Wow! This is a great resource that you've created, Mark II! If I could indulge you for just one more TIFF-to-PDF conversion, I forgot the Estes Mini-Scale Combo Pak (#0874, see: http://www.spacemodeling.org/JimZ/est0874.htm ), which contains break-apart recovery scale models of the Exocet missile and the I.Q.S.Y. Tomahawk sounding rocket. (These rockets got particularly positive reviews on EMRR, see: http://www.rocketreviews.com/review...calecombo.shtml .) To my knowledge, this completes Estes' line of break-apart recovery model rocket kits.

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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

Your wish is my command...

0874 Estes MSCP fin patterns
0874 Estes MSCP fin marking guides
0874 Estes MSCP alternate fin patterns and fin position guide #1
0874 Estes MSCP fin position guide #2

MarkII

Attached Files

	est0874 Estes MSCP fin position guide02.pdf (110.8 KB, 91 views)
	0874 Estes MSCP fin patterns.pdf (32.6 KB, 97 views)
	est0874 Estes MSCP fin marking guides.pdf (58.5 KB, 84 views)
	est0874 Estes MSCP alt fin patts & position guide01.pdf (88.5 KB, 107 views)

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SAM # 0011

Mark, I agree with Black Shire..... great stuff.

I used your .pdf of the Sky Bird II (why do I now have one of the songs from the Jonathan Livingston Seagull soundtrack stuck in my head, I wonder...) to confirm that my printing 24% of "actual size" out of Preview on my Powerbook yielded the correct result.

I have an interpretation of the Sky Bird II much as I was musing about earlier well underway. I think I'm going to cut a second set of fins - these out of firm 3/32 inch balsa - since the 1/16th ones seem a bit thin for the way this is going to land (even though that's what's called for in the plan). It should be flyable but not finished for 1/1/10...not that the weather looks like it'll cooperate.

If this one works out well I'll also make a slight downscale using ST-8 tubing fitted with a 13mm motor mount for flying in a nearby elementary school playfield.

BEC - 3/32" would be something to try; use hard C-grain balsa. You can also paper the 1/16" fins using either 20 lb. printer paper or Tyvek from USPS Priority Mail envelopes. (Free from your local PO!) That will give them more toughness and resilience and make them much less likely to split.

One idea that might have some application with break-apart recovery is break-away fins. These are used extensively with water rockets, which often don't have very sophisticated recovery systems. The idea would be to have each fin attached at the root to some sort of small, narrow sleeve that attached to the airframe and held on well during boost, but then snapped off (the holder, not the fin itself) when it received a sharp blow from the side, such as hitting hard ground when it landed. The holder and fin combination absorbs the impact by snapping off the airframe, which spares the fin from actual damage. Any fins that have broken away can then simply be snapped back onto the airframe for the next flight.

One thing to keep in mind, though, is that all of the designs that Black Shire has talked about are very small and very lightweight. Most, if not all, are minimum diameter BT-5 designs (Estes called them Mini-Brutes); some are so small and light that they could be launched with Micromaxx-II motors. (That is definitely true of the Super Flea, for one.) And the break-apart tumble/flat spin recovery method will slow down the descent a fair amount. As long as they don't impact on rock or concrete, I don't think that they will be at that much risk for damage. (Maybe the Jammin'/Lumina and the Sparrow might, on an especially bad day or as a result of a power prang.) Several of these designs use fiber (i.e., thick cereal box-type cardboard) fins which will not split. They will weaken if they are bent, though, but thin CA can be applied to them to stiffen them back up again. If you have these designs land in a grassy field, I doubt very much that you will see any damage. I have seen how much the tumble recovery method of the Astron Scout and the Sprite slow them down; the break-apart method should be even more effective.

MarkII

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SAM # 0011

Thank you very much! I also added the JimZ plans link for these two kits to my original posting, so that all of the Estes break-apart kits' plans links will be there in sequential (catalog number) order. As of Wednesday afternoon, Semroc was making eight custom sets of laser-cut Lumina and Sparrow fiber fins (four sets for each rocket) for me.

BEC, I'd go with the 3/32" balsa for the Sky Bird II fins as you suggested...although as Mark II wrote, paper/glue-laminated 1/16" fins might be strong enough for this application. The 13 mm mini motor-powered Super Flea and Mini Tri-Pak break-apart recovery rockets can go with 1/16" balsa fins because they are so small and light, but the Sky Bird II has considerably more mass than they do.

On grass or soft soil, though, even the larger and heavier Sky Bird II, Lil' Tinker, and Mitosis should touch down unscathed. My old Astron Mark II never suffered any damage when its mid-body ejection streamer jammed inside the model's forward section, even though my flying field was hard red clay and was bristling with hard corn stubble after the harvest.

One could become "spoiled" by these break-apart recovery models. It's so nice to not have to search for a landed rocket, but to just stand at the launch pad and note, "There it is!" and then walk just a relatively few paces to retrieve it. :-)

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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

There is one thing to be careful of with break-apart rockets. I built one of my own design and tried it out. It flew fine, and at ejection it separated at mid point like it was supposed to. Problem was that the front section, after ejection, is tip heavy. Think about it - we want the CG forward of the CP for stability, so the nose has to be a bit heavy to begin with. It came down with the nose cone pointing straight down and when it hit ground, the nose buried itself into the soil. The design was loosely based on the Sky Bird II and used BT-50 with a PNC-50Y nose cone (the long parabolic from Estes). As it came in, the nose lead the way, pulling aft fin can/burned out motor section behind. It was definitely a "Heads-up flight".

Greg

Mark,

I'd thought of papering the 1/16 fins - another new technique (for me) to try. But get-there-itis will probably have me going 3/32. What I have is fairly firm B grain stuff - though the 1/16 fins I've already rough-cut is closer to C-grain but of medium density. Being an electric-powered specialist from back in the days when it was hard to do and every gram mattered means my balsa stash is mostly towards the light (and therefore soft) end of the spectrum. Also, as Black Shire noted the Sky Bird II is toward the heavy end of the models he pointed us to - it's BT-50 based.

Greg,

An interesting thought about the heavier nose. As Black Shire noted these models tend to have a short aft section, not break near the middle of the body. In the case of the one I'm working on the aft section is 4 inches long, the forward 7.75 inches long. The forward section with a light Quest blow-molded nose cone in the T-25 tubing actually balances almost in the middle of its overall length. I should see where it balances with a BNC-50K in it before I committ to one or the other. I can see where making this type of model actually work correctly takes a little care.

Black Shire,

The Mitosis plan calls for 1/8 thick inch fins!

BEC, I had not noticed that feature of the Mitosis--the only other "A" - "C" powered model rocket designs with 1/8" thick fins that I know of (if memory serves) are/were the Estes Big Bertha and Estes Ranger!

Although I prefer to use parachute recovery for larger rockets such as the Estes Big Bertha and Quest Big Betty (to protect their downward-protruding fins), such large area-to-weight ratio models will usually land unharmed if they come down in "accidental nose-blow recovery mode" when their nose cones eject but their parachutes jam in their body tubes (or fail to open). My father's Big Bertha made several faster-than-normal but damage-free landings in this way. G. Harry Stine even mentioned this capability ("However, you occasionally see nose-blow used on large models with a high area-to-weight ratio.") in the section on nose-blow recovery in the "Handbook of Model Rocketry."

Greg makes a good point. My Astron Mark II, when its streamer jammed, fell in a horizontal attitude in a flat spin, with both shock cord-connected sections also rolling about their longitudinal axes. This was just a lucky chance CG/CP relationship for this streamer-equipped model, but it was one of the three ways that a properly-designed break-apart recovery rocket should descend (another common way is the same, except that the spinning motion is in a vertical plane or some other non-horizontal plane). The third type of motion is a nearly-horizontal tail slide (which is actually a low Lift/Drag ratio glide!).

The mini motor break-apart recovery models that eject their nose cones (Lumina, Jammin', Sparrow, Star Dart, I.Q.S.Y. Tomahawk, Exocet, etc.) go either into the combined spinning/rolling motion or into the tail slide type of descent. My MRC Wildfire (see: http://plans.rocketshoppe.com/mrc/m...7/mrcTR-107.htm ), which was like a stretched Estes Alpha III with a longer nose cone, would make huge circling tail-slide descents when its parachute occasionally got stuck in the body tube (but the nose cone and some of the shock cord were ejected). Long rockets tend to have this trait, and *really* long rockets such as the Estes Mean Machine and the MRC Big Ben (http://plans.rocketshoppe.com/mrc/m...0/mrcTR-110.htm ) would probably be great "tail-slider" break-apart recovery models!

__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

Happy New Year! (12:20 AM PST).

My almost-Sky Bird II is a few glue fillets and a tied-to-the-upper-section shock cord away from flyable. I'll get the second round of fillets on it before going to bed.

Final configuration:

Body cut from Quest T-25 to the plan lengths. Engine mount made from BT-20 from a supplier I don't recall (brown, not white), Semroc AR-2050 (top) and AR-2050S (bottom, flush with aft end of main BT), HR-20 mylar ring and a Quest motor hook. About 3 feet of kevlar line for a shock cord, with the lower end looped around the upper end of the motor hook. Quest plastic ogive T-25 nose cone a press-fit-with-blue-tape for now. Shock cord upper end will be tied to its attachment rather than glued to the tube as in the plan. Fins of firm B-grain 3/32 balsa.

The weather for New Years Day in the Seattle area does NOT look particularly flyable either for rockets or for RC airplanes (which means the Flaming Geyser Flyers' New Years Day fun fly will likely be postponed at least a day - *sigh*)

Regarding Greg's point, perhaps the thing to do is to insure that the break-apart designs have sufficient stability without being too nose-heavy. In addition, we can also make sure that we build them so that they separate right at the burn-out CG point, so that both halves are roughly equivalent in weight at separation. This can help prevent a situation in which one half leads the other half all the way to the ground as Greg's rocket did. The designs that Estes actually produced are probably OK, but we might need to modify any one of them or the EIRP designs in order to nudge the break point to this location. It is the CG location when the motor is all expended that is important here.

Having equal masses won't necessarily always enable both halves to remain in a horizontal orientation all the way to the ground, though; aerodynamics will also factor into the equation. If one half is significantly more streamlined than the other it can still end up leading both halves to the ground. So balancing the respective CPs of each half might also be necessary, if that is even possible or practical. RockSim might help here, along with good old trial and error, in any effort to balance the lift and drag of each half as well as balancing their masses.

MarkII

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SAM # 0011