Chute Release and Higher Altitude Flights

[MartyS]

I plan on launching a motor deploy-only rocket to about 5,000’ this weekend. This rocket was my Level 1 and, for better or worse, I have an emotional attachment to it. In the B.C.R. era (Before Chute Release), I wouldn’t have attempted a launch like this for fear I would never see the rocket again. At the same time, this rocket has been asking for more motor, and now, with some help from Chute Release, I’m finally ready to oblige. Be careful what you ask for!

I haven’t used my CR yet in the field. I have done ground testing with the CR and chute I’ll be using: multiple shake tests and release tests. All seems good. The thing is – I can’t recall, nor can I find, any accounts of CR being used for mile+ flights.

Are there special considerations when using CR with higher altitude flights?

Any thoughts, tips, experiences, etc. would be welcome.

 

[Oberon]

Can't say that I have done it, but as far as I know there are no special considerations other than to be extra certain of all the non-CR elements of your setup . I'd probably fly a couple times to lower altitudes and watch the chute bundle carefully just to make doubly sure that your chute stays wrapped and deploys nicely. Most likely high altitude specific failure mode would probably be an early open and very long walk.

 

[MikeMann]

I assume since it was level 1 it's probably not a super heavy rocket. The only reason I ask is that when I use my chute release it seems like everything comes down like a bat out of hell until the chute opens. It seems like a big rocket might get wrenched on pretty hard. I was thinking about attaching a small drogue chute that would open at motor deploy and then chute release the main. Unfortunately I probably won't be able to try that until April.

I would think you will be fine. You're gonna love it!

 

[Nathan]

A level 1 rocket should be fine without a drogue. I've seen some pretty large rockets come down drogueless with no problems

 

[tim cubbedge]

Just make sure you have a long enough delay.

 

[hball55]

The important thing is the weight of the rocket you are flying. If it's light enough and not too bottom heavy, you shouldn't have any problem. What you want is for your rocket to fall flat so you don't have too much velocity when the chute is released. I have used my chute release with mostly Aerotech rockets and they're light enough and fall flat, that the speed at chute release point isn't much more than 10-15 fps more than when under chute. No problems so far.

 

[John Beans]

Here's the thing: a rocket doesn't reach a higher tumbling speed from 5000' than it does from 1000'. It's just further up when it happens.

After a few seconds of falling, an opened rocket reaches terminal velocity (stops speeding up). So in those two flight examples it's going the same speed at 4700' that it is at 700'.

In many respects, a flight to 1000' can tell you everything you need to know about a rocket, and keep it in sight the whole time (with good eyesight, on a clear day). So if it makes you less nervous, test and measure at 1000' first.

That's true after Chute Release opens, too, and why it doesn't necessarily "help" to set Chute Release higher than necessary, assuming you've learned to fold your chute so that it opens promptly. Once your chute opens, your rocket will reach landing speed in just a couple of seconds. So in two examples (setting release to 800' and 400' ), it's going to be as slow as it's going to get (landing speed) at 650' and 250' (assuming your fold takes 150' to open, that's on the high end for me). It just drifts slowly down from there.

You would choose a higher release altitude for several reasons:
1. You want to have more time to see where it lands
2. You're not sure your chute will open quickly
3. You want the rocket to have more time to drift back to you

Look at the descent lines in the following graph. See how quickly they get "straight" (constant descent rate)? This is for a fairly light 3 lb rocket.

 

[mikec]

Are there any limits to maximum altitude? What is the spec on the barometric sensor? If I flew near or above that, would the software work correctly or are there potential overflow issues?

 

[John Beans]

Are there any limits to maximum altitude? What is the spec on the barometric sensor? If I flew near or above that, would the software work correctly or are there potential overflow issues?

Yes, it will be fine. Like all pressure sensors, the one in Chute Release has a calibrated range (up to 33,150 feet standard) but it continues to provide un-calibrated pressure values at higher altitudes. All of which make no difference to Chute Release, which waits for the rocket to fall to the release altitude.

 

[dixontj93060]

Yes, it will be fine. Like all pressure sensors, the one in Chute Release has a calibrated range (up to 33,150 feet standard) but it continues to provide un-calibrated pressure values at higher altitudes. All of which make no difference to Chute Release, which waits for the rocket to fall to the release altitude.

John, I agree that altitude and/or descent time is not an issue, but in your opinion what are the limits of this product. I would expect it would be related to overall parachute size/weight/bulk... True or not?

 

[stealth6]

If all goes as planned I'll be flying a 4.5 lb. rocket to 4000' or so this weekend, with a ChuteRelease.

Previously, this rocket has always flown with a CableCutter, with (mostly) fine results. The majority of the time it flew drogueless. Current/latest configuration includes a small "pilot chute" which acts as a drogue and pulls the mains out faster/cleaner. I plan to use this pilot with the ChuteRelease as well.

This will be my first in-the-field test day with ChuteRelease, and I've got full confidence going into it.
(I'll be running the maiden voyage test with a smaller rocket/motor).

ssix

 

[John Beans]

John, I agree that altitude and/or descent time is not an issue, but in your opinion what are the limits of this product. I would expect it would be related to overall parachute size/weight/bulk... True or not?

The short answer is that Chute Release works in pretty big rockets, and we're continually testing the limits. Do shake and release ground tests, protect with a blanket, gain experience before moving up. Perhaps we will see new additional bands for larger bundles, and new wrapping techniques. There are some very experienced rocketeers working with Chute Release now, so if you're not sure, just hang on until the techniques are more developed.

 

[MartyS]

Thanks for all the replies. The rocket is a PML AMRAAM-3 (QT airframe). It weighs 65 oz. RTF w/o motor. If there's an "anomaly," at least one person besides me will be upset:



A certain 5 year old is only smiling because he hasn't been told that the motor I'll be using will push the rocket to a velocity right at the limit of QT's capacity, according to Rocksim. In addition to Chute Release, I'll also be using an Altimeter 3 (thanks again, Jolly Logic) and a Trackimo, which will be on a sled in the payload bay. I'm trying to be thorough.

If all goes as planned I'll be flying a 4.5 lb. rocket to 4000' or so this weekend, with a ChuteRelease.

ssix

Good luck with your flight! Let us know how it goes.

 

[Bat-mite]

I have had two chute entanglements so far. I am obviously not doing a good wrap job. I would love to see people's pictures of how they wrap their chute, shroud lines, and harnesses. Thanks.

 

[John Beans]

I have had two chute entanglements so far. I am obviously not doing a good wrap job. I would love to see people's pictures of how they wrap their chute, shroud lines, and harnesses. Thanks.

How did the tangle occur/what did it tangle with?

 

[Bat-mite]

Well, at the risk of embarrassment...

The first time, I Z-folded my harness and wrapped the chute in a Nomex cloth. Foolishly, I put one hunk of the Z-fold forward of the chute. The tether held the fold together and it took the chute about an extra 200' of freefall to unwrap. My bad.

So the second time, I did not use a Nomex wrap, and I moved the chute to the NC, but I left the shroud lines free. Whereas I had a swivel on the chute, I did not have one on the harness, and so as the rocket spun in descent, the harness wrapped up the shroud lines and reefed the chute. Again, my bad.

But, since I haven't done it correctly yet, I thought it would be nice to see an example of a working set up.

 

[John Beans]

There is no "best" way, but I like to put my shroud lines inside (so they can't twist) and "roll them into" the chute, so that when they are pulled they unroll the bundle. Video below.

In the past I have not used a drogue, though I'm about to do some with/without testing on a heavier (~11 lb, 4" fiberglass). If you use a drogue, don't attach it to the peak of the main chute (it will pull your chute away from Chute Release); instead, attach it directly to the nose cone or shock cord. Plan your "stack" (how everything will hang in the slipstream) and imagine what can tangle with what. If you use a drogue I would advise a "single strand" approach, where all of your components are spaced out along the shock cord line so that they can't tangle with each other.

Wrap the Chute Release-held bundle loosely with your fire blanket (or use a baffle, or dog barf) so that the blanket flies free after ejection. Try to attach your blanket so that there is no chance it will slide up the shock cord and get wrapped around your parachute in the slipstream. Rather than let it slip, if you knot it in the shock cord with some slack between the fire blanket and the chute, the tension in the shock cord will automatically pull it away from your chute in the slipstream.

I like to roll the chute so that it is loose in the fuselage, and attach it close to the nosecone so that the momentum of the nosecone will pull it out.

[video=youtube;VgKmVZ0SbJY]https://www.youtube.com/watch?v=VgKmVZ0SbJY[/video]

 

[watermelonman]

I have a pending 9k flight with a Chute Release but weather keeps snuffing out our launches!