Skonk Wulf by Shrox
 

Douglas Shrock, you are an Artist! I am enjoying building your design and I appreciate the work you put into creating it.

Thank you.

Do not sharpen the wing probes, as you will skewer your hand at some point and get blood all over it.

Cool looking kit.

That's quite a building jig in last couple photos.

http://www.apogeerockets.com/Buildi...llotine_Fin_Jig

Thanks. That's a variant of my Guillotine fin jig. I figured I'd give it the "acid test" by building one of Shrox's rockets...along with a bit of shameless self-promotion. :D

Are you going with the 24mm mount?

Yes, as that's what your plans call for. I did notice that the return on the "B" fins was a bit short of reaching the motor mount (after cutting them, of course!). I should have checked this before gluing up the main fins but I think I can remedy the problem by gluing on a narrow strip of wood and sanding to fit.

No problem for a Ninja like me. ;)

Yesterday I glued small strips of basswood to each of the two wing fins and also the tail fin. I also built the 24 mm motor mount, using BT50 tubing and home made centering rings of 3/32" aircraft plywood. Today I test fitted these parts and now everything fits as it should. I am awaiting a PNC 80 nose cone and a shock cord assembly that I ordered from a guy on Ebay and will continue this build when they arrive.

This morning I also pulled sand stickers and mowed the lawn. As it was cool and cloudy most of today, I fired up the John Deere 950 this afternoon and finished demolishing the barn/outbuilding which was destroyed by last December's ice storm. Now I'm cooking salmon for me and my lovely bride.

So much for my day of rest. :)

After doctor's appointments, grocery shopping, building fin jig parts, lawn mowing and repairing all of the junk that goes along with it, I finally returned to this project. Macklin's rendition of the Skonk Wulf by Shrox is almost finished...except for the launch lug, painting, decals and flight prep. I should be 100% by Christmas. Maybe?

I deviated somewhat from the sequence shown in the plans and instead chose to mark and fabricate the fins first, as this would give the glue plenty of time to set while I worked on other aspects of the build. Next I fabricated the centering rings and made a 24 mm motor mount. Since I didn't have an Estes E size motor hook on hand, I used a standard hook for A-D motors, but installed with the hooks pointing outward using epoxy and fiberglass strapping tape. When I fly this exotic creation (if I get the nerve), I'll make a masking tape thrust ring on the motor and then retain the motor with a couple passes of masking tape.

It took a bit of improvisation to use my fin jig to set the "underfin", because the distance between the bottom of the aluminum alignment rails and the point of tangent on a BT80 is only about one inch, barely enough to capture the work piece. To solve this problem, I gauged the rails further apart by use of two 1/8" x 1" aluminum flats and two 1/8" x 2" x 2" angles which were set within the rails and sandwiched the fin. This allowed the fin to be adequately held while being glued. (See pics)

All in all I am very pleased with this kit and the way it is turning out. Were there things I would do differently were I to build it again? Sure. Aren't there always?

Here's some more pics.

Are you going with the colors on the guide or something different?

I intend to go with your original color scheme. (With a bright red chute so I can find it in the winter grass!)

Here's a picture of our new kitty, Elsa, rescued from the Collin County Animal Shelter in McKinney. Our last kitty died in 2011 at the age of twenty.

If my build turns out half as nice as this http://www.rocketryforum.com/showth...y-to-get-SKONKY I'll be a happy camper!

Has anybody figured out where the CP is located on this beast?

Here's the first round of painting the Skonk Wulf by Shrox. After priming and dry sanding, I applied Testor's White enamel overall and let it dry for over a week. Then I carefully masked off the "belly of this beast" and painted the "topside" with Testor's Desert Sand enamel, which is a dull coat of flat finish. The instructions call for "tan" but the paint chips didn't look right to me and I can almost see this bird providing air support for Rommel's tanks in North Africa.

Once this is thoroughly dry I'll mask and hand paint the detail work. This is quite a challenging project and I am enjoying it immensely!

Looks nice, Ted.
Is that 24 or 29mm powred ?

I went with the 24 mm motor mount per the Shrox original design. I'm not entirely satisfied with the Modern Desert Sand color but I dread re-masking the thing. The paint finish turned out excellent for a rattle can so I'd best just leave it be. Perfect is the enemy of good.

Perfect is the enemy of good. :chuckle: Aint it the truth!

Nice build, gorgeous kitty! Is she a Maine Coon cat?

Thanks, and yes, she's a Maine Coon. At least that's what my wife tells me. We got her from the animal shelter so she's probably a mixture. Whatever her ancestry, she's the sweetest, quietest and most gentle cat I've ever seen. And a good mouser too! :)

Despite my previous statement regarding "perfect vs. good", I just couldn't live with that Modern Desert Sand paint which looked more like Titebond II mixed with K9P. So I masked it again and repainted with Testor's Dark Tan flat enamel. (Shrock's original design called simply for "Tan") I'll post some progress pictures when the wind stops blowing.

Has anyone ever actually flown one of these beauties? I am technologically challenged and only have CP Technologies CP-1 program which really doesn't address weird fin configurations like this. The best I can do is find the fully loaded center of gravity with the heaviest motor I plan on using (E9 -something) and then do a swing test. Without additional nose weight the CG falls within the fin area which will make attaching the string a challenge.

Anyone have any ideas or prior experience with this. :confused:

Do two cardboard cutouts, one for top view one for side view. Find where they balance and measure the distance from the nose to those spots. Average the measurements and you get a very conservative cp location.

Should get you in the ballpark.

kj

Yes.

Thanks Kevin! I think I can use the paint patterns that came with the plan pack as templates and then upscale the results to actual size. At least that's what I'm going to try before I fly!

Do you care to talk about it? :D

I just looked over the instructions, looks like I left out the CG mark!

It should balance just in front of the leading edge of the main wing.

Thanks Doug.

With an Estes E9 dummy engine installed, the center of gravity (CG) locates just past the mid point of the launch lug, which I attached as per your design. The center of pressure (CP) should then be 2.60 inches aft to achieve one caliber of stability. I'm going to proceed with Kevin's suggestion just to be on the safe side and will post my findings here. If I can devise a way to attach a string without damaging the finished rocket I'll also do a swing test.

Post your findings here if you would be so kind.

Absolutely! :D

Put together a rocksim file for the Skonkwulf. CP using Barrowman was 15.0 inches. Using the rocksim method it was 15.7. I built using thickwalled bodytube and corresponding nose cone with a resultant measured weight and CG of 360 gm and 10.75 inches. Have only flown once on an E28, but flew great. Have yet to attempt the paint scheme so it is just a plain primer white.

That's amazing! Earlier tonight I made two cardboard cutouts directly from a copy of the side and top views on the paint schemes which came with the Skonk Wulf plan pack. The average center of pressure using this method turned out to be a bit over 15 inches. I'll take photos tomorrow and post them here along with my math, such as it is.

I couldn't do the Barrowman method if my life depended on it. Fortunately, it does not! :o

Yesterday evening I made cardboard cutouts and balanced them as closely as possible to get some idea of the centers of pressure in both the side and plan views.

First I made a copy of the Skonk Wulf decal placement and color guide which came with the instruction pack. These appear to be proportionately correct although no scale is given. Next I taped this copy onto a thin piece of corrugated cardboard and carefully cut out the silhouettes with a fresh Exacto blade. These silhouettes were then laid flat over an architect's scale and the balance points marked.

The overall length of the actual rocket I built is 23.75" nose to the end of the motor mount tube. The length of the cardboard silhouettes from the same two points of reference measures 7.0625".

The center of pressure looking at the side view silhouette measures 4.375" from the nose, or 61.9% of the total length. Thus, 0.619 x 23.75" = 14.71" on the actual rocket.

The center of pressure looking at the plan view silhouette measures 4.750" from the nose, or 67.2% of the total length. Thus, 0.672 x 23.75" = 15.81" on the actual rocket.

The average between these two shapes is 14.71" + 15.81" / 2 = 15.26" on the actual rocket.

With an E9 dummy weight of 67 grams installed, the center of gravity locates 16.625" from the nose. To obtain one full caliber of stability I will then have to add enough nose weight to shift the CG 3.965" forward.

I built this rocket with Apogee thinwall BT80 tubing and and an Apogee PNC-66A nose cone. The empty weight of my build stands at 8.5 ounces. The total lift off weight with an Estes E9 stands at 310 grams or 10.9 ounces as is. In order to achieve one caliber stability I'll have to add at least 3 ounces of nose weight, which will bring the total lift off weight to about 14 ounces. It looks like any 24 mm composite would be a better bet.

Anyway, here's some pictures I took this morning.

And here's the new paint job. It's a little darker than Doug's color guide, but I through buying paint!

I can't do the Barrowman method myself, but Rocksim has option to have Cp calculated using Barrowman or its own method. Your paint job looks great, so far. I bought a bunch of small cans of paint to paint mine, but can't get up the initiative to start.

It's pretty cool that two different methods (one rather low tech and the other state of the art) have resulted in such similar results. Having gone through this exercise I feel much more confident in having a good flight with this odd duck!

I'm getting better at this painting thing but I've got a way to go. This one has seven different colors and so far my biggest expense with be paint. I've decided to go with brush on paints for everything else except the flat black and light gray on the nose.

Thanks for your interest and input. :)

It's a nice model. Shrox, please don't stop designing.

Ted, I just would have found a way to swing test it. :D

Maybe I could devise some sort of elaborate harness so as not to crush the fins? I guess I should have done that before I started painting. Oh well, they don't call me Mr. Bass Ackwards for nothing!

Seriously, this is a challenging project that requires thinking and planning and I'm really enjoying it! I too hope that Douglas Shrock continues producing his unique Shrox designs. :)

Ted,

Tonypv built one last year and has flown his a few times. Go to http://www.cmass.org/ site and look at last seasons pic's for shots of his rocket. Tony is a master at construction and painting. :D

I appreciate the link but try as I might I could not find the pics of tonypv's Skonk Wulf. Can you narrow it down to a specific date?

Thanks!

Try this link

http://www.cmass.org/index.php?view...emid=70#gallery

or

Go to gallery, Page 3 at the top, November 2, 2014. Tony is the first pic with the Skonk Wulf.

Got it! You are a gentleman and a scholar! Do you think Tony would mind if I post his pictures here?

Nope, I don't think he would mind. He pop's in every day, twice a day. Once in the A.M. 5:30ish and again about 5:00 P.M. billspad took and posted the pic's on the CMASS forum.