9 Cylinder Radial Build using Cox Sure Start 049's - Page 5 - RC Groups
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Oct 16, 2011, 03:05 PM
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RknRusty's Avatar
You could do that with an infrared photo or video too.
I love this! Can't wait to see it fire up.
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Oct 16, 2011, 08:47 PM
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Originally Posted by pmackenzie
Unless that 2 stroke is an inline alternate firing twin


Pat MacKenzie
That it is!
Oct 16, 2011, 11:34 PM
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iamplanecrazy2's Avatar
Thanks for the comments and suggestions fellas!

I was finally able to get a bit more work done. I was so anxious to get to it
that I forgot to take some "before" photos of the Super Tigre 60 parts but I
figure anyone interested in this project will have the general idea of what I
started with. Nine more holes were drilled in the mounting plate that will
accept screws for the yet to be fabricated clamping plate that will pull down
the 9 Sure Start cases (remember the screw lugs that were ground off).

I also enlarged all the holes in the mounting plate to allow for adjusting the
backlash on the gears. After some trial assembly it quickly became clear that
this was necessary. Should help with gear wear and noise.

I finished altering the crankshaft for use as the prop shaft. The bulk
of the counterweight was ground of on the bench grinder with a fairly coarse
stone. It was slow going, largely because I didn't want to get it very hot so
spent a lot of time cooling it down. Finished grinding it on the bench sanding
wheel using a simple jig made of a piece of plywood and a screw that fit
snugly in the hole in the cranks center.

The mounting flange was ground off the front housing in the same way except
that it did not need a turn on the bench grinder. Only the bench sander was used.
The degree of accuracy can be seen by the grinding marks left on the part of the
housing that fits inside the case. I stopped the grinding as soon as scratches
began to appear there. The grinding wheel would cause the part to spin at
a pretty high rate of speed. With a gloved hand I gripped the part to keep
the rotation to a manageable speed. If left to spin freely it wanted to fly off
the jig. Especially so with the front housing as it was riding on the crank
shaft. The downside is I contaminated the bearings with grinding debris so
will be replacing them.

Still need to cut small radii around the housing so it will clear the 9 crank
cases. Here is a shot with the housing resting on the reed housings to show
what needs to be removed. I'm currently working on a fixture to hold the
front housing for cutting the radii. Hope to post photos of it tomorrow.

Will attach the prop shaft, front housing, and mounting plate to a piece of
steel plate as shown below to drill mounting holes for screws that will attach
the front housing to the mounting plate. These holes will be located just a
bit to the inside of the 9 holes used for securing the hold down clamp for the 9 cases.
The center hole in the mounting plate was enlarged so the
prop shaft fit it snugly. The hole will later be enlarged so the prop shaft will
pass completely through and rest only on the large bearings inner ring.

Early on in this thread T.L.A.R. eng suggested that "A distribution fan inside
the intake housing would certainly help with the mixture distribution
problems that are common with radial engines". I always thought that would be
really cool to do and the hole in the center of the prop shaft is going to serve
well to make this happen. It will be simple enough to drill a hole for a set
screw in the prop shaft and use it to secure a small shaft that an impeller
of some sort can be mounted on. The 8cc Bee tank has an inside diameter
of around 1.035". I'd like to find a three blade prop that would fit it inside
the tank with little or no removal of blade material. I'm thinking a nylon
prop would work and would be better in case a piece came off and found its
way inside one of the engines internals. Here are a couple of photos to help
get an idea of what I mean. Cut down the prop just might work. Anyone
know the engineering principals behind impellers?

Last edited by iamplanecrazy2; Oct 17, 2011 at 12:11 PM.
Oct 17, 2011, 12:23 PM
Double Naught Spy
iamplanecrazy2's Avatar
Googled "impeller design" and found a photo of this impeller. Would like to find one with a 1" diameter.

Oct 17, 2011, 12:51 PM
Jack of all master of none
splinterz25's Avatar
Originally Posted by iamplanecrazy2
Googled "impeller design" and found a photo of this impeller. Would like to find one with a 1" diameter.

have you tryed looking at RC boat props? I don't know if they would work for your app. maybe if you reversed it when mounting? just a thought, good luck you have very creative thinking with this project! and I will keep watching your progress with great admiration.

Oct 17, 2011, 01:15 PM
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gkamysz's Avatar
You want something with radial vanes.
Oct 17, 2011, 08:14 PM
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boingk's Avatar
Ditto the radial vane remark. If you can check out a Pratt & Whitney R2800 engine's vane-type supercharger you will get the idea. Essentially its a crank-driven centrifugal supercharger with vanes (usually disc mounted) radiating from the crank or another central point.

Cheer - boingk
Oct 17, 2011, 08:37 PM
Double Naught Spy
iamplanecrazy2's Avatar
I have looked at boat props and it looks like that is the direction I will have to go
as I haven't been able to find anything else with a diameter as small as 1 inch.
While a little manifold pressure would be nice I wonder how much the reeds would be
able to take before they started to float. I'm thinking the best benefit will be a more
even distribution of the air fuel mixture within the manifold. I have a couple of 1/2a
nylon boat props with a 1" diameter. May just put one on and see what happens.

As for the prop shaft housing I had to order a couple of drill bits and they won't be in
for a couple of days. In the mean time I'm going to get started on the hold down clamp.
Will be using another aluminum spinner back plate for that.

Have also been considering a way to mount the engine. I've always liked the looks of
the Morton M5 tubular mount. May give a shot at fabricating something similar. Here
is a link:
Oct 18, 2011, 11:35 AM
T.L.A.R. eng
I am not sure how much a boat prop will stir up the mixture, especially running at less than crank rpm. You definately will not have any problems overcoming the intake reed with forced pressure.

You need a radial type impeller, brings air in from the center and discharges it radialy outwards towards the intake tubes. It doesn't so much "supercharge" as it does changes the direction of the incoming fuel and helps keep the fuel stirred up into the air stream.

With the inginuety that you have shown problem solving, a radial impeller should be realatively easy for you to carve out of aluminum. Perhaps a small radial impeller from a small electric water pump could be made to fit?
Oct 18, 2011, 02:29 PM
Two left thumbs
Hand held vacuum cleaners use radial impellers and are ubiquitous at garage sales.
Oct 18, 2011, 07:37 PM
I don't want to "Switch Now"
pmackenzie's Avatar
How about the cooling fans on the 450 size heli motors?
For example on this one:

Not sure if they would stand up to glow fuel though.

Pat MacKenzie
Oct 18, 2011, 07:42 PM
Registered User
RknRusty's Avatar
Maybe one of those little keyboard vacuums has one.

Oct 18, 2011, 08:37 PM
Double Naught Spy
iamplanecrazy2's Avatar
Thank you for the suggestions everyone. I think I have found a suitable
impeller and believe it is a radial type as was suggested. Best thing about it
is that it is a Cox part! I was looking around the shop and spotted a
Cox Baja Bug type engine and thought that the cooling fan might work.
Having several spare fans I commenced to reshaping one of them. Used
the screw in a board jig again to get the initial shape. Finished sanding a
bit of a radius on the blades with a sanding block. It took a while but the
effort paid off, the blades fit inside the manifold very nicely.

The part came off of one of these. Most of you are probably familiar with them.

Here is what I ended up with.

Here it is in the manifold. I'm going to hold off on cutting the end off until
I'm sure how it will be mounted to the shaft. Don't want to have to make
another one!

If I'm looking at it right it will be necessary to have a clockwise rotating shaft
in order for the impeller to create pressure in the manifold. That is a bit of
a downer as I'll have to buy pusher props while I have a ton of regular props on hand.

What do you think fellas? Will it work?
Oct 18, 2011, 09:31 PM
Registered User
earlwb's Avatar
You are using reed valve engines, they run equally well in forward or reverse rotation . So there is no problem for you in this case. I remember times where the only way I could get one to run was in reverse. You might have had times like that too.
Oct 18, 2011, 09:57 PM
Registered User
boingk's Avatar
Looks good to me, mate. Also, don't buy pusher props... they're a myth! Simply reverse rotation of the engine and mount a conventional propeller back-to-front for pusher operation. The real item you'd need would be a 'counter rotating' propellor which is quite a different beast altogether. Good for you they're also fairly common.

Cheers - boingk

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