My "first" high powered build (Binder Devistator) - advice needed

[zeotherm]

Don't suppose the inside of your nosecone is accessible?

Unfortunately no Had I thought ahead, I would have made it accessible, but I did not. I can modify it for the future, but not overnight.

I did some back of the envelope calculations, given the weights of the loaded rocket, and where I measured the CG to be now treating the rocket as a pair of point masses (spherical rocket in a vacuum level stuff here) suggest that adding 7 oz of mass to the "front" mass will shift the CG ahead by 3" giving me a 1.25 caliber of stability.... I will see what tomorrow brings.

 

[T-Rex]

Use the rkt file you have to adjust the CG. Put it as far forward as you can. Forward=less weight for the same change in CG. Once you have a weight figured out, then use just enough.... As others said fishing weights, fender washers etc. I like to use BB's and epoxy, but that is usually mounted in the nose. You could make a 'donut' from weights and epoxy, then bolt it in place. A fishing weight can be attached the eye bolt with wire, string, or a zip tie. A wood screw, lag bolt, extra nut on your eye bolt, lots of ways to add weight.

 

[Handeman]

So.... Did you fly it at LDRS and how did it go?

 

[AfterBurners]

More work has been done. The fins are all epoxied in place so that they won't let go of the fin can until sometime around the heat death of the universe The fin can fit back into the body tube like a glove, super easy construction technique.

Started on the top part, got the eye bolt and center plate set in place. Also got a pair of fin stiffeners on! I am really loving this rocket, but man LDRS is coming up FAST and I need to hurry up!! I need a motor casing and to pay my range fees for the weekend! Gah, thankfully my kids rockets are all done and it is just me we are waiting on


View attachment 315311

View attachment 315312

View attachment 315313

View attachment 315314

View attachment 315315

View attachment 315316

View attachment 315317

A quick question: what is the best way to protect the parachute here from the ejection charge heat? I have a bag of dog barf somewhere here in the basement, but does that scale up well enough to work on a 4" diameter body tube? Would a big handful of that do the trick or do I need something more advanced? Thanks again all!

Did you take a router to the fins / wings or did the kit come that way?

 

[zeotherm]

So.... Did you fly it at LDRS and how did it go?

Sorry, work was insane this week and I haven't had a chance to update the thread...


Well, my daughter and I were at LDRS Friday to pick up some hardware from Wildman and an engine from AMW. We watched a few flights, then headed back home. It was Friday night, that I realized my mass problem once I had the rocket all set up as it would be for flight. Saturday morning I headed to Home Depot and bought a bunch of big steel nuts and some wire ties. When I got to the range on Saturday both my kids launched their rockets and had successful flights! (zeolite A is shown below with her rocket "Pinky") I went back to the car to start prepping my rocket, and I wire tied 6 nuts to the eye bolt on the payload section of the rocket. A quick hand check showed that the CG was still only ~2.5" in front of the CP...



The walk from the car to the RSO table was my rocket's highlight. I got numerous compliments from people who saw it and I am very grateful for the feedback, I really enjoy the modeling portion of things . I made it to the RSO table and they were worried that the CG was not far enough in front of the CP to provide a stable flight. I had attached all the nuts I had to the nose cone, but they didn't shift the CG forward far enough, so no flight for my Devastator at LDRS ;(

So, that brings us to the second part of this build thread, Devastator Block B design and construction! I figure I will put my 9.5 years of college for engineering to use. So, I need to move my CG forward... a lot. I was planning to fly on a 38mm CTI I242 engine (a 4 grain engine) which should be on the lighter side of things, since I would love to fly this on a big K engine. So, my thoughts on design. I am going to cut the payload section a few inches below the nose cone. From the bulk head at the bottom of the payload section, I am going to fit in four long bolts. Along with these, I am going to make up a few wooden plates with different masses of lead shot epoxied to them. If the bolts are long enough, and fully threaded, then this will allow me to create a mobile CG platform that will allow me to move the CG forward and back to allow for various weight engines.

I also figured that as long as I have the patient open, I would be remiss in NOT adding a camera to the rocket to see what it looks like from it's perspective. TO that end, does anyone have any recommendations as to a good on-board camera? I'm going to order a coupler and head out to the hardware store sometime next week (assuming work dies down a bit) and get parts to implement my idea. I will keep updating this thread with progress, and hopefully will be able to get my bird off the ground at MDRA's May launch

 

[zeotherm]

Did you take a router to the fins / wings or did the kit come that way?

I did not, the wings came as simple cut plywood, I put the bevel on them with a simple palm sander and 100 grit sandpaper.

 

[zeotherm]

Welp, I made it out to MDRA's ESL today (missed May due to illness). The weather was perfect, I had rebalanced my rocket, and got it loaded on the launch pad. I flew it on an I241 and it took off and flew gloriously. Sadly, it never landed. It drifted back to the trees that abut the sod farm we were flying at and got stuck a good 55' up in the very canopy of a tree. Even with their huge reach pole, I could not get to it. Total suckage... My daughter is completely upset, but I kept telling her, this just means we get to build another one.

Matt's Devastator 2016-2017, RIP.

 

[BDB]

I'm sorry for your loss.

 

[Binder Design]

Sorry to hear about the loss of your Devastator! We discontinued this kit for a few months, but due to popular demand it's back in production.