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EAA Experimenter

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What Our Members Are Building

...or in this case, rebuilding

By Charlie Johnson, OneSkyDog@aol.com

Viking Dragonfly MKII
Charlie Johnson next to his mostly restored and highly modified Viking Dragonfly MKII.

Spring of 2006 was met with the snow being pretty much melted off of the lower elevations. The annual condition inspection was in the logbook. The annual tandem-wing gatherings start out with the Mountain States Canard-Wing Fly-In that has been held at Laughlin, Nevada, for several years, but in May 2006 Jean, Nevada, was selected for our fly-in.

I had to attend to some things in Carson, Nevada, and following the fly-in I had a business appointment in Long Beach, California. I packed the plane and called flight service to do a final check of the weather and was soon in the air heading west.

Viking Dragonfly MKII
Heading west through the corridor, coming up on Wendover, Nevada. Restricted to the north, restricted to the south.

In order to get out of Ogden, Utah, on a westerly heading you have to funnel into a corridor along I-80 or risk the dreaded F-16 intercept. I left Ogden, crossed over the Great Salt Lake, and 45 minutes later was passing by Wendover, Utah, climbing through 9,000 feet to my cruise altitude of 10,500 feet it was another hour and 45 minutes to my first fuel stop at Battle Mountain, Nevada. With a quick turnaround for fuel I was on my way to Carson. I arrived in Carson around noon and took care of the things I needed to do before I left for the fly-in.

Viking Dragonfly MKII
South bound to Jean along the Sierras. Mono Lake ahead- time to turn west.

I left Carson and flew south feeling pretty small flying along the Sierra Nevada mountain range. Soon I was approaching Mono Lake, my turn point to cross the Owens Valley and decision point whether to stop at Bishop for fuel or slow down stay high and continue on to Jean. I decided that I had enough fuel to make it to Jean and continued on, contacting flight watch for flight following as I was entering into barren dessert. Crossing the Inyo and White mountains by going through the passes I was soon on the north end of Death Valley listening to a couple of F-18s maneuvering around the mountains. As I passed by Baker I was on the downhill to Jean.

Viking Dragonfly MKII
Looking south into Death Valley, east of Owens Valley. Beatty, Nevada ahead then landing at Jean.

Once settled in at the Jean gathering, I gave my friend Sam Kittle a ride and the climb-out was not impressive with about a 2-mile departure climb before I felt it was safe to turn. We flew southwest along I-15 trying to hook up with our friend Jim in his Quickie Q-200 until we were at the California-Nevada border, then turned back to Jean and flew loose formation. Actually I just went to wide open throttle (WOT) and Jim flew circles around me.

Sunday I departed with a gaggle of Dragonflys and Q-birds headed for California. My friend Tim Iverson and I set a course for Mojave Spaceport for lunch and to pick up some parts for Tim.

Viking Dragonfly MKII
Charlie's Dragonfly in the background, Tim's in the foreground, both VW-powered.

Taking off from Mojave, little did I know that this was to be my last takeoff in N157JG. Making the turn point at Santa Monica Airport we entered the VFR corridor at 3,500 feet MSL over LAX with a scattered cloud deck below us. Ten minutes later we were rolling out at Torrance, California. I tied up in transit parking and Tim gave me ride to Long Beach.

During the next week Tim and I decided to go to another canard gathering (Canards West, formally known as 'Canards de Mayo') at Columbia, California, and we would leave Thursday afternoon.

One of my officemates dropped me off at the Torrance airport and I packed the plane with my luggage and waited. Tim called and said he was running late and would meet me near the run-up area. I decided to taxi over to Tim’s hangar where I shut down while Tim was getting his plane out. On the way to Tim’s I smelled something burning but dismissed it as coming from the hangar construction site as I could smell hot tar wafting by intermittently.

Tim decided to top off his fuel and taxied to the fuel pumps. I started up and taxied out to the end of the hangar row and messed with the mixture because I was getting just a hint of roughness and was trying to determine if it was real or if it was just me being nervous about the airspace dance coming up. I cycled the engine up and down a few times but didn’t pick up on anything being wrong and shut down the engine. Tim returned from fueling and I started my engine and got taxi clearance and followed Tim out to the run-up area.

I did a quick mag, mixture, and carb heat check and indicated to Tim that I was ready to go. As I applied power to pull out of the run-up area (to line up at the hold short line) and pulled the engine back to idle I noticed something strange: My prop did not seem to be responding to the change in engine speed! I called Tim and asked him to hold, then shut my plane down and jumped out. As I rounded the canard tip and looked toward the prop I saw oil running down the bottom cowl. I approached the prop and went to check my compression by pulling the prop through. I can’t describe the feeling when the prop spun around and went through three revolutions before stopping.

With the help of the EAA members at Torrance I was able to store my crippled plane in a hangar until I could return the following Wednesday with my brother Bob to help me disassemble and transport my plane back to Ogden.

Trucking the plane home
Larger view

With the help of the local EAA chapter and brother Bob, the plane was trucked home.

I was unable to separate the elevator torque tube from the elevators due to corrosion between the aluminum and the steel tubes. The elevators were cut off at the root to get the canard off. The plane was packed up on an open trailer and transported 750 miles to Ogden.

Removing the engine from the airframe
Once home, the engine was removed from the airframe.

The engine case and crank were wiped out when the hub failed, as you can see in the following photos.

Damage to the case
Larger view

With the propeller hub removed, we can see damage to the case. The oil slinger should not be visible.

Propeller hub attachment
Larger view

By contrast, here is an undamaged VW case with the same type of propeller hub attachment. Notice that the case has more material than the photo above, indicating what broke off from Charlie's engine case.

Prop hub
Larger view

Prop hub
Larger view

Charlie's damaged prop hub on the left; a new, undamaged one on the right for comparison. Note that the failure emanated from the keyway, a natural stress riser.

I made a decision to not rebuild or buy another VW engine for this Dragonfly. In spite of Dragonfly designer Bob Walters’ admonishments to not to put a larger engine up front or increase the gross weight (it can't be more dangerous than flying from my high-altitude airport with a VW's climb rate), I decided to install a Corvair engine. Another consideration is that this plane had been flying for 18 years and I put more than 500 hours on it; plus, it had 325 on it when I bought it.

At Hill Air Force Base they bring planes in for heavy maintenance cycles, stripping the old stuff off and refurbishing them. I guess this is Depot cycle time for my Dragonfly as it is 18 years old and has 850-plus hours on the airframe.

I surveyed the plane as is sat there in pieces and decided it needed more than an engine change. I formulated a list of items to be taken care of during this major modification.

1) Replace the VW engine with a 100-horsepower Corvair. This decision is based on the poor climb performance of VW engines (as installed in the Dragonfly) and three known successful O-200 powered Dragonflys, plus the success of the Corvair conversions on the KR-2 aircraft.

2) In order to comply with the plans, elevator torque tube revision, plus the fact that I could not disassemble the elevators. Torque tubes and bearing blocks were completely removed.

3) Elevators needed to be mass-balanced to handle the speeds (hedging against flutter) the Corvair will be capable of.

4) The wiring was frightful when I first bought it. Things would stop working and then start working later. I had an offer from a really good wiring guy to rewire my airplane, but he required that I remove the canard. Hmm…the canard is off and engine wiring to bus needs to change anyway, so complete rewire job.

5) I wanted to put in a reflexor ever since I had a ride in Justin's O-200-powered Dragonfly (featured in the October 2009 issue of EAA's Experimenter) because it trims so fine.

6) I never really liked the cowl cheeks on N157JG and they needed help no matter what I did up front. Since the Corvair is substantially narrower than the VW, there really isn't any need for the cheeks.

That is a big list and so far I have managed to fabricate one-piece elevator torque tubes and mounting bearings and install them.

Phenolic elevator bearings
Phenolic elevator bearings being manufactured.

Attaching the elevator torque tube
Larger view

The original method for attaching the elevator torque tube to the elevator was a simple bond between the aluminum tube and the foam core. This proved to be inadequate, so a mandatory change was instituted that called for a wooden rib to be bonded in the root section, to which a steel plate could be bolted. All twisting motions would then be transmitted through this rim to the elevator skin, not the foam.

Mass balance control surfaces
Larger view
Another mod that isn't required but is a great idea for any plane is to mass-balance the control surfaces. In order to keep the weights internalized, it's necessary to cut through what would be considered the drag spar on the canard of the Dragonfly. Although this sounds scary, it's a proven technique spelled out in the newsletter. See image below:

 Elevator torque
Larger view

Engine is hanging on the firewall December 17, 2006! I had to modify the engine mount that I bought from fellow Dragonfly builder-turned-Mooney driver Dave Morris to fit my firewall and add a lower truss to the back tube. I load-tested a mount like this to 3.5 g’s so by similarity I am confident that this mount will be adequate for the flying that I do.

Old engine mount
Dave Morris's old engine mount, redesigned by Charlie Johnson.

Now the work begins to fabricate all the systems and make it fit into a cowl. Here is the William Wynne nose bowl, an off-the-shelf part offered by FlyCorvair.com designed to be adapted to virtually any airframe, from a Pietenpol, to a Sky Coupe, to a CH601, including KRs and now Dragonflys.

Nose bowl

Nose bowl

Nose bowl

Nose bowl

Here we have the nose bowl, the shaped foam on the fuselage, and the sacrificial plug section in the middle sealed with blue latex paint, six coats of wax, and a coat of Partall #10.

Intake runners of mild steel join for the under-slung Ellison throttle body carb. Don't be alarmed with the appearance of the exhaust system shown in the first image. This is a tuned header system designed for automobiles and off-road buggies. It was there for planning purposes.

Engine installation
Side view of the engine installation. Note exhaust is now 3-into-1 and the intake is complete.

Engine installation

The installation is substantially complete. I decided against heat muffs for cabin heat and plan on using a pair of 200-watt ceramic heaters from Cadillac front seats. This will require the use of additional power, so I have decided on an East Coast mini-alternator with a 50-amp output. These things are rated at continuous service at more than 14,000 rpm. The pulley sizes are the same as on my GMC suburban truck.

Renown RK builder and flyer Mark Langford built fiberglass intake plenums that are working well for him, so I decided to make some for my plane. This took about three months, but I think that they will work fine. Four molds make the two plenums and the tops and bottom ramps are bonded together.

We look forward to hearing more from Charlie as his project progresses. As with good form, Charlie makes no predictions of when he'll be done. Please consider submitting an article on your project, regardless of its current stage. Our readers will enjoy reading about it as much as you've enjoyed reading about Charlie's. ~Pat


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