tribrid

[Sooner Boomer]

At Argonia last weekend, a gentleman launched a "tribrid" rocket. Are hybrid/tribrid rocket systems prone to cyclic burning (like a whistle rocket)? As the rocket reached altitude, the sound had a definite "flatulent" sound to it.

 

[teepot]

Something like a pulse jet?

 

[Sooner Boomer]

Something like a pulse jet?

Sort of, a kind of "fluttery" sound.

 

[rocket_troy]

Most likely combustion instability. Often HPR hybrids (in particular) are actually designed for that purely for that acoustic effect. It's not terribly great for performance though. It can often occur at some point during operation when the tank pressure (from depletion) drops to a certain point where there's minimal pressure drop over the injectors during some resonate high chamber amplitudes creating a toing & froing between injectors passing oxidizer (for chamber combustion) and being suppressed from minimal (or negative) pressure drop over the injectors. It generally won't last throughout the entire operation though. Below a certain threshold point, the injector throughput during the feed cycle won't react with enough energy within the chamber to maintain the pulsing cycle.
So to achieve it (for hybrids at least) , you generally design the chamber to run at higher pressures than typical design guidelines eg. larger injector: throat area ratios. Obviously there are limits to how far you can take that.

TP

 

[Voyager1]

I used to hear that occassionally with my earlier Rattworks 29mm hybrid motor, but I don't hear it much, if at all, with my current Contrail 38mm hybrid motor. I'll be interested to hear what my 54mm and 75mm Contrail motors sound like when they get to fly.

 

[OverTheTop]

The tribrids run alcohol and N2O in the tank. There is a changeover from alcohol to N2O as the alcohol is depleted, thus there are two distinct "burns" during the flight. Not sure about the flow dynamics in each phase.

 

[cwbullet]

I remember these being advertised right as the BATFE restrictions were coming to a close.

 

[kramer714]

um, well, they fart. I have launched, Sky Ripper, Hypertech, Contrail, Trojan, Rattworks hybrids and they all fart. The sound comes in two phases, the liquid phase fart sound, followed by the gas phase whistle. Not sure if the fart comes from instabilities or from bubbles forming due to the pressure drop of the oxidizer (or the bubbles causing instabilities).

The RATTworks 54mm is the loudest, I used to fly a RATT 54, 2 motor cluster, it was 128dB at 200 foot from the pad, the loudest thing I have ever heard at a launch. RATT Cluster The 75mm Contrail has a deep baritone sound, Trojan more of an alto. Not much from the 29mm Ratt. Skyripper is higher pitch without much whistle, more of a tenor fart. I launch at ROC if anyone wants to 'do hybrids'.

P.S. I am always looking for Hybrid Reloads if you have any you want to sell.

 

[heada]

P.S. I am always looking for Hybrid Reloads if you have any you want to sell.

Wish I knew that about 2 years ago. I tossed ~9x 38mm, 6x 29mm and 4x 54mm SkyRipper reloads since I didn't have the hardware any more.

 

[dhbarr]

um, well, they fart. I have launched, Sky Ripper, Hypertech, Contrail, Trojan, Rattworks hybrids and they all fart. The sound comes in two phases, the liquid phase fart sound, followed by the gas phase whistle. Not sure if the fart comes from instabilities or from bubbles forming due to the pressure drop of the oxidizer (or the bubbles causing instabilities).

The RATTworks 54mm is the loudest, I used to fly a RATT 54, 2 motor cluster, it was 128dB at 200 foot from the pad, the loudest thing I have ever heard at a launch. RATT Cluster The 75mm Contrail has a deep baritone sound, Trojan more of an alto. Not much from the 29mm Ratt. Skyripper is higher pitch without much whistle, more of a tenor fart. I launch at ROC if anyone wants to 'do hybrids'.

P.S. I am always looking for Hybrid Reloads if you have any you want to sell.

I have ProPoly hardware details, would love Trojan details.

 

[G_T]

That sound comes from when the liquid phase of the burn is over and you have a tank of moderate pressure oxidizer venting through the injectors and burning in the chamber. Think backdraft situation almost. Oxidizer goes in, it burns, pressure goes up, oixdizer flow stops. Flame goes down, pressure goes down, so oxidizer goes in. Rinse and repeat.

Hybrids (and others using liquid oxidizers) don't have to undergo this oscillation in the very low thrust tail of the burn. But lots do.

Gerald

 

[jderimig]

Farting sound depends alot on n2o temp/pressure. I can make my 54mm Contrail roar or fart.

 

[DRAGON64]

I have ProPoly hardware details, would love Trojan details.

Many years ago, Contrail designed a motor system that would utilize HyperTEK tank assemblies for the Nitrous... to give HyperTEK users options other than the screw on plastic fuel grains. I believe Tom still had a large stash of Trojan components components (54, 75 & 98mm), probably not the tanks, as they were, of course, HyperTEK assemblies...

 

[CoyoteNumber2]

Often HPR hybrids (in particular) are actually designed for that purely for that acoustic effect.

Source?

 

[rocket_troy]

I don't have a source handy but it's common knowledge from those who were around 15-20 years ago. One manufacturer (at least) even used to advertise it.

TP