Fantasy:"Spaceframe" design with possibly mysterious propulsive function, including cosmic warp rings.
Function: strong design with rear ejection and capsule/bumper nose.
Repaired rear end provided an art area. With 24mm adapter.
Wanted to show off my latest. Hopefully it will inspire more creative designs. I'm not giving out specific build info, but wouldn't mind generalized copying.
By way of introduction, I built 2 rockets as a kid which promptly dissappeared when launched on the largest allowed motor. So I build for visibility now. About 15 years ago I built 2 finless designs, based on the amount of trouble I was seeing with a friend keeping his fins on. One was an elongated triangular pyramid. I didn't want copy that again just bigger, plus it would have too much air resistance, so I came up with this. A new goal was for it to be able to come down fast, avoiding excess drift.
The original design used a smaller airframe tube and a pyramidal nose. Since that would be hard to build with an ejecting nose, I came here and looked up how to do rear recovery and found I needed to put the parachute beside the motor so I switched to BT70H tube. But that design wouldn't handle impact, so I came up with the idea of looking for some object that could be converted to a bumper nose, and found a hard foam mini-football. It would look better with a pointy nose, but this design is unusual in that the appearance still "works" (to me) with this blunt one. I also had a deal with a BT50 nose cone grafted on, but it broke off on first test, thus the sort of ring around the tip.
Other goals of the design were high visibility per air resistance, and low weight per air resistance to be able to use the widest spectrum of motors (since their results are all closer to the same). I did go over target on the weight, the thing must have gained 2 ounces in paint. Total is 17.5 oz. with default nose weight.
Yes I know the fins going well forward is destabilizing. The fin array in the rear helps, but the CG still needs to be within a couple inches of amidships. On the other hand, the long "rail" fins are of heavier wood which moves the CG forward. It needs nose weight just a little short of the motor weight.
The rail fins are made of True Value yardsticks. I do wish I had puttied all the markings out, sometimes I get tired of comments on that, but it was a convenient source of cheap, nonwarped wood of the right shape. So that makes them 36" long exactly
.. whole thing's about 39". Other woods used were 3" wide basswood for the returning section of the rails at the rear, 4" wide balsa, and some bits of Lowe's yardstick for the middle launch lug mount and turning a centering ring into a heavy bulkhead. The slight markings on the yardstick-rails do make it easy to track the CG. In testing holding it up in the wind, I found it to reliably act like a weathercock at the 19.75" point. Any further back and it loses stability at higher angles of attack. So far I've flown it with the CG at 20.5" or better. It angles some off the launch with smaller engines, but I haven't been able to map any tendency to weathercock in flight.
Rocket materials were from ASP, they had everything I needed (since a nose cone wasn't). Once I built a mount, I figured out I didn't need to cut the 30" tube, by cutting the 9" section down by 2" and sliding the 4" coupler tube a bit one way, the coupler provided a stop and measured a shock cord chamber above the engine.
Despite the airframe only being about 2.1", the calculated frontal area of the 2.5" nose and all the fins is equivalent to a 3.9" tube. Therefore I run sims with that area and low-ish, airfoil range drag coefficient, rather than trying to use the actual diameter and a high fudge-factor drag coefficient.
2 parachutes ago, sans wadding/wrap ... the plastic Estes did survive ejection at about 100 ft/s with only one ripped shroud line. A 24" Top Flight was too hard to pack with the 29 mm mount, so now I have a 22" Aerotech in there.
Originally I had both 24 and 29 mm mounts. Only 1 centering ring survives. Also added a steel leader after the first flight, now have Kevlar, and have to use special wrapping methods for the shock cord (now mostly 1/2"). That's my layout drawing for the main fin rail assemblies under everything.
On an E20-4.
Flights:
1. E20-4. Since the references here did it right, they didn't warn me about doing it wrong. The ejection charge burnt the shock cord resulting in a crash. I was very lucky it landed on a big pile of loose dirt. Not a scratch but a bit dirty:
2. E12-4. I did originally want this to able to use Estes Es, and my RASP sim showed about 200' with ejection around 150'. Liftoff would only be about 27 ft/s, but the motor thrust peak would be all but over by the time it even came off the rod, resulting in less need for strong stabilization. Well, it ejected at 40-50' instead and I watched the parachute appear to stop and the shock cord stretch, stretch down to a few feet above the ground. It actually was an awesome flight with the motor COATING the tripod with exhaust, but will not be repeated.
3. E20-4. About 400', success.
(attempt) F50-6. CATO, destroyed 29 MM mount and split open the bottom of the airframe (see 2nd pic). Fortunately, the inside edges of the fin structure help assure motor mount alignment.
(attempt) F30-4. Premature ejection on the launch pad. Many rockets would have been destroyed by the thrust fire coming out of both ends of the motor, as it was the 24 mm mount was destroyed (Aerotech has already replaced the motor and sent me some useful bits and pieces).
4. G40-7W (Estes Pro Series II). Awesome flight (~1100'), highest single deploy flight that day due to wind, and it still landed just within the main field. 2 close calls, motor was hanging 3/4 of the way out the mount and a snap swivel was bent and opened, but still held on.
Ballast bay door showing part of one of 3 permanent 1/2 oz. weights, 2 oz. removable weight with wedge holder, door latch. The "rails" have through the body tabs at the front, not the rear.
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