Rocket Car - A big one

[bzzh8c]

Greetings,

My next project, that's already underway, is a high powered rocket car.

I'm using an 8" PVC pipe, 1/2 steel axles and bearings, and 12" diameter rear lawn mower wheels.
Attached is a picture (the blue one, not the yellow one).

It rolls straight and true, and I've got a 1000 lb wire than I'll run through eyelets mounted on the bottom. Now working on the "stop" part of the design. A parachute would slow it down but not stop it, and there really isn't that much room to do so. The idea I'm thinking is a pad that triggers and drags on the ground behind the car.

Figuring it out as I go. How and where to run this thing has yet to be figured out. Ky Michaelson did these a number of years ago - much sleeker than my monster....

https://www.the-rocketman.com/whatchamacallit/rm_yellowRktcar.jpg

Todd

 

[hornet driver]

1000 lb wire---hmm- put the braking device there---you'll have to devise something , but that's what I'd be about. Or , blow the rear axle off and let it tail drag to a stop---just sound like a bad idea does'nt it?

 

[TopRamen]

How about adding Air Brakes to the Fuselage like a Jet has, in conjunction with a Double Chute. At the end of the Run, at Chute deployment, the Air Bakes would be triggered.

 

[djfuller]

Run two wires side by side. Tie them together at the point you want it to start braking. At the far end, stake the ends a distance apart so the whole thing forms a giant "Y". That way when it hits the point the two wires are tied together, the wires will start separating and the cause the car to slow down. Always try to remember the KISS principle!

And make sure to get video!

-Dave

 

[blackbrandt]

Onboard video would be cool, but make sure to set up a few mounted cams around...

 

[BABAR]

Hmmmmm......... With a rocket after the propellent burns out, vehicle decelerates due to gravity.
With your car, presumably some deceleration occurs after propellent burns out due to friction. Ideally you would have enough wire for it to coast to a stop before you hit the end of the wire.
If you do NOT do you think at least you have enough that the ejection charge will fire BEFORE you hit the end of the wire? With a horizontal "flight path" it seems ANY parachute would stop this IF
1. There is still enough wire in the "flight path" to give it a chance and
2. If the shock cord is elastic enough and the mount and shroud line strong enough to absorb the shock of a high speed deployment (thing regular rocket with a very early or very late deployment)
A final "safe" option would be two very strong elastic attachments, one at the "launch" end attached between stake and wire, and one T-square at the termination point. This is attached to two stakes and the wire is attached in the middle.

 

[cavecentral]

Just don't torch you wire with th motor exhaust! That could get ugly fast.

Gravel or sand pit to slow it down faster?

 

[bzzh8c]

Here's a picture of the chassis. It rolls straight and true, and the wheels are large enough to handle the 200 mph speed I'm shooting for. It's got a 54mm and a 38mm stacked motor mount in the rear for my K700 and J570 to run separate or together (planning 3 runs).

I like the idea of the Y wire. That could generate a lot of drag (heat) that would certainly cut into the thick steel loop under the car and slow it down. To decelerate from 200 mph to 0 in about 300 feet (wire is 1000 ft long), is no small feat with gravity not helping you and brakes being just about useless.

I'll keep thinking about the "Stop" part of this while I work on finishing the front end and steering tail fin (not that useful I don't think, but I thought I'd put one in just in case I find a gigantic empty place to try this thing out with a long burn low thrust motor.

 

[jimzcatz]

Greetings,

My next project, that's already underway, is a high powered rocket car.

I'm using an 8" PVC pipe, 1/2 steel axles and bearings, and 12" diameter rear lawn mower wheels.
Attached is a picture (the blue one, not the yellow one).



It rolls straight and true, and I've got a 1000 lb wire than I'll run through eyelets mounted on the bottom. Now working on the "stop" part of the design. A parachute would slow it down but not stop it, and there really isn't that much room to do so. The idea I'm thinking is a pad that triggers and drags on the ground behind the car.

Figuring it out as I go. How and where to run this thing has yet to be figured out. Ky Michaelson did these a number of years ago - much sleeker than my monster....

https://www.the-rocketman.com/whatchamacallit/rm_yellowRktcar.jpg

Todd

I think this is a VERY bad idea, and definately not a plus for the rocketry hobby. Please don't do this anywhere near any rocketry activities. Safety code, rockets must go up!!

 

[dave carver]

I think this is a VERY bad idea, and definately not a plus for the rocketry hobby. Please don't do this anywhere near any rocketry activities. Safety code, rockets must go up!!

Too late, Jim. This has already been done many times and with Tripoli's blessing. I witnessed it twice, once at El Dorado Dry lake and at Black Rock.

The Genie is out of the bottle, good luck stuffing it back in Besides, Estes had wire guided rockets before that even. All teathered to the ground with wire. I remember that it takes a VERY high ISP motor to get any real speed out of one the size bzzh8c is building, a K1100 would most likely be a better motor than he has selected. It's kinda embarrassing when you get a full burn from a motor and the car barely moves.

 

[bzzh8c]

No problem there, in fact with the 54mm and 38mm mounts I've put into it (to allow me lots of engine options), I could put my K700 and J570 in to create more than 300 lbs of push right off the bat. Even with gravity working against it, the K700 alone punched my 32 lb upscale X-Ray to around 300 mph in just a few seconds, going straight up. In a 40 lb rocket car going horizontal, things will get moving real fast real quick, and I'll need to have my stop method activated right at burnout.
Realistically, I'm looking into longer wire already....

 

[BBrown]

Too late, Jim. This has already been done many times and with Tripoli's blessing. I witnessed it twice, once at El Dorado Dry lake and at Black Rock.

The Genie is out of the bottle, good luck stuffing it back in Besides, Estes had wire guided rockets before that even. All teathered to the ground with wire. I remember that it takes a VERY high ISP motor to get any real speed out of one the size bzzh8c is building, a K1100 would most likely be a better motor than he has selected. It's kinda embarrassing when you get a full burn from a motor and the car barely moves.

I think you are confusing "blessing" with "indifference".

There is no way any activity such as this can be confused with model rocketry any more than the proposed Bloodhound SSC car can be confused with a model rocket. Just because someone uses a rocket motor does not make it a model rocket flight. If this gentleman hurts himself or others it will have no impact on our hobby anymore than if the Bloodhound SSC crashes on it's attempt.

Bzzh8c, what ever you decide to do please be safe. If you are a member of either national rocketry club, don't expect any assistance in the form of insurance if things go bad because it is outside of what we do.

BTW, if bad things happen on Mythbusters when they are playing with rocket motors, they too are on their own.

Bob

 

[shrox]

I converted an AeroTech Initiator into a rocket car, I made it so the nose was slightly down. It was fun to run.

 

[chadrog]

Add a couple rear facing "retro-rockets" for braking. I would think a simple accelerometer based timer would be suitable for initiation.

 

[Rex R]

er Chad, don't retro-rockets usually face the direction of travel? as in the flames proceed the vehicle....
rex

 

[chadrog]

er Chad, don't retro-rockets usually face the direction of travel? as in the flames proceed the vehicle....
rex

Yes they do, I was thinking bass-ackwards - call them anti-retro rockets.

 

[bzzh8c]

I agree completely and of course I'll take the steps to keep myself and everyone else around safe when we run this car. I've been in HPR for 25 years, doing 17' cluster monsters, Mach 1 rockets, 3 stagers, up-scales, the works. Being an engineer, I'll start slow (barely more than moving likely), and work my way up. The final goal of reaching 200 mph may be difficult to reach, and if results say "that's it" well, we'll stop. My math stays the car should be stable, the wire will hold, and the method of stopping is the challenge.

The retro rocket method has a lot of promise in terms of WOW factor, but it's very risky with ignition taking as long as it does sometimes and potentially not happening at all. I prefer mechanical load over distance - easier to design and make failsafe.

Working on a couple of methods that involve engagement of a wire which is attached to weights which gradually engage through angles. Along with the "Y" wire method suggested (which I really like), I think we can bring this 50 lb car to a stop from 300 ft/s in 500' pretty easily. Working on procuring a 2000' wire, since the 1000' I got originally just isn't long enough for anything over 100 mph.

I'll keep ya posted as the "Shazam Rocket Car" comes together! Looking to get it working during the winter and be ready to go when the weather breaks in the Spring.

 

[bzzh8c]

Working on procuring a 2000' wire, since the 1000' I got originally just isn't long enough for anything over 100 mph.

Pambina Impex - 2000 ft 1/8" galvanized wire - got it! Shipping was $30 - impressive since the coil weighs 40lb.

 

[jeffgeraci]

Are your 1/2" bearings rated for that kind of velocity?... better check. I see you have a pipe with wheels that's gonna run along a wire, but I'm just not seeing the science behind it. With race cars for example, you have a front scoop to keep the nose down so the car doesn't fly off, and then you have the rear spoiler to compensate for lift in the rear. You need to add an additional element to this project; I hope you do.

 

[Chrisn]

Are your 1/2" bearings rated for that kind of velocity?... better check. I see you have a pipe with wheels that's gonna run along a wire, but I'm just not seeing the science behind it. With race cars for example, you have a front scoop to keep the nose down so the car doesn't fly off, and then you have the rear spoiler to compensate for lift in the rear. You need to add an additional element to this project; I hope you do.

Well in theory it needs no wheels or down force to "work" as it is running on a wire anyway by the sounds of it

 

[mrwalsh85]

If you want a braking system that will activate at burnout, perhaps you can consider a brake system that releases the brake via thrust from the rocket motor, and then when it loses thrust at some point, the failsafe brake system will start to apply brakes again.

Just a thought.

 

[bugwubber]

Biggest challenge I see is the sag of your wire. Gonna require some incredible tension and even then, it will still sag more than an eyebolt's worth over that distance. On the otherhand, that may give you your braking solution. Look to zipline decelleration devices. Just raising the wire on the far end so the wheels begin to lift off the ground will give you plenty of drag.

 

[BABAR]

The final goal of reaching 200 mph may be difficult to reach, and if results say "that's it" well, we'll stop. My math stays the car should be stable, the wire will hold, and the method of stopping is the challenge.

Working on procuring a 2000' wire, since the 1000' I got originally just isn't long enough for anything over 100 mph.
.

Couple thoughts.
First, at up to 200mph will there be any significant issues from friction between your guide wire and your guide wire attachments (?launch lug equivalents?)
Second is "simming" this. As opposed to a rocket that has a propulsive burn phase, then a coast phase, eventually hits apogee, and then requires a recovery phase (what goes up must come "down")' if your guide wire is long enough you don't need any brakes, the vehicle will accelerate to burnout, then slowly decelerate due to air drag, wheel drag, and guide/cable drag. If you work it perfectly, your car stops just before the end of the cable. Since there probably are not any good commercial simulators for a rocket CAR, perhaps you could collect your own data starting with a really small engine that definitely won't reach the end of the cable and work your way up to more powerful engines.

Oh yeah, third: where are you gonna run a 2000' cable?

 

[bugwubber]

Ok here's one of the devices that sounds like it would work.

https://www.alienflier.com/product_p/af-23000000-za.htm

It's a block that clamps around your cable but is loose enough to slide. Eyebolts at the bottom or sides are connected to bungee cords which are in turn anchored to the ground or nearby trees etc.