Amateur Rocket Vehicles

 

What is a Rocket Plane?

A Rocket Plane is powered via solid rocket boosters. Typical rockets are made for launching vertically, but there isn’t enough danger involved with vertical liftoffs. Hence, Rocket Plane. Let’s talk a little about the physics of these things and what to keep in mind when designing your rocket plane.

 

What do I need to know before building my own Rocket Plane?

  • Gliders are only under the forces of gravity and the lift of their wings once thrown. They make lousy rocketplanes. Continuous thrust causes them to loop unless you unbalance the plane by placing ballast at the nose (or on a stick protruding from the nose). Once the thrust stops, you have an unaerodynamic hunk of lead falling from the sky.
  • Silly, non-technical designs (like the one shown) will fly, given enough thrust. Estes rockets provide ample thrust.
  • Balance is all-important. Keep engines along the fuselage or exactly balanced on wingtips so that the center of gravity (COG) is in the front of the wing dead in the middle of the fuselage.
  • Durability is rather important. These things come smashing into the ground at probably 15-30mph, depending on the weight of your plane and the size and number of engines you pick.
  • You need a way to start these engines in a safe, preferably multi-engine friendly, sort of way. We have a trickle charger with a host of copper pairs coming off of the clamps, enough to ignite 8 engines at once. These vehicles used no more than 3 pair.

 

Experimental Trials

Vehicle 1: The Rocket Assisted Styrofoam Glider

My first attempt, of which I have no photographic evidence unfortunately, was of the 3’ wingspan styrofoam glider variety. These can be purchased at a local hobby store for about $7 or less. This particular plane has two separate wings, a smaller tail fin and a rear stabilizer, all of which fall out of the holes every time you throw the damn thing. While this plane is excellent for getting the feel for building rocket powered horizon-based vehicles, it has inherent limitations and problems with durability. I bought a small 1/4" dowel rod and CAREFULLY drilled out holes in the foam wings, and inserted a single dowel segment as a crossbrace into both wings, thus locking them into the fuselage. A little glue helped keep them honest, too. Then, I drilled a hole through the rear section of the fuselage just before the tail fin (a plane terminology expert I’m not… the little wing in the back). I stuck a small dowel segment through this hole and wrapped a rubber band around either end of the dowel, with the tail fin snugly sandwiched inside the rubber band. It’s hard to visualize, but it works great. I didn’t put any real effort into keeping the rear stabilizer in its place, since mine fit pretty well already.

In order to get power to the plane, I took the remaining dowel rod length (about 2 or 3’) and taped it a couple of times around the fuselage, with a foot or more protruding from under the nose of the glider. Next, I delicately set an engine against the finishing nail and wrapped it around the dowel with duct tape or bailing wire or an unwound coat hanger, depending on what was handy. This formed a rough cage to put future engines in as well. Generally you don’t need to worry about an engine falling out the back. Since it’s thrusting forward as long as you care to have it in there, so I only concentrated on preventing it from slipping through the front of the cage with a small finishing nail through a predrilled hole in the dowel rod.

Results:

    1. Oh, not bad. The first two were A sized (puny) engines. It took off and went about 5’ or so, and stopped. Lame.
    2. B sized engines (bigger, but not really large) carried it as many as 30’ away. Impressive.
    3. C sized engines (very large, lots of thrust and for several seconds) took it in a huge loop, almost hitting a car on the other side of the barn. *

Notes:

Doh! Styrofoam melts quickly when exposed to extreme heat. Rockets produce flame. Flame thrown back from the engine caused the underbelly to look pretty haggard within two or three launches. We took metal backed tape and put on a nice strip down the fuselage to protect the belly a little, deflecting the heat away from the tender shell. It worked remarkably well, but looked stupid. What the heck? It flew.

Also, always try out your new rocket plane with only one of your smallest engine size. You have no idea how it’ll perform, if at all, so don’t waste a good engine on a bad plane. Along the same lines, if it’s a good plane, you will have more of an idea what to modify on the plane before putting in a more dangerous engine for the next launch. The A engine showed me that there was plenty of lift. The B engine showed me there was too much lift, so I extended the dowel a little further to increase the torque weight of the engine off the front of the plane, to balance it somewhat. It worked. I also added spent engines as more weight to the belly just because.

Keep a bucket of water or two full all the time, and be prepared to lose some tread on your shoes stamping out fires. Ejected engines or flaming bits of your prized plane are fairly likely to set blazing fires in numerous places along the flight path.

Fiery Conclusion:

All fun must come to an end. Dry weather conditions makes the grass very flammable in east Texas (or anywhere in Texas, for that matter). These engines tend to be hot enough that they can easily start a forest fire. I had single-stage engines, which have a little ‘pop’ at the end to kick out a parachute or streamer for recovery of a normal rocket. How silly. Anyway, this has enough force to set a fire as well. The last flight was a C engine and was really well balanced, achieving about 50 feet of altitude, about 100 feet of cruising distance from the launch pad, and coming to a lighting quick descent as soon as the thrust was exhausted. Moments later, it crashed into the ground. We started running towards the site, just in time to hear ‘pop’ and watch the flames engulf the area. A bucket of water later and I had the wreckage back in the workshop for inspection. The wing holes were enlarged about twice their original size, one of the wings was decimated to a thin shell of a styrofoam wing, and the nosecone was vaporized off the fuselage. About 10 or so launches for $7 + rocket engine costs ain’t bad!

* Move anything you think might get hit by an errant rocket plane. Far away. Rocket planes are naturally geared for seeking any target you would rather they don’t smash into.

Vehicle 2: The Homemade Rocket Plane

This was a labor of love. I bought raw parts and pieced it together in spare time. The total cost was about $6. The wings and tail were made of 3/8" basswood, with rounded corners and sanded surfaces at 400 grit for reduced friction. The fuselage was a bullnosed strip of balsa, as was the rear stabilizer. I drew the plans for the surfaces on a paper towel and traced them onto the wood after cutting the towel with scissors. It was remarkably easy to get the plane together. The hard part was figuring out how to make it more durable, easier to swap out engines, and slightly better performing in the air.

Above is a photo of the top side of the plane. Notice the reflective tape on the rear fin? That’s the metal coated tape that worked as a heat shield on the first plane. It was used here to protect any surface that might come in contact with heat directly. Worked rather nicely, as this tape was coated in soot after the first few trials.

 

Above is a photo of the belly of the homemade rocket plane. The carriage which contains the rocket engines was crafted out of thin steel bars from leftover scrap from a kitchen/laundry room rack I put up a while ago. It turned out, serendipitously, that rocket engines are just slightly larger than the width of the rungs, so I could set several engines side by side for parallel engine takeoffs if I wanted to. I cut two pieces of this rack, one for the bottom part screwed onto the wing and one for a top part under which I sandwiched the rocket engines. I left one screw standing tall enough so that the top rack couldn’t move, and used unfolded coat hanger wire to wrap the carriage tightly together. Once set, I could add or remove engines at will and very little effort was spent in maintaining the carriage itself. This worked out well.

Results:
    1. Encouraging. I put an A engine in the center slot (my carriage could hold three engines side-by-side). The launch ramp was angled up as seen in the photo above. Lots of smoke, no fire. The plane skipped off the end of the runway and fell about 5 feet away into the grass. Not very remarkable, but it told me how much thrust was necessary to get off the ground. Lots. It was a fairly heavy plane.
    2. Pretty good. After the initial trial, I never put less than two engines on the rocket plane. Twin B engines took it about 35 feet up into the air, as seen in the picture below, but with so much lift, or so much air racing off the surfaces providing positive pitch, that the plane looped within 2 feet of the ground, only a few feet from where I was standing! Scared the crap out of everyone who was watching, because it took a couple of seconds to reach apogee, but whizzed past us in just a fraction of a second, making half the arc in no time flat. It landed a good 20 feet away in the grass after a nice extended glide to the ground. Good dynamics, but too much lift. See the video
    3. Rebalanced, with twin B engines, there’s still too much lift. Be aware that any hard surface on the landing zone will attract rocket planes at maximum falling velocity. Bring a toolkit and be prepared to spend some time rebuilding. Heavier materials carry more force, which means bigger splash effects when they land. J
    4. Several more trials later, we decide to give it all or nothing. Twin C engines. This carried the plane about 100 feet away, somewhat near that big tree in the distance. Too much lift, yes, but it went plenty high and had lots of time to glide back down, gaining distance all the while. The engines popped so forcefully that it split the plane into its component parts, on fire. Then it hit the concrete driveway. Nice. See the video See next incarnation below.

Notes:

Since I was familiar with having segmented wing architecture from the styrofoam plane, I built my homemade plane with a two-piece wing. Big mistake. Every joint will break. Don’t add new ones unless you really need them. I had to repair the carriage a couple of times, add a little wood to the wings, squeeze them back into place and wire them into place. My next incarnation was a slight improvement, in some ways, due to this realization.

 

Vehicle 3: The Jury Rigged Homemade Rocket Plane

Given the amount of work I’d put into the homemade rocket plane, I wasn’t going to give up on the hardware after a mere 6 or 7 flights. I had a box full of engines just begging to light ‘em up. The wings were shot, the tail sections were twisted and cracked, the fuselage was split down the middle, and the carriage was broken off completely.

I found a piece of scrap siding or flooring board, which is made to be fitted together tongue and groove. I didn’t care too much that it was a veneered pressed board, or that it was easily three times heavier than my previous basswood wings. I simply cut out the blank one-piece wing, dog eared the corners at 45 degrees, and drilled for the carriage to fit onto the wing. What took me hours of labor the first time, only took 10 minutes this time. No sanding, not prettying up, only the raw essentials. Prep time was a minimum, because the audience was getting restless.

Results:
    1. Twin B’s. The jury rigged plane didn’t have too much lift anymore. Heh, it looked like it was draggin’ ass the whole way. It went about 30 feet and landed relatively hard on the concrete driveway again. No major repairs necessary, but the fuselage was wearing thin.
    2. So much for grace. We decided to go full out on Triple C engines. Who knows how many times we’d get to fly this heap? Take no chances, insure destruction! It took off with three C engines and soared! It flew and flew, must have been about 120-150 feet, curving a little bit as it went, was this hideous brown plane. Finally the engines gave up and it coasted another 20 feet or so, losing altitude rapidly and moving fast. Just before reaching the ground, all three engines gave up that satisfying ‘pop’ to eject the imaginary parachute (yeah right!), and we were treated to the sight of flaming bits of plane everywhere, falling in different directions. NEW! See the video

Fiery Conclusion:

By the time we all arrived at the scene, we scoured the area and found all the parts, but they were scattered and irreparable. The fuselage was split in half. The tail fin was broken free of the fuselage completely. The wing was a board with flaming hot engines strapped to it, but nothing more. The plane was totally razed. We put out the minor grass fires here and there, carried back the parts and pieces with glee, thinking about what next to build. And strap rocket engines to it.


18926 BACK