Monday, September 12, 2011

Weighted Question

Balancing on my CG stand
OK, the wings are fixed and ready for flight testing.  As I prep all my stuff for the next available flight time, I see that there is another issue that should be resolved and cleaned up.  Until now, I've been using a stack of washers as a nose weight to balance the CG (Center of Gravity or balance point) of this plane.  The Wild Hawk is notoriously tail heavy and needs much attention to get the CG much forward of the center of the wing.  After much research I have come to the conclusion that the CG point should be between 2 to 2.5 inches from the leading edge of the wing.  After moving my battery as far forward as I can without cutting more than the battery retaining foam, I still needed the weight of three 1/2" washers to balance out at about 2.25 inches.  This was OK, but they were just stuffed into the compartment with the battery and could come out in a crash.  Also, if I used a different battery (LiPO) they did not fit in as snug and were usually not enough weight.
Just about 2.25 inches

New position for the battery to improve CG.
(This is an old photo)
So I decided to take the opportunity to make a change.  I had seen someone on the Internet use a fishing "egg" sinker to balance their Wild Hawk, and out to the garage I went to find my tackle box.  I came back in with a few old drop style sinkers that my late Grandfather had made way back in the day, and some newer smaller pinch style shot weights.  The drop style I estimated at being 1/2 and 1/4 ounce while the shot were probably about 1/8 ounce each.  Now the Wild Hawk that I had seen with the egg style sinker just had a hole drilled into it and the sinker hot glued in.  I did not want to do this and I also wanted to be able to change the amount of weight installed so I could add more when using a lighter battery.  I accomplished this by slicing a wedge of foam out of the top of the nose and then boring some holes down into the foam to make room for the sinkers.  I used my modified soldering iron to create the holes with the idea that the melted foam would actually provide for some stability in the nose and hold the weights better.
Holes bored in with solder iron

With the NiMH weights
After some experimenting I was able to balance my Wild Hawk at the point I wanted, 2.25 inched from the leading edge. This was with the original NiMH battery and the two drop sinkers and four shot weights.  I made the holes for the shot weights deep enough so that I could add more later.  I found the "more" amount to be 5 of the shot weights to give me the same CG balance point.  I hot glued in the first set of weights and made sure there was room for the "more" weights.  To hold everything in I just used some fiber strapping tape and taped from the nose over the top of the piece that I cut out.  This worked out just fine in practice.
With the "more" weights

Now for the test.  I finally got some flight time and the plane flew great with the original NiMH battery and I had no issues!  The wings held up great too and showed no signs of bowing even pulling through a loop!  After flying until the NiMH battery was dead, I switched to my LiPO battery.  I opened the front hatch by pulling back the strapping tape and dropping in the extra shot weights.  Then I closed the hatch by sticking the tape down again.  I flew this one till dead also.  Even with a few crashes I had no issues with the nose weights!  I am very pleased with these two new mods!

For some added fun, here are two vids of my Dad flying.  First he's flying my brothers Wild Hawk and then his own Wild Hawk (O'l Hickory).

Thanks for stopping by my blog and please post comments, good or bad.  Be sure to come back and check for future posts.

Sunday, September 11, 2011

Wing repair

Ok, so in my last post, I had issues with my wings starting to buckle at the end of the wing spar and where I cut out for the aileron servos.  I finally decided to repair this by cutting a slot in the wing and inserting a support in the form of a bamboo rod.  Not something really special, just a couple of bamboo cooking skewers!

I really had some issues with how I would cut a groove for these bamboo rods.  My original thought was to use my razor knife and cut a track of foam out of the wing.  Although this might have been the easiest way to accomplish this, I did not want to remove foam from any part of the plane anymore.  My thoughts are that the removal of foam will lend to the weakening of what ever part it is removed from.  So my ultimate decision was to modify my soldering iron and to use it to melt the foam out of my way.  My theory is that the melted foam will maintain the strength of the part but allow for the modification.  So I removed the original tip from my soldering iron and created a new one from a nail and inserted it and set the tightening screw.

After I came up with my final location for the re-enforcement rods, and laid out some markings, and removed the support tape covering this area of the wings, I was finally ready.  I got out a metal straight edge (the back of a steel saw blade).  Lined it up with my markings and began to cut/melt the foam and open the slot for the bamboo rods.

I performed this task on both wings and was pleased with the results. Now it was time to affix the rods. I simply used my hot glue gun to lay a bead of glue in the slot and quickly inserted the rods. Then I laid in some more glue on the top side to ensure the bond and to fill in any gaps.

Now that this was all done, I re-taped the wings with fiber strapping tape from root to tip.  Re-installed the aileron servos and taped down the servo wires.  All ready for a test flight!

Testing went very well and I am happy with the results!  I have been able to fly in heavy wind and do stunts pulling heavy G's without any wing issues.  I feel that melting the foam had added extra support to what the bamboo rod adds and makes for a better repair.

Thanks for stopping by my blog and please post comments, good or bad.  Be sure to come back and check for future posts.