The O-200 Is Here

The new Continental O-200 came today. I have included some shots of the engine still in its shipping crate an well as some after it has been hung on the engine mount. Looks like it is going to work out just fine. I was relieved to find that the engine mount lined up very nicely. The biggest challenge will be designing the exhaust system. I hope to have a 4-into-1 system with the collector exiting out the bottom of the cowl just in front of the firewall.

O-200 Engine Mount

The new engine mount for the Continental O-200 is fitted and tacked ready for final welding. Based on Hawkeye's aft C.G. condition and comparison to the weight and geometry of the Jab 3300, I decided to move the O-200 forward by 2" from the position specified in the plans. The plans call for 10" between the firewall and the back of the engine mount but this mount is 12".




At the risk of over doing a simple subject, I have put together a full sequence of fitting a tube to two parallel intersecting tubes using the "tube miter" software to print patterns. www.ozhpv.org.au/shed/tubemiter.htm




We are mating a 3/4" tube with a 1/2" tube. The tube miter program assumes that the 1/2" tube will pierce the 3/4" tube. This means that about 1/2 of the printed pattern will need to be discarded. Note that the tube miter program works in mm dimensions.



This is the part we need.




I use 3/8" flat stock to find the center line of the 3/4" tubes. Clamp the tube to the bench and mark each end on opposite sides. This will be used to align the patterns on each end.




Determine the length of the tube. This requires a little estimating using a tape measure and "eyeballing" the portion where the tape won't fit in. Align the pattern with the center lines on the tube and tape it in place.


Rough cut the tube on the band saw.



Grind the tube to match the pattern and check the fit. Because we are fitting a 3/4" tube to a 1/2" tube, the shaped end of the larger tube will need to be squeezed down for a better fit to the smaller tube.



I was very pleased that I managed to cut and fit all of the tubes for this mount without scrapping a single tube!

New Engine Choice

The short version is: I have sold the Jabiru 3300 engine and ordered a custom built O-200 to replace it!

The long version is after reviewing the cooling problems others are having with the 3300 Jab and considering my options, I decided that it is best to make the change now rather than fight it for a long time and then possibly still have to make the change. I have already sold the Jab/prop/TBI and ordered a "slicked-up" O-200 from Don Swords of Griffin, GA. More about this engine later.

Refitting for the O-200 should go quickly as the plans provide all of the details for the installation. I think that most of the cowl can be salvaged but I have already started on the new engine mount.

In retrospect, all of the extra work required to adopt the Jab has set me back about a year from where I would be if I had originally gone with the O-200. Live and learn!

Weight and Balance

I weighed the Skyote yesterday sans paint and covering. The empty weight (with engine oil) is currently 579 pounds. Assuming that paint and covering will weigh 60 pounds, I project a finished empty weight of 638 pounds with an empty plane C.G. of 15.5". According to the info supplied by Pete Bartoe, N27PB weighs 641 pounds empty with a C.G. of 12.3 inches.

I did the calculations for "normal" and extreme forward and extreme aft loadings. I distributed the projected 60 pounds additional for paint and fabric by area and location relative to the datum. The following table shows the results. (Click to enlarge.)


Here is a graph of the same data.


Note that the extreme forward condition is with a 100# pilot, no baggage and 100# fuel. The extreme aft position is with a 225# pilot, 20# baggage and 13# fuel, both of which are unrealistically extreme.

I am very pleased that the projected normal loading is right in the middle of the range at 19.5" while the extreme conditions are also still in the allowable range. It looks like NX88NX will be very forgiving of variations in loading.

Aileron Slave Push Rods

I have been putting off making the Aileron interplane push rods for too long. I turned 8 plugs from 4130 and drilled and tapped them to 1/4-28 while they were in the lathe.



The tubes were cut to length and "bird-mouthed" for welding on each end.



Ready for tack welding and assembly check before welding.

Center Section Handle

It would be really helpful to have something to hold on to while I coax my 70 year old bones into the cockpit. The trailing edge of the upper wing center section seems to be a good location. One possibility is to replace the 3/8" steel tube trailing edge with combination trailing edge/handle cut from 1/4" aluminum plate. This would allow the handle to be incorporated into the trailing edge and also provide a better interface for attaching to the ribs. I made a prototype from 1/4" plywood and it looks like it will work okay. The middle ribs will be cut so that the upper flange of the ribs laps over the aluminum plate.




I decided to add some tabs to aid in attachment to the ribs. The final part was water-jet cut from 1/4" 6061-T6.


Center section ribs marked for Cutting.


Cutting with an abrasive wheel worked well.



The handle/trailing edge is now in the final position flush with the upper surface of the ribs. The next step will be to install 0.020" skins to tie the handle to the center section ribs and the aft spar.

Fabric/Painting Test Panel

With the covering/painting phase of the project on the near horizon I have started thinking about the alternatives. I have attended EAA workshops for both TIG welding and fabric covering. The welding class convinced me that I would never reach the skill level required to do a top notch job on the Skoyte fuselage structure. The fabric school, however, convinced me that I have a good chance of doing an acceptable job covering the Skyote myself. I have participated in a couple of covering jobs since the workshop, both using the PolyFiber system and PolyTone paint.
http://www.polyfiber.com/

I have also studied the line of waterborne adhesives and paints offered by Stewart Systems. I certainly like the user friendly qualities of the waterborne products. Stewart also has an excellent set of DVD's which illustrate the covering and finishing process in great detail. I think they are worth watching no matter which system you choose. You can go to: http://www.stewartsystems.aero/ or you can go to YouTube and enter "Stewart Systems" to see the videos.

I decided to make up a test panel and cover and finish it with Stewart products. This will give me a good comparison of the two systems. I am leaning toward the Stewart products but I want to have a little more experience with it before I make the final decision.

I glued up an imaginary airfoil panel using some plywood scraps and other junk. It is about 20"x20".


Stewart Systems Ekobond adhesive is blue/green in color. Unlike Polyfiber Polytac adhesive it has no oder. I covered this test panel in the kitchen during a recent snow with no complaints from my wife!

I am keeping up with the uncovered, covered, primed and painted weights of the test panel.

The panel in the photo below has two "cross-coats" of Ekofill primer/filler/UV barrier applied by brush. The next two coats of Ekofill will be sprayed. The color is actually a charcoal grey.

Two coats of EkoFill white provides a good base for the "Federal Yellow" EkoPoly topcoat.


Four "cross-coats" of EkoPoly gave good coverage for the final top coat. The EkoPoly gives a nice high gloss finish. I got just a little bit of orange peel. The small test panel didn't allow much opportunity to experiment with gun settings but I am only off about one click from ideal.

Wheel alignment completed.

The wheels and axles were were reinstalled. Skyote #88 now has zero toe-in when it sits in the three point position.

The 1.8 degree axle correction is visible in the photo below. This shot is from above the right wheel with the airplane facing to the right.

Toe-in Correction Contd.

Rather than use shims to correct the toe-in problem we decided to machine the face of the axle flange to give the same results. This was done by holding the axle in a vertical chuck and tilting the head of the Bridgeport 1.8 degrees. A fly-cutter was then used to face off the axle flange. Robbie Grove confirmed that these axles are way over built for the Skyote application. A maximum of 0.062" of material will be removed from the flange.

We used a digital level to check the angle of the milling head.

Axle held in vertical vise mounted on the BridgePort table.

Fky-cutter pass in progress.

The photo below shows the 1.8 degree angle on the face of the axle flange. The axles will be reinstalled later this week. The toe should now be zero in the three point attitude. Any further adjustments can be done with shims which are available from Grove Aircraft.

Landing Gear Progress

The next step is to transfer the axle flange hole pattern to the brake torque plate flange.

Before drilling, the airplane was put in the three-point attitude and the adapter flanges were aligned to vertical. This will allow toe-in to be adjusted with a simple wedge shim or a wedge cut on the aluminum axle flanges.

The torque plate flanges were drilled using the flange adaptor as a guide.

After drilling the Grove axles were temporarily installed.

With the wheels installed, the center-line of the airplane was laid out on the floor.

A four foot straight edge was aligned with the brake disks to establish the actual toe dimensions.

Each wheel was within a tenth of a degree of 1.8 degrees toe-in with the airplane in the three point attitude.
>

The aluminum axle flanges will be machined to give a 1.8 degree toe-out correction for each side. This will give zero toe in the three point attitude and a little toe-out as the tail comes up.