*****Skyote #88 gets Bronze Lindy for "Airventure-Oshkosh 2016 Plans Built Champion"******

October, 2007

Welcome to "Skyotelog", the build record of Skyote #88. I assume that you are familar with the Skyote biplane. If not, you should visit http://www.skyote.org/ for a complete introduction to this unique but elusive biplane.

The posts are presented in reverse chronological order (newest first). Or you can click on one of the "Labels" to see all of the posts concerning a specific topic. Click on any photo for a larger image.

All my building experience is limited to Van's RV's so I have no experience with building tube and fabric or "plans building". I have much to learn so take everything I write with a grain of salt and reasonable skepticisim.

I do not intend to follow a "traditional" path for the construction of #88. I intend to employ low level technology and $ to reduce the construction time and difficulty where possible and practical. By low level technology I am referring to CAD, laser, waterjet, CNC. For example:

  • I have purchased a complete wing spar kit from Jerry Kerr.
  • A rib kit from Mr. Bartoe.
  • Brunton Flying Wires and Drag wires from Harvey Swack.
  • CNC profiled tube kits for the fuselage, tail feathers and landing gear from VR3.

In addition I have converted all of the wing fittings, brackets, links, lugs etc. to CAD and had them cut by water jet. I have designed a laser cut wing spar drill template/jig which positions the five spar components so that all of the holes can be drilled in a complete spar as an assembly. I plan to continue converting as many parts as I can to CAD so that I can reduce the "hand-made" components to a minimum.

Note: As of June 2015 I have over 100 CAD files which provide 600+ water jet cut parts for the Skyote.

While it takes a little time, converting the design to CAD is a great way to truly understand the drawings. plus a huge amount of information has been extracted from the rather complex drawings. This can be a great help to others in understanding and interpreting the design.

The Skyote is uniquely suited for conversion to CAD in that a "computer" was used in it's original design. I have read that Mr. Bartoe used a HP calculator to "compute" the design and dimensions of the Skyote. The plans show all of the critical dimensions to three decimal places for X,Y and Z axes.

Amazingly, when I put the design into CAD the resulting 3D models agree with Mr. Bartoe's thee decimal place dimensions about 99.9% of the time. I have found one discrepancy but less than 0.030"!

If you want to build your Skyote as cheaply as possible, or if you enjoy handcrafting the same parts over and over again then my approach to building is not for you!

If you want to build your Skyote in the minimum possible time with highly accurate parts then this approach may be the answer. I personally get a lot of satisfaction out of organizing the project so that it can be produced accurately. Hopefully some of this work will prove useful to others in the future.

Comments are welcome. I will respond as time permits

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Sunday, April 20, 2008

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"

Monday, April 14, 2008

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

Sunday, April 13, 2008

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.

Saturday, April 12, 2008

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/

Thursday, April 10, 2008

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.