Upscale Semroc Hydra VII

[dpower]

Fellow Semroc Fans,

This was supposed to be ready for NARAM-54, for entry in the classic model competition. Well, it didn't get done in time, and I couldn't make it, but at least it was completed before years end!

This is a 1.55x upscale of the classic Semroc Hydra VII, that started with parts purchased in the 2011 SAM Christmas sale. I've attached a photo of the completed bird, next to its original Semroc kit build. The original has flown many times on 7 motors. Since I didn't enter this in competition, I was free to use only 9 finlets instead of 12, which I prefer the look of, and free to paint it matching current cover art. Otherwise it is a very close scale build, varying from 1.52x to 1.58x, IIRC, with a height of 47.5"

This is my original, which I built during Heart surgery recovery:
https://www.rocketryforumarchive.com/showthread.php?t=25439

The goal of my upscale was to be as large as I could fly on 7 BP 24mm motors, attain reasonable altitude, yet be small enough to still be a "Model Rocket", for entry in competition. Since we now have C11, D12, E9, and E12 motors, this gave me a fair amount of flexibility.

It was built with primarily Semroc parts, which was another goal of mine, since this is an original Semroc design. ST-9 motor tubes, centered within ST-11, BC-1122 small cones, and a BNC-80HVE large NC. The NCs are all upscales of the original, and the ring is LOC 5.5" tubing.

Final weight, balanced for a max 7xE9 load, is 42oz; With a combo of C11 & D12 motors, it just squeaks under the 1500g limit, and 125g propellant limit. The NC has an adjustable weight system, so I could remove another 2-3oz for smaller motors if needed.

I'll attach a few more pics in a subsequent post, showing a few construction details. I was going to document the entire build, but kind of lost steam. The finishing touches were decals by Stickershock.

I'd like to thank Carl for this fantastic design, shown in the 1970 catalog: https://www.ninfinger.org/rockets/catalogs/semroc570/570semroc12.html

 

[dpower]

This pic shows detail of the transition joint. With 6 of the 7 ejection charges hitting these joints, I felt some additional glue area would improve the lifespan of this bird. Instead of having the NC halves just hanging off, I made the top tube a bit longer, and notched it for increased glue surface. I also inserted half couplers into the outer ST-11 tubes of the base (sorry no photo) to provide even more gluing area to this top tube, and get a solid seal at the joint.

 

[chadrog]

Beautiful work Paul, looks like I won't need to bring a rocket to the meeting in January!

 

[dpower]

This photo shows detail of the motor retention, seen in 2 of the tubes here; 3 threaded inserts in the space between the ST-11 tubes. The inserts required small rectangles cut from the ST-11, providing a solid mechanical bond. This was another benefit of using ST-11 outer motor tubes, with just enough space between the ST-9 and ST-11 to epoxy the toothed edges of each insert. Each ST-9 has 5 Semroc laser cut cardstock centering rings, 2 at the top, 2 in the middle, and one at the bottom. They're pretty thin, so I doubled up the top & middle. The ST-9 tubes were inserted from the top, since the bottom is now partially blocked by the inserts; The bottom CR was glued in last (this photo shows only 4 of 7 tubes completed).

 

[dpower]

Holy cow, look at the size of that nose cone! More later, gotta go.

 

[sodmeister]

Geeze Paul, that turned out very nice.....great workmanship !! That must have been plenty of work ,and the paint looks the part !

Nice show ,and yes,SEMROC is great !

I sure would like to see that one rip off the pad.I love clusters.

Cheers

Paul t

 

[dpower]

Beautiful work Paul, looks like I won't need to bring a rocket to the meeting in January!

Thanks Chad. There's always good competition there, that's the best part about the meetings!

Geeze Paul, that turned out very nice ...<snip>... I sure would like to see that one rip off the pad.I love clusters.

Thanks Paul; This'll be my biggest cluster to date, I'm looking forward to seeing it fly too! Hopefully I can get one of our more talented photographer members to get a lift off shot or a video.

 

[dpower]

More later, gotta go.

Well, that's 3 hours I'll never get back - went to see "The Hobbit", and after sitting through a half hour of previews, about 1 minute into the show the fire alarms go off, and we're all sent outside. After waiting around, finally we're sent home, there was a problem in the sprinkler system that needs to be fixed before they re-open.

Anyhow, here are some shots of the fins - The big fins clearly needed to be through-the-wall of the ring, so I cut 3 of the strakes in 2 pieces, leaving space for the 3" tab. The ring slot leaves enough of the ring to keep it round, and structurally sound. The tabs, sanded to a V, fit nicely in between the motor tubes, for what seems to be a very strong structure.. Eventually, epoxy fillets were used on both sides of the ring, but not until after painting.

 

[stickershock23]

Now that just looks like fun!

 

[dpower]

This shows a dry fit of the subassemblies. The lower section was painted without the ring or large fins, which were painted separately, with areas masked for later gluing & fillets. Once it was all glued, I simply brushed the unpainted areas. It was quite a bit of work to get this 3 color scheme done, especially with the TTW fins.

That's it for pics. This old post from Carl helped determine where to put the CG. Using the largest diameter, this gives me about 1.5 calibers. https://www.rocketryforumarchive.com/showpost.php?p=93712&postcount=2

 

[Scotty Dog]

I missed the fact that the picture in your first post IS the finished rocket.
I was waiting for more build pics.....:cyclops:
Now that I read thru it again,all I have to say is...."AWESOME BUILD."!!!!

 

[sodmeister]

Paul ,

I was looking at your latest pictures ,and there is a closeup of the aft end showing the motor tubes and what appears to be some engine blocks ? at the end of each.Are these for re-enforcement or are they even engine blocks ?

OH.....you mentioned centering rings (should have read more carefully) ,forwd ,middle and aft. Can you explain why you have these. or am I just a little slow this morning :caffeine:

Great pictures BTW ,could always use more though LOL

Take care

Paul T

 

[dpower]

I missed the fact that the picture in your first post IS the finished rocket.

Yeah, sorry about that. Kind of a backwards build thread.

I was waiting for more build pics.....:cyclops:
Now that I read thru it again,all I have to say is...."AWESOME BUILD."!!!!

Thanks Scotty!

 

[dpower]

Paul ,

I was looking at your latest pictures ,and there is a closeup of the aft end showing the motor tubes and what appears to be some engine blocks ? at the end of each.Are these for re-enforcement or are they even engine blocks ?

OH.....you mentioned centering rings (should have read more carefully) ,forwd ,middle and aft. Can you explain why you have these. or am I just a little slow this morning :caffeine:

I understand the caffeine part! Its a bit hard to tell in the photo, but the 7 engine tubes are ST-9, centered in ST-11, and the aft centering rings are flush with the end of the tubes. The shadow in the tubes is just where I reinforced them with CA. There are engine blocks, to easily load up with E9 motors, but they're not visible in the pic. ST-11 provided the scale I wanted, and the dual tubes make for a surprisingly stout build, despite the thin wall tubing.

I've attached a photo of one of the ST9 tubes with some CRs before going into the ST-11. The aft CR is not yet on this tube. Pay no attention to the curved tube, it's just a cheap camera.

 

[sodmeister]

Thanks Paul ,I understand now.

Paul T