Topic line is my question and comes from my review of the set-ups listed in the first sticky topic.  (BTW, a BI-I-I-G-G hand of applause     for whoever started that thread!  I've been trying to get some of the guys in the SAM OT Electric world to do the same to help ease the way in for electric powered participation.  I personally would like to see about 10 times that number of entries.)  It comes out of a lengthy transition from Astro 050's for electric launch R/C sailplanes in the early '80's thru Graupner and GWS brushed motors for sport and park flying, to geared Hacker inrunners for electric launch sailplanes and Axi outrunners for my OT R/C models.  Right now, if it weren't for the really short nose moment on a lot of OT designs, I'd probably use my Hackers for anything bigger than 36"span.  That application of electric can benefit from a heavier, shorter outrunner rather than ballast up front.  Someone said, "...add copper, not lead".  I bought into it.  But by and large, I'm probably a Hacker bigot.

So for C/L, it seems to me that having a smaller diameter rotor as in the geared inrunners ought to result in less problems with gyroscopic forces on the motor in the abrupt attitude changes of the C/L pattern maneuvers.  Comments please!

Although I'm trying my hand at the slimer side of C/L out of nostalgia's sake, I really rather be trying the electric side of things.

TIA for any insights and input.
Jim Howell

I suspect that any gyroscopic effects from the motor itself are far overshadowed by the gyroscopic effect of the prop, which would have a much larger moment of inertia.

Granted the radius of the prop is greater, but for a large diameter outrunner, there's a lot of copper/mass in that revolving bell.  It would be interesting to do some of the math to actually calculate relative moment of inertia contributions.  I think the lesson to be learned is to do a good, strong job on the mounting mechanism for the motor.

So, what thickness of plywood or metal is being used for the motor mounts for models around 400 squares?  I've got a modified - lengthened fuselage - Flite Streak ARF that's gathering dust in a corner, and several Axi's of various configurations in the motor stash.  Sounds like I need to get off my duff and try something.

Thanks the response Tim,
Jim

[,there's a lot of copper/mass in that revolving bell.  
[/quote]

actually there is no copper in the revolving bell - there are the magnets - but all the copper windings stay put on the housing.  

... And if you do use an inrunner, keep in mind that the gyroscopic effect will be mostly coming from the prop and not the motor, so not only does the gearbox need to be solidly mounted, but it has to have good stout bearings if it's going to enjoy a long and happy life.

And there-in is probably the deciding factor for me for using an outrunner vis a vis a geared inrunner.  And thanks for the number crunching.  I didn't use the same set of numbers, but get similar relational results.

Jim

Hi All,
No one has successfully used a geared inrunner for the simple reason that the existing gearboxes do not survive Stunt maneuvering loads.
If, some fine day, someone builds a "gearbox" that allows us to use high Kv inrunners successfully, then we will reap the benefits of very low winding resistance in terms of both efficiency and improved RPM control loop dynamics.
Gear noise is not to be ignored, and the Pattern guys have dealt with this by using soft mounts!
In Pattern, the gearboxes were blowing up until they were beefed up, and the weight of doing this makes them weigh very nearly the same as outrunners.
In our case, I suspect the weight will be prohibitive, barring some clever mechanical design.

Dennis and Archie A. messed with a simple gerabox, and until it blew up, they were most pleased with the results. Maybe if you searched on "Astro-Flight superbox" you'd find the thread that describes their journey.

later,
Dean P.

Actually I only knew that a gearbox would have to be stout, not if there was or wasn't one out there that's stout enough.

Dennis and Archie A. messed with a simple gerabox, and until it blew up, they were most pleased with the results. Maybe if you searched on "Astro-Flight superbox" you'd find the thread that describes their journey.

Guilty as charged.  I used an Astro motor with their "Superbox" in a Brodak Hellcat (uses a Nobler wing) - see post #20 in the List your Set-ups thread.   The helical cut gears were set to factory specs plus a dollup of silicone grease.  Worked PERFECT - but failed on the 10th flight.  Structurally the gear box was fine, however the pinion gear was stripped clean, had a groove exactly the same size as the idler worn through it.  I suspected the culprit was the governor mode, with a loading and backloading of the gears simply taking its toll.  It sounded different than an outrunner, and governed wonderfully.  However I could not see a clean way out of the gear wear issue so I abandoned further work - at least for now...