Lakeroadster's Cygnus Probe Ship

[lakeroadster]

Friction fitting with tape is an Old School Art, not a science. An oddroc with all the motors friction fit, flying off a 1/2 rod with a balsa cone finished with dope, brings tears to the Old Fart's eyes.

The nose cone has so much ballast... I'm just not comfortable friction fitting the motor. The equal - opposite reaction on this one is pretty stout, for such a small rocket.

Plus, it already shredded the steel motor clip on the 1st launch. But that was my fault for not installing a retaining ring to take the force. In hindsight, it's no wonder it failed. Whoever is checking my design drawings is going to get a stern talking to.

 

[lakeroadster]

Applied Spar Urethane to the new outrigger. All better now... like it never even happed...

I think for motor retention I'm going to go "Steam Punk" and use copper wire.... I'll post up some photo's later this week.

 

[lakeroadster]

2nd Launch of The Cygnus Probe Ship

We used an F42T-4 composite motor. Rocket was recovered undamaged.

It's a neat looking little rocket and flies awesome... to a point. This rocket simply isn't stable enough to continue flying it. It was stable up to about 100 feet, then started summersaulting AoA, then deployed the chute maybe 20 feet off the ground. It needs more nose weight, but there's simply no room. I could add more BT-55 to the top of it, but that screws up the proportions. And if it doesn't look like the movie version, what's the point?

I'm going to go ahead and build the mast for it, paint the carboard transitions with some hammered copper paint, and set it on a shelf.

In case you're wondering, I added some red crepe paper to the outriggers just because on the first launch we had trouble finding it in the weeds.

 

[jqavins]

There might be one last ditch possibility for stability if you want to bother. What are you using for nose weight? What is your nose weight made from? One can buy tungsten powder at a surprisingly reasonable price, so removing your existing nose weight and replacing it with more weight in the same volume may be possible. But likely not worth the effort.

 

[lakeroadster]

There might be one last ditch possibility for stability if you want to bother. What are you using for nose weight? What is your nose weight made from? One can buy tungsten powder at a surprisingly reasonable price, so removing your existing nose weight and replacing it with more weight in the same volume may be possible. But likely not worth the effort.

Thanks Joe. For ballast I used a 5/8" Hex Head Machine Screw.



This is just a weird, shaped rocket, and it's based on a fictional ship. It passed the swing test, but (I like big but's) that test was done before the outriggers were added.

Just for s-h-i-t-s and g-r-i-n-s I'll do another swing test before I put it up on the shelf.

Maybe the outriggers made the rocket unstable? It's worth investigating.

 

[lakeroadster]

As promised, I did another swing test. The outriggers appear to make the rocket more stable. The swing test is rock solid.

So why does the rocket tumble AoA at speed? Go figure?

 

[Daddyisabar]

There might be one last ditch possibility for stability if you want to bother. What are you using for nose weight? What is your nose weight made from? One can buy tungsten powder at a surprisingly reasonable price, so removing your existing nose weight and replacing it with more weight in the same volume may be possible. But likely not worth the effort.

Beware! If Lakeroadster uses powdered Tungsten his journey to the Dark Side will be complete.

Weighting high end golf clubs ok. Silly oddrocs...no. Stay to the Light Side young Padawan! P.S. Only very naughty National Socialist rockets use Tungsten cores... until the supply runs out. Very Un PC. Will only lead to a discussion of WWII anti tank munitions.

 

[jqavins]

So why does the rocket tumble AoA at speed? Go figure?

This is a guess based on very little solid information.

Solid: for a "regular" rocket, 3/4FNC or similar to that, the CG shifts forward as AoA increases. That's (one of?) the main reason(s) that we call a static margin less than 1 caliber marginal, and why less than one is OK for stubby rockets while long skinny ones need much higher margins.

Guess: maybe that's what's happening here? Were you able to somehow induce a large AoA during a swing test to see if it would recover? When I do swing tests (which is rare) I make the rocket brush the ground to start it tumbling, but I do my tests on grass and without delicate sticky-out bits, so that is not recommended for you.

 

[lakeroadster]

I glanced over & noticed The Cygnus Probe Ship was leaning. What's that all about? I found a stress fracture on one of the legs.

Dr. Wood Glue says the recovery will take about 24 hours.

 

[lakeroadster]

This is a guess based on very little solid information.

Solid: for a "regular" rocket, 3/4FNC or similar to that, the CG shifts forward as AoA increases. That's (one of?) the main reason(s) that we call a static margin less than 1 caliber marginal, and why less than one is OK for stubby rockets while long skinny ones need much higher margins.

Guess: maybe that's what's happening here? Were you able to somehow induce a large AoA during a swing test to see if it would recover? When I do swing tests (which is rare) I make the rocket brush the ground to start it tumbling, but I do my tests on grass and without delicate sticky-out bits, so that is not recommended for you.

Upon further review, @neil_w questioned the use of the Base Drag Hack in Open Rocket for this rocket.

.... Not sure if it's needed here; the tail end is not that large.

If I remove the base drag hack cone, the rocket is marginally stable, 0.392 caliber.
If I look at adding a flight only removable BT-55 / C-55 extend-a-tube. An 8" long piece brings the rocket up to a stability over 1.0 caliber.

(See simulation screen shots below)

I'll make this modification, anoint it as version 2.0, and fly the Cygnus Probe Ship once again.

A couple other advantages of the stretched version:

• More room for the parachute and wadding
• More volume to help reduce the impact of the composite motor ejection charge... which I've found to be "harsh" compared to BP motors.

The weird thing to me is why the swing test shows the rocket as stable in the original short version, and not just kind of stable, but stable. And it flies stable under thrust. But once the thrust stops, the vomit comet begins.

​

 

[lakeroadster]

The extension fits "Snug as a bug in a rug".

 

[lakeroadster]

Finally got around to doing launch reports for the 07-08-2022 and 07-28-2022 flights.

 

[sr205347d]

But once the thrust stops, the vomit comet begins.

Here are some thoughts for the mind sim:

The landing legs are cylinders with not insignificant diameter. When fluid flows fast enough across a cylinder, a vortex will form on one side or the other in an unpredictable manner. The static pressure in a vortex is less than in the free stream. Less pressure on one side of the cylinder produces an aerodynamic force towards that side. With three legs, it is possible that each has the vortex on the same side, in which case it would produce a pure rolling moment on the rocket. But if one vortex is counter-rotating, the net force will induce a pitching or yawing moment which will act to tumble the rocket.

At low speed, the air is more viscous, and there will not be any vortices. Vortices will form at higher speed, faster than your swing test can produce.

 

[sr205347d]

Has there been any other oddroc that, in place of fins, has three body tubes sticking out (straight or swept)?

 

[Art Upton]

The extension fits "Snug as a bug in a rug".

View attachment 533833

Like on their NCC-1701 flying rocket, Estes used to call those extensions "Atmospheric Flight Probes"

 

[Art Upton]

Has there been any other oddroc that, in place of fins, has three body tubes sticking out (straight or swept)?

Not body tubes, but long dowel legs attached to a Foam Ball for a Sputnik, making it a tractor thrust rocket

 

[lakeroadster]

Like on their NCC-1701 flying rocket, Estes used to call those extensions "Atmospheric Flight Probes"

I like that... thanks for posting.