I've used Marvel Mystery Oil to loosen up & clean bearings. Not sure if it would react with the rubber or not.
A Rocket That Launches Attached To A Horizontal Track That Transitions To Vertical
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I would be concerned that the 2 lb sled, once free of the rail, could continue upward and then fall back to earth and land on the launch rail, or you, causing unwanted damage. I think it would make sense to have the exit of the rail at 10 or 20 degrees from vertical, pointed downrange, away from you and the rail. As you (or someone ?) posted earlier, having the sled "snag" a long, durable, streamer (or X-chute) on its way past the end of the rail could slow the sled down, without shredding itself in the process. I believe that the Estes made rocket cars sucessfully "snag" a small parachute at the end of their straight tether guided horizontal runs.
Making a rail/sled launched "Fireball XL5" has been on my bucket-list since 1962. One day though ...
Making a rail/sled launched "Fireball XL5" has been on my bucket-list since 1962. One day though ...
<f i r e b a l l [space] x l 5 [search]>
Ooh, heck yeah! With or without a sled, that's a nice design. Do I surmise correctly that it was sled launched in the show?
Ooh, heck yeah! With or without a sled, that's a nice design. Do I surmise correctly that it was sled launched in the show?
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Okay, let’s get out of the box, go with something easier and low mass and low resistance.
Ditch the track.
Have pivot assembly, two rods and a rocket “basket”. Moment arm is, say, 4 feet. central pivot point is about 5-6 feet above ground surface.
Start with basket on far right, rods horizontal, rocket aimed Down (unless in Australia.).
Simultaneous cluster ignition of sled motors and long delay, preferably long burn, rocket motor.
Burn strings (actually rubber bands would work admirably) hold the basket in place, BASKET DOES NOT MOVE UNTIL BOTH THE SLED AND ROCKET MOTORS ARE LIT.
Upon burn string release, gravity, sled motor, and rocket motor forces swing the rocket down to horizontal (use gravity to overcome inertia and initial “starting” friction.).
Once horizontal, the motors and kinetic energy will continue the swing until the rocket is vertical on the far left.
The moment bars hit a “stop” at the left 90 degree vertical point. (The basket could be pretty light, most of the mass would be the motor mount and motor casing, and maybe a very short “tower” holding the rocket in appropriate orientation.). Rocket keeps moving straight up based on its still firing motor and the kinetic energy it got during its half circle basket track.
What could go wrong?
Ditch the track.
Have pivot assembly, two rods and a rocket “basket”. Moment arm is, say, 4 feet. central pivot point is about 5-6 feet above ground surface.
Start with basket on far right, rods horizontal, rocket aimed Down (unless in Australia.).
Simultaneous cluster ignition of sled motors and long delay, preferably long burn, rocket motor.
Burn strings (actually rubber bands would work admirably) hold the basket in place, BASKET DOES NOT MOVE UNTIL BOTH THE SLED AND ROCKET MOTORS ARE LIT.
Upon burn string release, gravity, sled motor, and rocket motor forces swing the rocket down to horizontal (use gravity to overcome inertia and initial “starting” friction.).
Once horizontal, the motors and kinetic energy will continue the swing until the rocket is vertical on the far left.
The moment bars hit a “stop” at the left 90 degree vertical point. (The basket could be pretty light, most of the mass would be the motor mount and motor casing, and maybe a very short “tower” holding the rocket in appropriate orientation.). Rocket keeps moving straight up based on its still firing motor and the kinetic energy it got during its half circle basket track.
What could go wrong?
Here it is - rocket sled launched - at about 0:40 seconds. It was on post #39, above.
Sorry for the thread highjack -
This was the opening sequence for every show of Fireball XL5. During the show episodes, the front end of the spaceship could separate from the main section, for excursions onto alien planets. It would later link back up to the main craft before returning to earth (similar to, but 7 years in advance of our Apollo moon missions with the lunar lander redocking with the command module). The main craft would occasionally need repair or maintenance and would land on Earth by stopping forward motion, then decending vertically, similar to a helicopter, in a horizonal position, onto its retractable landing skids. A bit like Elon Musk's rocket landings, but the XL5 was horizonal, and Musk's are vertically oriented on landing on its skids.
During World War II, the Germans launched their V-1 flying buzz bomb in a similar way to the XL5. But instead of a rocket sled, they used a "rocket motor/piston/sled" in a tube. The tube was built into and under the launch rails. When the V1 and the rocket piston reached the end of the rail, the V-1 flew off under its pulse jet power, while the rocket motor/piston/sled separated from the V-1, and went tumbling through the air, then splashing into the English Channel.
This was the opening sequence for every show of Fireball XL5. During the show episodes, the front end of the spaceship could separate from the main section, for excursions onto alien planets. It would later link back up to the main craft before returning to earth (similar to, but 7 years in advance of our Apollo moon missions with the lunar lander redocking with the command module). The main craft would occasionally need repair or maintenance and would land on Earth by stopping forward motion, then decending vertically, similar to a helicopter, in a horizonal position, onto its retractable landing skids. A bit like Elon Musk's rocket landings, but the XL5 was horizonal, and Musk's are vertically oriented on landing on its skids.
During World War II, the Germans launched their V-1 flying buzz bomb in a similar way to the XL5. But instead of a rocket sled, they used a "rocket motor/piston/sled" in a tube. The tube was built into and under the launch rails. When the V1 and the rocket piston reached the end of the rail, the V-1 flew off under its pulse jet power, while the rocket motor/piston/sled separated from the V-1, and went tumbling through the air, then splashing into the English Channel.
lakeroadster
When in doubt... build hell-for-stout!
Sled leaving the track? That idea was soooooooooo yesterday...
As suggested by jgavins:
As suggested by boatgeek:
I'm hoping to combine the bungee / parachute while the sled is still in the track... with the bumpers being the last resort.
My big incentive to keep the sled on the track is to minimize damage to the sled and in the event the rocket motor doesn't fire, to minimize damage to the rocket also.
Although there's no denying the sled coming off the end of the track trailing streamers and a chute would be spectacular....
Once the cart and track are built I can do some testing. There are so many variables it's unknown just how fast (2) D-12's will push a 2 lb sled.
Those variables include:
- Friction of the wheels (bearing friction & wheel to track friction),
- Track horizontal length (yet to be determined),
- Track vertical length (yet to be determined),
- How much speed is scrubbed off in the radius section of the track.
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lakeroadster
When in doubt... build hell-for-stout!
Ye ole pit and the pendulum scenario! Very nice!
A couple of thoughts...
- Everything would happen so quickly it would be a blur....
- What's the burn rate of a rocket motor through a string or a rubber band?
- Why do you even need a sled motor?
Cool. Experimenting and testing will tell all. Keep us posted.
I have sprayed WD-40 on lots of different plactic and rubber seals (on vintage and new motorcycles, RC cars, RC boat nitro race engines) and never had it attack or degrade them. It works well for cleaning grease out of bearings. I have found a good light oil for bearings in general is "air tool oil" and "Marvel Mystery Oil". These would last longer and protect better than something like WD-40, but is still light/low friction.
For the rocket motors on the sled, it shoud be easy to add booster motors by just taping the boosters onto the ends of your D-12's, if more oommphh is needed. No need to have them encased in a body tube.
I have sprayed WD-40 on lots of different plactic and rubber seals (on vintage and new motorcycles, RC cars, RC boat nitro race engines) and never had it attack or degrade them. It works well for cleaning grease out of bearings. I have found a good light oil for bearings in general is "air tool oil" and "Marvel Mystery Oil". These would last longer and protect better than something like WD-40, but is still light/low friction.
For the rocket motors on the sled, it shoud be easy to add booster motors by just taping the boosters onto the ends of your D-12's, if more oommphh is needed. No need to have them encased in a body tube.
The peak thrust for a D12, 1/4 second after ignition, is just under 30 N. So two of them push a 1 kg sled at 60 m/s², or about 6 gees.
The average thrust is only just over 10 N, so that would give about 2 gees.
Both of those are horizontal, no friction. Subtract 1 gee if going vertical. It's enough for a starting WAG, if you can WAG the wheel friction.
The average thrust is only just over 10 N, so that would give about 2 gees.
Both of those are horizontal, no friction. Subtract 1 gee if going vertical. It's enough for a starting WAG, if you can WAG the wheel friction.
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I have inserted the answers into your quote
lakeroadster
When in doubt... build hell-for-stout!
Online Calculator backs jgavins numbers: https://www.omnicalculator.com/physics/acceleration
In reality I'm not sure how much rolling the cart will be doing... as opposed to skidding and be-bopping. (those are hi-tech industry terms.. feel free to use them at your own risk).
It has the potential to be scary fast on a D motor... especially (2) D motors. But if it's to fast it's easy to drop motor size and/or small motors with a booster stage (which the rocket is designed for too).
lakeroadster
When in doubt... build hell-for-stout!
Point well taken. Depending on how the testing goes I may not need any motor on the sled at all. Just use a multi stage rocket design.
But the motor on the sled could be used to launch other stuff, like small gliders, Political figurines or ???
Some thoughts on a sled design - Since you want the rocket and sled to be as light as possible, in order to obtain maximum accelleration and max speed on the track, then I would think that you'd want a lightly built sled that would be just strong enough to survive launching the rocket as well as coming to a stop. So I thinking that there would be advantages to decellerating the sled as gently as possible,
after the rocket leaves the sled. Sudden decelleration (from a tether, a wedge, or a bumper) would put a lot of force on the sled, which could destroy it. So the sled would need to be built stronger to survive the decelleration. Stronger usually equates to heavier, which would equate to lower accelleration and lower launch speed. I think that there could be advantages to building a very light weight sled, and then letting the sled free itself from the track, and then decellerate slow enough not to destroy itself, and then return to the ground at a safe speed. Just my 2 cents.
I'm amazed at how your launch project has generated so many responses in such a short amount of time! Very cool!
after the rocket leaves the sled. Sudden decelleration (from a tether, a wedge, or a bumper) would put a lot of force on the sled, which could destroy it. So the sled would need to be built stronger to survive the decelleration. Stronger usually equates to heavier, which would equate to lower accelleration and lower launch speed. I think that there could be advantages to building a very light weight sled, and then letting the sled free itself from the track, and then decellerate slow enough not to destroy itself, and then return to the ground at a safe speed. Just my 2 cents.
I'm amazed at how your launch project has generated so many responses in such a short amount of time! Very cool!
beeblebrox
8 C6-0, 12 D11-9, 20 D20-0, 20 E5-0, 3 Cinerocs
Just get skateboard bearings, they are 608zz's you can get them very cheap, they are free wheeling. commonly used in 3d printers and accessories. make your sled with pivoting trucks like a roller coaster...
RocketTree
Well-Known Member
Hi, Great concept.
I have a question you might have already addressed elsewhere, but how does the Estes rocket dragster car not require the same launch "rod" specs as a vertical flying rocket? I see they use a piece of string or something to guide it down the track. A modified car and track with the final launch over 30 degrees for the flying rocket section. Would that be ok/legal in the rocketry world?
All the best.
I have a question you might have already addressed elsewhere, but how does the Estes rocket dragster car not require the same launch "rod" specs as a vertical flying rocket? I see they use a piece of string or something to guide it down the track. A modified car and track with the final launch over 30 degrees for the flying rocket section. Would that be ok/legal in the rocketry world?
All the best.
One problem is that you impart angular momentum to the rocket. It will continue to rotate until the angular momentum is gone.
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I am not so sure about that. If I understand my physics right, if you swing a ball on a rope, and suddenly release the rope, the ball will continue on a straight trajectory on the exact heading it was on when you released it.
Where is @prfesser when you need him?
lakeroadster
When in doubt... build hell-for-stout!
I'm with BABAR on this one.
David would have had a tough time slaying Goliath if the rock kept arching....
For the direction of motion of the center of gravity, that's correct. But the ball will retain the angular momentum it gains before it is released. If you look carefully, you'll see that the ball is spinning as it travels on it's straight path. For a ball that doesn't matter. If the rocket leaves the launch trapeze spinning on an axis parallel to that of the trapeze, it matters a whole heck of a lot.
lakeroadster
When in doubt... build hell-for-stout!
Well, the rule Steve referred to (see below) was for High Power Rocketry.... and my sled will not be High Power, and neither were the Estes Dragsters.
It also doesn't say it can't be launched horizontally (and then a period). There is a comma and then it goes on to state specific cases.
I believe the case could be made, based on the data Steve provided, that a rocket can be launched horizontally as long as the rocket is not launched "at a target, or so that the rocket's flight path during ascent phase is intended to go into clouds, directly over the heads of spectators, or beyond the boundaries of the launch site, or so that the rocket's recovery is likely to occur in spectator areas or outside the boundaries of the launch site."
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Assuming the basket maintains the orientation of the rocket perpendicular to the radius of the curve, the CENTER OF MASS of the rocket will keep going straight. You are correct that the rocket has a non-neglible length, therefore the tip of the nose at moment of release is NOT going exactly the same direction as the CG and even more catywampus relative to the tip of the tail. But I THINK by definition these forces are balanced at the CG, so I wouldn't anticipate any pitch or yaw forces.
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The regular NON High Power Code specifically prohibits targeting and launch angles over 30 degrees from vertical.
Something I thought was a very mild faux pas at NSL 2019 (otherwise a spectacularly well run operation) last year was a competition to see who could land a rocket closest to a cone placed maybe 50 or 100 feet from the low power pads, measured tangential or even slightly away from flight line. Technically I would think anything other than "closest to the pad" would be called targeting.
https://www.nar.org/safety-information/model-rocket-safety-code/
My interpretation is that “launching at a target” would be to aim your flight in the direction of a target with the intent of striking the target at speed.
Attempting to land a rocket safely at a specific spot wouldn’t count as that, again in my interpretation.
lakeroadster
When in doubt... build hell-for-stout!
Interesting... but I submit this for your review:
Codes are subject to interpretation... I guess if you fly with a club the only way to get an answer is to ask the RSO at the launch site.....
In response to your comment I would submit that my launcher is pointed within 30 degrees of the vertical. The code doesn't say "I will ignite my rocket", it says "I will launch". My rocket is attached to a sled "to ensure that the rocket flies" within 30 degrees of vertical.
Using your logic you couldn't bench test a rocket horizontally. When does a rocket launch? I would say when the motor is ignited AND the rocket is no longer constrained.
Pay specific attention to the wording... especially "to ensure that the rocket flies nearly straight up".
Item 6 of the MODEL ROCKET SAFETY CODE:
"Launcher. I will launch my rocket from a launch rod, tower, or rail that is pointed to within 30 degrees of the vertical to ensure that the rocket flies nearly straight up, and I will use a blast deflector to prevent the motor’s exhaust from hitting the ground. To prevent accidental eye injury, I will place launchers so that the end of the launch rod is above eye level or will cap the end of the rod when it is not in use.
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Logical. I think however this became a potential concern with active recovery devices (of which the only routine and accepted version is RCBG). If you intend to land your rocket somewhere OTHER than its point of origin, could that ability lend itself to nefarious uses. An example was using active recovery and GPS guidance. Slippery slope.....
Addendum
Code does cover this however as it DOES say your rocket as launched should be intended to land within confines of launch field
I agree with both points.
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I wholeheartedly agree with you, so long as the trajectory at release is 30 degrees or less from vertical you are meeting that measure of the code.
IMO, however, launch should ALWAYS be vertical with exceptions.
1. At a crowded event where it may be advisable to INTENTIONALLY have all rods or rails 5 degrees away from flight line
Or
2. Compensation for winds (you can argue if you go past 15 degrees winds are such you probably shouldn't be flying anyway.)
To me, any other angulation from vertical is "ground targeting", aiming at a recovery site which is not you launch site. At that point things get a little "iffy".
That said I'd like to see your final product with a 5 degree off vertical final ramp angle so your rocket (and possible sled) can be aimed in the safest direction for your launch site.
You are launching on private land so as long as you stay below HPR size and propellant and local rules you can do whatever you want. But if this pans out, you may want to show this off at a local club, so design accordingly.
Rocket leaves the trapeze at 50 fps. One full rotation of the trapeze would be 8π ≈ 25 ft. At release the rocket will be tumbling at about 50 fps ÷ 25 ft/rev = 2 rev/sec (or 120 rpm). That's not a rocket, it's a firework. (Use a sparky motor and don't release the rocket at all, and it's a pretty cool firework.)
This could be reduced with a longer arm, so that the same launch speed gives a lower rotation rate. I don't know what rotation rate would be recoverable quickly enough; my decidedly non-calibrated gut feel is that you'd need at least 20 feet.
Then you have to get a rather heavy arm spinning fast enough within 60 feet of rocket travel. Average speed while attached to the arm is about 25 fps, so you've got about 2.4 sec to get up to speed. I can't even guess the trapeze's moment of inertia, except to say that it'll be a lot harder to push than the rocket alone. So you need a high thrust motor, but it can't be a short burn or there won't be any burn left after the 2.4 sec. High enough thrust and a pretty good burn time means, according to my distinctly non-calibrated gut, an I motor at least (but I could be way off).
The advantage of a track is that as the cart comes out of the curve into the final, straight launch section, the ramp provides the torque needed kill the angular momentum.
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Joe, Steve, I humbly stand corrected.
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