Newbs MadCow 2.6" DXi3 Build Thread

[markfsanderson]

Greetings,
Not sure if this is the correct venue, admin please move if not. I thought I'd start a build thread showing my building progress . . . trouble stops and starts and etc. For first rocket in years, and first mid-powered rocket ever I chose the Madcow 2.6" DX3. I purchased an AT 29mm40/120 RMS case as well as an AT 24mm/60 case for lower powered E and F engines. I'm also using an Estes 29mm Engine Retainer (plastic) and a 29mm/24mm converter. My goals for this rocket are very simple: Mid-Power ONLY with a focus on repeat recovery success. No electronics technology (except maybe an altimeter in the cargo bay!), no parachute release, dual recovery . . . just basic rocket goes, pops chute, comes back down - I recover it in (hopefully) one piece. I am saving my Level One for a 4" MadCow DX-3 . . . I've purchased an AT38mm/480 along with forward and rear enclosures, and insert kits so I can run with minimum power to help with recovery success. If anyone believes my approach a bit conservative . . . I'll plead guilty! Let me know you opinion on this, and my build progress (or lack of!):

Thanks in advance for your indulgence and opinions . . .

Mark

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[Rex R]

2 comments. 1) you'll be wanting a bit more epoxy on the aft end of your payload thingee (a visible filet will suffice) to ensure that the bulkhead stays put.
2) when last I looked the 24/60 had only F reloads, the 24/40 had D - F reloads. 2.5) tuck that shock cord into the motor mount tube before you install the motor mount in the airframe.
Rex

 

[markfsanderson]

2 comments. 1) you'll be wanting a bit more epoxy on the aft end of your payload thingee (a visible filet will suffice) to ensure that the bulkhead stays put.
2) when last I looked the 24/60 had only F reloads, the 24/40 had D - F reloads. 2.5) tuck that shock cord into the motor mount tube before you install the motor mount in the airframe.
Rex

Rex,
Thanks! That was my next step . . . first letting it dry a bit more. Yeah, the 24/60 currently only has F . . . supposedly they're coming out with more? But I can still use single usage 24mm with the converter thing . . .

Question: (correction)Should I take the time to 'filet' the aft-end of the motor mount centering ring against the main tube?

Mark

 

[Rex R]

well... if done right the fins should take care of transferring the thrust loads to and from the motor tube, however as long as one doesn't over do the glue/ epoxy,(no, no, do not use 1 pound of epoxy on filets ) it wouldn't hurt. note some of us like to hold off on securing the motor retainer/ aft ring until after gluing the fins in place so we can do interior filets(generally with high power rockets).

 

[markfsanderson]

well... if done right the fins should take care of transferring the thrust loads to and from the motor tube, however as long as one doesn't over do the glue/ epoxy,(no, no, do not use 1 pound of epoxy on filets ) it wouldn't hurt. note some of us like to hold off on securing the motor retainer/ aft ring until after gluing the fins in place so we can do interior filets(generally with high power rockets).

Rex,
No high-power on this one . . . I saw others folks build threads where the leave the rear centering ring off until the fins are installed - but no need for this one. I'm building pretty light . . . just want to make sure I don't build too light! Ok cool . . . I won't worry about that then . . . Thanks!

Mark

 

[markfsanderson]

More work in progress . . . took pictures so far the build is going very well. I hope to be ready this Saturday for mid-power launch w/Alamo Rocketeers. If not, I've built an Alpha III, Mongoose and Riptide . . . we're inviting some neighbors over for the launch. Should be fun!

Something that I ran into, I screwed up the nose cone in that it appears that I should of applied the spray paint directly over the adhesion promoter. Is this correct? What I did was to put adhesion promoter, then the primer (plastic friendly) and then the pain. I noticed that the paint seemed to 'shrink' or contract thus exposing the white primer. I didn't do ( this time ) the bondo filler, just primer and paint. Should it be plastic -> Bondo -> adhesion promoter or ? Thanks!

 

[markfsanderson]

More pictures . . . learning by making mistakes . . . Some things work and others . . . don't! Tamiya tape definitely works for filets . . .

 

[Rex R]

lol, I don't see any landing gear(w/ 2.5" wheels) on that rocket.... I trust that you used a straight edge to check the alignment of your launch guides(if nothing else you remembered to attach them before painting(some people seem to overlook that step ). good luck and fly safe,
Rex

 

[markfsanderson]

lol, I don't see any landing gear(w/ 2.5" wheels) on that rocket.... I trust that you used a straight edge to check the alignment of your launch guides(if nothing else you remembered to attach them before painting(some people seem to overlook that step ). good luck and fly safe,
Rex

Rex,
Estes makes this tube marking guide that is just big enough to fit the 3" tube. I marked the line I wanted it on, roughed up both surfaces and used 30 minute epoxy. The guides straight pretty much guaranteed a straight install for both the guides and lugs . . As far as I can tel they're straight . . .

Mark

 

[markfsanderson]

Is 634 Grams ready to fly w/no motor or casing installed heavy? I've everything I'm going to fly with except dog barf and engine . . . Pictures of finished rocket to be posted soon.

Mark

 

[Rex R]

an F50/ F52(or bigger) motor should have no problem getting it off the pad, probably wont get over 2k on a G though should be a nice sport flyer.
Rex

 

[markfsanderson]

an F50/ F52(or bigger) motor should have no problem getting it off the pad, probably wont get over 2k on a G though should be a nice sport flyer.
Rex

There's an E that will get it off the pad at 17m/s . . . . that might be marginal . . . 2K is great for me . . . I'm more into the launch than chasing it around after going 2K . . . I've run some simulations to find out what motors are good . .


Question: AT F67W-10 Economax . . . my son was given one of these at the launch we went to for his birthday. Can I shorten the delay to 7 or 8 seconds using the RMS delay tool from Aerotech?
Mark

 

[Rex R]

I am going to weasel out and say conditionally yes it is possible to shorten the delay. I would suggest however that you get onsite help/demonstration because it is a bit involved...you would need to a) remove the ejection well cap(rubbery red cap) from the yellow end of the motor. b) pour out and capture the black powder ejection charge(you want to reuse it). c) run your 1/4" drill down to the delay element(dark gray) and put a 1/16" - 3/32" (1/32" per second) divot in the top of the delay, dump out the residue. d)pour the black powder back into the delay well and reinsert the rubbery red cap. e) hold the motor yellow end up and gently tap that end(a knuckle works well). and you're done. and this is why I suggested getting help in person .
Rex

 

[markfsanderson]

Here is a picture of my rocket, complete and ready to fly . . . well at least I hope. The CG is about 5 1/2 inches above the stated CG which is aligned with the upper side of the top rail guide - 31 inches. I found this by by weighing an AT G76 motor ( the largest I'll use, for now) and putting that much weight in a plastic bag which then I stuffed into the AT 29mm40/120 motor casing. Once installed I found the CG and marked it on the tube. I'm assuming that this is an acceptable method. The black dots are nose cone holders, I am running both launch rail guides and 1/4" launch lugs as well. Here is my DX-3, with all its faults modeled by my 5 yo son Charles and 3 year old Standard Poodle Ava. . . . Charles loves rockets, and Ava for some reason likes fireworks! She also believes that she is Charles mother as well . . . Anyway . . . Also laid out is how I hooked everything up. In particular I have a couple of questions:
1) Is the hankie in the right position?
2) I hooked the parachute up this way because I had read this approach works better to prevent in-air impact during ejection and descent . . . Is there anything here that is obviously bad/wrong?

Thanks Again
Mark Sanderson
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[Rex R]

one doesn't want the sections to hang from the chute even with each other, most commonly the forward section is set to hang higher than the booster/fin can. you want to keep the nylon shock cord(and chute) on the cooler side of the hankie. from here it would appear that you have things right. couple of things that may come in useful, 1) I normally get the next size larger 'hankie' and 2) I try to remember to mark the chute size on the chute(a sharpie works nicely). looks nice, have fun.
Rex

 

[markfsanderson]

one doesn't want the sections to hang from the chute even with each other, most commonly the forward section is set to hang higher than the booster/fin can. you want to keep the nylon shock cord(and chute) on the cooler side of the hankie. from here it would appear that you have things right. couple of things that may come in useful, 1) I normally get the next size larger 'hankie' and 2) I try to remember to mark the chute size on the chute(a sharpie works nicely). looks nice, have fun.
Rex

Rex,
Thanks! My hope is that the addition of dog barf should help give more protection to the chute and cord. That was recommended to me by the folks at the field . . .

Mark

PS: Thanks again for your time and help! Hopefully we'll get a couple of good flights from her.

 

[markfsanderson]

Greetings!
Yet another question . . . There seems to be two schools of thought between fixed and sliding Nomex hankie. Currently mine is at a fixed location on the kevlar part of the shock cord next to where its tied to the nylon portion. Should the hankie slide? On my set up, with the parachute on the other side of the nosecone from the body tube, no interference with the parachute is possible. Is there any advantage to a sliding Nomex Hankie?

Thanks!

Mark

 

[Nytrunner]

I'm in the fixed camp.

I want the nomex to stay where it is while the nose pulls the chute out of it into the airstream.

 

[markfsanderson]

I should close this thread out by stating that I flew my DX3 twice, but recovered it only once! Overpowered for the field, it floated into the trees across a bayou and caught the trees about. Sigh!

 

[kjkcolorado]

RIP..... Reading your very first post I know one of your goals was repeat recovery success. Well, as far as the ‘mechanicals’ it looks like you are on the right track. However, you admitted overpowering your field. Not unlike my golf swing at times - mechanically sound, but sometimes the decision to try a certain shot/club is the mistake.

OK, lesson learned. Go grab your next build and enjoy the roller coaster ride of rocketry! Good luck with your 4” Madcow DX3!

 

[markfsanderson]

RIP..... Reading your very first post I know one of your goals was repeat recovery success. Well, as far as the ‘mechanicals’ it looks like you are on the right track. However, you admitted overpowering your field. Not unlike my golf swing at times - mechanically sound, but sometimes the decision to try a certain shot/club is the mistake.

OK, lesson learned. Go grab your next build and enjoy the roller coaster ride of rocketry! Good luck with your 4” Madcow DX3!

I learned a lot from that rocket . . . The LOC Goblin is just about built . . . will be a bit more cautious about when I fly it - haha!

mark