Some CATO pictures from LDRS. This was a Contrail Rocketry Hybrid "O" class motor...
Rocket reduced to confetti.
My hypothesis? The grain collapsed, plugged the nozzle. Chamber pressure rose over the nitrous tank pressure. Flame got stuffed into the nitrous tank...the nitrous went MonoProp and detonated!
Most impressive (in a bad way) CATO I've ever seen pictures of.
Massive CATO
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Ray
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Massive CATO
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leo
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Re: Massive CATO
I don’t think so, the must have a one way valve somewhere inside, and the bottom side of the rocket seems to explode I think the placed the nitrous tank in the top.Ray wrote:Chamber pressure rose over the nitrous tank pressure. Flame got stuffed into the nitrous tank...the nitrous went MonoProp and detonated!
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Ray
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re: Massive CATO
I'm familiar with the Motor system. No one way valve anywhere in the system. Link to their website. This is the motor I believe was used in the photo.
Can you explain why you believe it blew up?
Can you explain why you believe it blew up?
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HattoriHanzo
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re: Massive CATO
That is one hell of a rocket engine :o
Do you know what kind of fuel grain configuration and O/F ratio they are using. Seems to be a highly regressive burn in the movie.
If I have to guess whats happened to the rocket, I would guess that the explosion was supersonic due to the small fragments of the engine and rocket body seen in the picture. I am not a pro of rocket motors, but wouldnt the fuel grain in a hybrid rocket motor be "inert" and not made possible to detonate? So, I think it was the oxidizer that blow up the rocket.
Do you know what kind of fuel grain configuration and O/F ratio they are using. Seems to be a highly regressive burn in the movie.
If I have to guess whats happened to the rocket, I would guess that the explosion was supersonic due to the small fragments of the engine and rocket body seen in the picture. I am not a pro of rocket motors, but wouldnt the fuel grain in a hybrid rocket motor be "inert" and not made possible to detonate? So, I think it was the oxidizer that blow up the rocket.
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El-Kablooey
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re: Massive CATO
I know next to nothing about rockets, but.... It looks to me like the nozzle simply got clogged somehow, causing an overpressure. I don't think the nitrous tank blew (can nitrous oxide detonate???? can it even burn without some kind of fuel??) I think if the nitrous canister ruptured there would be nothing left of the rocket. When I was a kid we would sometimes make "firecrackers" with CO2 cartridges loaded with BP. They would disentegrate a 8"x12" cinder block. A detonation in a similar canister would be far more powerful. It looks to me like the rocket just blew apart from overpressure.
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Ray
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re: Massive CATO
I would agree that it was a detonation as opposed to an overpressurization. I've seen both, this is far and away the most significant CATO I've seen to date...and I've seen some big ones.
When I talked with him last he was using HTPB rubber for the grains...I guess some of his grains are PVC. All are inert. It had to either be an overpressurization, or a detonation of the oxidizer. I'm betting on the detonation simply because of the fragmentation...overpressurization usually blows one or both ends out, depending on how much the overpressure is.
If you look closely at the picture you can see a fragment of the aluminum the tank/motor was made from...it *is* a fragment. If the tank had simply ruptured, it would have remained largely intact and only had a split in it. When tanks rupture, even high pressure tanks, they usually tear in one spot and open enough for the gas inside to escape. They stop tearing when the pressure is low enough that the material overcomes the pressure that caused the tear in the first place. There usually isn't much if any fragmentation.
Nitrous will go monoprop, and when confined, detonate...it becomes its own fuel/oxidizer mix, in much the same way as Hydrogen peroxide.
I believe that the only reason the forward half of the rocket survived (at least until it hit the ground) is for two reasons. 1. The two halves of the rocket are loosely (comparatively) held together, just a slip fit and usually some shear pins of nylon. 2. The forward bulkhead of the motor would direct at least some of the force of the detonation away from the front of the rocket. You can see that the rear of the rocket sort of survived too, the fins are intact, albiet ripped from the air frame with obvious force. They were further from the blast and likely not directly across from the Nitrous tank.
Hybrid motors usually have a regressive profile if they use a self pressurizing oxidizer. As the liquid escapes and turns to a gas it cools the tank, the pressure in the tank drops due to reduced temp and vapor pressure. In the tank the liquid flashes off to gas to take up the space left behind when the liquid leaves and further lowers the temp. The lower pressure in the tank leads to a lower pressure in the combustion chamber. That leads to lower thrust as the burn continues.
You can over come some of the pressure loss by heating the oxidizer prior to entry into the combustion chamber. This motor doesn't do that.
Just my thoughts...
When I talked with him last he was using HTPB rubber for the grains...I guess some of his grains are PVC. All are inert. It had to either be an overpressurization, or a detonation of the oxidizer. I'm betting on the detonation simply because of the fragmentation...overpressurization usually blows one or both ends out, depending on how much the overpressure is.
If you look closely at the picture you can see a fragment of the aluminum the tank/motor was made from...it *is* a fragment. If the tank had simply ruptured, it would have remained largely intact and only had a split in it. When tanks rupture, even high pressure tanks, they usually tear in one spot and open enough for the gas inside to escape. They stop tearing when the pressure is low enough that the material overcomes the pressure that caused the tear in the first place. There usually isn't much if any fragmentation.
Nitrous will go monoprop, and when confined, detonate...it becomes its own fuel/oxidizer mix, in much the same way as Hydrogen peroxide.
I believe that the only reason the forward half of the rocket survived (at least until it hit the ground) is for two reasons. 1. The two halves of the rocket are loosely (comparatively) held together, just a slip fit and usually some shear pins of nylon. 2. The forward bulkhead of the motor would direct at least some of the force of the detonation away from the front of the rocket. You can see that the rear of the rocket sort of survived too, the fins are intact, albiet ripped from the air frame with obvious force. They were further from the blast and likely not directly across from the Nitrous tank.
Hybrid motors usually have a regressive profile if they use a self pressurizing oxidizer. As the liquid escapes and turns to a gas it cools the tank, the pressure in the tank drops due to reduced temp and vapor pressure. In the tank the liquid flashes off to gas to take up the space left behind when the liquid leaves and further lowers the temp. The lower pressure in the tank leads to a lower pressure in the combustion chamber. That leads to lower thrust as the burn continues.
You can over come some of the pressure loss by heating the oxidizer prior to entry into the combustion chamber. This motor doesn't do that.
Just my thoughts...
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Pratt Hobbies
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re: Massive CATO
I'll tell you exactly what happened, to quash the rumor potential.
The Contrail O motor has multiple injector ports, each of which is connected to a nylon tube. Two of the tubes fill the motor. On the day before the failure, they were attempting to fill from a tank that had been sitting in the sun all day and was way over pressure; I heard 1200 psi. Twice, one of the tubes failed, spraying the inside of the fuel grain with liquid N2O at -65 degrees. This probably weakened the cast rubber grain.
THe next day, the tank was chilled and pressure was too low; it was about 700 pounds instead of the ideal 850-900. They filled and fired. The motor lit and lifted. Then, apparently, a piece of the fuel grain broke loose and plugged the nozzle. Under ordinary circumstances this would cause a casing failure at the lower snap ring groove; that's the way it's designed. However, because the N2O in the tank was at lower than normal pressure, the flame from the combustion chamber propagated through the injector into the oxidizer tank. This phenomenon has been observed in smaller motors too.
It was a big disappointment, but it was not a design flaw. It was "go fever," which happens to the pros too. As the bumper sticker says, another damn learning experience.
I intend to fire one of these motors next year and I have complete confidence that it'll work. In fact, after I get my flight in, I plan to rent the hardware; I'm setting up a rental program for all the Contrail 54, 75 and 98mm hardware now.
And before we start a "hybrids are dangerous" meme, let me ask, you've never seen a conventional motor fail?
Doug Pratt
www.pratthobbies.com
The Contrail O motor has multiple injector ports, each of which is connected to a nylon tube. Two of the tubes fill the motor. On the day before the failure, they were attempting to fill from a tank that had been sitting in the sun all day and was way over pressure; I heard 1200 psi. Twice, one of the tubes failed, spraying the inside of the fuel grain with liquid N2O at -65 degrees. This probably weakened the cast rubber grain.
THe next day, the tank was chilled and pressure was too low; it was about 700 pounds instead of the ideal 850-900. They filled and fired. The motor lit and lifted. Then, apparently, a piece of the fuel grain broke loose and plugged the nozzle. Under ordinary circumstances this would cause a casing failure at the lower snap ring groove; that's the way it's designed. However, because the N2O in the tank was at lower than normal pressure, the flame from the combustion chamber propagated through the injector into the oxidizer tank. This phenomenon has been observed in smaller motors too.
It was a big disappointment, but it was not a design flaw. It was "go fever," which happens to the pros too. As the bumper sticker says, another damn learning experience.
I intend to fire one of these motors next year and I have complete confidence that it'll work. In fact, after I get my flight in, I plan to rent the hardware; I'm setting up a rental program for all the Contrail 54, 75 and 98mm hardware now.
And before we start a "hybrids are dangerous" meme, let me ask, you've never seen a conventional motor fail?
Doug Pratt
www.pratthobbies.com
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Pratt Hobbies
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re: Massive CATO
Well, I goofed. I said that the supply tank pressure was around 700 psi...it was more like 500. I have a terrible memory for numbers, which is why I'm a writer and not an engunear.
I appreciate the tone of the discussion here. It's gotten a little hot over on the hybrid Yahoo group, but since I moderate that joint, I can stomp on it if I feel like it. (The power! Bwahahaha!)
The pictures posted here seem to me to support the idea that a piece of propellant lodged in the nozzle long enough to increase combustion chamber pressure enough to force the flame front back through the injector, leading to what the British call "catastrophic self-disassembly."
I appreciate the tone of the discussion here. It's gotten a little hot over on the hybrid Yahoo group, but since I moderate that joint, I can stomp on it if I feel like it. (The power! Bwahahaha!)
The pictures posted here seem to me to support the idea that a piece of propellant lodged in the nozzle long enough to increase combustion chamber pressure enough to force the flame front back through the injector, leading to what the British call "catastrophic self-disassembly."
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Ray
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re: Massive CATO
I have to agree that in general hybrids are much safer than "conventional" rocket motors. I've seen enough of those in rapid disassembly mode to have a healthy respect for the kind of power they can generate.
I have a buddy that does experimental hybrids very successfully. I've never seen any of his motors blow up, despite some very impressive failures.
How in the heck did Contrail get that tank pressure to 500 PSI? I heard it was hotter than hell at LDRS this year.
Seen go fever destroy more rockets than anything else.
I have a buddy that does experimental hybrids very successfully. I've never seen any of his motors blow up, despite some very impressive failures.
How in the heck did Contrail get that tank pressure to 500 PSI? I heard it was hotter than hell at LDRS this year.
Seen go fever destroy more rockets than anything else.