Building an AeroTech Strong Arm - Hints??

[ApolloMaker]

Howdy All ----

Well, decided on a Strong Arm for my first mid-power model. Was wondering if any experienced veterans out there might have any hints or tips on this model as I wait for my kit to arrive.

Also wondering if the stock motor mount is what most go with? This mainly in terms of length and the retainer clip length. I plan to use an AeroTech RMS 29 motor system in it.

Any tips or comments???

Many Thanks --- Bob

[AndyC]

Great Kit.

I built mine stock, with the clip. Its a good flyer on F and (mostly) G reloads for the 29/40-120 case. Clip works fine with that hardware. For me, a G load in this kit goes high enough. I've seen others who have left the clip out, or filed the top of the clip off to allow for larger motors.

[ApolloMaker]

Hi Andy ---

Hey, great news and input. One of the reasons I chose it, based on what info I could get, was some versatility in the kit. I have run a number of sims on RockSim and it looks real good. Has some leeway to tinker around a bit. I also assume you used the deployment baffle system as well --- that method really appealed to me as a "cleaner" method of cooling the ejection gas.

Anyway, super! Appreciate the inputs and feedback. Have you seen the instructions posted anywhere? I have looked everywhere I know how and cannot find a copy online.

Thanks Again --- Bob ---

[jdbectec]

Hi Andy ---

Hey, great news and input. One of the reasons I chose it, based on what info I could get, was some versatility in the kit. I have run a number of sims on RockSim and it looks real good. Has some leeway to tinker around a bit. I also assume you used the deployment baffle system as well --- that method really appealed to me as a "cleaner" method of cooling the ejection gas.

Anyway, super! Appreciate the inputs and feedback. Have you seen the instructions posted anywhere? I have looked everywhere I know how and cannot find a copy online.

Thanks Again --- Bob ---

You might find them here:

http://www.aerotech-rocketry.com/resources.aspx?id=4


scroll down to kit instructions

[slogfilet]

If you haven't checked it our already, take a look at Essence's Model Rocketry Reviews and Resources (EMRR) at www.rocketreviews.com

There's a pretty good writeup on the Strong Arm: http://www.rocketreviews.com/reviews...rong_arm.shtml

[hardinlw]

With the Aerotech baffle system you need to periodically use a wire hook to fluff up the wire mesh and shake loose any ejection residue to keep it from plugging up. 30+ flights on a Cheeta and still going strong. Also, make sure you soak the aft end of the motor mount tube with CA to harden it and be careful installing the motors so you don't fray the end of the tube.

[Boosterdude]

The Strong Arm is a good flyer, mine goes great on the G64. I built my stock and so far zero issues.

The only thing I would change is the elastic shock cord.

[UPscaler]

Very nice choice! My dad is going to build one soon, He plans on eliminating the baffle and fitting a 38mm mount into it. So he can get his L1 on H or I and his L2 on a J350 or J500. He's going to put a nomex heat shield in to prevent the parachute from melting. We are also putting a bulkhead into the coupler made form half inch ply and we are putting a screw eye in it to mount the shock cord. Pretty crazy huh?
overall, the stock strong ARM flies great. He just wanted a little extra zip

[ApolloMaker]

Wow Guys --- super feedback and pointers. I will check them all out. Looks like the Strong Arm has some good history with lots of possible tweaks and mods to make it a little better (or even a higher flyer) --- but most of my work for a while will be with G-impulse or below. Well now I am jazzed up on the bird and looking forward to it. Should be fun and I am glad that I am going with the rebuildable motor approach -- some Gs are going to be burning for sure.

Thanks Again --- now, to check out the sites.

Bob ---

[roadkill]

[QUOTE=UPscaler;74914]My dad is going to build one soon, He plans on eliminating the baffle and fitting a 38mm mount into it. So he can get his L1 on H or I and his L2 on a J350 or J500. He's going to put a nomex heat shield in to prevent the parachute from melting. QUOTE]


I got the feeling that 'chute melting
is gonna be one of the minor problems....

[ApolloMaker]

Hi-Yall Again -----

Here is a pic of an actual AGM-78.



Hope the pic turned out but it does show the coloration of the radar-transparent nose cone the Standard (AGM-78) carried. In tradition I may paint mine a brown-copper tone for a dab of realism as others have done.
Another pic has more of a blackish coloring.

For those not familiar with the application trivia of the AGM-78, it was an early anti-radar site missle.

Cheers --- Bob --

[Initiator001]

If you are going to fly it with nothing more than 'G' impulse motors, I would follow the instructions and build it 'stock'.

That's how I designed it.

[UPscaler]

My dad is going to build one soon, He plans on eliminating the baffle and fitting a 38mm mount into it. So he can get his L1 on H or I and his L2 on a J350 or J500. He's going to put a nomex heat shield in to prevent the parachute from melting.

I got the feeling that 'chute melting
is gonna be one of the minor problems....

Ha, no kidding.
We decided against the bulkhead mount earlier and we are going to attatch 1500 lb nylon directly to the motor tube.

We carlsons have a sense for putting big rocket motors in WAY too small rockets.

[als57]

Ha, no kidding.
We decided against the bulkhead mount earlier and we are going to attatch 1500 lb nylon directly to the motor tube.

You might want to make that tubular kevlar. Performance Hobbies sells some nice 3/8" stuff. Nylon tends to get crispy after a few launches.

Al

[roadkill]

'We carlsons have a sense for putting big rocket motors in WAY too small rockets. '

You might also want to
use birch ply fins, ttw mounted
and glass that puppy from tip
to tip and nose to tail...

Sims at 1.15 Mach and a boatload
of Gees at liftoff, way more than AT
plastic fins and finlock system can take...

Plus your apogee is over a mile high,
with single deployment its likely gonna be
a hike to the next county over for recovery...

[ApolloMaker]

If you are going to fly it with nothing more than 'G' impulse motors, I would follow the instructions and build it 'stock'.

That's how I designed it.

Well Bob, that is how I plan to fly mine anyway I like to get mine back in one piece and keep them that way. Looking forward to the fun.

Cheers --- Bob ---

[blackjack2564]

Ha, no kidding.


We carlsons have a sense for putting big rocket motors in WAY too small rockets.

You mean like this???



[Sorry folks I couldn't help myself!]

[roadkill]

You mean like this???
!]

[ApolloMaker]

Hi Yall Again --- another question came to mind after watching a couple of videos where the fins on the Strong Arm hit first in some landings. Did not fare too well.

Wondering if soft ground is the only answer or has someone has come up with another idea whereby the rocket body takes the hit, not the fin tips. Or is this the price for fins that protrude beyond the exhaust port???

Curios. Comments??

Thanks -- Bob ---

[roadkill]

AT finlock system is designed to be used
with superglue which is brittle resulting
in fins popping out rather than breaking
at rough landings.

Most of the time you can just pop them back in
with another drop of superglue. If you use epoxy
they are most likely to break...

Spare fins are available just in case...

Larger 'chute also helps a lot...

[ApolloMaker]

AT finlock system is designed to be used
with superglue which is brittle resulting
in fins popping out rather than breaking
at rough landings.

Most of the time you can just pop them back in
with another drop of superglue. If you use epoxy
they are most likely to break...

Spare fins are available just in case...

Larger 'chute also helps a lot...

Thanks Susan --- was wondering about the glues. Looks like a very light cementing with CA and fins locked well in place will be the answer as well as lighter landings with a larger 'chute. Looked over the assembly instructions and could not see any other way without much extra work and added weight.

Thanks for the comments !!!! --- Bob ---

[roadkill]

Couple more things that popped in
my oh so wondering mind..

Dry fit everything together first
outside the airframe
before you do any glueing.

Install a 29mm motor or casing into the
motor mount before fitting the fins, its
rather easy to crush/dent the mmt while
snapping the fins on if not properly aligned...

Toss the bungee shockie and use twice the length
of kevlar cord or better yet 1/4" tubular kevlar...

[Stymye]

also check the fit of the rings on the motor tube, for some reason, mine have all been way too tight, I think I measured .018 too small !
I ended up sanding the rings quite a bit to keep from destroying the motor tube installing them.

[AndyC]

I'd like to second the idea about using CA for the fins. When I built mine, I used epoxy, since its stronger right? Well, hmm. We have a soft grass field, but wouldn't you know it? The durned rocket landed on the gravel road and sheared the fin off just above the root. While I can't know for sure, a light CA joint would at least have had a shot at avoiding this by popping out. Urg. Rather than digging it out, I just epoxied the fin back on. Not as pretty as before, but still flies like a champ.

Also, the dry fit is important. When I built mine, I had not used the finlock system before, and missed some flashing on the fins since I only dry fit one of them. Final result was pushing them all in too hard since the flashing was in the way, which squished the tube a slight amount. If you look at the aft end, the tube is distorted/squared a tad.

[ApolloMaker]

Thanks all for the added comments. Some of these appear to be universal since I did read about the fit issues on the new parts and sanding and fitting prior to gluing...especially around the fins and MMT. Warnings and advice well taken. Mine will get heavy scrutiny and fitting prior to final assembly. Good to note the availability of spare fins and other MMT-oriented parts.

I will have my motor tube (29mm) to use to ensure the form of the MMT. Some CA stiffening of the mount may be in order if there is any undue flexibility.

Looking forward to the kit. Should be a fun build.

Bob ---