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Old Jan 07, 2015, 08:48 PM
wadasczi is offline
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InJamNoOneCanHearYouScrea m
United States, NH, Nashua
Joined Jun 2009
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Build Log
Building A "BONG BOOMER"

Well I had the notion for building something for NOS at this years NATS and while surfing the threads found an article on the venerable Bong Boomer. I ordered the plans from somewhere [Carstens??] and they came very quickly.

First impression of the Bong Boomer plan was I need a lot more money for balsa....

So I start this thread to meet folks out there that like to build, gather some advice along the way, and maybe meet you flying at the NATS or somewhere along the Northeast and Mid-Atlantic corridor flying in the Eastern Soaring league.

I am starting the project by cutting the wing ribs using a desktop CNC machine I picked up with some squirreled away TDY money. The Shapoko2 is available through "INVENTABLES" at https://www.inventables.com/. Marvelous little machine for 3-AxisCNC for $650. I use CAMBAM CNC software found here. http://cambam.info/. You can use other free CAD/CAM/CNC software but the CAMBAM application is really "WallyByGolly" proof. I added some pictures below of the equipment in use...

EDITORS NOTE: CAMBAM REQUIRES SOMETHING TO START WITH!!!! YOU THEN MODIFY THE AIRFOIL IN CAMBAM TO GET TO THE TARGET AIRFOIL. I UNDERSTAND THE RULES OF NOS WHICH REQUIRE AN EXACT AIRFOIL OF THE ORIGINAL SAILPLANE....

I got the airfoil from here: http://m-selig.ae.illinois.edu/ads/coord_database.html
I used an AG37 airfoil as a base template. It was close in shape to what I wanted to end up with for the Boomer, well sort of. For giggles I measured my SUPRA chord and inputted the value into CAMBAM, drew the cut profile, outputted the NC file and cut it. Presto I got a rib so close to the same outline of the center panel SUPRA!!!

I then imported the coordinates into CAMBAM and then "resized" them up to the root template chord of the Bong Boomer. Of course the resize needed some tweaking to get it to look like the Bong Boomer airfoil, but dragging the polylines of the airfoil here and there and joining them all up at the end gave me an airfoil when laid over the drawing was identical to the root rib. I stuck a BIC pen insert into the CNC machine and drew the airfoil outline. Close enough for Government work. A resize again for the tip rib of the main panel gave me the same profile....good to go!!!! Yehhh...CAMBAM rules.

Tomorrow I will cut the wingtip panel ribs. They only take minute or two too cut as well and then get some of the rib spar cutouts done. Maybe even wrap the spar boxes if I feel ambitious.

I guess the goal of the project is to give the Challengers a run for their money at the NATS by blocking as much sunshine as they do, add some spoilers to it to get it down [allowed per the NOS rules] and annoy the wife by not working on the kitchen. Priorities....
Regards,
Wally by Golly
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Old Jan 08, 2015, 03:03 AM
Thermaler is offline
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Pretty nice stuff you got going on here Wally.
But there is one small problem, using the AG37 airfoil you will not be Nostalgia eligible. . .
Sorry to be the one to let you know that.

Joe
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Old Jan 08, 2015, 05:02 AM
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InJamNoOneCanHearYouScrea m
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Joe thank you for the comment - Further clarification is necessary and thank you for keeping me honest! CAMBAM requires something to start with for an airfoil cut and it is just one polyline of x and y value. I could have used a Clark-Y airfoil coordinate set, or a Wortmann profile set, or any coordinate set from that site and then worked the X and Y values to get the "donor" airfoil coordinates that mimic the Boomer airfoil. I just needed values to start with as they are not on the plan from the year 1967.

After loading the "donor" airfoil coordinates I then stretched the airfoil in chord and thickness and then "smoothed" [modified the X and Y values for the polylines outside or inside of the airfoil] to outline the base rib pattern in the plans. I must have gone through a reem of paper drawing pen outlines, playing with the hundreds of polylines that comprise the airfoil, until it was spot on.

It may have been faster to cut, stack and sand the rib outlines, but you don't learn anything new there. I have learned that soaring community is not forgiving from a purist perspective so it is better to do it right or not at all. Importing something, modifying the Sugar Honey Iced Tea out of it to get what I need...Its just another way of starting somewhere....

When I get home tonight I will take screen shots and show how I did it. I am sure other folks want to know how it works. I would rather have acceptance from the community over a finger in the eye.

Alas and with a great sigh...Woke up in the middle of the night and realized I glued all the leading edge material together....backwards.
Wally
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Old Jan 08, 2015, 11:05 AM
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Gee Wizzzzz Wally it's not even foam ... Are you sure you'll want to fly it? I guess there are no foam planes that meet NOS rules.

Kerry
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Old Jan 08, 2015, 01:18 PM
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Ethel!
What the blazes are you up to?

It looks cool, would an airfoil change still be NOS legal? If you know something I don't about this I'll be most upset, but some how I trust Joe's opinion on this topic more than I would yours.

About time to call you up and shout some abuses ...............

Kerry, it will be hard to imagine him flying wood models after all these years.
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Old Jan 08, 2015, 01:45 PM
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NOS rules require using the original airfoil, but if I read everything correctly the OP is not changing the airfoil. He simply used an easily obtainable set of airfoil coordinates to preload his computer program he then modified the coordinates to duplicate the original airfoil printed on the plans. So there should be no issues with eligibility.

Looks like a fun design, I will be lurking.

Wayne
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Old Jan 08, 2015, 02:01 PM
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InJamNoOneCanHearYouScrea m
United States, NH, Nashua
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Well another planet heard from Alex...Yep I have to give it a whirl. When you read through the build article Mr. Hill even put a nitro motor on the front! The Balsa nose is removable. If I can get the thing flying OK sans motor I will convert it to...gasp...electric. My retinas are still burning from the Malta beach commercial....

Alex dear friend, even I as a 19,000 hour Test Pilot know you can't just substitute something and get away with it. When we run into each other I will show you how to make any airfoil you want in a jiffy now. The Selig site has almost all of them. If they don't we can modify any coordinate set and make an airfoil per your plan through trial and error of course.

Wayne...you are the man and understood what I was doing! Yah. Rest assured I will be documenting the bejusus out of the build and getting buy in from the crowd!!!!
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Old Jan 08, 2015, 02:25 PM
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Duane
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I use Wind and Wet's airfoil plotter for making airfoils. It creates an SVG that goes right into Inkscape. Ungroup twice, then copy the airfoil profile and paste into a new document. Inkscape can export to DXF, but it's in millimeters and only lines are exported (no text). Inkscape is also great for tracing shapes over a scanned bitmap, which I've done quite a bit.
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Old Jan 08, 2015, 02:28 PM
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Malta & Newport
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I see! Said the blind man.

Its like, oops, I accidentally sanded in a Phillips entry , raised the leading edge radius by 3/16th of an inch and that by all coincidences it looks remarkably similar to an Ag series foil.

Wal, out of curiosity do you have a scan of the article? I'll be interested in the read.

Cheers, Al


p.s. Duane, thats a really neat site!
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Old Jan 08, 2015, 03:03 PM
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My father and each built these in the '70's. Speked them out in giant Arizona thermals. Great fun.

WinchDoc

when I had more hair than Robert Plant
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Old Jan 08, 2015, 03:13 PM
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InJamNoOneCanHearYouScrea m
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Duane,
I wished I had your knowledge a few weeks ago. Razzleberrys and Nuts. I tried Inkscape and got frustrated and just stuck with CAMBAM. Roger that on the metric way of life. Funny when you import a coordinate set in CAMBAM it gives an airfoil that is only one millimeter in length. Oslo, Norway....I say. I should have stayed at a Holiday Inn Express....the airfoil will always be one millimeter as that is the largest coordinate value!!! Sizing away and sculpting it to get where you want to go is easy now that I understand the CNC software better. I will try and do a show and tell tonight on how it all works. Technology at its finest. My wife's only comment was positive----she was happy I did not have to stack a rib set and sand it and get balsa dust all over the laundry area!!! Only seal of approval so far. What about the Kitchen?
Wally
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Old Jan 08, 2015, 03:26 PM
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Quote:
Originally Posted by Windependence View Post
NOS rules require using the original airfoil, but if I read everything correctly the OP is not changing the airfoil. He simply used an easily obtainable set of airfoil coordinates to preload his computer program he then modified the coordinates to duplicate the original airfoil printed on the plans. So there should be no issues with eligibility.

Looks like a fun design, I will be lurking.

Wayne

By golly, I like the way Wally got his airfoil. It works for him!
Just like some of use put Monokote on different, we get the same results.
Well, most of us. I know a guy that can not build or cover to save his behind no matter how many of us tried to help him. Moldies and foamies are good for him and us. It means no more aerial bombing from his planes!


Joe
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Old Jan 08, 2015, 04:28 PM
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ShapeOko Question

Hi Wally,

Really like this build, I'll be following the thread. In the meantime, I am curious if you are using the stock or an extended Z on your ShapeOko build?
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Old Jan 08, 2015, 05:25 PM
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from the Soaring History thread

http://www.rcgroups.com/forums/showp...&postcount=977
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Old Jan 09, 2015, 07:05 AM
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InJamNoOneCanHearYouScrea m
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For Stan - Stock Shapeoko2 with an upgraded spindle. I am thinking forward and see no need for the precision on the Z-Axis. The stock system does a real good job. My only modification in the Z-Axis was to add 2 one-inch hollow aluminum square mounts behind the stock spindle mounts to move the spindle out away from under the Z-Axis Nema 17 motor fixture. I now get full travel in Z where it was limited before. If you look at the middle image from my very first post you will see what I have described.

For JRS - That is where the project originated from. You are the weekly winner and thank you for posting it!!!

For Joe - A tear in my eye for someone else that understands.

For the World - I started writing a "How-To" last night and split my time between that and building a bit. I noted that the plans call for you to glue on a trapezoidal piece of balsa to a D-Shaped leading edge [pre-shaped]/ or glue a square to the leading edge and make it a trapezoid and then glue the D-Shaped leading edge on. Prepare for a laughter moment...
You have to remove a piece of the nose at a slant to do this but when I overlaid the built up nose piece onto the rib looking for how much of that "slanty" piece to remove it did not look right/fit right/ or stay within the bounds of the airfoil outline. Also, I had to take into account the 1/16" sheeting of the top and bottom of the airfoil that connects that mess all together.
Start laughing...A couple of posts before you remember me saying I glued the leading edge together wrong...yep this is why it did not fit or look right. I think I have to notch the nose of each rib now, rather than just cut it off, to get the messed up pieces together to correctly fit within the airfoil outline. An "AH-HA" moment so to speak. The old do one thing at a time has reared its ugly head...
With that I spent more time building....the Kitchen will wait.

Wally by Golly
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