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.