L3 Winter Build Thread - 3/4 Scale PAC-3 Patriot

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Ground testing was completed today. I'd say it looks like the 4.1 g charges were perfect. The tape blew off the back on the drogue test, so the force was robbed. Otherwise, it was energetic enough.
I tested the nose first. Small mistake since that meant those shear pins were now cut. So the nose shook loose a bit on drogue deployment. I'm not worried about that though. The 4 x 4-40 shear pins take up to 250 or so lbs of force to cut.

[video=youtube;uUueS-RUK18]https://www.youtube.com/watch?v=uUueS-RUK18[/video]

[video=youtube;bp24wJUDfEU]https://www.youtube.com/watch?v=bp24wJUDfEU[/video]

Just need to put on the camera shroud, and I'm good to go! Need to finish the documentation also.
 
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Hehehehehe. I love testing charges when it is really quiet.
 
Just my simple oipinion, but if I were you, I'd take a little powder out of the main charge and put it in the drogue charge. The drogue charge is where you really want a lot of separation, whereas with the main, it is usually enough to just get the laundry out. YMMV
 
Bat-mite said:
Just my simple oipinion, but if I were you, I'd take a little powder out of the main charge and put it in the drogue charge. The drogue charge is where you really want a lot of separation, whereas with the main, it is usually enough to just get the laundry out. YMMV
Click to expand...

Yep. I'm upping the drogue charge to:

Primary: 4.5 g
Backup: 5 g
 
Bat-mite said:
Just my simple oipinion, but if I were you, I'd take a little powder out of the main charge and put it in the drogue charge. The drogue charge is where you really want a lot of separation, whereas with the main, it is usually enough to just get the laundry out. YMMV
Click to expand...

I tend to disagree with this. You only need enough separation on the drogue to "get the laundry out", get the drogue into the air stream. Once that happens, the drag of the drogue should pull everything into the right formation for the drop to main deploy. Using too much charge just invites the nose cone to come off when hitting the end of the shock cord and the main deploying at apogee, thus the overuse of shear pins IMHO. I think your drogue charge is good, you just need to put the drogue chute closer to the payload tubes to make sure the payload stays well above the fin can.

I know people talk about an inverted V when dropping from apogee, but I think that is not right. You really want an inverted check mark. The payload on the short side and the fincan on the long side. If they are floating and falling near each other, you don't have enough drogue.

Thus the dilemma of getting answers on TRF, there are always differing opinions and you still need to decide for yourself what is the best way to do it.

Good luck

BTW, are you using swivels? I would recommend one on the fincan because if anything tends to spin on the drop to main deploy, it's the fincan...
 
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Handeman said:
I tend to disagree with this. You only need enough separation on the drogue to "get the laundry out", get the drogue into the air stream. Once that happens, the drag of the drogue should pull everything into the right formation for the drop to main deploy. Using too much charge just invites the nose cone to come off when hitting the end of the shock cord and the main deploying at apogee, thus the overuse of shear pins IMHO. I think your drogue charge is good, you just need to put the drogue chute closer to the payload tubes to make sure the payload stays well above the fin can.

I know people talk about an inverted V when dropping from apogee, but I think that is not right. You really want an inverted check mark. The payload on the short side and the fincan on the long side. If they are floating and falling near each other, you don't have enough drogue.

Thus the dilemma of getting answers on TRF, there are always differing opinions and you still need to decide for yourself what is the best way to do it.

Good luck

BTW, are you using swivels? I would recommend one on the fincan because if anything tends to spin on the drop to main deploy, it's the fincan...
Click to expand...

Yes. An inverted checkmark would be a more accurate description. My drogue is about 5' from the payload bay while the fincan is on the other 45' of shock cord. The fincan is attached to the shock cord by a 3000' swivel on a kevlar bridle epoxied to the motor mount.
 
Looks like we are a go for my cert launch next Sunday, 12/17. The extended weather forecast looks good.

I noticed with the colder weather, the payload bay coupler is a teeny bit looser now. This lets the airframe wobble maybe 1 mm when there are no shear pins in it. Debating if I should add a layer of fiberglass tape to tighten it up again. Probably not... When he shear pins are in, it's all rigid.
 
Personally I'd just let the shear pins do their job. is this the payload bay to nose cone (main) or bay to body tube (drogue)?
 
Patriot MSE came up at work this week, and I was just thinking about this thread! Great timing!

Looks you're trying to get that cert in the bag for this Winter Build before 'next winter' starts lol

Good luck!
 
mccordmw said:
The shear pins are for the drogue, so payload bay to the fin can.
Click to expand...

I'm assuming you're worried about drag separation. I'd leave it with the shear pins.... otherwise there's a chance it'd be too tight.
 
mccordmw said:
Looks like we are a go for my cert launch next Sunday, 12/17. The extended weather forecast looks good.

I noticed with the colder weather, the payload bay coupler is a teeny bit looser now. This lets the airframe wobble maybe 1 mm when there are no shear pins in it. Debating if I should add a layer of fiberglass tape to tighten it up again. Probably not... When he shear pins are in, it's all rigid.
Click to expand...

Masking tape? Tried and true since the birth of HPR!!!

Living in the Midwest, and being year round flyers, means A LOT of expansion in warm summers and contracting in the frigid winters. Thus, I expect to add/subtract masking tape on couplers and nose cone shoulders depending upon the weather....especially with dissimilar materials. Plastic nosecones being the worst offenders.

I have encountered shear pins that have sheared prematurely due to loosely fitting sections. An example being a large rocket requiring two people to haul to the pads (like the 3/4 Patriot). Typically one person is near the nose and the other near the fins; their movement is never 100% in unison. If there's slop in the booster-to-payload joint, that joint is moving up and down during the walk and with enough slop WILL shear the pins prematurely. Have seen it happen; this is greatly exaggerated with a lot of slop in the joint and/or heavily weighted cones/sections.

Final thought: the "Proper" way to do this is with vertical strips of tape built up to desired fit; NOT with wraps around the mating surface. One way gets you a consist fit along the length of the surface, the other gets you balled up edges and hills and valleys!
 
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Listen to this guy ^^^^^^ he knows more than me.

With that being said- I've had more issues due to "parts being stuck together" than "things are too loose"
 
If you add tape, ground test again. Add the pins at the pad, so they don't break on the way out. You can bring it out in pieces that way if you are having trouble handling it.
 
mccordmw said:
Looks like we are a go for my cert launch next Sunday, 12/17. The extended weather forecast looks good.

I noticed with the colder weather, the payload bay coupler is a teeny bit looser now. This lets the airframe wobble maybe 1 mm when there are no shear pins in it. Debating if I should add a layer of fiberglass tape to tighten it up again. Probably not... When he shear pins are in, it's all rigid.
Click to expand...

You've got a good group of guys to fly with. Let me know if you need help. I have a truck if you don't... It helped Dan with arming his electronics last time!

-Mike
 
We had our launch yesterday. The weather was beautiful, but a bit windy with 11 mph winds that gusted up to 20. The launch went beautifully. Unfortunately, while charging my camera last night, I must have bumped the power button and it filled up with video. I have a terrible success rate with my keychain camera. :facepalm:

We did get launch video. It was also Facebook live streamed, and there was a videographer with a few cameras on tripods around.

My sims said I'd have an apogee of 5800'. My instruments recorded an apogee of 6300'. It flew completely stable with no observed spin. It should be fine going up a step to an N motor, but I want to upgrade the tracking before I do that. Maybe I'll shoot for an N launch at MWP 2018.

It was a fun build, and it was thrilling to see it go up on that loud, angry Loki M1969. Thanks for everyone's input!

Here's what my wife recorded.

[video=youtube;YIIUF67jmmI]https://www.youtube.com/watch?v=YIIUF67jmmI[/video]
 
mccordmw said:
We had our launch yesterday. The weather was beautiful, but a bit windy with 11 mph winds that gusted up to 20. The launch went beautifully. Unfortunately, while charging my camera last night, I must have bumped the power button and it filled up with video. I have a terrible success rate with my keychain camera. :facepalm:

We did get launch video. It was also Facebook live streamed, and there was a videographer with a few cameras on tripods around.

My sims said I'd have an apogee of 5800'. My instruments recorded an apogee of 6300'. It flew completely stable with no observed spin. It should be fine going up a step to an N motor, but I want to upgrade the tracking before I do that. Maybe I'll shoot for an N launch at MWP 2018.

It was a fun build, and it was thrilling to see it go up on that loud, angry Loki M1969. Thanks for everyone's input!

Here's what my wife recorded.

[video=youtube;YIIUF67jmmI]https://www.youtube.com/watch?v=YIIUF67jmmI[/video]
Click to expand...

Looked like a great flight. Where is your launch site located?
 
Finally got around to downloading the flight data from my two altimeters. They were pretty close in agreement. Here's the averaged data.

Apogee: 6,324'
Max Veloc.: 855 mph (mach 1.11)

It flew about 10% higher than my sims.

PAC-3_L3.png.jpg
 
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My understanding is that whilst pretty accurate with altitudes, most rocketry altimeters only give a rough approximation of velocity, with a tendency to exaggerate. Maybe that's the case here..?
 
Awesome flight! congrats on the L3!

mccordmw said:
Unfortunately, while charging my camera last night, I must have bumped the power button and it filled up with video.
Click to expand...

I feel ya- I have several 15-20 min videos of the inside of the trunk of my car :)

This just means you'll have to do it again on the same motor!
 
mccordmw said:
Likely another M1969 because I love that motor, but I might go M3464 Loki Blue for more punch. But mmmm....sparky....
Click to expand...


latest
 
Blue is always a good bet. I haven't seen a loki blue in person, but i hear it's a much more vivid shade than the CTI/AT flames.

Now you just need to build 11 more and you'll have your own emplacement!
 

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