Question 260: "Karl, I have a Ziroli C-47. It weighs roughly 40 lbs. has a 114" wingspan and a 92" fuse. I have 2 Zenoah G-38's for the power plants, swinging a 19X10 3W carbon fiber prop. Here's my question, I get a maximum rpm of 5900(left) and 6000 (right) on a 32/1 fuel mixture (89) octane. Engines are just about broken in. Is this sufficient to fly the plane? It feels like it has good thrust, I have not flown it, just taxied it. I'm trying to figure out how to maximize my set-up. Should I change props?Should I change fuel mixt.? The engines run great, sound great, idle smoothly, transition perfectly. This is my first large scale warbird, and my first twin. I just want to make sure I cover all the bases. Please advise. Thanks Frank V. Puccio, Jr. "
Karl: "Thanks for visiting our site, Frank. Hope we can help you out here. I believe the G-38s will be plenty for your plane. Regardless of the wingspan it IS only 40 lbs. so that shouldn't be too much.
One suggestion I have is to look into getting a SoloProp for that. Not only would it look cool but you can adjust the thrust with the pitch.
The SoloProps are ground-adjustable which means you either tether the plane to an anchor and test the thrust (in a twin that may be one way to check the yaw-rate so you can make sure you're flying true without having a boatload of rudder trim to keep it true..the tether will bias to one side or the other to show which engine is pulling more--assuming you've adjusted fuel/carb and props evenly), and they have the round-tipped blades used on this transport. You can get them in many diameter ranges from 16" to 32" (they're at www.soloprops.com).
Now, I haven't seen the owner's manual for the Zenoah line but I'm assuming that for break-in purposes they have listed that fuel/oil mix for a reason. Normally they recommend 50:1 regular unleaded fuel so
32:1 would tend to make it smoke more. Make sure you've read the differences between pre-and post-break-in fuel/oil mixes to keep the thing from giving you grief early on. The Zenoah line is just one of the best 2-stroke gassers out there and the competition is strong so you've made a good choice. Of course, being who I am and loving round-engines I would try to put radials on that bad boy and wow the pants off anyone at the airfield. But that's just me. Hope this helps. Karl"
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Question 261: "I have a 1/4 scale P-51D, Quadra 100, and a lust for that big throbing 4-blade propeller. OK that was a little wiered. My question for you is very simple. I have develouped a conversion plate for Mick Reeves' Tourque Master that will fit on the front of my quadra 100 and alow me to swing a near scale propeller ( I think). I, like every other P-51 groopy, am looking for a 4 blade option with a happy medium between thrust and speed in order to swing a 4 blade and not feel like I am on a six flags ride for 5 year olds and under. I have seen how this engine can pull a 50lb. one quater scale P-51D with the correct two blade prop. My question FINALLY is; at 40lbs.,112 inches, Quadra 100, 1 to 1:1.75 reduction ratio, 32" Solo prop, what pitch would give me 70-80 mph clean and flat, but enough thrust to climb out on takeoff confidentlly. I know I may be dreaming. but remember this is a huge engine. There are paraplanes flying around with people hanging under them with 100cc reduction. Could this be enough mussle to get up with a speed pitch? Your thoughts and opinion are? greatly appreciated."
Karl: "Hi Randy and thanks for the question. I love these type of questions because they force me to stay up on some of the developments (not ALL of them of course) in the RC hobby, especially in what we could call here the "accessories" category.
I took the liberty of sharing some of the plane spec's with what I call an "electronic friend" since I've never met the guy in person.
His name is Joe Boyd and owns an operation called Warbird PropDrives.
He and the crew of designers/engineers (all fellow RC plane hobbyists) have been developing what is, in my opinion, the best full-functioning
reduction drive that also has true constant-speed prop adjustability.
Just the ticket for all you rabid P51 fans out there. Go to www.warbirdpropdrives.com and look at the movie, the info and you will be amazed. They even found an outfit in Oregon that can make the fully- functional scale side exhaust stacks. Just go there and you'll see what I mean.
For a plane your size and spec's I believe the Q100 is a good choice.
The prop on a plane works the same in principal as the rear-end gears and transmission does in a car. I have a couple other questions in these posts that address that more in-depth. As far as the SoloProp you might have to change that since the wide, square-tipped blades on the Mustang are unique I'm not sure if Solo has that kind of profile in their product line. I might be wrong so don't hold me to that.
Anyway, it sounds like you're planning properly so have fun. It's good
to hear as well the passion in the hobbyists voice like you shared.
That sort of love of the sport is what keeps it going--and going--and
going....you get the picture. Hope this helps. Karl
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