18mm supersonic build (1st attempt)

[ChesleyB]

So for the update, The rocket is done and ready to fly, I did add about 2g of fishing weight to the base of the nose cone (easily removed) so later I can try an altimeter in its place. I however don't want to shoot $50 worth of electronics into oblivion if something goes wrong or I never find it. I'm a broke college student, if I was swimming in funds I would have built an aspire and been done with it. As for the launch I am waiting for a sunny day off. possibly Saturday if the wind is down. This 6mm F motor, is this a reload, a custom build or what? I'm a Chemical Engineering student so I'm interested in eventually building my own motors. I found motor company called US Rockets

https://www.v-serv.com/usr/18mm.htm

they have some sweet single use motors but they aren't for sale until they get their NAR cert

 

[JPVegh]

I think he was saying that the F motor was only 6mm larger diameter than an 18 mm D. 18+6=24mm F240.

 

[krusty]

So for the update, The rocket is done and ready to fly, I did add about 2g of fishing weight to the base of the nose cone (easily removed) so later I can try an altimeter in its place. I however don't want to shoot $50 worth of electronics into oblivion if something goes wrong or I never find it. I'm a broke college student, if I was swimming in funds I would have built an aspire and been done with it. As for the launch I am waiting for a sunny day off. possibly Saturday if the wind is down. This 6mm F motor, is this a reload, a custom build or what? I'm a Chemical Engineering student so I'm interested in eventually building my own motors. I found motor company called US Rockets

https://www.v-serv.com/usr/18mm.htm

they have some sweet single use motors but they aren't for sale until they get their NAR cert

I think not flying an alt. Is a wise move I suspect getting the rocket back will be a challenge!

From what I've read, US Rockets motors are going to remain unavailable for the foreseeable future, sweet as they look

Krusty

 

[JordanT]

I'm a Chemical Engineering student so I'm interested in eventually building my own motors. I found motor company called US Rockets

they have some sweet single use motors but they aren't for sale until they get their NAR cert

If that's who I think it is, I wouldn't hold your breath on those. The owner is, um, well known in the rocket community. I'll leave it at that.

I can understand your hesitation on flying an altimeter in that little speck of a rocket that's going to be going 1000+fps. I watched my 24mm speck re-kit at about 60-80 feet going about 600fps, knowing that there was $30 of case in the rear end and $160 of altimeter in the nosecone. You can imagine the feeling in the pit of my stomach when I found the streamer and BT with no sign of the nose cone or the case. It took about 30 minutes of searching between other launches, but I managed to recover both. Had it not failed so soon, I might not have been as lucky. The next model I'm hoping to have space for both the altimeter and a beacon tracker. I can probably live with the loss of the case; I really don't relish the thought of losing a 250g Raven.

 

[ChesleyB]

[video=youtube;fSBRM68jFfk]https://www.youtube.com/watch?v=fSBRM68jFfk[/video]

there it goes. I got the body back. Lessons learned use high heat paint, the D21 has a hot ejection charge. It bubbled paint on this rocket and an Estes crossfire. The fins worked well and use a longer shot cord.

 

[Christian D Michael]

I just finished off a cheap 18mm design, though it doesn't have room for an altimeter, even a 1.8 g total adrel alt-bmp. With the parts listed out it should be around $30-35 to build. Here's the OpenRocket file:


If you can, film the launch in slo-mo and analyze the footage right at the time OpenRocket says it should go supersonic. You should be able to hear the small bang. Those D21's are quiet enough that they don't wash it out. That's how I've verified my small scale supersonic flights.

Hope you get a successful flight and recovery!

 

[jqavins]

I wish I could try it on weaker engines but that wouldn't be accurate since the weight is not the same. Any advise?

You could attach some "tail weight". Do you have an engine block installed? If not then it's easy; if so, use an LP motor that's shorter than you've designed for. Glue some 3/4" washers to the front of the motor to make up the weight. 3/4" is about 19 mm, so you'll have to turn down or file down the washers' OD a bit. (As an engineering student, surely you have access to a machine shop on campus.) The ejection charge gas will pass through the middle of the washer stack. The effective motor CG will be a smidgen forward of your designed motor CG, but that should be negligible.

 

[Nytrunner]

The question is 6 years old and the subject rocket has flown (see post 35). Thread resurrected last week

Interesting project nonetheless.

 

[jqavins]

Oops.