Madcow "Level-2" Build, 4" Fiberglass Airframe w/54mm Motor

kcobbva said:

Kevin - Here's what I did: three pins in the nosecone. 2-56
TWO shear pins in the lower body tube attached to the Ebay 2-56

As for the Ebay Band I drilled three equally spaced holes: two 3/32" and one 7/64 to allow the screw driver to go through.

As for the Blackpowder: GROUND TEST! I also came up with 1.2 for the lower half and it just sat there and I heard "POP" when I ground tested. I believe I ended up with 1.4 or 1.5 for a decent separation with the two pins during the ground test.

Click to expand...

Thanks Kevin. I have six of Apogee's 4-40 Tube Fasteners arriving tomorrow. I can either install 3 or 4 in place of the stock rivets. I'm still leaning toward 4. I suppose the worst that can happen is that I'll need to fall back to 3 holes.. and have to drill 2 new holes 120 degrees off one of the 4 I'm planning to drill. It makes sense to have some symmetry between 3 or 4 shear pins so that the sections don't cock sideways and bind up when the charge fires. I don't know if I'm comfortable stepping down to 2 pins for this reason.
I've watched your ground testing video at least 10 times now... considering things and your charge findings. I assume you were using 4F BP? I've just got my supply of 4F, so I hope to fire some tests as soon as this weekend.. likely without paint. Hmm.. that got me thinking about how the unpainted rocket might make a neat night time video for a high speed camera with the translucent FG tube when the charges fire.

SCrocketfan said:

4 pins should be fine, and your load estimations seem quite reasonable. I run 3 in the main section on both a 3" MAC canvas rocket and a 4" cardboard, and one on the drogue section on the 3" rocket (friction fit on the cardboard rocket). So far that has held well including some somewhat aggressive flights on the 3" (CTI J760 to 6800'). The fit on the canvas is tighter than fiberglass though, so extra pins can't hurt.

One note since you are already going to run redundant altimeters and charges, definitely consider making the charges connected to the backup altimeter a bit bigger. For example, on the 3" rocket I mentioned above I run 1.4g on the primary drogue and main (the drogue compartment has a larger volume than the main but only 1 shear pin), but 2g on the backups. That way if for some reason a charge isn't enough to separate the components, the backup has a better chance of deploying the chute.

This actually has saved my 4" cardboard rocket on one flight-I was using masking tape instead of shear pins and the nose cone separated at apogee, but not enough to deploy the main. The 1.5 gram main charge fired but since the nose cone was separated already, the main didn't deploy-but the 2g backup got the chute out just in time!

+1 to ground testing as well.

Good luck on the testing and flights-looking forward to seeing it fly at DA!

Click to expand...

Thank you for your reply and consideration of my load estimates. I was considering bumping up the second/redundant charge, but only by .1 or .2 g. You're suggestion of going up a good amount makes better sense. Thank you for that too. I really appreciate the feedback.

I'm hoping to get this done in time for DA. Work has been dragging me down this week, so progress has slowed. I need to post some more pictures of what I have gotten done..

I finally got around to working on the Altimeter Bay over the weekend. However, I didn't get as much done as I'd hoped.
My plan is to use dual redundant altimeters. I've decided to use one StratologgerCF with an external Amplified Beeper, and a Eggtimer Quantum with WiFi on a single Battery. I purchased some rotary switches from Doghouse Rocketry that I plan to mount facing out and 180 degrees apart. I'll need to turn the altimeters on with a screwdriver through 2 opposing vent holes. I'll have 4 vent holes in all, 90 degrees apart, lined up between the fin lines. The Stratologger instructions suggest that four 0.109" vent holes are needed for my 3.9 x 9" altimeter bay. I'm planning to drill four 0.125" vent holes, as I need to have a wide enough screwdriver to turn the switches on.

Here's my current stash of parts to work with.. I'm planning to use a pair of 2S LiPo batteries. At least 300mAh and 35C or more. The Eggtimer Quantum will likely get a 450mAh 2S 25C LiPo, since the WiFi unit draws about 85mA.



I've mounted dual charge canisters on either end of the altimeter bay. I opted for the taller grey charge canisters for the booster/drogue side, as they'll allow for a little more black powder, and will release the charge gases just above the pezio amplified buzzer rather than right next to it's opening.



The payload/nosecone/main chute charge canisters are the Apogee PVC pipe caps. The one is black inside from testing my Eggtimer Quantum inside the compost bin. Works great.


The stock altimeter sled was rather short, and would not easily accommodate both altimeter setups. I had a good suggestion (Thanks Chris) to simply install a second plywood shelf to the other side of the sled. Here's what it will look like, should have plenty of room for an altimeter, battery and switch mounted to each side:

Kevin - I am really looking forward to the day you fly this. I have no doubt you are going to be posting a HUGE SUCCESS! You're really putting good time and effort, and learning things and incorporating them rather than just blowing through this. It's going to be great! Look forward to seeing what you do with the paint job!!

I haven't posted to this thread for a while.. and have some catch up to do. I've continued to progress on the build. I finished the fin can fillets inside and out last week. Over the weekend, I installed the aft centering ring and the engine retainer. Here's some pictures:

Aft centering ring set with Rocketpoxy. I use a flashlight to see the center of the ring vs. the glue fillet thickness. It's one of the nice things to take advantage of when working with a fiberglass tube.


After the centering ring was set I bonded in the AeroPac Engine 54mm motor retainer:


I picked up a 54mm 1280 case to compliment my 38/720 case and Aeropack adapter. I think I'll end up flying lots of 38/720 loads in this bird.. since 2000+ ft is a nice flight for a bird without tracking.
I have some 38mm loads ready to fly, a I600R and an I327DM. I'll have to make sure my vision or visual aides are up to the task before I launch with anything larger in the 54/1280 case... Those loads will push somewhere around 5K ft if I recall my simulation results correctly.

I did some homework regarding shear pins, rivets and other means to secure the "removable" tubes. I decided to go with 4's, keeping with 4 fins. Thus there will be 4 shear pins (2-56) in the nosecone and also 4 shear pins in the booster to altimeter bay. However, rather than use the plastic rivets that were part of the kit, I decided to install composite tube fasteners from Lumadyne. I need to get a better picture showing the final assembly, but for now here's the pictures I've taken before and after installing these. they worked out perfectly.. a very nice fastening method. They only protrude 0.027" from the body tube, as they are countersunk for flathead screws. When installing, a smooth epoxy fairing is built up around the fastener to both secure and blend it smoothly into the airframe.

I finally got around to finishing the Altimeter bay. I added a second side to the stock madcow plywood tray, then ginned up some plywood switch holders and used CA and microballons to build and install the switch "boxes". I opted to go with 2S LiPo batteries to power both sides of the altimeter bay. On one side I'll have a StratologgerCF with red wires for main and drogue. On the other side I'll have an Eggtimer Quantum with black wires for the main and drogue charges. I used opposite gender connectors for the main and drogue charges, to minimize errors when prepping for flight.
Here's some shots:

Building up switch mounting box:


Drill and tap 3mm metric threads right into the plywood, then use colored nylon standoffs to mount the altimeters:


I ordered a connector set from amazon that had locking connectors.


I built longer wires with disconnect for the main charges, and shorter wires with disconnects for the drogue charges. Here's what the near finished sled looked like:

Yesterday and today I worked to test out the new altimeter bay. The Eggtimer Quantum was working great as far as I can tell. I used it's built in WiFi web page access to fire test charges for both the drogue and main.
However, I also tested the StratologgerCF using a shopvac to simulate a flight. While both of my Ematches fired, the StratooggerCF was alerting me to an over current event. After digging into this problem, I found that using the combination of a 2S LiPo (8.4Vdc) and inexpensive Ematches bought from Amazon, the current drawn through the firing circuit was anywhere from 6 to 8 Amps, well over the 5 Amp limit. After some research and discussions on another thread, I opted to build up a 1S (4.2V) 850mAh LiPo battery to replace my 2S (8.4V) LiPo. This, by Ohms Law, will reduce the current draw when firing the low resistance Ematches from Amazon. I measured the Ematches at 1.0 to 1.3 Ohms. So I =V/R seems inline with the current draw reported/warned by the StratologgerCF.
After replacing the 2S with a 1S (1 cell) LiPo, all ground tests with the StratologgerCF were within limits and worked very well.
Here's some pictures:

I used a single cell from a 3S LiPo that had a cell go bad last year. I had saved the 2 good cells, hoping to find a use for them some day... Well today was the day. A little solder, hot glue, shrink wrap and a connector and voila I had a drop in replacement 1S LiPo:


Here's a pictue of the Ematches I got from Amazon. Cost was $17 for 100:


Here's a picture of the StratologgerCF data when using a 2S LiPo vs the 1S LiPo. Notice how well LiPo batteries hold their voltage under load. At the bottom, there are values "PID" and "PIM", which are the maximum current draws from the Drogue and Main channels.

Here the 2S LiPo worked, but the StratologgerCF sourced 8 Amps for the drogue and 6 Amps for the Main charge channels.


Here the 1S LiPo did it's job and held 4.1 Volts nicely, while sourcing 4 Amps to the Drogue channel and 3 Amps to the Main channel.

I managed to finally test just a single ejection charge last night. I used the Eggtimer Quantum to fire a 1.4g 4F BP charge to eject the main chute and nosecone. The BP caclulaor I used said I needed 12 PSI to get 150 lbf on the nosecone, and if each of the 4 2-56 screws takes 35lbf to shear, the minimum force to eject would be 140 lbf plus friction. So I set the calculator to find the BP charge corresponding to 15 psi. It suggested using 1.36g BP. So I measured 1.4g and went with it for my first test. The charge worked nicely, sending the nosecone and chute to the full extension of the stock shock cord (10 feet for main, 15 feet for drogue). Here's some pictures:

Packing 1.4g 4F BP:


Dog Barf, 3 handfuls seemed about right:



Packed the chute, just the 50" chute for now and the stock 12" parachute protector. I think both the chute and protector are too small.


With the rocked assembled and just the unloaded 38mm/720 motor case, closures and 38-to-54mm adapter installed, The rocked weighed in at 9 lbs 2.125 oz.



Test fire! Nose cone and chute came out with umph! I have a video.. not sure I'll post it.


Some shots of the BP mess... I'm going to have to figure out how to prevent the terminal blocks from corroding from all the BP residue.


Chute protector did it's job:


And there's the remains of 4 shear pins!

Not having any paint on the rocket, made for some interesting photos and video of the ejection charge testing as darkness settled. Heres a few time sequenced shots of the main deployment. I love the first shot.. the charge lit up the yard from inside the FG tube! 1.4g BP was plenty to get the laundry out.. and then some:

This is a very well engineered build, I love it! The Level II kit from Apogee Components always looked like the Loc EZI-65 to me... and that is a good thing! The ground test sequence is pretty sweet, let's you see just how hot and strong BP can be in a recovery system... if someone did not think that they needed to protect their recovery gear from a charge, then this sequence should give them food-for-thought! Can't wait to see this rocket on the pad and in the air!

A couple of comments.

Experimental Data on Shear Screws. https://web.archive.org/web/2015021...rials.org/datastore/cord/Shear_Pins/index.php

For 2-56 nylon shear screws: 50 pounds force required for (2) 2-56 shear screws; 22 pounds per screw for 3 or more screws.
For 4-40 nylon shear screws: 81 pounds force required for (2) 2-56 shear screws; 39 pounds per screw for 3 or more screws.
Above Values are average: You should use enough extra BP to generate at least 20% greater force than minimum to account for lot differences.

A reliable BP calculator: https://www.vernk.com/EjectionChargeSizing.htm
Caution: Calculator is based on 15 psi pressure generation. This is good for small rocket but overkill for large diameter rockets.
The separation force is the internal cross-sectional area of the rocket in square inches multiplied by the pressure in PSI.
As stated on the page, in a 7.5" rocket, 15 psi x pi x (7.5/2)^2 = 15 psi x 44 sq.in. = 663 pounds. If the ejected mass is 6 pounds, that over 110 G acceleration for 6" acceleration length. The separation velocity in fps is 8 multiplied by the square root of the product of the acceleration in g multiplied by the shoulder length in feet. For a typical 6" shoulder on a 7.5" airframe, the separation delta V is 60 fps which is pretty high. 7.5 psi is plenty so you would use half the BP the calculator suggests.

An altimeter/battery/igniter spreadsheet is I puth together is here. View attachment ohmslawigniter.xls

Bob

DRAGON64 said:

This is a very well engineered build, I love it! The Level II kit from Apogee Components always looked like the Loc EZI-65 to me... and that is a good thing! The ground test sequence is pretty sweet, let's you see just how hot and strong BP can be in a recovery system... if someone did not think that they needed to protect their recovery gear from a charge, then this sequence should give them food-for-thought! Can't wait to see this rocket on the pad and in the air!

Click to expand...

Thanks Dragon. The first couple of frames from the video at t=0+ for the ejection charge were more interesting that I expected. I had to check my chute twice after watching that. It seems sparks flew out the nosecone/payload tube gap as soon as the nosecone shoulder gave them space. I'm guessing that some, if not all, of those sparks are dog barf embers.. that don't ignite.. but do smolder.
I found that my nylon shock cord got a little singe in proximity to the main charge flash.. but nothing forward of that. So, I'll be adding more masking tape as a stop gap until I "open my wallet" for a nice long Kevlar setup.
You have a great avatar.

bobkrech said:

A couple of comments.

Experimental Data on Shear Screws. https://web.archive.org/web/2015021...rials.org/datastore/cord/Shear_Pins/index.php

For 2-56 nylon shear screws: 50 pounds force required for (2) 2-56 shear screws; 22 pounds per screw for 3 or more screws.
For 4-40 nylon shear screws: 81 pounds force required for (2) 2-56 shear screws; 39 pounds per screw for 3 or more screws.
Above Values are average: You should use enough extra BP to generate at least 20% greater force than minimum to account for lot differences.

A reliable BP calculator: https://www.vernk.com/EjectionChargeSizing.htm
Caution: Calculator is based on 15 psi pressure generation. This is good for small rocket but overkill for large diameter rockets.
The separation force is the internal cross-sectional area of the rocket in square inches multiplied by the pressure in PSI.
As stated on the page, in a 7.5" rocket, 15 psi x pi x (7.5/2)^2 = 15 psi x 44 sq.in. = 663 pounds. If the ejected mass is 6 pounds, that over 110 G acceleration for 6" acceleration length. The separation velocity in fps is 8 multiplied by the square root of the product of the acceleration in g multiplied by the shoulder length in feet. For a typical 6" shoulder on a 7.5" airframe, the separation delta V is 60 fps which is pretty high. 7.5 psi is plenty so you would use half the BP the calculator suggests.

An altimeter/battery/igniter spreadsheet is I puth together is here. View attachment 290732

Bob

Click to expand...

Thank you Bob. I looked over the explicit data presented for the ejection charge sizing page you linked. I think I'm right inline with the numbers suggested. However, I found it interesting that there appears to be a correlation, beyond just the simple volume correlation, for longer tubes. It appears that he had to add up to 125% more powder than calculated for his longer tube. I wonder if this could relate to a wave front delay and escaping pressure... hmm.. I'll save that thought. For now, my numbers are inline between the page I used, and that page you linked.. and the intensity seemed about right.

I look forward to getting on a PC on which I have Excel installed.. so I can look at the ohmslawigniter.xls file you've linked. Sounds like good stuff.
Best,
Kevin

kevinkal said:

I look forward to getting on a PC on which I have Excel installed.. so I can look at the ohmslawigniter.xls file you've linked. Sounds like good stuff.
Best,
Kevin

Click to expand...

OpenOffice/ Google docs?

You could always nomex sleeve the nylon, typically done from the connection point to above the body tube.

https://topflightrecoveryllc.homestead.com/page3.html

kevinkal said:

Earlier today in this new thread, I posted about my parachute issue and hinted that I was worried I would not have the replacement parachute in time for the May Launch date.
I said that too soon. I just walked in and found that with the mail, I had a package from Madcow Rocketry. Thank you Amy at Apogee and Madcow.

View attachment 289079

I measured it to be about 50 inches across on the flat sides. So much better than 36".
It appears to be Madcow's 50" Ripstop Nylon Chute:
- 8 Shroud Lines
- Recommended Descent Weight: 5-9 lbs (I will need to look for a bigger chute when I fly heavier motors.)
View attachment 289080

Ok, so I updated my open rocket model with this as a 51" chute to see what it showed for my under main canopy descent rate at ground hit. It appears to be too high, even with the smallest J motor, it's hitting the ground at 24 ft/sec minimum with the smallest motors. So, it would seem this parachute is still too small. Should I buy a new bigger chute for my L2 cert flight or risk ground impact damage? I don't think I want to risk anything. Ok, Gene... time to look at a Fruity Chute. =]

My open rocket sim is not updated for actual weight, just actual components that I've integrated so far.. it does not include lots of odds and ends nor glue or paint.. thus I expect my model to be even heavier and come down faster that what this version is showing below:
View attachment 289097

Click to expand...

What a bout a 60" flare chute? They are reasonable and I'm sure will be able to handle the weight of your rocket?

dhbarr said:

OpenOffice/ Google docs?

Click to expand...

I think I'm getting too old... I haven't kept up with Google Open Office.. I just use my old MS Office installations! I'll have to look into that for my laptop.. save some bucks and get up to speed on open office. Thanks for the recommendation.

Banzai88 said:

You could always nomex sleeve the nylon, typically done from the connection point to above the body tube.

https://topflightrecoveryllc.homestead.com/page3.html

Click to expand...

Good point. I have a hunch that the stock shock cords will leave me wanting longer cords. So, I'll either get a longer sleeved nylon or longer Kevlar setup. I think Kevlar is about 2x the cost. hmm.

AfterBurners said:

What a bout a 60" flare chute? They are reasonable and I'm sure will be able to handle the weight of your rocket?

Click to expand...

Thanks for the tip. I'll look into that. I haven't heard of a "flare" chute. I wonder if that's a different term for elliptical? For the time being, I picked up a Top Flight PAR-70, it's probably slightly too big.. but I figure with dual deployment.. it can't hurt too much, and will save a few dings upon impact... assuming there's no wind to drag my rocket away.

Main Ejection Charge Test, 1.4g 4F Black Powder, Four 2-56 nylon screw shear pins. This seems like a good strong ejection. Eggtimer Quantum test page used to ignite charge.

[video=youtube;4vA9ZT7cFFY]https://www.youtube.com/watch?v=4vA9ZT7cFFY[/video]


Drogue Ejection Charge Test, 1.7g 4F Black Powder, Four 2-56 nylon screw shear pins. This ejection seemed a little weak. What do you think? I my try again with 2.0g 4F BP. Eggtimer Quantum test page used to ignite charge.
Note the spout of flame shooting out of a 0.125" vent hole just below the altimeter bay.
[video=youtube;tmeKzMlwN8Q]https://www.youtube.com/watch?v=tmeKzMlwN8Q[/video]

I think both look very good. I'd even say the nose cone is a little aggressive. I wouldn't increase the drogue from what I see.

Drogue looks perfect, nose a little aggressive. Then again, I'm not a "blow it out or blow it up" kind of guy.

From looking at the video, don't know that I'd do anything other than lengthen the nose harness first, then retest (jerking up short, as I was taught, is a sure sign that your harness is too short or your charge is too big).

With what you have available and already built, I'd put the 10 foot on the drogue and the 15 foot in the nose and retest.

kcobbva said:

I think both look very good. I'd even say the nose cone is a little aggressive. I wouldn't increase the drogue from what I see.

Click to expand...

Banzai88 said:

Drogue looks perfect, nose a little aggressive. Then again, I'm not a "blow it out or blow it up" kind of guy.

From looking at the video, don't know that I'd do anything other than lengthen the nose harness first, then retest (jerking up short, as I was taught, is a sure sign that your harness is too short or your charge is too big).

With what you have available and already built, I'd put the 10 foot on the drogue and the 15 foot in the nose and retest.

Click to expand...

Thanks for the feedback guys. It gives me confidence.

I agree that my nose shock cord is too short, else charge a bit aggressive. Per the black powder calculator, both charges are only generating 15 psi. It makes sense that the nose jumps out give it's lower mass. However, in order to shear the Four 2-56 pins, I need to make darn sure I get no less than 12 psi. So, I don't want to go below 15 psi. I think you're right that the droque charge is good as is. It makes sense that it doesn't shoot across the yard since it has significantly more mass.

As for swapping my 15' booster-2-payload shock cord with my 10' nosecone to payload shock cord... I think I'm stuck with this configuration until I buy a new cord for the following reason. I need to be certain that when the main chute charge fires the nosecone out.. that it cannot hit the booster. I think I need to take a close look at the OneBadHawk options. Hmm. 25' and 20' might be the way to go. This bird keeps getting more and more valuable.

I uploaded my current version Open Rocket Model for the Madcow/Apogee Level2 for my build. See the model, a simulation screenshot and a 3D view in Post #4.

kevinkal said:

I think I need to take a close look at the OneBadHawk options. Hmm. 25' and 20' might be the way to go. This bird keeps getting more and more valuable.

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You cannot go wrong with onebadhawk harnesses. They will protect your investment. Also the longer cord will ensure your nosecone doesn't eject with such a force that it separates from the rocket. You've put so much time and awesome effort into this; that that would be a primary security blanket in my mind. Also enough to zfold and tape the cord to reduce the stress the nosecone receives at ejection.

kevinkal said:

Thanks for the tip. I'll look into that. I haven't heard of a "flare" chute. I wonder if that's a different term for elliptical? For the time being, I picked up a Top Flight PAR-70, it's probably slightly too big.. but I figure with dual deployment.. it can't hurt too much, and will save a few dings upon impact... assuming there's no wind to drag my rocket away.

Click to expand...

I believe this chute from Aerocon is what he's refering to. https://aeroconsystems.com/cart/all-parachutes/60-inch-white-parachute/

Thanks for the link. Seems like a good deal for $12. Shipping to CA started at bout $10.

I need to have this bird ready to fly in 6 days. I'd like to finish the paint before then.
I'm looking at two types of paint, and will choose a path this morning and start with primer.
The choices are:
1. DupliColor (If I can find it locally with decent color selection)
2. Rustoleum 2X UltraCover (known availability at Home Depot and Wallmart)

Here's some OpenRocket Images of the current paint scheme Ideas:

I like lime green.. but worry about visibility..


I like orange for visibility....


I'll mostly likely stagger the fin can colors.. but it was too much work in OpenRocket to spend my limited time to implement right now.

I like both, especially the green! Rustoleum has a nice 2X green, although it's a bit light for lime green. I don't think green would hurt visibility much. At TCC it can't hurt to add a small audible beeper to the rocket to find it if/when the rocket lands in alfalfa, especially if you aren't running a tracker yet.

As for charges, I'd probably keep the main the same and maybe increase the drogue a bit (0.1 or 0.2 grams, and then +0.5 more on the backup). I usually run two 20' harnesses on rockets of this size, with the main chute a few feet back from the nose cone on the front harness and the drogue chute a few feet back from the payload connection to limit tangling. Your recovery configuration seems good, but definitely consider Onebadhawk down the road.

Looking forward to the launch!