Bending the Tip Bows

Today was the day for bending tip bows. Pete recommends bending the bows around a 13" radius block which seems to be the right number. We cut a 13" radius block with a few degrees of draft on the cut to help snug the tube down on the table while bending. Add a scrap of 2x4 and a 3/8" lag bolt and you have all you need to do a nice job of bending the tubes.





Our bending block has about 180 degrees of arc which is not enough to bend the tube without repositioning. It requires about 255 degrees of bend at the 13" radius to equal the same length of tube when it springs back to the 18+" final shape.


In the photo above you can see that Tom has repositioned the tube to get additional bending. The slider block which is screwed to the 2x4 does not need to be real tight as a little play lets the block have better leverage against the tube while bending.

Fun Time.

Last week Tom and I flew our RV8 from RocK Hill, SC to Newnan, GA and met Glenn Bridges who flew his RV4 over from "China Berry Ranch" near Dublin, GA. Dale Doane, who lives about 2 miles from the Newnan airport, came over and took us to his shop where we rolled out #88 on its gear. The pictures show the RV8 (blue) and the RV4 (yellow) at the Newnan airport. It's always nice to have an excuse to fly but when you get to fly to see your Skyote on the gear it's a real bonus. Seems like RV's are popular with Skyote builders.

More Wing Assembly Progress

After Tom got everything well organized we managed to assemble the false ribs and leading edge spar this afternoon. The spar still needs to be trimmed to the proper length on both ends so it is just clecoed for now. I should point out that I am using a modified approach to the interplane strut attach fittings. I am using "mirror image" fittings on the back side of the spar to eliminate the need for drilling holes in the spar angles. You can find more on this in an earlier post. Check the "fittings" category.

Wing Assembly Progress

Tom has been working away with the rivet squeezer and puller and we almost have a wing assembled. Tomorrow we hope to get the leading edge spar fitted and then move on to the tip bow. So far everything has gone together nicely with just a few small adjustments. The biggest challenge is getting the assembly procedure just right to avoid taking things apart too many times.

Fuselage on the Gear!

Today was an exciting day as we rolled Skyote #88 out of the shop on its gear. Dale Doane has done a fantastic job of fitting and welding both the main fuselage structure and the landing gear. You can tell that Dale is proud of his good work.

The gear turned out far better than I had anticipated. The geometry came out just right and it matches the fuselage attach fittings perfectly. The VR3 Landing Gear Kit was a huge help but the landing gear is still the most difficult part of the project so far. Well, maybe figuring out the drawings might be the most difficult, with the landing gear number 2 in difficulty!

Here are a few random detail photos:

From left to right thats Dale Doane, me, Glenn Bridges. Glenn's fuselage is about two weeks behind mine and will be on the gear soon.

Painting Small Parts

Painting small parts is always difficult. One trick is to use masking tape sticky side up to stabilize the parts. The tape will actually hold the parts in most any position so that all of the edges can be covered. After painting one side allow the paint to cure sufficiently to be "tape proof" then turn them over and do the back side,

VR3 landing Gear Tube Kit

The VR3 landing gear tube kit has been jigged up and welded. Even with the assistance of the VR3 tube kit, getting the landing gear assembled and welded correctly has been the most difficult part of the project so far. Dale Doane came up with the assembly jig pictured here. The jig is referenced off the firewall and holds the two axle tubes in the correct position for when the gear is compressed to the normal ride height and the tail wheel one foot off the ground. At this condition the toe is zero and the camber is 2.5 degrees.

The tube cluster at the axle is relatively easy, especially with the VR3 tubes. The difficult part is the upper ends of the gear tubes where they interface with the fittings on the fuselage. Getting the correct shape at the upper ends while maintaining the correct dimensions and alignment is a challenge. This could all be simplified if a correctly welded landing gear assembly were used to perfect a "stand alone jig "that would hold the tubes in the correct alignment for welding and not involve using the fuselage in the process. Maybe I could convince Dale to offer completely welded landing gear kits !

Assembing First Wing

Tom and I started "dry fitting" the first wing today. This is essentially a matched hole assembly task as all of the parts with the exception of the ribs have been "pre-drilled" by the water jet cutter. So far everything is going well. The plan is to get all of the parts and the assembly procedure perfected then make a run at the remaining three wings.

Weight and Balance Estimates

Based on his experiences with NX8XX Hawkeye Hughes has suggested 19" t0 19.5" as a good normal flying weight CG for the Skyote. It is my goal to achieve that CG without adding dead weight or extending the nose past the position specified in the drawings for the O-235 installation. I have utilized the Excel worksheets posted in the "Files" section of the Yahoo site by Mike to see if it is possible to achieve the above objectives.

The above CAD images show how the battery can be located near the front of the engine to help move the CG forward without adding dead weight. Also, by utilizing a carbon fiber tail spring an even greater forward shift can be achieved while eliminating 2# of unnecessary weight.

I currently estimate that the airplane can have an empty weight of 583# and a normal flying weight CG of 19.15"

Aileron and Elevator Bell Cranks

The bell crank bearings finally arrived after a 45 day back order delay. The aileron and elevator cranks are all final drilled and ready for paint before riveting.

After painting and riveting

Forming the Cabane Attach Finger Plates

Dale Doane came up with a good way to partially form the finger plates which make up the attach point for the aft cabane struts. 3/4" steel shafting was used to weld up a model of the appropriate tubing cluster. Note that this is a 3-D model as the cluster is not in a single plane. After tack welding the cluster to the tooling it is placed under a thick rubber pad with a backing plate and compressed in a hydraulic press.

Landing Gear Bungee Replacement Concept

Most airplanes that utilize landing gear bungees also have STC'd modifications available to eliminate them. Must be a message in there somewhere! With that in mind, I have been designing a modification which eliminates the bungees but avoids conventional springs as well. The design utilizes commercially available polyurethane die "springs". Preliminary tests indicate that 6 springs 1-3/4" tall will do the job. I have selected polyurethane springs of the appropriate diameter, length, and durometer to give the equivalent of 300#/in. spring rate.

Referring to the CAD image, the silver tube is the lower strut tube which attaches near the axle while the red tube is the upper strut tube which attaches to the gear strut/flying wire attach point. The green split clamp collar represents a method of adjusting the bottom spring perch position. It can be adjusted up or down on the lower strut to change the spring pre-load. The polyurethane die springs carry the load by being compressed between the green Clamp collar and the red flange .

Note that there is one urethane die spring above the flange on the red tube. This provides a cushion for when the strut is fully extended.

Others have done similar modifications using steel die springs. I anticipate that the urethane will offer beneficial dampening (damping ?) compared to the steel springs. Another potential advantage is elimination of the total collapse failure mode of the bungee. It will likely take more than one try to arrive at the correct combination of variables. The urethane springs are interesting in that the effective spring rate decreases with compression. I have ordered enough polyurethane springs to mock up a test strut. You can see them at http://www.polyprod.com/

Modified Rudder Pedals

I have previously mentioned the possibility of incorporating RV rudder/brake pedals in the Skyote. I went so far as to buy a set of RV4 pedal weldments from Van's. What I like about Van's design is the location of the master cylinder on the pilot's side of the pedal assembly. Also the master cylinder is an integral part of the pedal assembly making for easy adjustment of the pedal assembly in the fore and aft direction.

After laying everything out in CAD, It appears that I can move the pedals forward maybe 1.5" using the modified design. The plan is to build the pedals per the modified design, then adjust them as far forward as practical at assembly.

If I make the vertical dimension the same as the pedals in my RV7A, (which work very well), then there appears to be sufficient space above the pedals for a 2+ gal. reserve fuel tank. The RV pedals are 8.5" tall while the Skyote pedals are 13" tall leaving 4.5" of space above the pedals. A 14"x14" by 3" deep tank would have 588 cubic inches or 2.5 gallons capacity. I won't decide on the reserve tank until the pedals are actually in the airframe.

In the end, I decided to make my own pedals, using some of the Skyote design, some of Van's geometry and some of my own. The CAD images show two options, one with plate type pedal and one with a pedal constructed from tubing. The Skyote drawings show similar options. The images are for a left pedal. In both variations I have used non-lubricated "plastic" bushings for the overhead pivot as well as the pivot at the base of the pedal. These bushing are readily available in many material variations. One easy source is http://www.mscdirect.com/.

I was originally enamored of the tube style brake pedals but have lately come around to liking the plate style pedals better.

Jabiru Engine Workshop

On March 14, 15 and 16 I attended a Jabiru engine workshop at Jabiru USA in Shelbyville, TN. I enjoyed the experience and found it very helpful in planning the installation of the Jabiru 3300 in the Skyote.