Sneak Peak: Jolly Logic's Easy Dual Deployment

The Rocketry Forum

Help Support The Rocketry Forum:

gary7

Well-Known Member
Joined
Aug 2, 2009
Messages
701
Reaction score
82
Location
Mattoon, IL
There was earlier discussion here about venting a rocket for the Chute Release to work properly. I have't read the entire thread so if I am redundant please excuse me, it is a rather lengthy discussion.

I fly a couple of fat, stubby rockets like you see in my avitar. I am not too concerned about the altitude for these so I don't need a vent for an altimeter. John has suggested having some sort of vent to let the rocket reach ground pressure prior to launch. If I put a hole in the shoulder of my nose cone which is open on the end as you see in my attached graphic, I can slowly slide the nose on and that would push out enough air to equalize the pressure inside the tube more quickly prior to flight.

Is my thinking correct here or did I miss or misunderstand John or something?

The hole shown in the graphic is not to scale, it is only to show placement.
 

Attachments

Scott_650

Well-Known Member
Joined
Sep 16, 2015
Messages
1,201
Reaction score
732
Location
Louisville OH
There was earlier discussion here about venting a rocket for the Chute Release to work properly. I have't read the entire thread so if I am redundant please excuse me, it is a rather lengthy discussion.

I fly a couple of fat, stubby rockets like you see in my avitar. I am not too concerned about the altitude for these so I don't need a vent for an altimeter. John has suggested having some sort of vent to let the rocket reach ground pressure prior to launch. If I put a hole in the shoulder of my nose cone which is open on the end as you see in my attached graphic, I can slowly slide the nose on and that would push out enough air to equalize the pressure inside the tube more quickly prior to flight.

Is my thinking correct here or did I miss or misunderstand John or something?

The hole shown in the graphic is not to scale, it is only to show placement.
The JLCR only works when it’s outside of the rocket so the vent hole isn’t involved in how it functions after the ejection event - the vent hole is only needed, as you stated, to keep the rocket body from pressuring as the nose cone is inserted (with the motor in place, of course).
 

cerving

Owner, Eggtimer Rocketry
TRF Sponsor
TRF Supporter
Joined
Feb 3, 2012
Messages
4,684
Reaction score
2,252
The JLCR needs to be able to sense apogee to "arm", however most rockets have enough air leakage in the body so that's not an issue. If you really want, you can drill a small hole in the body like you would for an HPR rocket to prevent the nose cone popping off from trapped air pressure, but that's probably not really necessary.
 

Scott_650

Well-Known Member
Joined
Sep 16, 2015
Messages
1,201
Reaction score
732
Location
Louisville OH
The JLCR only works when it’s outside of the rocket so the vent hole isn’t involved in how it functions after the ejection event - the vent hole is only needed, as you stated, to keep the rocket body from pressuring as the nose cone is inserted (with the motor in place, of course).
The JLCR needs to be able to sense apogee to "arm", however most rockets have enough air leakage in the body so that's not an issue. If you really want, you can drill a small hole in the body like you would for an HPR rocket to prevent the nose cone popping off from trapped air pressure, but that's probably not really necessary.
I most definitely concede that I was incorrect - Cris has probably forgotten more about how hobby rocketry electronics work than I’ll ever know 😎
 

John Beans

Founder, Jolly Logic
TRF Supporter
Joined
Jun 5, 2010
Messages
846
Reaction score
202
The JLCR needs to be able to sense apogee to "arm"

The logic for release (simplified) is:

1. At least 100 feet of altitude detected
2. Flight is steadily descending
3. Altitude passing release altitude

All of which can be satisfied after ejection by a rocket with no vents, but venting improves reliability and is necessary for other avionics.
 

BEC

Well-Known Member
Joined
Feb 19, 2009
Messages
4,002
Reaction score
926
Location
Auburn, WA
I have a couple of models whose nose cone/payload section fit to the body is tight enough, and the shoulders long enough, that I have to be very careful closing them up to not pressurize the compartment so that when it leaks down the CR doesn't release, thinking it has already been flying. Putting a vent or two in these models' main body tubes would save me that little bit of "fun". Outside of that, venting isn't absolutely required. But it can't hurt.

But I see that's kind of what you guys have been talking about.

As an aside @John Beans — good to see you come up for air....
 

John Beans

Founder, Jolly Logic
TRF Supporter
Joined
Jun 5, 2010
Messages
846
Reaction score
202
I have a couple of models whose nose cone/payload section fit to the body is tight enough, and the shoulders long enough, that I have to be very careful closing them up to not pressurize the compartment so that when it leaks down the CR doesn't release, thinking it has already been flying. Putting a vent or two in these models' main body tubes would save me that little bit of "fun". Outside of that, venting isn't absolutely required. But it can't hurt.

But I see that's kind of what you guys have been talking about.

As an aside @John Beans — good to see you come up for air....
You can trigger Chute Release by "pistoning" a tight nosecone, but it takes some odd circumstances. Since ground is set at startup, the pressurization will appear as negative altitude—but Chute Release is still looking for sufficient positive altitude. Vents are good to avoid those odd circumstances, but hopefully the filtering makes them relatively rare in normal handling...
 

fyrwrxz

latest photo
Joined
Jun 6, 2011
Messages
6,682
Reaction score
169
Can't say enough good things about Jolly Logic customer support! Seriously, forget about the "ripoff" Estes altimeter and get one of John's! Accurate and built tough. The JCLR is a break through in smaller HPR frames and work great for just about any mid power birds without the hassle of e-bay. I have a bird that flies dual deployment with just an apogee event, then the Chute release takes over. At least half the work, more flying time!
 

BEC

Well-Known Member
Joined
Feb 19, 2009
Messages
4,002
Reaction score
926
Location
Auburn, WA
Yeah, I think what I've done a couple of times is pulled the model apart after activating the release to check if it's turned on and having it release when I've put it back together. As
You can trigger Chute Release by "pistoning" a tight nosecone, but it takes some odd circumstances. Since ground is set at startup, the pressurization will appear as negative altitude—but Chute Release is still looking for sufficient positive altitude. Vents are good to avoid those odd circumstances, but hopefully the filtering makes them relatively rare in normal handling...
I think what I've done a couple of times is check whether I turned the CR on or not by pulling the payload section (which of course decreases the pressure in the tube as it gets longer making the CR think it's flying) then, seeing it was already on, put it back in without power cycling it. At some point in this it will release. I need to just put some vents in the Leviathan and the big Nova Payloader and be done with it, so I should get off the computer and just go do it now.... :D
 

Culprit

Well-Known Member
TRF Supporter
Joined
Jun 26, 2015
Messages
141
Reaction score
105
Below are two AltimeterThree graphs from the same rocket, and the same motor (different delays, different chutes). The second graph also includes a JLCR.

This rocket is more air tight than most: the nosecone fits tighter than most/all of my rockets, the vent out the aft end where the Kevlar shock cord passes through both centering rings to get tied around the motor mount where it is accessible/replaceable from outside the rocket is sealed over with epoxy, the through holes for the rail buttons are sealed/smoothed over inside with epoxy, and the tube is HDPE vice paper/cardboard.

I realized Saturday that I never drilled altimeter vents in this rocket. I realized it because of the anomaly in the first graph showing an initial descent below ground level. Subterranean rockets usually make that portion of their journey at the end of their flight. LOL! I always start recording on the AltimeterThree after the nosecone is on. For some reason Saturday, I started the recording BEFORE putting the nosecone on - and the first graph is the result. The second graph is a previous flight where I started recording after the nosecone was on, like I normally do.

I have 5-10 flights on this unusually airtight rocket, and all but the last one this past Saturday used a JLCR. Maybe more flights: my records are incomplete because there was at least one flight where I did not fly an AltimeterThree, a few flights where I forgot to start recording on the altimeter, and a flight where the altimeter battery died. The AltimeterThree graphs and visual tracking of the flights confirm that the JLCR was never triggered early - due to pressurization of the body tube from installing the nosecone, or any other reason.

The nosecone shoulder isn't overly long, so that helps, but if a Jarhead can't break a JLCR, it's a pretty solid piece of gear!

PS: we won't discuss the night it spent in the rain on a roof. :) I did replace the battery after that one.



IMG_3489.jpg


IMG_5875.jpg
IMG_5887.jpg

IMG_2556.JPG
IMG_2566.JPG
 

gary7

Well-Known Member
Joined
Aug 2, 2009
Messages
701
Reaction score
82
Location
Mattoon, IL
You can trigger Chute Release by "pistoning" a tight nosecone, but it takes some odd circumstances. Since ground is set at startup, the pressurization will appear as negative altitude—but Chute Release is still looking for sufficient positive altitude. Vents are good to avoid those odd circumstances, but hopefully the filtering makes them relatively rare in normal handling...
John, a couple of questions:
1) What might those "odd circumstances be?
2) Flying relatively lower altitudes for instance say, under 3500 feet, if I vent the ground level air to prevent the "pistoning" as in my earlier posted graphic, will any "odd circumstance" be circumvented even without an open vent?

Again, the attached graphic shows my proposed location for for a nose cone vent hole. Then slowly insterting a nose cone allows for any air pressure to get vented as the cone is pushed into place. Said vent hole would then be covered by the air frame.

3) John, I think you have recommended venting a rocket anyway for your Altimeters to properly work. So if one is flying with an Altimeter 1,2 or 3 would all of this be a moot point?

I probably forget to either place the altimeter or forget to turn it on half the time when I do get it in the rocket.
 

Attachments

cerving

Owner, Eggtimer Rocketry
TRF Sponsor
TRF Supporter
Joined
Feb 3, 2012
Messages
4,684
Reaction score
2,252
Nose cone shoulder vents are fine, I've flown them past Mach (in Wildman HED rockets) and the data didn't look bad at all. For a model rocket with a JL altimeter, it's no problem at all.

Inserting the nose cone isn't the problem, it's when you pull it off after inserting it that the fun begins. When you push it on, the pressure inside increases, so it makes the baro altimeter "think" that the altitude has decreased. Since it's busy taking "zero altitude" readings, that's not a problem... you haven't gone "up" as far as it's concerned because the pressure has not decreased. If you leave the nose cone alone at this point, everything is fine. Howerver, if you subsequently pull the nose cone off, the decrease in pressure may be enough to make it think that you've gone "up", so when you push the nose cone back on the pressure increase makes it think that you're going down, and it may trigger the device. It's relatively easy to trap for this occurrance... just make sure that the pressure decrease/increase lasts for a second or so before settling. I'm sure that John does something like that with the JLCR... this isn't his first rodeo.
 

gary7

Well-Known Member
Joined
Aug 2, 2009
Messages
701
Reaction score
82
Location
Mattoon, IL
What effect if any, does an ejection charge have on the Chute Release? Does that not artificially and suddenly affect what pressure is sensed? I know its a very quick reading but …
 

John Beans

Founder, Jolly Logic
TRF Supporter
Joined
Jun 5, 2010
Messages
846
Reaction score
202
John, a couple of questions:
1) What might those "odd circumstances be?
You'd need to push and pull the nose cone to simulate a flight profile well enough to fool the logic I listed above. Keep in mind 100 feet is a tiny amount of pressure. The fact that sensors can discriminate less than a foot is amazing to me.

2) Flying relatively lower altitudes for instance say, under 3500 feet, if I vent the ground level air to prevent the "pistoning" as in my earlier posted graphic, will any "odd circumstance" be circumvented even without an open vent?

Again, the attached graphic shows my proposed location for for a nose cone vent hole. Then slowly insterting a nose cone allows for any air pressure to get vented as the cone is pushed into place. Said vent hole would then be covered by the air frame.
Once the hole is blocked, the situation still remains.

3) John, I think you have recommended venting a rocket anyway for your Altimeters to properly work. So if one is flying with an Altimeter 1,2 or 3 would all of this be a moot point?

I probably forget to either place the altimeter or forget to turn it on half the time when I do get it in the rocket.
Yeah, my advice is to make vents a standard feature of your rockets.
 

John Beans

Founder, Jolly Logic
TRF Supporter
Joined
Jun 5, 2010
Messages
846
Reaction score
202
What effect if any, does an ejection charge have on the Chute Release? Does that not artificially and suddenly affect what pressure is sensed? I know its a very quick reading but …
"Quick" things get ignored hopefully.
 
Top