Ballistic Approach Recovery

cerving said:

What's to keep the relatively heavy motor mount from being pulled out of the back by deceleration after burnout? Sounds like it may pull out the drogue immediately after burnout, especially on a J with a light rocket...

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The mount has no contact with outside air... only the airfame. The burnout drag is only sustained by the airframe, thus causing the inner piston stack (mount, sleeve, e-bay) to get crushed UPWARD, not downward.

Sorry for all the late replies... Aera66 informed me that there was a 1 week long convo about my rocket on this forum, without my knowledge
I figure I'd give everyone a quick reply. I'm glad she stirred so much talk!

To sum it up
1) Yes it worked
2) No, no heavy duty shock cords in fact half the cords are elastic nylon dual strand (2x1/2in).
3) Yes it drifted minimally, less than everyone else who flew 2800ft+ like this one
4) No the mount has no danger of popping out after burnout
5) No, the shearpins won't break during drogue. There's three bloody 4-40 pins on a 3in airframe I don't know what more I could put. More than that would require 5gr of powder! lol
6) She's a two-shot rearward canon
7) She flies awesome.

Don't be afraid to try one for yourselves... but before - I will try to write up documentation on this to help everyone out with it.
It's picky with how it's assembled and the e-bay alignment uses 3 reference points.

The only real issue is my RSO hates the rocket because if a cord breaks between main & upper airframe, she goes ballistic for real; but main only comes at 500ft. I'll keep that from happening and get some trust (not just thrust hehehe) built up LOL

Last but not least yeah I own an army of stereo-3D cams and I just can't go back. I relive my s**t with depth perception, end of discussion

PS: If you pull the 54mm mount you can swap it with a 75mm motor casing with a hook on top. Hello minimum diameter without modifications!

budwheizzah said:

PS: If you pull the 54mm mount you can swap it with a 75mm motor casing with a hook on top. Hello minimum diameter without modifications!

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Funny you mention this, this why I was so interested in this! Except with a 54mm motor...

budwheizzah said:

Touché but also too late. I thought of exactly that... it would just make assembly simpler by eliminating the drogue sleeve and the weight that goes with it. I thought of this AFTER building this one. LOL
Still, the sleeve isn't a problem and has proven to help keep the main airframe clean of the blast soot, acting as a liner at drogue deploy.

Note though just having a part of the mount exposed to the outside of the airframe could be subject to that dreaded burnout drag. A counter-solution would be to have shear pins on the motor mount as well and just use the same 3gr of powder as the main deploy. Given the mount would already rest on the airframe, the shearpin's vulnerability would be only unidirectional, only being breakable if the mount is pushed rearward violently and wouldn't ever risk snapping from the thrust. This is a lot like the current e-bay piston. The shearpins on it can only break with the e-bay going down since the bay pushes against a fixed thrust ring and can't go further upward, so those pins are safe from thrust and drogue deployment.

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Unless you have actual fins attached to the motor mount, a tiny 1/4-1/2" ring exposed won't be enough to drag separate, especially when the super-draggy (by comparison) fins are mounted on the airframe.

CarVac said:

Unless you have actual fins attached to the motor mount, a tiny 1/4-1/2" ring exposed won't be enough to drag separate, especially when the super-draggy (by comparison) fins are mounted on the airframe.

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That's what I was hoping.
The design can indeed be adapted for this. However upon component inspection yesterday I noticed the sleeve is serving an interesting role: It protects the lower segment from gunpowder residue (and a lot of it) and thus allows the e-bay to slide out smoothly at main deploy.
Without the sleeve the e-bay will need to plow through the smudge left behind by the drogue deploy. Maybe I'll go with both MMT outer retention & drogue sleeve. Ha!

troj said:

Though, if I remember correctly, in the video he says something about a thrust ring up at the top.
-Kevin

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I read the comments and wonder if people even listened to the first video
Thanks for doing so... keyword: thrust ring.... all this talk about weak-link shearpins is funny.

Area66 said:

a CTI 867-J244 the rocket is a 3" dia, 71" long and weight 2,60 kg. He will use a droge of 24" and a main of 40"

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Actually it wound up being a 683J250... she weighed "dry" @2.85kg, "wet" @3.65kg.
It's 75in long and even had a GPS tracker in the front that wasn't really needed. Perhaps for higher flights.
Drogue was a 30in and main a 42in.
Apogee was 2820 and descent was 50km/h for drogue and 25km/h for main.
I forget her top speed I was too busy focusing on the descent data I'll report that later.

budwheizzah said:

5) No, the shearpins won't break during drogue. There's three bloody 4-40 pins on a 3in airframe I don't know what more I could put. More than that would require 5gr of powder! lol

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It didn't happen this time, but if three nylon shear pins are the only thing holding your av-bay in after drogue deployment, chances are it will happen sometime. Three 4-40 shear pins only hold a peak load of ~115 lbs. During a drogue or main deployment event you can often see 25 to 30 gee applied to the components at separation, maybe more depending on the exact sequencing and rocket trajectory. That means that any one piece, either the ejected motor assembly, or the balance of the rocket, should be less than 3.83lbs. Given that the rocket weighs ~8 lbs likely one of the components weighs more than the limit above (unless I misunderstood the video and you were breaking the rocket into three pieces at the top instead of two) and thus will likely exceed the 115 lbs holding force during a recovery event sometime in the future.

I'm also having a tough time understanding your exclamation regarding 5g of powder. Your 3" diameter rocket has about 7 sq. in. of surface area to push against, thus you need to develop a pressure of just over 16 psi (115 lbs/7sq. in.) to break the pins. To be safe this should be about 50% extra or 24 psi. Even if your main compartment was rather large with 18" of free space, you would only need 1.6g to develop the 24 psi needed. If you added another 4-40 shear pin you would still only need a little over 2g of powder to achieve a reliable event.

So what you're saying is a fourth shear pin is an option if the system proves unreliable?

I'm thinking of my big rocket (6in diam, 6.5ft tall, 9kg on a 6 grain 54mm) which used three shearpins to avoid the main segment from coming loose at drogue ejection. The nose alone was 3.5kg. That rocket didn't have elastic nylons, nor masking tape to slow the hit, and I never had shearpins come loose after ten successful flights. If anything Ballistic Approach is as reliable as my old rocket (the old rocket was traditional by all means) as the shearpins sustain the same type of force (prevent premature separation or ejection) as any normal coupler rocket. Given she's a light 2.8kg dry and she's got elastics, it's actually more reliable than your traditional build. I must protect the elastic with all my might; that's my responsibility and yes if you're not careful elastic can be a rocket killer.

Remains to see at what speed the 115lbs threshold will be reached. Since it's just a risk of popping the main early (and not a risk of going ballistic or losing everything) I might just push until I reach it and I'll let you know.

So far I haven't let her freefall without the drogue. I'll start with 1s and work my way up in 1s increments.

dixontj93060 said:

I'm also having a tough time understanding your exclamation regarding 5g of powder.

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We're using high powerformance Pyrodex a lot in this province lately.
4FG is hard to come by. Take all the numbers you know with 4FG and multiply it by 1.5 in terms of requirements.
This stuff is somewhere between 4FG and 3FG. It's great but one must put a little more than expected.

I had 2gr in the lower and 3gr in the upper.

Also keep in mind I calculate the upper charge by considering the length of both the drogue and main compartments since the e-bay should travel out clearing through BOTH areas.
All that volume needs to be in the equation. So it's like discharging in 31.5in long of 3in airframe plus three shearpins.
The 2gr in the drogue is overkill. So sue me, I like to hear a bang. lol

budwheizzah said:

We're using high powerformance Pyrodex a lot in this province lately.
4FG is hard to come by. Take all the numbers you know with 4FG and multiply it by 1.5 in terms of requirements.
This stuff is somewhere between 4FG and 3FG. It's great but one must put a little more than expected.

I had 2gr in the lower and 3gr in the upper.

Also keep in mind I calculate the upper charge by considering the length of both the drogue and main compartments since the e-bay should travel out clearing through BOTH areas.
All that volume needs to be in the equation. So it's like discharging in 31.5in long of 3in airframe plus three shearpins.
The 2gr in the drogue is overkill. So sue me, I like to hear a bang. lol

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I can understand the extra with the Pyrodex. You might try Hodgdon Triple 7 (if available where you are) as it is a BP substitute that performs closer to BP vs Pyrodex.

OK, my assumption was different... On the main deploy I was assuming that you only needed to break the pins and that the drogue would finish the job of pulling out the main (not that you would have to assure that the bay completely separated from the aft airframe by the charge alone).

The main *should* be pulled by the drogue but I keep thinking what if it doesn't, hence why I consider the whole entire chamber.
As long as it doesn't blow the frame to smithereens, why not play it safe that way, I thought.

The switch ports acting as pressure relief holes must have helped at not breaking the air frame. If not, at least the phenomenon looks cool, like the exhausts on the sides of NASCAR vehicles.

budwheizzah said:

The main *should* be pulled by the drogue but I keep thinking what if it doesn't, hence why I consider the whole entire chamber.
As long as it doesn't blow the frame to smithereens, why not play it safe that way, I thought.

The switch ports acting as pressure relief holes must have helped at not breaking the air frame. If not, at least the phenomenon looks cool, like the exhausts on the sides of NASCAR vehicles.

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Actually I agree and I applaud your success, all I was saying originally is that you may be closer to the edge of working than you think and it may behoove you to look at upping the margin a bit whether it is adding an additional shear pin or by other means.

Allright coming soon (likely this weekend) flights #2 and 3 of Ballistic Approach 354. This is a keystone moment since I'll push her just enough to know if building a 4inch upscale will be worth it.

First flight is on a 54mm K160 4 grain longburn. She's just a tad over 4 kilos at launch and that motor can handle 5kg+ for its first three seconds, and RockSim seems to give it enough speed to clear the burn without wanting to "fly backwards". For this flight she'll have the original plastic nose cone.

Next flight I'm going 54mm K400 4 grain Green3. This should push the speed higher and give me an idea of vehicle integrity and increased performance behavior. This time she'll be equipped with her slightly longer fiberglass nose cone with aluminum tip (This will become much more relevant next year). Of course this pushes her weight up closer to 5 kilos but falls short that of about 300gr.

Despite both flights going below 5kg she does have full redundancy... makes her a safe flier.

Also the recovery is changed a bit... the drogue is down to 24in from 30in. The main is up to 48in from 42in (if available, otherwise I might try fitting a 54) and the apogee delay goes from 0s to 2s, with a 3s backup. The delay is to allow a slight nosedive before drogue, as I'd like to see this design being capable of handling.

The rocket has had a 6 inch extension installed between the nose and the old payload bay. This had to be done because the old bay didn't let GPS signals in, being covered in carbon fiber. The new extension is fiberglass covered LOC airframe. It should be plenty for the weekend since she's not expected to bust 800km/h.

My son will take some pics, well the time we will see it.

Also I'm going to try to get her one rear-looking camera and one forward looking camera this time.
She will see herself looking at you who will be looking back at her.

No 3D though, not this year. 3in airframe is a PAIN to fit my stereoscopic rig on.
I'll bring the stereo ground cams yes, but no onboard awesomeness.

It's a bummer for 2013 given that in 2012, every single event the club made I shot entirely in 3D INCLUDING my onboard video.
If some have the equipment to watch: https://www.youtube.com/watch?v=1wTFh6oYgq0

I'll probably be 3D-onboard-ready next year once more; The Ballistic Approach descent is so steady it should give for an exciting stereoscopic show.