stability question

[captbk]

Sometimes I build a rocket around a particular motor. In this case the AT 1103x. Trouble is when loaded with the 1103 the CP and CG are right together.
The only way I can get 1 caliber is add 10 ounces of weight in the nose. I really don't want to add permanent weight and 10 ounces is a lot of mass. I'm already tight on space in the nose cone. I have flow the rocket on h & I loads no problem but I really want to break 10,000 ft with the K1103x. If the motor burns out in 1.5 seconds then will the rocket become stable?
Here are some pics and the OR file.

Cant seem to copy and paste the OR file any suggestions?

 

[rstaff3]

I think the answer might be yes. You can go to thrustcurve.com and find out how much the propellant weighs. Unfortunately with the CP/CG together when the button is pushed, it will be very unstable and, if it becomes stable, could be pointing at the spectators. :eyeroll:

 

[dhbarr]

If using tungsten powder, you only need about 25cc to get 10oz.

 

[Bat-mite]

If you are talking about launching a K motor, then you are Level 2, right? So you took the test, right? What are the options for making a rocket more stable? Nose weight, longer airframe, bigger fins.

I'm not sure what you mean when you say that you built the rocket around a particular motor, if that particular motor makes the rocket unstable.

 

[samb]

I'm a little confused. Sounds like you know your way around OpenRocket. You designed a rocket around the K1103. You saw it was unstable with that motor. You built it anyway but you still want to fly with that motor. Do I have that right ? I agree with rstaff, it's a crap-shoot where that puppy will be pointed when the mass reduction from expended propellant takes place. So... I think building a stable rocket for the K1103 or adding mass to this one are your choices.

Oops... Bat-mite and I are on the same wave-length... Scary ! :wink:

 

[rstaff3]

I agree with Bat-mite and samb. It is scary that someone would be flying a K and not see the issue. But, it could be the wording of his post?

 

[wighty44]

...when loaded with the 1103 the CP and CG are right together...

I can't image an RSO letting it launch in that configuration, or am I missing something? I know it would not launch at my field.

 

[markkoelsch]

Your only options with it built it to add mass to the nosecone, or make it a traditional dual deploy by adding addition length/tube.

You did the sim before building it, and knew about this problem? This is really does not show understanding of rocketry that someone at your cert level should have.

 

[captbk]

I knew I would have to add weight from the beginning. Im really trying to figure out a way to temporarily add weight. Maybe attach the extra weight to the shock cord? I was thinking of using #8 lead shot, wrap 10 ounces of it in some duck tape. Make a small bundleabout 6" long with it and then tape that to my shock cord.

 

[Bat-mite]

Here's thread on the subject of temporary nose weight.

 

[rstaff3]

OK, it seems we didn't get the concise question and maybe focussed on the wrong part of the post. If your sim says the 10oz at that point (somewhere below the cone) is enough, that is a start. Make sure it is really secure so it doesn't shift backwards.

 

[Bat-mite]

I haven't done this, and I have no idea how much dog barf weighs (maybe someone does?). But, perhaps you could measure out ten ounces of dog bark, cut a door in the NC shoulder, and shove it in; tape over the door with masking tape. After launch, remove tape and shake it out. I have no idea if this is feasible.

 

[slaak]

OK, it seems we didn't get the concise question and maybe focussed on the wrong part of the post. If your sim says the 10oz at that point (somewhere below the cone) is enough, that is a start. Make sure it is really secure so it doesn't shift backwards.

There is definitely ways to do it but we might need more pictures of your setup to see what kind of space your dealing with. If your recovery gear is in the nose then you could replace your quick links with some beefier versions of themselves or if your using knots at your bulkheads and parachute connections replace the knots with some steel quick links. it might take quite a few to get 10oz but I don't think there would be any problem with daisy chaining some quick links together.

 

[Wallace]

I knew I would have to add weight from the beginning. Im really trying to figure out a way to temporarily add weight. Maybe attach the extra weight to the shock cord? I was thinking of using #8 lead shot, wrap 10 ounces of it in some duck tape. Make a small bundleabout 6" long with it and then tape that to my shock cord.

May be a bit late, but....When I built this nc I had the same quandary. Since my av bay and easily replaceable tether attachment needed to be foamed in, I added a 9" length of schedule 80 pvc wit a threaded end cap so it would be easy to add weight as needed. Maybe you have room for similar?

 

[Wallace]

Basically drill a hole and install a tube that you can fill/subtract weight as needed..

 

[djs]

Note- if you're adding temporary weight (such as quick links, etc), be careful how much weight shift can occur laterally. I've had rockets fly crooked because the weight leaned to one side, the rocket flew slightly in that direction, weight caused it to shift more, etc. The rocket didn't do flips or anything, but definitely wasn't a straight upwards boost.

 

[captbk]

Its head end deploy so space in the NC is scarc with a 36" chute and 15' of 1/4" Kevlar shock cord. I have a GPS in the NC shoulder also. Will lead shot mess with it like all thread?

 

[Wallace]

Its head end deploy so space in the NC is scarc with a 36" chute and 15' of 1/4" Kevlar shock cord. I have a GPS in the NC shoulder also. Will lead shot mess with it like all thread?

I also have an Eggfinder mini in mine. Have yet to fly it on anything big enough to require added weight. Their are currently plenty of alternatives to lead shot out there, maybe one of those?

 

[captbk]

As you can see things are very tight but do-able. The long duck tape thing is the lead weight taped to shock cord. It lays flat so it doesn't take up a lot of room. It's not going to shift so not really worried about that. I'm still concerned about the lead being close to the GPS antenna. I can get it tucked way up inside the nose cone so it won't be next to the antenna.

 

[slaak]

View attachment 325970 View attachment 325971 As you can see things are very tight but do-able. The long duck tape thing is the lead weight taped to shock cord. It lays flat so it doesn't take up a lot of room. It's not going to shift so not really worried about that. I'm still concerned about the lead being close to the GPS antenna. I can get it tucked way up inside the nose cone so it won't be next to the antenna.

Not sure which tracker you are using but that's the transceiver antenna not the GPS antenna yeah? It might be spooky if you loose a packet or two on the way up but its only really important to be receiving your location on the way down when the lead shouldn't be anywhere near the antenna. Just make sure the lead weight is secured on your harness securely, id be more worried about 10oz of lead flying out of the sky onto my head than antenna interference.

 

[rstaff3]

I haven't done this, and I have no idea how much dog barf weighs (maybe someone does?). But, perhaps you could measure out ten ounces of dog bark, cut a door in the NC shoulder, and shove it in; tape over the door with masking tape. After launch, remove tape and shake it out. I have no idea if this is feasible.

That would be a lot of barf, indeed.

 

[rstaff3]

There is definitely ways to do it but we might need more pictures of your setup to see what kind of space your dealing with. If your recovery gear is in the nose then you could replace your quick links with some beefier versions of themselves or if your using knots at your bulkheads and parachute connections replace the knots with some steel quick links. it might take quite a few to get 10oz but I don't think there would be any problem with daisy chaining some quick links together.

Quoted the wrong post. Probably will be seen by the right person anyway...

Sent from my SAMSUNG-SGH-I337 using Rocketry Forum mobile app

 

[dhbarr]

How much does that lead chunk weigh? Tungsten powder should be about 1.5 times denser, so if you just make that lead swappable you could probably get away with only a dozen cc or so of additional space.

 

[samb]

Ok, alot going on in the nose. I'm a big fan of "duck tape cures (almost) all ills" but I'd be more concerned about a harness attached package shifting or coming loose at the wrong time in this application. How much more airframe length is needed to make it stable ? Could you make a temporary extention by having one end attached to the bottom of the av bay with screws and a coupler on the other end ?

 

[soopirV]

That would be a lot of barf, indeed.

a frat-house worth of barf, I'm afraid...

 

[captbk]

Ok, alot going on in the nose. I'm a big fan of "duck tape cures (almost) all ills" but I'd be more concerned about a harness attached package shifting or coming loose at the wrong time in this application. How much more airframe length is needed to make it stable ? Could you make it temporary by having one end attached to the bottom of the av bay with screws and a coupler on the other end ?

Believe me, there it zero room for it to shift. Everything is packed in tight.

 

[markkoelsch]

Is the tip of the nosecone threaded?

 

[samb]

Believe me, there it zero room for it to shift. Everything is packed in tight.

I have no reason not to believe you. I believe that you may be correct and that the "up" part might go as planned. I believe there is a greater than zero chance of the package letting go on the down part. How much greater I don't know. I believe an RSO might let you try it (if you fly with a club). Have you already made up your mind that's the way to go ? Good luck, stay safe !

 

[blackjack2564]

First off, you probably will go higher with the weight added. Run it in OpenR & see.
You designed the rocket around the motor....so make it so! Add the weight. Leave it.
Fly it on smaller motors that can lift it. 10z. should not make that much difference.

I did 8oz in 54mm cone, that barely used space [1.5 inch] as you can see...use powdered lead.
So far forward it did not interfere with chute at all.




Here's how I added a full pound in a 3in. and only used 2in in Tip. Link for where to buy still good. Get extra for future builds, no extra charge shipping for more than 1. [I got 6]

https://www.rocketryforum.com/showt...-Head-quot-75mm-to-54mm&p=1487927#post1487927

 

[captbk]

Your right Jim, I'm going to epoxy it into the tip and be done with it. And there will be 0 chance of the package letting go.