L3 Build: LOC 5.5" Sandhawk

[krislhull]

Got through one of the last two objectives before I do the ejection testing (hopefully next week). Today I laid out the shear pin locations, then drilled and tapped the holes for 4-40 nylon screws. Next, I laid out the locations for the bolts to secure the payload section to the upper half of the electronics bay. I will be using 8 8-32 screws to do the job. The screws will thread into nuts that I still need to epoxy to the inside of the bay.



I also at the same time drilled out the holes for mounting the arming switches. Taking a page from Nick@jets playbook, I first used a 7/8" forstner bit and drilled both holes through the airframe, and to the coupler. I then finished the holes with a 3/4" forstner bit. This allows the switches to site somewhat recessed into the airframe, and not protrude as much.





Of course, I had to attach the Remove Before Flight flags!



The switches were then wired up, and I am now waiting to finish the ejection tests, and final paint of the bird before I final install them into the rocket.

 

[Steve Shannon]

That’s looking really good Kris. The only thing I don’t fully endorse is the use of key switches. That’s for two reasons:
First, and most important, I’ve never found one that included mechanical shock ratings. I’ve never seen one fail though. Key switches are designed to provide security, not necessarily reliability. They’re usually used in panels which never are subject to gee forces.
The other reason is because nobody but you can disarm your rocket.
I don’t think you should change them because of my personal opinion. Neither NAR nor Tripoli has made a stand against them. Just something to think about for future projects.

 

[krislhull]

That’s looking really good Kris. The only thing I don’t fully endorse is the use of key switches. That’s for two reasons:
First, and most important, I’ve never found one that included mechanical shock ratings. I’ve never seen one fail though. Key switches are designed to provide security, not necessarily reliability. They’re usually used in panels which never are subject to gee forces.
The other reason is because nobody but you can disarm your rocket.
I don’t think you should change them because of my personal opinion. Neither NAR nor Tripoli has made a stand against them. Just something to think about for future projects.

That is actually good information, and the shock rating something that I actually hadn’t considered. I’ll definitly take your suggestions into serious consideration on future builds. This is my first time using key switches, and I am not certain I will use them again, partially because of their cost. After installing these, I think I prefer the unobtrusiveness of the internally mounted screw switches I have used on basicall all of my previous builds.

 

[rharshberger]

That is actually good information, and the shock rating something that I actually hadn’t considered. I’ll definitly take your suggestions into serious consideration on future builds. This is my first time using key switches, and I am not certain I will use them again, partially because of their cost. After installing these, I think I prefer the unobtrusiveness of the internally mounted screw switches I have used on basicall all of my previous builds.

I like you Kris, prefer the internal screw switches, most commonly I use the ones from Missleworks, but increasingly find myself drawn to something like Steve Thatchers SMT Designs screw operated slide switches.

 

[Bat-mite]

That’s looking really good Kris. The only thing I don’t fully endorse is the use of key switches. That’s for two reasons:
First, and most important, I’ve never found one that included mechanical shock ratings. I’ve never seen one fail though. Key switches are designed to provide security, not necessarily reliability. They’re usually used in panels which never are subject to gee forces.
The other reason is because nobody but you can disarm your rocket.
I don’t think you should change them because of my personal opinion. Neither NAR nor Tripoli has made a stand against them. Just something to think about for future projects.

Steve and I have had this debate before. I love key switches because 1) if you use a flagon them and if they can only be removed in the on position, you will never forget to arm your electronics at the pad, and 2) I don't ever want anyone disarming my rocket except me. If they find it in a field with unspent charges, contact me and let me know where it is.

Just the other side of the story.

 

[Steve Shannon]

Steve and I have had this debate before. I love key switches because 1) if you use a flagon them and if they can only be removed in the on position, you will never forget to arm your electronics at the pad, and 2) I don't ever want anyone disarming my rocket except me. If they find it in a field with unspent charges, contact me and let me know where it is.

Just the other side of the story.

Those are both valid points, but the lack of a shock rating still bothers me. I think I’m going to switch to those pull pin microswitches for your first point.
As far as not having someone else disarm the rocket, we sometimes have ranchers or surrounding land owners who find our rockets and have picked them up to prevent their calves from being frightened. Landowner relationship always trumps potential loss of data. In the extremely unlikely event that an unspent charge went off while they were loading a rocket into their truck, that would be very bad for our club. Most of our electronics record the data so being disarmed doesn’t lose the data.

 

[Bat-mite]

Those are both valid points, but the lack of a shock rating still bothers me. I think I’m going to switch to those pull pin microswitches for your first point.
As far as not having someone else disarm the rocket, we sometimes have ranchers or surrounding land owners who find our rockets and have picked them up to prevent their calves from being frightened. Landowner relationship always trumps potential loss of data. In the extremely unlikely event that an unspent charge went off while they were loading a rocket into their truck, that would be very bad for our club. Most of our electronics record the data so being disarmed doesn’t lose the data.

A fair point.

 

[Steve Shannon]

A fair point.

Yours is too. If I just launched a rocket on an RRC2 and when I got to it someone had turned off the altimeter and now I would never know what altitude it reached, I would be POed.
A lot depends on local circumstances. When I first got into the hobby the big thing was never touch another person’s rocket. For most ranges that’s still safe advice, but at a range like ours where it’s very hilly and very easy to lose a rocket, most of us give tacit approval to bring our rockets back if you happen to find them. It’s way better than having a thousand dollars worth of rocket lost.

 

[krislhull]

Got the nuts that will be used to secure the payload section to the electronics bay epoxied in place today. (Dont worry, I wont be using those long screws for flights!)



I then took one of the 54mm centering rings I have, and using the 7/8” forstner bit, I drilled 8 holes around the center 54mm hole, and created a parachute shelf for the payload section.



This ring was then epoxied 16” from the forward end of the airframe, and will provide a shelf for the parachute and recovery gear to sit on during boost, preventing it from all from sliding down and sitting directly on top of the electronics bay. I also took the time and used the epoxy I mixed up to seal the electronics bay lids. Once the epoxy is fully cured, I should be ready for ejection testing on this beast. However, with rain in the forecast, and a work trip coming up this weekend, I probably wont get to that until next week at the earliest.

 

[Steve Shannon]

Very nice work, Kris.

 

[cwbullet]

Subscribed

 

[krislhull]

I had planned on getting some ejection testing accomplished today, but I seem to have made a rookie mistake! I got everything prepped and set up, fire the charge, and realized I forgot to put a casing in the motor mount to plug it... D'OH! Oh well... Lesson learned there! I was going to recycle, but it started to rain, so no more attempts today. I did, however, get all of the recovery gear installed for the first time, and was able to get a preliminary weight of this beast minus the final paint... and it weighs in at 26.9lbs... nearly 8 pounds under my estimated weight! So I should be sitting right around 28 pounds or so when it is fully painted, and ready to go, minus the motor. Seeing this weight is making me consider putting it up on a L1000 for its maiden flight, since I still do not have my 75mm motor casings yet, and am beginning to wonder if I will have them anytime soon. This final weight also reassures me that I will be solidly well over the 5:1 T/WR for all flights I plan to make with this beast.

Now for a little eye candy... The 5.5" Sandhawk with its little 3" brother, both currently in the same state of completion

 

[Steve Shannon]

Very nice work.

 

[krislhull]

I was able to get out and perform the ejection testing today. Yes, I did remember to plug the motor mount with a casing this time!

I used 2 grams of black powder in for the drogue charge, and had a nice clean seperation. I will keep the primary charge at 2 grams, and use 2.5 grams for the backup charge. For the main, I used 4 grams for the test. The results were very energetic, and I will be backing the primary charge down to 3.5 grams, and using 4 grams for the backup charge.

And yes, there is video...


Next up will be paint, which I hope to get done over the next couple of weeks. Based on the final weight, and circumstances that are coming up in my near future, I dont think I will be able to fly the shakedown flight on the planned L1390G, as my ordered casings still have yet to arrive. Instead I will most likely be debuting the beast for its maiden flight at the April Tri Cities launch on a L1000, which should see an altitude of around 3000ft. A nice gentle flight for its maiden.

 

[Steve Shannon]

That looks great.

 

[rharshberger]

Looks great Kris, by the way those exact same charge weights are what I used in my Cherokee-D.

 

[krislhull]

Finally got some great weather...



I know that the red is not the correct shade, but it is the best I could find in the area without spending $15/can or special ordering. Plus, this rocket already isnt exactly to scale... and it will just look damn good on the pad!

 

[rharshberger]

Finally got some great weather...

View attachment 377511 View attachment 377512

I know that the red is not the correct shade, but it is the best I could find in the area without spending $15/can or special ordering. Plus, this rocket already isnt exactly to scale... and it will just look damn good on the pad!

It looks like Banner Red, it a nice shade of red.

 

[krislhull]

Its actually Rustoleum Cherry Red. I do like it on this bird. It will definitely be visible!

 

[Bat-mite]

Its actually Rustoleum Cherry Red. I do like it on this bird. It will definitely be visible!

That is some serious red!

 

[krislhull]

I completed the majority of the painting today. I have a little bit of touch up to do here and there, but overall, I am pleased with how it turned out.



I have a couple of decals to put on it, then I will hit it with a clear coat. Once that is done, I can get a final weight, and this build will be DONE! then it is completing the L3 packet and paperwork, submitting it to my TAPs for review, and then the flight. If all goes well, I will launch the beast on its shakedown flight on a L1000 in a few weeks at the April Tri Cities Rocketeers launch in Pasco, before making the cert attempt at the regional Fire In The Sky launch Memorial Day weekend.

So, without further ado, the 99% completed Sandhawk:

 

[Bat-mite]

Very nice. Should be easy to see in the air and on the ground.

 

[krislhull]

Well, I am officially going to call this build complete now! It received the Stickershock treatment today. I couldnt fly this bird without Mark's decals, as my L1 and L2 birds both had them. So I decided to go non standard and apply the 1960's Thiokol logo. I think it looks great! Oh, and Teddy at OneBadHawk gets some recognition on the bird as well, as does MissileWorks!



And finally, I also finished the 3" Sandhawk... With any luck, both will see maiden flights next week: the 3" on a I211, and the 5.5" L3 on a L1000

 

[rharshberger]

Looking forward to it Kris, see you next week, so far weather is looking good.

 

[krislhull]

Well, I am thinking that I am going to have to put any attempts to certify L3 with this build on hold for the year... Life and switching jobs is just getting in the way. I was hoping to fly it on its maiden/shakedown flight this past weekend, but the launch was cancelled due to weather, and I will not be able to make it to another launch until the Memorial Day Fire In The Sky event, where I was planing to make the cert attempt. Now, I will only be able to attend one day of the launch at most, and feel that any attempts to certify would be rushed, and I do not want that. So, I will probably maiden the bird at that launch on a L1000, and then either make the cert flight at either another launch that aligns with my new, tighter schedule and that one of my TAPs will be at, or wait until next year, when I know I will be able to make it to an event.

 

[Steve Shannon]

Well, I am thinking that I am going to have to put any attempts to certify L3 with this build on hold for the year... Life and switching jobs is just getting in the way. I was hoping to fly it on its maiden/shakedown flight this past weekend, but the launch was cancelled due to weather, and I will not be able to make it to another launch until the Memorial Day Fire In The Sky event, where I was planing to make the cert attempt. Now, I will only be able to attend one day of the launch at most, and feel that any attempts to certify would be rushed, and I do not want that. So, I will probably maiden the bird at that launch on a L1000, and then either make the cert flight at either another launch that aligns with my new, tighter schedule and that one of my TAPs will be at, or wait until next year, when I know I will be able to make it to an event.

Let me know which events you will attend. If I don’t have a conflict I’ll try to be there. Or you can come to Montana and fly with us!

 

[Charlie Harnett]

Wow great build thread! love all the attention to detail! any updates on this project?

 

[rharshberger]

Wow great build thread! love all the attention to detail! any updates on this project?

Kris drops by every once in a while to TRF, with his current job as 747 flight mechanic (?) he spends a lot of time flying. Maybe he will answer soon, so stand by.

 

[FlyBy01]

This thread is a long time coming for me!

Earlier in June 2018, I started planning my L3 project, and decided I wanted to build a large rocket. I decided to use the Madcow 8" DX3 as a starting point and modify it by adding nearly 40" in length, and using CNCed interlocking fin pockets and centering rings from Upscale CNC.

View attachment 370470
After taking a step back, and adding up the costs of all of the components, plus a 98mm case and a M1939, I realized that this was going to be an expensive build, and also a large one that would not be easy for me to transport any time soon. So, I took a step back and looked at my options. On the grounds of economy, I already had a LOC 5.5" Sandhawk that I had just started to work on, and had just finished fiberglassing the airframes on. I immediately stopped all work on that project, and wrote a new proposal for an L3 attempt using the Sandhawk. This would benefit me in several ways. First, the total cost of the project would be about half of the DX3, once I bought a 75mm case and a motor. Second, I already had the kit, and third, the wife would be extremely happy I wasn't breaking the bank on one rocket!

After submitting my proposal packet to a local L3CC member, I had a false start and a bunch of what I will call miscommunications between the two of us. One of the issues was that I had already started the build, which is a no go under NAR L3 rules. After it was pointed out to me by Steve Shannon that that was perfectly ok under TRA cert rules, I decided to switch up and do the cert under my TRA membership. After some more communications with my L3CC member, who is also a TAP, and asking Steve to be my second TAP, I have been given the green light to proceed.

The Rocket:
As mentioned, I am using the LOC 5.5" Sandhawk as the basis for the build. I decided to do away with the plastic nosecone, and picked up a Madcow fiberglass nosecone. I also will be using a SC Precision thrust plate with an Aeropack retainer.

View attachment 370483

View attachment 370471
The basic components, still with the plastic nosecone

View attachment 370472
Thrust plate and retainer

As I mentioned above, I had previously fiberglassed the airframe. I used Soler Composites heavy sleeve for the fiberglass.

View attachment 370474

View attachment 370473
Airframe section in work.

Of course, I had to do the obligatory dry fit photo of the project after I fiberglassed the tubes...
View attachment 370475

So, what's next?

I need to start assembly of the motor mount and fin can. I will most likely be fabricating plywood fin pockets for fin mounting, and also need to decide if I want to bevel the fins or not. Then there is also the avionics bay that will need to be built. I have already decided to use my tried and true combination of a MissileWorks RRC3 and a StratologgerCF for my altimeters, as well as the MissileWorks RTx tracker.
For recovery, I have a custom harness from Teddy at OneBadHawk on hand, and I plan on using Rocketman chutes for recovery.

The cert flight is currently planned to use a M1550R, which should see an altitude of right around 8,000ft. One of the requests from my primary TAP is that I fly this on a 75mm L first, and I was already planning on such. So its first flight will be on a L1390G, hopefully at the Fire in the Sky launch on Memorial Day weekend.

I'm getting away from cardboard tubes but this build is awesome; especially the glassing.

 

[rharshberger]

I'm getting away from cardboard tubes but this build is awesome; especially the glassing.

I went the other way no more all FG kits, but my cardboard rockets get a couple of wraps of FG to improve toughness without sacrificing much in the way of lower end motor selection. Kris was doing a fantastic job on this one hopefully he will find time with his busy schedule to finish it and get his L3. He was in Guam yesterday so it looks like he's on another flight rotation.