Rocket sleds and cars

I have some left over B and C rocket motors and want to build some rocket sleds. I assume the physics will be simular to a rocket car but I've built neither. Me and my wife both built a sled that will use B motors with little planning just doing what we thought would work but for the C motor I'm doing a bit more planning. My question is, does anyone know if it's better to have the thrust at the front or rear when dealing with land based rocket vehicles. These are going to be un-guided.

They will both work better if guided and they are unlikely to work if not guided.

In my misspent youth. I tried a couple of unguided rocket cars and they would invariably spin out of control when rear engined, unless the wheelbase was very wide. Never tried a front engine design.

Estes has produced various rocket cars and they are all run on a guideline. Safer and more repeatable performances.

In that case do you have any idea how long I should make the guide for a B motor and for a C motor?

The C engine sled has a front mounted motor so I'll try it unguided. To my untrained eye it should work.

I believe the guide line/string is 90 feet long, but that is for an A 10 PT.

Not knowing the size and weight of the car, I would go with a 200-300 foot guide line for a B or a C.

tab28682 said:

Not knowing the size and weight of the car, I would go with a 200-300 foot guide line for a B or a C.

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Talk about a mis-spent youth! We'd use the longest nails we could find and pound them into the asphalt. We'd run about 300' of kite string thru a launch lug mounted on the bottom of the ex-slot car then tie it off. It evolved over the summer to a tower bridging the "drag strip" with streamers or parachutes grabbed by a hook cobbled on the jerry-rigged 'spoiler'. Booster motors strapped on each side were expensive (to a kid) but were rewarding with the smoke and flame.

Model Rocket Motors are legal to use for their intended use as defined by Federal Regulations. Any other use would be illegal and expose you to massive liability and possible criminal charges should something go very wrong (injury, fire, death - especially death of firefighters who are battling fire cause by illegal activity).

Estes tried to get larger rocket cars made legal, but the CPSC rejected anything over an A total impulse and required MASSIVE safety warnings in the products. They are required to be tethered (i.e. they slide worn a cord or cable).

https://www.google.com/search?q=cps...microsoft:en-US:IE-Address&ie=&oe=&gws_rd=ssl


Some States only allow Model Rocket Motors to be fired when used in a Model Rocket.

shreadvector said:

Model Rocket Motors are legal to use for their intended use as defined by Federal Regulations. Any other use would be illegal and expose you to massive liability and possible criminal charges should something go very wrong (injury, fire, death - especially death of firefighters who are battling fire cause by illegal activity).

Estes tried to get larger rocket cars made legal, but the CPSC rejected anything over an A total impulse and required MASSIVE safety warnings in the products. They are required to be tethered (i.e. they slide worn a cord or cable).

https://www.google.com/search?q=cps...microsoft:en-US:IE-Address&ie=&oe=&gws_rd=ssl


Some States only allow Model Rocket Motors to be fired when used in a Model Rocket.

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Worth noting that the original poster is in Canada.

I had not noted that.

hopefully it does not "blow up real good".

Eh?

"koo-LOO-koo-koo koo-koo-koo-koooo"...

tab28682 said:

Worth noting that the original poster is in Canada.

Click to expand...

update: The two I had put guides worked great, the one I didn't put on a guide soon turned into a unstable plane haha, guides on all sleds. I'll put a video up once I edit it.
[video=youtube;3hoD96IC-tc]https://www.youtube.com/watch?v=3hoD96IC-tc[/video]

'

Don't know what you mean by an "unguided" sled.
Real rocket sleds are guided by a rail.
IF I were to do it (and not addressing any rule or law violations) I would get some kind of rail, like a mini or micro rail, and bolt them together. Lay them on a flat level surface. Epoxy a couple of micro buttons on the sled/car. Braking can be by a chute or water trap at the end of the rail. Length depends on the weight of the vehicle and the amount of friction between the button/shoe and the rail. And the aerodynamics of your design.
2-300 ft. of any rail can be expensive. Probably why nobody's done it that I know of.
String or even wires/rods will sag and bend over that length.
EDIT: I see you've posted a video after my post went up. So, sled as in SNOW. Duh.
How about cutting a channel in the snow ? Won't keep it from going airborne though.
This is what I thought you were talking about:

Are these rocket powered cars?
https://estesrockets.com/product-category/miscellaneous/dragsters/

I found this, tethers.

https://estesrockets.com/product-category/miscellaneous/dragsters/

Yes Estes makes a small series of Rocket Cars