Hydra-IRIS Two-Stage Sounding Rocket (3D Printed Parts + BT-80 / BT-60 + Plywood Fins)
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I don't know if anybody noticed, but @John Brohm builds BEAUTIFUL rockets! I gotta get to a PSC launch sometime!
John Brohm
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Catching up on this thread, I noticed a lot of earlier discussion about two-stage operation and associated build considerations. I know the subject in this thread is the three finned Hydra-IRIS, but for what it's worth, I'd like to offer a little of my own experience with a two-staged IRIS.
The blast deflector cone on the seven-motor booster prototype was a sheet metal affair and was made to be removable. The deflector cone fastened to the base of the deflector assembly by way of three equally spaced screws. For my model I also needed the cone to be removable, as this was where I was installing the timer and battery to ignite the sustainer stage. So I made the cone portion with a bayonet mount; that way I could simply screw it on and off at the field. Doing so also allowed me to stay reasonably faithful to the prototype, as the separation line between the cone and base is visible in several prototype photos.
The upper stage flew on an F50; I anticipated that my blast deflector would need to be functional, so I filled the nose portion of the cone with an epoxy pour, hoping that would be enough to get at least a flight or two out of the thing. Well, as the following photos show, I was able to get exactly two flights out of it before the cone portion was nothing more than a flaky crisp. The second flight also torched the timer and battery.
Again, apologies if I'm veering off thread, but hope this helps.
The blast deflector cone on the seven-motor booster prototype was a sheet metal affair and was made to be removable. The deflector cone fastened to the base of the deflector assembly by way of three equally spaced screws. For my model I also needed the cone to be removable, as this was where I was installing the timer and battery to ignite the sustainer stage. So I made the cone portion with a bayonet mount; that way I could simply screw it on and off at the field. Doing so also allowed me to stay reasonably faithful to the prototype, as the separation line between the cone and base is visible in several prototype photos.
The upper stage flew on an F50; I anticipated that my blast deflector would need to be functional, so I filled the nose portion of the cone with an epoxy pour, hoping that would be enough to get at least a flight or two out of the thing. Well, as the following photos show, I was able to get exactly two flights out of it before the cone portion was nothing more than a flaky crisp. The second flight also torched the timer and battery.
Again, apologies if I'm veering off thread, but hope this helps.
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Do you suppose something like stove paint or engine paint would have helped?
Maybe a highly polished, heavy electroplating of platinum; that surface would both reflect the radiant heat and withstand the hot gas contact.
(Well, it would. Really.)
John Brohm
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I would agree; that one is not.
John Brohm
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As for the stove paint/engine paint, don't know. It would be a good subject to test, as to what materials could be used that would provide a useful life for the cone while still being sort of lightweight. I say sort of, as my blob of epoxy certainly wasn't.
John Brohm
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Whereas this photo does show a curved airfoil at the tip. Perhaps a different fin type was used on the Hydra-IRIS?
Note that one can just make out the leading-edge cuff line on the fin closest to the gentleman.
Note that one can just make out the leading-edge cuff line on the fin closest to the gentleman.
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This construction is similar to the Aerobee fins, which are also built up with skins welded at the perimeter and an LE cuff.
One of the attachments in CTimm's post #49 indicates that the Hydra/Iris booster fins were solid aluminum.
https://www.rocketryforum.com/threa...bt-60-plywood-fins.181486/page-2#post-2479980However, the photo above seems to be a Hydra rocket as a single unit with four fins attached, not in the clustered form used for an Iris booster with one fin per motor. So a different rocket altogether.
The blast deflector cone is not "structural," so I would think a stainless steel sheet cone would be within the parameters of the LPR safety code here. As discussed elsewhere, the vertical rods connecting the booster to the sustainer need to be something other than metal, but could, for example, be solid c.f. with non-structural stainless sleeves. A ceramic might also work well. Shouldn't need more than standard clay that could be formed with the resources of a high school arts classroom.
CTimm
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Some more Hydra-IRIS pics.
There were several flights so each round had slightly different paint schemes (as well as nose cone shapes.)
There was even a dummy upper stage flight.
Sparrow fin colors could be red or white, IRIS fins sometimes were all red, 2-red and 1-white, and a splotchy blackness round.
The conical nose round had the dummy upper stage.
The "img036" pic has all white fins but with a shorter ogive cone.
There were several flights so each round had slightly different paint schemes (as well as nose cone shapes.)
There was even a dummy upper stage flight.
Sparrow fin colors could be red or white, IRIS fins sometimes were all red, 2-red and 1-white, and a splotchy blackness round.
The conical nose round had the dummy upper stage.
The "img036" pic has all white fins but with a shorter ogive cone.
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Cool -- you are an awesome hoarder of rocketry pics and information!
LOL, that is some kind of understatement.
Any thread that lures John into posting some pics of his rockets is automatically a Good Thread.
Looking back at your post it is making me think more about the cone transition. Most of my 3D printed parts experience an ejection charge or contained 2nd stage ignition that immediately pops off the booster and forces rapid separation (and I usually have not even painted the parts). In these cases the top layers of ABS seem to dry out some and occasionally there is a small amount of peeling but the blacked layers seem to protect the lower layers (or at least hide further damage). I rarely launch rockets dozens of times though.
In this model the conical portion on the booster will take lots more direct heat from the 29mm engine in the sustainer since I think that separation will be a bit slower due to the gap. I need to think about how to make it replaceable like you did or something. That cone part is simply the nosecone for the booster in this design (so is pretty replaceable) but its a bit built up interfacing with 3 tubes below etc... It would be better if I made the top portion of the cone removable.
I will do a test launch and see how badly the top gets melted to figure out how far I need to go. Maybe I will paint it with some high-temp paint just to see how it does.
CTimm
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Amateur Archivist seeks unpaid intern to organize the hoard.
Seriously, there is so much information on just the Hydra-IRIS that it takes time to sift through for specifics.
Enough history and pics for a thick coffee-table sized book if anyone has the inclination
Then there are the proposed variations and future projects to mull over.
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