Tractor Helix rocket (front engine rocket that spins) project

[georgegassaway]

I first did a “tractor” rocket around 1973. Two engines near the nose, pulling. But also, angled outwards about 30 degrees or so. Both engines ignited well, and the model screamed into the sky. Too fast, it shredded halfway into the burn. I used two D12’s, shoulda used C6’s or built a larger diameter sturdier model with stronger fins. Also a contributing factor to that model’s breakup, was that the engine pods had balsa pylons under them, to produce the cant angle. But that also acted as a canard, which I am pretty sure lead to the shred.

Below, screenshots from old super-8 film of that rocket's first and last flight. The liftoff smoke trail indicates the exhaust was canted outwards in a way that does not happen with a parallel cluster. About 1 second into the flight, one engine canard pod ripped off, the other stayed on, as seen by the "dogleg" smoke pattern when it broke up and the broken pod tumbled around still thrusting.

Anyway, the last couple of years I have been wanting to do another tractor rocket. But with a twist. Literally. With the engine mount tubes skewed to cause roll. I finally got around to that a bit over a week ago. This time, C6 power, sturdier structure, and no pylons to add to a canard effect, only the engine mount tubes.

So, this rocket is 2.22” (BT-70) tubing 34” long, with two C6-3 engines up near the nose, angled outwards. And also, skewed to produce roll. During boost, it spins and makes a helical smoke trail (as well as a unique sound usually associated with an unstable rocket spinning end over end).
Below, a view of the skew angle that causes roll, and umbilical to the left.

I flew it at the MASA launch a week ago (Oct 23rd), with mixed results. I used a 6 foot rail, but the “H” lug I used did not match that rail, so the roll torque at ignition caused the model to slide out of the rail with maybe 12” of guidance from the rail. It pitched over to about 45 degrees before “stabilizing”, with a nice helical roll. Fortunately the chute ejected before it hit the ground. BTW - at the time, I did not know what had happened at launch, I only found out at home later, watching the at-pad-looking-up camera that the model had slipped out of the rail. This is why I use at-pad and side-view cameras a lot).

Flight 2, I used C6-0’s with a bit of BP in front of them so they would eject the chute when they burned out, in case of an even worse boost than before. This time, the roll torque caused enough friction that the model went up the rail a few feet then stopped as the engines kept thrusting like a weird static firing. Then at burnout, the ejection kicked the tail plug and chute down hard enough to cause the rocket to go up the last few inches to fall off the rail and hit the ground.

So, here is a video of those two flights. Plus my “Pumpkin Surprise” rocket.




(splitting this for a 2nd message)

 

[georgegassaway]

My initial thoughts on addressing those problems, were to change the rail lug, and change the engine mount skew angles to about 1/3, to reduce the roll torque.

After posting a thread about this model on a couple of Facebook groups, a few suggested going from a rail to a rod. Well, a normal rod on the side would be problematic with the off-center spin causing major wobbling of the rod and probably a bad “rod whip” as the model left.

Others suggested a rod thru the center. Well, that would solve the wobbling, but major issues with how to eject the chute(s) out the back, with a “vent hole”. I was first imagining a complex system to duct the ejection charge directly from each motor, with two sets of 18mm tubes inside the BT-70 body tube, each motor rear ejecting its own parachute. But that would be too much of a hassle. I was thinking that changing the engine mounts for a reduced skew angle, and a better rail lug, would reduce the torque friction enough.

But a not-too-hard method finally came to mind. And then an even simpler method came to mind….*IF* I had the right parts. It turned out that I did.

Two tubes , about .316” O.D (Tube #1) and about .357” OD (Tube #2), that are a slip-fit with each other. Plenty big for a 1/4” rod to slide thru with room to spare. So, the idea was to retain the original ejection method, pressurizing the whole tube and ejecting the tail plug out the back as before (no special tunnel tubes and stuff like that). Below, the three telescoping tubes (tubing from left to right is #1, #2, and #3)

The launch lug tubing would run thru the center, aligned by two centering rings. That lug tubing would be both tube #1 and Tube #2, for extra stiffness, except that about 1” of tube #1 would stick out from tube #2 at the back. The telescoping tubing would allow having an outer sleeve (Tube #2) on the tail plug, which would slide into that projecting 1” of tube #1, and therefore maintain pressure until ejected out.

Below, the axial lug assembly before installation, in its approximate lengthwise location to the model.

Also note the short tan tube (#3) that was later epoxied into the nose cone. It slips over the #2 tube that makes up the outer section of the axial lug.

One tricky thing was drilling a hole thru the nose cone. I used a different nose than the original blunt nose, as the blunt one was going to be tricky to locate the hole in dead-center (fortunately, I never glued the nose cone on. It was taped on with vinyl tape). First I cut the tip off, a bit larger in diameter than the final hole would be, and starting the drilling process, first with a small bit, then a larger one. As it is, I drilled the hole larger than needed, to fill in later with epox (I found yet a third tube, a tan coupler, that telescopes over tube #2, to glue into the nose cone as a sleeve, while being aligned over the axial lug).

The centering rings were not “tricky”, mostly easy steps (since I had the right tools on hand), but it took a number of steps. Two centering rings out of 1/32” plywood. I used my arc-scribing method to cut the rings. Took about 60-90 seconds of arc-scribing to cut each hole/disk. http://georgesrockets.com/GRP/Articles/CentRings/Rings.htm

After making the BT-70 discs that would become rings, I drew reference lines for locating the four 13mm vent holes, and arc-scribed those holes. I did not have an arc-scribing tool for the diameter of the center hole needed to align the lug tube #2, and did not want to make one. I taped the two rings together, making an alignment mark for later use. I used a round file to enlarge the hole a bit. Then used a couple of different tapered Dremel grinding bits to enlarge the center hole. This was done in a manner to try to keep the hole concentric with the taped together rings. Finally, got the correct diameter to match the outer tube (#2).

And it was “easy” from there. Gluing the centering rings to main lug tube #2, after determining where I wanted the rings to end up inside the model (and using the reference marks so that the rings were aligned. This way, if the center hole was slightly off center, the center lug would be parallel to the body and not at an angle). Modifying the ends of some tubes to either be rounded, or funnel-like, to assist with aligning and plugging them together.

After the lug and centering ring assembly was inside the model, I drilled a hole into the balsa tail plug (1” long balsa tube coupler). The hole a little bit oversize, to allow a short segment of tube #2 to be glued centered into it (while it was plugged into the model for proper alignment), and the gaps filled in. This was the last step of assuring no leaks during ejection, that short piece of tube #2 sliding over tube #1 that extends about 1” from the back of the 34” long tube #2.

So, it took few steps to get there, but not tedious, and relatively easy. Pretty much as I had imagined in that "A-ha!" moment.

Since there is now a lug in the center of the tube, I cannot count on wadding to help eject the chute. I set it up for my “Semi-Drogue” method. A small and loosely packed chute attached directly to the base plug, making sure the drogue gets ejected out, and then to help to pull out the main chute. And the main chute packed in a slim manner so it can slide out easily.

 

[georgegassaway]

Weather forecast for Saturday was pretty good, low wind, and not too cold. I was going to fly from a local field, which the original forecast wind direction would work with. But the wind blew more towards the East, and that local field would not work. So, I went to another field far away. Only to find when I got there that it was being used, lots of people there, no good. So, “Plan C”, a field in a huge new home construction/development area (with a lot of empty space).

Flight 1, both C6-3 engines ignite, model starts spinning as it moves up the rod and is vertical as it leaves the rod. Yay….uh wait, it is dragging wires with it and slowing down! The umbilical set-up failed, allowing a clip to grab a fin, and the wiring wraps around the spinning body. So, the model gets up to about 20 feet then is dragged back down. It hit nose-first, landing in soft dirt, causing superficial damage. If I build another version of this, I will use highly swept back fins (kind of ASP-like) that would not grab any clips.

So…… a change from a single umbilical about 18-24” away, to two umbilicals about 3 feet away. Fortunately I had a 6 foot fiberglass post for a 2nd umbilical and the ground was soft enough to push it deep enough to hold well. Also, fortunately, I had enough excess wiring on hand to make a super-long “Clip Whip” to have twin umbilicals that far apart.

I felt that the new umbilicals would solve that problem, and the first part of flight 1 seemed to go very well as far as spin-up and leaving the launcher. So, for flight 2 I stuck with the original plan. CHAD-staged C6-0 to C6-3! Got the model prepped, cameras ready, Mavic up in the air recording, started the ground cameras and launched. It took off very nicely, weathercocking a bit into the wind (I had also tilted the pad a bit into the wind to be sure the model would not drift close to a tree line downwind). It spun well, then the C6-0’s Burned out and the C6-3’s took over. It got mostly horizontal by burnout, but it was plenty high up. At ejection, the tail plug popped out, the 12” drogue chute came out, and so did the 18” main chute.

The TRACTOR HELIX!

I was surprised the model descended a bit slower than I expected (I was wanting to use a 24” chute, but the 18” was the only reinforced plastic chute I had . Fabric chutes are too thick when folded to fit into the limited space due to the launch lug tubing in the center, and the need for the chutes to slide out easily). So, recovery was very good and it landed safely. An odd thing, the roll rate seemed to decrease a lot near the end of the burn of the upper stage C6-3’s. The fins are on straight, no counteractive aerodynamic roll forces, so that was odd.
Note the Semi-Drogue system, 12" Estes drogue chute and 18 (red) main chute.

Unfortunately, the iPhone I used for the side view camera, did not record either flight, memory was full. So, my only videos were the at-pad camera and Mavic Airborne camera. But, a passer by shot video of flight #2 and was nice enough to share it with me (he might show up at the next MASA launch).

I had the Mavic up too high to get good views of the launch (360 feet up on flight 1, about the same for flight 2). I had hoped for the model to fly more vertically and ascend more towards the Mavic (very very tiny chance of collision). Even what you see in the video is closely cropped (well, zoomed-in a lot), which is why the resolution is not so good (the above screenshot is cropped even tighter). But you can see the initial spiral/helix at launch, and in flight #2, the way the helix actually tends to flatten out a bit as it gains more speed while the roll rate does not seem to increase a lot after the early part of the launch.

Below, screenshot from the at-pad camera, looking up

The axial lug set-up works very nicely. And by giving more attention to the umbilicals, it should be a pretty reliable flier as long as both engines always ignite and perform properly.

Ironically, I expected cluster ignition to the the most likely problem, but it has been fine. I risked using old (good ones from the days of pyrogen) Estes Solars last week. This week not taking any chances, I used Quest Q2G2 ignitors (going to get some e-matches that fit Estes nozzles, and save the OOP Q2G2’s for more important things).

So, it took three flights and a major upgrade to make it work well. I like the final result. And also glad I did not reduce the skew angle as I was thinking of doing, before realizing a not-too-hard way to mount an axial lug in it.

Onlly after getting home, did I realize a big reason why the wiring got hung on the model on flight 1, and why the farther-apart umbilicals for flight two were lucky not to have the same problem. When I used Estes Solars, I used the normal nozzle plugs, and when the engines began to ignite, the plugs popped out, releasing the ignitor (Also on those rail flights, the model could not spin until after launch). With the Q2G2's, I did not trust the plastic straw friction method. So, I used window putty (sort of like clay), and put a strip of scotch tape over the nozzle to hold them in from coming out early (the scotch tape melts easily, which is why I do not use masking tape for that). I now realize that method caused the ignitors to stay with the engines for a lot longer time than it takes for Estes plugs. Also, the fact that it was staged, with the engine nozzles much farther apart, may have had a big effect in preventing tangling. So I still need to come up with a better way. I plan to go with e-matches that fit Estes 18mm engines, but I do not have any yet and and not know how I may need to secure them. I might end up adding some SIP pin/socket sets to the ignition leads, with the wiring taped securely, so that the pins will unplug with a small amount of force pulling on then. Or, perhaps the M.R. e-matches I mentioned may fit a SIP socket well enough to do that directly and avoid clips.

I will probably fly this model mostly single stage, and only do staged engines once in awhile (when it’s calm enough).

Here is a video for the two Oct 30th flights:

 

[georgegassaway]

So, there is film of the 1973 tractor rocket flight and shred. From my Prang Film #1.Starts at 9:25

 

[SecondRow]

Oh, man. That is cool.

 

[KenECoyote]

Amazing and fascinating!
Believe it or not, yesterday (or the day before) I was thinking of forward canted tractor motor designs!
Now I'm wondering about your design on a spinning fin can...
However I digress - very cool design and launch and I cant () wait to see more!

 

[Daddyisabar]

Amazing and fascinating!
Believe it or not, but yesterday (or the day before) I was thinking of forward canted tractor motor designs!
Now I'm wondering about your design on a spinning fin can...
However I digress - very cool design and launch and I cant () wait to see more!

Beware! Mindsiming canted tractor designs can lead to the dark side! Combined with canted fins! A real screwball! Spinnerella!

 

[Daddyisabar]

Central lauch lugs, canted and staged tractor motor clusters! My inner RSO is in toil!

 

[Daddyisabar]

I have had good luck with really long clip whips. The weight brings the leads down along with the motor thrust pushing them down and out of the way very quickly. All the clips are wound with tape to avoid catching any silly oddroc bits that might be hanging out. Tractor motors rule!

 

[georgegassaway]

Central lauch lugs, canted and staged tractor motor clusters! My inner RSO is in toil!

At the MASA club launch on the 23rd, all the people who do RSO duty were quite excited to see this one fly. Or.... try to fly (in the case of flight 2).

I had mentioned to Neal Higgins, who is an extremely experienced RSO, that I had some test flying of some gliders that were #1 priority, then flying the Tractor rocket was priority #2. He replied, that for everyone else, flying that Tractor rocket was priority #1.

Oh, fun thing I did when I revealed it to a few people. I had said on the MASA Facebook group, the night before, that I planned to fly a new unique cluster rocket. I put the rocket under my arm, nose to the back, tail forward. I said “Here’s my cluster rocket”, and in the tail ,where they expect to see engine mounts....there is just a BT-70 balsa plug. Giving them about 2-3 seconds of puzzlement, then I took the model from under my arm and showed the nose section.

Oh, BTW, if one is gonna do a tractor rocket, it’s a good idea to make it roll at least some, to even out thrust variations. Maybe not so extreme as I did......

Safety-wise, the “obvious” risk is what if only one engine lights. Probably not a good day. Though that can be true of other twin engine clusters when only one lights. Though it would tend to roll, so it might stagger into the sky, but probably not get high enough for the 3 second delay to eject in time. I’m going to get some e-matches that fit C6’s, as an alternative to the very limited number of Q2G2 igniters I have left, but was willing to use for the last two flights. Those e-matches should be able to release from the nozzle way quicker than what i did to secure the Q2G2’s.

 

[BABAR]

very cool. Not a tractor design but another up the middle model

 

[georgegassaway]

Long long ago, 1980’s, maybe even 1970’s, I saw a photo of a finless rocket with skewed engine mounts to make it spin, and rod up the center. Photo in a magazine or newsletter (do not recall info on whether it worked).

So, how well does that fly? Any video?

 

[Daddyisabar]

Tractor motors rule! 3-4FNC drule!

Q2G2s rule! Starters drule!

Pendulum theory rocks! Modern aerodynamics socks!

 

[Daddyisabar]

Long long ago, 1980’s, maybe even 1970’s, I saw a photo of a finless rocket with skewed engine mounts to make it spin, and rod up the center. Photo in a magazine or newsletter (do not recall info on whether it worked).

So, how well does that fly? Any video?

That was pre VHS and pre MTV so I doubt much exists from those ole tyme days!

 

[Daddyisabar]

It would be cool to put super long red and white streamers on the fins and see if you could get a nice candy cane or barbers pole effect off the pad.

 

[Charles_McG]

As I understand it (which is incompletely), roll has the effect of showing an angle of attack to the fins - which they will try to damp out. So the faster the rocket is going, the harder it is to induce a spin with applied torque.

Tim Lehr first pointed this out to me when I was showing him my 1/5 scale Black Brant 11a - with 13mm spin motors. He said he's tried it over the years, and it doesn't work like you'd think. I attempted to estimate the magnitude of the effect from figures available in the details of OpenRocket sims - but as a biochemist, I'm not really equipped for aerodynamics.

 

[boomtube-mk2]

http://d23sq69wqfvv5f.cloudfront.net/sd/54dab338449d350b60175a84.mp4

This is Peek-a-Boo also a twin canted motor (24mm) I built as a means to loft a video-camera installed in the lower body-tube between the fins.
The idea was to provide a view without any motor exhaust and pointing down during both the ascent and decent stages of flight.

Sadly I never got around to doing that.
I built a thingamabob that routed the igniter wires from the launchpad up and to either side of the rocket, thus keeping them out of the way.
Worked perfectly.

 

[beeblebrox]

Long long ago, 1980’s, maybe even 1970’s, I saw a photo of a finless rocket with skewed engine mounts to make it spin, and rod up the center. Photo in a magazine or newsletter (do not recall info on whether it worked).

So, how well does that fly? Any video?

Ace Rocket Manufacturing made a kit 4" dia. with central launch lug and two canted motor mounts. I do not remember the name of the rocket, but had seen it fly in the early '80s... Still hunting for photos... I sent a message to Korey Kline to find out.

 

[georgegassaway]

As I understand it (which is incompletely), roll has the effect of showing an angle of attack to the fins - which they will try to damp out. So the faster the rocket is going, the harder it is to induce a spin with applied torque.

Well, the angle of attack is greatest at launch, when it is not moving fast but already rotating fast. Then as the rocket moves faster, the fins "see" a lower angle of attack....as far as the airflow goes. But I certainly do expect for the fins to limit the spin rate (I think of it as a paddle wheel effect, if you spun the rocket on the pad withoiut moving upwards, the air drag of the "paddles" (fins) would increase the faster it spins. If I used smaller fins, particularly less fin span, then the "paddle wheel drag" effect of limiting the rotation would be less.

Not sure I get why it would slow rotation at higher speed, But that does seem to be what happened during the second stage burn. Hmmm..... do I have a small altimeter that can record roll rate?

I did theorize a trick that could be done for the heck of it. Use spin tabs on the fins te other way, to oppose the thrust induced roll. So it would roll one way at launch, slow the roll, stop the roll, then roll the other way the faster it got (aerodynamic forces increase with the square of the velocity, so the increasing aerodynamic roll torque would be exponential rather than linear).

 

[georgegassaway]

It would be cool to put super long red and white streamers on the fins and see if you could get a nice candy cane or barbers pole effect off the pad.

To do that well, it would be better if there were dowels sticking out 12" or so from each side, otherwise the streamers might just twist into a "rope". But the issues with ignition leads tangling would be even more so.

That is a nice idea though for a purpose-built rocket that is not a tractor, with a 2 engine cluster at the back that is skewed (or to avoid the need for an axial lug, use spin tabs to make the rocket spin shortly after liftoff).

 

[Daddyisabar]

OMG! The Perfect Cheer! Roll to the left, Roll to the right, stand up, sit down, fight fight fight! Would make a great SNL skit!

 

[Daddyisabar]

To do that well, it would be better if there were dowels sticking out 12" or so from each side, otherwise the streamers might just twist into a "rope". But the issues with ignition leads tangling would be even more so.

That is a nice idea though for a purpose-built rocket that is not a tractor, with a 2 engine cluster at the back that is skewed (or to avoid the need for an axial lug, use spin tabs to make the rocket spin shortly after liftoff).

Motors at the bottom of the rocket would burn off the streamers. Motors on top rule. Twisting the streamers into a candy cane or barbers pole "rope" is the whole point. Getting the leads to fall away is part of the trick but it will work, even with mid cant motors like below. Crazy.

Given the extreme cant angles of you motors the streamers would be real safe. Dragging up silly things with tractor motors is cool! A mid core rod placement wouldn't matter. Those extreme cant angles will give real rocket scientists nightmares due to the loss of efficiency. Putting on more drag with silly streamers might just push them over the edge.
Oddrocs rule!

 

[georgegassaway]

Motors at the bottom of the rocket would burn off the streamers. Motors on top rule. Twisting the streamers into a candy cane or barbers pole "rope" is the whole point. Getting the leads to fall away is part of the trick but it will work, even with mid cant motors like below. Crazy.

For a spinning model to pull up different color streamers to create a barber-pole type effect I didn’t mean for streamers to be attached to fin tips anyway.

I specifically referred to having dowels (well maybe 1/16” music wire) sticking out at least 12” (longer = better) to get good distance between the streamers, at the tail of a rocket with skewed engines at the back. And that would solve the burning problem.

Otherwise the sttreamers would just get twisted up like a “rope”. Well, you said twisting into a rope is the idea.... well.... that's one way. But that would not interest me as much as seeing streamers widely apart. I'd like an effect more like a plane with trailing smoke off the wingtips, you could really see the helix pattern. A few times, I flew my R/C Gliders with 15-20 foot long 1" mylar streamers on the tips, a neat effect.

Although, the drag of the streamers would really resist the roll torque of the skewed thrust the faster it got. So such a model might need spin tbs as well (or as I also said, maybe not use skewed engines, and use spin tabs only, to avoid the axial launch lug complication).

There is a really neat way to stabilize a rocket with streamers, that is not done much, but it works. Imagine say a plastic baseball with an 18mm engine mount in it. Instead of fins, mount three pieces of music wire, about .039” dia, where they stick out 6 inches and are swept back 30 degrees to 45 degrees, with a loop at the bottom end. Then attach a 3 foot long streamer to the end of each wire loop. It will fly very stably, so stable it will weathercock into the wind. And also be so draggy that it could use “pre-deployed streamer recovery”. Because I’ve seen a few that didn’t eject anything….except sometimes eject the motor (light models not easily damaged, of course). Never saw one burn off a streamer (these type models do require special care for liftoff to be sure the streamers will not get into the exhaust during launch, also care to not get tangled with anything during launch).

Anyway, that is an example of streamers being widely apart, which do not burn (And Jim Flis has flown a model that has 8 or more streamers trailing off of it, but it’s a bit Flying Saucer-ish so the rocket is stable anyway, the different color streamers are for fun, the key reason to fly that model (streamers incredibly long, like 50 feet.)

 

[Daddyisabar]

With tractor motors you don't need wires or stinking fins! With no spin you could pull up a banner. One with the picture of Comrade Stalin on it would be cool. Or even a buff shot of Putin would be the ticket in today's world of Russian personality cults. Tractor motors are tight! Pendulum theory ruled for a thousand years!

 

[georgegassaway]

Flew the Tractor Helix rocket a few more times at the Nov 20th MASA launch.

Due to the club’s set-up at the field, one of the side umbilical posts I used was a soccer goal. The other was a pad with a rail when nobody else needed to use it. I had a couple of long rods to stick into the ground, but those were more convenient and secure.

Flight one went very well, mostly vertical, in wind of 7-9 mph.

Flight two was Chad-staged, using a C6-0 taped securely (Scotch tape) to the upper C6-3, in each mount.

It took off and weathercocked some. It is more nose heavy with two extra engines up front, so that may account for a good bit of that. Anyway, also, at staging it “veered” a bit, to make it get even more horizontal. Later, I saw from the at-pad-looking-up video, that one engine staged 7 frames before the other engine (that’s about 1/4 second difference, which is a pretty big mismatch for the high thrust spike of the engine that staged first). So, it may have by coincidence pitched more horizontal due to the direction it was rolled (meaning, if the opposing engine 180 degrees away had staged first, it might have actually veered a bit back towards vertical).

And definitely it stopped rolling during the second stage burn. Not only does the smoke trail stop being a helix, but the pulsating thrust sound goes away into a constant “normal” thrust sound at high altitude. Weird. The same had been noticed on the previous CHAD-staged flight, but the at-pad camera did not show that as clearly (both staging “puff” moments) as with today’s flight 2.

Fortunately, it ejected before hitting the ground, landing far away mostly upwind. Definitely if I stage it again as-is, it will need to be pretty calm. Or else do the C6-0 to C6-0 (with BP charge) trick. If I really want for it to keep rolling when CHAD staged, I’d add some spin tabs to the fins.


Flight three…..actually didn’t happen but I call it that anyway. Only one engine lit, and…….it stayed on the pad. That was a good surprise, that it didn’t get into the air, so no damage. It was not the ignitor’s fault, it was a clip whip not making the proper electrical connection to set it off, I did not double-check it as I should have.

Flight 4, one of the e-match ignitors was the same one that did not fire before, because it was not at fault. Single stage, two C6-3's. Ignition was great, and it took off very well for a mostly vertical flight, best so far.

The chutes have gotten worn out (Main chute lost half its lines even though it’s a reinforced over-the-top type chute. Just….old and worn out. Like, one is 10-15 years old, and I borrowed the 12” chute from a model built in the early 1990’s). So I need to make new ones before it flies again. And the next club launch won’t be till late January. Do not say nylon/cloth chutes, the chute packing space is way too limited due to the axial lug running thru it.

These flights were my first time using e-Matches that fit model rocket nozzles, from MJG Technologies (they say they fit in 13mm BP engines like 1/2A3, have not tried yet). They worked great for this model, so no more using precious OOP Q2G2 ignitors. They come in 12” & 36” lengths, for 3 cents more I went for 36” since this model can make good use of that length for the twin umbilicals so far apart. https://electricmatch.com/roc.../see/23/6/bp-rocket-starters.


To help make sure of a “clean” separation of the e-Matches when the engines ignited, I could not use tape to help hold them (that was the prime cause of taking up the leads a few weeks ago). So, I used a window putty sort of like modeling clay, but it does not melt in sunlight in summer. On a cold day like this, it is stiff and did not stick to the nozzles too well, but I managed to get it to work out. Though one time, the wind eventually caused one to wiggle out.

I was surprised to see in slo-mo of the at-pad video for flight 2, Chad-staged, that the model started to rotate the opposite of normal, as the motors began to ignite. Then I realized the putty plugs were causing exhaust to vector a bit sideways for a moment, and the CHAD staged nozzle distance gave extra leverage to cause the roll the opposite way for a moment. But that had no effect on flight, the model was rolling the other (normal) way before it moved much up the rod. The screenshot below, you can see the moment of ignition, with exhaust being momentarily deflected by the putty (note the sideways engine exhaust at upper left, and non-parallel flame at lower right).

Yet again, the odd stuff you sometimes see with an at-pad camera view like that.

I had tack-glued the axial lug assembly in, and it has come loose, sliding out at ejection (the two 1/2” vent holes are not big enough. I kept sliding it back into place. And the fit with the nose cone’s sleeve tubing (Tube #3) is not good anymore. So I need to do some overhauling of that lug system. What I really wish I had was a stiff fiberglass tube (more like arrowshaft or kite spar, not rocket tube), that was a bit more than .25” I.D, and some sleeve tubing to fit over it, rather than the paper tubes I have been using. But shipping is cost-prohibitive to order just a couple of such things (No, Amazon, I do not need to buy 12 arrowshafts for $49 with free shipping, even if the I.D. was right. Or buy one from elsewhere for $15 shipping).

I’m really happy with how well this model flies.

So, yes, of course there is video.

 

[Daddyisabar]

I have to agree with the little girl in the crowd who you can hear saying "That's Crazy!" on the YouTube video.

Hard to get precision staging when you go CHeap And Dirty!

 

[georgegassaway]

Hard to get precision staging when you go CHeap And Dirty!

Thing is though, with two C6-0's from the same pack, they ought not to be as far as 1/4 second off in burn times. Although looking at the at-pad camera frame by frame it does seem one engine ignited about 1 frame (1/30 sec) later than the other, but still does not account for such a big mismatch at staging time.

 

[Sandy H.]

Thing is though, with two C6-0's from the same pack, they ought not to be as far as 1/4 second off in burn times. Although looking at the at-pad camera frame by frame it does seem one engine ignited about 1 frame (1/30 sec) later than the other, but still does not account for such a big mismatch at staging time.

I know you've been a prolific flier and innovator for years and really like this rocket. I'm curious if you've ever measured the mass of motors from the same pack to see if there were weight differences that were significant. I haven't, but at times in my day job mass (even to 0.01 gram or less in my big machine world. . .) can be an indicator of go/no-go.

Purely looking for validity-of-test based on your experience, not suggesting a change in methodology.

Best Regards,

Sandy.

 

[Daddyisabar]

Cluster ejection charges can go pop, pop...pop! Just think of all that happens on a staged cluster. One motor can easily light a bit late, burn a bit longer, burn through the top a little slower with a bit less pressure and heat, maybe taking a burning chunk a bit longer to find the sweet spot to ignite the upper motor, etc . So many variables they can all add up to a disastrous delay. Cheap and dirty is not NASA style rocket science. Precision electronic ignition with all around, high end gear is the cool dude way to go. Blind them with science!

 

[lakeroadster]

@georgegassaway you sir are a steely eyed rocket man... just sayin'. What an awesome rocket!