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Kruegon

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The other day I was discussing the Explorer I with a NASA engineer.

The Explorer I was a final stage finless dart rocket. The only noticeable point of drag was a protruding shroud near the very aft.

According to him, the launch vehicle was "spun up" on the pad. The motors were canted to promote continuous spin in flight. The second stage was also canted to promote spin. Once the Explorer I completed final separation, the spin was the contributing factor to maintaining flight stability.

Of course, I now want to simulate this effect in an HP rocket. My current thoughts are this:

1) Stacked 45° recessed shrouds to created some drag for stability.

2) Dual, canted, high thrust 29mm motors. Probably two I200s. Sims and testing will determine this for sure.

3) Use a launch tower instead of a rail. Possibly custom build one that can spin up the rocket prior to ignition. I'm not sure the canted motors will be enough to generate stable spin without the jumpstart of the pad spin.

What are the thoughts of the hive mind?
 
Try to find a picture of the launch tower for the Loki Darts. I believe they imparted spin by have the fin guides in a spiral. This might be the best way if you have the fabrication skills.
 
The other day I was discussing the Explorer I with a NASA engineer.

The Explorer I was a final stage finless dart rocket. The only noticeable point of drag was a protruding shroud near the very aft.

According to him, the launch vehicle was "spun up" on the pad. The motors were canted to promote continuous spin in flight. The second stage was also canted to promote spin. Once the Explorer I completed final separation, the spin was the contributing factor to maintaining flight stability.

Of course, I now want to simulate this effect in an HP rocket. My current thoughts are this:

1) Stacked 45° recessed shrouds to created some drag for stability.

2) Dual, canted, high thrust 29mm motors. Probably two I200s. Sims and testing will determine this for sure.

3) Use a launch tower instead of a rail. Possibly custom build one that can spin up the rocket prior to ignition. I'm not sure the canted motors will be enough to generate stable spin without the jumpstart of the pad spin.

What are the thoughts of the hive mind?
The details are here: https://history.nasa.gov/sputnik/expinfo.html Two electric motors spin in the tub (containing the second, third and 4the stages) at a rate varying from 450 to 750 rpm to compensate for thrust imbalance when the second stage clustered motors fired. This is not unlike using the rifling in a gun barrel to stabilize a bullet to minimize the trajectory dispersion.

Trying to fabricate a Loki type spiral launcher would be prohibitively expensive for a hobbyist and is not necessary to spin a hobby rocket. Spiral launchers were used on the Loki rockets because the burn time was very short, and on the Arcas which had a very long burn time (and burns at altitudes where aerodynamic forces are not effective.). Also any device to spin up a rocket before launch will be overly complicated and expensive.

Spin fins are easy to fabricate and used on virtually all unguided sounding rocket to minimize dispersion. For hobby use, air-foiling or contouring only one side of the fins is simple and should provide the same effects as canting the fins on a conventional sounding rocket. You need to remember the sole purpose of the spin is to minimize the trajectory dispersion which arises from asymmetries in the vehicle's CG and thrust axis which can not be accounted for before launch. Spinning averages these effects out if the spin rate is relatively fast.

Bob
 
Exactly. And on a finless scale variant of the Explorer I, there wouldn't be fins to of any type to create the initial rotation. And long before I launch the 4" version, there will be several smaller variants. Based on my initial thoughts, I'm looking at two canted A10Ts in a BT-55 or 60. Small, light and safer if it fails. But the biggest point to this challenge is that there will be absolutely no fins whatsoever. Therein lies the physics issue. But it's theory for me right now. I'm going to start with a no spin launch tower. See how the motors can compensate for spin. I expect the first attempt will be a failure. But the data from that failure will save me crap tons of money vs a failure on a 4" build and dual 29mm motors and cases.
 
Exactly. And on a finless scale variant of the Explorer I, there wouldn't be fins to of any type to create the initial rotation. And long before I launch the 4" version, there will be several smaller variants. Based on my initial thoughts, I'm looking at two canted A10Ts in a BT-55 or 60. Small, light and safer if it fails. But the biggest point to this challenge is that there will be absolutely no fins whatsoever. Therein lies the physics issue. But it's theory for me right now. I'm going to start with a no spin launch tower. See how the motors can compensate for spin. I expect the first attempt will be a failure. But the data from that failure will save me crap tons of money vs a failure on a 4" build and dual 29mm motors and cases.
One big difference. How are you planning to vector your first stage thrust..... to keep your rocket going vertical? The Redstone was a guided missile, and that's why it didn't need fins. The rocket did not spin either, it was the upper stages that were spin stabilized.

Bob
 
Well this is an experiment. And will be started at small scale.

Think of a bullet. No fins. Stable flight due to its spin. Generating a stable spin within the launch tower, followed by the increased force of the dual high thrust motors, the theory is to generate a spin that will stabilize the rocket before it ever leaves the tower.

Like a bullet leaving a barrel, it will remain stable under spin. As spin dissipates and gravity takes over, it will roll near apogee. And from that point on, it operates as any other rocket.


The theory is sound. The only issue I perceive at all is maintaining drag sufficient enough to move the center of pressure aft of the CG. If I can achieve that, it won't take much spin to hold it stable. And I'm looking at a rather large amount of spin for launch.

I will be honest. I may never be able to get this to work. Oh but if I can, how wonderful the reward will be. I expect the first test flight to be ready in a month. BT-55 with two canted A10T motors. One will be -3 the other will be -P. Streamer recovery. Since I only have one delay to play with, I want to limit shred possibility on the chute. I'll have pics of the build and vid of the flight for review. The president of our local NAR is on board to assist in the experiment.
 
This has me dreaming of building a spinning launch tower, spin the tower to 500 rpm then launch the rocket.
 
Well perhaps within the next year or two I can have video of a spun up launch tower. Cost and construction not withstanding.
 
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