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This is a story of a contest glider project that began in 2010, to try to develop a very competitive design to fly at the 2012 World SpaceModeling Championships (WSMC). As such, I did not publicize the project at the time, not wanting other countries to perhaps copy the design for 2012. Recently I was going thru old computer files, and realized I ought to finally document it, And, to create a video.
In some ways this will be like a "build thread" that is about 10 years after the fact.
The project began as this......
And led to THIS:
I’ll briefly mention that there have been gliders that fold up to fit inside of model rockets for a long time. There are Flex-wing (Rogallo) type gliders, but I’m focusing on solid winged gliders. In the May 1976 issue of the NAR’s Model Rocketeer newsletter, there was a plan for the “Beaver”, a swing-wing canard glider that fit inside of a BT-60 body tube. It was designed by Steve Behrends for E & F power Boost Glide, as in those days there were very few successful E & F gliders of any design. There were some folding gliders before his but that one stuck out as a sort of practical model, for that power range.
Folding flying wings have been experimented with for number of years. I recall at least one article in the Apogee newsletter about them. But more in the sense of either theoretical, or tested out but didn’t perform well. I mean, I'm sure some have done them, but do not recall much about successful ones (which should have shown up at contests if they worked well enough).
I tried a flying wing for 1/4A Boost Glide many years ago, in a 30mm body tube, but it had terrible yaw stability problems, so I gave up on it. (I’ll cover it later).
At the 2010 WSMC in Slovakia, US Junior Team member Caleb Boe flew a flying wing in the S4A (Boost Glide) event. It fit inside of a 40mm FAI body tube. It had mixed success, but showed some promise. So that got me to thinking,
After getting home, I decided to try to work up a flying wing that would be bigger and try to solve some other issues. The minimum diameter for FAI events like Parachute (S3A), Streamer (S6A), and Helicopter (S9A) duration events is 40mm. But I quickly decided that the resulting glider would be too small, at least in wing chord, so I ended up going for a 50mm diameter. Well, in the chicken or the egg sense, I decided on a 1-5/8” wing chord, and allowing for the total thickness of the wings and “stuff” sandwiched in between, that 50mm was about right.
Well, not exactly 50mm. I had some paper tubes 2” in diameter that I could use as mandrels for doing a one-wrap Kapton tube over, so that is what defined the final diameter. Also, I did not want to turn a balsa mandrel for the nose, and found that the Estes “Space Ship One” kit’s 2” diameter nose cone would be a nice shape as a master to vac-form very lightweight nose cones from. The bodies used .02" Kapton for the cylindrical section (one wrap plus 1/4" overlap), and a paper tailcone. For WSMC boosters, I'd likely have come up with a mandrel to make fiberglass tailcones. But paper was OKJ for testing, for a few flights. Below, a booster prepped for flight with a Flying Wing inside.
I got to thinking more on how to go about solving the Flying Wing yaw problem, and how to get a bigger more efficient glider out of the available tube volume. I’d had a lot of success with FAI helicopter models that used flop-wing type folding blades, which doubled their spans once deployed. So, I planned on doing it as a flop-wing flying wing. As with the copter models, the hinges for the outer flop panels were simply small strips of “Skyloft” covering to act as hinges, CA’ed along the bottom of the wings (ends of the balsa rubbed with candle wax to keep CA from gluing the balsa. Krevin Kuczek came up with the Skyloft hinges and wax trick). Those are a great way to do simple thin light rugged-enough hinges to fold 180 degrees.
But the center section was different. It needed to fold "UP", on the top fo the airfoil. So, the model needed a mechanical hinge that could fold 180 degrees. There were no practical model plane hinges for my needs. So, I designed my own “door hinge” type of hinge master, made out of styrene sheet and short pieces of styrene tubing. Used that to make a 2-piece RTV mold, and cast copies. This worked out great and was the key to the mechanical success. Also, when folded “up” like that, the bottom area of the hinge was spread apart, stretching rubber bands for good leverage, to be able to easily deploy the center section. Below is an image of the RTV mold, with one cast hinge half still in one of the mold halves. And to the right, a second cast hinge half, before the "flashing" was trimmed away and before removing the 1/16" rod (which had mold release applied) that cast the holes.
I added elevons to the tips as with typical flying wings. But it had two problems in glide. For one, still the yaw problem, very bad. Also it seemed like maybe pitch stability too, on the rare times it wasn’t yawing too much to tell. So, it seemed like I needed to add folding rudders to the wingtips. Then it occurred to me….no they did not need to fold. They could be half-round, just smaller than the inside radius of the body tube, and glued to the wingtips. I tried that, and that solved the yaw problem.
The pitch problem persisted though. I did not want to mess around with fancy (or even not-fancy) reflexed airfoils (and the up-elevons near the tips provided some of that effect anyway). At one point, I temporarily glued a fixed canard up front to see if that solved it. If so, I’d work out the fold method later. But that did not solve it. So it was flaky for awhile. But eventually I ran across a tweak the helped. I accidentally had the flop-panel hinges a bit “off”, where the outer panels were not flat compared to the main inboard panels. They extended up a bit with a bit more dihedral. But it was not the dihedral itself. It was the fact that the hingelines were at 90 degrees to the wings, which for the swept-back wing it meant that the outer dihedral caused the whole outer panels to be at a bit lower angle of attack to the airflow than the inner main wing. So, when coming close to a stall, the forward inner panels would stall first, like a canard does. And that made things better.
The trim was still a bit flaky, but acceptable to fly with.
Here is a composite image showing the completed Flying Wing, deployed, being folded, and folded for boost.
A close-up set of folded views. Note the rounded rudders, main hinge, and rubber bands to deploy the main wing.
(continued on next post)
In some ways this will be like a "build thread" that is about 10 years after the fact.
The project began as this......
And led to THIS:
I’ll briefly mention that there have been gliders that fold up to fit inside of model rockets for a long time. There are Flex-wing (Rogallo) type gliders, but I’m focusing on solid winged gliders. In the May 1976 issue of the NAR’s Model Rocketeer newsletter, there was a plan for the “Beaver”, a swing-wing canard glider that fit inside of a BT-60 body tube. It was designed by Steve Behrends for E & F power Boost Glide, as in those days there were very few successful E & F gliders of any design. There were some folding gliders before his but that one stuck out as a sort of practical model, for that power range.
Folding flying wings have been experimented with for number of years. I recall at least one article in the Apogee newsletter about them. But more in the sense of either theoretical, or tested out but didn’t perform well. I mean, I'm sure some have done them, but do not recall much about successful ones (which should have shown up at contests if they worked well enough).
I tried a flying wing for 1/4A Boost Glide many years ago, in a 30mm body tube, but it had terrible yaw stability problems, so I gave up on it. (I’ll cover it later).
At the 2010 WSMC in Slovakia, US Junior Team member Caleb Boe flew a flying wing in the S4A (Boost Glide) event. It fit inside of a 40mm FAI body tube. It had mixed success, but showed some promise. So that got me to thinking,
After getting home, I decided to try to work up a flying wing that would be bigger and try to solve some other issues. The minimum diameter for FAI events like Parachute (S3A), Streamer (S6A), and Helicopter (S9A) duration events is 40mm. But I quickly decided that the resulting glider would be too small, at least in wing chord, so I ended up going for a 50mm diameter. Well, in the chicken or the egg sense, I decided on a 1-5/8” wing chord, and allowing for the total thickness of the wings and “stuff” sandwiched in between, that 50mm was about right.
Well, not exactly 50mm. I had some paper tubes 2” in diameter that I could use as mandrels for doing a one-wrap Kapton tube over, so that is what defined the final diameter. Also, I did not want to turn a balsa mandrel for the nose, and found that the Estes “Space Ship One” kit’s 2” diameter nose cone would be a nice shape as a master to vac-form very lightweight nose cones from. The bodies used .02" Kapton for the cylindrical section (one wrap plus 1/4" overlap), and a paper tailcone. For WSMC boosters, I'd likely have come up with a mandrel to make fiberglass tailcones. But paper was OKJ for testing, for a few flights. Below, a booster prepped for flight with a Flying Wing inside.
I got to thinking more on how to go about solving the Flying Wing yaw problem, and how to get a bigger more efficient glider out of the available tube volume. I’d had a lot of success with FAI helicopter models that used flop-wing type folding blades, which doubled their spans once deployed. So, I planned on doing it as a flop-wing flying wing. As with the copter models, the hinges for the outer flop panels were simply small strips of “Skyloft” covering to act as hinges, CA’ed along the bottom of the wings (ends of the balsa rubbed with candle wax to keep CA from gluing the balsa. Krevin Kuczek came up with the Skyloft hinges and wax trick). Those are a great way to do simple thin light rugged-enough hinges to fold 180 degrees.
But the center section was different. It needed to fold "UP", on the top fo the airfoil. So, the model needed a mechanical hinge that could fold 180 degrees. There were no practical model plane hinges for my needs. So, I designed my own “door hinge” type of hinge master, made out of styrene sheet and short pieces of styrene tubing. Used that to make a 2-piece RTV mold, and cast copies. This worked out great and was the key to the mechanical success. Also, when folded “up” like that, the bottom area of the hinge was spread apart, stretching rubber bands for good leverage, to be able to easily deploy the center section. Below is an image of the RTV mold, with one cast hinge half still in one of the mold halves. And to the right, a second cast hinge half, before the "flashing" was trimmed away and before removing the 1/16" rod (which had mold release applied) that cast the holes.
I added elevons to the tips as with typical flying wings. But it had two problems in glide. For one, still the yaw problem, very bad. Also it seemed like maybe pitch stability too, on the rare times it wasn’t yawing too much to tell. So, it seemed like I needed to add folding rudders to the wingtips. Then it occurred to me….no they did not need to fold. They could be half-round, just smaller than the inside radius of the body tube, and glued to the wingtips. I tried that, and that solved the yaw problem.
The pitch problem persisted though. I did not want to mess around with fancy (or even not-fancy) reflexed airfoils (and the up-elevons near the tips provided some of that effect anyway). At one point, I temporarily glued a fixed canard up front to see if that solved it. If so, I’d work out the fold method later. But that did not solve it. So it was flaky for awhile. But eventually I ran across a tweak the helped. I accidentally had the flop-panel hinges a bit “off”, where the outer panels were not flat compared to the main inboard panels. They extended up a bit with a bit more dihedral. But it was not the dihedral itself. It was the fact that the hingelines were at 90 degrees to the wings, which for the swept-back wing it meant that the outer dihedral caused the whole outer panels to be at a bit lower angle of attack to the airflow than the inner main wing. So, when coming close to a stall, the forward inner panels would stall first, like a canard does. And that made things better.
The trim was still a bit flaky, but acceptable to fly with.
Here is a composite image showing the completed Flying Wing, deployed, being folded, and folded for boost.
A close-up set of folded views. Note the rounded rudders, main hinge, and rubber bands to deploy the main wing.
(continued on next post)