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Jake Jaks’ Pober Junior Ace

15 years of work

By Patrick Panzera, EAA 555743, ppanzera@eaa.org

Doug Jacks, Paul Poberezny, and Jake Jacks
Doug Jacks, Paul Poberezny, and Jake Jacks
Photo: Pat Panzera

Pober Junior Ace

Like many of us, Jacob (Jake) Jaks was a little undecided when it came time to choose a plane to build. He knew he wanted to build something from scratch but really didn’t have a firm mission in mind, except “low and slow” as a main criteria. Of course that term should immediately conjure the venerable Pietenpol, which is the direction Jake took. Plans in hand but no material purchased, Jake and his wife Donna flew their trusted 1963 Mooney (which has since been replaced by a 1982 version) from their home in Tallahassee, Florida, to EAA Oshkosh1994.

But then they saw Paul Poberezny’s Pober Junior Ace sitting on the flight line. The coziness of side-by-side seating (and relative roominess as compared to the Piet) as well as the overall lines sold them on it. Although the plane didn’t have much of a commute to get to the event, it was flown for exhibition nearly every day. Returning to Florida, Jake ordered a set of Junior Ace plans.

The Engine
Progress was slow, as it is for many of us who have to put family and earning a living far above building planes. Jake had it extremely difficult; he had just moved from California and was setting up shop as a self-employed civil engineer. But with the support of his family and help from his sons and his father, the project eventually arrived to the point of needing an engine decision.

Discouraged that the certified engine route would be cost-prohibitive, Jake started looking at auto conversions. Jake was already familiar with the VW conversion, but it wouldn’t be an appropriate replacement for a C-85. While perusing EAA Sport Aviation Magazine for engine options, Jake came across an ad for William Wynne’s Corvair conversion manual. So he bought it.

Using a hint found in the manual, Jake found the owner of a barn that contained not less than 40 Corvair engines lined up, just sitting there. Jake handed the owner $125 after a little hunting and went on his way with his new core engine.

Corvair College
Right about that time, William Wynne started inviting those who purchased his manual to come to his hangar and use his tools and tutelage to open, inspect, clean, rebuild, and potentially run their engines. Opening one of these core engines that have been sitting in a barn or bolted into a wrecked car for untold many years (decades) is akin to opening an oyster hoping to find a pearl. They all look horrid on the outside, and many look the same or worse on the inside, but the majority contains that pearl, each of a varying degree of gem quality. I’ve seen some people open their engine and see all new parts inside while other people have basically had to toss it and start over, with most somewhere in between. As a digression, William Wynne’s happening (to use an old hippy term) started becoming a regular event and was soon dubbed “Corvair College.” The concept has been a huge success, each happening more so than the previous one. The most recent event was Corvair College number 17, which was a tremendous hit.

Jake, alumnusof the very first Corvair College, arrived there with his engine already disassembled, cleaned, and with fresh new parts in hand. By the end of the weekend, Jake took hispainted, fully assembled, andrefurbished engine back home. It wasn’t ready to be installed, though; Jake thought it best to keep the engine in his air-conditioned office, where it quickly became a conversation starter with the curious customers of his engineering business.

Donna inspecting the workmanship
Donna inspecting the workmanship

Dad and Jake next to the Junior Ace skeleton.
Dad and Jake next to the Junior Ace skeleton. It looked like this for a long time as different components, controls, etc., were installed.

Jake and his youngest son, Doug
Jake and his youngest son, Doug, “hangar flying” the plane in its skeletal stage

Eventually Jake couldn’t hold off covering his airframe any longer. He decided it was time to install the engine. With a cobbled “hood” as a cooling plenum and all the necessary systems installed and ready to be monitored with the proper instrumentation, Jake ran the engine for the first time. Once the hiccups were ironed out, the plane was ready for cowling, fabric, and paint.

Pober Junior Ace

Ready to Fly
Taxi-testing began in 2004. Soon after, the FAA inspection was completed, and NX1028A was ready to fly. A hand-made fiberglass nose bowl was the original cowl. The engine wasn’t set up with a starter and had no true electrical system. NX1028A was flown in this configuration for approximately 30 of the requisite 40 hours.

A hand-made fiberglass nose bowl

Creating a mold to fiberglass the nose bowl 
Creating a mold to fiberglass the nose bowl 

The homemade wind generator
The homemade wind generator provided enough electricity for the automobile-style ignition system during the first 30 hours.

But the hand-propping aspect started to become bothersome, especially with the overly thin Warp Drive propeller not giving much to grip. Coupling this with the propeller’s low moment of inertia and the engine’s relatively high compression ratio, it was becoming quite the chore to get the engine started. The elevation of the propeller, as measured from the ground, wasn’t very ergonomic, either. Jake had enough.

Jake taking his father
Jake taking his father for his first flight in the plane after phase one was completed

A call to William Wynne resulted in the decision to convert the engine to electric start. At this same time there was (in essence) an airworthiness directive mandating that any Corvair conversions that were currently flying or destined to fly in fast aircraft (such as a KR-2, Dragonfly, or even a CH 601 XL) must have the crankshaft (Magnaflux) inspected and be treated with a surface-hardening process called nitriding. So when William was presented with an opportunity to help one of his customers convert to electric start and to change the crank for the sake of safety (even though it wasn’t necessary for the “low-and-slow” Pober), he went out of his way to help Jake. The decision was made; the engine was pulled and delivered to William’s hangar.

Wings suspended from hangar roof
Wings suspended from hangar roof, getting ready to take the fuselage to William Wynne’s to install the refurbished engine with starter, alternator, and new crankshaft

The revised installation with several new items including an electric starter
The revised installation with several new items including an electric starter

Unfortunately, the installation of the starter on the front of the engine necessitated a new cowl, which also meant a new baffling system and a new spinner, giving the airplane a completely different look. Along with the new starter, Jake installed a permanent magnet dynamo (generator), revised the intake system, and extended the exhaust to complement the revised cooling air outlet.

ake reworking his cowl
Jake reworking his cowl with a William Wynne nose bowl and a 13-inch spinner

So with the new cowl completed and phase one still in effect, Jake began taxi-testing. All this time Jake was using the stock (approved) oil cooler with satisfactory results. But as many of us know, a small change to the airflow under the cowl can net huge results – some good and some not so good. Testing showed that the oil wasn’t getting cool enough for Jake’s comfort level. Cylinder head temps were getting a bit high, too.

So Jake removed the cowl and started to rework the baffles when he discovered an oil leak, and worse still, a blown head gasket. One phone call later to William (Jake seeking at a minimum a shoulder to cry on) netted the offer by him to bring the engine back, still installed on the airframe. Once William inspected the engine, the blown head gasket was verified, the root cause discovered as detonation.

Jake left the engine and airframe with William and went back to Tallahassee. Undaunted, Jake started modifying the cowl by increasing the size of the cooling air exhaust in an effort to increase the flow through the engine compartment. Meanwhile, William was getting the engine back in top form. Once William was finished with the engine, Jake made the trip back to pick it up, but not before both of them ran the engine on William’s test stand making sure everyone was satisfied with its operation.

Back home with the resurrected engine, Jake continued to refine the installation with the addition of a larger oil cooler. Successfully taxi-testing, Jake was back in the air with some pleasing temperatures. The oil was still a bit high, hovering around 230 degrees(most likely as a result of poor sensor location), but cylinder head temps were below 350 degrees Fhrenheitat all times.

Completing phase one just in time for Sun ’n Fun 2009, Jake set his sights on making that trip with his youngest son, and that’s where we caught up with them. We had a rare opportunity to coordinate the introduction of Paul Poberezny to Jake’s plane early one morning. I’m not sure who was more excited to make this meeting, Paul or Jake, but they hit it off like long-lost buddies. It seems that they had already developed somewhat of a relationship during the build.

Back to the Airframe
With rare exception, Jake followed the plans to the letter, even as updates (addendums) arrived in the mail, most of which were caught in time. Only one addendum caused some rework as the plans contained an error that at the time seemed wrong to Jake, but he was bent on following the plans verbatim. As it turned out, his instinct was correct, and one of the welded-in cross members had to be removed and repositioned. There were a couple of times during the build where Jake had a question. “A phone call to the EAA – they put me right through to Paul every time,” he said.

“I probably talked to Paul at least three or four times with different questions,” Jake said. “And there were a couple of times during the building when I’d see him at either Sun ’n Fun or Oshkosh, and I’d get a chance to talk to him again about my project. Paul was valuable encouragement for me during the building process.”

Overall, Jake is pleased with the performance, hitting the advertised numbers with relative ease. “It stalls about 35, cruises about 70. Empty weight is 822 pounds and gross is 1,320, all within the LSA [light-sport aircraft] limits. The one thing I would change is the angle of incidence on the wing; I think it’s got too much, so I ended up having to shim the tail surfaces to counter that, to give me a little more nose-down attitude.”

It turns out that after Jake completed the aircraft and was amid phase-one flight testing, his attention was brought to a mistake in the cabane drawings. The aft members should have been an inch-and-a-half taller, which would reduce the angle of incidence.

Overall Opinion
The entire process of building his own plane, as somewhat of a family affair, has been very rewarding. When he started, his three children were three, six, and seven years old and demanded a lot of Jake’s time, but as they got a little older, they were enlisted to help the build process. Fifteen years later they’re all adults, having grown up in a home where an aircraft was built from scratch. Jake’s youngest son, Doug, was fortunate enough to have flown with his dad to Sun ’n Fun 2009 where he got to meet Paul.

On the other hand, maybe it’s Jake who is the fortunate one. He had the opportunity to build a plane with his family as well as making the Sun ’n Fun trip and the meeting with Paul with his son. Jake’s other two sons were certainly influenced by the build. His eldest is currently serving his second deployment in Afghanistan as an F-15 crew chief, and his middle son is at the U.S. Navy Officer Candidate School and is supposed to go on to Pensacola for flight training.

But as the saying goes, all good things must come to an end – the same is true for this project. The Pober is one too many planes for Jake’s hangar, and it must go. Of course he’s not thrilled about getting rid of it, but if you’re looking for such a plane, send him an e-mail and maybe you can work out something.  

To see more photos of Jake’s plane, check out the photo gallery.


Pober Junior Ace
P.O. Box 462
Hales Corners, WI 53130

Top speed 130 mph
Cruise 80 mph
Stall 38 mph
Range 250 nautical miles
Rate of climb 500 feet/minute
Takeoff distance 350 feet
Landing distance 450 feet
Service ceiling 25,000 feet
Engine used Continental
Horsepower/horsepower range 85/85-125
Fuel capacity 12 gallons
Empty weight 750 pounds
Gross weight 1320 pounds
Height 7.33 feet
Wingspan 34 feet
Wing area 168 square feet
Length 20 feet
Number of seats 2
Landing gear Conventional
Building materials Steel, wood, fabric


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