Makers Corner

Dear Forum,

I'm a new member buying my first motors for an Aapogee Zephyr rocket kit intending to use them for a Level 1 Certification attempt. My question is: How many motors of what sizes should I buy for a Level 1 Certification attempt? I've ordered (2) Apogee G61W's and one Apogee H123W (for the certification attempt). Your recommendations?

Kevin Scannell

Hi Kevin,

That's a nice looking rocket for your L1 attempt. Even though two G impulse class motors will in fact add up to an H, by the L1 certification rules you will need at least one(1) H motor, even if using a cluster powered rocket. You wouldn't want to cluster anyway, as it would add complication at a time when you really don't need it; unless you really want the challenge of it. Unless something has changed (and to my knowledge), you can only buy one motor for your certification attempt from a dealer (they will be asking for your proof of certification). Good luck!

NAR #74527 L1

For my L1 certification, I also used a 4" diameter rocket, with a 38mm MMT and an optional payload section (BSD Horizon - OOP). After sim'ing in Rocksim, I tested the rocket first without the payload section on a high impulse 'F' motor, and then with the payload section on a G80. Both in Acton, both 29mm motors with an adapter. Both flights with a JLCR, and both recovered without harm.

After building confidence using those motors, I cert'd with an H238 (I think) at Amesbury.

Looking at the Rocksim data for your rocket, I would fly first with an F52-5T (optimal delay is 4 seconds - 420' at apogee), and then something like a G77 (optimal delay is ~5 seconds - 690' at apogee). Both would result in lower (but not too low) altitudes. But the G61s that you bought would also work, with an altitude at deployment of 775' (optimal delay 5.25 secs), which is recoverable at Acton with the added insurance of something like a JLCR.

To answer your question, you won't need more motors than what you have to verify your build and finally cert. Fly it a couple of times on the Gs, and then cert with your H.

Great background info (& advice). Thank you. I'll be using a Aerotech 29mm G78G-4 motor in a Motor Mount Adapter Kit 29/38. Does it matter whether I get a threaded or flat bottom retainer to hold in the adapter & motor? (The Zephyr motor tube extends out of the rocket 1/2").

Hi Kevin,

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

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,

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.

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)?

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.

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?

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".

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 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 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.

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.

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!

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?

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.

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?

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.

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.

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).

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’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.

Since there are always unknowns and since you are flying a well-designed kit, I suggest you fly it on a small H as its first flight.

I don't think there is much to be gained by flying it on G first.

Jim

Thank you to all who replied for your advice!

I learned a lot. Thank you for running the Zepher through Rocksim. I just ordered myself a JLCR.

Kevin Scannell

Wow! Motors are expensive. $80 shipping! I ordered straight from Apogee. What's my best option for purchasing motors? - Kevin

Apogee is pricey. Believe it or not try Balsa Machining Services. They offer a decent selection of motors and at a reasonable price, assuming they have stock on the motor(s) you want.

Buying at the field is a great option when available. Unfortunately, we usually only have an HPR vendor there once or twice a year.

You could also go in with others to share the ~$50 HAZMAT shipping fee. There's often several others looking to share that cost.

I love Balsa Machining as a vendor. Apogee too, though I agree the latter is an expensive options for motors. BuyRocketMotors.com also offers good discounts.

You'll also need to decide whether to buy a reloadable motor and case, or use a single-use (DMS) motor. If you've never assembled a motor before, then DMS is a good option. Or at least go with a Cesaroni case and motor since those are much easier to assemble.

Even though you have a 38mm MMT, you'll save a little bit in motor cost if you go with a 29mm motor with an adapter. Make sure your motor retention will retain both the motor and the adapter. I strongly recommend against friction fit for HPR.

Our next launch is in ~10 days in Acton which can't allow HPR. So that would be a good time for a first flight on a G motor. While the 29mm Gs are more common, I do love the 38mm 1 grain motors like the AT G67R

Where are you? I am planning to go to METRA this weekend and URRG next week, soI could potentially pick up an order for you. I won’t be in Acton, but we could arrange a pick up if you are close to Brookline or Cape Cod.

Sam

Thank you both Jim & Sam. I'm in Hingham but already ordered a RMS-38/120 casing with closures and an Aerotech 38mm HP SU DMS Motor - H100W-14A to go in it. I need to decide what I want to do for future launches before investing in more motors. So far I just have my first rocket kit (Apogee Zephyr) coming and the one H motor kit w casing for the Level 1 certification. I'm counting on one certification flight to work the first time this September at Amesbury. I built & launched a few Estes A rockets as a kid and am just getting back into it. Any recommendations for what to build and/or launch after the Zephyr would be most welcomed. - Kevin

I usually either buy them in person, or if I pay hazmat I am usually spending enough to make the shipping reasonable (often >$1000). There are a few L1 motors that qualify for normal ground shipping which you might also want to consider. Also Wildman CT isn't that far, and he can arrange pickup at his house.

I'm interpreting that you wrote that you bought a DMS motor to go in the casing. To be clear, a DMS (Disposable Motor System) motor does not use an RMS casing - it comes with all necessary parts that you assemble and use once. You'll need the RMS/DMS delay drilling tool do bring the 14s delay down to ~5s.

You also wrote that you're going straight from Estes 'A' as a kid, to an L1 first flight getting back into the hobby. Why not build and fly on some F or Gs first at Acton, or buy an Estes Pro Series and fly on one of their 29mm black powder motors? Even Wernher Von Braun got some pre-flights in before going "all-up" on the Saturn V. :-)

I agree that its a good idea to get some experience with F's and G's before jumping to HPR. There are some really good high thrust F's that will send an L1 rocket up 200-300 ft. And there are of course G's that can easily lift a light weight 4" rocket. I have flown my Estes PSII Nike Smoke on motors from F to H. You can even fly it on a small I if you beef it up a bit.

I agree with Sam and Todd. Just going by what you mentioned about your rocketry experience so far it looks like you are looking to go from flying some A impulse Estes rockets when you were younger straight to an L1 cert attempt. You should get some experience with the lower impulse motors first. Have some fun. Play around with that JLCR you just bought. Try out some different sized parachutes. If you haven't already, use RockSim (or OpenRock if you would prefer) to play around with some simulations and see what the different motors can do for that Zephyr. Sam is absolutely right. You can get some decent lifting power just from some of those F and G motors. Jim also brings up another very good point. Keep that 38mm motor mount that came with the Zephyr kit, and then use adapters for whichever motor you want to fly it with; many more rocket motor options for you to try out and play around with. Remember to build the kit as strongly as possible (the kit instructions look pretty good) so that it can handle those higher impulse motors (and some rough landings!).

Alright, I'll try the Zephyr with smaller motors first. I was hoping to save $$$ by not ordering the smaller engines but what fun is that?

And yes, I bought a DMS motor and an RMS casing. I guess I'll now get 1 or 2 F or G RMS motors to go with it.

Just for reference, I've flown my Zephyr on Both G64-4 and G76-4 motors. Mine weighs 52 oz with no motor. I got a nice safe 538 ft. at the June 15 Acton launch on a G76-4.

Thank you for your response. Are the HPR vendor visits scheduled? How can I find out when and where they will be?