Madcow AGM Pike - first dual deploy and other questions

[rockyrocket]

Learned tons on here, reading searching and reading again. Awesome info!! First post, but lots of questions to confirm a few things on my first dual deploy. Rather than posting different questions in different forum's here, thought I would just consolidate them here on the HPR thread. I am at the final stages of my Madcow AGM 4" Pike. It is set up for dual deploy with the madcow avbay, missile works RRC3 altimeter and sled. Have done some (one) ground testing and using a centrifuge for the powder, inside 1/2" pvc pipe and cap. Have done the diagnostics with the missile works LCD, Christmas lights for main and drogue, everything seems to work great. Upgraded from 38MM motor mount to 54MM. Left to finish the build are the rail buttons, shock cord, chute and balancing, and more ground testing. I plan to launch with engine ejection a time or two first and let the altimeter go for the ride before I try dual or single deploy with the altimeter and engine ejection as back up.

Now for the questions - (thanks in advance as there a few of them)

- What size drogue chute would be appropriate? And a simple nylon chute also be appropriate? When all finished with the avbay, I estimate total weight will be close to 7 lbs excluding the engine, and with a drogue, do you decrease the size of the main chute from what you would normally use for single deploy, or use a single deploy size chute?

- When packing single deploy rockets, I would "Z" fold and pack the shock cords into about two sections with masking tape, then the chute, then the 3 ft or so cord from the chute to nose cone. For dual deploy and the drogue section, does it matter which is packed first - shock cord or chute? Same for main section. I will have about 4 ft of Kevlar and 15 ft of tubular nylon cord, then about 3 ft of kevlar from chute to avbay (or nose cone) for each section, so almost 22 total ft each section. Ok to have drogue and main cords same size, or one longer than the other?

- When using some of the BP calculators for the drogue and main, it computed around 1.2 grams of 4F BP. Reading posts on here, some have used like 2 grams or more for a 4" rocket. I thought I would try 1.5 grams of 4f thinking that would be conservative for the drogue and to push out the top payload and AV bay. Glad I didn't have shock cords attached, it shot the main section w/ avbay across the yard and into our bushes. I will try again with the cords and chutes attached, but 1.5 grams seems plenty, and will go down to about 1.2 next time - any thoughts on that for the drogue and main for this size rocket. I also have Null B black powder that will last forever - it is quicker burning than 4F, but all the calcs are for 4F - if any rule of thumb conversions of 4F to Null B, please let me know - otherwise I will stick with 4F.

-Shear pins - I plan on using 4 2x56 shear pins for the nose cone. Since this is a cardboard body tube rocket, I read the pins can tear up the tube on ejection. I bought some 1/2" x .015 brass strips, and will fiberglass the inside of the tube for the shear pins. Anything else I should consider? I want to avoid another ground test and tear up the tube before my first launch.

- Madcow instructions mention I will have to add nose weight - not sure if the weight added by dual deploy (cord, chute, etc) in the main section will help or not to avoid adding nose weight. I have not balanced it yet - will do once complete and load up an engine, but is adding nose weight to this rocket common (for those that have it and dual deploy). If so, I plan to use BB's and Gorilla Glue?

- Thrust to weight ratio. I have read on here - 5:1 on calm day, and 10:1 on windy days?? Before I place an order for engines for my first "conservative" flights, want to see if any suggestions here at our mile high altitude and what thrust to weight I should consider or not go below for this size rocket.

This kit is awesome, and Madcow customer service also awesome - can't wait to launch it. Thanks again in advance for any suggestions. Here's some pics before the final items to get her ready... I'm sure I will have more questions to follow....

 

[Handeman]

First, welcome to the forum!

It sounds like you had way too much powder on your first test. I use just enough powder on the drogue side to open the rocket. I have a 4" rocket with 24" of space in the drogue compartment. I use 1.0g of 4F. The drogue is attached about a foot below the upper section and when stretched out, about 2' long. All I need is the two parts of the rocket to separate at least 3 ft and the drogue will catch air and work the way it is supposed to. You don't need the shock cord to come out of the bays, just the drogue chute. If you keep the charge small, you don't need the shear pins on the nose cone, a snug friction fit will do.

As for the main bay, ground test, ground test, and ground test. I you do use the shear pins and it tears up the BT, then you need to solve that issue anyway if you want to fly the rocket much. Might as well get the issue out of the way when you are ground testing, before an in-flight issue can really cause some damage.

With the weight of the av-bay and main recovery, I've never needed nose cone weight on any DD rocket. I would approach it that way and when everything is done, then check the stability and add any weight if needed. Don't assume you need it. If you put it in and don't need it, you probably can't get it back out. One thing you can do is swap nose cones. If you have a rocket that needs the weight, you can swap that nose cone to this rocket if you need it, and go without when you don't.

As for using motor deploy with a DD rocket or using the altimeter for just the main deploy, I've never done either. The altimeter has fully controlled all my DD flights. I don't even put the powder in the motors as a back up. I've found the electronics to be so much more dependable then the motor ejections, I trust the electronics way before I trust the motor ejection.

Good luck on your flights and again, welcome to TRF!

 

[jcaswell94]

I will be following this thread as well. I have a lot of the same questions since im building my L1 rocket. Welcome to the forums! Good Luck!

 

[rockyrocket]

thanks for the info handeman.., and good to know on the BP amounts you used for that size space, definitely will go lower than the 1.5 grams. Friction fit on the nose cone sounds good to me as well to avoid some potential scaring on the body tube - interesting on the length on cord length for the drogue. thanks and looking forward to that first launch with it after some more ground testing.

 

[BillG]

I can 2nd handeman's advice. I have a Madcow Pike setup for dual deploy and 1g is enough BP for the main ejection. I'm using shear pins on the nosecone but I've fibreglassed the body tubes.

 

[rockyrocket]

Bill - how much did you end up using for the drogue ejection too? Also what size chutes for main and drogue are you using? I had tested the main with 1.2 and seems plenty, so might go to 1.0 for main/nosecone. Lowered the drogue to 1 gram, and I think I need more there - 1 gram barely separated the top payload/av bay from the lower section. I have brass plates on the nose cone, and put some fiberglass on the inside of tube for pins, but was way too tight even after sanding, so might just go with friction fit for the nose. thanks

 

[Handeman]

thanks for the info handeman.., and good to know on the BP amounts you used for that size space, definitely will go lower than the 1.5 grams. Friction fit on the nose cone sounds good to me as well to avoid some potential scaring on the body tube - interesting on the length on cord length for the drogue. thanks and looking forward to that first launch with it after some more ground testing.

I don't want to give the wrong impression. I use about 12 - 15 ft of shock cord between the fin can and upper section. I only need the two parts to open about 3 ft to ensure the drogue catches air. At that point, the drag from the drogue causes the fin can to drop below the upper section and any remaining shock cord is stretched out. The whole point of the drogue is to keep the upper section with the main above the fin can so the fin can can't foul the main when it is deployed.

 

[Cory]

+1 on Handeman's advice. In my opinion more is better with shock cord. I also agree with Handeman to attach the drogue nearer the main's section to keep the main deployment in open air. I set up my L2 so the booster section fell below the main, kind of fun to watch, but the booster section fell the entire length of the shock cords to SNAP under shoot. I was lucky, but this could definitely foul the main chute. Also, a drogue attached directly to the center of the recovery harness can cause the two sections to collide during descent.
The RRC3 is a great DD altimeter, ground test ground test ground test, take your time on launch day and fly like you test and you should have no problems. I remove the CTI charges and fly altimeter only, but I've seen many flights using the motor as backup. Most times the delays are left undrilled to let the altimeter have a chance with the motor only providing backup several seconds later.
My 4" Formula 98 uses 0.9g for the drogue (4-2x56 shear pins) and 1.1g for the main (4-2x56 shear pins).

Good luck!

 

[BillG]

Bill - how much did you end up using for the drogue ejection too?

Roughly the same amount of BP. I use friction fit on the booster and it works fine. I use a 24" drogue and a smaller one too (maybe 15 to 18"?). Size is less important on the drogue (you don't want too big, obviously) just enough to keep things stabilized as it falls. I've gone drogue-less on other rockets but not the Pike. I wouldn't hesitate to try it myself though. For me, I use land testing for the BP amounts. Try it on land and if I get a robust ejection including all the chute and paraphernalia and the shear pins shear well, I go with that BP amount in flight.

If you've tested the BP amount with your friction fit nose cone and you feel confident it will remain in place during the drogue ejection (lots of shock cord helps reduce nose cone ejection from momentum) you should be good.

My Pike is pretty heavy and sturdy due to the glassing and foam in the fin can. I've had it land with the main bunched up and no damage. Because I used a flat green paint, it's become a work horse - a tough rocket I'm not afraid to launch and worry about scuffing it up.

 

[Rocket86]

The Pike is a very cool rocket and fun to fly. Ground testing your own configuration is the best way to come up with a reliable DD setup. Just for reference, here is what I did with mine.

Drogue is a 24" 4-line with adjustable opening. The big fins on the Pike seem to make it want to come down horizontal under the drogue so I have been experimenting with descent speed. I use 1.1 grams of 4F for the drogue and (2) .060 styrene shear pins. I've heard never use 1 or 2, but mine are spaced exactly 180 degrees apart and it works well. I use 18' of shock cord.

For the main I use 1.6 grams of 4F and (1) shear pin. Again, I fit the NC so there is no rocking motion and the single pin works without issue. With the 1.1 gm charge on the drogue it separates everything nicely without a big shock so the NC pin is probably not needed. I use a 40" chute for the main and it lands softly and relatively close to the pad.

So far I have used an RRC2+ with motor backup for the drogue with the delay set for just past apogee and 1.6-1.7 gm. So far that has worked very well. I now have it configured to use fully redundant altimeter control if I run into a situation where I can't get the right delay. I really like the RRC2+.

Ground test with your own build to fine tune and make sure it's reliable. I opted to start small and make numerous tests rather than risk blowing it up. You'll have fun with the Pike!

 

[rockyrocket]

great info guys. Nice info and on the Pike too - it is a cool looking rocket and I enjoyed building it. Will do some more ground testing this week when the new chutes arrive. Based on the testing and comments here, I'm pretty sure I can dial in the BP amounts now before I launch hopefully this weekend. Although based on close to a 7lb rocket, I was anticipating more in the 58" size chute for the main which sounds like might be a little on the large size? and 18" for the drogue. The calculators for the chute show even larger than 58". The RRC3 is pretty cool. Got the LCD and the USB/software to tweak the basic features for me. Have the main set now to deploy at 700 ft. Too high/too low?? I have CTI I285, I 255 and I 303 for its maiden/initial flight(s) which will be under 2K feet for any of these motors. Now deciding to go with dual deploy for its maiden flight or with the engine ejection. I'm sure after hopefully the first successful dual deploy the paranoia will subside after seeing the Pike fly and hopefully land without a hitch....

oh yea, did any of you have to add weight to the nose to balance it? the engines should be here tomorrow as well and will balance it with the largest engine - still curious how much weight was needed if any in your DD set ups.


thanks for the comments.

 

[Rocket86]

oh yea, did any of you have to add weight to the nose to balance it? the engines should be here tomorrow as well and will balance it with the largest engine - still curious how much weight was needed if any in your DD set ups.

I didn't add any nose weight and have flown it DD only. I've flown it on AT I284W, I327DM, and I364FJ, to about 2,600 ft so far. Total weight on the pad was 7 lb, 2 oz, and I had about 5 inches stability margin, worst case. A lot will depend on how you built it and recovery system, since that weight does add up and is pretty far forward. Check balance with the actual flight ready configuration. I'm hoping to fly mine on a J420 in a few weeks and it should be pretty cool. You will have fun with it.

 

[BillG]

oh yea, did any of you have to add weight to the nose to balance it? the engines should be here tomorrow as well and will balance it with the largest engine - still curious how much weight was needed if any in your DD set ups.


thanks for the comments.

I did add nose weight but only because my booster section had grown quite porky by the time I finished. I glassed the tubes, used a lot of epoxy with filler and foamed the fin can. I also balanced it initially to fly without the a-bay so I used 200g of nose weight to allow for a largest 38mm motors. However, it wouldn't have been necessary with the a-bay installed and I highly suspect you won't need to worry about it either. All told, with an a-bay and ready-to-fly she comes in at 6.8 lbs . I really wish I'd put in a 54mm motor mount. It was a learning experience (the Pike was my L1 cert rocket.)

 

[Handeman]

I have my HiAlt45 set for 400 ft because that is as low as it will go. My Stratologger has the main set at 300 ft which I like better.