aerotech engines

[ddanhra69]

Why is it that every RMS I put together has to be modified before assembly? Customer service says they are aware of it and it is normal to sand or peel a layer off the tube for it to fit. Do y'all agree with that, do y'all do the same thing? Dwight

[ghrocketman]

About 40% of all the Aerotech RMS reloads I have assembled (18mm,24mm,29mm Hobby Line and 29mm High Power RMS) have required peeling / sanding the propellant or delay grains. It is normal and would be very difficult to manufacture without this as they do not know the temperature and humidity of your specific area when you assemble the reload.
It unfortunately is a neccessary evil with RMS; you must either learn to accept this or stick to single use composites, which gets VERY expensive.

[Ramjet]

I've only used a half dozen or so 29mm reloadables and a couple 18mm's, But I've never had to peel or sand one.
Mind you I really had to push on the 18mm's, and I was a bit concerned about it, but they went in. And they worked fine. Those were assembled on a VERY humid day. And they were old.

I'd say that it's probably helpful I live at low altitude, they have more ambient air press on em, and I tend not to open them until the rocket is otherwise ready for flight.

How about a poll, Just what reloads were tight? Mine were H-97J's for the 29mm and D15's for the 18's.

Ramjet

[ddanhra69]

Ramjet, every one i've layed my hands on. E16's 29 mm. F52's 29 mm. E28's 24 mm., but i've read that it's normal and i've accepted that and will sand and move on. The way I see it, my time is worth something. To clean up and reload is not a problem with cost, but clean up, sand and peel and test fit and reload? SOB!! Cheaper to slap a SU motor in? I'll just settle down and relax and do "it". Dwight

[Ramjet]

OK, lots of tight fits. I wonder...
Who made the casings you use?
Mine are the gold ones ; Monster Motors by ROUSETECH INC.
Perhaps they are a tiny bit larger inside diameter?
No problems at all with these so far.
Hmmm, another thought, I seem to always load them when they are hot from sitting in the sun. Thermal expansion maybe?

Anyone else got any input on this?

Ramjet

[Mach1]

All the 38MM loads I have flown lately with the phonilic liner have needed sanding / hammering to get the motorliner in the case. This is very frustrating. I sanded the heck out of the last one with 50-grit, and still needed a jackhammer to get the liner in!! :mad:

Weather it is normal or not, flying should not be that hard.

[ddanhra69]

You mentioned your case sitting in the sun. What I'm talking about is propellant grain adapter fitting into the liner tube and the delay spacer fitting into the delay insulator. The liner tube with propellant grain inside fits fine in the motor case. I am now also pissed at the Strong Arm kit I bought from aerotech. When fitting the fins through the main body tube and snapping them into the fin locks, the fin tabs aren't long enough to snap in with out slightly bending the main tube in. I just couldn't get it without some modifying to the fin. I had no idea a kit would be so hard. I get tired of it and have to set it down and think, "what can I do to make this work"? Dang it!! But someone previously said, "learn to live with it and fix it". :mad:

[Initiator001]

I am now also pissed at the Strong Arm kit I bought from aerotech. When fitting the fins through the main body tube and snapping them into the fin locks, the fin tabs aren't long enough to snap in with out slightly bending the main tube in. I just couldn't get it without some modifying to the fin. I had no idea a kit would be so hard. I get tired of it and have to set it down and think, "what can I do to make this work"? Dang it!! But someone previously said, "learn to live with it and fix it". :mad:

Here's how I resolved the issue with the fins pushing in the body tube.

1) Without using any glue, pass the fins through the slots in the body tube and snap them
into the Fin-Lok rings.

2) Using your fingers or a dowel, reach inside the body tube behind where the fin enter
tube and, carefully, push the wall of the body tube outward towards the fin. It should
pop back into place. Repeat for the remaining fins.

3) Apply Medium CA adhesive to fin/Fin-Lok joints and where the fins enter through
the body tube. Do not get glue on the back/rear of the aft-most Fin-Lok ring.

4) Seat aft centering into back of model and press it into the body tube until it stops
against the backside of the rear Fin-Lok ring. Apply CA to ring/motor mount and
ring/body tube joints.

That should do it. It can, also, be an issue with these same fins and the I.Q.S.Y. Tomahawk model.

Hope that helps.

Bob "Strong Arm Designer" Sanford

[ddanhra69]

I know you designed it Bob. I thank YOU for replying since you designed it. I always try to try all conservative fixes before modification. The front root edge on all fins would not snap. Since the root edge was say 1/16 from the tube, the snap lock was say 1/8 from locking. I tried everything my pea brain could think of. However, the aft locks would lock since there was no centering ring in yet so it slightly flattened the body tube in ALL 4 fin positions. Then of course the centering ring won't go in. :confused: Therefore I HAD to modify. I am sorry! VERY! I hate screwing with stuff that should work. It makes me feel like I must be some kind of engineering GOD and I'M NOT! At any rate, it's cool. I know I sent off the warranty paper, but I won't use it if it's because of me screwing with it (the fins). I glued all well and barely had to flatten the cent. ring in all 4 fins positions and glued it all up. I think she'll be fine Bob. I just reloaded a 29 mm with an F22J and had to sand all the white off the grain adapter tube and she went together fine from there. Later, I hope to launch some today!! Dwight

[Ramjet]

Like I said, mine have all been fine except the 18mm D-15's, those were tight getting the liner with grain inserted into the casing.

How about it folks, who else has or has not had problems here?

Ramjet