Hi, I have purchased the ezi-65 with intent to certify level 1. Which motor choice is best? It can accommodate a 29mm, 38 mm or 54mm motor. I am looking for versatile, cheap, and reliable. I know-pick two, but now all three. I am looking at the RMS 38/240 case with an H-123W reload. Is this a good choice? Also, what does the second number after the forward slash mean in the case size? For instance 240? Is there a choice of case that will accommodate an H or and/or I motor? I appreciate the help. Laura
Doh! Sorry, Ken's 38mm motor system just has the lower three casings. You'd need to buy the upper ones individually...
I forgot to add that there are currently three manufacturers of licensed Aerotech hardware: Aerotech, DrRocket, and RouseTech. All the pieces are interchangeable. You'll still find some Aerotech motor hardware inventory floating around. The
H-123W is a good choice. I certified on a PML D Region Tomahawk with an H-242T which also fits the 38/240 casing. It has a higher thrust and was recommended because it was pretty windy that day and a faster liftoff has less chance of weathercocking. I had to chase it almost a mile through waist high hay. With the Aerotech casings, you can usually find 3 or 4 reloads that fit each length casing. The propellent formulations are White Lightning (yellow flame and white smoke), Blue Thunder (blue violet flame and no smoke but high thrust, Black Jack (orange flame and black smoke), and Redline (red flame and smoke). I like to fly the Tomahawk on the H-123W because I like the smoke, but the rapid acceleration on the blue thunder is nice too.
I chose the 38 casings for my investment into HP reloadable motors. You can fly from G's (38/120) to J's (38/720 and 38/1080). The 29mm casings don't really cover the L1 range well at the top end. The 54's are all J and up, as far as I know.
The H123W is a very nice choice for that rocket with the 38/240, though not on the recommended motor list.
The post by Larry described the four different loads each one will take nicely. I like the Redlines and the BlackJacks myself. In general, the BlackJack will have the lowest thrust (slowest burn) and impulse for a given casing. The Redline and White Lightning are moderate thrust and impulse, and the Blue Thunder is a very fast burn with high thrust and total impulse.
If you multiply the weight of the rocket in ounces (loaded, ready to launch) by 1.4, you get the minimum average thrust in Newtons recommended for the rocket to maintain the 5:1 thrust to weight ratio for safe liftoff.
Rocket Weight (in ounces) x 1.4 = Minimum average thrust (in Newtons)
My Tomahawk was about 100 ounces (with the motor - you have to estimate first then confirm when you choose a motor) so I would pick a motor with at least 140 N of average thrust to launch it. An H148R would be rock bottom minimum thrust for 5:1. A J90 would not be enough thrust to safely launch it.
The ezi-65 has a published weight of 35 ounces. Using 42 ounces as a reference with a motor (G61W is about 7 ounces), the minimum recommended average thrust for the motor would be 42*1.4=59N. Any 38mm motor will launch it with enough authority for stable flight, even the G61W (check the weight) or G67R. Some of the big Blue Thunders will have it close to Mach
The I435T will launch it at 54 g's in the simulation. The EZI-65 is a light HP Rocket. Look for the lower thrust motors (my opinion).
The number after the slash is the approximate maximum impulse that the particular case will accomodate. Each increase in impulse of 120 Ns is another grain.
All of the enclosures for a particular size have the same fore and aft fittings, even between AeroTech and Dr. Rocket. You only have to by one full motor (tube and closures) and then just the case (tube) for every other motor you would like.
I launched a 3" PML AMRAAM on an H148R for my L1 with a borrowed 38/240. An I161W in my 38/480 case was also a nice AMRAAM launch. My first dual deployment a couple flights later with the PML Tomahawk on an I195J, also in my own case - 38/600.
Al's Hobby
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had a 25% off thing going on this summer, maybe until September. I picked up the 240, 360, 480,
600, and 720 casings for about $200. All except the 600 - which is a Dr.Rocket - are Aerotech. The special is not listed on their website now, but you may want to give a call.
Thank you Will, Great answer! Knowing the meaning of the impulse number clarifies much. I did notice an apparent discrepancy. On the page below, an H-238T is recommended for a 29/180 case. Am I missing something? Does it have to do with total impulse as opposed to average thrust?
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why would I want to put a H-112J into 38/360 as recommended on the same webpage? I appreciate your help in this. When visiting Illinois, I recently fired what I believe to be an underpowered loc precision 4-29ss using two F20-4Ws, which was a little scary and embarrassing - not to mention costly! (lost airframe tube, and transolve beeper) No one was harmed; the crowd enjoyed it, but... I will NOT repeat it! I needed to do the math :-( BTW, I took a look at your page, spaceflightsoftware.com. I'm located near Berkeley, and will be checking out lunar.org, which seems to be the only rocketry club in the area. Anyway-Thanks-Laura
Thomas, when you say it's not on the recommended list, whose list do you mean? Loc Precision's List? NAR's list? Please explain. I want to make sure that I can recover the rocket and I don't have any decent electronics for locating other than a transolve beeper. So I would rather fly the rocket at a lower altitude to increase my chances, but I still need to meet the certification requirements.
Thomas you are describ>H-123W is a good choice.
I saw that some other people qualified on the H-123W so it wasn't my idea, but why reinvent the wheel. If anyone has a better suggestion to keep the rocket lower in altitude, but meeting the requirements please let me know. Thanks again-Laura
Exactly, Laura! The total impulse is used to get the limiting number after the slash and not the average thrust.
Good find on the DrRocket sizing chart. Interesting question about the H112J in the larger casing. Maybe you want the BlackJack smoky propellant but you need a higher average thrust than the H73J?
Condolences on the loc! 8( Nothing like seeing a rocket drunkenly wobble off the launch rod! There are a couple of ways to do the math "back of the envelope." I divide the average thrust by 25 to get an approximate maximum liftoff weight in pounds. Of course, running RockSim is best and looking for an appropriate (45 fps or higher?) exit off of the rod.
Although I work full time for UCB, I actually live > Thank you Will,
The "180" in 29/180 is the total impulse. The "238" in H238T is the average impulse, in Newtons. The total impulse of the motor is 178 Ns. An H112J has 280 Ns of impulse and is a three grain motor for the 360 N case.
A great, free performance calculator for rockets is wRASP
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Use it to simulate the launch before you fly on an unknown configuration. Watch the "Launch Rod Velocity". If it is below 30 MPH, you do not have enough thrust to safely fly the rocket.
The 4-29ss at 29 ounces should leave a 6 foot rod at 39 MPH. If both motors lit, then your rocket was either significantly heavier than the 29 ounces, or it was sticking to the launch rod. Even at 50 ounces, it should have been fine at 29 mph.
I certified Level 1 on an EZI. I used an AeroTech I-161. Flew it again on an I-211. I-161 with medium delay worked perfect. Flew it, certified, rocket fell in road way, truck driver flattened nosecone with front tire. Seasoned!
Hi Laura, Welcome to the world of HPR - it's a great world in which to live.
I certified L1 using an EZI-65 and an H123W. It's plenty of motor for a cert flight and it won't go high enough to need any electronic gizmos for recovery or location. I've also flown it on H242T, H112J, I161W, and I211W. The I211W makes for a fantastic flight. I can't wait to try one of the new AT I225FJ motors (38/480 motor case).
I even did my L2 cert using this rocket and a J350W! During building I reinforced it to make it stronger and heaver for high thrust motors, but I don't reccommend putting a J350 in a stock EZI-65 :(. When the LCO pushed the button the rocket virtually lept off the pad and disappeared into the sky. It was overcast - bad. I looked and searched but never saw it again until some young spectator at the launch came up carrying it. Thanks! I have no idea where he found it. But I did get my L2 :).
I remember the first time I launched the EZI. The biggest thing I had launched before that was a mid-power AT Arreaux on a G40W. Anyway, as the EZI sat on the pad I kept asking myself if I really wanted to push the button or not. I finally got the courage and so up it went with a roar and smoke. It was absolutely awesome. I'd like to think I had a feeling similar to that of NASA people when they have a successful launch. Now I launch 2-stage rockets with 3 motor cluster boosters (like 2-J350W's & J540R staged to K185W). Although they're complex and expensive with many more possible failure modes, and more "exciting," nothing will ever compare to watching that EZI go skyward the very first time.
Now male bonding at launches is OK, but if you can pass on your secret I'd sure like to get my wife involved in rocketry too!!!
Hell, I even launched the EZI on a G80 as a test flight (to make sure the thing works) and it lands only a few hundred feet away. If you are trying for a cert, do it as low as possible to avoid complications.
I don't know what caused your problem,it should have worked with 2 F20's. About two years ago I launched my NCR by Estes Big Brute on a F20-4. This is a short, 4 inch diameter rocket that weighed just under
30 ounces at liftoff. It wasn't a real impressive flight, just a short lob up 3 or 4 hundred feet (just guessing), but it worked. Your flight sounds more like off center thrust, or on motor slow to ignite. Christopher Brian Deem NAR 12308 TRA 2256 level II
I've been using them for as long as I've had my brain damaged palm, and wouldn't be without them. Also from Wayne on the same site is CPcalc for staility checks, and NP, which is a port of my Neutral Point code for glider stability calculations.
You may have been the victim of rod whip. a 1/4"x6' rod will flex quite a bit. If it's aluminum and not steel, it will flex even more. An E-Z-I is a pretty big rocket for that size rod. Doesn't it have 1/2" lugs on it?
-- Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)!
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