|Oct 28, 2011, 11:53 AM|
Joined Feb 2007
You have done a great job on this. I have worked on many engines and made different airplane parts from metal but this is awesome. Brovo to you and thanks for sharing.
|Oct 28, 2011, 04:55 PM|
Many thanks for your interest and kind words Dan. All of the kind posts that have been made truly mean a lot to me.
I couldn't imagine a nicer bunch to share the project with!
Have put a little more time in on the engine today and hope to be doing a final
assembly shortly. Will be post photos later.
|Oct 28, 2011, 10:18 PM|
First off I have been enjoying your build of the 9 Engine (Cylinder) Radial engine.
One thing I would worry about is setting all 9 cylinders to reach TDC at the same time. All cylinders would be trying to suck in fuel and air at the same time. How big is the intake going to be?
My suggestion is based on, that I was trained as a precip engine mechanic and mostly trained on radials. When I joined the Air Force in 1953 they needed radar mechanics so guess what I ended up doing for a living, Electronics.
I have attached a sketch that gives you the data I came up with considering the gears you bought, 14 Tooth engine gears and a 35 Tooth crank shaft gear. A standard 9 Cylinder Radial engine firing order is 1, 3, 5, 7, 9, 2, 4, 6, 8.
I know we are working with 2 cycle engines (Cylinders) but to even out the intake for each cylinder as much as possible we need to vary the timing. I wish it had been a 36 Tooth Crankshaft gear but that is 20/20 hind sight. 36*2 =72. 72/9 = 8.
Therefore I recommend setting Engine (Cylinder) #1 at TDC and engaging the crank gear. Secure the #1 engine.
Next turn the crank till 8 Teeth on the crank gear passes the #1 engine Center line.
Holding Cylinder #3 at TDC engage the crank gear and secure the engine.
Next turn the crank till 8 more Teeth (16 Teeth total) on the crank gear passes the #1 engine Center line.
Holding Clyinder #5 at TDC engage the crank gear and secure the engine.
Repeat this sequence using the numbers on the sketch to engage the balance of the engines (cylinders). Note that Engines (Cylinders) #7 and #6 will only be 7 Teeth after the previous Engine (Cylinder). See why it should have had a 36 Tooth Crankshaft gear. Don't worry about it, when running it might give it a unique sound.
CORRECTION! I made an error on the sketch. Engine # 6 should read 54T in place of 50 T.
|Oct 28, 2011, 10:50 PM|
Joined Nov 2005
I would whole heartedly agree with Clancy on the cylinder timing. Trying to crank the engine over TDC with all nine against the gearing might be difficult if not impossible without damamging the gear train or the mounts.
Sequential firing would spread the compression load out during cranking and the firing impules during running.
You are doing a great job, looking forwards to this one running.
|Oct 29, 2011, 03:42 AM|
Joined Nov 2009
Have followed this build with ever increasing admiration:
You have made mr McGyver look like a slow kindergarten student....
But I am partly agreeing on the firing order. It should definitely be not all cylinders firing simultaneously, but the firing order Clancy suggests is based on the fact that those big old radials are single crank fourstrokers, and than you need to distribute the full cycle over 2 revolutions. In general on a multicylinder 2 stroke the full cycle is distributed over only one revolution.
On a 2 stroke in line engine, the only thing to consider when determining the firing order is balancing the crankshaft for 2nd order vibrations. On a radial this is not the case, and to be honest, firing order is completely irrelevant, as long as the firing moments are evenly distributed around the full cycle.
With a single crank as on the big fourstrokes, the firing order is dictated by this crank, on a geared 2 stroke, you are free to choose as you like. Especially if those 14T gears are not connected to their shafts by splines or woodruff keys or the like, Than you can set them as you like.
One thing to consider, is that it is no use to try and distribute the firings evenly over one revolution of the propshaft. The only thing that matters, is that 40 degrees of "cox-crankshaft" rotation after the first TDC, the next "cox-crank" reaches TDC, ans so on until you have completed the circle of cylinders. With the present gearing you will have of course 2.5 cycles on a full prop revolution, or 45 ignitions on 2 full propshaft revolutions (that will surely give a racket)
Indeed, if the cyclinders are firing separately, the induction of fuel and air is also spread evenly over the full revolution, which not only reduces needed intake diameter, but also helps in keeping the velocity in the intake more constant, thus keeping an even mixture distribution more consistant.
|Oct 31, 2011, 09:48 AM|
Many thanks for the input fellas. I really appreciate your time and thought
put into your posts.
You have convinced me go with sequential firing for the test runs.
on a single prop revolution gives some insight into how large a prop the
engine might be capable of turning. And yes, between the exhaust and
the gears it ought to get the neighbors attention.
I have run into a snag with the manifold impeller. I was surprised to find
that I could not drill a hole in the prop shaft for the set screw that will
secure the impeller shaft. While attending the swap meet in Manor Texas
on Saturday it was suggested to me that the shaft would have to be
annealed in order to drill it. As any drill bits I had would not even scratch
the shaft I am inclined to agree but I'm afraid of annealing for fear of
causing the shaft to wrap. The shaft would need to be hardened again too
and I just don't see it getting through all of that without some distortion
or loss of strength.
In light of this I was thinking of simply JB welding the impeller shaft in
place. The fit in the prop shaft hole is just a tiny bit on the loose side and
it goes into the hole about 1" so there would be a good bit of surface for the
JB weld to contact. It just seems like a cheesy method of attachment.
Also considered silver brazing but then I'd have the heat issue again.
I could sure use some input here. What to do, what to do?
Here is a shot of the prop shaft after enlarging the hole in the back plate.
With the impeller in place.
With the manifold in place. Oh, I added a piece of 049 crank case to the
manifold as a way to have more material for the venturi mounting screws
to hold onto and as a way to cover the 4 holes on the manifold. Thought it
would be neat to keep pace with the Cox engine theme. I clamped the parts
together until the o-ring was well compressed then drilled and tapped the
holes clear through. shortened the screws so they don't protrude into the
I wanted to show the engine off at the swap meet so put it together for
that. Will have to disassemble and solve the impeller shaft problem or will
need to make a new cover for the prop shaft opening without a hole in it
for the impeller shaft. When assembling this time I dug around the shop and
found a Fox prop shaft extension that worked out nicely.
On the scale with a 15-8 prop the weight is 1 lb. 10.2 oz. (minus the impeller)
I'll need to plug that hole or make a new plate to run without the impeller.
Here are all the parts laid out before assembly.
The question everyone asked at the swap meet was "Does it run?"
I'd like to throw in a tip for tapping as I used to be real good at breaking
small taps and would like to help keep another from having the same problem.
The key to successful tapping is to get the tap properly aligned with the hole
when going in. This can be pretty much a matter of luck when eyeballing it.
So, I was taught to use the drill press to get the tap started.
After you drill the hole take the bit out of the chuck and chuck up the tap.
Then lightly press the tap into the hole and rotate the chuck a few turns by
hand while putting light pressure on the drill press handle. You want to get
the tap started into the hole 3 or 4 good turns. Then loosen
the chuck and take the works out and finish running the tap in by hand.
That is how I tapped the holes in the prop shaft housing. The tap turned
effortlessly all the way through on all 6 holes. Trying to eyeball it I have no
doubt I would have broken a tap off in one of the holes.
Here is the tap chucked up in the drill press and in place for turning by hand.
When running in the rest of the way by hand.
Hope to be test running sometime this week! Will probably be trying it out
with no impeller unless I decide on a solution for the shaft mounting soon.
|Oct 31, 2011, 10:39 AM|
Regarding prop size. Each reedie is good for about 40W at oh 13krpm. So 360W at 13k/2.5 reduction is 360W @ 5200 RPM. If we count some loss it should be able to turn a 15x8 at the 5200. I see somebody else estimate prop size before. We electric guys can easily size props if the power and RPM is known.
I'm amazed at how good this looks with such simple tools.
How big is the venturi? To my eye it looks quite large.
|Oct 31, 2011, 10:55 AM|
Joined Nov 2009
If the units all get their mixture, I think this engine can amaze some people. If not, chances are it'll never run....
I really hope, it runs.
|Oct 31, 2011, 01:08 PM|
Have you got your glow clip harness already wired up?
You'll want to see if the cylinders are heating uniformly, maybe a laser thermometer. I don't suppose you have an infrared camera in your toolbox do you? Pardon me if that's been covered, I could have missed it.
Just one more question to pester you with, what are you going to lubricate the drive train with?
And don't forget your flak-jacket and riot helmet. Just kidding... sort of.
|Oct 31, 2011, 01:36 PM|
Joined Feb 2007
Fox shaft extension came in two sizes 1/2" and 3/4". Veco even had a 1/4".
It was uncommon but I wound up with one. Anyway its looking better and better. Does engine turn over with compression??
|Oct 31, 2011, 02:00 PM|
because I have been imagining the possibility of this think going to pieces
during a run. I'll be wearing safety glasses and will get behind it as soon
as it fires up. Don't have the harness wired up yet. Guess I'll have to rely
on sense of touch to see if the cylinders are getting hot.
Will put a bit of grease on the gears to start and hope the exhaust will
spray a bit of castor on them.
I have a ton of props so will try it out on several different sizes. Am now thinking of starting out with a 14-6.
The venturi is pretty large. I've sort of felt that it was to big from the beginning
but I just like the way it looks. I'll give it a try and if it won't draw fuel I'm
going to replace it with an RC carb. I believe that the real key to getting fuel
to draw will be getting the manifold sealed properly. Will be putting silicon
on all areas that air can enter. Want to get it to the point that I can't suck
any air through the venturi.
|Oct 31, 2011, 02:06 PM|
length but a few different shaft sizes.
As it is set up with All cylinders going to TDC at the same time it turns over
pretty hard, plenty of compression. It feels odd though because when turning
the prop it hits another compression stroke with so little prop travel.
|Oct 31, 2011, 04:42 PM|
Joined Oct 2004
|Oct 31, 2011, 04:53 PM|
Man that engine looks great. One things for sure, if it runs you're going to be inondated with kit request. I think the sound is going to be unique for sure. GOOD LUCK!
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