Drogueless with timer (Descent time question)

Hi guys,

I'm trying to do a really simple drogueless dual deploy rocket using only a perfectflite timer. The challenge I am running into is determining the appropriate delay to set the timer to for the parachute deployment. Ideally I would use an altimeter, but I'm not sure I'll have enough space in my nosecone for my current altimeters, and I'd like to keep the price down at least initially.

Specifically I was planning on using a chute cord cutter, to keep the chute either either in a burrito or reefed. Open Rocket can simulate decent rates for parachutes given dimensions, but has nothing on reefed or drogueless recovery.

Suggestions welcome!

Change the chute size to 2" or something similar. I was able to get pretty close to the actual decent my burrito falls by using a 2" chute. The PerfectFlight timer lets you start the timer on motor burnout so you should be able to get pretty close. I have been wanting to try a DD flight with timer alone myself but haven't gotten around to it.

Thanks! I can't find any mention of setting it to motor burnout (I have the one with the simple g-switch) but motor burnout comes at about 1.5 seconds with the F39s I have, so liftoff should be just fine for me. I think I'll start with a relatively short delay, and work my way up as I get more comfortable. I'd hate to have my rocket under perform, and thus end up a foot deep in the sod.

What's your rocket worth? For some reason you are having problems using a sim and it seem to me that you are just guessing what the delays have to be so you have 2 places to mess up.

A simple dual deployment altimeter is not that expensive and there's no guessing required. Your approach seems pennywise and pound foolish.

Bob

I agree that ideally I would use an altimeter. My idea is to try to keep this one small and cheap, but to experiment around a little with electronics while I'm at it. I love how tiny and simple the timer is. Moving forward, I'll swap it out for an altimeter, but before I start putting all sorts of electronics on board, I want to demonstrate to myself I can do the simple kind.

But I see your point. Depending on the fit, I'll see about swapping in my Adept22

I love my StrattoLogger but if I were going to do it again with an eye on cheap I'd pick up a RRC2. Easy to set up and they are under $50. No brainer.


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I've seen about 7-8 flights using the motor for apogee, and a timer for main deploy. A fellow club member, friend thought that it would be nice to try exactly what you are thinking. Only one rocket hit the ground before the main charge fired, the rest recovered without any damage. 3 of the flights main deployment occurred at 200ft or less. The remaining flights were ok as to expected main deployment. My conclusion was I would never try it. He has since used only altimeters for deployment. There are just to many variables involved in real flights verses one on a simulator to call timer controlled deployments reliable. All his timer settings were based on RS simulations.

DING DING DING!!!!! This is the correct answer. You have no control over whether the rocket might go ballistic for a few seconds, or wind shear helps it drop like a stone. What if the motor doesn't burn properly or the flight is off vertical? The RRC2+ is cheap insurance compared to a timer and it should be EASIER to set up.

Save the timer for staging.

rcktnut said:

There are just to many variables involved in real flights verses one on a simulator to call timer controlled deployments reliable.

Click to expand...

If you use a timer I would suggest using 1/2 the calculated time to be safe

The main problem with the timer I see is if the rocket doesn't get the altitude you expect your planned times are null and void. Say the rocket weather cocks and gets three quarters what you planned. You will be scraping rocket off the ground. I see it as something to play around with when you are looking for things to play around with. Normal dual deploy flying is best with an altimeter.


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I'm confused? If it has no Drogue, how is it "Dual-Deploy"? Does it start out by first deploying a Nothing?
Or, if I understand it like I think it's being put, it is actually "Single-Deploy", just a little late, and after a mostly Ballistic Descent?

rcktnut said:

There are just to many variables involved in real flights verses one on a simulator to call timer controlled deployments reliable.

Click to expand...

That makes a lot of sense. I will follow all of your advice. It seems altimeters really are the way to go.

TopRamen said:

Does it start out by first deploying a Nothing?

Click to expand...

Pretty much. But technically when the motor ejection fires it pops off the nose cone, pulling out a tightly wrapped parachute burrito. Because the rocket has separated into several pieces, it is now not very streamlined, and it tumbles for quite a ways (nonbalistically hopefully) before the parachute is released and allowed to open.

Lentamental said:

That makes a lot of sense. I will follow all of your advice. It seems altimeters really are the way to go.





Pretty much. But technically when the motor ejection fires it pops off the nose cone, pulling out a tightly wrapped parachute burrito. Because the rocket has separated into several pieces, it is now not very streamlined, and it tumbles for quite a ways (nonbalistically hopefully) before the parachute is released and allowed to open.

Click to expand...

Cool. Thanks for clarifying that. Sounds like a good Idea to me.

I put a feature like this into the Eggtimer firmware about a year ago by request, I was really holding my breath when I flight tested it using an F39 and a BT55 size rocket, drogueless from about 1400' with the timer set to pop at about 400'. I simmed the hell out of it so I was confident that it wouldn't smack the ground, but 20 seconds from burnout is a LONG time to wait... baro altitude deployment is MUCH more reliable.

To me, the original idea seems exceedingly BAD.

Glad to read you've reconsidered.



Later!

--Coop

ChuteTamer, way overpriced, failure to work for unspecified reasons in a comment I saw about it somewhere, and, I think, no longer manufactured :

https://www.cdimodelrocketry.com/proddetail.php?prod=CHUTETAMER

The primary benefit of delayed deployment via reefed chute IMHO:

"Anti-Zipper: Because the parachute is bound during motor ejection, it presents a much smaller profile to the air stream than an open parachute would have. This means less zipper damage should the motor ejection happen too early or too late and when the rocket is traveling at a high velocity."

Any additional altitude loss before 'chute deployment for reduction of parachute drift is just gravy.

A reefing method that doesn't require the use of BP avoids the need for a LEUP. According to a tech talk on rocketry electronics by John Beans during NARCON 2013(?), Jolly Logic is working on such a device.

EDIT: no use of BP also eliminates the hazard of using sensor-fired pyrotechnic charges.