequate strength.

Testing was conducted by hanging the wing upside down from a "pseudo-fuselage" (to avoid any possible damage to the real fuselage frame), and weighing the wing down with water in 2 Liter soda bottles at each of the approximately 100 ribs, lifting the wing up with a forklift. Each 2 L soda bottle had the right amount of water in it to give the proper elliptical lift distribution on the wing.

Day 1 -- Sunday 10/26/14 -- 33.3 m "v5" wing testing

The load testing of our regular 33.3 m span plane went great on Sunday -- we did a first test where the wing did not bend enough at 1 g, then we increased the lift wire length by adding a carabiner on each side, and the wing bent a bit more than desired, so we were able to zero in on the proper lift wire length.

Then we added more water in each bottle to give a load of 1.5 g to test the strength of the wing (the wing spar and lift wire are designed for 2.5 g ultimate loading). That test went fine and it passed with flying colors.

We had noticed after each lift that the forklift forks slowly tilted down over time, probably due to a slow hydraulic leak. So at the end of the day, we untied our safety cord and backed the forklift away from the wings to protect the center ribs from crushing if the forks went all the way to the floor overnight.

Installing the frame to hold the wings during transport

Strapping the frame into the truck

Two wing sections loaded

Tie down details

Loading the last wing section into the truck

Everything loaded and ready to go, including 120 2 L water bottles

setting up in the Hiller Aviation Museum atrium

Setting up the wings

Clamping the spar end to circularize so it will fit into the sleeve

Helping to align the spar from the far end of the wing section

Inserting a pin into the wing connection bracket

The wing was situated from one corner to the other of the atrium in order to fit

Inserting the shims and pin

Inserting the cotter pin

Pin inserted, cotter pin in place

Prepping the pseudo-fuselage

The wing ready for the pseudo-fuse

Installing the pseudo-fuselage onto the Center wing section

Inserting one of the wing mount pins

Lift wire wrangling

Lift wire connections

Learning the forklift controls

Preparing to lift the wing

Test lift with no weight

Prepping the weights

Forks getting ready to lift -- these caused us trouble later

First lift with 1 g of weight

Measuring the deflection along the wing

Measuring deflection at tip

1.5 g load test

Day 2 -- Monday 10/27/14 -- 40 m version of the wing ("v6-WE")

On Monday, we tested the longest wingspan version of the plane, v6-WE (v6 wing with further 1.5 m wingtip extensions), giving a total span of 40 m. We tested at 1 g with our original lift wire length, and were expecting to get larger than desired deflection because of the increased bending moment. Then the next step was going to be to fabricate shorter lift wires, and try again until we dialed in the lift wire length for that configuration.

Unfortunately, we had removed the safety rope that prevented the pseudo-fuselage from rotating (pseudo-fuselage is for supporting the wing and the lift wires, in lieu of using the real fuselage during the test), since things had seemed so stable on Sunday and the safety rope had remained slack. Ironically, we removed the rope to protect the wing -- so that we could back the forklift away from the wing overnight, since we had noticed there was a slow hydraulic leak that caused the forks to very slowly tilt down, requiring re-adjustment between each lift, and we didn't want them to crush the wing overnight.

What happened on Monday is we had the wing up for about 20 minutes, measuring deflection and taking photos, and were just about to lower it back to the ground to adjust the lift wire length, when it suddenly rotated and twisted. The tips hit the ground and there was some damage there, and the center section had the front-to-rear support tube break at the rear mount, thus rotating even further and breaking/delaminating most of the ribs, and causing creases in some of the trailing edge.

We had one eyewitness who was watching the wing when it fell (lesson for future testing/flying, ALWAYS have video on for everything...), and saw that it rotated first, then broke (so we know it wasn't a spontaneous break on the front-to-rear support tube that was the proximate cause). (Everyone else heard the crack, then looked and saw the wing rotating further, post break).

We're pretty sure what happened is the known slow tilting tendency of the forklift fork caused the the fuselage CG to eventually be too far away from the main spar location, and the moment overcame the friction in the system, and it rapidly rotated. Should have retied the damn safety line...

You can see the pseudo-fuse rotated about 45 degrees negative, and the wing itself rotate about 60 degrees negative (because the center front-to-rear support tube broke near the rear wing mount).

We're lucky that the edge of the top tube on the pseudo-fuse caught on the edge of one of the forks, otherwise it would have kept rotating until the whole thing ripped apart.

As it stands, the damage looks worse than it is. Both the front and rear spars appear undamaged. We just need to repair the front-to-rear support tube in the center section, along with most of the ribs that have breaks and rib cap delamination, and patch a few breaks/delaminations in the trailing edge.

The Middle wing sections survived with just minimal rib damage to a few ribs, and stretched out X-bracing that we will replace.

The regular Outer wing sections were not on the wing at the time, so need no repair.

The Longer Outer wing sections that were on the wing hit the tips and unzipped the trailing edge at the unsupported outer area with no rear spar, where the washout was. That will take more extensive repair to ensure that we rebuild the washout in the correct amount when re-gluing all the ribs. But we don't have to fix those right away to get an airplane that flies, we can just use the regular wingtips.