Video of a Spool Rocket?

[teflonrocketry1]

Anyone know where I can find a video of a spool rocket in flight, preferably on the internet? I have been searching for such a video and haven't found anything. I need a flight video to convince someone these designs actually fly stable. I wish I had a link to a flight from the Rocketry Challenge on the Discovery Channel; I know a HP spool rocket was flown at LDRS 22!

Bruce S. Levison, NAR #69055

 

[Rocketjunkie]

Here's one on a K550.

https://www.tripolisc.org/modules/xgallery/cache/albums/album31/aaa.mpg

 

[xxxREKxxx]

Originally posted by teflonrocketry1
I need a flight video to convince someone these designs actually fly stable.
Bruce S. Levison, NAR #69055

How about building one and showing them firsthand

Take two useless CD's and open up a hole for a 4-6" lenght of BT-20. I use some 1/2" EMT metal conduit or any 1/2" metal tube. I heat it up and melt the hole. You can also cut it with a drill bit. Drill a pilot hole in each disc for the launch lug. Use a piece of spent 18mm motor for a thrust ring. Do the 1/4 measure from the bottom push and remove the motor quickly thing, plug the top with epoxy soaked tissue paper. Let it dry and fly. I use epoxy for everything on this.

Launch this over soft ground. The CD's are very fragile and will break on ice, frozen ground, or hot top. It's OK though sooner or later AOL, MSN or someother provider will send you plenty of replacements.

Here's picture of one. It has been broken several times and is still awaitng repairs, but you get the idea.

These are really easy to build and the look on a disbeliever's face is worth the effort when they actually see it fly
Bob

 

[teflonrocketry1]

Originally posted by Rocketjunkie
Here's one on a K550.

https://www.tripolisc.org/modules/xgallery/cache/albums/album31/aaa.mpg

Thanks Rocketjunkie, this is exactly what I was looking for!

Bruce S. Levison, NAR #69055

 

[Ryan S.]

this may be a dumb question but how are they stabalized?

 

[wyldbill]

Their CP moves dramatically to the rear with an angle of attack of > 0. The greater the AOA, the more the CP moves back. The static CP is right in the middle tho... I think.

 

[lalligood]

Originally posted by Ryan S.
this may be a dumb question but how are they stabalized?

Not a dumb question at all! In fact, it's a pretty tough question... Check out this older TRF thread. That question/subject eventually comes up. teflonrocketry1 (who started this thread) "googled" & found out that the CP of a flat disc travelling perpendicular--the way a spool travels--is 4/3 the diameter behind it. In other words, a standard CD is 120mm (4.75") in diameter, so the CP of that disc is 160mm (6 1/3") behind the disc. That's why single disc "spool rockets" on 18mm motors fly stable whether the disc is mounted at the front or the aft end--the CP is actually way behind the entire rocket, making it super stable

The math is more complicated for 2 discs (aka a "real" spool rocket), which I really haven't taken the time to truly figure out, but through my own experimentation, I found spools are most stable when the length is equal to or less than the diameter of the disc(s). That ensures that the front disc has in no way pulled the CP far enough forward to actually be on the rocket & get anywhere close to the CG, thus remaining a stable design.

HTH,

 

[teflonrocketry1]

I am still working on figuring out the true CP of a spool rocket. I still believe it to be behind the aft plate but I have yet to come up with a meaningful theory and explain how the CP varies with wind speed. I may just have to build several models and test them in a wind tunnel; actually I am currently exploring this possibility.

Bruce S. Levison, NAR #69055

 

[Gus]

Lance,

Thanks for taking the time to provide that nice explanation.

 

[Chuck Rudy]

The basic reason spools work is (after the above explanation as per the first disk)......... as the air spills equally over the edges of the first disk the second disk runs in the 'draft' of the first. Equal pressure on the first disk equals an equal amount of air spilling over the edge. When pockets of air attempt to push one side of the disk up or down (depending on denser or less dense air) the air speeds up over the high side of the disk, the bottom disk pulls out of the air stream (draft) and is hit by the air sending it back towards central. Though they look as though they are going straight they are constantly adjusting themselves.

What may be eaiser to understand is the first disk creates a cylinder of air, anytime the bottom disk moves outside that cylinder air forces it back in. Hope it helps a bit

 

[lalligood]

Originally posted by Chuck Rudy
What may be eaiser to understand is the first disk creates a cylinder of air, anytime the bottom disk moves outside that cylinder air forces it back in.

Makes perfect sense to me... Which explains why they always have such straight flights regardless of the winds.

Then again, spools also appear to be bery good at resisting weathercocking due to their minimal horizontal surface area, which in the case of the CD spool rockets I've built is nothing more than 3-3.5" of BT-20 & the edges of the CDs (less than 1mm each). Not a lot of material to be influenced by wind!

 

[edwardw]

So I saw this thread and thought...hmmm...I have some thin walled PVC that my future mother in law gave me. I got an 18mm engine and sure enough, it fit like a glove. So I have some CD's that I burned wrong and they will be getting converted to a spool rocket. I'm going to love showing up at the next launch with one of these things Now, I understand that they work with either two CD's, or one. And it doesn't matter which end the one CD is located, forward or aft correct? Which is more dramatic, forward or aft.

Edward

 

[lalligood]

Originally posted by edwardw
So I saw this thread and thought...hmmm...I have some thin walled PVC that my future mother in law gave me. I got an 18mm engine and sure enough, it fit like a glove. So I have some CD's that I burned wrong and they will be getting converted to a spool rocket. I'm going to love showing up at the next launch with one of these things Now, I understand that they work with either two CD's, or one. And it doesn't matter which end the one CD is located, forward or aft correct? Which is more dramatic, forward or aft.

Edward

I prefer 2 discs over 1--regardless of where that 1 disc is located. However, if I must pick only 1 disc, then I would choose forward. (Although single disc spools fly the same regardless of disc placement.) Reason being is that someone is more likely to say, "Hey! Yer rockit ain't got no fins. Howz dat gointa fly?" It just allows you to smile really big & say, "Just watch. You'll see..." And don't be shy with the motors either. Go big (C6-5) or don't do it at all. Nothing like seeing a CD, some tubing, & a launch lug climb to almost 400ft (I'm not fond of the single disc spools because they fall like a wounded duck--the 2 disc spools recover much more gracefully!)

 

[edwardw]

Wounded duck - images if Nintendo's original Duck Hunt I think I will make one with just a forward CD and maybe glue in a small streamer to make it fall more gracefully. I can put some dog barf between it and the streamer. Make the streamer out of surveyers tape and just CA it to the plastic. That way it falls a little nicer


Edward