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Mark R Steitle wrote:
I have been working to resolve a problem for more than a month now and thought I would query the group for a possible solution.
If anyone else is running (or planning to run) a 3-blade M/T electric prop with the RD-2C gearbox, I have discovered a mating problem in using this prop/gearbox combination for my 20B. The problem is the RD-2C prop flange comes with 3/8 id x 5/8 od bushings. The M/T prop has a stepped hole that is ¾” for the first 3/32” and then goes to 5/8”. Tracy is not comfortable with drilling out the 5/8” bushings and M/T adamantly advises against using anything less than ½” prop bolts with this prop. So, I’m at a standstill until I can get this resolved. The only solution I can see is to press out the existing bushings and open up the holes to accept ¾” od x ½” id bushings. But that would require disassembly of the gearbox and some precision machine work, possible but not my first choice.
Mark S.
Lancair ES – 20B
(with a very pricey lawn ornament)
Mark,
On a Lyc the 6 drive lugs on a given installation are all the same diameter where they enter the prop, with no step. I'll bet that the 3/4" dia. step, if only 3/32" deep, is to allow mounting the prop directly on a Lyc prop flange without the flywheel (one lug in the crank flange has the oversize step on it to index the flywheel). Surely they don't expect <3/32" tall lugs to carry torque to the prop(?).
Attached is a snip from Lyc Service Instruction 1098G listing various drive lugs & dimensions, but I can't tell from the chart & drawing whether the .75" prop flange diameter necks down to 5/8" where it enters the actual prop. Why not call the US distributor for the prop & get clarification on whether they expect a drive lug (bushing) that's either 3/4"dia x only 1/16" high (can't be a full 3/32" or the prop might not seat on the flange), or a bushing that's 5/8" OD & 1/2" ID with normal height?
Neither sounds ideal, but if I had to choose, I'd go with door #2. :-)
Charlie
http://www.lycoming.textron.com/support/publications/maintenancePublications/serviceInstructions/SI1098G.pdf
lyclug.GIF
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