Big Daddy became a Lawn Dart

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sheepdog

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Two weeks ago my 10 year old ESTES Big Daddy became a lawn dart after a failed ejection. So I kept Calm and Launched on!!!!

I just finished my "New Big Bad Bumble Bee " ESTES Big Daddy This baby's stinger will be a F32-8T can not wait.....

Bumble Bee.jpg
 
Mine did, as well. NC too tight. Perhaps a slightly higher ejection charge than what comes in an E9-4 is required.
 
Mine did, as well. NC too tight. Perhaps a slightly higher ejection charge than what comes in an E9-4 is required.

General consensus is that sloping section for the attachment point of the shockcord/parachute is allowing the gasses to vent before the nosecone blows clear.
 
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I have gone through 3 Big Daddys. I think the BP ejection charge in the E class motors is not suited to the large volume of the BT. I had some success adding 1g of BP on an E-12 motor. The NC was quite loose as in if you picked it up by the NC it would dislodge. Yet I watched a tiny puff of smoke near apogee and a ballistic return with no chute deployment 3 times. FWIW, I built a Mini Magg and named it Bigger Daddy. It flies very well on I motors...
 
Interesting, My Big Daddy that I flew for about 10 years also just lawn darted and was completely destroyed about 2 weeks ago. Seems like a weak or failed ejection charge from the D12-3.
 
Add mine to the list. Flew 3 times on E9-4 and all three had failed recoveries. 1 ejected nose cone but no chute sandwiched by 2 lawn darts. I must say though, I build one heck of a rocket because it is still in flying condition.... Save for the unsafe side of that coin. I will put a larger motor in and see what happens.
 
There have been several threads on the Lawn Dart ability of the Big Daddy and the consensus so far has been that weak ejection charges/larger volume allow the long sloping portion of the NC shoulder to vent the gases before the NC is fully ejected. One fix is to remove the sloped section entirely and install a bulkhead with a shock cord attachment point in the NC.
 
There have been several threads on the Lawn Dart ability of the Big Daddy and the consensus so far has been that weak ejection charges/larger volume allow the long sloping portion of the NC shoulder to vent the gases before the NC is fully ejected. One fix is to remove the sloped section entirely and install a bulkhead with a shock cord attachment point in the NC.

This sounds interesting....Will be checking out the Bee tonight, considering my next launch I will be using the 24MM F32-8T this sounds like an excellent option....Someone else mentioned in the string they just Lawn Darted their Big
Daddy also. Maybe the Rocket God's had something to do with it.....Every now then they do require "sacrifices" at our expense.

Thanks
 
I fly mine exclusively on CTI 24mm, it has 4oz of lead in the nose, and I cut the bottom of the NC off and epoxied a bulkhead in creating more space for the chute/nomex blanket. It has 12 flights on it so far including 7 on the F240 Vmax, worst thing to happen to it so far is a tangled chute.
 
If you are into mods, piston ejection might solve this problem. I could easily see getting a Leviathan coupler and cutting a bulkhead, running the shock cord up the middle, and voila!
 
Fortunately mine survived its maiden voyage with no lawn darting.

I've been pondering the problem though, and a few observations:
1) The issue seems to be limited to the Big Daddy, and to a lesser extent the Leviathan. However, the Estes 3" is hardly the only sloped shoulder nose cone. If nothing else, every other PSII kit has sloped shoulders. I compared it to my Ventris transition, and that has an even larger sloped shoulder (relative to overall shoulder length), yet deployment seems very reliable (knock on wood). The MDRM has a bigger diameter, but the sloped area is shorter/smaller relative to overall size, and it seems to deploy reliably (knock on more wood).
2) The pressurized volume of the Big Daddy is large for an LPR bird, but it's not that big. In fact, once you get the nose cone fully inserted, there's only a few inches of length between the back of the shoulder and the front CR. I'd imagine there are several 24mm Estes rockets with the same or larger volumes where we don't hear about failure to separate unusually often (the Mean Machine is one extreme example).
3) One thing that is unique is the "stubby" aspect ratio - the pressurized volume is very short compared to its diameter.
4) I also noticed that, due to the length of the shoulder and the width of the tube, once you get past the non-sloped section it's fairly easy to tilt the nose cone back and forth, potentially binding it on the airframe. In the smaller diameter of the Ventris, you can tilt it a bit but it doesn't bind as hard.

So with all that, my theory is as follows:
Ejection is not an instantaneous event. Basically, the gas produced by the burning BP pressurizes the airframe until the force on the base of the nose cone overcomes the friction (and any aero forces, plus the cone's own inertia) holding the cone onto the airframe. At that point the cone starts to move, accelerating until the gas vents out and/or the cone is free. In a perfect world, the cone pops off with enough momentum that it pulls the laundry out behind it.

On the Big Daddy, the short airframe volume and long, sloped shoulder work against you in a couple ways. First, while the short volume helps get the pressure high, it also hurts you because as the cone begins to move, the pressure drops (because the available volume expands) more quickly. Also, once you pass the shoulder slope, you'll vent pressure very quickly because the vent area is large compared to the pressurized volume (on a longer rocket, there's more pressurized volume so the pressure drop won't be as fast). Also, the shoulder slope means that the forces on the base of the cone aren't quite symmetric - it's going to tend to rotate. As I mentioned previously, the Big Daddy cone seems easier to bind with a little rotation.

So basically, I think what's going on is that the cone starts moving quickly, but starts to vent/lose pressure before it can get enough forward momentum to overcome any binding friction on the last part of the shoulder and pull out the recovery system.

My ideas for a fix:
1) The somewhat drastic but probably effective approach of hacking off the whole sloped bit ant replacing it with a bulkplate and eye bolt. Has the added advantage of increasing your reccovery volume. You'd need to make sure you have sufficient shoulder to keep it on straight.
2) If you don't want to do that, make sure the nose cone is pretty tight at the unsloped shoulder, but fairly loose in the sloped part. That way, the pressure builds higher before the cone starts to move, yielding a bit more oomph, and the tail of the shoulder can still slide out freely.
3) Add weight to the nose. While maybe a bit counter intuitive, the friction forces are going to be a lot bigger than the inertia forces from the cone. So adding weight probably won't decrease your ejection speed much, but it will increase the momentum the cone has to pull out itself and the chute.
 
I had over ten flights on a Big Daddy "Der Grosser Vatti" until I launched into too much wind on and E9 4. It weather cocked and was going nose down when it ejected. All that wind pressure traveling fast on the nose cone is yet another contributing factor to holding the cone in. I cut off the fin can, fashioned a coupler and used it as a first stage to my other beat up and old Big Daddy. It didn't work very well, twice staging at about 45 degrees on a D12-0 to D12 3. The sustainer then had the same problem again, and after two tries it was even more beat up and the recovery walks were way too long. So it is retired. Not enough oomph from the D12 0 even in calm conditions.
 
I fly mine exclusively on CTI 24mm, it has 4oz of lead in the nose, and I cut the bottom of the NC off and epoxied a bulkhead in creating more space for the chute/nomex blanket. It has 12 flights on it so far including 7 on the F240 Vmax, worst thing to happen to it so far is a tangled chute.
THis is the second suggestion for cutting off the slope section of the Nose cone and expoxy a bulkhead in it's place. This is the route I believe I will be taking on my maiden launch.

As always this site continues to solve issues we all face as we advance through this hobby.

Thanks fellow rocketeers.
 
If you simply cut off the sloped portion and add a bulkhead, you will not have enough shoulder. I had to deal with that while planning to outfit my Leviathan for a cable cutter. I ended up purchasing a Balsa Machining nose cone -- same diameter, slightly longer ogive, less of a sloped portion.

I'll try to find the picture that someone so kindly posted for me.
 
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