By Grabthar's Hammer! A LOC Skinwalker thread!

[lr64]

If it's an EX motor, can't you just use a smaller grain? Or use less powerful fuel?

 

[Rschub]

You could add drag, as I did for my level 2.

 

[krislhull]

If it's an EX motor, can't you just use a smaller grain? Or use less powerful fuel?

I'm working with the motor maker on that. He hasn't gotten back to me yet, but is working on a few tweaks...

You could add drag, as I did for my level 2.

View attachment 656836

Not a bad idea... might look into that as an option.

 

[trueoink]

You could add drag, as I did for my level 2.

View attachment 656836

That's a pretty good idea. Are you able to sim that in openrocket or rasaero?

 

[lr64]

Bag of water or other innocuous substance* set up to burst open with parachute deployment?

Drag sounds pretty good, though.
------------------

sugar or epoxy fuel and less intense oxidizer** instead of composite..... (I hope that's not going too far, am trying to be vague here)

Nozzleless for short burn, long coast. http://serge77-rocketry.net/nozzleless0/nozzleless0e.htm

I realize some of these things are too much trouble unless you find them educational and entertaining.


*Sand, dry, crunched up leaves, cheap kitty litter.....
**Different nozzle sizes or grain configurations might be required. A lower than optimal Kn might be enough by itself. https://www.nakka-rocketry.net/design1.html#Deter

 

[Rschub]

That's a pretty good idea. Are you able to sim that in openrocket or rasaero?

No, but my mindsim says they will keep this rocket under 9000 feet.

 

[lr64]

No, but my mindsim says they will keep this rocket under 9000 feet

It probably wouldn't be too hard to set up a spreadsheet using the motor's thrust curve, drag derived from Openrocket without the extra drag bits, and assuming a Cd of 1 for the extra bits.

 

[Chuck Rogers]

I'd set up four vertical drag plates mounted to the base bulkhead of the rocket. They could be bolted or screwed into the base bulkhead.


These can be modeled as four 90 deg Inclined Flat Plates using the Inclined Flat Plate Protuberance inputs in RASAero II ( www.rasaero.com ), see Pages 24-29 in the RASAero II Users Manual.


The input is here; put in a Flat Plate Angle of 90 deg (vertical), and put in the Frontal Area of the four Flat Plates combined together. Be sure to set the Streamlined - No Base Drag and Streamlined - With Base Drag Frontal Area inputs to zero. (Note that there are two Inclined Flat Plate Protuberance inputs so that two sets of Flat Plates with two different Flat Plate Angles can be entered.)




I'd make sure the rocket sims to only 90% of the waiver altitude, just to make sure you don't exceed the waiver. You can adjust the Total Frontal Area of the four vertical drag plates until the rocket sims to 90% of the waiver altitude.


Be sure of course to use your actual Launch Site Elevation, and an estimate of what the Temperature will be when you expect to launch the rocket, or a range of Temperatures (morning cooler, afternoon hotter).



Charles E. (Chuck) Rogers
Rogers Aeroscience

 

[krislhull]

The past few days have been off and on again working on the Hammer. I marked out the location for the booster section shear pins, and then drilled 4 holes through the airframe and coupler. I then took and cut out some .025" brass strips and made some reinforcements so that the cardboard would not get worn out quickly with use.





I then started to finally assemble the electronics bay and endcaps. I had previously epoxied G10 fiberglass bulkheads onto the plywood bulkheads that came with the kit to add resistance to black powder residue, and to aid in cleanup. I assembled the 4 lengths of all thread, and temporarily installed the Additive Aerospace altimeter sled with a StratologgerCF and Eggtimer Quantum installed. I still need to install the wiring, and get that all sorted, but I discovered that I do not have any screw switches, so those are on order. Two RocketJunkies large charge wells are also used on each endcap, as well as a 4 place terminal block.





Now not much is left. Once the screw switches arrive, I will get them wired up and mounted, and then I will locate the arming holes and vent holes, locate the holes to bolt the electronics bay to the upper airframe, drill out shear pin locations for the nosecone, and then move on to ejection tests and paint.

One thing I have not mentioned yet, is that I have tracked down a 5:1 ogive G12 fiberglass nosecone for this build. Ken at Performance Hobbies found one while going through his storage room, and it is now on its way to the Seattle area for me. I think that this nosecone will make the rocket look a lot more proportional than the stock LOC plastic cone..

On another note, the motor that this will fly on has been finalized. It will be an EX M. It will be my second L3 class motor, and my largest to date, and that is all that I will say at this time. The builder has made some tweaks to the motor that when I run it through the sim, show it performing very well, and comfortable within the waiver I will have to play with at the launch site.

 

[Tim51]

One thing I have not mentioned yet, is that I have tracked down a 5:1 ogive G12 fiberglass nosecone for this build.

I think if LOC marketed a long version of their 7.67" PNC analogous to their 5.5" one, they'd be on to a sure fire winner. I don't understand why they don't.

 

[Theory]

I think if LOC marketed a long version of their 7.67" PNC analogous to their 5.5" one, they'd be on to a sure fire winner. I don't understand why they don't.

Agree, though molds are expensive and the overall ROI might not be there or take too long to realize. Doubt they sell very many 7" kits

 

[krislhull]

I think if LOC marketed a long version of their 7.67" PNC analogous to their 5.5" one, they'd be on to a sure fire winner. I don't understand why they don't.

I know that LOC is working to supposedly bring back the PML fiberglass nosecones, from what @ECayemberg has said on his Force Ten thread. They are still several months out from what I have been told. That is the nosecone I was originally hoping to get for this, but one of the Composite Warehouse G12 ones will work just as well.

Agree, though molds are expensive and the overall ROI might not be there or take too long to realize. Doubt they sell very many 7" kits

If LOC is going through the process of refurbishing a damaged mold, and obtaining a second, new mold, I would think that the demand is probably there, or at least they predict it to be there. See below:

I don't have an exact timeframe, but I do know that the primary mold had a damaged tip, and that there's an effort to repair the tip asap...just need some free time to do so. Additionally, a second mold has been secured; just needs a few surface blemishes cleaned up.

 

[krislhull]

Well, more work on the avionics today. I drilled out the holes for accessing the screw switches in the airframe and the electronics bay, and while I was searching around my work bench for a few things, I came across some surface mount plate from Additive Aerospace for mounting screw switches to the inner surface of a coupler, so I decided to go ahead and make use of them, since they were a perfect fit!



I then drilled out for vent holes for the bay, and at that point, major construction of the bay itself is complete, and All that is left is install the wiring. So I went ahead and Installed the upper electronics bay endcap permanently at this time, and installed the other stiffy coupler that goes in the top part of the assembly. Once all epoxy dries, I will drill out the holes to bolt the upper airframe to the coupler.



I then took advantage of the decent weather and took the booster section outside and gave it a sanding down, followed by a first coat of primer.





The beast is coming together! She will probably be ready for ejection tests next weekend, or in the days after...

 

[krislhull]

Another week gone by, another huge update on progress!

Tuesday, I came home from work to a box from Ken at Performance Hobbies on my porch...Inside it was a nice large 7.5" 5:1 ogive nosecone!


I certainly prefer the look of the 5:1 ogive to the shorter stock LOC plastic cone that came with the Skinwalker kit.



I also located and drilled the holes to mount the electronics bay to the upper airframe, and installed the flange nuts into the upper section of the coupler. At the same time, I coated the inner surface of the coupler with a layer of West Systems epoxy as a layer of protection from ejection charge blasts and residue.



Work has then started on the upper airframe. I marked out the location for the 4 4-40 shear pins for the nosecone, and drilled the holes, then as I did for the lower airframe section, I fabricated brass shear strips, and installed them in sides of the tubing using relief cuts I made earlier. Once the brass strips were epoxied in place and cured, I placed the nosecone one the airframe, and marked inside the tube where the shoulder ended. I then brushed on a layer of West Systems epoxy over the whole upper section of the airframe tube where the nosecone shoulder will sit to act as a reinforcement.



It took a whole lot of sanding this morning, but I the results are perfect. I have a nice, strong section of tubing that holds the nosecone shoulder perfectly. Nest, I bolted the electronics bay to the upper airframe, and placed a cluster centering ring that I drilled out with more 1 inch holes in it at the top of the coupler, and tacked it to the airframe with CA. The centering ring will act as a parachute shelf to keep the recovery gear from sitting directly on top of the ejection charges, and instead will keep them about 8 inches above at all times. I then removed the electronics bay, painted more West Systems epoxy into the airframe above the parachute shelf, and slid a coupler in and epoxied it in place.



Meanwhile, in between epoxy curing and all, I was taking advantage of sunshine and nice weather, and priming the rocket!



I think it is ready for its top coat now................

Of course, I had to do the first full up assembly of the rocket!

So, I present to you, a not so naked Grabthar's Hammer, in primer



Up next is final touches to the electronics, finishing up the nose tracking bay so I can finish the nosecone assembly, and then ejection testing and final paint.

 

[Tim51]

Great work. And the longer NC enhances the overall look x 10.

 

[KenECoyote]

Another week gone by, another huge update on progress!

Tuesday, I came home from work to a box from Ken at Performance Hobbies on my porch...Inside it was a nice large 7.5" 5:1 ogive nosecone!
View attachment 659527

I certainly prefer the look of the 5:1 ogive to the shorter stock LOC plastic cone that came with the Skinwalker kit.

View attachment 659528

I also located and drilled the holes to mount the electronics bay to the upper airframe, and installed the flange nuts into the upper section of the coupler. At the same time, I coated the inner surface of the coupler with a layer of West Systems epoxy as a layer of protection from ejection charge blasts and residue.

View attachment 659529

Work has then started on the upper airframe. I marked out the location for the 4 4-40 shear pins for the nosecone, and drilled the holes, then as I did for the lower airframe section, I fabricated brass shear strips, and installed them in sides of the tubing using relief cuts I made earlier. Once the brass strips were epoxied in place and cured, I placed the nosecone one the airframe, and marked inside the tube where the shoulder ended. I then brushed on a layer of West Systems epoxy over the whole upper section of the airframe tube where the nosecone shoulder will sit to act as a reinforcement.

View attachment 659531

It took a whole lot of sanding this morning, but I the results are perfect. I have a nice, strong section of tubing that holds the nosecone shoulder perfectly. Nest, I bolted the electronics bay to the upper airframe, and placed a cluster centering ring that I drilled out with more 1 inch holes in it at the top of the coupler, and tacked it to the airframe with CA. The centering ring will act as a parachute shelf to keep the recovery gear from sitting directly on top of the ejection charges, and instead will keep them about 8 inches above at all times. I then removed the electronics bay, painted more West Systems epoxy into the airframe above the parachute shelf, and slid a coupler in and epoxied it in place.

View attachment 659533

Meanwhile, in between epoxy curing and all, I was taking advantage of sunshine and nice weather, and priming the rocket!

View attachment 659536

I think it is ready for its top coat now................

Of course, I had to do the first full up assembly of the rocket!

So, I present to you, a not so naked Grabthar's Hammer, in primer

View attachment 659538

Up next is final touches to the electronics, finishing up the nose tracking bay so I can finish the nosecone assembly, and then ejection testing and final paint.

 

[krislhull]

Great work. And the longer NC enhances the overall look x 10.

It definitely improves the aesthetics!

 

[krislhull]

Maybe I should find some cosplayers as Thermians to carry it out to the pad?

 

[bschultz32]

" . . cosplayers as Thermians to carry it out to the pad . . ." - in their human form, that would be cool, but probably a bit clumsy. But in their octopoidal form, well now, that would peg the Cool Meter at 10!

 

[krislhull]

The majority of progress on the past week has been on paint. And final touches to the avionics and nosecone tracker bay. First, the tracker bay. Several years ago I bought the MissileWorks RTx system, and I have really liked it, and now I have 4 rocket units, and I decided to no longer have them dedicated to individual rockets like I originally planned on. its just too expensive! So two years ago I started building my builds with nosecone bays that can accept the 54mm sleds from Additive Aerospace, and mount my GPS units to those. I can now easily swap them between rockets as needed, in a matter of minutes, in the field. So, for the Hammer, I took a 7.5 inch 54mm CR, and used that as the bulkplate for the nosecone. I then used a 4" bulkplate as a removable hatch to mount the sled to with a section of 54mm tubing to act as a buffer to keep the sled from whipping around inside the nose.





The whole assembly will be epoxied up inside the nosecone shortly, in the next day or two.

So, now with that done and out of the way, on to paint! I have decided to go with the Ace brand of spray paint from Ace Hardware, and I have been very pleased with the results. For just over $5 a can, this stuff sprays on very nicely, has decent coverage, and dries somewhat fast. In the very first post, I had a preliminary paint scheme idea...... well, that has gone out the window. I have decided I don't have the patience for something that time consuming or complicated. The masking alone would take a day or more. So i simplified it. And I am still very happy with it so far. It is far from perfect, and it is certainly not symmetrical, but i like it!

First up was a couple of coats of grey on the booster.





Followed by a couple coats of purple on the upper airframe sections and nosecone.





After letting those all sit out in the sun for several hours Saturday, they then came in the garage and sat in there until this afternoon further curing some more.



That brings us to today.... After work, I came home and masked off all of the booster except for a triangular section on the top of the front, and I did the same thing for the bottom of the lower airframe tube on the back. For the lower airframe, I sanded down the unmasked area of its purple paint, and then sprayed on a couple coats of the grey. On the booster, I sanded down the grey, and sprayed on a couple coats of the purple. The results look good, if I don't say so myself!





Granted, its a little off center, but eh, I dont care. So now I need to assemble the nosecone, drill the holes for the shear pins in the upper airframe/nosecone joint, and then mask off and paint one last area of trim grey on the upper airframe. Then ejection tests and decals!

 

[trueoink]

Can you share a few more pictures on what you did for the removable fin section? Whenever I end up doing my L3 that's likely the route I'll take so it can fit in my car

 

[krislhull]

Can you share a few more pictures on what you did for the removable fin section? Whenever I end up doing my L3 that's likely the route I'll take so it can fit in my car

I didnt do anything special, really. The base kit comes from LOC with 3 30" sections of airframe. After I installed the coupler into the top of the top of the booster section, and inserted the stiffy coupler inside it, I slid the lower airframe on and drilled eight holes for 8-32 screws, two inline with each fin approx. 2 inches up from the joint, and 2 inches apart that would serve to bolt the two sections together. Blind flange nuts were then epoxied from the inside of the coupler assembly, and the whole thing can now be bolted together in the field with ease. See post 26. Many builders use the same, or similar technique to make rockets modular for transport and ease of storage. I use the same method for attaching the altimeter bay to the upper airframe. Many builders also like to use well nuts on composite airframes for their smaller size and lower profile. I have used those on my canvas phenolic builds with great success in the past.

 

[krislhull]

And here she is!







I might have screwed up and gotten the decals slightly askew in places, but eh, who cares! It will look great from 20 feet away! Thats all I care about!

Now I just need to complete ejection tests this weekend, and she is ready for flight at Sod Blaster VI over Labor Day weekend! she will be going up on a EX motor that will be roughly equivalent to a M1419 in power, and sims out to around 7300ft. Rough weight using the scale I have here at home comes in under my estimate at 33 pounds. I am probably going to take it into work one day this week and weigh it on a scale in our shipping warehouse for a more accurate weight, but I am happy with the results!

 

[bad_idea]

Have a great launch!

 

[-Slick-Ice]

Woah! That's awesome!

 

[KenECoyote]

Looks awesome!

 

[rharshberger]

I feel like Grabthar was more of a concussion weapon kinda guy. Hammer, mace, morning star, flail…

Grabthars Skillet... its a saucer...

 

[rharshberger]

its a 9,000ft waiver, and it will be a 98mm EX motor. Sims out to 9,500 feet with my preliminary rough estimated weights at the moment.

Anything approaching within 10% of the waiver has special requrements with the club. Please check TCRs page and submit the required information please.

 

[krislhull]

Anything approaching within 10% of the waiver has special requrements with the club. Please check TCRs page and submit the required information please.

Yep, not to worry, Rich. The current sims are showing it well under the waiver at 7300ft, and I plan on sending the email to notify the board this week per the requirements for L and M motor flights anyways! Hopefully it will go off without issues! Looking forward to seeing you guys there!

 

[Rschub]

Only one thing left to track down...