Hydra-IRIS Two-Stage Sounding Rocket (3D Printed Parts + BT-80 / BT-60 + Plywood Fins)

[BigMacDaddy]

Over the last few weeks I have been working on designing and building a BT-80 scale/sport-scale IRIS Hydra sounding rocket w/ booster. This is the later version of the IRIS sounding rocket that had 3 fins on the sustainer and a 3-tube booster w/ Sparrow engines inside and smallish booster fins.

Anyway, I finally nearly completed / built my first full prototype. When I originally looked at this design I thought it was going to be much easier than it turned out to be (just lots of interconnecting parts). The rocket is definitely the largest rocket I have built at 174cm/68.5" and 650g w/o chutes or engines (Big Bertha in pictures for size comparison).

I am designing this so it can be built with BT-80 or 2.6" thick-wall tubes and can use 24mm or 29mm engines (I am planning to launch with 3x D12 engines in the booster and 1x D12 engine in sustainer which gives me a 200m estimated flight - the lowest and least powerful launch combination that will work with this rocket). This model channels / vents two booster engines to hopefully ignite the sustainer engine and uses 1 booster engine (with delay) to eject a booster chute. Gap staging should be interesting (the little nozzle-extension part can be replaced with the pyramid tip for display). Nosecone is made in 3 quarter-twist locking parts and has mounting points for swappable nose weight (to go inside of tip or 2nd section) as well as generic mounting points for a sled (to position sled inside of 2nd or 3rd sections).

I need to add a bracket to the top of the booster section below the booster nosecone to help stabilize the weight of the sustainer, need to add the 3rd bracket details around the sustainer fins, and need to glue in motor blocks. I will also probably do a final coat of glue to clean up the fillets (still a bit wet in these pictures). Finally, I will also need to tweak parts to work with the 2.6" tubing version.



The scale data for this was provided by @Ez2cDave in this thread - https://www.rocketryforum.com/threads/iris-sounding-rocket-scale-data.155495/ (although I am still not 100% sure about the correct height for the sustainer fins on this model per my comments in that thread).

 

[NOLA_BAR]

Let us know when you are ready to sell! Also don’t forget the BT-80 F-104!

 

[jmasterj]

Well that looks epic. 3mm fins and such? Will you supply the dowels with the kit? Did you use BT-80 or thick wall tubing?

 

[BigMacDaddy]

Well that looks epic. 3mm fins and such? Will you supply the dowels with the kit? Did you use BT-80 or thick wall tubing?

Thanks!

I used BT-80 to keep things light so I could use 24mm engines.

It has 3mm fins but I need to find a supplier of better plywood for high-powered 29mm 2.6" version...

 

[jmasterj]

Thanks!

I used BT-80 to keep things light so I could use 24mm engines.

It has 3mm fins but I need to find a supplier of better plywood for high-powered 29mm 2.6" version...

That's kinda what I figured, with weight being such a big consideration. 3mm should be fine for 29mm. LOC has 4" rockets with 1/8" fins.

 

[Ez2cDave]

Over the last few weeks I have been working on designing and building a BT-80 scale/sport-scale IRIS Hydra sounding rocket w/ booster. This is the later version of the IRIS sounding rocket that had 3 fins on the sustainer and a 3-tube booster w/ Sparrow engines inside and smallish booster fins.

Anyway, I finally nearly completed / built my first full prototype. When I originally looked at this design I thought it was going to be much easier than it turned out to be (just lots of interconnecting parts). The rocket is definitely the largest rocket I have built at 174cm/68.5" and 650g w/o chutes or engines (Big Bertha in pictures for size comparison).

I am designing this so it can be built with BT-80 or 2.6" thick-wall tubes and can use 24mm or 29mm engines (I am planning to launch with 3x D12 engines in the booster and 1x D12 engine in sustainer which gives me a 200m estimated flight - the lowest and least powerful launch combination that will work with this rocket). This model channels / vents two booster engines to hopefully ignite the sustainer engine and uses 1 booster engine (with delay) to eject a booster chute. Gap staging should be interesting (the little nozzle-extension part can be replaced with the pyramid tip for display). Nosecone is made in 3 quarter-twist locking parts and has mounting points for swappable nose weight (to go inside of tip or 2nd section) as well as generic mounting points for a sled (to position sled inside of 2nd or 3rd sections).

I need to add a bracket to the top of the booster section below the booster nosecone to help stabilize the weight of the sustainer, need to add the 3rd bracket details around the sustainer fins, and need to glue in motor blocks. I will also probably do a final coat of glue to clean up the fillets (still a bit wet in these pictures). Finally, I will also need to tweak parts to work with the 2.6" tubing version.

View attachment 597696

The scale data for this was provided by @Ez2cDave in this thread - https://www.rocketryforum.com/threads/iris-sounding-rocket-scale-data.155495/ (although I am still not 100% sure about the correct height for the sustainer fins on this model per my comments in that thread).

Looks great !

One thing concerns me . . . The length of the coupler on the Booster looks very short to me. If it doesn't engage the upper stage deeply enough, the rocket might be prone to separation, during powered flight, due to "torque" being imparted by the upper stage.

 

[BigMacDaddy]

Looks great !

One thing concerns me . . . The length of the coupler on the Booster looks very short to me. If it doesn't engage the upper stage deeply enough, the rocket might be prone to separation, during powered flight, due to "torque" being imparted by the upper stage.

Thanks, very much.

Yes, I am worried about this as well.

The booster coupler makes contact with the sustainer on both inside and outside rings as well as against the flat surface of the lip of the ring. If it turns out to be a weak contact point I can make these parts nest more deeply (these parts can still be modified since they are removable).

Actually the bigger issue I am getting now is that the nosecone on the booster has a tendency to shift or wobble. I initially thought the issue was that one of my booster tubes is like .5mm shorter than the others. However, now I think that the issue might be that the dowels are over the spaces between booster tubes so any shift in weight tends to tilt the nosecone. I am planning to add a 3D printed bracket to the top of the booster tubes that will make contact with the booster NC around the outside edge. I think this will make a much more stable structure for the booster NC to sit on.

 

[BABAR]

Love the idea, would like to see more details on the booster nose/staging/chute deployment plan.

I am guessing two zero delay motors ducted to the center to gap stage (all good to me). These motors cannot be allowed to blow the nose off.

third motor is a short delay (the booster will still initially be ASCENDING for first second or seconds after separation due to inertia, you do NOT want to deploy chute Immediately AT staging. I speak from experience.

question, how do you get third motor to blow the cone but first two do not?

or are you going rear eject with motor three?

or something else brilliant that I simply haven’t imagined?

other question, can you do REVERSE manifold? Booster with a single 24 mm motor that ducts to THREE sustainers? Basically Estes MIRV concept but designed with a booster mount that actually can HANDLE a motor adequate to the task, which Estes in that case sadly did not do. Can the plastic hold up to repeated motor burn through events? (Zero delay motors technically have no ejection charge, although the burn through event Can function as a slightly weak ejection charge.)

 

[BigMacDaddy]

Love the idea, would like to see more details on the booster nose/staging/chute deployment plan.

I am guessing two zero delay motors ducted to the center to gap stage (all good to me). These motors cannot be allowed to blow the nose off.

third motor is a short delay (the booster will still initially be ASCENDING for first second or seconds after separation due to inertia, you do NOT want to deploy chute Immediately AT staging. I speak from experience.

question, how do you get third motor to blow the cone but first two do not?

or are you going rear eject with motor three?

or something else brilliant that I simply haven’t imagined?

other question, can you do REVERSE manifold? Booster with a single 24 mm motor that ducts to THREE sustainers? Basically Estes MIRV concept but designed with a booster mount that actually can HANDLE a motor adequate to the task, which Estes in that case sadly did not do. Can the plastic hold up to repeated motor burn through events? (Zero delay motors technically have no ejection charge, although the burn through event Can function as a slightly weak ejection charge.)

Thanks - First time I am doing this so still learning / testing...

Basically, I have the 2x zero-delay motors in motor-mount tubes that go inside channels that funnel into gap-stage nozzle. The other motor (assume D12-3 in my setup) ejects up against a shoulder in the last 1/3rd of the booster nosecone. Part of what I assume keeps the booster nosecone from blowing off when the 2x zero-delay motors go off would be the weight of the sustainer. I am a bit worried about the last motor not ejecting the nosecone due to asymmetric pressure jamming up the nosecone. I kept shoulders relatively short to help avoid that but need to test.

 

[jhill9693]

other question, can you do REVERSE manifold? Booster with a single 24 mm motor that ducts to THREE sustainers? Basically Estes MIRV concept but designed with a booster mount that actually can HANDLE a motor adequate to the task, which Estes in that case sadly did not do. Can the plastic hold up to repeated motor burn through events? (Zero delay motors technically have no ejection charge, although the burn through event Can function as a slightly weak ejection charge.)

Not scale accurate and probably would not improve reliability.

 

[Ez2cDave]

Thanks - First time I am doing this so still learning / testing...

Basically, I have the 2x zero-delay motors in motor-mount tubes that go inside channels that funnel into gap-stage nozzle. The other motor (assume D12-3 in my setup) ejects up against a shoulder in the last 1/3rd of the booster nosecone. Part of what I assume keeps the booster nosecone from blowing off when the 2x zero-delay motors go off would be the weight of the sustainer. I am a bit worried about the last motor not ejecting the nosecone due to asymmetric pressure jamming up the nosecone. I kept shoulders relatively short to help avoid that but need to test.

Short Nose Cone Shoulders and short Couplers invite trouble from "flexion", which may cause structural failure.

 

[SolarYellow]

One possibility might be to use longer pillars that slide into receptacles in the sustainer, rather than just the shoulder. But you'd need to ensure they had near-zero friction and effectively resisted binding even with side loads applied.

 

[jmasterj]

To make the booster shoulder longer you can make the sustainer motor mount longer and secure it with centering rings higher up, leaving a longer gap for the booster shoulder to slide into. You've probably thought of this already, but I can't see inside so I thought I should make the suggestion.

 

[BigMacDaddy]

One possibility might be to use longer pillars that slide into receptacles in the sustainer, rather than just the shoulder. But you'd need to ensure they had near-zero friction and effectively resisted binding even with side loads applied.

My original design had the dowels themselves inserting into the sustainer retainer part (bottom most part). However, they had a tendency to get stuck and it seemed less stable than making the entire booster transition bracket part (on top of dowels) insert inside the sustainer.

I can make the insert on the booster transition part as deeply recessed as I need to since it is just recessing inside of the retainer cap that holds rear of sustainer motor.

 

[BigMacDaddy]

To make the booster shoulder longer you can make the sustainer motor mount longer and secure it with centering rings higher up, leaving a longer gap for the booster shoulder to slide into. You've probably thought of this already, but I can't see inside so I thought I should make the suggestion.

I will try to add some CAD drawings so you can see the part design better. Need to reassemble the model in CAD since I have revised parts many times since my original modeled complete rocket.

 

[SolarYellow]

My original design had the dowels themselves inserting into the sustainer retainer part (bottom most part). However, they had a tendency to get stuck and it seemed less stable than making the entire booster transition bracket part (on top of dowels) insert inside the sustainer.

I can make the insert on the booster transition part as deeply recessed as I need to since it is just recessing inside of the retainer cap that holds rear of sustainer motor.

Yeah, I wouldn't try it with wood dowels. The safety code prohibition on metallic structure can be a pain, as it is interpreted conservatively even for small brackets and stuff. Maybe carbon fiber or fiberglass rods, or something sheathed with non-structural metal or polymer sleeves to get the friction down.

 

[NOLA_BAR]

Looking at your idea further, I would probably use a timer to ignite the sustainer motor. Use 3xD12-3 in the booster, then a mini-timer for the sustainer motor. Apogee still sells a mod-kit that was for the Cosmodrome Aerobee to reroute the motor tube to make room for a timer sled. The booster would still come down on parachute(s).

 

[BigMacDaddy]

Looking at your idea further, I would probably use a timer to ignite the sustainer motor. Use 3xD12-3 in the booster, then a mini-timer for the sustainer motor. Apogee still sells a mod-kit that was for the Cosmodrome Aerobee to reroute the motor tube to make room for a timer sled. The booster would still come down on parachute(s).

Yes, electronic ignition for sustainer is definitely easier, in many ways. Would also allow you to use composite engines in booster.

I am hoping to do a test with BP engines and direct two-stage ignition but for higher-power I am sure most people would use electronic ignition.

 

[jqavins]

First and foremost, that's very damn cool, and I want one. (OK, first and second.)

(I am planning to launch with 3x D12 engines in the booster and 1x D12 engine in sustainer which gives me a 200m estimated flight - the lowest and least powerful launch combination that will work with this rocket).

I doubt that's exactly true. 3×D12 + 1×C11, I just bet, would also work.

Gap staging should be interesting

I've heard of open air gap staging, but I've never seen it. Interesting indeed. I look forward to the tests.

In confined staging, whether direct or gap, the ignition charge and/or initial sustainer exhaust forces separation and is only able to scorch the insides of tubes. With an open air gap like this, how is separation ensured, and how does the outside of the booster nose not melt?

I am still not 100% sure about the correct height for the sustainer fins on this model per my comments in that thread.

I'm too lazy to go read the other thread. The fin dimensions seem pretty clear on the drawing, so what are you unsure about?

Yeah, I wouldn't try it with wood dowels. The safety code prohibition on metallic structure can be a pain, as it is interpreted conservatively even for small brackets and stuff. Maybe carbon fiber or fiberglass rods, or something sheathed with non-structural metal or polymer sleeves to get the friction down.

Powdered graphite dry lube might also be very useful there. And there are spray-on silicone dry lubes as well.

Yes, electronic ignition for sustainer is definitely easier, in many ways. Would also allow you to use composite engines in booster.

I am hoping to do a test with BP engines and direct two-stage ignition but for higher-power I am sure most people would use electronic ignition.

You might consider mentioning that in the kit instructions, including suggested layouts and wire routing. Maybe even make wire channels in the sustainer CRs and wherever else they might be needed internally. All added parts are provided by the builder, but you can make it easy.

 

[NOLA_BAR]

Yes, electronic ignition for sustainer is definitely easier, in many ways. Would also allow you to use composite engines in booster.

I am hoping to do a test with BP engines and direct two-stage ignition but for higher-power I am sure most people would use electronic ignition.

Hopefully you get the direct staging to work. That would be cool to see. Even with electronics, I would stay with BP motors, as they are east to ignite. Looking forward to your progress!

 

[BigMacDaddy]

First and foremost, that's very damn cool, and I want one. (OK, first and second.)

I doubt that's exactly true. 3×D12 + 1×C11, I just bet, would also work.

I've heard of open air gap staging, but I've never seen it. Interesting indeed. I look forward to the tests.

In confined staging, whether direct or gap, the ignition charge and/or initial sustainer exhaust forces separation and is only able to scorch the insides of tubes. With an open air gap like this, how is separation ensured, and how does the outside of the booster nose not melt?

I'm too lazy to go read the other thread. The fin dimensions seem pretty clear on the drawing, so what are you unsure about?


Powdered graphite dry lube might also be very useful there. And there are spray-on silicone dry lubes as well.


You might consider mentioning that in the kit instructions, including suggested layouts and wire routing. Maybe even make wire channels in the sustainer CRs and wherever else they might be needed internally. All added parts are provided by the builder, but you can make it easy.

Thanks very much!

Haha... you are correct... C11 or maybe even C5 in the sustainer would likely work.

Here is the question / thoughts about the fin height on sustainer. The only fin height dimension that I can see is for the booster fins. Photos seem to suggest that the sustainer fins are NOT the same height as the booster fins. Alternatively, we could assume that the fins have a 45 degree sweep angle (like all the IRIS models) then we can use the difference between root and tip length to calculate the fin height.

Original post: "However, it was not clear that the sustainer fins were the same height as the booster fins. Do you think they are?

That will significantly change the sweep angle of the sustainer fins from the 45 degrees of the 4-fin IRIS sustainer fins. The left fin is what these would look like if the booster fin height is assumed to be the same as a booster fin height given. The right is what the sustainer fins would look like if you maintain a 45 degree angle (i.e., the height is the same as the difference between the root and top fin length given).

The sustainer fins also look larger in the pictures (there is obviously some perspective distortion going on here but they still look taller).

Ah, also just noticed another photo from the 2nd page of the brochure above that shows the sustainer fin fairly square on. Unless some photo manipulation is going on this looks like a photo of the 3-fin sustainer. It also looks like the 45 degree sweep angle for the fin is more accurate proportion.

 

[BigMacDaddy]

I've heard of open air gap staging, but I've never seen it. Interesting indeed. I look forward to the tests.

In confined staging, whether direct or gap, the ignition charge and/or initial sustainer exhaust forces separation and is only able to scorch the insides of tubes. With an open air gap like this, how is separation ensured, and how does the outside of the booster nose not melt?

Need to test this - inevitable that the booster nosecone gets a bit scorched. Right now I am relying on gravity and a stable platform to hold the sustainer on the booster (not really stuck on per se) so hopefully it scoots away pretty quickly but should be an interested test...

 

[jqavins]

Here is the question / thoughts about the fin height on sustainer. The only fin height dimension that I can see is for the booster fins.

Huh? The sustainer fins' height is right there on the drawing, 99.2 cm at the root and 52.7 cm at the tip.

The only thing that might be missing is the span. Section AA gives the span as 35.6 cm, and if it is a proper, accurate view then that would be the same for the booster and sustainer both, but I guess there might be some room for doubt.

Here are the fin shapes per the dimensions marked on the drawing. There is a problem: the sweep angle for the booster fin is not consistent with the lengths; I'm showing the angle based on the lengths. Also, I'll admit the shapes don't really look like the drawing, but they follow the numbers; blame the draftsman.

 

[SolarYellow]

Foil tape?

 

[jqavins]

Foil tape?

For booster blast protection?

 

[BigMacDaddy]

Huh? The sustainer fins' height is right there on the drawing, 99.2 cm at the root and 52.7 cm at the tip.
View attachment 598493
The only thing that might be missing is the span. Section AA gives the span as 35.6 cm, and if it is a proper, accurate view then that would be the same for the booster and sustainer both, but I guess there might be some room for doubt.

Here are the fin shapes per the dimensions marked on the drawing. There is a problem: the sweep angle for the booster fin is not consistent with the lengths; I'm showing the angle based on the lengths. Also, I'll admit the shapes don't really look like the drawing, but they follow the numbers; blame the draftsman.
View attachment 598495

Sorry, I am using "height" in the way that Open Rocket does (i.e., span) and length as chord length (root and tip).

What do you think of the photos? The fin profile with 35.6 as the span/height does not create a fin that matches the photos as far as I can tell.

 

[SolarYellow]

For booster blast protection?

Yes.

 

[BABAR]

Over the last few weeks I have been working on designing and building a BT-80 scale/sport-scale IRIS Hydra sounding rocket w/ booster. This is the later version of the IRIS sounding rocket that had 3 fins on the sustainer and a 3-tube booster w/ Sparrow engines inside and smallish booster fins.

Anyway, I finally nearly completed / built my first full prototype. When I originally looked at this design I thought it was going to be much easier than it turned out to be (just lots of interconnecting parts). The rocket is definitely the largest rocket I have built at 174cm/68.5" and 650g w/o chutes or engines (Big Bertha in pictures for size comparison).

I am designing this so it can be built with BT-80 or 2.6" thick-wall tubes and can use 24mm or 29mm engines (I am planning to launch with 3x D12 engines in the booster and 1x D12 engine in sustainer which gives me a 200m estimated flight - the lowest and least powerful launch combination that will work with this rocket). This model channels / vents two booster engines to hopefully ignite the sustainer engine and uses 1 booster engine (with delay) to eject a booster chute. Gap staging should be interesting (the little nozzle-extension part can be replaced with the pyramid tip for display). Nosecone is made in 3 quarter-twist locking parts and has mounting points for swappable nose weight (to go inside of tip or 2nd section) as well as generic mounting points for a sled (to position sled inside of 2nd or 3rd sections).

I need to add a bracket to the top of the booster section below the booster nosecone to help stabilize the weight of the sustainer, need to add the 3rd bracket details around the sustainer fins, and need to glue in motor blocks. I will also probably do a final coat of glue to clean up the fillets (still a bit wet in these pictures). Finally, I will also need to tweak parts to work with the 2.6" tubing version.

View attachment 597694 View attachment 597695View attachment 597696View attachment 597697

The scale data for this was provided by @Ez2cDave in this thread - https://www.rocketryforum.com/threads/iris-sounding-rocket-scale-data.155495/ (although I am still not 100% sure about the correct height for the sustainer fins on this model per my comments in that thread).

View attachment 597698 View attachment 597699

Reviewing your pics almost got a bit misty eyed. Mainly the background Big Bertha for scale. Der MicroMeister pretty much always seemed to put an Estes Mosquito i the picture for scale. I miss him. He was an Experienced, wise, helpful, and enthusiastic curmudgeon,

 

[jqavins]

Sorry, I am using "height" in the way that Open Rocket does (i.e., span) and length as chord length (root and tip).

What do you think of the photos? The fin profile with 35.6 as the span/height does not create a fin that matches the photos as far as I can tell.

I think I've got the answer, or at least part of it. The drawing clearly shows that the fins have the same span measured from the center line. But the booster has a greater body diameter, so the fin has less height (in your frame) from root to tip. And that changes a number of things. And I'm supposed to be working, so I'll have to get back to this.

 

[jqavins]

This shows that the motor tubes as having 20.3 cm diameter, but also seems to show that two side by side add up to 41.3 cm, so a 7 mm difference somewhere. That may be due to a 3.5 mm skin?

So, I'll go with the 41.3 cm, and calculate that the root of the booster fins is 22.25 cm from the center line, and thus the tip is 57.85 cm from the center line.

No, we know graphically that the tip of the booster fin and that of the sustainer fin are the same distance (22.25 cm) from the center line. The diameter of the sustainer is given as 30.8 cm. So the sustainer fin's span is 57.85 cm - (30.8 cm)/2 = 42.54 cm.

Thus, here is the revised sustainer fin.