DAY 2 unguided rocket sled. 3 more launches. more power. (video)

[mbecks]

Finally I got around to another day of firing off the rocket sled. I had some great launches and some more "plane" like launches. hope you enjoy. soon ill be putting a camera on the sled.

[video=youtube;v15s8CvK-Tk]https://www.youtube.com/watch?v=v15s8CvK-Tk[/video]

 

[mbecks]

Wow I'm surprised I'm getting no comments, usually my rocket sled start up a conversation.

 

[McKailas Dad]

Wow I'm surprised I'm getting no comments, usually my rocket sled start up a conversation.

I'm happy to see you're back

I wish I could give solid advice to keep it from going airborne. I know a spoiler has been mentioned, and possibly angling the motors differently, but I'm not sure. To make the sled heavier may help keep it down, but then you would lose distance. Not much for a 'coast phase' after burnout in your particular situation...

Maybe keep the mass the same, but use longer and/or narrower skis? Like the long, skinny Top Fuel cars, motor in the back, and a loong front end?

The footprints in the snow don't help, any chance you have a smooth, frozen lake nearby?

 

[Rob702Martinez]

Ha! Pretty cool!

 

[tab28682]

The upturned ski tips are going to create lift at the front at high speed and help cause it to flip. The cluster launch might not have gone airborne only because of a bump: I predict speed was a significant factor.

The staged launch seems to keep things at a more reasonable overall speed.

As mentioned, a spoiler might help a little by supplying some down force, but it might not be enough to keep it from flipping at high speed or when it hits a bump.

A horizontal stabilizer might help keep it from flipping with less drag than a spoiler. That and a vertical stabilizer might help is survive a hop into the air and not allow it to flip or tumble.

 

[RocketryBill]

Are you planning on putting yourself on one of those rocket sleds?

 

[McKailas Dad]

Any opinions on angling the motor up, maybe even a couple degrees? So, say an ~1/8" higher at the front of the motor? Would that help to keep the front end down, or just make it want to bring the rear end up? That and maybe lower the motor mount in the chassis to just above the ground, for a lower CG?

Don't mind me, I'm thinking of this in an 'automobile' type scenario.

 

[mbecks]

I think what I got to try before I make any big changes is find a nice flat launching location to get a better sense of how much the sled going airborne is caused by speed and how much is caused by hitting a jump. I may try angling the motor like you said but with the front of the motor slightly down since the motors are basically on CG. Thanks for the suggestion.

 

[BABAR]

Cool.

Is this really completely unguided, or do you run the sled forward ahead of time to make a "track" for each runner?

I was thinking you'd want to have your CG as far forward as possible to keep front end from lifting at all. Well, not forward of the forward edge of your runners, but as far forward AS the front edge of the runners.

Since you are unguided, it is a little bit like a shooting range, where since you are not sure just how far this thing is gonna go you want to make sure there is nothing "down range" you could possibly hit if you suddenly had an "optimal" launch that went 200 or 300 feet. Your set up looks good, just concerned some imitaters might try this in their front yard or something. Obviously your NAR insurance isn't going to cover any mishaps on this puppy.

 

[tab28682]

Your set up looks good, just concerned some imitaters might try this in their front yard or something. Obviously your NAR insurance isn't going to cover any mishaps on this puppy.

Note that the OP is in Canada....

 

[RocketRob]

Looks cool!

Id like to see it with a spoiler and composite motors.

 

[mbecks]

Response to:

Mckailas dad- I think the issue with having no coast phase is that all three launches in this video ended in a tumble. In the previous video the D12 rocket coasted pretty good. I think I have to find a way to keep the speed down such as staging a D12 to something smaller. I still have to try E9 motors which might be just the right speed.

tab28682- I agree completely with the up word bend of the skis contributing the "flight". My solutions I'm thinking of are either to cut the bent ski section into points lessening the amount of lift it has or staging to smaller motors like smaller C motors. think that will work?

RocketryBill- I value my life so probably not haha but here is an image of a guy who did do that. https://www.the-rocketman.com/rkt_sled3.JPG and https://i.kinja-img.com/gawker-media/image/upload/s--gQwJmkf_--/18m5a502koyg7jpg.jpg . I bet there's videos out there to.

BABAR- I guess you could say its not completely unguided because I do make ruts for the sled to start off in in the hopes of the sled having a chance at going strait, but normal rockets almost always use a guide rod to get started but we don't consider them guided rockets.
On the other part of your comment, if I go any bigger I will definitely be going to where I launch my normal rockets because it is a huge open field that is miles long and wide. As for imitators I'm not to concerned. kids and teens these days are doing YouTube challenges now a days, in mass numbers, that are far more dangerous then learning about rockets. one of those "YouTube challenges" involves lighting them selves on fire. I would rather them be trying to be creative and make an effective rocket sled then a lot of other things they could be getting involved in.

 

[mbecks]

Any suggestions what my next launches should be?

 

[mbecks]

Has anyone here tried to make rocket boats?

 

[McKailas Dad]

Any suggestions what my next launches should be?

I think once you get your chassis design dialed in perfect...24mm APCP

Has anyone here tried to make rocket boats?

I saw a -full sized- fishing boat on (probably) YouTube that a guy launched (pun not intended) on a rather large composite motor. I forget the details, I'll see if I can find it again...

 

[mbecks]

For some reason I got the desire to strap rockets to all sorts of things except rockets lately. I even have a scratch build rocket built and with a motor in it sitting on my shelf for like 2 months now. something is wrong with me.

 

[TRFfan]

Well, rocket sleds are really cool. Maybe even marginally cooler than rockets. (somewhat)

 

[mbecks]

Well, rocket sleds are really cool. Maybe even marginally cooler than rockets. (somewhat)

Haha well thank you, I think a lot of people might argue that. I am having a lot of fun figuring it all out. It's fun being a pioneer on something and not having strict plans to follow. I wish a few more people would give it a try if love to see someone do it better so I can learn.

 

[TRFfan]

I would like to try rocket sleds but unfortunately conditions aren't good enough (snow is too powdery and deep)

 

[TRFfan]

BTW, I think your launches are really cool. What you should try is upgrading the MMT to 29 mm and then try a 3-stage with Estes F15s. :wink: :surprised: :shock:

 

[mbecks]

BTW, I think your launches are really cool. What you should try is upgrading the MMT to 29 mm and then try a 3-stage with Estes F15s. :wink: :surprised: :shock:

go big or go home I guess eh.

 

[mbecks]

I would like to try rocket sleds but unfortunately conditions aren't good enough (snow is too powdery and deep)

My first launches were on deep fluffy snow, as long as the sled is light it should stay up top.

 

[TRFfan]

mbecks,

Would you be able to fit E9s in the sled?

 

[mbecks]

mbecks,

Would you be able to fit E9s in the sled?

yes I was thinking about that. My original plan was to use an E9 for this launch but I spent all the money on other rocket stuff haha. I feel like they might be the ideal thrust and burn time. I need to get a little camera to strap to it.

 

[McKailas Dad]

...spent all the money on other rocket stuff haha.....I feel like they might be the ideal thrust and burn time. to it.

You know...I am -going- to sell you on the idea of buying a 24/40 case...

Seriously, price out your 24mm Estes motors compared to Aerotech reload prices. Someone made a spreadsheet on how long it would take to get the 'return on investment' back from buying the reload case, but I forgot who lol. There are some very reputable vendors up in Canada if shipping is a concern.

You know you want to !!


EDIT- Pssst, the 24/40 case is ON CLEARANCE at Hobbylinc!!!

https://www.hobbylinc.com/htm/aro/aro91241.htm

 

[neil_w]

Whoa that's a good deal!

 

[mbecks]

Thanks I'll look into it. Hopefully I can get my hobby store to start selling them.

 

[Nick@JET]

Looks like a lot of fun! You could use a sprint car wing ( reverse wing)

 

[TRFfan]

yes I was thinking about that. My original plan was to use an E9 for this launch but I spent all the money on other rocket stuff haha. I feel like they might be the ideal thrust and burn time. I need to get a little camera to strap to it.

That would be cool!

 

[dhbarr]

That's a lot of surface area to be contacting the snow. Have you considered a catamaran-style hull? I'm thinking two hollow triangular sections tied together with a crossed box.

The fore-ends of each "float" come to the same or similar curved point as you have currently, you wouldn't have to have those big heavy offset blocks, plus you could stick motor mounts in the top back end of each empty ski.

Expansion gases pushing partially against snow vs. pushing against air....

EDIT: Come to think of it, eliminate the crossbeams and just build it off of a single shared flat top plate. Should simplify construction significantly, and better ensure the two snomaran edges are exactly parallel.

EDIT2: Eliminate the top plate entirely, move the inside face of the skis to touch each other, bring back the crossbox for stiffness. Notch the top edges of all four catski faces so the rods don't grab air.