Suggestions for Blacksky Altimeter Bay in PML AMRAAM 4"

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Well-Known Member
Mar 24, 2004
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As a TRFr of modest means my 4" PML AMRAAM does not use the CPR system. I've had terrific flights using motor ejection but I'm now ready for the challenge of dual deployment. Can anyone provide me with ideas / suggestions for the addition of an altimeter bay into this kit? I'll be using a Blacksky AltAcc2C unit.
altrimeter bays are pretty simple to construct.
The basic 4" bay consist of:
2. 4" couplers
1. short piece (about 4" or 5") 4" body tube
4 bulkheads (2 to fit coupler ID. 2 to fit OD.)
2 pieces 1/8" allthread with assorted nuts and washers.
Eyebolts or U bolts for reacovery attachment.

epoxy couplers equal distance into body tube.
Epoxy 1 each IDand OD. bulkheads together.
Drill holes in bulkhead assys. for allthread (about 3/4" from outside edge and 180 degrees apart.
Install 2 allthreads into 1 bulkhead assembly along with whatever recovery hardware and epoxy in place.
epoxy entire bulkhead to one end of bay.
uswings for other bulkhead.
Make a slide with your choice of material to slide onto allthreads with your electronics.
NOTE before epoxy anything to bay make whatever vent holes and safety switch holes first.
I install 3 blind nuts inside one end of bay to correspond with holes in payload bay (this is to gain access to ejection canisters and still deploy from other end of payload tube after bolts are in place)
Hope this helps.
I will post some pics when I get home from work tonight.
Peter, does your amraam use a piston? you are going to have to get rid of that to make dual deployment work.

if you don't want to cut up your existing top section to make the altimeter bay, then make the altimeter bay as missleman described, and put a new top tube and nose cone on it! voila, insta-switch rocket.
Actually the piston can stay with dual deploy.
It just wont serve a purpose and will pull out under chute.
Then when you want to fly with motor ejection it will still be there.
missileman, maybe leaving it in is a better idea.
Here are some pics.
This first one shows the aft end of bay.
Note wiring to arming switches and shoulder on bulkhead created with 2 sizes of bulkheads epoxied together
This pic shows other end of bay.
Note vent holes, arming switches, ejection canisters and if you look closely you can see where 1 of the blind nuts is located about 1" from the end. These are used to attach to airframe.
This pic shows the electronics slide.
Made from 1/8" ply and 2 1/2" by 1/2" pine strips with holes drilled to line up with allthread.

There are some very good suggestions here, however it appears from your post that you already have the model built and flown. If you constructed the Amraam 4 without dual deployment, that means you epoxied the coupler into the upper bodytube. This will make it more difficult to incorporate, but not impossible. Please note that with the following suggestion, you only need to modify the coupler bulkhead additional tubes need added and the original coupler can remain in place.

I would suggest cutting a 2.1" hole in the bulkhead at the end of the coupler, which is glued to the upper body tube. You can use another CR to overlay it and draw the hole. This will convert the bulkhead into a centering ring with a 2.1" center hole. Next, you can glue an internal centering ring at the top of the coupler...a 3.9" to 2.1" coupler CR could be used. Then I would glue a piece of 2.1" body tube to "link" the two CR's. If you wish, you can glue a Piston strap to the side of the 2.1" tube and have it protrude out the top of the rocket so you can connect a piston.

All that remains is to build a Alt bay. A 2.1" coupler can be used with a 2.1" bulkhead plate at the upper end and a 3.9" bulkhead plate at the lower end. You can attach a eyebolt to the bottom 3.9" plate(to replace the original you cut out) along with a cheap BP canister made from PVC or copper tubing. A board can be built to slide inside the 2" Alt bay and two all thread rods running the length of the bay along the sides can bolt the end caps together.A PVC or Copper ejection canister can be bolted to the top 2" plate and with the unit assembled, it inserts into the 3.9" coupler and bolts in place.

I would use a couple 8-32 or 1/4-20 T-nuts inside the lower lip of the original bulkhead, which is now a coupler. This can be used to bolt the alt bay in place. I have attached a couple pics of similar bays I have built below.

Good luck and keep us up to date,


Building an altimeter bay-

Building a 1/2" copper tubing Ejection System-

View of what your bay could look like- 248.jpg
Originally posted by Smokin' Rockets
Or you could go the easy way and use a Smokin' Rockets Alti-Tube :D


I have used both methods (never bought an altitube but I made one from Bill's design) and the altitube is the, hands down, best method to create an altimeter bay. Getting to your altimeter in as simple as backing off a nut and pulling out the sled. No allthread to fool around with, you dont need to make you coupler reusable.

Everyone is doing it ;)