Chute Release in MD 38mm

[ActingLikeAKid]

I'm (hopefully*) getting a PML Cirrus Dart soon and with a minimum diameter 38mm rocket, I know I'm going to be punching a hole in the sky. Hoping the Chute Release will help bring it down relatively close. On the Jolly Logic site, it says "May work in some 38mm rockets". Okay, so ... any tips for making it work? Anyone with experience on this? The engineering part of my brain started churning on some sort of solution where the CR sits above or below the chute in the BT, then there's a wrap around the chute that holds it tight and it's somehow tied to the CR so that when the...

Then the pragmatic part of my head said "The product's been out for a year or so. Someone else has done this and done it well, I'm sure. Ask. Don't reinvent the wheel."

So I'm asking

*- USPS tracking has it stuck at a distribution center since Thursday. If it makes it, awesome. If it doesn't, then I'm on to some other project....

 

[mpitfield]

Good timing.

I am just trying to finish up a few stragglers on my work bench, two of which are 38mm MD. One is a GLR Mariah and the other an oldie but a goodie, one of the OOP CF Mongoose 38s. I also happened to pick up a CR a month or so ago and would love to use it for this application but from my quick configs things are a bit too tight for my liking. So while I have nothing to add as for a solution, I will be following to see what others have to say. On a related note I did request that the unit had a smaller footprint and that was specifically for what I call these marginal airframe sizes.

 

[rharshberger]

So what method are you using for apogee deployment, most motor delays are too short for MD screamers or is the longest delay simming as good?

 

[ActingLikeAKid]

So what method are you using for apogee deployment, most motor delays are too short for MD screamers or is the longest delay simming as good?

It's been a little while but I was mucking around in OpenRocket with 29mm 2-3g CTIs (Fs and Gs) which simmed OK with long delays. I don't want to go full 38 until I have a GPS.....probably. The alternative is getting a travel alarm (for door or luggage) that "screams" when its leads are disconnected. That should be "packable" in the body; the idea is that when the rocket separates, the alarm wails until you find it. My new launch site is REALLY open and I have it on pretty good authority that you can hear things from a long way off. Going to do some experiments. If the screamer works, then I may cross my fingers and stuff a 38mm G up the rocket. Otherwise I'll wait and build an Eggfinder.

 

[BDB]

I had an issue with packing a JLCR bundle into a BT-60 (40 mm I.D.) a couple months ago. I got it to work once, but the second time the burrito got stuck in the tube. I'm pretty sure that the culprit was my nomex blanket. I am going to try again next month using only dog barf for protection. So long as your chute is thin and your bundle is tight, I think you can make it work.

 

[rharshberger]

It's been a little while but I was mucking around in OpenRocket with 29mm 2-3g CTIs (Fs and Gs) which simmed OK with long delays. I don't want to go full 38 until I have a GPS.....probably. The alternative is getting a travel alarm (for door or luggage) that "screams" when its leads are disconnected. That should be "packable" in the body; the idea is that when the rocket separates, the alarm wails until you find it. My new launch site is REALLY open and I have it on pretty good authority that you can hear things from a long way off. Going to do some experiments. If the screamer works, then I may cross my fingers and stuff a 38mm G up the rocket. Otherwise I'll wait and build an Eggfinder.

Personal alarms work, they are small, loud, and are triggered by pulling a pin.

 

[ActingLikeAKid]

I had an issue with packing a JLCR bundle into a BT-60 (40 mm I.D.) a couple months ago. I got it to work once, but the second time the burrito got stuck in the tube. I'm pretty sure that the culprit was my nomex blanket. I am going to try again next month using only dog barf for protection. So long as your chute is thin and your bundle is tight, I think you can make it work.

I've used the JLCR with BT-60 several times with no problems*. I just used barf and it was fine.

*- No problems with it coming out. There were problems with a plastic chute (I think some talc/chalk may have helped?) and there was a problem when deployment was perfect and a gust of wind blew it into a tree (UGH, THAT WAS TERRIBLE GETTING IT BACK). But yeah, I've popped it out of a BT60 with no issues.

 

[EXPjawa]

I use the CR with BT60 tube frequently as well. In fact, I modified several designs that were still on the drawing board to go from, say, BT55 to 60 for that reason. It helps to use thin-mil chutes. It also helps to have a bit of tube length so that the chute can be folded longer and thinner. One that has a nomex blanket would up having the blanket repurposed as permanently attached wadding, but not used to burrito-wrap the chute. As far as 38mm goes, its a matter of whether or not you can get the CR to slide smoothly in and out on its own. If you can do that, then the chute can be wrapped tightly (again, long & thin) alongside it. But if the tube doesn't accommodate the CR in the first place comfortably, that's the end of it...

 

[boatgeek]

I had a couple of unsuccessful ejections on my JLCR until I changed my approach on packing the chute. My theory was that the plastic of the CR was getting caught on the inside of my tube. My new approach is to fold the chute into a long skinny shape, then fold it completely over the CR body. The rubber band ends up going around the chute 1.5 times (0.5 inside the chute, and 1 outside). The extra slipperiness of the nylon chute seems to help the whole burrito get out the top better. YMMV on plastic chutes. I also only use dog barf on that rocket.

 

[mpitfield]

So what method are you using for apogee deployment, most motor delays are too short for MD screamers or is the longest delay simming as good?

In my case I have and AV bay for both rockets, however I would prefer to use the CR for simplification. In the case of the Mariah the AV bay is fixed but I have my concerns with the shotgun deployment method so a CR would be preferable. In the case of the 38 Mongoose I have an AV bay that I just ordered a 3D sled for. However ideally if using the CR I may be able to shave some length off the airframe by inserting the chute and CR into the booster and using the AV bay as my nosecone coupler. This would allow me to have a single split in the airframe then deploy the main from the CR.

 

[ksaves2]

I did a ground test with a Madcow/RW 38 Special with an EggFinder tracker nosecone. 1.3 grams (the stock amount with a reload) blew the 24 inch chute wrapped with a JLCR out with authority. You'll need to sim these projects and some motors
might end up unusable due to the lack of a long enough delay grain. I have another project where even the long delay is too short for an I200.

Don't be tempted to use an ematch canister stuck in the end of an empty motor for a ground deployment test with the intent to cut the powder charge. I did that on a project and .8 to .9gm in a canister took the nylon shearpin nosecone off nicely on the ground. When I poured that amount into the motor well, I had a ballistic flight. The charge fired but wasn't strong enough. What happened is I inadvertently cut the charge too close. Some of the powder ostensibly falls into the motor on top the the delay grain and expends its energy out the back of the motor. When using an ematch in a plastic ultra-centrifuge canister for the powder all the energy is directed forward. I now throw all the powder in that comes with the motor in to the forward well and call it good.

Kurt

 

[Flyfalcons]

On BT- 60 tubes I'll take a couple squares of Estes wadding and wrap them around the JLCR/chute combo. The wadding slides easily against the body tube and helps prevent the chute release or rubber band from catching.

This is in addition to stuffing my normal amount of wadding in, of course.

 

[mpitfield]

blew the 24 inch chute wrapped with a JLCR out with authority.

:grin:

 

[dhbarr]

The Dino JLCR protector helps mine slide a whole lot better.

 

[Tonimus]

Wrapped for a 38mm tube:

 

[John Beans]

Nice techniques. Using a sheet of LPR wadding to make the band more slippery against the tube is clever.

 

[ActingLikeAKid]

Looks like no MD 38MM for me - USPS has declared the package to be "dead mail". Hoping that the paypal/USPS insurance process is an easy one to navigate.

Guess this means I need to start thinking about what I want my next HPR project to be.

 

[cbrarick]

might want to look at another md project, but I'd go with a small ebay vs chute release. You will run into issues with apogee deployment otherwise, and it willjust get uglier the further you go from G.