Lakeroadster's "Hammerhead Shark"

[lakeroadster]

I'll take that to mean "A penny and..." but FYI a penny weighs 2.5 grams. Prior to September, 1882 they weighted 3.11 grams, but most of those have enough wear by now to weigh closer to 3 even.

Since you've been successful with 2.5 gram pennies, you obviously can leave well enough alone (and don't need me to tell you that). But if you want 4.67 grams, go with a nickel (5 grams even) or a better yet penny plus a dime (2.500 + 2.268 grams). Do I get credit in the nerd pride thread for this?

As a handy mental reference for small gram weights, I like to think of how many nickels they would be.

He takes the hook... and the hook is set....

"The first series of Indian Head pennies were minted in 1859. These pennies weigh 4.67 grams and are composed of 88% copper and 12% nickel."​

So to summarize: A 2.5 gram penny and a 12 foot streamer = an even slooooower decent.

I never did a calc to determine how long it would take the streamer to drop. Maybe I can get a good launch video? Again, problematic with just me and the wife at the field. The rocket has a 28" diameter chute though, and with an apogee of 1030 feet it should be easy to see.

That's all assuming a straight stable flight. I know some folks are thinking with that big hammer head, a straight stable flight may be unobtainium. Who knows? It passed the swing test with "flying" colors. Only thing left to do is drop the "hammer", and light the fire.

 

[jqavins]

Ah, I see. So you're using Indian Head pennies? I'm impressed by your chutzpah in launching pennies that are about 161 ± 2.5 years old. I bow to your superior numismatic nerdiness and testicular fortitude. (Are they made of cupronickel 88/12? Not the pennies, I know they are.)

 

[lakeroadster]

Launch Report

My wife and I launched the Hammerhead Shark.

The rocket flew stable.


I gained a lot of respect for you folks that post up flight videos and photos. We were so focused on not losing the rocket since it was its maiden flight, that I wasn't able to get any apogee or recovery photo's.

So... my apologies in advance for the poor-quality photos and video.

 

[Daddyisabar]

It is a coner but you meant it to fly that way! A shark must swim through the air. You meant to do it...yeah, that's the ticket! A natural, artistic and biological flight profile gained through asymmetric fin geometry, power, nose weight and big fins up front on the nose cone. Completely pre planned by the use of pure scientific method and confirmed with ample swing testing! Kid tested, mother approved! Safe to swim with the Hammerhead shark. Trust in thrust! Oddrocs rule!

 

[lakeroadster]

It is a coner but you meant it to fly that way! A shark must swim through the air. You meant to do it...yeah, that's the ticket! A natural, artistic and biological flight profile gained through asymmetric fin geometry, power, nose weight and big fins up front on the nose cone. Completely pre planned by the use of pure scientific method and confirmed with ample swing testing! Kid tested, mother approved! Safe to swim with the Hammerhead shark. Trust in thrust! Oddrocs rule!

One of the guys there at the park flying RC planes said.. "It fishtailed"... I replied "Exactly what you'd expect from a shark, right"

 

[Daddyisabar]

One of the guys there at the park flying RC planes said.. "It fishtailed"... I replied "Exactly what you'd expect from a shark, right"

That is what you get with a powerful rear wheel drive. Maybe some powerful, multiple motor front wheel driving in the future? Riddin' in a Mercury!

 

[lakeroadster]

Here's the streamer that acted as a piston. The plastic cap from the composite motor is stuck in the streamer.

As stated above, at ejection the motor popped the chute out, but the streamer didn't fully eject because the motor pushed past the retaining clip and also ejected.

 

[Daddyisabar]

Did you have wadding? Really long streamers are an art to pack. Lots of care, talc powder and ancient Chinese Secrets. Lucky it acted like a piston. Lots of pressure to blow the motor out the back with a clip. Lucky no damage. I have never flown with chute and streamer together. For heavy oddrocs I pack as big a chute as possible or use two smaller chutes, one for the heavy nose cone and one for rest.

 

[lakeroadster]

Did you have wadding? Really long streamers are an art to pack. Lots of care, talc powder and ancient Chinese Secrets. Lucky it acted like a piston. Lots of pressure to blow the motor out the back with a clip. Lucky no damage. I have never flown with chute and streamer together. For heavy oddrocs I pack as big a chute as possible or use two smaller chutes, one for the heavy nose cone and one for rest.

The streamer is the wadding. When I got home I pushed the streamer out of the body tube and it took very little force to do so. But remember, the nose cone on this rocket has over 9 ounces of nose cone & ballast (a 3/4" dia. bolt) that the ejection charge has to move.

I think the issue was my home-made motor clip. I didn't bend it 90 degrees.... my bad. Also, in this case, the motor wasn't a tight fit in the motor tube. A cluster of opportunities.

 

[Daddyisabar]

Wow, your wadding technique is way beyond my reality. Usually folks tear up the crate paper into little bits to eject like confetti or regular sheets of wadding. I like dog barf.

 

[Daddyisabar]

It was a good thing your motor hook gave way before your body tube burst. There was quite a bit of instant pressure that streamer was holding back in order to drive the plastic cap in and the motor out. Funny things happen with ejection.

 

[KenECoyote]

I think the issue was my home-made motor clip. I didn't bend it 90 degrees.... my bad.

Actually you should bend it inwards more than 90 degrees since the motor can still slip out at 90, but if it's more than that, the edge of the clip will dig into the motor as it tries to push out, ensuring better motor retention imo.

 

[Rktman]

Launch Report

My wife and I launched the Hammerhead Shark.

The rocket flew stable. I wish I could have gotten a flight video. The back end of the rocket orbited the c/l, but the nose didn't. It went straight up, but you could visually see the circular rotation of the motor end. Let's call it "fish tailing". (@Daddyisabar tells me this is "coning")

This rocket weighs nearly a pound, a lot of nose weight. At ejection it popped the chute out, but the streamer didn't fully eject because the motor pushed past the retaining clip and also ejected. Basically the streamer acted as a piston. See Post 277I have to thanks the God's of Chute Deployment for their assistance in preventing the Hammerhead Shark from being a lawn dart.

The flight was on a F42T-8 single use composite motor, and was my first launch with a composite motor. It's impressive. Next time I launch this I'll bend the motor clip a bit more, and wrap a small twist tie around it and the motor.

The 28" chute and the 1,000+ (estimated) foot apogee meant a bit of a walk to recover the shark. No damage occurred upon ground impact.

I gained a lot of respect for you folks that post up flight videos and photos. We were so focused on not losing the rocket since it was its maiden flight, that I wasn't able to get any apogee or recovery photo's.

So... my apologies in advance for the poor-quality photos and video.

View attachment 525011View attachment 525012View attachment 525023View attachment 525024View attachment 525015View attachment 525016View attachment 525017View attachment 525018View attachment 525019View attachment 525020

Again, big congrats on a successful concept/design, build, and flight! She's beautiful and came back in one piece, not much more you can ask than that.

 

[lakeroadster]

It was a good thing your motor hook gave way before your body tube burst. There was quite a bit of instant pressure that streamer was holding back in order to drive the plastic cap in and the motor out. Funny things happen with ejection.

This bird, as are most of my designs, has a full-length coupler. As my boss used to say "we build hell-for-stout". Since these aren't designed to maximize altitude, the heavy wall minimizes a lot of the issues associated with thin-walled airframes.

 

[jqavins]

At ejection it popped the chute out, but the streamer didn't fully eject because the motor pushed past the retaining clip and also ejected... Next time I launch this I'll bend the motor clip a bit more, and wrap a small twist tie around it and the motor.

Does the clip land on the sloped part of the back end of the motor, or the flat part?

That slope can make retention with a hook difficult, as you found. Bending more so it bites (as Ken suggested) sound like a good idea. Many people just use a wrap of tape around the motor and hook together, and that seems to work quite well. Tape seems to me like a better idea than a zip tie, since a zip tie, being without adhesive, could just slip off the end. If the tape also goes over the end of the MMT then it's hard to say: is this tape retention assisted by a hook, or hook retention assisted by tape? Doesn't matter, if it keeps the motor in place.

I have to thanks the God's of Chute Deployment for their assistance in preventing the Hammerhead Shark from being a lawn dart.

Sure, on your first launch day in so long. That's how they get you.

Oh, and, I almost forgot: congrats on a good flight! And all the flights that day!

 

[lakeroadster]

Does the clip land on the sloped part of the back end of the motor, or the flat part?
View attachment 525122
That slope can make retention with a hook difficult, as you found. Bending more so it bites (as Ken suggested) sound like a good idea. Many people just use a wrap of tape around the motor and hook together, and that seems to work quite well. Tape seems to me like a better idea than a zip tie, since a zip tie, being without adhesive, could just slip off the end. If the tape also goes over the end of the MMT then it's hard to say: is this tape retention assisted by a hook, or hook retention assisted by tape? Doesn't matter, if it keeps the motor in place.

Sure, on your first launch day in so long. That's how they get you.

Oh, and, I almost forgot: congrats on a good flight! And all the flights that day!

It fits into the flat slot.

 

[jqavins]

Hmm, I wasn't aware of that notch that brings the flat in toward the center. Nice. I see the clip isn't flat against the MMT; that could be your problem. Still, tape will fix it all.

 

[neil_w]

It fits into the flat slot.

View attachment 525140 View attachment 525141

Why so much gap there? On all mine the fit is quite tight, never have ejected a motor.

 

[lakeroadster]

Why so much gap there? On all mine the fit is quite tight, never have ejected a motor.

Maybe I'm just a hack?

It's a homemade retention clip made from the stainless strip inside a windshield wiper. First one I ever made myself.​

It'll work fine with a piece of tape around it.​

Maybe it's an acquired skill?

I'm getting better though, here's the one for my Cygnus Probe.​

 

[neil_w]

Maybe I'm just a hack?

It's a homemade retention clip made from the stainless strip inside a windshield wiper. First one I ever made myself.​

It'll work fine with a piece of tape around it.​

Maybe it's an acquired skill?

I'm getting better though, here's the one for my Cygnus Probe.​

View attachment 525147 View attachment 525148

Homemade clip is fine, just make them tighter and bend the hook slightly past 90 degrees (optional but slightly helpful) and you should be fine. In my rockets , the motor hooks tend to clip in very tightly to the composite motors.

 

[lakeroadster]

Homemade clip is fine, just make them tighter and bend the hook slightly past 90 degrees (optional but slightly helpful) and you should be fine. In my rockets , the motor hooks tend to clip in very tightly to the composite motors.

Yep, got it. Do you make your own clips?

 

[neil_w]

Nope

 

[lakeroadster]

Nope

DIY Engine Hooks

Depending on the material of construction, (steel vs stainless vs brass) and the tempering of that material, it could break during the forming process (I've had that happen). Additionally, if you make the radius at the bend to tight, it'll break (I've had that happen, too).​

​

Work Hardening: You only get one chance for each bend. Flatten it back out and bend it again, it'll break. Might even break when you flatten it out.​

​

If the temper in the material isn't right, or if the clip is retained to the motor tube to close to the end of the clip, the clip will bend and permanently deform when the motor is installed. Then it will not retain its original shape. That's why this one isn't tight.​

But, as previously stated.... nothing a piece of tape won't fix.

 

[jqavins]

I don't make my own hooks, except once, and that was from a paper clip in a weird case, so never mind.

In commercial hooks, I've had the best luck with those that are slightly bowed away from the tube.

Once a centering ring or other band is placed over it, above the middle, the hook is pushed firmly against the tube so it will spring hard against the motor.

With the CR that far up it shouldn't cause the hook to be plastically distorted.

A couple of times I've taken hooks that did not have that bow and introduced it. Usually I don't remember to check, and often I make my own retainers of a wholly different style.

 

[lakeroadster]

.... With the CR that far up it shouldn't cause the hook to be plastically distorted. ....

The thrust end of the motor in your illustrations... is it on the right, or the left?

 

[jqavins]

The motor isn't in the illustrations.

There you go.

 

[Daddyisabar]

Aerotech motors are designed for their bigger metal clips.

 

[lakeroadster]

Aerotech motors are designed for their bigger metal clips.

Bigger metal clips?

 

[Crawf56]

The success of the Hammerhead Shark is a testament to your building skills.

I was very concerned about the Hammerhead 'canard' fins causing a dramatic shift in flight angle. But you made it work!

What is really interesting is how this rocket reminds me of the SpaceX Starship.
https://en.wikipedia.org/wiki/SpaceX_Starship

 

[lakeroadster]

The success of the Hammerhead Shark is a testament to your building skills.

I was very concerned about the Hammerhead 'canard' fins causing a dramatic shift in flight angle. But you made it work!

What is really interesting is how this rocket reminds me of the SpaceX Starship.
https://en.wikipedia.org/wiki/SpaceX_Starship

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