9 Cylinder Radial Build using Cox Sure Start 049's - Page 3 - RC Groups
Thread Tools
Sep 27, 2011, 10:36 PM
Double Naught Spy
iamplanecrazy2's Avatar

Probable Crankshaft Solution

I have a new plan for the crank shaft.
After going through some parts I found the front housing assembly off of a
Super Tigre rear rotor G-60 and it looks as though it may be an easy solution
to my prop shaft needs. Work on it will begin soon and will post some photos
if I actually get it to work.
Sign up now
to remove ads between posts
Sep 28, 2011, 12:21 AM
Registered User


Wow, what a project. Venturi and K&B racing NVA look great. Look foward to seeing front end built. Leroy Cox would be amazed at this engine. Good luck with it. Dan
Sep 28, 2011, 04:00 PM
Registered User
earlwb's Avatar
it is definitely looking pretty spectacular. Nice job.
I was curious as to what gears you chose to use with it.
I myself would have acquired the gears and then laid out the engines with the gears to get the layout and then made the rest of the engine up to fit the gears chosen.
So it had me wondering what you did to arrive at your current engine setup.
Sep 28, 2011, 05:06 PM
Jack of all master of none
splinterz25's Avatar
very nice project; what do you think your end cost to produce this engineering marvel will be? way to think way out side the box, keep up the good work I'll keep watching this build for sure!

Sep 28, 2011, 10:55 PM
Double Naught Spy
iamplanecrazy2's Avatar
Many thanks for the comments fellas!

Great to hear from you Dan! Hope all is well in Tucson. I like that K&B NVA too. Hope it will work.

Earl, I used the calculator on this page to help with gear selection. It is a great tool.
Once I had the number of teeth and pitch I had an idea of what to look for.
Will be using metric module 1 pitch, 14t on the engines and 35t on the prop shaft.
Ratio will be 2.5:1
It took a lot of searching to find gears with a usable thickness and center hole bore.
I'd think I had the right one only to find it was too thick, had too large a bore, or had
an hub issue. I must have looked at every gear site on the web. Ended up buying 9 of these:
and 1 #SSAY1-35 on this page from Quality Transmission Components:

At $115 the gears have been the biggest expense Bruce. Then there are the 9 Sure
Starts at $6.99 each. The rest of the parts I had laying about the shop but I suppose
they do have value. All in all I say I have around $225 in it. If you want to figure in
work hours I've got about 100 hours in it so far. That includes head scratching and
parts hunting time.

Have not yet started on the front housing but I have planned out what to do.
I think it is going to work out great.
Sep 28, 2011, 11:01 PM
Grumpa Tom
Kmot's Avatar
It's truly amazing what someone can accomplish when they put their mind to it. And using basic tools to boot. Man this thing is looking awesome!!
Sep 29, 2011, 09:09 AM
Registered User
earlwb's Avatar
That is so cool, thanks for sharing the info.
Yeah the gear cost goes up fast with lots of engines to couple together.

The current draw for 9 glow plugs gets pretty spectacular too. You will likely need a bunch of D cells that you can use for each separate cylinder. Getting a 9 cylinder on board glow ignitor is another way to go, but they are fairly costly though.
Sep 29, 2011, 11:21 AM
Registered User
Originally Posted by earlwb
Getting a 9 cylinder on board glow ignitor is another way to go, but they are fairly costly though.
I don't think that any of those multi cylinder drivers would work as well as a separate sub C cell for each plug IMO.
Sep 29, 2011, 05:00 PM
Registered User
fiery's Avatar

9 cyl cox radial

A 2 volt 25Ah Enersys Cyclon Bell Cell battery with 4 foot leads (to drop the voltage) will light off the plugs no problems. Perfect for bench testing.
Sep 29, 2011, 05:42 PM
Registered User
earlwb's Avatar
Well, a glow plug typically draws about 3 amps or so. So 3 amps times 9 cylinders is 27 amperes of current. That is a pretty hefty amount to run to the engine all at once.
Unless you use a 9 cylinder glow starter unit, you want to have each glow ignitor separate from each other (albeit they all have a common ground though). You can't just run them all in parallel off of one battery because if a glow plug or two or more burns out and is open then the other glow plugs may wind up taking the load and getting too much current then.
So the classic 2 D cell in parallel battery pack per glow plug is a good starting place to keep the costs down.
of course trying to keep all the wires organized and neat gets to be a problem.
Sep 29, 2011, 09:27 PM
Earlwb: There would be NO PROBLEM in running 9 plugs off of one power source in parallel. If one or two plugs burn out, the others would not be in danger of drawing too much current. A battery or other power source delivers what is demanded of it, not pushing its maximum power out under all conditions. If you turn on only one 100 watt lightbulb in your house that has at least 100 amp (12,000 watts) service, does it burn out? Sorry to put it that way, but that was the only analogy that I could quickly think of.
Sep 29, 2011, 09:37 PM
Double Naught Spy
iamplanecrazy2's Avatar
Thanks to all for posting!

Great point Earl. I have only given powering the glow heads a passing thought.
I like Sonic Tronics 9 cylinder igniter but you are right, at $150 they are costly.
I really like Radio South glow drivers but don't think they make one for 9 cylinders.
The cost of a driver may be worth it if it will extend the life of the heads. The
cheapest I've seen heads lately is $6 each. If the engine actually ends up running
I'll definitely give buying a driver more consideration.

For initial testing Jim's 9 sub C suggestion is likely the way I'll go as I have them on hand.

I like fiery's 25Ah Enersys battery suggestion. I checked on one and it looks like a
great battery. But there again is more expense and as I already have the sub C's
it just seems like, at this point, a waste to buy something else.

I know I sure can't wait to get to the point of actually needing to ignite all of those heads!
Sep 29, 2011, 10:44 PM
Registered User
boingk's Avatar
Man, this is an amazing build. I'm curious as to how you are going to drive a single prop, though - perhaps each crankshaft could turn a central gear via a smaller gear mounted directly to its crankshaft in lieu of a prop?

The overall RPM of the output shaft would be greatly reduced but it should enable you to swing a fairly large prop.

Cheers - boingk
Sep 30, 2011, 07:14 AM
Double Naught Spy
iamplanecrazy2's Avatar
Thank you boingk!
The prop will be mounted on a central gear driven shaft. Ratio will be 2.5:1.
I have been pondering just how large of a prop to use, have been thinking maybe
a 14 X 6 to start with. Being that gear drives were the way to turn a large prop at
one time there is bound to be some established formulas or rules of thumb used to
determine prop size. I'd welcome any input.
Sep 30, 2011, 11:59 AM
Registered User
boingk's Avatar
No worries plaecrazy, it is afterall a very impressive build.

Seeing as you've got roughly 60W x 9 of power, you should have enough power to swing that prop. In fact, you may have enough to swing a 16x8 if you were unsatisfied with initial testing. This is all (possibly flawed) calculations on my behalf, assuming a maximum speed of no more than 15,000 loaded rpm per engine. I would definitely start 'small' on this with the 14x6 you mentioned as a precaution.

Also, glow drivers could be as simple as 9 x AA NiMh batteries with glowplug attachments. I know that my C size 1200mAh NiMH cell gives quite adequate power for my glow plugs, and AA's are much easier to obtain. Worth a thought!

Please keep us informed of the ongoing trials.

Cheers - boingk

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold 2 Cox 049 Sure Start Engines fchriss Aircraft - Fuel - Engines and Accessories (FS/W) 2 Dec 09, 2008 12:36 PM
For Sale 2 Cox .049 sure start's snomobila Aircraft - Fuel - Engines and Accessories (FS/W) 3 Dec 07, 2008 10:36 PM
Question Which fuel for Cox .049 Sure Start? ndb8fxe 1/2A Planes 6 Aug 30, 2008 11:52 PM
Question Cox Sure Start .049 EricClark 1/2A Planes 25 May 15, 2008 01:16 AM
Question Need info about Cox Sure Start .049 engine please JLW5178 Beginner Training Area (Fuel) 16 May 03, 2008 05:20 PM