R/C TD.010 plane

Second

Very nice, my .010 throttle ring attempt only got me down to 10k idle.

You could put me down as a third. Is the circlip the only thing holding
two halves of throttle ring together? John

FIXR7 wrote:G'day folks,

Just joined up and thought I'd show you this little model I built from scratch a long time ago.
Originally I designed it for .049 power which I used for many years with a Medallion R/C 049 until I crashed it.
I bought the 010 in the early 90's(I think) and so I scaled down the plans to suit this little engine.
The only thing I couldn't bear was no throttle so we made one. It's along the lines of the exhaust throttles of the other Cox engines but of course it was much more tricky as we couldn't(wouldn't) machine the step off the bottom of the cylinder where it meets the crankcase. So we had to slit the tube, lap the mating halves smooth,weld it together, machine the outside then bore the inside before breaking it apart again to fit it to the engine.
Here's some pics...

damn that looks great, love the throttle ring and welcome to the forum

Glad you like it lads!
I have to admit I have only run the engine in without a throttle back in the mid 90's.
So I suppose I better try it soon eh?
Yes the circlip holds it on and it is a very tight fit.
I remember back in the day, a hobby shop owner told me it wouldn't work because of the porting of the TD engine!? Wtf?
I said; what's the porting got to do with it? If you restrict the exhaust you restrict the flow regardless of what's inside the engine!
Anyway you guy's have proved it works.

FIXR7 wrote:Glad you like it lads!
I have to admit I have only run the engine in without a throttle back in the mid 90's.
So I suppose I better try it soon eh?
Yes the circlip holds it on and it is a very tight fit.
I remember back in the day, a hobby shop owner told me it wouldn't work because of the porting of the TD engine!? Wtf?
I said; what's the porting got to do with it? If you restrict the exhaust you restrict the flow regardless of what's inside the engine!
Anyway you guy's have proved it works.

Oh yeah they work!
I think he meant the exhaust ports or something.

FIXR7 wrote:...I remember back in the day, a hobby shop owner told me it wouldn't work because of the porting of the TD engine!? Wtf?
I said; what's the porting got to do with it? If you restrict the exhaust you restrict the flow regardless of what's inside the engine!
Anyway you guy's have proved it works.

Does an .010 have sub piston induction? Maybe he was talking about the exhaust ports. A lot of times SPI and throttle rings or mufflers don't work well together, since it sucks hot exhaust gasses back in to the crankcase instead of cold fresh air at TDC.

I'm not a .010 expert, so if there's no SPI, then you're right, no problem.

Maybe that was what he was referring to?
I don't know, are the .049's and such the same in terms of porting?

FIXR7 wrote:Maybe that was what he was referring to?
I don't know, are the .049's and such the same in terms of porting?

the .010 does have SPI but throttle rings are still OK on them if you can get the fits right.

FIXR7 wrote:Maybe that was what he was referring to?
I don't know, are the .049's and such the same in terms of porting?

First be sure not to confuse exhaust ports with bypass ports, which are fuel delivery channels inside the cylinder.
There are several different exhaust port configurations for the .049s and they later changed the method of obtaining SPI. Originally the port was set low enough so the piston skirt had a gap under it at TDC, for cold air induction. Some cylinders had it, and others did not. They basically all used the same piston.

But later the exhaust ports were all the same height and you then used a shorter piston to obtain the same gap at TDC. That made it easier to manufacture and mix and match parts for different performance levels. Putting a short piston in an old style SPI cylinder will make too much SPI and hurt performance.

There are several different configurations of bypass ports also.

I think he(the shop owner) was referring to the bypass ports.
Thanks for the info on the SPI RknRusty!

FIXR7 wrote:I think he(the shop owner) was referring to the bypass ports.
Thanks for the info on the SPI RknRusty!

Here's some more on SPI in a thread at RCGroups.com. It went on for 4 pages, but the first post pretty much tells the story.
http://www.rcgroups.com/forums/showthread.php?t=1538781

There is a similar one here, but I couldn't find it.

Ok so it stands to reason that the exhaust throttle could upset the inward flow of air to the crankcase? Enough to cause poor operation? Possibly? You could argue though, that the exhaust throttle is deliberately causing poor operation.
The problem would not be there at WOT therefore.
Does anyone have an original exhaust throttle engine with SPI? I'd say most likely.
I'll have at look at mine.

FIXR7 wrote:Ok so it stands to reason that the exhaust throttle could upset the inward flow of air to the crankcase? Enough to cause poor operation? Possibly? You could argue though, that the exhaust throttle is deliberately causing poor operation.
The problem would not be there at WOT therefore.
Does anyone have an original exhaust throttle engine with SPI? I'd say most likely.
I'll have at look at mine.

Good Luck with it Pete.
If you do a little research you'll see the recurring theme is lower top end on all the throttled Cox's.
I'm not sure what fuel supply is like down under but do yourself a favour if you can't find some fresh stuff
buy some new plane or car fuel and knock up a bit of castor into it.
I've been faffing around with my 010 since before Christmas and have only just realised the problem
has been dud fuel. Compounded by the fact it actually ran OK(ish) in my Cox 049's.

FIXR7 wrote:Ok so it stands to reason that the exhaust throttle could upset the inward flow of air to the crankcase?
Enough to cause poor operation? Possibly?

That is true, but if it all works fine despite what we think, just fly it and think no more of it.

FIXR7 wrote:...The problem would not be there at WOT therefore.

WOT is where the sub induction is greatest, so watch out for overheating, especially while bench running. The effect on idle, I hear, is that sometimes it won't run slow enough to suit your needs.

FIXR7 wrote:Does anyone have an original exhaust throttle engine with SPI? I'd say most likely.

As far as I know Cox only ever sold non-SPI engines with mufflers or exhaust throttles.

Am I getting on your nerves yet?

Nope rusty, I asked the questions because I don't know and it's all good info! Thankyou.
So you're saying that even though there is no restriction in the exhaust ports by the throttle sleeve at WOT it still adversely effects the SPI operation? Because of the extra thickness of the sleeve creating an effectively longer port?

Ok, everyone who has made an exhaust throttle for one of these .010's lets hear the details about your engines' running?
I've heard about the high idle...Large sleeve tolerances perhaps?
and how about fuel? The last lot I got was a blend of Klotz and castor with 25% nitro...twas good.

Oh thanks also John.
btw, I remember an old RCM mag with an article about "tarno" carbs being available for .010's and, was it Clarence Lee who ran one on a tiny little sea plane? Rare as rocking horse [bleep] no doubt?

FIXR7 wrote:...So you're saying that even though there is no restriction in the exhaust ports by the throttle sleeve at WOT it still adversely effects the SPI operation? Because of the extra thickness of the sleeve creating an effectively longer port?

Exactly. The crankcase vacuum caused by the ascending piston is suddenly relieved when the SPI gap cracks open. Instantly the vacuum inhales whatever is right outside the exhaust port. In the case of a muffler or exhaust throttle, that "whatever" consists of poorly oxygenated hot spent fuel and dirty castor oil, rather than the cold clean oxygen rich air it was designed to use for boosting the next intake charge.

Righto, just took this pic of my Medallion .049 by shining a torch up it's date. You can see the gap between the bottom of the piston and the exhaust port. Does that mean it has SPI?



Also checked the Black Widow I just bought and it's the same gap on this non throttled engine.

That's it. Some have more than others. Is there a number stamped on that Medallion cylinder? The #1 on BW cylinders is usually a tiny stamp on the corner facing of one of the exhaust ports. Hard to see. The Medallion might be stamped on the barrel. For a non throttled Medallion the old originals had #2., usually on the barrel between the ports. That was a single bypass cylinder.

I'll have a look.

They both have a 1.

Someone put a Black Widow cylinder on your Medallion. That's good, it's considerably more powerful than a #2. I have one of the new type SPI sets with the slit exhaust ports and the short piston on my Medallion. It really woke it up.