Im probably becoming a pest, but......HELP! Ive got a Semroc Arcas coming, its my first mid/high power rocket and i dont understand ANYTHING about the engines.......1)the recomended engines are an E18-4 and an H128-10...i looked on the Aerotech website and cant find them, so who or where do i get these engines from? 2)Do they make these engines like the low power stuff, or do i use "reloadable" engines ? 3) What the heck are reloadable engines, and how complicated are they to use, and what do i need for a complete reloadable engine? 4) What is used to ignite these things? ANY and AS MUCH information that somebody could give me would be GREATLY appreciated as i am TOTALLY LOST and want very much to get it right the first time! Many Thanks, a very confused Bill

The motors listed for the ARCAS aren't everything you could use for the model. They are the upper and lower range.

(Edit: Did you download the Aerotech PDF catalog? Click on the "product" tab.)

The E18W-4 is a reload kit for the RMS-24/40 casing.

The H128W- is a reload kit for the RMS-29/180 casing.

Reloadable motors require a reload casing. An aluminum tube with threaded end caps.

For each flight, you purchase a reload kit. The kit has a fuel grain (sometimes more, for really big motors), a plastic nozzle, a delay slug and an ejection charge . . . plus carboard liners and rubber O-rings to hold things snugly in the case. It takes about ten minutes to put a reload motor together, plus another five to ten minutes of cleaning afterwards.

In exchange for the labor you save a lot of money.

* * *

There are also Aerotech single-use motors. For example, there is an E15-4 and a E30-4, both of which should work fine. Aerotech also makes inexpensive "Econojet" motors in F sizes.

For example, there's a Econojet F27R-4 that should work well. (This is a "low" F; if you use a full F you'd want a -6 or -7 second delay.)

* * *

Igniters are included with Aerotech motors. You'll need a 12 volt launch system, with nice long leads.

Based on your jumping into mid-power I think you are eventually going to wind up at Aerotech. I would suggest you download the current Aerotech catalog and give it a serious read. The AT single use motors can be a little confusing between the Econojet and Hobby-Line brands, and be careful to look at the motor mount size. For example there is/are Econojet D's that are 18mm motors. I think you will find that there are equal numbers of proponents of black powder single use and more exotic reloadable motor systems. The main issue for you is going to be how often am I going to fly, do I want to deal with component wear and spares on a reloadable motor, how long am I going to keep reloads around the house. If you are happy with an ARCAS that goes 300 feet, then the Estes D is probably going to be fine (just don't let anyone sell you a "P" motor. They are boost glider motors - plugged without an ejection charge).

http://www.aerotech-rocketry.com/im...ech_catalog.pdf

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Okay, you guys are definetly starting to clear some things up for me.......i downloaded the building manual for the Arcas and it says that the ship will accept 29mm motors as built, so i reffered back to the Aerotech catalog ......it appears to me that there are several single use motors both in the Econojet and hobby line that go up to a G80T in power.......i would like to get some altitude out of this ship as the field we launch on has plenty of room! I would also , at least for now, like to use a simple, (i hope) single use motor that you can just install and launch, then replace with a new, ready to go motor......the ship can handle up to "H" motors according to the manual, but i only found H motors in the RMS catagories........ what do you guys think? Does it sound like im kinda headin down the right track? Please feel free to respond with any suggestions, as im wide open to it! Thanks! OH! What about igniters? Are they similar to an Estes igniter?

I'd start with a Econojet F motor. Work your way up from there.

The estimate on the Semroc website for altitude on the H128 is WAY off (to the tune of 1000' !) and this was confirmed by Carl at Semroc but has not been corrected on the instructions or website.
The Arcas will hit around 3700' on even the "baby H" H128-M(10)W.
I have not launched mine on anything over a 80n-sec F50 and it gets plenty high on the F50. The H128 has more than DOUBLE the total impulse of the F50 !

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I agree with Stefan and GH for starting out with either single use or EconoJet F motors for your first few flights. Personally I've found that the F42-8T EconoJet gives a nice flight profile for a smaller field. It will obtain a respectable altitude even with EconoJet motors given it isn't a very heavy model for it's size. That's my buddy Whit in one of the photo images loading it on the rod at our Luling field for it's first flight.

If you are flying on sod you can reduce the 24" chute to 18" to bring it down a little faster provided you have a soft field to fly from or if you have limited area to recover the model in.

I used self adhesive label stock on the fins but did not sand the diamond airfoils. I built mine using the alternate HPR build suggestions for H motors as detailed in the SEMROC instructions for the Arcas and used epoxy for the entire build but as you can see in the photo with the model in primer I kept the fillets small to keep the model light. It is strong and I've never cracked or lost a fin on landing even on G motor flights with the 18" chute.

Enjoy your SEMROC ARCAS. It's a great SLS model and well worth the money.

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I want to thank everyone who has offered input to help me out with my first mid/high powered rocket project to this point, i certainly have a better grasp on the engine issue thanks to you folks......i even found a local web store to purchase the engines from here in Florida....i havent even started on the kit yet, but i just want to get my ducks in a row by the time i have it built......im still AMAZED at how much fun im having since i got back into rocketry......i just put a coat of paint on my retro Sprint, so i hope to be starting on the Arcas next week! If those of you that have built and flown the Arcas have any additional advice that might come in handy to me, please feel free to give me a shout! What a GREAT hobby! (more like an obcession!)