Cox .01 /.02 /.05 /.09 /.15 Speed Planes

Brad,
I will step up for a TD.020 back plate if you have any left.....

Steve.............

10/4 Steve I was given some to test. The machinist will be making them and will send me a link next week to post here
for everyone to buy them as many as you wish. TD .010 and .020 sizes he will continue to make them as long as folks
want them / so keep the contact info when it happens.

Today I bench tested the TD .020 with a stock 4.5D x 2P results are as good as anticipated.
Best static 18,330 rpm (best thrust I have seen 6.3oz) .036hp / 27w / 35 mph
20% castor / 30% nitro. Most impressive will fly quite a bit of plane!  

Have you made any comparisons with the stock backplate on the same engine?

From memory I thought the TD .020 would do around 19500rpm on the cox 4.5x2 prop?

Depends on condition of the engine, oil / nitro %, humidity, elevation and temp.

Both engines used for my tests are not new, used with the Lil Speedy I and II and so very familiar with what
they have done in the past in my environment with posted vids back when they where new this gives a direct
best possible comparison to share here on CEF.

Plastic backplate:
TD .020 / Cox 4.5Dx2P prop 17,472
TD .010 / Cox 3x1.25 / 27,112

Aluminum backplate:
TD .020 /4.5Dx2P / 18,330 rpm +1,130 rpm
TD .010 / 3x1.25 / 27,939 + 827 rpm

Backplate Weights: TD .010 / .020
Aluminum with O ring 2.4g  / 2.9g
Plastic 1.3g / 2g

Note on Sceptre Flight link:
TD .010 / 27,000
http://sceptreflight.net/Model%20Engine%20Tests/Cox%20Tee%20Dee%20010%20(1).html

TD .020 / did not have the 4.5x2 tested the prop was not produced yet. Did show a  5.25x3 /11,200 rpm
http://sceptreflight.net/Model%20Engine%20Tests/Cox%20Tee%20Dee%20020.html

Brad what do you think is the reason for higher rpm with the alu backplate? Smaller crankcase volume = higher initial pressure of fuel-air mixture scavenging the cylinder?

Hi Balogh

Please read this information:
http://www.flyfreeflight.com/Site/Cox_020_Rework.html

"A weak area in the 020 design is the joint between the radial mount and the engine.  It can be difficult to obtain a good seal due to deflection of he plastic mount and the case. During test runs considerable vibration has been observed around 21 to 22000 rpm on most engines.  Often the vibration seems to limit the rpm but once the vibration decreases the rpm rapidly increases.  This appears more severe for with the red plastic tank mount.  To help both the sealing and vibration aluminum mount are available that along with deburring and silicone sealant provides a very ridged, leak-free mount. "


The harder ridged aluminum backplate with O ring improves the reduction of vibrations and
the seal when assembling the O ring is set in a groove on the backplate when oiled it literally
snap locks in place as you push the backplate on the crankcase. A superior seal has occured.
It's quite a treat to assemble one and feel / hear the click that seal just made.

Yes you got this part of it Balogh:
The tight tolerances and seal of the crank case reduces over all internal volume producing
additional fuel draw capacity and compression performance.

If this is the case then I would also buy one or two alu backplates..do they ship internationally?

Yes Balogh I am sure he will send to your location, for all keen Cox engine enthusiast!
I look forward to hearing your feedback and from everyone that tries them out.

Odds are many folks will want additional backplates after assembling the first one.
Again the snap locking seal must be experience to truly be appreciated among
the other attributes it has been very enjoyable on my end and exciting to share here.  

Holy crap it's finally done, started Dec. 18th, few hours here there when possible
ok I confess was watching TV and building it at the same time while surfing the net
and such, at least this sucker is ready for a engine run up and setting up the throttle.
So going into the 14th day I could fly it but the weather is very cold for a Texan 26F
with drizzle drazzle and 25 mph winds feels like 14F according to the weather channel.

Perhaps next weekend word is 60F on Sat. The yellow neon has help with getting some
extra orientation so worth the effort to hand cut out the letters and numbers. The number
fifteen was used to represent 150 mph the speed I will strive to obtain with various .05
size engines. Cox engines first then Fuji .05 which took the .09 size DART to 148mph.

Finished weight less fuel is now 9oz .09g

With the carbon speed prop shown I am close to a 1:1 thrust ratio:

Published on Oct 22, 2017

Tee Dee RC .050 - All Carbon 4 x 4.5 speed prop.
Best static peak 27,051 / .164hp / 122w / 8.5oz thrust / 115 mph
Nelson plug / aluminum carb body / pressure tap on muffler.

A 4.5x4 would get me over the top from idle to vertical but really this thing will be mostly set up
for down wind passes at 130 mph + and get up and out of sight before it runs out of steam anyways.
I plan to use a carbon / nylon 4x5N after a few orientation flights for a possible shot at 140+ for a
Cox TD .050 RC this will be outstanding.

A real chance at seeing more from the Cox engine. Retirees that flew CL speed classes 70's / 80's
should get a kick out of what's possible with a purpose built 1/2A RC straight line runner. If anyone
wants to build one refer to the thread and feel free to ask questions, would be a treat to see some additional
efforts towards top end speed. Cox .049 Reed Speed would be another niche with this design. Note the yellow
has put the camera in check and is now able to capture the neon bit better.

This is a beautiful all wood speedster!




Posted top vid speeds thus far:
Cox .010 / 130 mph / 4P
Cox .020 / 106 mph / 3P
Cox .049 / 118 mph / 4.1P
Fuji .05 / 148 mph / 4.5P / Profi Pipe
Norvel .061 / 108 mph / 4P / Profi Pipe
SH .07 / 120 mph / 4.75P / Profi Pipe
Cox .09 / 144 mph / 6.25P

This is really beautiful Brad..I wish I could build one freehand without parts laser cut as in ARF-s that I mostly build. Looking forward to seing your vid.

1/2A Nut wrote:

Plastic backplate:
TD .020 / Cox 4.5Dx2P prop 17,472
TD .010 / Cox 3x1.25 / 27,112

Aluminum backplate:
TD .020 /4.5Dx2P / 18,330 rpm
TD .010 / 3x1.25 / 27,939

Here's what the cox manual says;



I will tach my own again when the sun returns and spring comes...

My VA .020 did 18800rpm on the cox 4.5x2 prop, with a muffler and 10% nitro, so that should be an encouragement for those who managed to get one of those.

Thank you Balogh very kind of you to say much appreciated happy to share

Hey Kris what do you think of the aluminum back plate for the TD .010?

Perhaps Roy Cox selected a brand new engine for the test and they used 50% nitro.. who knows.
None of my TD .020's have made it to 19,500 static with the 4 x 2.5 prop see vid:


AmpAbuser / AKA 1/2A Nut
Published on Jul 12, 2014

TD .020 3ch Lil Speedy
21in span exhaust throttle sleeve, flying with a Cox 4 x 2.5 prop.
10cc tank / With fuel RTF  5.3oz / 25% nitro 18% castor
Static 17,603 rpm / Best pass unloaded 25,579 rpm / 61 mph.

Kris I don't have a non RC VA .020 but here are some other TD .020 results:

Cox TD .020:
RC Carb / 3.75 x 4 prop / 23,032 rpm / 87 mph static
25% nitro / 20% castor

RC exhaust throttle ring used on the following:
4 x 2.5 prop / Static 17,603 rpm / 25% / 18% castor oil
3.5 x 3.5 prop / 24,644 rpm / 35% Nitro / 20% oil
3.75 x 3  prop / 22,529 rpm / 35% Nitro / 20% oil
3 x 3 prop / 29,985 rpm / 35% Nitro / 20% oil
3.3 x 3.15 / 24,794 rpm / 25% nitro / 20% oil

G-Mark .030 RC carb / 4.5 x 2 /17,728 / 25% nitro / 18% oil

I contribute with my experience here: TD 020 r/c
I have a Cox 4 1/2 x 2 and 19500/19800 RPM propeller

Out of curiosity I tached my TD020 with 20% nitro.
1. 18.5k with the grey 4.5x2 prop
2. 24.6k with the stock 3 bladed

Thank you Mauricio and Balogh good prop data I will make note of it.

I have never flown with the 3 blade I know they rev. well and the plus
is being a 2.5P you get that extra bit of pep, I just prefer two blade props.
You may recall I said the TD .020 used for the test has had quite a bit of flying time
with the Lil Speedy I and II, yet still made more rpm with the new backplate.

Tonight I set the throttle up with the NANO III
I used a known prop by most folks a APC 4.5x4 / 21,640 / 8.8oz thrust / 82 mph static

1/2A Nut wrote:Thank you Mauricio and Balogh good prop data I will make note of it.

I have never flown with the 3 blade I know they rev. well and the plus
is being a 2.5P you get that extra bit of pep, I just prefer two blade props.  
You may recall I said the TD .020 used for the test has had quite a bit of flying time
with the Lil Speedy I and II, yet still made more rpm with the new backplate.

Brad I have flown TD 020-s with both the 3 bladed and the 2 bladed props and my experience shows the 3 bladed fares better. At least the shaft power of the TD 020 maxes out around 23k (see below curves, blue for the TD 020, courtesy Martin Happerle) and assuming the shaft power transforms to propulsion power at similar efficiencies with the 4" 2-bladed, and the stock 3 bladed props, I would assume the 3 bladed generates more propulsion power at 23-24k than the 2 bladed 4" at 18,5k where the shaft power is less...


The COX 020 instruction sheet also advises users to let the 020 scream and not overprop it...anyway practical experience may differ from the above considerations.

balogh wrote:Out of curiosity I tached my TD020 with 20% nitro.
1. 18.5k with the grey 4.5x2 prop
2. 24.6k with the stock 3 bladed
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Those are good numbers, it seems I might have confused my readings between the 4.5x2 and the 4x2.5 prop. The 4x2.5 is a little lighter load on the engine, and yours would likely reach around 19500rpm on that prop then.

Mauricio is really on to something though, 19800rpm with an RC ring, that would be the backplate to mass produce!

Surfer_kris wrote:
Mauricio is really on to something though, 19800rpm with an RC ring, that would be the backplate to mass produce!

Thank you for your assessment, I am glad that it is useful, here I support the measurement, in this video you can see the variations in Static and the real functioning of the RC ring.
The back plate is self-made, it has an original Cox gasket.

I will replace my precious Pee Wee r / c, for a TD r / c, simply make experience as one engine and another engine behaves in the same model ....
To this TD 020, also make an aluminum plate and acceleration ring made at home....

Awesome job on the upgrade should enjoy the extra power on the bigger plane!
What is the ready to fly weight now? Let me know what rpm you can get out of this other TD .020 over
there with the 4.5x2. I imagine your living in a rich oxegen environment, perhaps lower elevation closer to sea level?
I am testing indoors of course, 653 ft. from sea level, within a large city environment. 

NANO II and NANO III

III has closely followed the footsteps of II as you can see it was simply blown up to 28" from 15.5"

Looks great, Brad, we are looking forward to seeing the maiden flight vid...whether in Texas permitting?

1/2A Nut wrote:Awesome job on the upgrade should enjoy the extra power on the bigger plane!
What is the ready to fly weight now? Let me know what rpm you can get out of this other TD .020 over
there with the 4.5x2. I imagine your living in a rich oxegen environment, perhaps lower elevation closer to sea level?
I am testing indoors of course, 653 ft. from sea level, within a large city environment. 

Friend Brad, here are my results with another engine:
https://www.coxengineforum.com/t11454-cox-td-020-r-c-achieving-your-minimum-turns#146002