Hi All;
I have good intel that says I'm getting an Aerotech G-Force for Christmas (having kids is occasionally a good thing ) If this is true, I love the rocket- have loved it for some time, actually, just couldn't stomach the MSRP. In reading EMRR about it, my concerns have been validated- it's too big a rocket to fly on much of a variety of motors- as the name implies, you're pretty much stuck with G motors. In my stable now are AT's Initiator, Arreaux, and in sick-bay the Barracuda. Each of those have a plethora of MP AP motors on which to journey. I also had the Mirage, but it died...same problem as the G-Force tho: when one operates at the upper limit of design, the number of available options diminishes.
While I'm not currently a member of TRIPOLI or NAR, nor a member of any sanctioned area rocket club, I'd not like to inhibit my future endeavors.
The aforementioned G-Force seems like the ideal transition- I can fly it in the local field on 29mm, but can also use it to get my L1. EMRR suggests forgoing the motor hook and retaining block, which makes sense, but what else can I do to expand the number of motor options available?
Should I build it as a 38mm? 54mm? Where does one obtain the MT for such things? How do I mitigate the loss of the FinLoc rings?

I would just stay with the 29mm mount-there are some really nice 'H' and 'I' motors. UNLESS you intend o go bigger into the 38mm and 54mm motor range...

I would also suggest forgoing the ejection mesh..the mesh in my Mustang had gotten clogged and caused a small fire inside the rocket burning up the shock cord..

__________________
Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

Second what PJ said.

I just finished a modified G-Force build. Mine is modified for 54mm and dual deploy.

Here's a list of what was changed:

1) MMT changed to 54mm
2) Fins/Finlock ditched, replaced with TTW fins made from 0.100" carbon fiber plate.
3) Both body tubes replaced with thin wall BT-101 which was then wrapped in enough glass to bring the resulting tube back to the original thickness.
4) Nose cone modified to accept a GPS transmitter
5) Replaced the coupler with a longer unit, added hardware to make it an e-bay.

Aside from the nose cone, there isn't a single part on this build that came from the original kit. Even the nose underwent some surgery.

In the end, I really ended up doing a scratch build clone, and didn't need to purchase the kit after all.

Moral of the story... There's plenty of good 29mm motors that will be perfectly fine in a G-Force.

Discard the mesh, motor hook, and motor block. Replace all that with an Aeropack (or similar) retainer. Leave off the plastic pseudo-baffle/shock cord mount point if you want to use the longest of 29mm motors. If I recall correctly, the longest 29mm motor is 1-2" longer than the motor mount.

Cheers,
- Ken

I'd leave it at 29mm myself. As stated earlier, leave out the motor hook, thrust ring, and the cooling mesh. I certified with a modified Mirage on a H238. It has since flown on a H180 and a H128. For motor retention, use Kaplow Klips or something similar.

__________________
'Til next time,

Mike Toelle

NAR 31692 L1

SAM 0373

+1 for pantherjon and tsai.

Lot's of options when you include the CTI 29mm stable.

Leaving out the motor block/thrust ring gives you those options.

The only caveat that I can think of:

1) Add a longer MMT with a CR to minimize the volume the BP has to pressurize. In lieu of this you could put a 9" or 12" chute on the nose cone to add insurance that all the laundry comes out.

2) After the mods, double check the CG to make sure it is at least the distance required in the stock build.

I think keeping it a 29mm bird has the least amount of headaches, or as tsai has said you need to re-engineer the airframe internals. Keep it fun and simple.

Greg

I built and flew a G-Force for several years.

It's fine for the way it was designed.

If you are looking for a rocket for use with 38mm/54mm motors, I would get a kit which was designed for those motors and has the proper motor mount(s).

Bob

I don't mean to imply that the design is faulty, only that I'd like to consider expanding its potential...three recommended RMS is pretty boring, and if I can use a commercial kit of Aerotech quality to get my L1, I'm going to go with the tried and true.

To the other posters, I understand why I should ditch the motor hook and engine block (restricts to the use of 29/40-120 casing), but is there any real danger in keeping the baffle? I've flown my other AT kits dozens of times, and aside from failed ejection charge (once was a dirty delay grain (I think) and the other was the ejection charge was still in my trunk), have not had a problem. Also, I think Aeropack retainers are the bees knees, but find their price a bit much. I Googled Kaplow Klips because I'd not seen them before, and found a lot of hits but nothing pertaining to the actual devices. On some other site I read about using tee-nuts and washer-headed screws to retain the motor, is the Kaplow Klip different? (Am I the only one nervous about using such an onomatopeic device on a relatively expensive rocket? KAPLOW!!!)

Lastly, in researching the CTI reloads as mentioned by Greg, what's to stop someone from buying multiple MPR motors (G76 for example) and stacking the grains all together in a larger Rouse Tech casing (thereby creating a Level 1 (or 2?) motor without the regs)? This is probably the dumbest question of the decade, but the only limitations I can see are:
A) Ignitor length (to hit the top of the stack)
B) Delay time (longer burn time)

Am I missing something (besides the obvious violation of the law)?

I don't know how much AP you have flown, but these motors are "tuned" to their particular environment. These motors operate in a narrow window where performance is a function of temperature and pressure for the given propellant type and configuration, nozzle geometry, and length of burn. Modification of AP will likely cause "issues" with your investment, unhappy ones such as loss of case and rocket. Legal issues aside, you just can't cram in extra propellant (like Tim "The Toolman" Taylor) and hope that physics will take a holiday and ignore what you are doing. Motors, by design, will blow the aft or forward closure, and in some instances split somewhere in the middle. Or it may "roman candle" and just sit there as you watch your rocket enter the "Hall of Flame".

Igniter length (solved by ones with longer leads) and delay times are sub-topics that by comparison are minor compared to what I have outlined above.

The best advice I can give here is don't make motor modifications period unless they are prescribed by the manufacturer. Besides, manufacturers nowadays have just about any impulse and effects you care to fly anyway. The only limitations are your launch conditions and pocketbook.

Greg

The AT baffle can get clogged if you do not clean it. Be sure to remove any cap over the ejection charge after every flight. The mesh can get compacted over time and lose some of its effectiveness. Some people use a piece of clothes hanger to reach in there and "fluff" it back up. Personally, I think it is more trouble than it is worth; dog barf (fire resistant cellulose insulation) is very cheap.

There is not a Kaplow company selling motor retainers. Kaplow is actually a long-time rocketeer named Bob Kaplow who popularized the design. It repurposes parts commonly available at any hardware store.





The safety code at most club launches prohibit modifications to motors unless recommended by the manufacturer, that's what. If you are Tripoli level 2 or higher and fly at a Research launch, you are free to try it.


Bill

The cooling mesh needs about 6" to work properly. The Aerotech 29/180, 29/240, and 29/360 cases eat up progressively more space as the case size lengthens, so you run a greater chance of the mesh clogging. Also, the HP-style reloads have more black powder in their ejection charges than hobby-line motors. I avoid any clogging issues by leaving out the mesh. An alternate method is to use a piston like the Aerotech Sumo uses. Instructions can be found at the Aerotech website.


Kaplow Klips use a pair of T-nuts in the rear centering ring on opposite sides of the motor tube, then brass strips are bent to grip the rear closure of the motor. Each strip has a hole for a bolt that screws into the T-nut.

__________________
'Til next time,

Mike Toelle

NAR 31692 L1

SAM 0373