Big Daddy Dart: What now?

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ActingLikeAKid

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I did a stupid with a Big Daddy. It had been years since I'd flown this one. Loaded it up with a d12-3. Launched perfectly, arced over, and plowed into the dirt. Looks quite repairable; the NC just pushed into the body tube a little - maybe 3/8". I realized afterwards that (I think) the problem was that I didn't use a spacer on it - the mmt is designed to be long IF you're using an E, but if you want to use the (shorter) D motor, you just need a spacer. Motor slid up in the mmt on ignition, then instead of the charge blowing the nose off, it just made the motor slide back. Stupid mistake and lesson learned.

So here's the question. I haven't done a thorough postmortem on it yet, but I think I have two options:
1. Trim off as little body tube as possible. Probably repaint. Go on with my life.
2. Buy a coupler and a section of 3" body tube and make a Long Daddy (see mockup below). I haven't simmed it yet but I'm guessing that it'll probably be fine.

Interested in thoughts and opinions here.

Also: Did a couple of LPR launches in the past week and wow, the bug has bitten me again. Time to dust some stuff off and get flying again!!


xldaddy.jpg
 
Bummer. If the motor was still retained by the hook, I would think there would still be sufficient pressure to pop off the NC. But, there seems to be a problem with these lawn darting due to the long slope in the NC shoulder venting the charge before separation (that's the theory anyways). Many of us cut off the base of the NC and install a ply bulkhead. This seems to make for more successful separations.

If you trim off the minimal amount of tube, cut the nosecone shoulder off and do a bulkhead, you'll still end up with more room for the laundry than before. That'd be what I would do.
 
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I would suggest shortening the body and get on with it. On my Big Daddy I cut that end of the nose cone off and glued a piece of plywood inside the end to connect to, now I have more room for recovery device and no taper to worry about.
Mine might be older, I think it only has a D mount. But I also have an Executioner with an E mount and I did the same thing- put in a D motor without the spacer. It burned up part of the rear end of the motor mount tube. I added some pieces of tube to rebuild the rear of it and restore its strength.
Now come to think of it, the Executioner has fins and nose similar to the Big Daddy but is much longer so the stretch Big Daddy might be a good option. I'm starting to like the looks of that one.
Here is the modification I did to my Big Daddy nose cone.IMG_4818b.jpg
 
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Made that mistake once. Didn’t cause any issues other than a little charring on the bottom of the motor tube. Ejection worked fine.

The issue was more than Likely the slope on the nose cone.

Cut the body tube down and cut the slope off the cone then let it rip.
 
My leading theory as to how this happens is a little more involved than "just the slope". While the slope is a *MAJOR* contributor, the instructions, and aerodynamic forces are also involved.

The BD is a short high drag rocket attached to a pretty aerodynamic nosecone. And while Estes says to adjust the fit of the nosecone, they don't give clear instructions on how to determine if the NC is too loose. The result is that when launching it, the high drag rocket falls away from the nosecone in the coast phase (drag separates), exposing the slope. The slope then acts as a vent for the ejection charge, which follows the path of least resistance, and fails to separate the nosecone from the rocket completely, and thus the rocket comes in as a lawn dart. I suspect that wind conditions also play a role in this... perhaps "cocking" the rocket (relative to the NC), and thus when the ejection charge blows, the NC is just a little bit stuck which then exacerbates the problem.

If the instructions said that the fully loaded, flight ready, rocket needs to be able to be picked up by the nosecone and not separate, and to adjust the fit of it with layers of tape until it does, and make this clearer than the small "adjust fit" instructions currently found, the problem would likely be solved, presuming that the builder/flier sees the instructions and follows them.

1653881837136.png
Here's a video from Back_at_it that shows a lawn dart, and there's wind involved...
Watch the video below at the 22:10 mark. Perfect example of the ejection not fully pushing the nosecone out



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To add what K'Tesh and other have said in posts above.
Drag separation is a possibility but so is air trapped inside the large volume BT expanding and pushing the nose cone out. It is recommended on large volume BTs to put a vent hole in the tube to allow pressure equalization.

There have been many threads about Big Bertha's and other large tube rockets that lawn dart. Typically the reason stated is not enough ejection charge for the tube size.
Other have mentioned modifying the Nose cone base to remove the beveled section help eliminate issues.
If the nose base mod helps then the idea the nose cone comes partly off exposing an opening from the bevel seems reasonable. But question is why does nose come partly off?
Drag separation is possible but I think it may be the internal pressure. Reasoning is if it is drag then the nose is more likely to come all the way off but that is not seen. Internal pressure will push on the nose until the bevel is exposed relieving the pressure.

Has anyone flying Big Daddy sized rockets put a vent in the BT and then have success deploying chute?

Of course, proper fit of the nose into the BT is very important. This also should be re-checked at the field when prepping for flight since temperature and humidity can charge the cardboard tube and nose cone dimensions.
 
I seriously doubt that in the few hundred feet that the BD can achieve on the recommended engines that expanding gasses are a factor in these lawndarts. If we were pushing a thousand feet I still think it'd be insufficient to even be a problem.

In the video I linked to, you can hear the wind... I suspect that wind really increases the odds of this happening. The rocket drag separates from the nosecone, but if conditions are right, the wind can jam it together just beyond the ramp, leaving enough of a gap to allow the force of the ejection to vent. Perhaps if the user packs the motor tube with enough wadding (or dog barf), that may be enough to knock it loose, but people tend to be conservative of wadding (that's not cheap stuff anymore), and the gasses just blow past it on their way out the vent.
 
Just remember that the Big Daddy 3" tube is not the same as LOC 3" tube.
Not sure who is cheapest, I bought mine from Balsa Machining.
 
On my Big Daddy I cut that end of the nose cone off and glued a piece of plywood inside the end to connect to, now I have more room for recovery device and no taper to worry about.
What glue or epoxy did you use? I've been planning to mod a Big Daddy cone for a scratch build I'm working on and wondered if I was going to have to put stakes through the cone walls in order to anchor epoxy like I recently did to an NC-80K that seemed to fail an epoxy test (it was a poorly designed test, but I thought it best to err on the safe side).
 
My BD's that are upgraded to 29mm and 38mm both have vent holes in the BT. Both have flown on AT 29/100 G motors and both have worked flawlessly. I have the modded NC as well (as one should!) and I have the NC shoulder taped so that its a rather tight fit. Bare in mind though, I have a captive motor retainer, not a hook, so ALL the energy in the charge is pushing into the BT and there is no chance of blowing the motor out. Either the laundry is coming out, or I just flew a skyrocket. No in-between.

I dumped the entire AT BP charge in as well.....it sounded like a 410 going off from 2100' up. 😆 😆 😆 :haironfire: :haironfire: :bravo: :bravo:
 
What glue or epoxy did you use? I've been planning to mod a Big Daddy cone for a scratch build I'm working on and wondered if I was going to have to put stakes through the cone walls in order to anchor epoxy like I recently did to an NC-80K that seemed to fail an epoxy test (it was a poorly designed test, but I thought it best to err on the safe side).


This is what I did.

I wanted the flexibility to still take the NC apart. As well, I did not trust epoxy adhering to polypropylene......it doesn't all that well.

 
What glue or epoxy did you use? I've been planning to mod a Big Daddy cone for a scratch build I'm working on and wondered if I was going to have to put stakes through the cone walls in order to anchor epoxy like I recently did to an NC-80K that seemed to fail an epoxy test (it was a poorly designed test, but I thought it best to err on the safe side).
I used ordinary Bob Smith 30 minute epoxy.
The inside diameter of the nose cone is larger at the base of the cone part, above the shoulder, than it is at the shoulder. I cut a round piece of aircraft plywood and slowly sanded down the outside diameter and periodically test fit it in the nose cone- stick it in there and rotate it to see if it fit and would bear against that slight change in inside diameter. Then I roughed up the inside with sandpaper, put in the epoxy, and stuck the disk in there. I had looped a piece of wire through 2 holes in the disk to give me something to hold on to and something to tie a shock cord to.
I don't know if the epoxy is holding a little or holding a lot, but the disk is also an interference fit so it couldn't pull straight out anyway.
 
This is what I did.

I wanted the flexibility to still take the NC apart. As well, I did not trust epoxy adhering to polypropylene......it doesn't all that well.


The Estes nosecone is high impact polystyrene... They're only a few nosecone designs that were ever made out of polypropylene in the Estes lineup, and as far as I know, they're all for BT-56 based kits, of which, this is not one of them.
 
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