Hydra (Semroc) 54 MM Upscale Build

[gary7]

I have done one upscale of these really nice kits from Semroc. Finally got the stuff to begin another. Don't let the supplies fool you at first glance. They all need to be cut down, trimmed and turned! I got double the amount of bass wood needed in case I mess up turning the cones.

See the Hydra in two different versions from Semroc at:
http://www.semroc.com/Store/scripts/....asp?SKU=KV-29
http://www.semroc.com/Store/scripts/....asp?SKU=KA-18

See the attached photo of my current Hydra on an H170 last summer in Champaign, IL with my local club (http://www.ciarocketry.org/), a great bunch of guys! Plan flying the new one on J800 up to K700 and this one will be dual deploy.

Planning on getting this done in time for flying at Thunderstruck 2012 (http://www.indianarocketry.com/thunderstruck/). I'll try to include different parts of the build I think might be most interesting since this is not your ordinary 3FNC rocktet! Cool. Hope you all like it!

[dixontj93060]

Subscribed--gonna be a nice build I'm sure!

[gary7]

I am putting this in the thread because it may be helpful to someone out there trying to figure out a way to cut motor tubes or air frames. If you don't have a miter saw don't sweat it. Just take a couple of 2 x's and screw them together to get your right angled "bed" to set your tubes on. I think I got the idea for cutting tubes this way on this forum a couple of years ago. It works, maybe not the best but it works and is cheap. Although it took three blades to cut this 10 inch Menards sonotube to a 7.5 inch length. Still had to finish it with my carpenter's knife.

First picture shows the set up of my compound miter saw with the blade and motor set back out of the way of the big tube.


Second picture shows the stop block to keep the tube where it needs to be as I rotate it against the blade. Notice the penciled on arrow? That gives me a quick reference to make sure the stop block is still working.


Third pic shows the tube against the blade.


Just keep turning the tube with gentle pressure against the blade until your cut is complete (or almost complete as was the case with this piece). Only nine more pieces to cut! I'll be awhile.

Last pic is the completed piece which will eventually become the ringtail for this bird.


I'll next show the configuration of the single motor mount and the pod tubes in relation to the main air frame. Stay tuned, but it may take a couple of days to get these tubes cut. Unless I get busy. Right now.

[gary7]

I had to change the location of the blade to cut the 4 inch Loc air frames. They were easier than the Menards sonotube but the 54 mm Loc motor tubes were a breeze to cut. Got the motor tubes done in about a minute each. I also made all those cuts on just one blade. See first two pics.

The last pic reveals the relation of the pods to the MMT and how that structure is secured to the aft air frame. I probably could have got by with two centering rings but like we all so often do for no reason other than it just makes us feel good or it feels right to do something, we do it so I am putting three rings in. No, they are not glued just yet. This is a dry fit only.

The ply behind the tubes is what I forgot to show in the "materials" pic in the first post of this build thread. It is 3/16 inch birch. Yes, I'll use most all of the 2 ft x 4 ft piece for this rocket.

The most difficult part of the entire build is about to take place. I have to cut not just slots for the three main fins, but an actual section out of each pod to enable thru the wall fin attachment to the motor mount tube. You will understand when I post those pics later.

[bill2654]

Did your current Hydra need nose weight? Looks like this one will. .

[gary7]

Rocksim gives a margin of ~3 in this rocket so no nose wt necessary. Didn't need it in my other one either. Happy to post both Rocksim files for anyone interested.

[jungmann1]

Subscribed! Love upscales, this should be spectacular. Keep up the good work. John.

[gary7]

Don't usually do much on Sunday but go to church and visit with family so limited work today.

Look at the Rocksim file below. If you look at the main red fin you can see it goes "thru the wall" of the ring tail all the way to the MMT. It also go thru the pods. As you can see, a small slit like we usually make will work for the ring tail, but a section rather than a slot must be removed from the pods to receive the main fins.

The next pic shows my fin marking guide we are all so familiar with from our low power builds. It works for the big rockets too! If you cut or fold it to the proper length, you can mark not only the width of the slot but also the length. You only have to measure once, from the end of the tube.

The final Rocksim graphic is a close up shot of the TTW main fin through these large fin slots. If you notice where the fin intersects the arc of the two tubes in two different places, you get an idea of what needs to be cut away for the fins to go TTW.

With the guide marks in place, I use my angled aluminum to complete them.

Tomorrw I'll cut the slots then post a pic to show how the fins go thru to the MMT.

[gary7]

Unlike Quake, who is fortunate enough to have all kinds of time to build rockets, I have to work. I also have to take a recertification exam every six years to keep my job. I passed so we celebrated by going out to eat after my real job thus the only thing done today was getting the pod slots cut for the main fins.

You can see how large the slots are, nothing like regular fin slots. However, if you turn the pods' slots towards each other, those slots look more like regular fin slots now as in the second pic.

The pods are assembled in pairs this way and then attached to the central MMT. That will provide slots for the three main fins. The six tubes surrounding the MMT are the same size as the MMT so they fit perfectly around it therefore providing hassle free placement of the main fins.

Look at the final two pics, you can now see how the "thru the wall" assembly will look when completed at this level. That is a piece of scrap tho, not one of the fins to be used in construction. The more conventional "thru the wall" takes place at the ring tail.

Finally, the Rocksim graphic showed this TTW configuration would be the case before construction began.

[Woody's Workshop]

I have to admire your entuseasim sir.
Your upscale looks like a lot of calcs and work, especially if your adding things in RockSim to their exact weight before starting to get a handle on the areodynamics!
Truely a credit to our hobby!
Best of luck on getting it done in time for your scheduled launch, and more so on your first launch!
Thank you for sharing, I have my eye (when I can) on your progress.

[gary7]

I have to admire your entuseasim sir.
Your upscale looks like a lot of calcs and work, especially if your adding things in RockSim to their exact weight before starting to get a handle on the areodynamics!
Truely a credit to our hobby!
Best of luck on getting it done in time for your scheduled launch, and more so on your first launch!
Thank you for sharing, I have my eye (when I can) on your progress.

I would love to take the credit, but Rocksim takes so much of the work out of it. And we must not forget the person, whoever it was that designed this rocket initially way back whenever. Without the two, I could not be doing this. I do appreciate your kind words tho, thank you!

[gary7]

Was going to cut some 2 inch foam board circles to prop the 10 inch tail fin for glassing but a band saw tire snapped. So I scratched the tail fin glassing for the time being while I await the arrival of a new band saw tire.

I marked and glued up the pods in what I'll call "pod pairs".

First pic again shows the fin slots. The pencil points to the center of these slots. I extended a pencil line the length of the tube as a gluing guide so I could get a good bead of Titebond II in a straight line then set the pod pairs in my cheap "pod pair glue up jig". See second pic.

In the third pic you can see the ends of each pair of pods aligned by the pencil mark on the end. This is critical so that the slot is "opened" properly to accept the fins. Last pic shows the scrap ply inserted in one of the pairs to check the alignment of the slot.

[gary7]

As stated earlier, my goal is to show what may be different in this thread for this truly different rocket. Consequently, although I am working on the electronics bay this evening, there really isn't anything different than what we have all seen on this forum in the past. So look at others' bays, this one isn't a whole lot different. Just picture in your mind and on your screen some pics of a bay under construction with copper tubing ejection canisters and two altimeters then leave it at that.

Trust me, there will be an electronics bay for dual deploy on this rocket!

[qquake2k]

First pic again shows the fin slots. The pencil points to the center of these slots. I extended a pencil line the length of the tube as a gluing guide so I could get a good bead of Titebond II in a straight line then set the pod pairs in my cheap "pod pair glue up jig". See second pic.

Now there's a great use for canned soup!

Unlike Quake, who is fortunate enough to have all kinds of time to build rockets, I have to work. I also have to take a recertification exam every six years to keep my job. I passed so we celebrated by going out to eat after my real job thus the only thing done today was getting the pod slots cut for the main fins.

Hey, I have to work too! But I'm divorced, so I don't have all the family things anymore. I also don't build rockets anywhere near as complex as this one. It's gonna be great!

The ply behind the tubes is what I forgot to show in the "materials" pic in the first post of this build thread. It is 3/16 inch birch. Yes, I'll use most all of the 2 ft x 4 ft piece for this rocket.

Where did you find 3/16" plywood? I haven't been able to find it anywhere!

[gary7]

Did little to nothing last evening. Had to take an all day trip for family matters. Back to work tonight tho.

Someone might have asked "how do you glue up both sides of three centering rings?" Well, it isn't that difficult. It takes time but you can do it.

First pic shows the middle CR already glued to the MMT. In the next pic you can see the other CRs dry fitted to the MMT. This is to assure that the main, aft air frame is on the CRs and MMT straight. They help by holding everything in alignment while the middle CR is drying. Look inside the aft frame in the next picture. You can see the middle ring in place, glue only on the visible side. When dry, we'll take apart the dry fit pieces, flip it over and glue up the other side of the middle CR.

[gary7]

In this pic the pencil is pointing to the approximate location of the top of the MMT. It is a full length Loc MMT and is 34 inches long. Remember this is the aft air frame only on top. There will be a 1 inch section of air frame on top of that with the electronics bay inside, then the forward bay, same length as the aft bay, then on top of that, the nose cone which you will see in the next post. Both aft and forward air frames are the same length at 24 inches.

[gary7]

Ok, the real fun begins. If you look at my "About Me" in my bio section on this forum, you'll see my intersts besides rocketry include wood turning. See below!

Look again at the first post at the 5 inch block of bass wood. That block is now about a 4 inch diameter x 10 long nose cone. The first two pics were taken during the process of turning the nose. The last needs no explanation as completed nose cone sits atop a left over piece of Loc 4 inch air frame. Rocksim puts it at 6.5 oz. It has to weigh at least that. But not to worry. It will be no match for a J800, K550 or K700. Which one would you like to see it fly first?

[gary7]

When you are guy my age (Quake's age too), you sometimes wake at 5:30 on a Saturday morning even if you don't have to go to work, to go to the bathroom. It's called BPH.

Anyway, since I couldn't get back to sleep, I took the time to prep the pod cone blocks for turning. This you might find interesting.

The first pic shows an up close view of the pod cones. On first glance you see six cones (on the real rocket, not in this pic). But the build requires only three really. So you make three and split them in half. It is easier and cleaner to split them before you turn them. Begin by cutting the blocks then glue them back together, but glue only enough of the ends to hold them on the lathe while turning. One glued end will be turned off at the tip of the nose cones. The other will be parted off when the cones are done. The most critical point here is to make sure they get chucked up on the lathe exactly on center at the joint or the cones will come out a bit differently. Some may be shorter or not exactly in half for instance. Hope it works!

The second pic is just a reminder to show where we started with the bass wood. You have seen the results of turning the main cone. I cut the 3 inch piece down to correct length allowing enough extra length to chuck it up on the lathe.

It doesn't take alot of clamp pressure to hold basswood together. I'll let it sit for about 8-10 hours then try turning the pod cones. I'll need a bit of help parting them off since they will want to fly way off on their separate ways when done. Maybe rather than part them all the way off, I should leave a little then cut the nubs off of them with my Japanese flush cut saw instead.

There is going to be another little trick to make the cones work and fit properly. Are there any engineers out there who have noticed the "flaw" in the design that will have to be corrected when the cones are attached to the pods? A clue lies in the pod cone close up.

Stay tuned! Or shall I say, stay turned?

[gary7]

When dry fitting CRs as I did in the glue up of the middle CR, you can not forget to drill a small hole in the dry fit CR. If you don't and it's a tight fit, you may be a while getting it back out. The hole will allow you to place a screw to grab onto with a pair of pliars so that you can pull it out later. Easy enough to epoxy the hole shut if necessary. The second pic again shows the location of the top of the MMT inside the aft air frame which is now flipped upside down to allow glue up of the other side of the middle CR as was discussed in an earlier post. Two more CRs to go. That will take me about 32 hours! Know why it takes so long?

[jungmann1]

I have used a similar technique on some of my wood workng projects, when I needed a turned, applied moulding for the front of a cabinet or bookcase. In my case, I glued the two halves together with a sheet of thick paper between them. After they are turned, it is a pretty easy matter to split them along the joint because of how much weaker the paper is than the wood. I haven't yet had a reason to use it on a rocket yet, guess I haven't chosen an interesting enough project yet!

When you are guy my age (Quake's age too), you sometimes wake at 5:30 on a Saturday morning even if you don't have to go to work, to go to the bathroom. It's called BPH.

Anyway, since I couldn't get back to sleep, I took the time to prep the pod cone blocks for turning. This you might find interesting.

The first pic shows an up close view of the pod cones. On first glance you see six cones (on the real rocket, not in this pic). But the build requires only three really. So you make three and split them in half. It is easier and cleaner to split them before you turn them. Begin by cutting the blocks then glue them back together, but glue only enough of the ends to hold them on the lathe while turning. One glued end will be turned off at the tip of the nose cones. The other will be parted off when the cones are done. The most critical point here is to make sure they get chucked up on the lathe exactly on center at the joint or the cones will come out a bit differently. Some may be shorter or not exactly in half for instance. Hope it works!

The second pic is just a reminder to show where we started with the bass wood. You have seen the results of turning the main cone. I cut the 3 inch piece down to correct length allowing enough extra length to chuck it up on the lathe.

It doesn't take alot of clamp pressure to hold basswood together. I'll let it sit for about 8-10 hours then try turning the pod cones. I'll need a bit of help parting them off since they will want to fly way off on their separate ways when done. Maybe rather than part them all the way off, I should leave a little then cut the nubs off of them with my Japanese flush cut saw instead.

There is going to be another little trick to make the cones work and fit properly. Are there any engineers out there who have noticed the "flaw" in the design that will have to be corrected when the cones are attached to the pods? A clue lies in the pod cone close up.

Stay tuned! Or shall I say, stay turned?

[dpower]

Nice project. So this is 3x? I noticed you've set it up for 3 finlets between each fin, instead of 4. is this to get a 2nd set of 3 TTW fins with the smaller finlets?

How are you going to handle the TTW fin tabs, along with the internal strakes?

Thoughts about what parts to paint before assembly? Even at this size, seems like it would be tough to get a decent finish inside the ring.

Oh, and where do the other 6 motors go?

[gary7]

Nice project. So this is 3x? I noticed you've set it up for 3 finlets between each fin, instead of 4. is this to get a 2nd set of 3 TTW fins with the smaller finlets?

TTW fin tabs aren't necessary with the strakes, only the main fins sticking out of the ring tail. It will become more obvious when I get to that part of construction.

How are you going to handle the TTW fin tabs, along with the internal strakes?

Thoughts about what parts to paint before assembly? Even at this size, seems like it would be tough to get a decent finish inside the ring.

Oh, and where do the other 6 motors go?

I decided to go with only three finlets between each fin on the ring tail because I think it makes it look more symmetrcal since they line up with the strakes. Besides that, it makes for three total fewer fins to cut, finish, attach, paint... You get the idea.

Before when I painted, I just did it when the build was done. Of course the inside of the ring tail isnt' the greatest, but who'll look or even care. If I have to I'll paint it by hand. Finish and painting aren't my strong points.

Regarding the amount of upscale? It depends on whether you use the Hydra One or the Hydra VII. I have sort of a hybrid of the two. And it isn't an exact replica either. I use tubes/materials that are readily available so it's a bit off the originals. But it looks close enough. I know some out there would scold me for that but such is life.

The Semroc Hydra One is 22 inches long with a 1.17 inch upper body tube diameter. That gives this one about a 3.5 x upscale. This one also can fly some clustered 38 mm motors if I ever want to configure it that way but for now only plan a single 54. If you look at the Hydra VII, that is 30.5 inches long with an upper body tube diameter of 1.64 inches giving this one only a 2.5 x upscale. So the upscale depends totally on which of the two stock kits you compare it to.

Oh yes, the other six motors? They would go in the pods as in the original Hydra VII.

[dpower]

...Oh yes, the other six motors? They would go in the pods as in the original Hydra VII.

Yeah, I was just wondering if you left that option open. Funny, I like the 9 finlet version better too. Regarding scale, this one is nearly impossible to upscale exactly, since 3 tube sizes are needed, I was just curious what your approximate goal was. Keep up the progress posting!

[gary7]

First big mistake in my calculations. I like long shock cords. This is roughly going to be a 77 inch long rocket. I chose to go with 1/2 inch kevlar at 25 feet. I know, some of you are shaking your heads. But one can look on this forum and see all kinds of reasons why a cord should be long or short with plenty of evidence, math and experiences to back up those opinions. But again, I chose to go long. There may also be as much difference of opinion regarding my choice of the 1/2 inch kevlar. Don't need or want comments on either please.

My problem is that my drogue bay has enough room for the cord, chute and nomex blanket but that's it! I'm up to the electronics bay, all the way down to the (booster section) forward CR with the U-bolt.

The question: is that too much crammed into that space? Is "dead space" necessary for the ejection charge? Do I risk insult to the chute, even with the blanket? What do you think?

My choices are:
1) Bite it and get a shorter cord but how much shorter to make it fit? It would probably have to be 10 feet to make a difference.
2) Put a coupler and 8 inch extension in to make it about four inches longer. But then I would have to shorten the Main bay, maybe?
3) Do nothing. It will work inspite of things being so tight.

[gary7]

My problem is that my drogue bay has enough room for the cord, chute and nomex blanket but that's it! I'm up to the electronics bay, all the way down to the (booster section) forward CR with the U-bolt.

The question: is that too much crammed into that space?

Got a reply from my friend, Tim Dixon over in Indiana, also a member of the http://www.ciarocketry.org/. He has suggested leaving the blanket and chute out of the booster and fly drogeless. Just might work and just might be the answer I was looking for.

In the mean time, got some more work done on the electronics bay sled. Also got the CR's all glued in. Will turn the three pod cones this evening. The bandsaw tire is supposed to be delivered today so can start cutting fins tomorrow. But I am on call tomorrow so hopefully all will be quiet and I can get some things done.

Have given myself a deadline of March 24 for getting this thing done including paint, so that she will be able to fly at Thunderstruck (http://www.indianarocketry.com/thunderstruck/) as earlier planned.

Had mentioned earlier (post #18) a "flaw" in my design/version of this rocket regarding the pod cones. Will explain that flaw and my solution when the pod cones are done. Did anyone ever see the problem?
__________________

[gary7]

My trick with the cut basswood stock worked. Take a look again at post #18. See the wood split on the table saw? That was glued together just at the ends then turned down to the pod cone. The ends were turned/parted off and the two pieces separated.

As you can see in the second and third pic's, the half cones match almost perfectly.

In the last pic tho, you can see the discrepancy I mentioned earlier. Take a look one more time at the close up drawing of the completed rocket in the last post. You can see that the pod cone tips do not meet the air frame. I knew that when I upscaled the design. But I also came up with a way on my first Hydra upscale that worked beautifully. All I had to do was take a piece of balsa and shape it to match the cones. It has to be a bit long on the tip so that you can carve or sand to get the cone to appear to be one piece in a nice symmetrical line up to the air frame. In other words, the point will meet the airframe at "0" on the "x" axis rather than being -x which is where it is now. You want to slope the carve up to the point or it will end up straight across from the airframe which wil look rather bad in my opinion.

The side of this block of balsa that contacts the cone is flat. The side in contact with the airframe is rounded to match the contour of the tube. This is done by wrapping sand paper on the air frame then sanding down the balsa until that side matches the air frame. When completed, I'll show this step. You just have to sand the contour on the airframe side of the balsa block first, then sand to the thickness required before shaping the rest of it.

[gary7]

Family and work commitments continue to slow me down. But I did get something done today.

The band saw tire arrived and I finally got that and a new blade installed so will cut fins tomorrow.

Today I turned the remaining pod cone pairs. The woodturner that got me interested in turning told me once that you cannot turn two identical pieces. Close, but not identical. For instance table legs or in this case the pod cones. They are separated enough that the eye will not see minor differences in the pieces. Hopefully such will be the case when these half cones are applied. They look very good on my first Hydra and only under very close scrutiny can one see the differences. Here they are side by side then dry fit on the rocket.

[gary7]

Quake likes to pin his fins together with dowels for cutting them out. I'm too lazy to do that and just tack pieces together with small nails. They are so much easier and work fine for me. If I have to put nails thru an area that will be finished, it's easy enough to fill the hole with something before priming.

After cutting the main fins, I dry fit them to the pods and ring tail. These are the main fins and will actually be coming out of the ringtail, TTW, not sitting on top of it. Just wanted to test the fit.

In the last pic you can see that there is plenty of space for a 1010 rail to pass thru the ringtail for launching this rocket. I couldn't do that with my last Hydra upscale because this space wasn't enough. I fly that one off of a 1/2 inch rod. I'll feel alot more at ease flying this rocket on a K700, off a rail. Fully loaded it will top off at close to 16 pounds.

Only 15 more fins to cut, I better get with it. That ringtail you see will be the only part of this rocket getting glass so that must be done too before the hardest part of the assembly begins.

[gary7]

12 down, 6 fins to go. These all go arond the ringtail, 3 each between main fins.

The pod fins while easier to cut, will be more difficult to calculate. I have to bevel the root cord edge that will go down between the pods a bit. I have yet to make that bevel calculation. Thank goodness I found a cheap router table which will make the beveled and rounded (if I do them) edges much easier to do.

On my last Hydra, I left all the fin edges squared. I am considering a gentle rounding of all of them on this rocket but haven't decided yet. Any one with an opinion on that? The squared fins look fine and it isn't like rounding them is going to reduce enough drag on this thing to make a difference.

[gary7]

Was going to make a fin alignment jig out of 1 x but changed my mind. Yes, this one is big and bulky and heavy but it's going to work in both directions keeping the fin aligned until the epoxy is dry. I'll have the pod pairs and central tube assembled when it is going together. Actually though, some of the side supports on this jig will have to be cut back a little so that it fits inside the ringtail during assembly but you get the general idea. I only hope it works.

Why are half the strake fins shortened? So they can meet the main fins just inside the ringtail. The long set will span the length of the pods. Almost.

Tomorrow we have our local NAR club meeting so no work on this until Wednesday when I'll glass the ringtail. Next up will be the pod cones' space filler blocks (see, we have a name for everything). What a pain that will be.

I am running short on time to get this thing done by my deadline.