A team of scientists and engineers at UBC in Vancouver, Canada is developing rockets and systems to collect weather data up to 20,000'. The unguided rockets will be launched from buoys out in the middle of the Pacific Ocean, in almost any weather, to improve weather forcasting. This year we are developing the rockets to reliably achieve 20,000' and fit in as small diameter launch tube as possible. We received a 20,000' waiver to launch at a lake in BC. Sorry, we're not allowed to share our waiver with hobby rocketeers. This summer I built about 30 rockets to test various fin designs. Most of the rockets were tested on G through J engines at HPR meets in Oregon and Canada. We're still waiting for our special Cesaroni K-1,000 engines to arrive, to achieve the goal altitude.
So far, we successfully sent a weather measuring sonde to over 9,000' at the Lethbridge, AB meet this year, out of a 4" launch tube, on a J engine. We also built and used a floating launch pad for our lake launches. Ever try to track a high altitude rocket from a rocking boat? We quickly found that we would lose most of the rockets we launched at the lake. Ever try to add enough floatation to a a minimum diameter rocket for a water recovery? We have photos and movies of many launches, including water launches.
We have tried every kind of fins, anyone could think of, to make the rockets fit in small launch tubes. Concentric circular (tube) fins have proven to be reliable and can be surprisingly small in diameter. We are concerned about their drag at supersonic speeds, however. Anyone know where to find information about that?
I am back home in Texas, continuing developement using Cesaroni G engines in 38mm minimum diameter rockets, launching out of a 3" launch tube. Mike Dennett of Cesaroni has been very helpful, making special engines for us, and sharing his vast rocketry engineering experience.
I have learned a great deal about launching out of tubes, minimizing drag, circular fins, folding fins, and minimizing fin size. If anyone has any specific questions, don't hesitate to ask. I am making new rockets every week, testing various designs.
Launching out of launch tubes requires no lugs, so I am achieving some amazing altitudes. If you're interested in our project, below is my latest "in house" memo. If there is enogh interest, I'll continue to post developement progress.
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After trying every radical approach in Vancouver, I am working on more conservative/subtle improvements. I tried moving the circular fin down a couple inches, but it was not strong enough down there. I am able to move the circular fin down about 3/4", and still have excellent strength. That has the same effect as moving the engine's weight up 3/4", which moves the center of gravity up about 1/2".
I am using long, narrow, radial fins to support the circular fin. I agree with Catherine that this will help broadside center of pressure significantly.
Another subtle improvement is using carbon fiber for the fins. The carbon weighs about half of what fiberglass or aluminum does. It is an obvious way to move the center of gravity up a little... more on my light weight test rockets.
Using the engine casing as the bottom of the rocket body helps a lot. It can move the center of gravity up significantly on your full sized rockets.
One way to decrease drag is to make the rockets less than minimum diameter. Normally, a minimum diameter rocket uses the engine OD as the body tube's ID, with a small clearance. For example: Our 54mm rockets are 57.5mm diameter. Since we plan to use the engine casing as the bottom rocket body, it's not too hard to make the rocket engine be the largest OD of the rocket body. So our 54mm rockets can be just 54mm diameter. Mike already told us it is no problem making the top of the engine include an addapter to attach the small upper body tube directly. So there won't be anything at the transition that makes the rocket larger diameter. The fins can be glued directly to the engine casing to eliminate the fin ring at the bottom. The drag at the bottom of the rocket is 12% less with a 54mm OD, since the area of the end of the body is proportional to the square of the diameter.
Reducing drag allows a lighter optimum weight... so reducing drag will keep us from having to add weight to our rockets to get them to coast high enough.
My second test rocket here has all of these improvements. I made the upper 3/4 of the rocket out of smaller, lighter, 1+1/4" OD, spiral wound, carbon tubing. This moves the center of pressure and center of gravity down a lot. I glued the fins directly to the engine casing, and used the top of the fins to connect to the upper body tube. This rocket should weigh half of what my first one weighs, not counting the engine and recovery system. It should accellerate much faster, attain a much higher maximum speed at a much higher altitude, and coast really high. This will push a circular fin to a faster speed than we've ever tested.
My third rocket will test making the circular fin taller. That makes it have much more broadside stability. Mechanically, it lets me have more of it extend below the engine. This will move the center of pressure way down on the rocket, allowing me to make the nose cone very light. I tapered the thickness of the circular fin so the bottom of it is very light.
I'm still making different sizes of tubing out of fiberglass and carbon fiber. I decided it is easier to make tubing to fit a store bought nose cone, than to make custom nose cones.
So far, we successfully sent a weather measuring sonde to over 9,000' at the Lethbridge, AB meet this year, out of a 4" launch tube, on a J engine. We also built and used a floating launch pad for our lake launches. Ever try to track a high altitude rocket from a rocking boat? We quickly found that we would lose most of the rockets we launched at the lake. Ever try to add enough floatation to a a minimum diameter rocket for a water recovery? We have photos and movies of many launches, including water launches.
We have tried every kind of fins, anyone could think of, to make the rockets fit in small launch tubes. Concentric circular (tube) fins have proven to be reliable and can be surprisingly small in diameter. We are concerned about their drag at supersonic speeds, however. Anyone know where to find information about that?
I am back home in Texas, continuing developement using Cesaroni G engines in 38mm minimum diameter rockets, launching out of a 3" launch tube. Mike Dennett of Cesaroni has been very helpful, making special engines for us, and sharing his vast rocketry engineering experience.
I have learned a great deal about launching out of tubes, minimizing drag, circular fins, folding fins, and minimizing fin size. If anyone has any specific questions, don't hesitate to ask. I am making new rockets every week, testing various designs.
Launching out of launch tubes requires no lugs, so I am achieving some amazing altitudes. If you're interested in our project, below is my latest "in house" memo. If there is enogh interest, I'll continue to post developement progress.
************************************************************
After trying every radical approach in Vancouver, I am working on more conservative/subtle improvements. I tried moving the circular fin down a couple inches, but it was not strong enough down there. I am able to move the circular fin down about 3/4", and still have excellent strength. That has the same effect as moving the engine's weight up 3/4", which moves the center of gravity up about 1/2".
I am using long, narrow, radial fins to support the circular fin. I agree with Catherine that this will help broadside center of pressure significantly.
Another subtle improvement is using carbon fiber for the fins. The carbon weighs about half of what fiberglass or aluminum does. It is an obvious way to move the center of gravity up a little... more on my light weight test rockets.
Using the engine casing as the bottom of the rocket body helps a lot. It can move the center of gravity up significantly on your full sized rockets.
One way to decrease drag is to make the rockets less than minimum diameter. Normally, a minimum diameter rocket uses the engine OD as the body tube's ID, with a small clearance. For example: Our 54mm rockets are 57.5mm diameter. Since we plan to use the engine casing as the bottom rocket body, it's not too hard to make the rocket engine be the largest OD of the rocket body. So our 54mm rockets can be just 54mm diameter. Mike already told us it is no problem making the top of the engine include an addapter to attach the small upper body tube directly. So there won't be anything at the transition that makes the rocket larger diameter. The fins can be glued directly to the engine casing to eliminate the fin ring at the bottom. The drag at the bottom of the rocket is 12% less with a 54mm OD, since the area of the end of the body is proportional to the square of the diameter.
Reducing drag allows a lighter optimum weight... so reducing drag will keep us from having to add weight to our rockets to get them to coast high enough.
My second test rocket here has all of these improvements. I made the upper 3/4 of the rocket out of smaller, lighter, 1+1/4" OD, spiral wound, carbon tubing. This moves the center of pressure and center of gravity down a lot. I glued the fins directly to the engine casing, and used the top of the fins to connect to the upper body tube. This rocket should weigh half of what my first one weighs, not counting the engine and recovery system. It should accellerate much faster, attain a much higher maximum speed at a much higher altitude, and coast really high. This will push a circular fin to a faster speed than we've ever tested.
My third rocket will test making the circular fin taller. That makes it have much more broadside stability. Mechanically, it lets me have more of it extend below the engine. This will move the center of pressure way down on the rocket, allowing me to make the nose cone very light. I tapered the thickness of the circular fin so the bottom of it is very light.
I'm still making different sizes of tubing out of fiberglass and carbon fiber. I decided it is easier to make tubing to fit a store bought nose cone, than to make custom nose cones.