Madcow Mini DX3

[Caley]

Rich, I know what friction fit is, and I do have a problem with the lower section. It was very loose. What I did was built up the coupler/EBAY with epoxy. I think I will have to add one more layer. As for testing that friction fit, just how do you do that. I know that the lower part of the rocket that fits in with the EBAY/upper body slides out very easy. The nose cone/upper body joint is fairly stiff. Kind of makes a popping sound when I separate them. It's actually fairly difficult to pull them apart with my arthritic hands.

Not sure what masking tape is meant in your reply. Do you mean to put small tabs of masking tape on the outside at the coupling joints?

From what you are saying, shear pins are really for larger rockets, in particular, the fiberglass/composite types.

 

[crossfire]

Yes that is what you do with the masking tape. Put a strip of masking tape on exposed part of the coupler. Check the fit. If to loose add another. This had been used for HP rocketry for many years with no problems. What most of us do is have rocket all loaded for flight and lift rocket by payload section give it a little shake if booster slides off add a section of tape. I like to have a tight enough fit so there is just a little booster movement on the coupler. I have used this method on M powered flights.

 

[Rex R]

I am with crossfire on this, reason; the perfect fit you get at home at room temperature probably will not be perfect when you get to the field (hotter/colder). although I will note that I used 1/2" wide strips of masking tape as sheer tape on my L2 bird (to hold the e-bay onto the fin unit).
Rex

 

[Caley]

If masking tape is too thick, I will try clear tape. Thanks

 

[crossfire]

Caley
Use masking tape. I would bet one strip of masking tape will help out a lot. We have been using masking tape in rocketry for over 25 years. Its just works. Like Rex said masking tape also works well for a sheer tape. I have never used clear tape so it may work?

 

[rharshberger]

Others have replied to your questions and done it more than adequately. Sometimes not even a full wrap of masking tape is needed, on occasion I have used a quarter wrap or less to get the proper fit, and I too like Crossfire and Rex have used masking tape as "shear tape" usually just two narrow pieces across the joint between the upper and lower payload bays or nose cone is all that's needed.

 

[Caley]

I have blue masking tape. Tried some, and an inch made the fit snug. I doubt air turbulence after motor burnout will loosen the coupling now.

In order for me to have it easier to work on things, I am using quick links. Unfortunately, I have not found anything shorter than 1 3/8 inches b 1/8 inch diameter stock. I was hoping to find something an inch or less to keep both the bulk and mass down.

 

[rharshberger]

I have blue masking tape. Tried some, and an inch made the fit snug. I doubt air turbulence after motor burnout will loosen the coupling now.

In order for me to have it easier to work on things, I am using quick links. Unfortunately, I have not found anything shorter than 1 3/8 inches b 1/8 inch diameter stock. I was hoping to find something an inch or less to keep both the bulk and mass down.

1/8" is about the smallest rated quick link available, and its pretty much my go to QL on 38/54mm rockets.

 

[Caley]

I finally got the parachutes and shock cords installed, with their swivels and quick links, and Nomex protectors. Unpainted air frame is now 11 ounces. Still fairly good. I guess a paint job will add another ounce.

I did have problems with the shock cord because it is so bulky. I am wondering if I need 1500# test Kevlar? I wonder if my first purchase, which I thought was a mistake, of 300# Kevlar might be OK for this little rocket. Of course, I have no idea what the dynamics/forces are when the ejection charges are blown, and how much of a snap the model goes through as it suddenly slows/stops on the parachutes. If I can get the diameter of the shock cords down, it won't be so difficult to pack these parachutes. The drogue was easy, but the main was a super tight fit.

 

[Rex R]

I generally figure that 50 gee's is a reasonably good point to design for...you may have surpassed that by a bit .
Rex
*edit*
1/8" quick links are rated to 220 pounds...

 

[Caley]

OK, Let me ask this another way.

If I use this 300# Kevlar shock cord for my Mini DX3, which is about 37 inches in length, how long should I make it. Remember, this is a dual deploy setup now, not just the simple rocket motor ejection setup.

So I would need to get two things set up. One for the drogue (12 inch diameter) which is in the main body that connects to the EBAY.

The other is the main (18 inch diameter) that connects to the top of the EBAY, and extends up to the nose cone.

If possible, I would rather use this thinner cord, as it is not as bulky. My only other alternative is to order something else, which so far, I have not been able to locate. It seems you go from this thin 300# which is about 5/32 inch diameter to 3/16 diameter shock cord, nothing between.

If my quick links are rated at 220#, then maybe this thinner shock cord is OK, just don't know. I am trying to learn, and I do so by asking questions until I get something I understand. One thing to tell you, I do not do higher math at all. I had no aptitude for it when in school. I got to geometry and quit, as I couldn't memorize the formulas, and consequently the teacher told me to go the administrative education route. Love science, but me and math do not get along, except for the basic stuff.

 

[crossfire]

Caley remember Kevlar doesn't stretch as dose a nylon material so you will need to use a longer section of Kevlar. I would use 3-4 times booster length for that section. And as much as you can fit in main chute tube along with chute and chute protector. 1/8 QL are about as small as you going to find. At this time we have some soft and very packable 1/8" Kevlar in stock. I am using it on my WM Wildchild which I believe is the size tube as the MC mini's


Gary
Top Flight Recovery LLC

 

[rharshberger]

If you can get one I would recommend a smaller drogue than 12" or even use a streamer.

 

[Caley]

I finally quit going to model rocket sites, and went to Amazon.com. Here is what I found https://www.amazon.com/gp/product/B01850OSTK/?tag=skimlinks_replacement-20 I ordered the 2mm 750# 30 meter spool. This should do for most mid powered models. The stuff I was trying to cram into the tubes is 4mm diameter, which doesn't allow me enough length. I only had about 4 feet in each section, which I know isn't enough. That is why I came here asking.

Anyone know where I can come up with an 8 inch diameter drogue chute that isn't plastic. I'm not really sure that a streamer is going to slow down a rocket that is around 15 ounces fully loaded. There needs to be some kind of stable flat surface area.

 

[rharshberger]

TFR probably carries a 8" or so chute at a reasonable price.

Edit: TFR has a 9" Thin Mill nylon, I love Thin mill chutes for smaller rockets since the pack pretty small.

 

[qquake2k]

Top Flight has 9" thin mil parachutes.

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

And Balsa Machining has 9" nylon chutes (on their School Rocket page).

https://www.balsamachining.com/#

 

[Caley]

Thanks Everyone. That should do it for me. Seems I have had difficulty putting things together every step of the way. Guess that is normal for the first of anything you do. I did look at streamers, but not sure they would slow things down enough, and they are still pretty bulky because you need to roll up the streamer with shock cord and protector, still making things a pretty snug fit. The little Nomex hankie is bulky enough already. Looks like I need to wait a few more weeks to get all these little orders for this and that together.

Then I can take things to the flying field and have someone who is qualified inspect my work, and tell me what I need to do to make it ready for fright. Yes, I plan on having a preflight inspection just to be safe.

 

[crossfire]

The BMS Par9s. Are not TM fabric but still fold up small. Your doing a great job. You are learning a lot for your next build. sometimes the small rockets are harder to build than large ones. Have fun and fly safe

 

[Caley]

Hi again, I've been doing more research on this and that. One of these is parachute size based on the weight of the model. Someone mentioned using a smaller drogue chute, and that seems to be one thing that I will have to do. The calculator said that a 9 inch would probably be fine, but below, it said that I needed a 27 inch main to slow down to a safe landing. Right now I have an 18 inch inside, but the way the recovery system is configured, would not fit inside the upper body.

So I am asking, is it absolutely necessary to put the main in the upper body? I have plenty of room for a light weight 30 inch parachute in the main lower body. The drogue chute would fit perfectly in the upper body. I will await someone providing an answer before ordering these two chutes.

I finally received my battery charger from Altus Metrum, and also got the small vials of gunpowder from RCS for my ejection charges. I will be preparing these charges and testing when I go to the next club fly in this coming 13th. At the same time, I need to have someone there check out the rocket, and teach me how to fold and install the chutes properly.

 

[crossfire]

Carley
We manufacture the chutes for both WM and MC for there line of mini FG kits. WM uses a Par15 and MC uses a Par18. They are not DD. Not sure if I would use a Par27-30" for your rocket.

 

[Caley]

Hi, this is Caley. Crossfire, I am relatively new to model rocketry. Last things I did were back in 1971. So when you say you manufacture the chutes, I still haven't a clue as to what business you are referring to, not am I familiar with things like WM, MC, FG or DD.

The online calculator I used said the optimum main chute was 27 inches for my sized and weight rocket. Weight after propellant is burned off is about 14 ounces. And when I finally can purchase a reloadable casing with reloads, it will probably be a bit heavier.

Someone on this thread said that my 12 inch diameter drogue was too big, and that the smallest available, 9 inches was still too big. It was even mentioned by someone to use a streamer. Needless to say I am totally confused, because I keep getting a lot of answers that conflict. More than likely they still haven't seen in this thread that I will be flying off the Lucerne Valley Dry Lake Bed in southern California. During the summer months, that lake bed is like concrete. I was told by one of the participants to up the size of the main chute one size, which probably means 21-24 inches.

So far I haven't gotten an answer to the previous question, which was, is it necessary to put the drogue chute in the main body, while the main chute resides in the upper body. This Mini DX3 has a very small upper body, which means it is very difficult to even install the stock 18 inch chute. Can I reverse things, main chute in main body, and drogue in upper body?

 

[Rex R]

Gary is in the parachute biz. his company 'Top Flight Recovery, llc' has a number of different models to chose from. they also make 'chutes for Mad Cow rocketry(MC), Wild Man rocketry(WM), to name a couple. the main reason that folks like to have the drogue in the lower body section is if they use the motor for a backup deployment charge. if one choses to forego this option, then there is no reason one could not reverse the placement of chutes. IMO a 12" chute is probably the smallest I would go for a drogue...if I needed/ wanted something smaller I would use a streamer(which one can also buy from Gary).
Rex

 

[crossfire]

Carley
This is what I would do use a Par12 in booster tube for the drogue and an Par18 as the main in the upper airframe. Just using a Par18 would give you 20fps decent. Now by adding the Par12 as the drogue things should work out great for you.

Thanks
Gary
Top Flight Recovery LLC

 

[Caley]

Gary, this is Caley. Then I should be fine, as I have both of those inside the tubes, though the 18 inch is a rather tight fit in the upper body tube. Should be getting some help on parachute folding next week. Seems that I am fumble fingers, and every time I get ready to insert the bundle in the tube, it comes undone.

 

[crossfire]

Carley. Is the 18 made a thin mill fabric? Do you know who made the chute? A 18 tm fabric chute would fold up smaller than standard fabric made chute.

 

[Caley]

Crossfire, Not sure why you keep calling me Carley, but maybe it is just a typo.

The fabric of the main chute is .05mm thick. I used an electronic device that I have been using for years. It is accurate.
The fabric of the 12 inch chute is .09mm thick

I am using 6x6 inch squares of Nomex for my chute protectors. They are thick, and probably the reason it ends up being so bulky.

Anyway, hopefully things will work fine on the 13th. Caley Ann

 

[crossfire]

Caley I got it right. Its not a typo its my eye sight. Yes a 6X6 protector is a little big for the tube. Maybe some dog barf cellulose insulation would work better.

 

[Caley]

Gary, Yes, that would work fine. Unfortunately I live in a tiny house with not a lot of room for a bale of that stuff. I will have to be happy with the Nomex hankie.

 

[dhbarr]

Gary, Yes, that would work fine. Unfortunately I live in a tiny house with not a lot of room for a bale of that stuff. I will have to be happy with the Nomex hankie.

With whom will you launch? There's usually a few barf bags floating around, if they've a mailing list one could potentially confirm.

 

[Caley]

I don't plan on launching until June. What I will do this month is have an experienced person look over my model to ensure I did things correctly, and of course, hopefully have enough time from his own work to teach me how to properly pack a parachute and all those long cords. I will also be doing the my first ground testing of the recovery system. According to the online calculator, I need 1/4 gram black powder for my main body, and only 1/10th gram for the upper body. The lower body is only 1.6 inches diameter with a length of 14 inches, and the upper the same diameter with a length of 5 inches.