"Safe" Deployment & Landing Speeds

How fast can a rocket be moving and safely deploy a parachute? I realize it's going to be different for every rocket, but are there any general guidelines?

How about when it hits the ground?

I'm RockSimming a possible design for my Level 1 certification, and I'd like to minimize running after my rocket so I'd like to have a reasonably small parachute, and I'm thinking about delaying the ejection to long after apogee. My plan is for a 6FNC using unreasonably durable materials... 3" ID cardboard tube with 0.75" thick walls, G10 fins "into but not quite through the wall mounted", maybe a turned pine nose since it's easier to find pine than balsa blocks large enough.

Yes, I want the rocket to be that heavy, I don't want it to go out of sight.

Not to discourage you, but this doesn't sound like that good an idea all around. With a heavy rocket and a small chute, you're going to definitely want your fins to go through the wall to the motor mount.

Perhaps you might want to go the draggy route instead of the heavy route? A 3" or 4" tube-finned rocket will stay at a very reasonable altitude on an H motor and will result in a relatively short walk to retrieve.

One other option is to bring kids. Kids are perfect for shagging rockets!

If you are interested in an easily recovered rocket for Level 1, check out a 12 inch Applewhite saucer. As an added incentive, they sell for $30.00. After you cert, you can move on to other designs and expirement, and if it fails, it won't cost you your certification.

.....that is so easy it almost seems like cheating

Hi all,

So I'm totally new to high (or even mid) powered rocketry, but it seems to me that one might be better served building a more standard rocket for one's certification. Isn't the point of the certification process to teach you what you need to know before you start lighting the big motors? I don't mean the tests, per se, but rather the process a rocketeer goes through him/herself to learn enough to earn certification.

Seems like, if you goal is to fly big, but standard (3FNC, etc.) rockets, you ought to start working toward the goal right away and cert when you've learned what you need to know. Certing as soon as possible with a saucer or some other exotic rocket and THEN starting to learn to build an L1 (or 2 or 3) standard rocket seems backward to me.

So am I misunderstanding this?

I'm really interested. I don't see myself sticking to model rockets forever.

Thanks,

Will

Will,
I see your point, but I have to disagree for level 1 at least. I could fly a G-Force with a G64, and as long as I changed the motor retention during the build, a level 1 29 mm H in the same day. The difference between a level 1 cert flight and a large model flight are minimal. I built a 4" Crayon with interchangable mounts. I could go from a 3 x 24mm Estes E9-4 cluster to a 38 mm 2 grain Pro38 in about fifteen seconds. No question that no certification is needed for the cluster, and it is the same rocket for both flights. I have already achieved the knowledge to design, build and fly large, standard type rockets, and technically, I am not required to prove it for level 1. If I use a saucer, it doesn't mean that I don't know enough about regular rockets. The saucer is a cheat if it is your first rocket and you fly it on a Pro38 2 grain for its first flight. If you have already built and flown rockets capable of level 1, it is not. A person could probably build a simple 3FNC Aerotech kit and cert on a SU motor with little or no experience, which would be a cheat.
Just my opinion, of course. I've been wrong once or twice before.

Hi Bob,

Thanks for the reply.

Seems to me that, in your case surely, my point is moot. You have the skills I was talking about learning during the cert process.

So let's take my case. The largest motor I've lit under one of my rockets is a C6-5. I know squat about fiberglassing, or even epoxy beyond the standard 5-minute double-barrelled tube stuff from Home Depot.

Should I decide to go for my L1 cert, I have a LOT to learn yet to fly safely. Or at least I think so...I don't even know what I don't know.

Now, I could go and buy one of Art's very cool saucers, study, and cert with it. But, I feel like I'd have sorta cheated myself by not taking advantage of the opportunity to build a standard rocket and learn what I need to know to proceed.

Nothing against Art's rocket, BTW. I think they're great. But if my goal is to eventually fly L3 standard rockets, I just think I'd be better off starting down that road from the beginning.

Does that make sense?

Thanks again.


Will

P.S. I love this place. Imagine how this conversation might have gone in other forums! I never once felt the urge to mention asbestos underwear, and I'm pretty sure nobody is likely to use this thread as yet another vehicle for protesting the policies of the BATF

Will,
I think you'll be more comfortable if you build a few larger models yourself. After a few E-F-G kits and maybe a homebrew like the Crayon (which is an excellent platform, in my opinion) you might change you mind about the saucer. Learn what you need before you cert, not while building the level 1 project rocket. You really don't need fiberglassing and such for level 1. As far as what epoxy you use, it does the same job whether you buy the syringe type at WalMart or an expensive West kit. The skill is in how it is used, which will come in quickly in practical epirementation.
I think we agree. It is about the journey, not the end.

Oh, by the way:

Jack Booted Govmint Thugs!

Gotcha

So, if a saucer is cheating, per se, then you would pretty much have to say that Pro38 is cheating on the motor side as well.

This kinda reminds me of a post I made a little over a year ago on ROL and got royally flamed for it. What I meant to say was that, when I would go fly rockets across from my mom's house or out at the county park, from time to time you'd run across other people doing the same thing. The next good launch weekend, you'd get dads (and moms) out there with their kids flying RTF rockets. You might see those parents out there once or twice more and that was it. Others would come out with rockets that they actually built with their kids and those families would last much longer in the hobby because the kid got some real pride out of seeing something THEY built go THAT high (I remember this fondly myself with my own daughter).

Anyway, this guy posted something about offering building services and what came out from me sounded more like something along the lines of "if you ain't gonna build it, you shouldn't be in the hobby". BAD MOVE!!! I got soundly trounced by people asking me who I thought *I* was to tell other people how to enjoy the hobby. They were right too. It was definitely a (not so uncommon) stupid remark on my part and I deserved a good thrashing for making it.

Part of the beauty of a saucer for the cert is EXACTLY that nobody thought about making it just that easy till these little beauties came along. The reality is that we all get our own pleasure out of the hobby. I personally started out loving the woosh but now enjoy building a functional rocket just as much as I do launching it. I like doing things a little differently (hence the disastrous forward swept wings on the L2 attempt) sometimes, and sometimes I like just throwing a kit together in an hour. I hate finishing, but do it just to make the rocket look like I didn't build it in 10 minutes. Carl, bless his freakishly obsessive-compulsive little soul, loves getting every detail correct down to the 10th of a mm.

Someone had a thread earlier about attempting to cert all 3 levels in one day. A lot of people chimed in saying that it's not a good idea and that you won't learn as much by doing it that way. So what? Yes, for some people it's the journey that counts. For others it's the result. Nobody's right and nobody's wrong with either assessment.

L1 is easy, whether it's a standard kit or a saucer (don't tell that to the guy who's shaking so badly that his picture of the rocket still on the pad looks like a badly blurred launch pic, though). When the flight fails, it's usually either to a bonehead move (forgot that washer in the forward closure and got blow-by, did ya? ) or a freak of nature. A 3 or 4 FNC HPR kit to me is easier to build than to shape a saucer shroud correctly without creasing it somewhere along the way.

You wanna do a saucer? Go for it. When you succeed I'll be there to congratulate ya just as enthusiastically as I did the guy who did it with a LOC. If I'm not there, though, make sure you get a launch pic. If you don't bring a launch pic, you DON'T belong in the hobby!!

Originally posted by KermieD
Yes, for some people it's the journey that counts. For others it's the result. Nobody's right and nobody's wrong with either assessment.

Click to expand...

Somewhere between my first post and my second, a similar thought occured to me. That's one of the reasons I changed my wording from "your" and "one" to "my"

Each person enjoys the hobby differently, and more power to them for that. If Art's saucer make the number of ways to enjoy certification and big motors larger, wonderful.

Sounds to me like we're all in violent agreement.

You wanna do a saucer? Go for it. When you succeed I'll be there to congratulate ya just as enthusiastically as I did the guy who did it with a LOC. If I'm not there, though, make sure you get a launch pic. If you don't bring a launch pic, you DON'T belong in the hobby!!

Click to expand...

Will

Oh, yeah...and if yer gonna wear asbestos underwear, just PLEASE make sure it's not a thong.

I have redecided my plan for L1, and I won't be trying for a high-speed recovery. I'm still interested to hear what a maximum safe impact speed might be, though.

I don't want to go with a kit (saucer or otherwise) for my L1 cert, I want to build mine more-or-less from scratch, but that's just me.

I've always been told to aim for around 17-18 feet per second drop rate. Much faster and you'll be picking up pieces. Much less and you'll be driving to the next county to find your bird.

Build the bird strong, and add weight if you need to. Any idea of what motor you are planning to cert on? Some of the smaller H's have a great initial thrust, but only have a .5 second burn time. So there's a lot of coasting involved. Some have a longer burn time, but a much lower thrust rate.

Figure out what kind of motor you want to use and then build the bird for it. That way you'll have a better idea of what to expect as far as altitude and airspeed.

I didn't see any other responses to your question about the chute. You really don't want the chute to pop out too long after apogee. Regardless of how tough the tubing is. When that chute pops, it's going to add a bunch of stress to every part of the rocket.

Good luck and keep us posted!!

I suggest you poke around ROL InfoCentral. It gives speed guidelines and has chute calculators, etc.

I have heard of people designing for chute ejection while the rocket is moving fast. The main issues are whether the recovery system will hold togther and whether the rocket will. The recovery system here includes the recovery harness, the chute, and the attachment points. The rocket components involved definitely includes the tube and the attachment points. Note that the amount of zipper allowed in a cert varies with the person signing off. I've heard of small zippers failing the cert.

What the rocket can take on landing depends on the materials, construction and design. For instance, making the fins swept upward goes a long way. I have had decent rates in the low to mid 20's on a solidly built rocket without damage. The recovery field also may make a difference. remember, what worked for me may not work for you.

{Sorry if I went over material that was already known or stated in earlier posts}

The terrain makes a big difference too desert > sod

It doesn't take much decent speed to damage a fin on a hard surface!

For reference, the recommended speed of decent usually falls between 15 and 25fps, depending on the model. I have noticed through my many experiences with PML that most of their kits decend at around 22fps or so, which is not too bad, but they are pretty strong. Note that as mentioned, the surface will make a big difference. I wouldn't go over 20fps on a hard surface and have gone as much as 30fps on softer surfaces with a fiberglassed model on a windy day. It all depends on weather, weight and terrain. Also, remember a heavier rocket tends to do more damage to itself (unless strengthened) than a lighter rocket; kinda has to do with that Physics thing regarding mass and energy.



All in all, if you keep it at around 15-20fps, as mentioned, you stand a good chance at having many more launches in the future.

Carl

One observation....even on soft terrain, it seems my rockets often find the one hard road, the irrigation system, the side of a shed. This must be a corollary to the Law of Rocket eating Trees

If you don't want to walk, use a PML Tethys on an H128W. Only goes about 950'. It looks really cool too.

It also builds really easily. I built it in one night. Of course, it was all night

Originally posted by KermieD
So, if a saucer is cheating, per se, then you would pretty much have to say that Pro38 is cheating on the motor side as well.

Click to expand...

Like it has been said ; it the journey , not the destination. Join the local club. Fly rockets. Tap into the info there and on the web ( like here ).

High spped recovery usually equates to a zipper. Not a good thing on your cert flight.

Motor choice. Well now days availability is also a factor. Nothing is cheating as far as I can see. BTW I used an AT for L1 and a PRO38 for L2. Just what was available at the time.

Some ideas for L1: LOC IV , PML Tehys , BSD Horizon , Yank 3" IRIS.

Enjoy the trip.

Al

Justy,
the bottom line is
your better off with a low altitude flight, than a high speed deploy in a log type rocket to keep the rocket in range .750 wall is a VERY thick body tube for a 3" I.D.

I'm sure It can be done ,but you would be risking too many chances of something failing(recovery,fins) atleast for a cert flight

Styme makes a good point. I can also add that if you have too late a deployment, it can be deemed unsafe and you will not certify... part of the qualification is your ability (for safety sake) to judge the correct delay required for your motor. This "failed-Cert" is a call by the person performing the certification, but the whole idea is to do it by the book, deploy at apogee and land safely.

Carl

Carl and Kermie have good points. The common wisdom is to be conservative when certing. I personally have never heard of anyone failing because of a late delay. However....

One one hand there is the fact that the rocket should perform as designed. That says you could tell the witness your plans. On the other hand, if you admit this the witness may decline your flight in advance, and/or the RSO would say no. The bottom line is a lot rides on the person who'll sign off.

If you are really ambitious use a dual deploy rocket, with a small drogue, streamer, or just separation at apogee. The purist will argue that you shouldn't (gasp) risk electronics on a cert-1 flight.

All moot since Justy recanted his desire for high speed separation.

Every person has different objectives in a certification flight, in addition to passing the certification itself. In my L1 flight, I just wanted to get the rocket in the air, get it back, and get my L1. I also wanted a rocket that could be used for L2 if I decided to go on. I settled on a PML Tethys with a H128W for L1, and about 8 months later I used the same kit on a J275W for L2. Between L1 and L2, I made a cruciform chute to replace the standard chute. I used motor ejection for both cert flights.

Some people like to push the envelope for a cert flight, or build a scratch-kit for their cert.--go for it. If you want to keep the rocket close to earth, go for a saucer or a large diameter kit (e.g. LOC Warlock or Magnum). If you want to go for extreme altitude, go for minimum diameter. Some people prefer to expend efforts and show their expertise in construction (min. diameter), while others prefer to show their expertise in recovery (large, heavy kit). That's part of the challenge anf fun of it all-everything has trade-offs that you get to choose.

None of these choices are wrong or right--they are just choices. Pick one that you like to do, and enjoy learning from watching the choices that others have made.

Hi Mark,

In the words of one of my coworkers, "Rock on." Well said.

And, by the way, welcome to the forum. A bit belated, perhaps, but still.

Will

Well I've abandoned (temporarily) my plan to use the 3" ID, 0.75" wall tube. My new plan involves 2.5" mailing tubes (0.060" wall). A 42" long rocket including a spacious payload bay and a 38mm motor mount for Pro38's, I'll be able to fly it on G60 (1-grain) at club launches, H110 (2-grain) for certification, and it'll have room to take an I170 (3-grain) or I240 (4-grain). I'm not entirely sure it'd SURVIVE an I240 (RockSim says it'd be pushed to Mach 1.07!), but the motor mount will have space. In Canada the certifications are a bit different anyhow (L1 = H, L2 = I, L3 = JKL, L4 = M+), so I'd probably build another rocket for I-class motors anyhow.

Whatever motor I use, I'll put a spacer in the motor mount tube, so the engine + spacer will always be the length of a 4-grain motor, and clamp it in with positive retention.

Based on what you guys have told me, I'm going to build the fins strong and set my descent speed to 25 ft/s with the 2-grain motor, using a 27" chute (which I'll probably sew myself to save $$) on motor ejection, and I'm expecting a flight to around 4000' for my certification (13 sec delay is just a second or so past apogee). If I go to the Sullivan Lake HPR launch, I'll voulenteer for the fire crew, so maybe I can borrow the ATV for my recovery walk

And the thick wall tube? I'll save it for my Level 3 attempt.