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As someone who

, I offer my most hearty congratulations.

One question though: Why are your fins the shape that they are? I'm used to "normal" fins with the semi span being about the size of the root chord (read: a square with an angled cut running from the top of the fin to near the middle). It seems as if your fins are a little different. That's certainly not a bad thing, but I'm just wondering why.

Oh, and once again, I always love showing off my most Kerbal rocket... this link is certainly worth a click if you're interested ;)

-Upsilon

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Upsilon, you went to NARAM? also we should reboot the Model Rocket Thread (again)

I'll be going to NARAM this year too, as it's relatively nearby. If anyone else is heading over there, shoot me a PM; I'd love to meet ya :)

...and yes, the Model Rocket thread does desperately need a reboot...

-Upsilon

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so Neil did you enjoy watching my schools rocket? we were the one with the Quad copter in it :)

Honestly, they were all pretty good! I didn't get a chance to find out, but how did your payload work? (Also, did you spot me while you were there? I was the guy with the black cowboy hat!)

As someone who
, I offer my most hearty congratulations.

One question though: Why are your fins the shape that they are? I'm used to "normal" fins with the semi span being about the size of the root chord (read: a square with an angled cut running from the top of the fin to near the middle). It seems as if your fins are a little different. That's certainly not a bad thing, but I'm just wondering why.

Oh, and once again, I always love showing off my most Kerbal rocket... this link is certainly worth a click if you're interested ;)

-Upsilon

The reason why the fins ended up that way is an interesting story. Originally, the payload weights were distributed differently, but then our payload team changed their minds a bit and things had to be moved around. This small change actually made the rocket overstable! Most of the other parts had already been manufactured, but we still had to CNC route the fins. So I just swept them forward on the CNC trace until the stability was back where we wanted it. It incurred no extra cost and took all of half an hour (and the final product looked extra cool). A good engineering decision if I do say so myself.

Edited by Neil1993
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If you use solid fuel could you not use an fuse similar to the one who set off the charge on firework rockets.

its use an hole in upper corner so it ignites then the lower stage is burning the last part of its fuel so its TWR is tapering off.

No you couldn't. What you're proposing is basically a mechanical version of the electronic timers which have previously been used on multi-stage rockets. The timer (which is pretty cheap and compact) uses an accelerometer to detect launch, then waits a pre-programmed amount of time before firing an electronic igniter on the second stage motor. If anything, this system gets the timing more accurate than a fuse would. As the first two videos demonstrate, a first-stage failure can easily result in the timer firing when the rocket is in an unsafe attitude.

At least for two stages an fail where the rocket is mot vertical would be just as dangerous for an 1 stage one designed to reach the same attitude.

No, the two stage is far more dangerous. Here's why:

There are several potentially dangerous failure modes for an amateur rocket that occur before apogee.

1. Failure of the motor in (aka a "CATO"). Basically the motor blows up. There are three kinds of CATO:

1A: failure of the nozzle or aft closure. This results in an abrupt loss of thrust, and may eject burning fuel grains downward towards the pad. However, the rocket will remain mostly intact.

1B: failure of the forward closure. This results in either the fuel being ejected from the top of the motor or the motor burning from both ends. In either case, the rocket immediately separates with varying amounts of damage. However, there is loss of thrust and the rocket now has very high drag due to being separated, so it will not travel very far.

1C: failure of the side of the casing: total loss of thrust. The fuel is ejected sideways along with debris from the motor casing and lower section of the rocket. However, air drag will prevent the debris from falling in spectator areas if the minimum safe distance in the safety code is obeyed.

On a single-stage rocket, the main hazards are ejected propellant grains starting fires (not a major problem since extinguishers are on hand, assuming there's even vegetation around), or in an extremely unlikely case, a partial nozzle failure resulting in reduced thrust that causes the rocket to arc towards spectators. On a multi-stage rocket though, the second stage may arc over, be sent into a tumble, or even land on the ground before its motor ignites, potentially sending it towards people at very high velocity.

2. Structural failure under aerodynamic forces and/or thrust (aka a "Shred"). These ordinarily happen at or near Max Q, which with the low altitudes amateur rockets reach occurs at or near the end of the burn. Either the fins fail or the airframe buckles, making the rocket aerodynamically unstable. It may spiral or veer off sideways, but ultimately the vehicle will tumble, resulting in relatively low velocities. On the other hand, an upper stage that ignites after a shred may have its fins intact, allowing it to take fly straight towards wherever it's pointing, possibly ending in a supersonic impact with the ground.

3. Aerodynamically unstable rocket. The rocket tumbles for the first part of the burn, but may fly straight later in the burn as its CG moves forward. This is extremely dangerous, but also extremely unlikely because it's easy to simulate your rocket's stability. However, an underperforming motor can result in insufficient velocity off the rail for aerodynamic stability, as seen in the first video I linked to. A single-stage rocket can still crash in a bad spot, but a multi-stage one is capable of having the upper stage light on or near the ground, sending the rocket towards people at much higher speeds.

Anyway an abort system would simply be an device who cut the fuse.

How is this device triggered? Manually via a radio signal? Now you're reliant on the operator's reaction time and ability to see the rocket A break wire? You'd be out of luck in the first video where the vehicle stays together. On the other hand, a flight computer using either an accelerometer-barometer combination (measuring altitude and velocity at a given time: if they're too low something's wrong) or a combination of accelerometers and gyroscopes that directly measures how far from vertical the rocket is can simply not fire the igniter. Furthermore, it will not fire if something happens like a spike of acceleration during a CATO or shred ripping the battery wires loose; the same cannot be said for any device which cuts a fuse.

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1. Failure of the motor in (aka a "CATO"). Basically the motor blows up. There are three kinds of CATO:

1A: failure of the nozzle or aft closure. This results in an abrupt loss of thrust, and may eject burning fuel grains downward towards the pad. However, the rocket will remain mostly intact.

1B: failure of the forward closure. This results in either the fuel being ejected from the top of the motor or the motor burning from both ends. In either case, the rocket immediately separates with varying amounts of damage. However, there is loss of thrust and the rocket now has very high drag due to being separated, so it will not travel very far.

1C: failure of the side of the casing: total loss of thrust. The fuel is ejected sideways along with debris from the motor casing and lower section of the rocket. However, air drag will prevent the debris from falling in spectator areas if the minimum safe distance in the safety code is obeyed.

On a single-stage rocket, the main hazards are ejected propellant grains starting fires (not a major problem since extinguishers are on hand, assuming there's even vegetation around), or in an extremely unlikely case, a partial nozzle failure resulting in reduced thrust that causes the rocket to arc towards spectators. On a multi-stage rocket though, the second stage may arc over, be sent into a tumble, or even land on the ground before its motor ignites, potentially sending it towards people at very high velocity.

I think we had at least one of each of those at this year's IREC! :D

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Neil I was not there myself, but i hear our rocket and payload went fine, (only flew to almost 9k feet and we did not place)

How many years has your team been competing so far?

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i BELIEVE since the very first or second one, we are a very senior team... I could be wrong though, and we normally bring 2 rockets a two stager for Advanced and a single stager for basic (and the basic category one is mainly "built" by freshmen or others whith no rocket experience)

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  • 4 weeks later...
Finally!! Thanks for the video.. perfect launch.

Some surprise in the data collected?

At what height you guess it had the max dynamic pressure?

The data we collected from a commercial Stratologger sensor indicated a constant temperature from ground to apogee. Since the sensor uses temperature and pressure to calculate altitude based on an International Standard Atmosphere model (I think) the final altitude reading was skewed. We're trying to avoid these kinds of issues in future rockets

Not sure at which altitude maxQ was encountered. Since there was no supersonic flight, we weren't too concerned about it.

Edited by Neil1993
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The solid fuel was manufactured by your team? Not sure if there are exact formules in internet and how easy is to get the elements.

Is kinda similar in looks to the fuel of the movie october sky?

We bought a commercial solid motor. We haven't the facilities at our University to go mucking around with rocket fuels. The motor we bought had an Ammonia Perchlorate Composite Propellant.

Edited by Neil1993
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