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 Post subject: Big electric variable pitch prop.
PostPosted: Sun Jul 26, 2015 3:37 pm 
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Joined: Mon Jan 21, 2013 8:26 am
Posts: 72
Location: Prince Albert, Saskatchewan, Canada
Hey all. I was so thrilled to find that the podcast was back on the air it inspired me to dig out a shelved project and try to get it functional. While listening to the sweet sounds of Ben and Chris enabling the masses to purchase more cutting edge R/C technology I made some mods and got my variable pitch prop setup working.

A bit of background. I am an aircraft mechanic by day. A lot of my time is spent with turbine powerplants and I think it would be neat if we could mimic the functionality of the small turboprops with our electric setups. We have the smooth power and the torque, all that was missing was pitch control. I set about designing and building a mid size variable pitch prop setup. My first design used delrin (hard plastic) bushings but at high rpm the blades would lock up as the centrifugal forces are very great at the blade root even on a 13" prop. Skip ahead to version 3 and I have it working well. Still tuning and playing but it is functional.

The prop is a 13" - two blade design capable of about 15" positive pitch and 12" negative.(beta). It is swung by a eflite power 52-590kv on 6s. A helicopter governor setting on the speed control(hobby wing) holds max rpm at 10000 and throttle and pitch curves are set to mimic a Pratt and Whittney PT6a turboprop. 1500 watts are available in forward and I have reverse limited to 1000w. A Savox metal gear servo takes care of the pitch control through a hollow motor shaft. The hub of the prop is machined from 7075 aluminum and the blade hubs are chrome moly utilizing a rather big roller thrust bearing and two smaller axial bearings. The blades are glass filled nylon moldings from Vario-prop and are bonded into the blade roots using aircraft grade structural epoxy using a special jig.

Here is a quick video of it in action.

Chris



Last edited by JustPlaneChris on Sun Jul 26, 2015 7:00 pm, edited 1 time in total.
fixed YT to embed


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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Sun Jul 26, 2015 7:02 pm 
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Joined: Mon Jul 25, 2011 11:58 am
Posts: 4774
Location: Austin, TX
Oh man, that is super cool! I've always thought that would be a really neat project, especially for a scale model. Congrats on the successful test! Can't wait to see where you go from there. :thumbup:

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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Sun Jul 26, 2015 9:44 pm 
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Joined: Mon Jan 21, 2013 8:26 am
Posts: 72
Location: Prince Albert, Saskatchewan, Canada
Thanks Chris.. Have a plan to do a bit more testing with a few different speed controls to find a governor that is better suited to this application... Planning a Takeoff and landing mode with full RPM and reverse available on the power lever (throttle stick) and a cruise mode where the rpms are pulled back but more pitch is available to max out the power in flight.. Basically mimicking a full scale turbine..

Can't wait to be able to land and pull full beta and put the brakes on... The sound of blades going into reverse is so neat and this one sounds great grabbing "back-up"

Future plans might even include a microprocessor based governor that would actually regulate power levels so max motor power could be attained regardless of RPM setting.. could include a "constant speed" mode also where the prop could switch gears based on load.

Plans right now are to build a "Mule" to do some in flight testing after the tuning is sorted out.. won't be pretty but trying to put something together to show off the benefits of the prop..

Will keep you posted.


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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Mon Jul 27, 2015 7:35 am 
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Joined: Sun Jul 31, 2011 3:43 pm
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Location: Houston, Texas
Very Cool project

Will follow with interest

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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Wed Jul 29, 2015 12:57 pm 
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Joined: Fri Dec 05, 2014 6:43 pm
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Location: Mason City, IA
oh my god, I can't wait to see some onboard and ground footage of that baby in action.


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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Thu Jul 30, 2015 4:56 am 
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Joined: Wed Nov 27, 2013 12:07 pm
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Very cool work! I could see this being popular in pattern for really good downline braking and absolutely constant speed. Not sure of the legality though.

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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Thu Jul 30, 2015 11:59 am 
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Joined: Thu Aug 16, 2012 12:08 am
Posts: 294
It would be legal for pattern. Variable pitch props were all the rage in the 70's and early 80's with the FAI crowd. These were the days of the "ballistic" pattern planes and the variable pitch was used to optimize the torque of those 18k RPM piped engines.

I don't think they had that much range in pitch, certainly didn't go into reverse. Radios for years later had mixing provisions for those types of props. I think my Futaba 9Z had it and it was from the 90s.

Very cool design Cat1! I always wanted to build an F-27 (the Fokker from my name) and this setup would be just the ticket!

Tom M




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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Thu Jul 30, 2015 9:16 pm 
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Joined: Mon Jan 21, 2013 8:26 am
Posts: 72
Location: Prince Albert, Saskatchewan, Canada
Hey Tom. An F27 would be a great project. I remember them as a kid as a local airline flew them. This is what I envisioned this setup to be good for - for mimicking full scale turboprop engines

I found a mule airframe in my "barn". A Sig kavalier. Looks to have enough room for the power plant and battery. Was a good flier in the nitro days and should be a good test bed for this power system.


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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Fri Jul 31, 2015 2:42 am 
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Joined: Thu Aug 16, 2012 12:08 am
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I remember the Kavalier, never had one but always seemed like a great flyer. Please keep us informed on your progress.

The F27 was a great airplane. Underpowered, sure, but one of the best most honest planes to hand fly that I've ever come across. I'd love to have a model of it someday. Frankly, there's a lot of things I'd love to have, just too lazy to make it happen! Lol

Tom M


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 Post subject: Re: Big electric variable pitch prop.
PostPosted: Mon Aug 03, 2015 4:45 pm 
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Joined: Mon Jan 21, 2013 8:26 am
Posts: 72
Location: Prince Albert, Saskatchewan, Canada
Hey all. Been very busy but got a little more testing in with my graupner radio system hooked up providing telemetry and a much better governor and tuning of the throttle and pitch curved. Here is a short video.

A few mods and the into the plane.

http://youtu.be/qmv_8R8dLDA


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