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Framework V2 - Design |
I created a full size scale drawing by scaling up the V2 image from Peter Alway's book Rockets of the World. I scanned it, scaled it using Photoshop, and then printed it out sheet-by-sheet and taped together into a full size blueprint. I selected 1/8 scale and the best to determine the feasability of the construction method. This makes the rocket about 8 inches in diameter and almost 6 feet tall. I always approach scratch built scale rockets this way. The full size image really gives you a visceral feel for what you're building.
Engines: at least a G25 - perhaps ultimately an H45 if the framework is strong enough to handle the loads. Target weight for the rocket itself is one pound to 1.5 pounds (about 450 - 675 grams). Due to the unusual weight/drag relationship, an altimeter will be required for ejection. It will be located far forward so it will contribute to stability.
Evaluating the design requires the ability to guess what the rocket will weigh when completed. Since the construction technique is nonstandard, RockSim won't estimate the weight. My initial guess is about 300 grams for the structure, 200 for the covering, plus whatever dead weight is required for stability - hopefully no more than the altimeter itself.
The cover estimates are based on using newsprint as the covering material. I guessed at the weight by calculating the surface area of the rocket, and using a scale to find the weight of newsprint per square foot. This yielded 50 grams for one layer of paper. I suspect multiple layers in places, and some stiffener (paper mache?) will raise the weight by at least a factor of 4.
The total surface area of the rocket is:
- Nose - pi x r x s = pi x 4 x 24 = 301 in-sq
- Body - pi x d x l = pi x 8.125 x 22.5 = 574 in-sq
- Tail - pi x r x s = pi x 4 x 16 = 201 in-sq
- Fins - w x l x 8 sides = 4.5 x 15 x 8 = 540 in-sq
Total = 1616 square inches = 11.2 square feet
Weight of newsprint is 4.5 grams/square foot
Since the entire structure is scratch built, the question of where to break the airframe for recovery is more complex than usual. Recovery would be easier if the break is close to the center or even right above the tail cone - but it can't be too far back or there will be a high risk of drag separation at burnout. I settled on making the break at the point where the curve begins on the real V2. This should put enough mass in the aft section to prevent drag separation.
You can explore the design further by looking at the RockSim design file.
As building progresses, each part is weighed to see if the actual part is close to the estimated weight. In any project it is critical to ensure that the weight doesn't get out of hand, but it is particularly critical in a V2 that the weight and distribution be controlled. Once the CG goes too far aft, every ounce of unnecessary weight in the tail must be balanced by an ounce in the nose. Unchecked, this can quickly run into a very heavy rocket.
Here are the actual weights of the components as built:
As the rocket comes together, the mass guesses turn out to be about right.
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