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Sep 14, 2019, 03:11 PM
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Chrome plating is usually used to refinish cylinders. While it's not terribly complicated, it still requires finishing the cylinder surface which is the hard part. None of these things are insurmountable, but it comes down to cost.
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Sep 14, 2019, 03:13 PM
Registered User
I just ran the exhaust throttle. Of course I was concentrated on the throttle and forgot to run it without the sleeve to see if the exhaust opening is restricting it much. Fuel was 25% Maxima Castor 927, and 25% nitromethane.

Greg

Prototype Cox Tee Dee Exhaust Throttle (1 min 48 sec)
Sep 14, 2019, 04:34 PM
Nitro User
1/2A Nut's Avatar
Thank you for sharing Greg well done, the absolute best way to document results.

I saw as low as 16.4k on your tach, with a servo you can dial in the best low idle with consistency.
The low pitch prop needs the rpm to stay in the air idle is suitable. I have flown many flights with
the throttled TD .010 trim is always set to insure no flame outs when I am ready to do slow passes
in front of the cam I will dial in lower rpm thus far no flame outs.

For reference best I can get is 11.7k steady - 28,082 top end with the grey prop.

5 popcorn salute!
Last edited by 1/2A Nut; Sep 14, 2019 at 06:15 PM.
Sep 14, 2019, 04:44 PM
Registered User
Yeah, it seems Mauricio got about 10k with the one he made, so there is room for improvement. Having never used an exhaust throttle, I was surprised by how instantaneous the acceleration is.
Sep 14, 2019, 04:54 PM
EB-66C Team Member
xplaneguy's Avatar
Quote:
Originally Posted by Kamtechnik
I just ran the exhaust throttle. Of course I was concentrated on the throttle and forgot to run it without the sleeve to see if the exhaust opening is restricting it much. Fuel was 25% Maxima Castor 927, and 25% nitromethane.

Greg

https://youtu.be/2mdZ2ielPEA
Excellent job, Greg! When I requested the .010 and .020 throttle sleeve back in Jul, I didn't think you'd get to them this soon. Nice to see you testing your designs. Many thanks!

Another suggestion: Aluminum back plates for Cox .010 and .020 plastic tanks. This one fits snug and is nice upgrade for those wanting to use the plastic tanks.
Last edited by xplaneguy; Sep 16, 2019 at 09:24 AM.
Sep 14, 2019, 04:57 PM
Nitro User
1/2A Nut's Avatar
Throttle sleeves and RC carbs have been in discussion for almost 2yrs.


Lol yes with the .010 it is the most aggressive with the rpm!

To get really low idle you have to give up some breathing or
really tighten up on the tolerances ID vs OD of the cylinder.
He used steel so things stayed tight when hot. Final results
showed best 9,750 rpm to 26,000 rpm ranges.

He gave up a good bit of top end for what I consider an unnecessary lower idle.
Most TD .010 planes unless a glider will loose altitude with anything under 13k.


A good TD .010 will make 28k with the black prop as the standard.
I have tested TD .010 / 3x3 all carbon prop / Best Peak 33,107 rpm / 94 mph pitch speed.
Ridged low weight prop with "most important good centering" will allow the very best peaks.
Last edited by 1/2A Nut; Sep 14, 2019 at 05:42 PM.
Sep 14, 2019, 05:08 PM
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1/2A Nut's Avatar
That second pic shows the aftermarket tank can you flip it around and take of pic of it?
Looks like the plastic has become brittle.
Sep 16, 2019, 05:40 AM
Registered User
I was thinking using magnetron sputtering to coat cylinder with maybe Titainium but yeah Nickel has less friction yeah? My thinking was cylinder longevity but that probably should be considered not a non issue but less important as a new such a small cylinder is such a small investment with little material, cost and time to produce.

The run in that video looked pretty good! So cool such tiny engines. I've only been a Groups member for maybe a year and was mostly reading and trying to learn about Tx's Rx's and programming at first. Uh actually mostly looking at the classifieds even when I couldn't afford to buy much... Truth betold.

What I seemed to notice with throttle response was pretty large change in rpm from idle to full and that it seemed to be a little linear down low but not very linear in the mid range. That may have been because the throttle actuation was pretty agressive.

I know thats basically all thats needed for a lot of the planes/types of flying that are going on. A decently low Idle and a good top end rev. Id like to use these 0.10, .020, .049 with as linear throttle as possible.

What would probably be ok for what I'd like to do maybe as low rpm as possible and 50% throttle half the rpms as at full. On you're next engine test run could you measure rpm's at half throttle actuation? I'd like to see what that looks like. Maybe a smooth and slow throttle actuation from 0-100% too?

Question. Have any of you seen the two stroke diesel manufactured by Junkers the Jumo 205? What could the feasibility of making a micro version of one be. Like .049 size? It seems to have a pretty simple theory for the port timing though the ports themselves look like they have to have precise size and placement. One of the things thats cool about the 205 engine is that its a two stroke that can be supercharged without any sort of mechanical or highly developed acoustic exhaust valve.
Sep 16, 2019, 12:52 PM
geoff
Thread OP
Hi both the Yellow Jacket is 24" and so is the Quickie 100 thay have both been made at same time with medium light balsa. I made a mistake with the white one and used oracover so you must take that into account. The Yellow Jacket was oralight. Quickie was made as pear Yellow Jacket 3/321/4 with 1/16 sheet L/E edge.The next will be 1/32 both will be TD or PEE WEE on front.Geoff
Yellow Jacket 89.61g
Quickie 106.40g
Sep 16, 2019, 01:16 PM
Nitro User
1/2A Nut's Avatar
Very nice Geoff they should both fly very well, will be interesting to see which one
you favor once you have some flights under your belt.

Look forward to your feed back on them.

Sep 16, 2019, 08:24 PM
Registered User
While refinishing a Cox cylinder is possible it's just too much time to be cost effective unless you're doing it just to do it.

The typical method for changing throttle response is linkage and servo travels adjustment. No carb is linear and it depends what you like. I did come up with a different shape of exhaust port in the sleeve. I should be able to test tomorrow.

Jumo 205 in .049? Model diesels require variable compression ratio.

Greg
Sep 16, 2019, 10:16 PM
geoff
Thread OP
Why not use expo on the TX ?
Geoff
Sep 16, 2019, 10:30 PM
geoff
Thread OP
Mauricio had a simpel butterfly on the venture the same as the cox medallion 049 Plus the sleeve
Geoff
They will run very slow for a long time and pick up fast
Last edited by GEOFF 27049; Sep 16, 2019 at 10:39 PM.
Sep 17, 2019, 05:36 PM
Registered User
Yeah I think I prefer flying to fiddling with things but then again I sometimes do things just to see if I can. Thanks for testing youre design in you can get R.P.M. measured at 50% throttle I'd like to see what you get there. As far as running diesel yeah I know of the need to use variable compression to have the engine run smooth. I was thinking it would be cool to attempt a micro Jumo 205 type for various reasons. The Jumo 205 and Wankel type are probably two of the finest engine designs in my opinion.

Building a micro 205 type to run on diesel obviously would offer a significant design challenge but what if it was run on nitro fuel? Seems to me that should work fine. Only thing would be the glow plug would have to enter the combustion chamber from the side which would provide an uneven combustion.

Such would be undesirable in an engine that needed sustained electronic ignition however nitro fuel only needs the glow plug for starting and Id think once engine operating temperature reached a 205 type could work well theoretically.
Last edited by Brianmh13; Sep 17, 2019 at 05:44 PM.
Sep 20, 2019, 11:50 PM
Registered User
Sorry for the overzealousness I was told I should read 500 posts per 1 post I write. I'm gonna just work on my own at least mostly I guess.


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