Lakeroadster's "Hammerhead Shark"

[jqavins]

All's well.... that end's well

Holy Crap, it's even got its own well?

 

[lakeroadster]

Hammerhead Nose Cone

Fabricated the Hammerhead nose cone today. All made from pine. Used a 4x4 for the cone and a 1x3 for the hammer.

Fitting the hammer to the cone was the most tedious part. The fit ended up being pretty tight. I could push the pieces together and they friction fit tight enough to stay in place. I'm not planning to use any mechanical fasteners so I wanted the fit to be pretty tight so the wood glue would bond well.

Used Gorilla Wood Glue and then clamped it.

 

[mbeels]

Oh man, I really like that.

 

[Daddyisabar]

It's Hammer time! Can't touch this! Get out the shades, bling, parachute pants and hair gel.

 

[Funkworks]

I'm late to this, but you had me look up what the actual profile was for a real shark head. It's actually an airfoil! (which I guess should be expected, Mother Nature being no dummy)


As for the fin configuration, it has 9 of them and the forward ones are huge, so yeah, not sure this would be safe on a fixed-fin rocket:


The fin configuration you chose looks great, but I can't comment on its stability. Not familiar with asymmetrical fins.

 

[lakeroadster]

It's Hammer time! Can't touch this! Get out the shades, bling, parachute pants and hair gel.

 

[lakeroadster]

I'm late to this, but you had me look up what the actual profile was for a real shark head. It's actually an airfoil! (which I guess should be expected, Mother Nature being no dummy)

The fin configuration you chose looks great, but I can't comment on its stability. Not familiar with asymmetrical fins.

Not late at all... right on time.

The fins are a proven stable design... almost identical to a Skonk Wulf but scaled down from a BT-66 to a BT-60.

The big ole Hammerhead.. we'll see. I tried to make it as symmetric as possible, to avoid lift in any one direction which, I think, would result a big ole loop!

 

[jqavins]

I had the same thought on the front lift hazard, and was on the verge of shouting a warning. Then I realized the slight lift due to slight irregularity in the hammer is no different from a slight irregularity in any other canard. That's what my head says. My gut is still nervous, but I think my head is right. As long as you've got good static margin I believe it'll be fine.

 

[ThreeJsDad]

This project is looking amazing !! You have inspired me to push harder and build even more interesting rockets.

 

[lakeroadster]

Motor Mount Redesign

Using Aerotech motors is a new experience for me. A couple members here suggested I remove the internal motor thrust rings to allow for using various motor lengths. Old dog new trick kind of thing. So I redesigned the 29mm motor mount and designed an adapter for a 24mm motor mount that slides into the 29mm.

The complete set of drawings is on post #24. I've attached the pertinent motor mount sheets below. Also un-clamped the nose cone and started building up some glue fillets. It's actually lighter than I expected. It weighs 2.8 ounces.

 

[Greg Furtman]

I love your design & build. I just ordered a Aerotech 24mm motor case. I've been flying a HPR using their 38mm reloadable motors and have never had a problem.

 

[Funkworks]

The big ole Hammerhead.. we'll see. I tried to make it as symmetric as possible, to avoid lift in any one direction which, I think, would result a big ole loop!
View attachment 406088

Yes I'd call that a symmetric airfoil (like a water droplet profile), which is probably an ideal shape.

The shark of course has active control to compensate for any looping tendency.

 

[BABAR]

I tried a search and couldn’t find it, I believe it was a model of a Python missile with large forward canards.

Anyway, they were attached on pivots so they rotated in such a manner that they had less effect on the Center of Pressure than fixed forward canards.

Of course, with this huge head on your model would be a pretty GOOGLY EYED Hammerhead, but it would be amusing. Maybe when you do the ShovelHead or SawTooth sequel.

 

[CalebJ]

For what it's worth, if you haven't already built the 24-29 adapter you might look at the estes version. It's dirt cheap for a two pack ($6 as I recall) and works great. Might save you some time to focus elsewhere on the model.

Edit - Amazon shows about $10 at the moment but it was $7 in my order history a few weeks ago. Must go up and down quite a bit.

 

[lakeroadster]

For what it's worth, if you haven't already built the 24-29 adapter you might look at the estes version. It's dirt cheap for a two pack ($6 as I recall) and works great. Might save you some time to focus elsewhere on the model.

Edit - Amazon shows about $10 at the moment but it was $7 in my order history a few weeks ago. Must go up and down quite a bit.

Thanks. I'd rather build my own than buy an offshore product.

 

[lakeroadster]

Papered Centering Rings, post 1 of 3

I'm so stoked about how great papering fins worked on my scratch build hammerhead that I decided to make some centering rings using the same technique.

The balsa breaks when I try to cut delicate centering rings on my jigsaw... maybe the papering will be just the thing to prevent that?

We'll see. Anybody here have any tricks / tips for DIY centering rings

 

[mbeels]

I'll be curious to see how that works. I've only ever cut centering rings out of plywood, but perhaps the papering will work. Is this the same heavy cardstock you used with the fins?

 

[lakeroadster]

I'll be curious to see how that works. I've only ever cut centering rings out of plywood, but perhaps the papering will work. Is this the same heavy cardstock you used with the fins?

It is, 61 lb 11 mil. It's actually matte photo paper.

 

[Daddyisabar]

Back in the day we would cut them out of the back side cardboard of our big chief tablets, glue them on and then give a soak with Dad's super thin CA. Poor boy phenolic!]

 

[neil_w]

I made some centering rings out of balsa, papered with 110 lb cardstock. You'll see them in a future build. My observations:

1) They are surprisingly strong
2) They still flex along the grain
3) I still don't know if I'd trust them for high-stress applications (mine are decidedly low-stress). In many cases centering ring strength doesn't really matter. I'm not quite sure I know when it matters, and how much.

 

[lakeroadster]

Back in the day we would cut them out of the back side cardboard of our big chief tablets, glue them on and then give a soak with Dad's super thin CA. Poor boy phenolic!]

On my lifting rocket I used cereal box cardboard for conical transitions. I made them with the shiny / colored side out. I had a couple of small issues with paint herpes on one of them. Was it related to the dye or whatever they use on cereal boxes? Don't know. Next time it'll be "brown side out"... exactly the opposite of placing sod in your yard.

I made some centering rings out of balsa, papered with 110 lb cardstock. You'll see them in a future build. My observations:

1) They are surprisingly strong
2) They still flex along the grain
3) I still don't know if I'd trust them for high-stress applications (mine are decidedly low-stress). In many cases centering ring strength doesn't really matter. I'm not quite sure I know when it matters, and how much.

Sweet! Did you paper them before or after cutting them out?

From an engineering standpoint centering rings by their nature are very strong since they distribute stresses equally from one round tube to the other, minimizing stress risers. That's why many kits can get away with paper centering rings, like the Estes Saturn V.

Lakeroadster's 1st Rule Of Engineering: With many things, from Rockets to Race Cars, you never know what it's maximum performance is... until it blows up.

 

[neil_w]

Sweet! Did you paper them before or after cutting them out?

Umm
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Nope, I do not remember. It was several months ago.

Papering first and then cutting would seem to make the most sense, thinking about it now, but if I had to guess I'd say I did it the other way, for some reason.

 

[BABAR]

two options. Paper is NOT one of them.

1. Balsa: Double them, i.e., two pieces for each ring, laminate them with yellow glue with grain 90 degrees to each other, stick them between wax paper (make sure they are still lined up perfectly), and let them dry in a book. They will be hard as rock. You'll be surprised at how tough a couple of pieces of 1/16" balsa can be when laminated orthogonally. This technique also works will the weird curvy fin shapes, particularly ones with pointy sections in different directions where it is hard to take advantage of the grain direction. It is what I used on the "Squirrel".

https://www.rocketryforum.com/threads/the-squirrel-2-almost-perfect-flight.146038/

2. Foam board: FIRST, Cut center hole with drill about 2 mm smaller than needed (leave enough room around this for the rest of the ring. Center this on the hole you have already cut (WHY? Because it is a bit harder, at least with a hand drill, to make sure the center of the drilled hole is EXACTLY where you need it to be, so drill the hole first.) NOW, Cut a template exact size of ring you want. Center the central hole on this on the hole you have already drilled (easy to get this pretty close to perfect.) Mark your outside diameter. Now ROUGH cut this out with scissors or a blade, leave about 1/4" or so around the outside. Now, using a straight edge and a blade, work your way around the OUTSIDE with tangential straight cuts. (Surprisingly easier to cut out the outside circle with a bunch of straight linear cuts than trying to exactly cut it out directly with the blade. Think the old Spirograph drawing toy, or dream catchers where the inside "circle" is made of outside straight lines.) I've used this for up to D motors. Knock wood, haven't had this be a failure point yet. Once you get outside cut out, put sandpaper around a motor casing and sand the inner circle wider (that's where the extra 2 mm comes in) until your mount tube just barely fits.

Could reinforce with longitudinal balsa "struts" (3 or 4, spaced equidistant around circumference), running from forward to rear centering ring, for larger motors, maybe up to G. Kinda like through the wall fins, except that you are only connecting outer wall of motor mount to inner wall of body tube.

 

[jqavins]

Anybody here have any tricks / tips for DIY centering rings?

Cutting with a saw or a knife introduces highly localized stresses that a centering ring never sees in service and is liable to split balsa unless you are cutting across the grain and supporting the wood vry well. And with a ring you can't go across the grain all the way around.

I know there are multiple ways that many have used successfully. I myself tend to be very cautious because I know I'm a klutz. I would only use the one method available to me that places essentially no stress on the wood while cutting.

Laser cutter. If you're not one of the lucky few who has one then find a maker space or a friend with one you can use. Once you've got your design down it's fool proof.

 

[mbeels]

On my lifting rocket I used cereal box cardboard for conical transitions. I made them with the shiny / colored side out. I had a couple of small issues with paint herpes on one of them. Was it related to the dye or whatever they use on cereal boxes? Don't know. Next time it'll be "brown side out"... exactly the opposite of placing sod in your yard.

I did the same with the cereal box transitions on Plasma Dart II XL, I think it came out slightly better with brown side out.

 

[lakeroadster]

two options. Paper is NOT one of them.

Laser cutter. If you're not one of the lucky few who has one then find a maker space or a friend with one you can use.

Thanks fellas.

I'm all in for balsa ply and foam board... for larger centering rings and components. I did the "make-my-own-balsa-ply" on my lifting rocket.

I like to use what I have at hand... some may call that frugal, others cheap. And I find a big part of the challenge to building model rockets is to make as many components as I can myself, with the tools I already have available.

So keeping that in mind and utilizing "form follows function" let's see how this papering technique plays out.

In this case, for my hammerhead rocket, the ring annular height is less than 3/16". A 1/8" thick balsa centering ring is more than adequate from a strength perspective. The sole purpose of the paper is to hold the balsa together during the cutting and sanding operations.

I'll probably revert to the technique I used to make some centering rings for the lifting rocket. I bought these, they were lite ply, and then turned them down on my lathe (See photo's below).

If I use the papered balsa rings I'm making, cut inside diameter first on the jigsaw, then cut the outside over sized, I should be able to turn them down on my wood lathe and get everything nice and concentric.

It's a plan... we'll see.

 

[lakeroadster]

Papered Centering Rings, post 2 of 3

So far so good.

I used a different approach to cutting the centering rings. Instead of cutting them I used the X-Acto knife to perforated all the way around the circumference. This pierced the paper and minimizes the stress of the somewhat fragile balsa.

I used a block of wood to space the papered balsa to hang over the edge of the block so the knife pierced all the way through.

After piercing I used the X-acto knife to trim the jagged edge right along the line. And it was easy to do, also while letting the piece being cut to hang over the edge of the wood block.

The ring fit over the tube right after cutting, a bit to snug, but it fit. If you've ever made home made centering rings that's a big deal. Only minimal sanding, and no slop... yippee!

I cut the I.D. of the ring 1st, then sanded it for a proper fit on the body tube, and then cut the O.D. of the ring. I cut on the outside of the line for the o.d. to ensure enough material for removal later.

Even with the papering the rings are still to fragile to sand the o.d.. So I decided to go ahead and glue the rings to the body tube(s) before sanding the O.D. This will ensure they are rigid and stable for the final sanding.

I might try to do the final sanding on the wood lathe.... that would ensure concentricity.

I'll let everything dry for a day or so... more later.

 

[OverTheTop]

Nice. Have you thought about calling it "Mallet" .

 

[BABAR]

Your differential diameters between outer motor tube and inner body tube are pretty minimal. There is a very EASY solution when you don't need much diameter.

Take a roll of 1/2" masking tape and a knife. Divide the diameter of the tape into equal thirds (you can pretty much eyeball it.) Carefully use the knife to cut the tape while still on the roll, working your way around slowly, so you will have three strips each 1/6" wide (you can make shallow cuts, remove what you need, and repeat the cuts as needed. Don't try to cut all the way to the core at the beginning.)

Now start with the edge of one strip and wrap it around your motor mount, building it up layer by layer, until you get the thickness you want. Doesn't take that many wraps to get to the thickness you are looking at here. I use this routinely for BT-5 to 20, and BT-20 to 50. Would not work for say BT-20 to BT-80.

Once you get it to the right thickness, wick some thin CA into it to lock it down tight. Otherwise the motor heat will loosen the tape adhesive.

 

[BABAR]

Nice. Have you thought about calling it "Mallet" .

Mullet Eating Mallet?