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Geared Drives Checks In - Firewall Forward for the RV-10

The loss of an aircraft, and survival of a dream; a tribute to Bud Warren and Phyllis Ridings

By Phyllis Ridings

Just over a year after the total loss of Geared Drives’ Wheeler Express, as described in the previous article, father and daughter team Bud Warren and Phyllis Ridings reported on their progress with creating a firewall-forward for the popular four-place Van’s RV-10. This article was printed in the November 2008 issue of CONTACT! Magazine and is reprinted here as part of our tribute to Bud and Phyllis. Read more

The new firewall-forward package by Geared Drives is shaking out nicely. Our customer and friend, Bill Gipson, (N730WL) has completed his Phase 1 flight tests with no engine-related issues, and he is all smiles these days. Performance exceeds projections. On takeoff, applying power slowly until rudder authority kicks in is taking some getting used to. There is a lot of torque available to the prop, considerably more than the airplane was designed to handle.

The official total empty weight of N730WL is 1,727 pounds, which is 207 pounds heavier than the advertised empty weight of 1,520 pounds. This includes 23 pounds of lead in the tail in order to keep the center of gravity in the acceptable range. Like most RV builders, Bill also has a lot of extras that Van’s does not factor in, such as a heater, additional instrumentation, etc. Odds are good that N730WL weighs about the same as the average tricked-out RV-10. Either way, there is still 973 pounds useful load available for fuel and passengers when respecting the 2,700 gross.

Larger view

Bill has not pushed the envelope yet, but Bud flew the first 10 hours in this plane and reports that 3500 rpm at 24-inch manifold pressure (mp) nets 188 knots, burning 11.2 gallons/hour at 5,000 to 6,000 feet. Reducing mp to 20 inches nets 159 knots, burning 7.8 to 9 gallons/hour. A cruise climb at 20-inch mp and 3,500 rpm nets 2,500 feet/minute. Bud also warns that one can easily bust Vne (redline) at just about any altitude. He once found himself indicating 195 knots in the pattern. The plane should be good for 200 knots no problem, and if you need some serious economy, 159 knots can be maintained at 18-inch mp.

Bud has several projects going all at the same time. One such is a Glasair that had 400 hours on an IO-540. When Bud removed it intact and weighed it, the scales tipped 530 pounds!

Larger view

The unassuming “box” does nothing more than support four gears, provide plumbing for the prop oil, and have the robustness to handle a heavy prop. Note, too, that the thrust line is maintained and the cowl is unaltered.

Another notable milestone is the success of the Subaru propeller speed reduction unit (PSRU) prototype. This is a double reduction drive with all of the same features as the original PSRU such as its own oil pump and filtration system, centrifugal clutch and flywheel assembly, and drive port for a prop governor. It can accommodate virtually any ratio you want and can be changed on a whim. Larry Perryman with his RV-9A made the trek from Conroe, Texas, to Lakeland, Florida, this past Sun ’n Fun, and the PSRU didn’t miss a beat. Larry also reports that he has doubled his climb rate and has picked up 25 mph – all due to the use of the Hartzell constant-speed propeller.
Larry had extensive time with an Eggenfellner engine and PSRU in his RV. Bud made three installation changes: 1) new PSRU, 2) constant-speed prop, and 3) replacement of the two smaller radiators with one large one. Note that no changes were made to the cowl – the PSRU is a direct bolt-up swap. In addition to better performance from the ability to run a true constant-speed prop, the engine now runs cooler, never seeing temps over 180 degrees where 250 to 270 degrees was the norm previously.

The new PSRU is not very attractive per se, but it is just a prototype. If Bud goes into production, a proprietary casting will be implemented. As with the prototype, the production unit will be a bolt-on assembly, designed with the homebuilder in mind.
Thanks for your support and we look forward to meeting CONTACT! readers wherever we go.

Although they suffered a total loss of the factory demonstrator in October 2007, by the spring of 2008, Bud Warren had developed a full firewall-forward package for the RV-10 and had it on display at Sun ’n Fun. The mock-up in this video uses the same PSRU that was on the destroyed Wheeler Express, with no changes except oil and gaskets.


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