Flytec
Wills Wing

Oz Report

Volume 5, Number 40
9 am, Wednesday, February 14 2001

https://OzReport.com
"Toto, I have a feeling we're not in Kansas anymore."
Wed, Feb 14 2001, 8:00:00 pm EST

to Table of Contentsto next topic Less down tube drag

carbon fiber|Steve Pearson|Wills Wing

A while back (https://OzReport.com/4.196) I wrote about the new Wills Wing aluminum down tubes.  Steve Pearson at Wills Wing wrote:

It's not possible to quantify the results with a single number because the drag is very sensitive to angle of attack and Reynolds number.  Very generally speaking, the results verify a drag reduction of 80-90% (Slipstream is 10-20% of the drag) of a standard Finstwalder section.  It also has a very wide low drag bucket.

I also gave readers the address of the paper that described the wind tunnel test results at http://www.willswing.com/articles/SlipstreamWT.asp. Finally, I was able to stop long enough to have a good Internet connection and I down loaded the paper.  After going through it I had a few questions for Steve and wanted to get a clarification of what the test results meant.

How good was this new aluminum down tube?  Was it really that much better?  How about compared to the carbon fiber downtube?  Here is what I asked Steve:

A couple of questions on your wind tunnel tests.

What is Ca?

Steve answers:

lift coefficient - cl

What is Cw?

Steve answers:

drag coefficient - cd

What is Alfa?

Steve answers:

angle of attack - aoa

On which charts can I find the coefficient of drag (Cd) from the Finesterwalder, WW standard, and new WW aluminum tube?

Steve answers:

The wakes from the Finsterwalder, WW standard, and the round tubes were too big for the tunnel and the pressure rake.  The drag was estimated from the lift vs. drag curves* (and other observations) and is tabulated separately on each page.

* If you look at the 2 graphs of the '1.1 WW standard carbon tubes' (cl vs. cd, and cl vs. aoa) you can see that there is a correlation between rapid increases in the drag coefficient and a drop or erratic change in lift coefficient.

How do I tell if the new tube drag is 80 to 90% reduced from the old tube?

Steve answers:

80-90% is the best case comparison.  15m/s is ~33mph.  Looking at the 'WW Standard Carbon' 15m/s curve, Cw stays at or below .04 over a wide angle of attack range ~ +/- 8 deg.  The estimated drag coefficient for the Finsterwalder tubing is .28 - .35. .04/.28 = 14.3% ; .04/.35 = 11.4%. The performance advantage diminished until at 30m/s we have .033 for the carbon vs. .11 - .2 for the Finsterwalder = a 70% to 85% drag savings.

None of the best comp pilots are flying with fat Finsterwalder type sections, so the Seedwing section is a better comparison.

At 10 m/s, the Seedwings section has too big a wake for the tunnel instruments (>.08). the advantage for the WW Carbon is ~ .04/.1= 40% (60% less drag). You can also see that from the Ca vs. aoa curve.  At 10 m/s the separation starts right away but by 15 m/s the Seedwings section is pretty good.

The inverted bucket shape of the cd vs. cl curve is a result of the squared of trailing edge shape.  The average cd is ~ 0.7. The WW carbon is < 0.4 for the entire aoa range, so the carbon has 40% less drag.

Another interesting result is '1.4 WW carbon, no Trip'. For this test, I asked Carsten to sand off the turbulator trip.  Comparing tripped and untripped carbon sections, at 10m/s the untripped section has so much drag that it doesn't even show up on the graph (Cw >.08 == more than twice the drag of the tripped section).

At 30m/s, the untripped section has less drag than the tripped section.  I was interested in this test because of the unconfirmed reports that the Freeman speedbar had high coefficients.

The aluminum profile as extruded measures ~ 21.0 mm. I designed the extrusion to use a slide-in web (.028 alum sheet) that can expand the width as required for structural requirements.  As you noted, the strength of the downtube is very sensitive to the finished width.  The finished WW downtubes are 22.0 mm. The slight dip in the rear of the alum section is an artifact of the extrusion process.  Fortunately, it seems to have reduced the drag coefficient so I'm leaving it as is.

I really need to prepare a summary of the results.  I understand that it's pretty hard to interpret the results.  What everyone really wants to know is 'how much better will I glide'.

Airfoil downtubes and speedbars that aren't canted the proper amount are probably completely separated.  Separated airfoil sections aren't much better than round tubes.  Compared to that, the difference could be 2 points or more.

Compared to a standard WW type control bar, the difference is probably more than 1 point.  Compared to a good section like the Seedwings profile mated to a good streamline basetube, with all the tubes oriented properly, the difference is probably 1/2 a point.  Those are just educated guesses based more on flight reports than calculations.  I always take observation over calculation anyway.

I commissioned the tests because I wanted some confirmation that the finished product met the performance predicted by the airfoil design programs.  Also, I wanted to know the drag behavior at higher angles of attack where the programs become less reliable.  Since the in-flight angle of attach range of both the basetube and downtube sections is 20 degrees or more, it's just as important to have a wide drag bucket as a low minimum drag coefficient.

(editor's note: My competition pilots and other readers are encouraged to look over the test results and think about the "proper" canting for their speedbar and downtubes.  There seem to be some very significant differences here between doing it wrong, and getting everything right.)

Discuss "Less down tube drag" at the Oz Report forum   link»

Wed, Feb 14 2001, 8:00:01 pm EST

to Table of Contentsto next topic Brauniger Instrument pod

Brauniger|Flugelectronic GmbH|Instrument pod|Mike Tryon

Mike Tryon «mtryon» writes:

Braeuniger has recently released an instrument pod very similar to the offerings of La Mouette, Betinho, and Flytec, which you covered previously.  The quality is superb and the price is right.  The biggest difference is the mount, which looks like their familiar standard mount, but is actually substantially sturdier.  The ball and clamping pieces are larger and lock it in position very well.  No problems with the pod rotating down in bumpy air.

The other major difference is the airspeed probe, which mounts higher and should put it in a bit cleaner flow.  The vario mounts in the pod by way of a countersunk screw through the back of the pod and the GPS is held in by small ridges in the pod which lock into grooves that run down the length of the GPS.  There is room for the wires to run under the GPS.  It's all very clean and simple.

At only 321.55 DM ($152.24) including shipping to the USA, it's a much better bargain than the other offerings.

 

 

 Wolf at Bräuniger Flugelectronic GmbH «info» responds:

The pod is brand new and at moment only available at our online shop on the German web page and "should" only be available in EU countries.  We are not the manufacturer, but it's a high quality product and we decided to promote it. Have a hit at our German web page too.

(editor's note:http://www.brauniger.com. Click the Germany Flag, click On-line shop, click IQ Serie, scroll on down to Drachen Halterung GFK, mit Kugelgelenkmontage.)

Brand new is the IQ-MOTOR instrument, which is available within two versions.  This can be seen at the English web site as well.  Only Aerolight Miami in the USA will distribute it!

Discuss "Brauniger Instrument pod" at the Oz Report forum   link»

Wed, Feb 14 2001, 8:00:02 pm EST

to Table of Contentsto next topic Landing with Ninos

Daniel Gravage|Paris Williams

Daniel Gravage «dang» writes:

I thought I'd pass along a little tip: Paris Williams mentions encounters with the ninos upon landing (vol.5, #38). Many of us found the same thing everyday in the Venezuelan countryside.  Those little fingers really wanted to carry a piece of the Icaro home with them, and with such a swarm of kids it was really hard to keep an eye on them all and get the glider folded up.

I solved the problem by packing a fresh American baseball cap with me everyday and presenting it as a gift to one of the older kids, who was then my new best buddy and took charge of keeping everybody in line.  One kid was so good that he orchestrated about ten others to carry the bagged wing nearly half a mile to the nearest intersection.  Oh, Yankee caps worked best…

Thank you so much for the daily competition reports from Oz and everywhere else.  The stories and strategies, successes and failures are all so fun and exciting.  I'm always sorry to see the Australian comps come to an end.  The time you spend getting them out each day is very much appreciated.  Wow, 38 issues already this year!

Discuss "Landing with Ninos" at the Oz Report forum   link»

Wed, Feb 14 2001, 8:00:03 pm EST

to Table of Contentsto next topic Some photos/videos of recent northern California flying

Andy Long|Davis Straub|photo|USHGA|video

Andy Long «andylong» writes:

A bunch of us here in Northern CA scored some fantastic soaring at a site where it is extremely rare to get a flight, even once a year.  And I just happened to bring along my brand new digital camera on the flight.  Check it out.  Slow loading on "Flight #2" but good shots: http://dwp.bigplanet.com/longdemo/21101gradeflight/

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Davis Straub
co-author of Windows Me Secrets
"I gotta tell you; you took a total moron and turned me into a guru!  I couldn't have done it without your books!"
«davis»
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The Oz Report, a near-daily, world wide hang gliding news ezine, with reports on competitions, pilot rankings, political issues, fly-ins, the latest technology, ultralight sailplanes, reader feedback and anything else from within the global HG community worthy of coverage. Hang gliding, paragliding, hang gliders, paragliders, aerotowing, hang glide, paraglide, platform towing, competitions, fly-ins. Hang gliding and paragliding news from around the world, by Davis Straub.

Discuss "Some photos/videos of recent northern California flying" at the Oz Report forum   link»

The Oz Report, a near-daily, world wide hang gliding news ezine, with reports on competitions, pilot rankings, political issues, fly-ins, the latest technology, ultralight sailplanes, reader feedback and anything else from within the global HG community worthy of coverage. Hang gliding, paragliding, hang gliders, paragliders, aerotowing, hang glide, paraglide, platform towing, competitions, fly-ins. Hang gliding and paragliding news from around the world, by Davis Straub.

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