27 July 2012

Second Propeller Build

Last weekend (July 21 & 22), we started the build of the new 3.66 m (12 ft) diameter prop.

The first task was cutting out templates for the foam cutting.  The prop will be made of 12 mostly-equal length foam pieces (they are shorter at the base and prop tip because of the large changes in chord there).  Each piece will be cut with the right chord and twist on each end to give the proper twist and taper, and then they will be threaded on a carbon fiber spar, glued together, sanded and prepped, and then covered with 2 layers of very light fiberglass, which will also be sanded and filled

Here are some photos and videos of the template laser cutting Saturday evening:

Registration marks marked, waiting for cutting outside of airfoil

Cutting an airfoil shape

Most of the Ribs cut




And here are some photos and videos of foam cutting on Sunday afternoon:

Complete prop templates grouped together
Prep work

cutting foam blocks



A sample prop section with short length and exaggerated twist


Site visits to Carrizo Plain and Black Rock Desert

About a week and a half ago, I made site visits to the Carrizo Plain in California, and then the Black Rock Desert area in Nevada on my way to and from a bike ride (Markleeville Death Ride) on July 14th.

Both sites are potential sites for longer flights with turns.  Carrizo Plain National Historic Landmark area is a 50 mile X 15 mile flat area with a 5 mile by 1 mile salt lake at the North end, and the San Andreas Fault running through it.

Black Rock Desert is a large salt flat (aka 'Playa'), much of which is in a National Conservation Area, and some of which is an official Wilderness area.  It is the site of the famous yearly Burning Man event, and other events such as land speed records and high-powered model rocketry take place there as well.

Both sites may be good ones for longer range flights of the DaSH aircraft.  Corrizo Plain is closer to our base (about 4 1/2 hours vs. 6 1/2 hours) and is a bit less remote as well.  It is also lower altitude (600 m [2000 ft] vs. 1200 m [4000 ft] for Black Rock desert), which means it will take slightly less power to fly there.  But Black Rock desert and its surrounding areas (like Smoke Creek Desert) have tons of room, a lot more than Carrizo, and virtually all of it is flat salt lake.

In between, I took a nostalgic side trip to Shafter airport to take a photograph of the Gossamer Condor monument.

Here are some photos I took:

Carrizo Plain


the approach from the North past the last few ranches
roads to nowhere
large power lines just North of start of National Landmark Area
the start of the monument, North end

the start of the salt lake ('Soda Lake')




view of Soda Lake from the lookout


a view South down the valley from the lookout

a 360 panorama from the lookout


phone lines in North end of monument

the road turns to gravel (but well graded)

taking the road East out of the valley, South of Soda Lake.  This is what the rest of the valley floor looks like
The Gossamer Condor monument at Shafter Airport

Another View of Gossamer Condor monument

Black Rock Desert and environs



Winnemucca Lake (dry lake East of Pyramid Lake)

Apprroaching Empire and Gerlach

The Gerlach sign

The BLM Black Rock field office

Looking North up the Playa

Map showing the Playa (left part) and Wilderness area (part to the upper right).  Smoke Creek desert is South and West of this map and is not shown.
Three Mile access point
On the Playa

Closeup of Play surface

Tracks

Looking South

A 360 panorama on the Playa

One of the few dune areas, easily avoidable

The gap in the hills between Black Rock Desert and Smoke Creek Desert

Start of Smoke Creek Road/Surprise Valley Road




There's lots of scrub brush between the road and the salt flats.  Three access points, one uncertain one near the start, one midway down the road about 20 miles and near-4WD road, 1/2 mile long, the other near the South end of the desert and short and easy acess.

North Access Road

Wild Burros (native here)

Getting closer

Middle Access Road (4WDish in places, but made it in a Prius)

On the Smoke Creek Desert plain



Looking South down Smoke Creek Desert

Back to the North side of Pyramid Lake.  The road is rough and washboard-y here.



26 July 2012

New Logo for DaSH PA project

Here is the new logo for the DaSH PA project, based on a concept from last year by Josephine Tsay.  I added a color-coded displacement map of the main spar to make this version of the logo.

Let me know how you like it -- Alec



Carbon Fiber Parts Ordered!

On Monday, 16-July-2012, we ordered all 28 Carbon Fiber tubes that make up the bulk of the frame of the airplane.

While we have designed the main spar, tail spars, tail boom, and many of the fuselage members using FEA analysis of CAD files (see for example this post:  http://dashpa.blogspot.com/2012/06/some-photos-of-2011-progress.html ), we don't have a full CAD model of the entire plane yet (coming soon!).

Since the tubes are fairly simple parts individually, and in keeping with the "keep it simple" philosophy of the project, we went old school and did some not-to-scale hand drawings to define all the tubing.  A few examples below.

The first parts should be arriving in about a week and a half (first or second week of August).

A simple tube used to pin the prop shaft in place




A longer version of the outer wing main spar that will let us increase the wingspan by adding longer wingtips.

06 July 2012

DaSH PA prop #1 at speed

We got a cadence meter set up so now we know how fast we are pedaling the prop.  We also carefully adjusted the propeller pitch (it turns out just a few degrees makes a big difference).

Here is video of the DaSH PA prototype prop #1 turning at design cruise RPM (110 RPM), pedaling cadence of 90 RPM:



Our next prop will be designed for 147 RPM (at 90 RPM pedaling cadence), and it will have a 3.66 meter diameter (12 ft), vs. 3.05 meters for this prop (10 ft).




03 July 2012

Static Test Rig Working/Prop Spinning

Wes got the final parts machined for the prop shaft for the static test rig, and we assembled them and got it running.  Assembling was quick, figuring out the right position for the idler wheels took a long time (and it still isn't perfect).

The prop is smooth, makes a lot of wind, and the Mobius twist in the drive chain seems to work fine.  We'll get a power meter installed in a week or two so we can make some power/thrust/rpm measurements.  In the meantime, this will help us get the geometry just right for the real plane.

This is the 10 foot prop, built of balsa, spruce and an Aluminum, designed for 16.5 mph and 110 RPM.  Our next prop will be 12 feet (3.66 m) in diameter, made of of fiberglass-covered foam with a carbon fiber spar.


The completed prop shaft assembly

Assembling a blade to the cross shaft

The completed prop shaft assembly in place on the static test rig

Ready for the prop blades.

attaching the prop blades with hose clamps.

Detail with chain installed









More photos and videos:  https://picasaweb.google.com/107455148378358982957/2Jul2012_DaSH_static_test_rig_running?authkey=Gv1sRgCMCn7py1jtPKMA