Glow Plug for the G-Mark 03

Greg , did you make bird cages for the Space Hopper??

getback wrote:Greg , did you make bird cages for the Space Hopper??  

Still in design stage. I hope to offer various parts I design and make, not only Cox related. I realize this kind of stuff has been done before, so I'll try to make it unique somehow.

Sounds good and thanks again , Eric

I have been working on a new backplate for mine, the stock plastic tank is simply too soft for the vibrations that are produced by the engine. The threefold symmetry makes it a little tricky (or rather time consuming), but otherwise it is pretty straight forward. Below is the result, I made it slightly larger than the stock one inside the crank (this helps to reduce the dead crankcase volume a little), and used an o-ring seal rather than the very thin paper gasket that was on there before.

Kris, that looks nice! I haven't designed one yet. I may keep the trilobe theme, but not that big. Does that match the existing tank mount?

I made the mounting holes (or "foot-print") for the firewall the same size as the original (optional) non-tank mount. This is smaller than the foot-print of the tank mount, but could be made smaller still. I was thinking of using only two screws horizontally but finally went with the stock foot-print.

The two foot-prints are shown in the second page of the manual:

Great job as always Kris, if you make a aluminum carb body with a good fitting carb
the engine will for sure perform much better than stock. The backplate aluminum and
carb body aluminum will help wick away more heat. The engine runs very hot on the
bench and could do with cooling fins on the glow head. With all the above said the
potential heat reductions could be as much as a 25% improvement.

For those who don't own one here is what a stock G-Mark .030 sounds like:



AmpAbuser / 1/2A Nut
Published on Feb 6, 2016

G-Mark  .030 /Cox 4.5x2 /17.72k / 34mph / 5.64oz Thrust

It is an odd engine, don't know what to make of it.

Mine runs strong now, without the muffler I'm seeing around 21700rpm on the cox 4.5x2 prop and 10% nitro, but the throttle is pretty useless...

Perhaps it is all the SPI and the fact that the carb has no low end correction. It also runs hot to the touch but doesn't sag and the needle is not very sencitive (at a constant throttle setting). I tried shiming both the head and below the cylinder (head shims for the cox .049 are a nice fit) but it doesn't seem to help with the temperature or the throttling.

Five glow heads for sale

https://www.ebay.com/itm/FIVE-VINTAGE-NIB-G-MARK-03-GLOW-HEAD-FOR-CL-RC-AIRPLANE-ENGINE-PART-NITRO-GMARK/392008437502?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D50425%26meid%3D40f02163fc17444db758b228f26ec248%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D392008437502%26itm%3D392008437502&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3Ae8169052-322d-11e8-8298-74dbd180640c%7Cparentrq%3A6a63a64c1620abd997c0895efffc93b2%7Ciid%3A1

Well, now we just need a time machine, so that we can go back and bid on them too...?

I have a few spare heads for mine, but I wanted to see if I could make a custom head that takes a turbo plug. In was not that difficult to make the parts, but even the hottest turbo plug from OS (the P3 one) seems a little colder compared to the stock plug. All out power is pretty similar but the stock head does not flame out as easily as the Turbo one near the "idle" at 10000-12000rpm...

What temperature is it running at? We used to use welding temp sticks that melted at different temperatures to approximate surface temps. Now there's laser equipped heat guns.
Running Nitro powered cars/trucks with large cooling heads with notches milled around the circumference increased the linear surface area increasing cooling as heat dissipates from the edges of the cooling fins.

Thanks to the management of Mr. P. Ojeda I was able to access six units of Glow Plug for G-Mark .03
Now I am willing to try this engine !!

They are beautiful little pieces of fine machine work and I hope to find a sleeper example of one on the cheap one of these days at a swap meet or estate sale. Please advise though when somebody's bench test of one definitely beats a Tee Dee .020.

Hi Tico, I have bench tested with the stock prop:



Published on Jan 20, 2018

G-Mark .030 stock prop 115Mx50M
Engine has  SPI. I removed the muffler / rare stock prop: 115M x 50M  / 4.53 x 1.97"
Static 17,280 Best Peak / 5.64oz thrust / .03hp / 22.4W / 32.2mph
Average: 16,818 per laser tachometer. New old stock engine was still a bit rich not quite holding a steady peak I would imagine best peak after some field flying around 17.4K  / 25% nitro / 20% castor. No effort was made to adjust for best low idle.

This is a 1962 British test of Tee Dee .020. Note that prop selection was not very good on this test and it was a Limey test conducted with old tech measuring equipment and very questionable fuel. It's a mixed bag, but I suspect a Tee Dee .020 with that G mark stock prop will beat the .030 and might even equal it with a stock Cox throttle ring from a Pee Wee .020 and still have better throttling characteristics to boot.

http://sceptreflight.net/Model%20Engine%20Tests/Cox%20Tee%20Dee%20020.html

Well here we are again ... because one of my G-Mark .03 glow plug has been damaged, so I took the Kris data and modified the original Glow Plug, to turn it into a glow plug adapter.
Take a Norvel Glow Plug and modify it, everything works perfectly, now I have to go to the field to see the results doing several test flights.

Good to hear that it is working what kind of rpm are you getting with the 4.5x2 prop?

I had posted a link twice on your plane thread to look at a good performance upgrade
to the .03 engine but no response:



Published on Apr 5, 2019
G Mark .030 / Cox 4.5D x 2P / OS RP6 Turbo Plug / Aluminum Radial Mount
Peak 21,237 rpm / .056hp - 42w /8.5oz thrust / 40.2 mph pitch speed
25% Nitro / 20% castor oil




Tested with the Cox 4D x 2.5P speed prop


Published on Apr 5, 2019

G Mark .030 / OS Turbo Plug RP6 / Aluminum Radial Mount
3 cooling fin plug adapter with extended cooling via backplate.
Peak 21,398 rpm / .045hp - 34w / 5.2oz thrust / 51 mph pitch speed.
Excellent throttle response / big boost in power! 2 clicks rich.
25% nitro / 20% Castor / 73F / 652ft, from sea level.
Cox 4D x 2.5P / .020 prop / Engine weight with prop 41.4g

Hey Brad !, if I had seen the links that you left me, now I'm visiting! ... very good result I see that you get there with the OS Turbo glow plug. That cylinder cover you made it? That is, the glow plug adapter ...
Ok, I'll make a few measurements of my G-Mark .03 and I'll share here to see the results.
We continue sharing friend!

Great thank you Mauricio look forward to your results with the insert plug.
Yes glow plug adapter and backplate to improve seal and cooling, will end up
being available at Kamtechnik.com

1/2A Nut wrote:Great thank you Mauricio look forward to your results with the insert plug.
Yes glow plug adapter and backplate to improve seal and cooling, will end up
being available at Kamtechnik.com

Brad Amigo !, I made this video a few minutes ago, I am happy with the result, now I know that every glow plug originel G-Mark that is ruined, I can modify it and place a Norvel plug !! ... I really like how it works !!
What do you think?

Battle of the G Mark .03 engines Cox 4.5D x 2P

Mauricio's / Norvel Insert plug
Peak 18,750 rpm / .038hp - 28.4w / 6.34oz thrust / 35.4 mph pitch speed


Brad's / OS RP6 Turbo plug
Peak 21,237 rpm / .056hp - 42w /8.5oz thrust / 40.2 mph pitch speed
+ 2,487 rpm

Thank you for sharing =) good fix well done, but my friend I won more rpm lol whoo hoo!

1/2A Nut wrote:Battle of the G Mark .03 engines Cox 4.5D x 2P

Mauricio's / Norvel Insert plug
Peak 18,750 rpm / .038hp - 28.4w / 6.34oz thrust / 35.4 mph pitch speed


Brad's / OS RP6 Turbo plug
Peak 21,237 rpm / .056hp - 42w /8.5oz thrust / 40.2 mph pitch speed
+ 2,487 rpm

Thank you for sharing =) good fix well done, but my friend I won more rpm lol whoo hoo!

.....you make this a lot of fun !! ... I will continue to investigate and see if I can increase the rpm!

 Yes was fun to compare! How many plug shims are you using?
I used 600 grit sand paper to increase compression on this prototype plug.
The stock plugs have very little compression once the engine heats up.