Madcow Super DX3

[davalf]

Well, my Madcow Super DX3 just arrived today. And because it is to cold out to be in the shop building I am in here. I do have one question about the build. And I think it is a pretty stupid one. The kits instructions do not mention anything about attaching the shock chord to the parachute or the upper airframe. It only mentions attaching the chord through the eye bolt on the upper centering ring using an overhand knot. Any suggestions? Thank you.

Dave

 

[Gillard]

Theres a review on EMRR.
https://www.rocketreviews.com/reviews/all/mc_super_dx3.shtml
i don't know this kit, but on some other madcow kits there is usually an eye bolt on the top half coupler, if not then i'd but one.
most people attach the parachute about 1/3 down from the top on the shock cord.
hope this helps

 

[ONAWHIM]

I did not find reference to an over hand knot for tying off to the upper airframe eyebolt.

There is a discussion on knots here

Good luck, good flying

 

[ONAWHIM]

Davalf,

If you haven't started your build I would like to suggest that you dry fit the lower engine tube centering ring when epoxying the upper to the lower airframe tube.

That way you can remove it to allow for interior fillets and strengthening.

The Madcow instructions don't suggest this.

Use two pieces of tape or other means to pull the lower ring out once the upper has had time to harden.

Have a good time with your build!

Wm.

 

[davalf]

I wish I would have read that earlier. I didn't even think of dry fitting the centering ring to install the forward one. I tried thinking of a way to do that but I thought I would have trouble keeping the motor tube centered. I guess this is how you learn.
I got most of the rocket built today. All I have left to do is the rail buttons, fin fillets, and motor mount fillets. Then paint. I came up with a couple more questions though. For the shock chord I just tied a double knot when I installed it. One thing I was wondering though, was the use of D-rings. Are they strong enough? And for the finishing of it. I bought some wood filler for the spiral grooves in the tube. I was messing around with it and put some on with just my finger. It worked well but was messy. Any suggestions?
And lastly, I was reading about the level 1 cert process on the TRA website. It mentioned you must mark the center of pressure on the rocket. What is the easiest way of calculating this? I will not be able to have a real accurate CG until I get to the launch site because that is where I am purchasing my motor. Sorry for the lengthy reply, but thank you for all the advice.

Dave

 

[Gillard]

I was reading about the level 1 cert process on the TRA website. It mentioned you must mark the center of pressure on the rocket. What is the easiest way of calculating this?
Dave

CP is either 44.00 or 44.71 inches from the nose - got information from EMRR.

 

[mikec]

CP is either 44.00 or 44.71 inches from the nose - got information from EMRR.

That was with the old, stubbier nose cone, though. The instructions for the new cone say that the CG has to be 47 inches from the nose tip or forward, which implies that the CP is 51 inches from the nose (1 caliber stability).

I did both my L1 and L2 with this rocket. For L2 you need a few ounces of nose weight.

I suggest you put the front rail button 47 inches back from the nose and then if the rocket balances there or forward with the motor you pick, you're good to go.

 

[davalf]

Thank you for the info. Know where I can get a rocksim file for it? Every link I try is busted.

 

[mikec]

Thank you for the info. Know where I can get a rocksim file for it?

The link on the Madcow website worked for me. https://www.madcowrocketry.com/catalog/superdx3.rkt

 

[davalf]

what do i do will all that info

 

[davalf]

Nevermind, I figured it out. Thank you.