"Built" Thread - Elvun V3

Yes, this is a "built" thread (as opposed to a "build" thread). For various reasons (not least of which the fact that I've been working on this sporadically for 6 months) I decided to post it once it was done, rather than along the way. And now it is. "Done" I mean. So, I present to you my latest creation - Elvun V3.

LOC tubing, 3" diameter, 49" tall, plywood semi-TTW fins, just over 1000 grams (2.2lb.) dryweight (everything but the motors - harness, chute, hardware, electronics, battery, wiring, etc.). Features a integrated baffle and fixed AV bay with a hatch door. It's powered by four motors - one central 29mm and three outboard 24mm.
It can be flown a number of ways - A) with all four motors firing off the pad, B) with just the single 29mm motor, or C) - the intended way it was designed for - utilizing a timer so that the cluster of three 24mms gets it off the pad and after a short post-burn coast, the central 29mm fires as a semi second stage.

I'll post a few "finished" pics here first, and then post a few of the "during construction" pics I shot along the way, with some explanation.



s6

A few construction shots:


I formed the boat tail from airframe tubing and expoxy.


The cutout for the hatch opening into the fixed AV bay, and the pod pieces.


This is the integrated baffle and fixed AV bay. The whole thing got inserted into the airframe and epoxied in. The baffle is coated in thinned out JB weld.


The boat tail attached to the airframe.

s6

A few more:


These are balsa nose cones conform shaped to fit on the top of the pods.


Here are the pods attached; you can also see the tubes that hold the wires that go from the timer to the central motor igniter.


Detail of the top of the pods, with conformed nose cones.


This is the AV bay with attachment points and such, before being installed in the airframe. It also shows the harness attachment point (which is a braided steel cable).

s6

Ok, this is how it's supposed to work - in theory anyway.

The AV bay holds an Altimeter Two that's just for data. It also holds a Perfectflite MiniTimer3. There are carbon tubes that run from the AV bay down the rocket and out the bottom of the boat tail. These hold wires from the timer output. On the pad, the three 24mm motors are wired to fire as a cluster. The timer has a G-switch that will start at lift off. I'll program a time that will allow the cluster motors to burn out and a short coast. Then the central 29mm motor will ignite and carry the rocket to apogee. Motor eject from the 29mm motor. I have in mind to use something like White Lightning on the clusters, and some form of black exhaust for the second stage.

I specifically designed this so that the second stage will fire at a fairly low altitude (400'-600' or so). The reason was that, for me, the excitement is that transition from white smoke to black and the short coast in between. It makes no sense to me for this to happen at something like 2000' where I can't hardly even see it.

Still, there is a lot of room for variation, with lots of different combinations of motors. I could easily fly this to 5000' with the right motors. It's just that the intended design was for a 500' or so first stage, and an apogee at 1000'-1600' or so.

I also "scratch built" my parachute for this - using the Vatsaas brothers design as a basic template.

I will of course post launch reports and possibly even pics/video when I get a chance to fly it.

s6

Oh, and by the way - I fully realize this is very much a "heads up" rocket. Quite honestly, I'd be pretty nervous to fly this around a crowd. I do the vast majority of my flying solo in very remote places, so it's safe enough to launch in my normal conditions.

But around a crowd is another thing. There is a lot to potentially go wrong between the time the first motor lights and the ejection charge pops the chute. And the fact that this is motor eject means that everything needs to go right on that first stage (and the ignition of the second stage).

So, I will absolutely be launching this a number of times on my own before it ever gets near a group launch. If it survives a few of those with consistent results, I'll introduce it to the public.

s6

That is certainly among the most beautiful rockets that I have ever seen. Awesome job!

Man, that is such a gorgeous rocket. I'd love to see or hear some detail on how you built that boattail. Can't wait for flight reports and hopefully video.

Very nice design and incredible results.....

Play it safe and keep that coast time short the first time you fly it.

Thanks for the kinds words, folks - I am pretty pleased with this one.

Chevis said:

I'd love to see or hear some detail on how you built that boattail.

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Not my own idea of course, but this is how I did it: I started with a short section of airframe. Then I cut a bunch of wedges out of the end of it - sort of like making a paper crown - so that I ended up with a whole bunch of points. I then pulled all those points together and secured them with tape (so I had a basic cone shape). The tubing is just flexible/strong enough that each of the bent points kinda curves down (rather than one hard fold) so that the end result is an ogive type shape. Next, I wrapped the outside with electrical tape - sticky side out (this is because epoxy won't stick to the tape - it's analogous to using peel-ply). Then, with a long brush I filled all the voids in between the points with epoxy on the inside of the piece (the tape provided the dam). After curing, I pulled off the tape and then filled all the voids on the outside of the piece with epoxy. After curing, at the appropriate point I sawed off the tip (of what was then a cone) and epoxied on a plywood centering ring. I made a short coupler (with a split piece of airframe) and used it to epoxy the tail onto the main airframe. Then I sanded/filled/sanded/filled/sanded/filled/etc. until I got the shape and surface I wanted. And, "just like that", I had myself a boat-tail.

DAllen said:

Play it safe and keep that coast time short the first time you fly it.

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Absolutely. In fact, on the maiden flight I'm pretty much planning to have no coast. I'll time it so that the airstart happens almost immediately following burnout of the cluster. Then I'll keep lengthening the coast time in increments until I feel safe/confident.

s6

Very cool! and fantastic craftsmanship.

That av bay rocks! I'm gonna steal that idea for my next build, but you've jarred my creative bug, so I'm also gonna add side rails so that the bay can be slid out the side of the airframe. Excellent job. That's a lot of craftsmanship you have invested; make sure your recovery is sound. I really like the way you isolated the main thruster from the boosters, novel. Combining the baffle and av bay, making them fit the diameter as one unit, very sweet! And of course, blending the boosters to the main body and avoiding that "cheap" slap-together look- good choice. Friggin keeeeewl rocket

I LOVE it, just like all your other rocket!

Looks so perfect...

This is a very fine looking, well thought out, expertly crafted rocket! You should be very proud taking it to a launch. Thanks for posting it.

So, today I final had the chance to put this into the sky.

Short story - it worked!

Longer story - I decided to launch this in "safe mode" on it's maiden flight by just using a single central motor. Loaded it with an G76G, and let her rip. Flight was smooth, straight and essentially trouble free. All that went wrong was the recovery harness got a bit tangled but the descent was still fine with no problems.

So for the next flight it was time to fly this as it was meant to. I chose three E18W's for the first stage, and an F40W for the second. Set the timer for a short coast, wired up all the ignitors, and crossed my fingers. Pressed the launch button and witnessed a perfect liftoff. The coast was perfect as well, and the second stage fired right on time for a nice, straight up flight. The chute popped a touch late it seemed but not too bad. Descent was nice, and the rocket landed about 300-400 metres away. SUCCESS! However, when I reached the landing spot I found a small zipper and a small crack along one fin fillet. These were not too serious so I.......

.....decided to do some quick and dirty field repairs and launch again! This time I planned to add a completely new element (for me) - videotaping the flight. I loaded the same motor configuration, kept the same timer setting, and gave my partner the launch control so I could step further away for a good camera position. This flight was ............not so great.
The first stage went fine, but it took the second stage motor a bit longer to light. This meant that the rocket started to turn a bit horizontal and when the second stage fired, the rocket did a nice powered arc such that it started to come in ballistic. The ejection delay of course was an AT "bonus delay" apparantly - something on the order of 6 or 7 minutes it seemed like. But the chute did pop at about 60-80' off the ground. I feared the worst. When I reached the landing point I was surprised and relieved to find that no damage resulted. I had taped up the zipper (from the previous flight) and all that happened was that tape got zippered a second time. No major damage.
The second element of this flight was my first ever attempt at videotaping the flight. This was a complete and utter failure. I basically missed the take off itself, almost/sort of found the rocket in the air again with a very shaky camera, and then when the second stage started to go badly I basically pointed the camera at the ground so I could watch the rocket with my eyes. There is audio of me saying, "that's not good, that's not good....." over a few times, which is kind of amusing I suppose.

But all in all a good and succesful day of launching. I flew a few other rockets, including another brand new/two stage cluster to single/experimental rocket that was even more of a success (more about that one in another thread coming soon). Hopefully I will patch up the zipper in Elvun V3 and have it ready for it's public debut at Hellfire17 in a couple weeks.

Sorry I have no vid for you all. Perhaps someone (who's not a complete video spaz such as myself) can shoot it up at Bonneville Salt Flats.

til then, thanks for watching, s6

That aft end looks smooth as....well, a baby;s but! Beautiful job!

Sheesh ,this is the first time I see this rocket of yours ,not sure how i missed it (was away for awhile)

WOW ,what great craftsmanship and a great design ,I love it !

I would love to see it fly ,an awesome sight to see no doubt.

Nice work ,you should be very pleased :handshake:

Sincerely ;

Paul T

stealth6 said:

I flew a few other rockets, including another brand new/two stage cluster to single/experimental rocket that was even more of a success (more about that one in another thread coming soon). Hopefully I will patch up the zipper in Elvun V3 and have it ready for it's public debut at Hellfire17 in a couple weeks.

Sorry I have no vid for you all. Perhaps someone (who's not a complete video spaz such as myself) can shoot it up at Bonneville Salt Flats.

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Will-do, good sir!

Ive got onboard cams, pad cams, my flightline cam and my 10fps Alpha A55 (for stills). I'll see what I can do.
See you there!

Alex

This would be a great build thread. Do you have a parts list?

You should make a clear plastic hatch for the avbay. Sort of like a clear amp box on a custom car, show off the goods.

Great build by the way, nice filets and paint.

BEAUTIFUL SIR! Don't know how I missed this one either. Outstanding build skills. Congrats on a successful flight. ---That's just about as nice as they come!!---H