Motor retention with boattail

All, I am planning to Cert level 1 soon. I am considering the Public Enemy
3" Bullpup for the flight. My main concern is motor retention. Due to the
boattail, I'm not sure what the best method is, because of the limited
space. If anyone has built (or is familiar with) this kit, I would
certainly appreciate some pointers.
Thanks in advance,
Tim Reidy
NAR #83657
Alamo Rocketeers
Reply to
Tim Reidy
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Perhaps a slimline retainer might help? I suspect you would have to router out some of the material in order to allow the retainer to fit.
I took an ASP 38mm WAC Corporal and modified the balsa boat tail to accept a 1/4" piece of spring steel. I had to spend $35.00 for a piece of .040 sheet and had my brother's shop shear the pieces for me in a hydraulic shear. The extra pieces I am going to use in other small models. I then heat formed the rear and forward bends. I tailored the forward bend to go up as opposed to down like one would do with a small Estes model. This allows me to use as long an engine casing as the model will accept. I threaded the forward piece through a notch I cut in the aft centering ring and epoxied it in. I then cut a 1/4" angled groove in the balsa boatail so I could move the clip up and down to put the engine in. I only plan to use RMS motors in the ship otherwise I would have to be concerned with putting a thrust ring on an SU motor.
The ship just has the little loop out the tail which will be hardly noticeable on the pad. I believe it will work in a positive fashion when finally flown.
Am also modifying the tube coupler that the nosecone is attached to, to become an internal payload bay so I can mount an Aerocon MAD detector for apogee deployment with a charge. The Aerocon unit will fit but I am going to cut away some of the nosecone base as ASP gave it an ample amount. Will be a little dicey when I load the charge but will mount the on/off jack internally in a box holder. The on/off plug will go through both the airframe and the coupler. I think this will work just fine. I can use the motor ejection as backup when I test the system. Am eventually going to use the mad as an ejection backup in a future two stage model. If the sustainer fails to light, the MAD will fire when the model goes over.
Kurt Savegnago
Reply to
Kurt
I suggest keeping it simple for your cert flight, then work on doing something like motor retention with bottail after you get certified. I think there's a slim line retainer or something which might work though... any 3 or 4 FNC rocket should be good for cert flight... I'd use something on the heavy side to keep the altitude low and ditch the factory shock cord and use kevlar if you like getting the rocket back in one peice...
-- TAI FU
Reply to
tai fu
Have you looked at the slimline retainers (and cones!) at Giant Leap Rocketry? I don't have the Bullpup, but these seem best for tight spaces...
David Erbas-White
Tim Reidy wrote:
Reply to
David Erbas-White
I may be old fashioned but I like stuff that I build myself.
If it's got an aft centering ring, I put blind nuts inside and use L bolts.
If it's got a boat tail, I use mirror hooks screwed to the boat tail.
And if I can't fit either, I just use masking tape for a friction fit.
I've never recovered a rocket and not recovered the motor and I've never spent more than a few bucks on motor retention.
May not be as pretty but I designed it, I built it, I flew it, I recovered it and best of all, it worked!
Dave
Reply to
David Bacque
Tim,
I'd suggest using a Giant Leap slimline retainer, and removing a little of the material from the lip of the boattail to allow the retainer to fit. I used this method with a GL screwthreaded slimline in a modified Rebel Rocketry 6" Sportsflier for my L3 last year. Works a treat and saves a load of 'faffing'.
YMMV
G.
Reply to
Graham
On my 3" PML Bullpuppy, I inserted some tee nuts into the side and fashioned some kaplow clips to fit the motor. It wasn't the prettiest, but it was what I knew to do at the time.
If I were to do it over again, I would use either an aeropack or a slimline retainer. But if you are looking for something easy to make, what I mentioned above worked out very well.
Reply to
SpartaChris

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