with a recently installed Elippse prop on an RV

REDRIVE and PROP

The M-200 Marcotte 1.92:1 ratio propeller speed reduction unit (PSRU) is driven through 6 rubber doughnuts to minimize crankshaft loading and provide some damping. The first set of rubbers was replaced at 70 hours. I’ll let the next set go for twice that before pulling them for inspection. A Teflon tube sight-gauge has been fitted to the PSRU to monitor oil level and it used to have a tendency to vent some oil periodically. This venting was reduced by extending a 1/4" vent tube down vertically about 1/4" into the space between the prop shaft bearings. After that, switching back to heavier 85W140 synthetic gear oil stopped it completely. 3/8" Teflon tubing is also used for wing fuel sight gauges.

With the ignition off, the engine will windmill down to about 40 knots but once stopped it will not rotate again without the starter regardless of airspeed. That is with a three-blade 72" Warp Drive propeller. To my surprise, the glide ratio is about the same whether windmilling or stopped on my installation. For more info on the Marcotte PSRU, see the side article to the right.

EXHAUST and ENGINE MOUNT

A fairly large stainless steel muffler accepts exhaust from both cylinder heads and then expels out one side. I used .049 type 308 stainless pipes and .035 sheet for the muffler. I gas welded the engine mount out of .058 tubing for easier welding for a first timer. It, too, is redundant in that any one broken weld will not cause a problem. The exhaust, like the intake system, was also TIG welded with Solar Type B backup flux and some argon purging. After much effort I concluded that there was no advantage to tuned headers on this engine since there is almost no valve overlap to exploit with the stock cam.

ACKNOWLEDGEMENTS

I would like to mention and thank Bob Nuckolls of the Aeroelectric website and newslist, the late Garfield Willis, Don Parham, Bob Patterson, and of course the publishers of and contributors to CONTACT! Magazine who all helped us learn to build a better airplane.

Ken Lehman, Ontario, Canada klehman@albedo.net

EFI: For the Do-It-Yourself Builder

For the true experimenter or do-it-yourself type of individual, there is another option in electronic fuel injection systems. MegaSquirt®, by Bowling and Grippo, offers a new option in EFI technology by providing experimenters with the guidance to build their own EFI Controller using just a few basic tools.

They are able to do this by offering a few key pieces such as the 68HC908 processor, a small integrated circuit chip, but the builder will need to gather the remaining components such as pumps, fuel rails, sensors, etc. A builder can design the EFI Controller for a variety of applications spanning single injector up to sixteen injectors and even-odd firing engines of nearly any make.

Bowling and Grippo emphasize the initial steps by addressing specifics in the beginning, helping the builder determine his needs, then building from there any custom features desired. Ultimately this is intended to provide an educational experience for those with a desire to learn, build and fly.

For more on the MegaSquirt® visit www.bgsoflex.com/megasquirt.html

Long-time readers of CONTACT! Magazine may recall Jean-Pierre Deschenes’ article in issue #51, featuring the Marcotte redrive, (July/August, 1999). The story included a cover photo of Guy Marcotte’s PSRU mated to a Subaru followed by an in depth walk through the entire manufacturing process. This is an excellent read for anyone wishing to understand the inner workings of a typical gear driven PSRU, including but not limited to gear machining, ratios and general design.

In brief, Marcotte originally set out to design an affordable aircraft performing missionary and other charitable work in third-world countries. He built the plane and opted to install a V-8 (for obvious reasons), thus creating the need for an affordable but strong (and simple) propeller speed reduction unit. The Marcotte PSRU was made available for varying engines ranging from 150-hp up to 450-hp with an option for variable pitch hubs for traditional controllable props.

There is a small inventory of redrives still available, with the promise of a new production run coming soon. We hope to produce a follow-up article to the one in Issue #51, but in the meantime, for more information you can e-mail Ray Fiset at raymondfiset@bellnet.ca