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Aeropack min dia retainer - why???
#11
If losing the case is a concern with friction fitting, you could use a wrap of tape over the body tube and rear closure seam, in addition to friction fitting. The aluminized HVAC tape, not duct tape, sold at Home Depot or Lowes works well.
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#12
Don't know why everyone is so afraid of friction fit. 
Here's my 98 minimum with a N motor friction fitted and a wrap of aluminum tape on motor to airframe joint.

           

Finally to be ultra sure, just put a 1-2 inch section of coupler with BP on top into airframe at the point of the largest motor you will fly ends. For that one you run eyebolt through BP/coupler into forward closure.

The coupler is held in airframe with 3 set-screws [ # 8 size] this also keeps any pressure from ejection charges kicking back on motor to jar it loose. So when flying smaller size motors, they are protected from any ejection charge pressure kick back & can be simply friction fitted + taped externally....the will NOT come out

   

 When flying any minimum on larger motors, you won't be using motor eject because delays aren't long enough anyway, so electronic eject is a must.
You rob yourself of altitude with any of these internal/external motor retainers, so what's the point?
Unless you just want to own a Ferrari and drive it 35mph! .....LOL

If you want to fly extreme stuff, you need to learn all the tricks necessary to do it. Start out on smaller rockets with smaller motors, & learn how to wrap the BOTTOM/REAR of motor like a screw with tape. No more than 25% of motor has tape on it, if you want to get it out easily. Screw it in & un-screw it to remove. Not that hard guys....really!

Look closely right above where top closure of 6xl motor is to see the set screw in airframe. I actually cover it with spot putty to make smooth, then dig it out when need to remove screws.
               

For smaller rockets like this Blackhawk38, glue a recovery harness in a coupler.

slice a section of coupler, so it will fit inside of coupler........glue harness between coupler sections like this [another rocket]

   


Actual 38 harness/coupler......NO bulkplate, so you can use motor eject & push friction fit motor out with stick.
   

Measure for largest motor to be flown. 
Place 1 inch above motor. 
Then hold in airframe with rivets or screws


   


Problem solved inexpensively & easily!

Or if you don't want to mess with all that, just use a tapped front closure or MAKE your own version.

CTI 38 & 54mm with eyebolts epoxied in..... yes  CTI allows it, I asked. Remove BP..enlarge touch hole so eyebolt screws in. cover with 5-10 minute epoxy.

AT tapped closure & standard one with a machine screw run through the knurled section and Kevlar loop tied on, for recovery attachment.
Plastic straw section covers threads, so no wear on kevlar.

These are all simple methods I came up, with to solve problems.
 Start thinking outside the box.

                                 

For smaller rockets like this Blackhawk38, glue a recovery harness in a coupler.

slice a section of coupler, so it will fit inside of coupler........glue harness between coupler sections like this [another rocket]

   


Actual 38 harness/coupler......NO bulkplate, so you can use motor eject & push friction fit motor out with stick.
   

Measure for largest motor to be flown. 
Place 1 inch above motor. 
Then hold in airframe with rivets or screws


   


Problem solved inexpensively & easily!
Jim Hendricksen
T 9693
L-3 Savannah Ga
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#13
Nice summary Jim!
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#14
Hey Tim,
missed you at MWP this year! Hope your healing up good.
You post at lot like me.......just a note about this pic stuff here. I found it a bit quirky at first [like anything new] but once i got it down, I really like how you can just keep stacking pics & comments on your own thread. Keeps some continuity in check. Make several pic posts. then hit new reply to make more, without all the attachments piling up to go through, just the new ones, but they all end up on one post like above. I did that in 3 distinct separate times but they all linked together....cool.

I think you'll like it too.
Jim Hendricksen
T 9693
L-3 Savannah Ga
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#15
Good points Jim. I remember you posting pics of your homemade retention ideas years ago but had forgotten them. Thanks for the reminder. Here is another one I picked up since my recent MD interests.


.jpg   Forward closure_image_150x163.jpg (Size: 5.77 KB / Downloads: 64)
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#16
Very nice, is that part of AT's spacer system?
You must use it in motors 1 grain shorter than the case for it to work, so a spacer goes under it?
Jim Hendricksen
T 9693
L-3 Savannah Ga
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#17
Yup. Use it for any spacer flight and still use motor eject as backup if you want.
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#18
(11-10-2015, 04:31 PM)grouch Wrote: The only real reason to use one of the MD retainers is they look cool before you glue them in. Friction fit works fine for motor eject so it would stand to reason that it works super awesome with a bulkhead set up and no motor eject.

Well, they are pre made, reliable, and work well. I used an SC Precision thrust plate once, not because my motors and airframe needed it but because it made for a nice place to screw in a flange mount retainer.

Also you do not have to glue them in; drill and tap a trio of rivets and now the unit can be removed for cleaning and maintenance.

Friction bothers me. It probably would not if I had a tool to measure it, and the force generated by charges. The engineer in me wants to see numbers, not an older guy saying it feels about right. Nothing against those who disagree, of course. The important part is the results.
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#19
I friction fit, then add the aluminum tape overlapping the rear thrust ring and past the motor. The excess is folded back over the end of the motor taking care not to block the nozzle. I've never kicked a motor. Usually the opposite, it is hard to remove after the flight.
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#20
(11-28-2015, 02:06 PM)Binder Design Wrote: I friction fit, then add the aluminum tape overlapping the rear thrust ring and past the motor.  The excess is folded back over the end of the motor taking care not to block the nozzle.  I've never kicked a motor.  Usually the opposite, it is hard to remove after the flight.

I've never used the aluminum tape before as my find are usually as far rearward as possible so there isn't enough room, but I agree with the motor usually being a bit more difficult to remove than it was to install.

NAR# 98194
Level 1: CTI I-216, 3,043'
Level 2: CTI K-740, 5,999'

Personal altitude record: 12,400' CTI L395
2014 total impulse: 9,018.2 Ns (76% M)
2015 total impulse: 7,171.7 Ns (40% M)
2016 total impulse: 18,664.2 Ns (91% N)
2017 total impulse: 8,281.1 Ns (80% M)
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