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True, the Thermians are just elusive in their natural form.... too skitish!
By Grabthar's Hammer! A LOC Skinwalker thread!
- Thread starter krislhull
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-- kjh
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I may steal that. I need a new saucer design in my life right now.Grabthars Skillet...its a saucer...
having only watched the movie once, i didn't recognize the reference. i really hoped it was a random name, which made chuckle. nice roc, btw.
Rschub
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The suit is out there....
rharshberger
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Use a Wocket....
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For better or for worse, I'm a scratch building kinda guy. But enough about me.
Is Grabthar's Hammer going to fly on Friday or Sunday? I need to plan my arrival time!
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Most likely Sunday. I will be on site very very early Friday, but Grabthar will most likely fly Sunday. The motor builder, who I am sure we all know (I know Rich knows) will be there Friday, but I am not sure what time. so I will need to get with him for the motor. I am hoping for a first rack (or one of the first racks) on Sunday deal.
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Rschub
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Last Friday I brought the Hammer into work, as I had a few coworkers who were curious about the hobby and just exactly what on earth it is.... So what better way to show them than with a eleven foot tall, 7.5" diameter beast? I also took the opportunity to use the shipping scale in our warehouse to get an accurate weight of the bird. With all recovery systems, altimeters, batteries, tracker, and attaching hardware loaded, Grabthar's Hammer comes in at a dry weight of 33.9 pounds. Measured empty CG is actually better than what I was predicting, at about 6 inches further forward than I estimated. Surprisingly, when I plugged these numbers into Rocksim, the simulations only changed by a very minor amount. I am looking at 7,300ft on the EX motor per rocksim, 6,980ft per OpenRocket, and I still need to run the numbers through ThrustCurve on the M1419. But I feel I have a good baseline.
On Sunday I was able to complete the ejection tests, and they went off without an issue. I will be using 4.5grams of BP for the primary drogue charge, with 5g as backup, with 3.5g as primary for the main with 4g backup. I will say, these are the largest charges I have made yet, and they certainly made a boom!
All that is left now is the pack the car up Thursday morning and head east after lunch Thursday, and then meet with a certain forum member and pick up the EX M motor that will give Grabthar's Hammer a swift kick in the rear....
On Sunday I was able to complete the ejection tests, and they went off without an issue. I will be using 4.5grams of BP for the primary drogue charge, with 5g as backup, with 3.5g as primary for the main with 4g backup. I will say, these are the largest charges I have made yet, and they certainly made a boom!
All that is left now is the pack the car up Thursday morning and head east after lunch Thursday, and then meet with a certain forum member and pick up the EX M motor that will give Grabthar's Hammer a swift kick in the rear....
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Well, Now that Sod Blaster has come, and for most of us, ended, I can safely say that Grabthar's Hammer flew successfully today. Its been a busy weekend, but after I arrived at the sod farm Thursday evening, I set up my camp for the weekend before heading to my hotel in Pasco to get some sleep for the night.
First thing Friday morning, it was back to the sod farm.....
I wasn't planning on doing much with the Hammer on Friday, since it wasn't going to fly until Sunday, but I did meet up with @bandman444 and @jpoehlman about the motor, since they are the two behind the propulsion for Grabthar. Originally I was planning on putting Grabthar's Hammer up on a 4 grain 98mm M that would have been comparable to a M1939, but simulations should it busting the waiver of the sod farm, so after talking with Bryce, he scaled it down to a 3 grain M, which the sims put it right at 7300ft. On arriving at Sod Blaster, for various reasons and simplicity with other motors being flown this weekend, the 3 grain M became a 2 grain L, which I had no simmed, but I was still very eager to try out and fly on the skinwalker. I also had the chance to fly a few other of my rockets on a couple 38mm and a 54mm EX motors using the same propellent formulation, and I am soundly impressed with the propellent that Bryce and Jack cast. It truly is quite the performer!
Saturday, after my planned flights were completed, I started the prep on Grabthar's Hammer. my goal was to get everything ready minus the motor and nosecone before I left the field for the night. When I arrived at the field this morning, I pulled the covers I had on the rocket overnight off, and started the final preps. around 10 am, Jack brought the motor over to my camp, and I installed it into the business end of Grabthar, and then proceeded to go and have an RSO come to the rocket to inspect it in place so we didn't have to carry it to the RSO table, and then wait for the next rack. With the RSO present, I activated the tracker, and then installed the nosecone and placed the final shear pins in place. the Hammer was ready for the pad........
Many thanks to Jack for helping to carry it out to the away cell!
Sadly I did not get any photos of the actual launch, but there are many there that did, and some of the students that Jack mentor had cameras at the pad for the launch, so hopefully I can get some of that footage in the coming days!
The boost was absolutely flawless, and she flew to just shy of 3,800ft on the EX L859(? I believe that is the designation!) of this amazing propellant Bryce came up with....... She landed on the sod about 2,500 ft away, and when I got to her, was stretched out in the classic textbook picture of what a rocket recovery should look like.
On inspection, however, there is some damage. I immediately noticed some impact damage on the top of the booster airframe, that appears to have occurred on landing. And then later this evening, when I was packing the car to leave, I noticed that one of the fins has a cracked fillet. Neither of these are show stoppers, and they won't be too hard to fix. I have no plans to fly Grabthar's Hammer again this year, or right away next year, so it will wait for repairs until the spring most likely. However, I have already started talking with Bryce about the possibility of making a full M for Grabthar for a launch next year...... maybe I will get brave and work with him on a N?
More photos and altimeter data along with the GPS plots to come in the coming days when i get home and have a chance to download the data and review it.
First thing Friday morning, it was back to the sod farm.....
I wasn't planning on doing much with the Hammer on Friday, since it wasn't going to fly until Sunday, but I did meet up with @bandman444 and @jpoehlman about the motor, since they are the two behind the propulsion for Grabthar. Originally I was planning on putting Grabthar's Hammer up on a 4 grain 98mm M that would have been comparable to a M1939, but simulations should it busting the waiver of the sod farm, so after talking with Bryce, he scaled it down to a 3 grain M, which the sims put it right at 7300ft. On arriving at Sod Blaster, for various reasons and simplicity with other motors being flown this weekend, the 3 grain M became a 2 grain L, which I had no simmed, but I was still very eager to try out and fly on the skinwalker. I also had the chance to fly a few other of my rockets on a couple 38mm and a 54mm EX motors using the same propellent formulation, and I am soundly impressed with the propellent that Bryce and Jack cast. It truly is quite the performer!
Saturday, after my planned flights were completed, I started the prep on Grabthar's Hammer. my goal was to get everything ready minus the motor and nosecone before I left the field for the night. When I arrived at the field this morning, I pulled the covers I had on the rocket overnight off, and started the final preps. around 10 am, Jack brought the motor over to my camp, and I installed it into the business end of Grabthar, and then proceeded to go and have an RSO come to the rocket to inspect it in place so we didn't have to carry it to the RSO table, and then wait for the next rack. With the RSO present, I activated the tracker, and then installed the nosecone and placed the final shear pins in place. the Hammer was ready for the pad........
Many thanks to Jack for helping to carry it out to the away cell!
Sadly I did not get any photos of the actual launch, but there are many there that did, and some of the students that Jack mentor had cameras at the pad for the launch, so hopefully I can get some of that footage in the coming days!
The boost was absolutely flawless, and she flew to just shy of 3,800ft on the EX L859(? I believe that is the designation!) of this amazing propellant Bryce came up with....... She landed on the sod about 2,500 ft away, and when I got to her, was stretched out in the classic textbook picture of what a rocket recovery should look like.
On inspection, however, there is some damage. I immediately noticed some impact damage on the top of the booster airframe, that appears to have occurred on landing. And then later this evening, when I was packing the car to leave, I noticed that one of the fins has a cracked fillet. Neither of these are show stoppers, and they won't be too hard to fix. I have no plans to fly Grabthar's Hammer again this year, or right away next year, so it will wait for repairs until the spring most likely. However, I have already started talking with Bryce about the possibility of making a full M for Grabthar for a launch next year...... maybe I will get brave and work with him on a N?
More photos and altimeter data along with the GPS plots to come in the coming days when i get home and have a chance to download the data and review it.
jpoehlman
Well-Known Member
Great flight Kris and a very busy weekend for all of us involved. Here's the pre-launch photo I took:
jpoehlman
Well-Known Member
The EX-propellant formula is named Mehhh-Thalox based on the goal of making a solid propellant look like a liquid Methalox (Methan - Oxygen) rocket motor that are powering some the newest commercial rockets. Here's the lift off shot:
And a little out of focus, but the fully deployed recovery system:
And a little out of focus, but the fully deployed recovery system:
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Nice shot of the launch, Jack! Glad someone got it! When I got to the hotel last night, I discovered that the onboard video actually DID capture the flight, so I will have that video in the coming days.
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Awesome launch! Sorry about the landing damage, but better than the movie landing!
Thanks for sharing this most awesome project!
Thanks for sharing this most awesome project!
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On board video from the RunCam4 that I had strapped to the side has been gone through and edited, and I put together a video last night of the project....
Fromm looking at the footage of the flight, I noticed a few things that caught my eye... At apogee ejection, the shock chord appears to have wrapped around a fin or two, and these are the two fins that just so happen to have cracked fillets. Coincidence? Maybe, but I doubt it. And then as the drogue catches air, the booster shoots forward past the payload section, and it almost appears as if it makes contact near the nosecone. Again, this is right in the area where I noticed some slight airframe damage when I was recovering the rocket in the field. So now it is looking like my damage may have happened at drogue deployment, and not landing. I am still reviewing possible repairs in my head, and will formulate a full repair most likely next spring.
Grabthar will fly again!
Fromm looking at the footage of the flight, I noticed a few things that caught my eye... At apogee ejection, the shock chord appears to have wrapped around a fin or two, and these are the two fins that just so happen to have cracked fillets. Coincidence? Maybe, but I doubt it. And then as the drogue catches air, the booster shoots forward past the payload section, and it almost appears as if it makes contact near the nosecone. Again, this is right in the area where I noticed some slight airframe damage when I was recovering the rocket in the field. So now it is looking like my damage may have happened at drogue deployment, and not landing. I am still reviewing possible repairs in my head, and will formulate a full repair most likely next spring.
Grabthar will fly again!
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