Ballistic Approach Recovery

Derek said:

I keep trying to come up with an eletro-mechanical solution to ejecting parachutes too. It seems there has to be a more elegant way (but certainly not as cool) to deploy a chute than using an explosive.

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Energy density, reliability, and robustness are very difficult problems to overcome. Solenoids need a lot of drive power, and grow bulky. Screw drives are slow. Springs can be bulky.

CO2 canister with servo valve? There was an Aussie who had a *very* elegant solution, but for the life of me I can't think of his name. It was a work of art.

Edward

Derek said:

It seems there has to be a more elegant way (but certainly not as cool) to deploy a chute than using an explosive.

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Looks like only few peoples try to innovate, peoples prefer fallow what others have done before. The Dual Deployment was a great innovation, but we have to continue to look at new things. For now I'm concentrating on my certification, after you gone see me build experimental rocket, not experimental in the way you have to go to a Tripoli EX events, but experimental in the way that I'm gone build them to try thing ( like as example; 4 similar rockets with 4 different type of fins ) . No funny color, bare primer.

CarVac said:

Energy density, reliability, and robustness are very difficult problems to overcome. Solenoids need a lot of drive power, and grow bulky. Screw drives are slow. Springs can be bulky.

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I have a stall motor system that use only 15 mA

AlphaHybrids said:

CO2 canister with servo valve? There was an Aussie who had a *very* elegant solution, but for the life of me I can't think of his name. It was a work of art.

Edward

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I've thought about co2 or compressed air and a valve.

Area66 said:

Looks like only few peoples try to innovate, peoples prefer fallow what others have done before. The Dual Deployment was a great innovation, but we have to continue to look at new things.

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Amen to that. Good luck with your project, I'm interested to see how it goes.

AlphaHybrids said:

CO2 canister with servo valve? There was an Aussie who had a *very* elegant solution, but for the life of me I can't think of his name. It was a work of art.

Edward

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Weight and power requirements were the issues, when I looked into it a bit several years ago

Solve that, make it fit in a three inch airframe and make it reliable, and I'm VERY interested

AlphaHybrids said:

CO2 canister with servo valve? There was an Aussie who had a *very* elegant solution, but for the life of me I can't think of his name. It was a work of art.

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You are probably thinking about Troy Prideaux and his device:
https://www.ausrocketry.com/forum/viewtopic.php?f=9&t=2043&start=60


One day, I'd like to build a minimum diameter rocket with rear deployment and a serial setup for the main (e.g. with an ARRD). Something that bothers me with this idea, are the expected deployment pressures with long motors. A long motor displaces a lot of air, much more than a coupler that travels only 1-2 calibers. If the ejection charge is not big enough, the internal pressure might fall below ambient before the motor clears the rocket - potentially sucking it back in in extreme cases*). To counter this, a bigger ejection charge is required, but especially in a rocket with a small parachute compartment (compared to the motor size), this will result in a much higher peak pressure than we usually see in our rockets. Even if the airframe is able to handle this pressure (glass and carbon tubes shouldn't be bothered by, let's say, 200psi), the motor will be ejected rather energetically, which will stress the rest of the recovery system. I guess, one could use an ejection system that generates lots of volume at a rather low speed to counter this problem. A sequence of multiple charges, really coarse BP (maybe even an Estes motor) or a CO2 based system could do this.


Reinhard

*) I dimly recall a similar issue a fellow flier had with a piston based recovery system. With pistons, this problem is less pronounced because the parachute can often be successfully deployed even when the piston is not completely ejected initially.

On a side note: The military has more experience with this type of "late recovery".

Most versions of the B61 are equipped with a parachute retarder (currently a 24-ft (7.3 m) diameter nylon/Kevlar chute) to slow the weapon in its descent. This offers the aircraft a chance to escape the blast, or allows the weapon to survive impact with the ground in laydown mode. The B61 can be set for airburst, ground burst, or laydown detonation, and can be released at speeds up to Mach 2 and altitudes as low as 50 feet (15 m).

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Source: https://en.wikipedia.org/wiki/B61_nuclear_bomb#Design

Given the sounds our parachutes often make on late depolyments, I have to wonder how this thing sounds. :y:

Reinhard

troj said:

Weight and power requirements were the issues, when I looked into it a bit several years ago

Solve that, make it fit in a three inch airframe and make it reliable, and I'm VERY interested

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Give me a weight and length requirement and I'll be on it I'm guessing I could do 3 ounces CO2 for deployment, hardware all up for about 1.5 pounds, 9" long, 2" diameter. You would still use an e-match to initiate everything.

Edward

Yes, the deceleration is caused by drag. It is true that every part of the rocket will decelerate equally, but if there is nothing to retain the motor mount in the body tube the resultant force on the motor mount will pull it out of the body tube. It's the same problem that others have noted with the AV bay, the deceleration may potentially break the shear pins that hold it into the body tube, and that would cause a high-speed main deployment just after burnout. The key to making this work is to have some kind of retention in the motor mount that lets go at drogue deployment, the drogue AND the motor mount need to be ejected together.

CarVac said:

The deceleration after burnout is caused by drag pushing on the front of the airframe. The motor would absolutely love to keep moving forward, but the airframe has drag pushing back on it. The motor is trying to go forward quickly, but the airframe is trying to slow down, so they stay together.

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cerving said:

Yes, the deceleration is caused by drag. It is true that every part of the rocket will decelerate equally, but if there is nothing to retain the motor mount in the body tube the resultant force on the motor mount will pull it out of the body tube. It's the same problem that others have noted with the AV bay, the deceleration may potentially break the shear pins that hold it into the body tube, and that would cause a high-speed main deployment just after burnout. The key to making this work is to have some kind of retention in the motor mount that lets go at drogue deployment, the drogue AND the motor mount need to be ejected together.

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What is trying to pull the motor out? If there is no force trying to pull the motor out, then there's no reason it will come out. If you do rear-ejection with the fins attached to the motor, however, then you have drag force that operates on the motor and then it will attempt to drag-separate. However, in the case of this, you only need to withstand internal pressure.

There IS a force, it's the deceleration x the mass of the motor mount. With a J and a light rocket, it's going to be substantial. It's just like under-gluing the motor mount to the body tube of an LPR rocket (something we've all found out about when we go from an Estes E9 to an Aerotech F24 with the stock paper mounts), the force may be tranferred to the rest of the airframe, but if the connecting medium can't handle it you're going to have issues. In this case, there is nothing at all retaining the motor mount in the rearward direction, so when the force due to deceleration acts on it, its going to slide out the back.

CarVac said:

What is trying to pull the motor out? If there is no force trying to pull the motor out, then there's no reason it will come out. If you do rear-ejection with the fins attached to the motor, however, then you have drag force that operates on the motor and then it will attempt to drag-separate. However, in the case of this, you only need to withstand internal pressure.

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cerving said:

There IS a force, it's the deceleration x the mass of the motor mount. With a J and a light rocket, it's going to be substantial. It's just like under-gluing the motor mount to the body tube of an LPR rocket (something we've all found out about when we go from an Estes E9 to an Aerotech F24 with the stock paper mounts), the force may be tranferred to the rest of the airframe, but if the connecting medium can't handle it you're going to have issues. In this case, there is nothing at all retaining the motor mount in the rearward direction, so when the force due to deceleration acts on it, its going to slide out the back.

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The force backwards on the motor mount during the coast phase is an internal normal force, incapable of pushing it out. The normal force is simply what is keeping the motor from moving forward through the airframe. Draw a free-body diagram of the rocket as a whole and of the part.

I've flown a rear ejection rocket before, my Giga Drill Breaker. It was a loose fit: if I held the airframe (the cone), the motor mount would fall out easily. Every single flight, it stayed together until the motors' ejection charges went off. There could not have been anything pushing the motor mount out during the coast phase, or else it would have come out.

If a rocket were in a vacuum and is coasting starting at 98 m/s, each second it will slow down by 9.8 m/s due to gravity. However, since rockets are not launched in a vacuum, the rocket airframe tries to slow down more than that due to aerodynamic drag. There is no aerodynamic drag on the completely-internal motor mount, so it tries to decelerate at "only" 9.8 m/s^2 while the airframe is slowing harder. This difference in external forces on the two parts results in a normal force between them but it is only able to keep their accelerations the same: if their accelerations are the same, they do not separate.

You're right. The deceleration force from the body will push against the motor mount, keeping it in until the forces equalize somewhere around apogee. A little tape on the motor mount would still be a good idea, it will help the drogue ejection charge build up pressure.

CarVac said:

The force backwards on the motor mount during the coast phase is an internal normal force, incapable of pushing it out. The normal force is simply what is keeping the motor from moving forward through the airframe. Draw a free-body diagram of the rocket as a whole and of the part.

I've flown a rear ejection rocket before, my Giga Drill Breaker. It was a loose fit: if I held the airframe (the cone), the motor mount would fall out easily. Every single flight, it stayed together until the motors' ejection charges went off. There could not have been anything pushing the motor mount out during the coast phase, or else it would have come out.

If a rocket were in a vacuum and is coasting starting at 98 m/s, each second it will slow down by 9.8 m/s due to gravity. However, since rockets are not launched in a vacuum, the rocket airframe tries to slow down more than that due to aerodynamic drag. There is no aerodynamic drag on the completely-internal motor mount, so it tries to decelerate at "only" 9.8 m/s^2 while the airframe is slowing harder. This difference in external forces on the two parts results in a normal force between them but it is only able to keep their accelerations the same: if their accelerations are the same, they do not separate.

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It work, we drink champagne after ( real one from France ) and I will post pics later

Area66 said:

It work, we drink champagne after ( real one from France ) and I will post pics later

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Sweet!!!

here we go ...... Good work Chris...
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Way cool!!!

I know what I'm doing with my tender dezzender now! Glad to see people pushing the limits.

Also, great liftoff shot.

awseiger said:

Also, great liftoff shot.

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it's my 10 years old son who play with my camera for the first time

Area66 said:

here we go ...... Good work Chris...
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Awesome shots! :-D Thank your son again for capturing the moment!

I'm going to be posting the onboard & ground video soon. Gotta sort all my stuff out, was a huge weekend. Ballistic Approach made it but my other experimental didn't; and not because it was an experimental... rather the chute decided it was a cool time to go into a stall with tangled shroud lines. Ugh.

Pictures like this definitely cheer me up though

budwheizzah said:

Ballistic Approach made it but my other experimental didn't;

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you means this one ..... was a nice lift off


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Dude your kid is a pro photograph!!
Daaaaamn!

You know what's heartbreaking.... the bird never had a clue she was about to get partially killed. lol
How can she know her chute will screw her over after such a nice lift off?!

Man, I have to get to repairs, pronto. July 6-7 awaits.

A really cool frame from the B.A. 354 deployment tests. The switch access ports in the airframe (1/2in diam) which line up with the electronic bay piston's access & capture ports (1/4in diam) turn into pressure relief vents when the electronic bay is kicked out of the building. I expected a little stuff to come out of them, but during the tests they outright performed like those exhaust pipes on the sides of NASCAR vehicles!

https://www.youtube.com/watch?v=0hzVE7sSD6Q
Ballistic Approach 354 video finally ready! Relive everything from the deployment tests to the launch.

budwheizzah said:

Man, I have to get to repairs, pronto. July 6-7 awaits.

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can't wait too, but this time I have to bring the wife

fyrwrxz said:

Obviously believes passionately in 'rear deployment'. I hope he's using eleventeen bazillion pound rated kevlar straps. It could work!

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It worked with cords made of half tubular nylon and and dual-strand elastic nylon cord.
The dual-strand elastic nylon is to avoid any zipper, which would be terminal to the aircraft (if you get zipper where the mtor mount is supposed to enter, or where the fins are, rocket's dead for good.
With this she can probably take the drogue's sudden shock upwards of 100km/h nose down.

LW Bercini said:

Was I supposed to be wearing a pair of these for that video?

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It's much better with a true passive 3D monitor. You can change the 3D mode on YouTube or turn it off if you don't have the gear, but yes 90% of my footage is filmed stereoscopic.

Gary Byrum said:

I have some of those glasses and all they did was clean up the video. No 3D speshul effex......

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You may be stereoblind. It's true stereo-3D.
(Depth perception ain't a special effect, it's an illusion just like the color on your 2D screen)

PS: I'll admit red/blue anaglyph isn't too hot, though. It's easy to not notice the depth, even more the foreground objects (aka "popping").

T-Rex said:

I think he is going to have a long walk... He is relying on a couple shear pins to support the entire rocket while the drogue deploys. My feeble mind believes that he will shear the pins early and end up with apogee deployment of the main, especially if his delay is off....

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It was a really long 450ft walk from the pad she took off on. What a torturous walk.
Apogee was @2800ft.

CarVac said:

I don't know why the thrust isn't transferred to the rear of the airframe directly instead of through that "drogue tube". Sounds like a recipe for tangling.

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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.