tech question

we are investing in hybrids and wondering how hard it would be to convert existing rockets to use them.
my main issue is rigging up an altimeter bay to handle ejection charges. I
was thinking of some way of doing it without adding tube lengths, like maybe an added internal compartment to the parachute bay(space allowing)
one idea I had was to put the altimeter into the nosecone, but most altimeters need to have pressure sensing holes 3 inches below the nosecone.....
I'd like to convert some to run either way without changing the outward appearance much, any ideas?
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I like mounting the electronics in the nosecone. On my L2 bird, the altimeter vent holes will actually be covered by the airframe until after ejection. However, I'm using G-Wiz electronics with both accelerometer and altimeter... accelerometer until apogee, then the altimeter takes over. The data recorded by the altimeter will be fouled, but I don't really care... all it needs to measure is the difference between ground (starting altitude) and ground + 800 (well after apogee). If you are using altimeter only systems, I'm not sure what to suggest. I've bashed a couple of kits to take hybrids, but always used the GWiz products to avoid the vent problems, especially if it's apogee only deployment.
Kevin OClassen
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Kevin OClassen wrote:

Without knowing a little more about what you are converting its hard to give precise answers. Are you converting 29mm or 38mm any larger and I would expect you to already be using electronic deployment.
The G-Wiz electronics is a very good option as long as you are careful as to the revision of the altimeter. There have been reported problems some units.
You idea of adding an internal is valid, PML uses just such an arrangement.
There is of course always a timer. Certainly something I would not use as primary deployment but it does fit nicely into the nose cone and serve as backup deployment.
We found that the booster section was our main concern at WOOSH. Will the hybrid motor fit into the booster? Coming up with electronic deployment solution was not a concern as any rocket we converted was long enough already to be to handle the added electronics bay.
Once you convert to electronic deployment (dual deployment) it is hard to revert back to strictly motor deployment. This is of course altitude dependent. Rockets that will fly to 1500 probably don't need dual deployment.
BW
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Tater Schuld wrote:

Do you have a coupler you can house your electronics in? That's a method that works quite well.
Otherwise, use accelerometer-based units for detecting apogee, and put 'em in the nose.
-Kevin
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I used to stick an altimeter into something like a coupler (I think someone sells a bay like that) that has a short section of body tube to accommodate the vent hole and safety switch and whatever. That way I could just pop them into any rocket if they needed one. So I guess it would probably work if you only used them during flight, but that is of course if your rocket is designed to breakdown (I used to do it on all of them because it made adding stuff and transporting them easy) then you can fit your electronics somewhere in there. Of course if your existing rocket is built the way they are (eg not fin can and body/recovery section then nosecone, but all one piece) then you could probably cut the tube cleanly (use a jig or alot of masking tape and careful cutting, you want to be careful here!) then fasten a coupler using nylon rivets so now you have a takedown rocket. Then its not too hard to fit an electronics bay inside without altering the external apprances of the rocket.
-- TAI FU

I
maybe
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one of the rockets in question is a LOC IV, so a lot of solutions mentioned don't fit. I also own an adept altimeter, so some of the other solutions don't fit either :)
I have not seen anyone mention setting up the altimeter under the payload section, as in an area between the fins just aft of the forward centering ring. this means setting up a door (or cutting part of the aft centering ring) but puts the ejection charge in the right place. the shift of the CG can be fixed with a corresponding amount of epoxy in the nose.
has anyone done this? is there issues of putting barometric altimeters too close to the fins? I'd say this would be easier than trying to get a payload section to work in a single chute rocket that pops the nosecone with no forward body tube section.
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I have used 2 Gwiz altimeters in a Warlock, one in the nose and one in a panel between the fins and they worked fine. But those are Gwiz altimeters, so my experience may not be relevant.
--
Tweak

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Tater Schuld wrote:

I have a LOC Forte that was converted to Dual Deployment. I stretched it by adding a airframe section for the drogue and a coupler for the altimeter. For a small rocket the drogue section could be fairly short. And stretching helps the CG/CP relationship. Doing it this way makes it very easy to fly with/without electronics. If you are doing engine ejection, just remove the coupler and aft airframe.
I have a Forte clone that has flown Hypertek 54mm 440 and 835CC motors as well as West Coast I110.
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You can mount a barometric altimeter into the nose cone if you add a siphon tube. Just a short copper or brass tube that extends from the base of the nose cone down an inch or two and then lining up with a hole in the airframe. Use a shear pin to keep things lined up.
I just use a timer for primary deployment on hybrids (in the nose cone) where motor ejection would normally be used on apcp loads.

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L&K wrote:

Doesn't (or didn't) PML sell a timer that slips in the MMT above the hybrid motor? A little PerfectFlite with a G switch launch detect connected to a single ejection charge could be easily added to most rockets as long as the booster was long enough.
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Tater Schuld wrote:

Tater, One thing to consider is that hybrid motors tend to be much longer and have a heaver 'burn out' weight than conventional motors. For example, the Hypertek J motor is about 25" long and has a burn out wt. of almost 2 lbs. Unless you built your booster section unusually long for a AP motor, it won't be long enough. The added wt. of the motor may also require stronger fins to prevent damage on landing or a bigger chute. I would check out the specs of the motors you plan to use before going much further.
Just something to think about.
Tony.
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yes I have. I am sure that the motor would fit in my LOC IV, hence the reason I wondered about the altimeter. Tweak sounds like he has the right idea, and I think I can fit a larger chute into a cannon on the LOC.
We tend to overbuild our rockets anyway. my first L1 attempt the shock cord ripped out, and the lower section hit ground without any recovery. a little superglue on the crack in the pain and the LSO let me certify on the next flight.
took hours to find the nosecone though
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We have successfully done a dual-deployment cannon nosecone in an Estes Pheonix. A Loc IV is HUGE.
;-)
--
Tweak

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