XP-2 Rocket Glider

[kooch]

That is very helpful and I appreciate it. There is still time to do that.

Does the presence of the rubber band have much effect in terms of weight? I understood that gliders are very picky about the least bit of weight.

Use a small rubber band! And a good question. Very likely the glue you use to permanently attach the stab/rudder will equal the weight of the rubber band (or exceed). So, no need to counter balance the front of the glider to account for the rubber band.

You do want to keep the tail feathers light though. A gram in the feathers means 4X in the front. However, on XP swing wings, they usually ALL ended up front heavy and reason for the larger negative incidence angles. Instead of more negative incidence, you could add weight to the tails ....probably more effective than adding more negative incidence angle. Large amounts of negative incidence will make this draggy model even draggier in boost and glide.

I'd probably now go with 2 degrees negative incidence on the stab maximum. And add tail weight to balance out the glide which shouldn't be much. Or, better, make the tail feathers stronger.

KK

 

[kjohnson]

How's the trimming going?

kj

 

[JAL3]

I've been derelict in updating this thread. Just too busy!

The glider is actually done and had it's first flight on Tuesday. To my amazement, it actually glided. There were a few problems and some damage that needs to be fixed before I leave for Dallas in the morning but its fairly minor. The damage came from landing on a road, not from any instability or such.

I am hoping to catch up on this thread when I get back.

 

[JAL3]

I used some thin CA to strengthen the vent holes in the BT.

 

[JAL3]

I also used CA to stiffen up the aft end of the tube.

 

[JAL3]

Some course sandpaper was used to scruff up the inside surface of the motor hook.

 

[JAL3]

A thin layer of epoxy was then laid down along where the hook would be placed and the hook was set in it.

 

[JAL3]

A wing was set on its shoulder and the Kevlar fished through its path.

 

[JAL3]

The hub was sanded a bit to get it to the right height and then the upper shoulder was glued into place and clamped.

 

[JAL3]

The same procedure was then repeated with the other wing.

 

[JAL3]

By this time the epoxy on the engine hook had set and another line of epoxy was run atop the hook. The BT was then set in place on the standoff.

 

[JAL3]

When the epoxy on the BT/standoff connection was fully cured, I used some Titebond Molding and Trim glue to fillet the joints and fair the roughness around the threads on the lug.

 

[JAL3]

I really had no idea as to how the dihedral of the wings was supposed to be achieved so I used an idea that came from my Semroc Swift Boost Glider and constructed a support at the right height for the wingtip out of balsa scrap.

 

[JAL3]

While I was waiting for the glue on the dihedral support to dry, I used some sandpaper to round the leading edges of the wing shoulders.

 

[JAL3]

A belt sander was used to approximate the angle of the dihedral on the shoulders. The spar was then set flat on a piece of wood and the shoulder was glued to the spar. The dihedral support was used to hold up the wingtip and clamps were used to keep everything tight.

 

[JAL3]

While the first wing was drying in place, I traced the horizontal stabilizers onto balsa

 

[JAL3]

2 stabilizers were then cut out with an X-acto and evened up with sandpaper.

 

[JAL3]

The same template was then used to mark out the vertical stabilizer which was a shortened version of the horizontals.

 

[JAL3]

The vertical stabilizer was then cut and shaped in the same manner as the horizontals.

 

[JAL3]

After the first wing had a day to dry, the second was placed in the same manner.

 

[JAL3]

After a day for the second wing to dry, the glider was finally starting to look like it might fly.

 

[JAL3]

I had not realized when I cut the horizontal stabilizers out that it would have been better to cut them as a single piece. I now proceeded to glue the two pieces together with a butt joint.

 

[JAL3]

Lines parallel to the seam were then marked to aid in the placement of the horizontal stabilizer.

 

[JAL3]

The airfoil ridgeline was marked on the horizontal stabilizer and masking tape was used to tape it to a piece of plate glass, masking the line. An airfoil was then sanded into the stabilizer, avoiding the centering marks.

 

[JAL3]

The horizontal stabilizer was laid across the end of the spar and its edge was marked on the spar.

 

[JAL3]

A sanding block was then used to put a 2 degree angle into the bottom side of the end of the spar from the mark to the end.

 

[JAL3]

At this point I should mention several things. My deadline was coming fast and I had no idea if I would be able to get this rocket finished on time. I wanted a chance to test fly it before leaving for Dallas. Knowing that it would be better to test it before affixing the stabilizers, I decided to affix them anyway and deal with trim issues by the use of weight. My goal was not to produce a winning design but to get a qualified flight.

At some point or another, I had put pins in to hold the rubber bands that power the swing wings. I used some thick CA to hold them in place and build up a bit of a barrier where the bands would grab.

The horizontals were glued in place and then the vertical set in place as well. It was a complete as it was going to get before its test flight.

 

[JAL3]

Stay tuned, there is much more to come although the build is complete.

 

[JAL3]

I really wanted a chance to test fly the XP-2c before taking it to the competition I had signed up for in Dallas. A friend and fellow club member who is a glider enthusiast agreed to accompany me to the test flight. We loaded a spent casing and tried tossing it a few times. It seemed to glide well for a first try. It pulled some to the right but did not do anything embarrassing.

I had no idea how to rig the burn string on this beast. The motor is way forward and the wings need to be tied towards the back. What I finally settled upon was running the string from the vent holes down to the lower, ventral, surface and then back to the tail. From there I crossed it behind the vertical stabilizer and wrapped the wingtips. It seemed like a Rube Goldberg approach but, then again, so does the whole project. That’s why I like it.

Tragedy struck when I found that I had no Estes C6-3s. My only choice was to use the Quest version.

Tragedy struck again when I tried to put the rocket on the launch rod. The fit was too tight. It was doubtful if it would be able to get off the rod.

Ken, master of improvisation that he is, came up with a fix when he used masking tape to apply a bit of Aerotech Copperhead protective tubing as a new lug. He had already used tape earlier to fix a fin, a body tube and several other items. The glider was taken back to the pad and set up for launch.

 

[JAL3]

I took a picture at ignition but not during the flight since I wanted to pay attention to what the glider was doing. It seemed as if the string around the wings slipped on boost but that air resistance kept them pretty much swept back; not all the way but enough to make a difference. It boosted straight for the first part but as the thrust tapered off it went more horizontal. I half expected this from the Quest motor. When the thrust ended, I did get to see the wing sweep the rest of the way forward and then it glided.

To me that was amazing. I know that it is supposed to glide but this is one that I built and it was rushed towards the end. It was nothing short of a miracle.

There were some issues. The circles it was turning were way too tight. The lug needed to be fixed and it did have a hard impact on landing, crumpling the tube around the vent holes and giving a blunted end to the NC but IT WORKED!