Motor for Apogee Zephyr

[b0g_nerd]

I recently finished building an Apogee Zephyr. I'm wondering if anyone has experience with this rocket, specifically what size motor is the best. I'm planning to use it for my L1 certification next month. Initially I thought an H would work, but now that it's fully assembled and painted I'm wondering if it's too heavy for an H and I should go for an I instead. I was a little generous with the epoxy that I used around the engine mount joints and the fillets since it's a certification flight rocket and I really wanted it to come out intact. Of course that added a little extra weight, and it currently weighs 1.4 kg. Thoughts?

 

[Scott_650]

Thrustcurve is your friend here - simple, straightforward, good results for conventional 3/4FNC rockets.

https://www.thrustcurve.org/

Plenty of H motors should work - either 38mm or adapted 29mm. Play around with TC and pick whichever fits your field best. Good luck on your L1!

 

[Titan II]

I'm wondering if it's too heavy for an H....

No
Run sims with openrocket

 

[Rob Campbell]

I certified L1 with a Zephyr. I used an AT H123 which is reloadable. If you prefer a single use motor, I've seen several people certify with Zephyrs on H100s.

 

[Scott_650]

I certified L1 with a Zephyr. I used an AT H123 which is reloadable. If you prefer a single use motor, I've seen several people certify with Zephyrs on H100s.

H100 looks good, an adapted 29mm H135 would be a similar choice - if the flyer doesn’t have any cases yet single use motors can be a better option than borrowing a case, loosing someone else’s case is one less thing to stress about

 

[Lotronex]

I did a Zephyr for my L1, it came in at 1.6 kg without motor. I adapted down to 29mm and used a H128W, had a perfect flight.

 

[Rob Campbell]

BTW, your Zephyr looks great.

 

[Rob Campbell]

I use an 8 second delay on mine. If you use a different motor, I recommend getting either Rocksim or Open Rocket to determine the optimal delay time.

 

[terryg]

The H100 does not have enough punch in my opinion. The thrust curve is very flat and is not a good fit, unless the rocket is built very light.

 

[GalantVR41062]

I do not have a Zephyr but the weight seems in line with others I have read about.

I built a 4" Madcow Torrent a few years ago trying to be a big park flier, and was able to make the 1500g weight class on the pad with a Loki G66r motor. I have flown this rocket with high power also. Be mindful, I had a pressure separation on a AT I 327dm attempt. I made the vent hole a little bigger and decided I would use shear pins if I was going to try a flight profile like that again.

Open rocket is my simulation of choice and can be a great tool to help hone in the flight profiles you could have with this rocket.

I hope you enjoy the journey and transition into a L1 attempt. A lot goes into motor and flight profile selection, CG/CP, thrust to weight, rail exit velocity (simulated and actual), flying the field, recovery plan, etc.

 

[loopy]

Looks great! The best thing to do would be to downlad the rocsim file from the Apogee website. You can then download OpenRocket if you don't want to pay for Rocsim, and open the file in OpenRocket. Change the overall weight of the rocket in the file to match what yours weighs, then load in some motors and see how they do.

What clubs are you looking at to do the launch for this? Our fields are full of crops for the summer...lol

 

[gldknght]

My opinion, but a sim program like Rocksim or OpenRocket is almost a requirement for cert flights. Can it be done successfully without? Yes. However, there is no way to measure how much EASIER the process is with a sim program. I use Rocksim myself, made my L2 cert almost a routine weekend flight. I wouldn't even consider an L3 attempt without a sim.

 

[neil_w]

My opinion, but a sim program like Rocksim or OpenRocket is almost a requirement for cert flights. Can it be done successfully without? Yes. However, there is no way to measure how much EASIER the process is with a sim program. I use Rocksim myself, made my L2 cert almost a routine weekend flight. I wouldn't even consider an L3 attempt without a sim.

We have observed multiple instances of folks asking for beginner-level help with OpenRocket to plan their L3 cert, which presumably means they did their L1 and L2 without any sims. I find that kind of fascinating. Maybe if they're doing their L1/L2 with kits they just use thrustcurve.org and don't feel the need to sim. Dunno.

 

[BDB]

Ask a simple question and get a variety of answers....it's what we do on the Rocketry Forum!

Fly this rocket and have fun. It's a proven winner. Eventually, you should learn how to simulate flights using Thruscruve (free website or app), Openrocket (free software), or Rocksim (paid software). All high-power motors have adjustable delays, so you need to run the sim so you know what to adjust the delay to.

I ran some sims for a 1.6 kg Zephyr using Openrocket. I downloaded the file from the Apogee website and then overrode the mass to 1.6 kg. You should measure the center of gravity of your rocket and put that in as an override too, but this should be a pretty good approximation. I then simmed it with all four of Aerotech's single-use 38 mm H motors. Here are the resits. The file is also attached.



Any of these motors will work well. The key things that you are looking for in the sim are the "Velicty off rod" and "Optimum Delay." The velocity off rod needs to be at least 50 ft/s for a safe flight. All of these motors should give a safe flight. The optimum delay varies by the motor, but this is what you will need to adjust the delay on the motor to. (+/- 1 s is close enough). Here is an Apogee video about how to adjust the delay of these motors. Tim uses a H100 in the video, but they are all the same. If you don't have the delay adjustment tool, you can probably borrow one from someone at a launch. If yo are buying the motor at the launch the person selling you the motor should have a tool that you could use.

Congratulations on building a great-looking rocket. I've seen lots of people do L1 certs with this kit. It flies great. Good luck and have fun.

 

[mundayr2]

As others have said, Sim it in Rocksim or OR with any motors you're contemplating. That said I did my L1 cert on a Zephyr, with an H115DM with a 8 second delay, flew perfectly. Your results may vary so Sim Sim Sim.
Just my couple pennies. And good luck
Bob

 

[Astronaut Cheeseball]

Great looking Zephyr! Did my L1 cert on H100W with 8 second delay.