V-2

Fin dimensions I knew I could get either from scale data or by reducing/enlarging the patterns from a kit. While I do have a copy of Peter Alway's Rockets of the World which has extensive scale info on the V-2, it is primarily concerned with the US examples and the drawing dimensions aren't condusive to design. When I went looking for other sources of info, I found The V-2 Rocket Page, which is, while still under some construction, the final word in German V-2/A-4 data. This drawing from that site gave me all I needed to size the body tube length (5.5") and draw the fins in RockSim, and the illustration at right of the world's simplest operational paint scheme made my desire to do an authentic German V-2 seem prophetic.

Even though I already had the fin templates (the first indispensible feature I've found in RockSim), I investigated the V-2 kits that were or had been around. Here's what I found:

Maker	Kit #	Avail.	Body Tube	Dia.	Len.	Scale (approx.)	Weight
Apogee	5021	current	BT-20	0.736"	6.75"	1/82nd	0.35 oz.
ASP	KV2-13	current	BT-50	0.976"	7.75"	1/67th	0.88 oz.
ASP	KV2-18	current	BT-55	1.325"	11.125"	1/49th	2.3 oz.
ASP	KV2-24	current	BT-60	1.637"	14.125"	1/40th	3.7 oz.
Centuri	KS-19	1969-1971	ST-16	1.64"	14.2"	1/40th	2.1 oz.
Dynacom		current		5.13"	43.38"	1/12.75
Estes	K-22	1965-1977	BT-55	1.325"	11.2"	1/49th	1.4 oz.
Estes	1267	1974-1981	BT-101	3.938"	33.5"	1/16th	12.6 oz.
Estes	1926	1984-1987	BT-80	2.6"	22.4"	1/25th	4.9 oz.
Estes	1952	current	BT-101	3.938"	33.5"	1/16th	12.6 oz.?
LOC	PK-85	current		5.54"	48.0"	1/11.5	4.9 lbs.
LOC	PK-100	current		7.67"	65.24"	1/8.5	12 lbs.
MTR		current		9.25"	78"	1/7th	26 lbs.
MTR		current		11.5"	93"	1/6th

While the Centuri ST-16 isn't exactly a BT-60, it is very close, so my model is most like that kit, though that one was about ¼" longer. The ASP BT-60-based model sports a 24 mm motor mount (with an E15 recommended motor, too!), unlike my 18 mm; there must be over an ounce of nose weight in that bird!

I had briefly considered doing a scale of the Russian R-2 (SS-2 SIBLING), a stretched version (17.7 meters .vs. 14) of the V-2, that would have eliminated most of the nose weight requirements. Performance would have been about the same, though, and I hated the idea that I would always have to be explaining what it was, so I dropped the concept. I include a rough RockSim file for the design at left.

While I did design them in originally, I eventually deleted the small, square shoulder on each fin trailing root edge that housed the gas vane electroservos. My motors are installed flush with the end of the tail cone, and I was afraid the plume would burn them off, anyway. The Estes nose cone is ogive, not the LH series used on the original, and the tail cone turned out to be too short, but she does look like a V-2.

Even though I had promised myself I wasn't going to go overboard on this project, I wound up with four coats of paint on her. I primed her with Kilz spray sealer/primer, then added a coat of Krylon sandable grey primer. On top of that I laid down a color coat of Testors olive drab spray enamel (the same I'd used on my Sidewinder nose cone, and a tip of the hat to Robart for their fine hobby paint shaker), and a final color coat of Krylon moss green. The yellow stripe was done with a strip of Pactra trim tape. While not as dark as the operational round, she'll still be a pain to find in tall grass.

All this paint added a lot of weight, and I wound up having to add another three grams of nose clay to get the empty Cg where I wanted it to be. I'm not sure that my L/D-as-margin-requirement rule of thumb for short birds (you only need as much margin as the L/D divided by ten) applies to ones with a boat tail, so I ran the static stability up to a true one (1) caliber for her heaviest engine. This brought her up to just over 2 ounces, which is also much like the Centuri kit.

RockSim gave me a bit of pause on this one, claiming the Barrowman calc.s show a highly unstable rocket, but I did some quick checking in VCP, and while it does show a margin of just .57 with the C6-5 loaded, its not nearly as bad as Rocksim would have you believe. Not good enough to fly, though, so I was glad RockSim is right on this one; any more nose weight, and I might as well have shelved her.

Her first flight on a B6-4 was perfect, even in pretty stiff wind. Boost was straight, if a bit jerky, you could tell that the thick fins were trying to stall the whole way up. Ejection was perfectly timed, and recovery was without damage. Her next flight on a C6-5 was terrific, too; a little wiggle off the pad, but great altitude, perfect deployment and a no-damamge landing. She did drift a fair amount, though, so I'll only fly the C motor on calmer days. She landed in tall grass, too, and I was right, she blends in pretty well. I spotted the orange-and-white Estes 12" 'chute long before I saw the bird.

She's since flown on five more B6-4s to perfectly timed ejections and flawless recoveries all but once, the second flight ended in a tangled 'chute. No damage on landing, though, she's a tough little spud. Three more efforts have been on B4-4s which are every bit as good as the B6 motors.

I flew her next on the A8-3, which isn't in her matrix. While it just does get her above 100 feet, its not a very spectacular flight. Ejection timing was perfect, though, and I'll be able to fly her on that motor in higher wind conditions. A demo launch for some kids on the B6-4 was much nicer looking, and ejected right at apogee. I hung her in a tree for a week on her next flight on a B6-4, and though she's none the worse for wear, I want to strengthen a few things before I fly her again.

Estimated Performance

Motor(s)	AGL	Speed	Accel.
B4-4	340	145	15.5
B6-4	340	155	14.9
C4-5	870	225	13.7
C6-5	825	260	16.3