LOC Precision EZI-65 for level 1 cert motor choice

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
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The H123W is a nice load. The 240 is the largest total impulse that casing carries. You can use the same closures and get different casings to give yourself a wider variety of loads. Take a look at the https://secure.consumersinterest.com/performancehobbies/store.asp?groupidH "complete motor systems" where Ken sells one set of closures but multiple casings to give you the complete set of reload possibilities. For about $150 you can get one set of closures and all three 38mm casings. That will get you your nice assortment of H and I reloads. See Ken's page at https://secure.consumersinterest.com/performancehobbies/store.asp?groupidD for a list of the reloads each casing takes.     Will
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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 http://www.drrocket.com/ and http://www.rouse-tech.com/ hardware is very nice...
I also like the http://www.lokiresearch.com/ products.
Will Marchant wrote: ...

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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?
http://www.drrocket.com/sizematters.asp Also 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

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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 in Virginia! So I get to fly with NOVAAR, TRA-VA, and MDRA and telecommute to boot! I went to a LUNAR launch many moons ago (sorry, I couldn't resist that 8) and they were nice folks. I need to try and schedule a business trip to coincide with one of their launches...     Will
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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 http://www.wrasp.com . 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.
http://www.spaceflightsoftware.com/will /

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I'll also recommend "pRASP" and "RocketCalc" utilities for your Palm OS handheld devices: http://members.shaw.ca/whortens/index.html . I never leave home without them...
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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.
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Thanks Bob, I'll definitely look into some software. The price of the rocksim is a little steep for me now, but I just downloaded winrock and although not fancy it seems that it will do the trick. I don't have a Palm or PDA as of yet. I'm a bit of a luddite in that regard-I hate to be too accessible.
Bob Kaplow wrote:

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Thomas Koszuta wrote: Thomas, it is possible that the rod was insufficient and slowed the take-off. It was six feet tall but a little flimsy. What diameter should the launch rod have been? I thought that when I worked the math F20s were underpowered. Both engines fired and I wouldn't say the rocket was significantly heavier than 29oz. (maybe 5 oz more at very most) The rocket went on a horizontal trajectory and hit the ground before ejection charge. (Thankfully away from all spectators, which were approximately 100 feet away.)
Thomas wrote:

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Sorry for above error. Thomas did not write that, Laura did.
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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
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Thanks Christopher, The rod was aluminum and 1/4 inch, so that might be the problem. There was also a fair wind and the rocket flew into the wind. weathercocking? the rod was also one that could be broken down with threaded sections and maybe there was too much friction. I did video tape it and maybe I'll post it when I have time. Christopher Brian Deem wrote:

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Thomas, it is possible that the rod was insufficient and slowed the take-off. It was six feet tall but a little flimsy. What diameter should the launch rod have been? I thought that when I worked the math F20s were underpowered. Both engines fired and I wouldn't say the rocket was significantly heavier than 29oz. (maybe 5 oz more at very most) The rocket went on a horizontal trajectory and hit the ground before ejection charge. (Thankfully away from all spectators, which were approximately 100 feet away.) Thomas Koszuta wrote:

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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?
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Bob Kaplow wrote:

Bob, she was referring to the LOC 4-29SS. Although it did come with 1/2" launch lugs.
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Thanks Darrell, There are too many good folks in this forum. I can't keep up. I wrote in another post that it was an aluminum 1/4 inch rod and even worse, it had threaded segments. I'll take a look at the video when I have a chance and the answer to why it went missle on me may be more apparent. Darrell D. Mobley wrote:

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Where in Illinois were you? There's a lot of us around the Chicago area. Stop by and say hello next time.
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Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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Bob, I was down in the Bloomington Normal area. Bob Kaplow wrote:

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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.
Larry
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