Nosecone AV Bays... Pros & Cons

[K'Tesh]

I'm building three 4" diameter Binder Design kits, including an Excel Dual Deploy... However, I'm looking to build it with a baffle located at the normal AV bay location, and I want a redundancy for the ejection charge. This poses a problem... If the baffle occupies the space that the AV bay normally occupies, where does the electronics go? My solution is an AV bay in the nosecone. I consulted the book (Mark Canepa's "Modern-High Power Rocketry 2" (published 2005)), but the blurb is small, and not very encouraging.

Altimeters can even be mounted in the nose cone, as seen in the middle photo of Tripoli member Richard King's rocket, which contained a blacksky Altacc mounted directly to the inside of the cone. Be aware, however, that turbulent air flow near the tip of the rocket, or near the fins, can inadvertently trigger the altimeter early

I feel this is a tad out of date, as it was published in 2005, and here we are 13 years later. But that warning sounds timeless.

My nosecone is the standard Binder Design 16" long 4" diameter N/C. My electronics have yet to be chosen, but a pair of JLCRs is planned for the actual deployment of the main.

Honestly, I wish I could figure a baffle/AV bay unit, but that sounds fraught with potential problems.

Any suggestions? Build links?

Thanks!
Jim

 

[OverTheTop]

I have the breathers for the NC avionics (TeleMega) located an inch or so below the NC curve on my Apache and Velociraptor (4" payload bay version). The breather holes also admit the RBF pins for powering and arming the apogee events (remove NC). No problems with early deployment, and has flown transonic mostly and supersonic (M1.4) no issues.
https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019

 

[SteveThatcher]

not that familiar with the Binder Design Rockets, but if the baffle is for a fail-safe, then it seems like the electronics bay could sit on top of the baffle. You would need shock cords below and above the bay of course. If the bay fails to deploy a chute, then the bay acts like a piston to push the chute out from the ejection charge of the motor. Four inch rocket would allow for a very "short" bay. Just an idea...

 

[Titan II]

https://www.google.com/search?q=ven...9j69i57j0l4.2680j0j4&sourceid=chrome&ie=UTF-8

https://www.rocketryforum.com/threads/show-us-your-hed.144744/#post-1766884

 

[MikeyDSlagle]

If you have an ejection charge coming from the nose cone you are still going to need protection from the ejection charge such as a blanket and/or dog barf; so why waste time and space with a baffle if you have to protect the chute anyway? Unless you want to put a baffle in the nose cone as well...interesting idea and doable though I have never done it. I have built two rockets with baffles and have since gotten away from baffles and just use nomex and dog barf.

For a nose cone bay, use a 1" or so vent band to move the sampling ports back from the curves on the nose cone a bit. You could go with a longer vent band but it reduces the amount of shoulder that holds the nose cone to the body tube. Or just put your ports through the body tube itself, as far from the nose cone as possible, just pin the nose cone to keep if from spinning and covering the ports. I don't think that would be an issue, but you never know.

I build nose cone bays in everything. Some for tracking, some for deployment, some for both. I have one for my 4" Cowabunga that uses a sink drain pipe and two centering rings, super simple; the sled itself can be made from plywood like my original or I have a file to have one 3d printed. These designs do not incorporate a vent band though with some imagination and modifying, you can use one no problem. The one for my Tyrannosaur is a bit more complicated but allows me to add tracking far enough up that it is away from the threaded rod; it uses a lot more parts and pieces. I have detailed drawings for the Tyrannosaur bay if you have access to a CNC or feel like cutting the parts yourself. Both of these use a RRC2+ and LiPo battery. The Tyrannosaur uses a Missileworks screw switch and the Cowabunga uses a micro switch with a screw holding the button in.

For my Ethos (still working on it) I am using one of MAC's nose cone bays. It is the same principle as my Cowabunga design. My sled is big enough to allow for redundant altimeters and an Eggfinder. I am only using one altimeter though.

You could do a piston type A/V bay as Steve mentioned. I have been tossing around that idea myself. I wouldn't use a short coupler though as it may get cocked a bit and stick. In order for it to benefit from the baffle you would have to have the ejection charge pointing up toward the nose cone. It would have to blow the nose cone off and rely on the nose cone to pull out the piston/bay and laundry. If you had it firing down, you would have to protect the chute.

You could make a removable baffle and incorporate an A/V bay into it and have the charge firing down into the booster section. Would be a neat challenge. Binder 4" couplers will easily fit three 38mm MMTs. Two would be used for a simple tube baffle while the other could house the altimeter. You would basically be building an A/V bay into a 38mm body tube, nothing to it right. Your sampling ports would need to all be on one side obviously. Alternatively, you could use two tubes for the baffle but have them pushed to one side leaving nearly half the coupler space for the altimeter. I could offer some sketches.

Or make a side access A/V bay below the baffle.

 

[K'Tesh]

Thanks for all the replies!

If you have an ejection charge coming from the nose cone you are still going to need protection from the ejection charge such as a blanket and/or dog barf; so why waste time and space with a baffle if you have to protect the chute anyway? Unless you want to put a baffle in the nose cone as well...interesting idea and doable though I have never done it. I have built two rockets with baffles and have since gotten away from baffles and just use nomex and dog barf.

You could make a removable baffle and incorporate an A/V bay into it and have the charge firing down into the booster section. Would be a neat challenge. Binder 4" couplers will easily fit three 38mm MMTs. Two would be used for a simple tube baffle while the other could house the altimeter. You would basically be building an A/V bay into a 38mm body tube, nothing to it right. Your sampling ports would need to all be on one side obviously. Alternatively, you could use two tubes for the baffle but have them pushed to one side leaving nearly half the coupler space for the altimeter. I could offer some sketches.

Mikey, You have made several important points... Now I have this idea for a removable AV Bay that is incorporated into the baffle. Locked into place by a key to keep the bay properly oriented to allow access to the arming switch and held into place (from the top) by a something like a motor retainer. At the bottom the charge well could be fired downwards into the fin can. Then again if I could find a reliable CO2 system that would eliminate the need for dog barf or a blanket.

 

[MikeyDSlagle]

Something else to think about is how you will hold the battle bay to the booster. It is going to be taking the recovery forces and I wouldn't trust removable rivets or some such, especially in a paper rocket, but in HED setups the sheer pins take a good deal of the recovery forces.

Maybe use a harness from the top centering ring as usual and just run it through your baffle bay then connect your gear to it. At least that way all the forces wouldn't be on the baffle bay to booster connection. But then that would have to be sealed against ejection gases.

If it was me, I would probably do a side access bay in the booster section or even in the coupler. That way you don't have to disassemble the whole darn thing. The payload I would leave removable of course. If done right you won't lose much strength. Frame the cutout with fiberglass or aluminum if need be. You may can even fit one between the runs but that would be tight. That is something I am considering on my 5" build, but with a 75mm hole, I'll be tight on space as well.

And of course now I am going to have to get in CAD and see what I can come up with.

And did you add the dual deploy kit? With the extra coupler and 4" piece of bodytube.

 

[K'Tesh]

Something else to think about is how you will hold the battle bay to the booster. It is going to be taking the recovery forces and I wouldn't trust removable rivets or some such, especially in a paper rocket, but in HED setups the sheer pins take a good deal of the recovery forces.

Maybe use a harness from the top centering ring as usual and just run it through your baffle bay then connect your gear to it. At least that way all the forces wouldn't be on the baffle bay to booster connection. But then that would have to be sealed against ejection gases.

The Baffle/AV Bay has some merit... The idea of a removable baffle has been seriously been advised against by Mike. He's told me that a few rockets have ripped out the screws that hold it in place. Me, I'm epoxying it in permanently. The AV Bay would be slid in place on one side of the baffle, and they'd be separated by a "wall" that would be glued in place. I'm thinking if I can fit the electronics inside a coupler for a 38mm tube, I can seal that from the bottom by a plate (bulkhead) and an "O" ring.

If it was me, I would probably do a side access bay in the booster section or even in the coupler. That way you don't have to disassemble the whole darn thing. The payload I would leave removable of course. If done right you won't lose much strength. Frame the cutout with fiberglass or aluminum if need be. You may can even fit one between the runs but that would be tight. That is something I am considering on my 5" build, but with a 75mm hole, I'll be tight on space as well.

And of course now I am going to have to get in CAD and see what I can come up with.

And did you add the dual deploy kit? With the extra coupler and 4" piece of bodytube.

I'm not doing a side access port. I like the idea of a "drop in" AV Bay. I'd need to disassemble it with the stock configuration, and I don't need to worry about how to access the electronics through a port cut out in the side while preserving the strength of the tubing. As it is now, I'm real close to being ready to post a concept image/.ork, but work got in the way from me finishing it this week.

Due to the concept I have for the paint and decalling, The 4" length of body tube will be applied to the baffle section. The concept of the AV bay inside of the recovery bay is losing ground to this integrated Baffle/AV Bay. I will likely do an AV bay up there, but it'll be for flight recording, and not deployment purposes.

 

[K'Tesh]

OK... Here's my concept for an AV/Baffle Bay




The Upper tubes are the baffle, and the lower tube is the AV bay's sleeve.

On the prototype Velociraptor, Mike told me that the original baffle was done with a pair of 1/2" PVC Pipes for the baffle tubes on the front bulkhead, and back bulkheads. In my sim, I'm using a single 29mm tube for each bulkhead. However, IINM, the area of the 29mm is larger than that of two 1/2" PVC pipes combined.

The AV Bay would be attached to the baffle by a Kaplow clip-like arrangement. As is, I can't show the keying arrangement, nor the vent hole for the electronics. I'm thinking that a 2nd charge well could be added to the front of it, as insurance to blow the rocket apart should the first attempts (electronic only) fail. At that point I think a Nomex blanket and short sleeve protecting the shock cord would be all I need. If it fires and the recovery has already occurred, no big deal. If it fires because there was no recovery, I'm not going to be worried about a BBQ'd parachute, as it'll likely be shredded by the forces involved. That said, I'm open to feedback.

 

[JohnCoker]

I also always use the nose cone for a bay, although usually for a tracker.

Here's a video showing how I typically do this in a plastic nose cone:

 

[SteveThatcher]

I went back through and read all the posts. I think it is going to be hard to balance the black powder charges. The intent is to have the electronics be the deploy mechanism for the chute of course and the motor be a backup. While the baffle is meant to dissipate heat so things don't scorch, it also absorbs energy from the pressure wave that is generated by the black powder being ignited. Air compresses and the baffle will slow down the wave front. Depending on the length and size of the motor you use, the fin can volume will vary, so that will need to be taken into account.

Personally, I would not use a baffle. I have used LOCs and Aerotech baffle. I have also had a friend have a motor closure that blew off and get stuck in a baffle. He didn't know it was there, couldn't see it and unfortunately, totalled his rocket the next time he launched it (no recovery). I would use the tri-tube bay you created. Two of them go straight through and the third one had a single deploy electronics bay in it with that charge pointing toward the nosecone. Use your favorite dog barf or acceptable substitute.

Please take my view with the best intent...

 

[MikeyDSlagle]

OK... Here's my concept for an AV/Baffle Bay




The Upper tubes are the baffle, and the lower tube is the AV bay's sleeve.

On the prototype Velociraptor, Mike told me that the original baffle was done with a pair of 1/2" PVC Pipes for the baffle tubes on the front bulkhead, and back bulkheads. In my sim, I'm using a single 29mm tube for each bulkhead. However, IINM, the area of the 29mm is larger than that of two 1/2" PVC pipes combined.

The AV Bay would be attached to the baffle by a Kaplow clip-like arrangement. As is, I can't show the keying arrangement, nor the vent hole for the electronics. I'm thinking that a 2nd charge well could be added to the front of it, as insurance to blow the rocket apart should the first attempts (electronic only) fail. At that point I think a Nomex blanket and short sleeve protecting the shock cord would be all I need. If it fires and the recovery has already occurred, no big deal. If it fires because there was no recovery, I'm not going to be worried about a BBQ'd parachute, as it'll likely be shredded by the forces involved. That said, I'm open to feedback.

I spent a little time on CAD yesterday before work and came up with something very similar, similar heck it was nearly identical.

For the sampling ports I would suggest having the holes in your inner sleeve and outer sleeve a lot bigger than the actual ports. Just easier to line up that way and doesn't have to be very precise.

I think this design would benefit from a stuffer tube. Extend your motor mount up to within a few inches of your baffle and add a centering to decrease the space to be pressurized. It would add a little weight but would help reduce the charge needed and get more consistent results.

Do you have access to a 3D printer? You may like to try my retention clips for this. If so PM me your email and you'll send you some info.

 

[K'Tesh]

I spent a little time on CAD yesterday before work and came up with something very similar, similar heck it was nearly identical.

For the sampling ports I would suggest having the holes in your inner sleeve and outer sleeve a lot bigger than the actual ports. Just easier to line up that way and doesn't have to be very precise.

I think this design would benefit from a stuffer tube. Extend your motor mount up to within a few inches of your baffle and add a centering to decrease the space to be pressurized. It would add a little weight but would help reduce the charge needed and get more consistent results.

Do you have access to a 3D printer? You may like to try my retention clips for this. If so PM me your email and you'll send you some info.

I suspect that the reason my design is so similar to yours is that it is based off of your suggestion.

The sampling port will need to be lined up well as it's my intention that the arming switch would use it too.

The idea of a stuffer tube is a possibility, and makes quite a bit of sense. It would also add rigidity to the design. Not that rigidity would really be a concern.

3D printer? No, I don't have access to one locally. I have friends stateside who do though.

 

[Handeman]

I'm a little confused as to why you want to put a baffle in place of an av-bay in a dual deploy rocket? I can understand nose cone deployment in rockets that are not set up for dual deploy but you still want the dependability of electronic deployment instead the inconsistency of motor deploy.

When you say you want to replace the av-bay in a dual deploy rocket with a baffle, I just don't understand what kind of advantages you expect from doing that. If you do that, it seems to me that you negate the advantage of electronic control and remove dual deployment from the equation. If you put an altimeter in the baffle, you also eliminate the usefulness of the baffle unless you put your electronically controlled charge facing the motor. If you put it upwards, you would still need dog barf or chute protectors.

I have used dual deployment and a JLCR. I haven't had any problems with either, but observing other's flights, I would say dual deployment electronics, especially dual altimeter systems, are much more dependable than the JLCR when it comes to consistent deployments. I have observed way too many issues with the JLCR letting the chute open at apogee, not opening at all, tangling, etc. to say it is even close to the dependability of a dual deployment setup. I also believe most issues with either system are user issues, not the electronics.

 

[MikeyDSlagle]

I suspect that the reason my design is so similar to yours is that it is based off of your suggestion.

The sampling port will need to be lined up well as it's my intention that the arming switch would use it too.

The idea of a stuffer tube is a possibility, and makes quite a bit of sense. It would also add rigidity to the design. Not that rigidity would really be a concern.

3D printer? No, I don't have access to one locally. I have friends stateside who do though.

Well I don't know how much it would cost to ship a couple of the clips to (I'm guessing you're still in) China, but I doubt it would be with it. If you have someone planning to send you something soon, I could send them one or two that I have here already printed and they can toss em in and send them on their way. What size tube

I'm a little confused as to why you want to put a baffle in place of an av-bay in a dual deploy rocket? I can understand nose cone deployment in rockets that are not set up for dual deploy but you still want the dependability of electronic deployment instead the inconsistency of motor deploy.

When you say you want to replace the av-bay in a dual deploy rocket with a baffle, I just don't understand what kind of advantages you expect from doing that. If you do that, it seems to me that you negate the advantage of electronic control and remove dual deployment from the equation. If you put an altimeter in the baffle, you also eliminate the usefulness of the baffle unless you put your electronically controlled charge facing the motor. If you put it upwards, you would still need dog barf or chute protectors.

I have used dual deployment and a JLCR. I haven't had any problems with either, but observing other's flights, I would say dual deployment electronics, especially dual altimeter systems, are much more dependable than the JLCR when it comes to consistent deployments. I have observed way too many issues with the JLCR letting the chute open at apogee, not opening at all, tangling, etc. to say it is even close to the dependability of a dual deployment setup. I also believe most issues with either system are user issues, not the electronics.

The intent is to have the ejection charge pointing toward the motor.

I agree that electronics are more reliable than motor eject. I've seen and had more damage from improper timings on motor delays, user error or not. I have never had a true dual deploy fail. But I have had the JLCR fail to open twice in the same day. I sent it in and got the all clear from Jolly Logic, said nothing was wrong. It has opened twice since then, in LPR test flights. So we still don't know what happened that day, cost me a Little John though.

 

[K'Tesh]

Well I don't know how much it would cost to ship a couple of the clips to (I'm guessing you're still in) China, but I doubt it would be with it. If you have someone planning to send you something soon, I could send them one or two that I have here already printed and they can toss em in and send them on their way. What size tube

Thanks for the offer... I'm still in China. My intention is simply to have the back/top of the AV bay fit flush with the top of the baffle's bulkhead OR just a single thickness of ply (3/32" or 1/4"). I'm thinking that a simple screw and washer (or 2) could do the trick

The intent is to have the ejection charge pointing toward the motor.

I agree that electronics are more reliable than motor eject. I've seen and had more damage from improper timings on motor delays, user error or not. I have never had a true dual deploy fail. But I have had the JLCR fail to open twice in the same day. I sent it in and got the all clear from Jolly Logic, said nothing was wrong. It has opened twice since then, in LPR test flights. So we still don't know what happened that day, cost me a Little John though.

Mikey is correct, The idea is not to eliminate the AV Bay, but to change the dynamics of how this is a DD. The motor ejection is a redundancy. My thoughts are that the delay charge (if there is one, depending on the motor) would be left full length (e.g. if it's a 9 second delay, it is not drilled to 7 seconds). The electronics would include 2 altimeters, two sets of batteries, and two matches (but a single charge), and would fire (into the fin can at apogee). The ejection would separate the rocket at the forward body tube section in a zipperless configuration, instead of from the fin can. The chute would then have 2 JLCRs tethered together to release at XXX feet. If both sets of electronics fail to separate the first ejection event, the motor would be a backup.

Another concept that has all of what has previously been mentioned, and a 2nd charge (pointed up into the recovery bay) that fires even later than the motor. This would be in the event that the electronics are working, but the rocket somehow has not separated and is now on a ballistic return. No dog barf (but maybe a nomex blanket), as this would likely occur after the rocket has reached a speed that would shred the parachute.

 

[K'Tesh]

I should also mention that I have a desire to retain the external appearance of the kit so lengthening it further is not a option (I also can't get additional body tubes as easily as folks in N. America).