Makers Corner

More questions. I just read about Shear Pins (https://northwestrocketry.com/?page_id=1651). The write-up recommended them for high powered rockets without tapered fin leading edges (my Zephyr) to prevent the nosecone coming off when the motor stops and causing a zipper. I plan to launch my Zephyr first with a couple of G67-14A kits in a RMS 38/120 cylinder which I don't think will trigger a premature release. But the H100 motor could, so if I want to test ejection charge amounts before launching:

Where should I buy black powder? How much? How do I measure grams of it?

What can I screw into the forward end of my 38/120 cylinder to plug it and test charge amounts?

How do you recommend I weigh the whole rocket?

I did not epoxy the adapter into the motor tube. I simply epoxied the centering rings and retainer onto the adapter which still slides in and out of the motor tube. I also attached an aluminum apogee retainer. (I tried to include a photo but couldn't figure it out).

Please tell me you didn’t epoxy the 29-38mm adapter into the rocket. The adapter is to make the rocket more versatile as far as using 29 and 38mm motors.

There's no substitute for flying. Simulations assume ideal conditions. The efficacy of construction techniques becomes apparent after you've flown a bunch

A great source of information is The Rocketry Forum (TRF). Have you found that web site?

Speed when the 'chute opens

You are correct that the speeds you're quoting sound high for a separated rocket of the Zephyr's size. I usually aim for a descent rate of less than 90'/second prior to main deployment. 15'-20'/second when under the chute and landing on grass.

JB Weld

JB Weld works fine for fine fillets, though it's overkill for a rocket of this size. Wood glue is fine for attaching the base. In fact, it or regular hobby epoxy would've been fine for the rest of the rocket.

Motor Retention

I don't recommend masking tape, even for the G motors. It's too unpredictable. My favorite commercial retainers are from AeroPack. Estes also makes a good 29mm plastic retainer. Those may be impossible to install since you've already glued the base together. In those cases, I've made motor retainers using threaded inserts, wing screws, and washers. TRF probably has some articles on this.

Chute protectors

I wouldn't expect holes in a well-made chute protector after one flight. Frank is correct that you can add an additional layer of production by adding dog barf (aka fire-retardant cellulose) under the chute protector.

I agree with using wood glue for the coupler. I've used Titebond II for decades and has served me very well. Apogee has some nice photos of the Zephyr on their website. Wood glue is fine for that cardboard tubing and the coupler, but as you know and were recommended, epoxy for everything else. It'll be neat to see it fly!

If you are looking to have a written log of your build, may I suggest you start/keep a notebook? That way everything is all in one place and documented..... I'm planning on having mine on me when I go see the NAR witness(es) and the LSO when it comes time for my L2 attempt....

A chute protector that burns through? Doesn't seem like it's offering enough protection for your parachute. What brand is it?

Hi Kevin,

I will only comment on what I know about. I don't see a problem using wood glue on the coupler. Best bet is to use Titebond III or epoxy because they do not set that fast. Don't use tape to hold a high power motor in place. You will not pass Safety Check. I wouldn't worry about the chute protctor. You can always drop in some dog barf in the body tube.

Alright, since documenting my Level 1 certification flight is a good thing, here's more. I epoxied the whole rocket yesterday (before it got too hot out!) including a 29-38mm adapter & the fins. I used JB Weld Extreme heat on the adapter retainer (as recommended) and not wanting to mix up yet a 3rd type of putty epoxy I bought, I used the excess JB Weld to make exterior fin filets.

Was this was OK to do?

I also used wood glue to adhere the base to the body tube with the coupler, (the instructions say to use liquid epoxy which I haven't found).

Again, was this OK?

My next step is to paint. I also have two launch questions:

• The Zephyr kit instructions say I can use masking tape around the rear motor retainer instead of adding a separate retainer. Will masking tape really be sufficient?
• The chute protector instructions say it gets holes burned in it after use. Would a small piece of Al foil over the top end of the motor tube extend the chute protector’s life?

Rocksim has the chute opening at 78mph even for a 600' flight that releases the chute at 300', so the 89mph release for a 1,500' launch releasing at 300' must be very close to terminal velocity for the separated rocket, though I have trouble imagining it falling that fast once separated. My G67 motor has only a 4 second ejection delay so that may separate before apogee, but the G61 & H100 motors should both eject at apogee. The replacement for my missing rail button came yesterday so today I'm now epoxying!

I’ve seen a lot of JLCR flights. I highly doubt you’ll zipper if you were to set it for 400 feet. Your shock cord should be fully deployed at that point.

Hi Kevin,

Thank you for posting so much information about your planned L1 Cert attempt. Could you please confirm that the rocket will separate at or near apogee and not be coming down ballistically when the chute is deployed. As you'll find out, I'm overly cautious with cert attempt by flyers who haven't flown with us much.

I re-ran Rocksim and a parachute deployment of 1,000' (JLCR max) still produces a parachute deployment speed of 83mph and a 1,000' drift at a 1,500' apogee. So I'll set my JLCR to deploy at 300' (89mph & 400' drift) and risk a zipper. I'll let you know how it goes.

I went to the Acton launch today, talked to people and solved my adaptor retainer issue.

I think I'm going to risk the high speed chute opening. Rocksim estimates a 89mph chute opening only with the H100 motor I'll be certifying on. As Sam says It's likely to be less than that. I'm also launching it with a couple of G motors first. I'll see how the cute does with those. One has only a 4 second delay (before apogee) but the JLCR should keep the chute closed until it descends to 300' or so.

I agree 89mph is too fast, but I wouldn't trust Rocksim's estimate. Rockets in a flat spin have a lot of drag, even without a drogue chute. In fact my experience is that a drogue chute can actually make them come in faster since the surface area becomes less. As long as you get the nose cone off at apogee you'll be fine. You get zippers and other bad outcomes if you deploy late, not because you don't have a drogue. I have never had any high speed deployment issues with the chute release or other drogueless dual deploy, even with much bigger rockets than the one you are flying.

I'm thinking that you may be cutting it kind of close there. 89mph = 131ft/s. Even if the JLCR releases the chute immediately (at 300ft AGL) and without any issues, you'd only have about 2.3 seconds for that parachute to open. Then again, I've never used a JLCR myself. For anyone who has experience using it, how does this look? Guess it would make for a very nice "HALO".

Thank you for the motor retainer advice. Rocksim says the rocket will be descending at 89mph when the 3' kit (plastic or nylon?) parachute deploys if I set my JLCR to open at 300' (~100m). Do I need to be concerned that is too fast and deploy higher (drift further)? Use a drogue or streamer to slow it down? Can I simulate a drogue chute or streamer in Rocksim?

The thrust ring on the motor takes care of forward retention. I usually have nothing in the front of my motor mount tubes so I can use any length motor, even if it sticks out of the tube.

So I see Rick Wildman is sometimes at launches selling motors. Thank you.

I've Superglued my Zephyr together but not epoxy'd it yet. It occurs to me I have no FORWARD retainer to hold my motor in. I did get a screw-on retainer for the back end, but what do you suggest for he forward retainer? Screws into the motor tube before I epoxy it? Buy a forward retainer and epoxy it in (I'll need both 29 & 38mm ones)?

Hi Kevin,

I own two HP rockets. One has an Aeropack retainer. I think there are some 38mm 3D retainers that you can purchase that are not as expensive. Make sure you use the long setting JB Weld to adhere the retainer to the motor tube.

My other HP rocket as well as many of my Mid Power rockets, use two clips to retain the engine. This method is known as Kaplow clips, after the person that came up with the design. I use threaded inserts and mirror clips. Some people use T nuts and make their own clips. This is something you can purchase online. Check out Loc Precision. They sell a LOT of accessories.

Rick is always at METRA launches, I just bought some motors from him on Sunday. Also I think someone normally attends CATO, but i haven't been to one of those launches in a couple of years. CMASS hasn't had a vendor for a while.

Hi Kevin,

At this time, Wildman Rick from Connecticut is not scheduled to appear at a CMASS launch.