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G-mark .061 prop question

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Old 04-04-2019, 10:54 AM
  #26  
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Originally Posted by mwohlenhaus View Post
Are yo still talking an .061 here? I am new to IC tuning/setup for air use, but that seems small for what is reccomended by the manufacturer as a 6X3 prop. But keep me posted with video/pics when you get everything in.

Quite right-but I suspect Pondskipper is referring to the .03 G-Mark.....but a 1K increase in either of them is a respectable goal and if achieved puts both of them right into TD territory.....which with their already excellent throttling, makes them rather useful... A 4.5x2 is a good match for the 03 ...which came with a 115x50 mm prop if purchased NIB......but a 4.5x2 on the 061 would result in a lot of noise......for a very short time...followed by a bang as the rod let go....

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Old 04-04-2019, 06:47 PM
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Here it is gents was referring to the GM-.030
Radial mount for more contact area to the firewall while still keeping a small foot print.
Turbo plug head with 3 cooling fins big plus over the stock plug. Have not ran it just
assembled at this point. Note the pressure tap on the muffler. The engine has SPI
I want to test it open exhaust to compare directly to the TD .020 in those regards.
Note the plug on the left was not producing enough compression once the engine
was warmed up. The new version is on the right with the extra 3rd cooling fin. These
engines run hot anything to help keep them cool should allow a leaner NV and more
rpm.





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Old 04-04-2019, 07:04 PM
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Here is a weight check could go without the starter spring to save more weight.
I use the Hornet 1/2A starter without the spring closer to 40g not bad for a .030

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Old 04-04-2019, 08:57 PM
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Great work pondskipper-you might well find a lot of takers for those turbo heads and backplates if you intend going into production-I'd certainly take several-I forget how many 03s I have...4 or 5 as I recall....2 or 3 R/C ones and the remainder standard....given the supply of original glowheads is virtually non existent, people would be happy just with an equivalent......one that is better than the original is gilding the lily.....and should be extremely well received....

One point to be aware of if using the original tank [irrelevant is using your alloy backplate]-the plastic is not as tough as the Cox tank material-and running the engine in open exhaust can melt the top front edge of the tank.....(you can imagine how I discovered this.....the hard way!)-the problem does not occur with the muffler in place obviously....and equally obviously-the effect depends on the exhaust port orientation with respect to the tank.....in my particular case the ports were fore and aft....supposedly the best for scavenging and performance

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Old 04-04-2019, 09:51 PM
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Pond skipper, where did you get the pressure tap??? I have scoured the internet to find a 4-40 size and have had no luck!
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Old 04-04-2019, 10:17 PM
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Bare weight no spring is shown in this pic. Thank you Chris, I do not make the parts I collaborate on what needs to be
made it's requirements and then test. Greg with https://kamtechnik.com/ does the Cad work and CNC milling. It's his
baby. My other capacity is to promote through results and video, direct folks to the source to make effort to insure he
can keep going with this. My benefit is parts to play with and beyond prototypes I buy additional parts too. It's a wonderful
collaboration and I am grateful to be a part of the process. Many new parts to test this year and if all goes well folks will
be able to enjoy them for years to come. Compression is excellent. One thing lacking with the stock plug / soon as the
engine heats up the compression goes very soft. The element is not very good quality another problem I will be testing
with a OS RP6 med heat gold plug / robust able to handle some nitro. I will be using two shims for the test.

I moved the hardware over to a new engine to test best results during early break in stage. These engine take some
run time to get them loose singing happy. The results will be a better base line knowing it will gain additional rpm
after handful of flights. Shown with a Cox 4 x 2.5 prop.The 4.5 x 2 provides good thrust but there is not much speed
to work with on a breezy day. The engine needs to do better than the TD .020 on the same prop, see vid.


This is a good weight for a RC engine vs a TD .020 with throttle sleeve is around 31g

Cox 4x2.5 note I had some vintage props after this flight test I encourage Bernie with Cox International to find the original mold and
have that vendor make a run. As luck would have it the original company still had the mold and bingo the rare prop was back in circulation.
Unlike a APC prop you can smack the rubber duckies around and keep flying.


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 peak: 17,603 rpm
Best pass unloaded: 25,579 rpm / 61 mph.

Break down of the engines performance:
Static 17,603 rpm / .025hp - 19w / 3.2 oz thrust / 42 mph pitch speed

Goal is to bust the above results perhaps I can get close to 18.4k
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Old 04-04-2019, 10:44 PM
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These are only for small engines TD .010 to .049 tops. Requires you use a cut piece of fuel tubing as a slip ring over the pressure line to help
bind to the pressure nipple. I use hemostats to expand and slip the ring over the line. There is not better proportionally sized pressure nipple for TD .010 to .03 engines.

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Old 04-05-2019, 01:42 AM
  #33  
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The power of the .030 engine can be increased over the stock version, for sure.
My best version will do about 21700 rpm on the Cox 4.5x2 prop (and 10% nitro), but even the hottest Turbo plugs from OS are colder than the stock glow head, so the throttling suffers and the engine tends to run very hot...


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Old 04-05-2019, 03:33 AM
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The engine runs hot with the stock plug the engine flat out runs hot.
Once the engine is hot compression fades bad when using the stock plug.

I do have some of these per OS they state them as "super hot"
OS Speed Tuned Gold Plated High Performance P4 T-Series Turbo Plugs.
22% castor may help will bench test this one in the next few days.


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Old 04-05-2019, 06:25 AM
  #35  
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The P3 plug from OS is hotter than their P4, while the thin gold layer is just bling bling I suspect...
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Old 04-05-2019, 08:01 AM
  #36  
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Yes I decided the P3 would be over kill and went with the P4. Gold is a better conductor as we know. Voltage travels
via "skin effect" so nice when heating up the plug, beyond that I like the anti corrosion benefits and aesthetics.
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Old 04-05-2019, 08:33 AM
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Originally Posted by Pond Skipper View Post
Gold is a better conductor as we know. Voltage travels
via "skin effect" so nice when heating up the plug, beyond that I like the anti corrosion benefits and aesthetics.
No, I'm sorry, the voltage doesn't travel via any skin effects....
The gold coating could replace a nickel coating and reduce the contact resistance, but that is about it. It will not do any difference once the engine is running.
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Old 04-05-2019, 10:25 AM
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Kris, no mention of the radial mount or the plug adapter didn't like it?
You stated:
"My best version will do about 21700 rpm on the Cox 4.5x2 prop (and 10% nitro , but even the hottest Turbo plugs from OS are colder than the stock
glow head, so the throttling suffers and the engine tends to run very hot..."

Do you have any video of those results?
I just used an OS RP6 - medium heat turbo plug - and it out performed the stock plug with fantastic idle response, see video below for proof.

Skin Effect:
As Voltage pushes the current density is largest near the surface of the conductor and decreases within the core of the conductor.
Silver is the best conductor of electricity because it contains a higher number of movable atoms.
Silver it also has the highest thermal conductivity of any element.
Gold has a much higher corrosion resistance.

G Mark .030 - BENCH TESTING RESULTS:
https://www.youtube.com/watch?v=Hgblj--ZWjo&feature=youtu.be

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 / 5oz 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



G Mark .030 Performance Upgrades Turbo Plug and Aluminum Radial Mount

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Old 04-05-2019, 11:09 AM
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Originally Posted by Pond Skipper View Post
Kris, no mention of the radial mount or the plug adapter didn't like it?
You stated:
"My best version will do about 21700 rpm on the Cox 4.5x2 prop (and 10% nitro , but even the hottest Turbo plugs from OS are colder than the stock
glow head, so the throttling suffers and the engine tends to run very hot..."

Do you have any video of those results?
Yes, i liked it very much. The radial mount is a big improvement over the stock tank, that simply vibrated too much. The Turbo plug gave a large boost in power too, but the throttling was better on the stock plug as the low end is very rich. I wrote about those findings on the cox forum about a year ago, I guess.

I took a video last winter with a head/hat cam, but the hat was off and the engine was not showing in the video (dooh) so I never posted it on youtube....

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Old 04-05-2019, 11:23 AM
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Originally Posted by Pond Skipper View Post
Skin Effect:
As Voltage pushes the current density is largest near the surface of the conductor and decreases within the core of the conductor.
Silver is the best conductor of electricity because it contains a higher number of movable atoms.
Silver it also has the highest thermal conductivity of any element.
Gold has a much higher corrosion resistance.
I'm sorry, I happen to teach physics at University level, and that's just wrong on so many levels....

Yes, there is a "skin" effect i electrical wires subjected to AC currents, but it only becomes important at high frequencies (MHz range). The electrical current carried by electrons is then located near the surface of the wire and not the whole cross-sectional area is being active. In DC applications, like when we use a battery do heat the glow plug, there is no skin effect and the whole cross sectional area of the wire is being used.

The electrical conductivity of silver is only marginally higher than for copper (at room temp.), and it is high for all of the noble metals and other free-electron like metals. It is the electrons in the free-electron gas that carries the current and this is fairly similar for the all the noble metals (mono-valent and free-electron like). The transition metals on the other hand (like nickel and palladium etc.) have a lower electrical conductivity due the partially filled d-bands. These electron have a large effective band-mass and therefore do not contribute much to the electrical conductivity. In addition the unfilled d-states will provide an additional scattering channel for the free-electron gas, thus lowering the mobility of these as well.

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Old 04-05-2019, 12:38 PM
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Kris, I had posted the info off the net just generalized per this search question: https://www.google.com/search?source...31.sKPye_08MYQ
Lets try to avoid the typical deflections and focus more on testing results. I am currently trying to sort out a G Mark .03 for performance.
Do you have any vid of the 4.5x2 hitting 21.7k, I am about to test that prop next cursory for those that like plenty of thrust.

Here is another test with the HQ 4x4.5 Carbon Prop looking for some more pitch speed I expect the thinner airfoil
and lower weight of the carbon mixed nylon prop has helped to gain some performance. Per this calc program Static Thrust Calculator - STRC

Static 21,560 rpm / 5.3oz thrust / .086 hp - 62w / 92 mph pitch speed very suitable for folks wanting some good speed. If unloaded to 26.5k / 113 mph



HQ Prop 4x4.5 carbon mix / G Mark .030


HQ Prop 4x4.5 carbon mix
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Old 04-05-2019, 01:17 PM
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G Mark .030 / Cox 4.5x2 / Turbo Plug 8.5oz static thrust 40 mph pitch speed


G Mark .030 / Cox 4.5x2 / Turbo Plug

See Vid:
https://www.youtube.com/watch?v=3tPDuYWEOMc&feature=youtu.be
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

I expect this will unload to 26k ish / good for 50 mph pitch speed / mega thrust for acro.

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Old 04-05-2019, 02:07 PM
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Summary of prop tests G Mark .030 / Turbo Plug:


Last edited by Pond Skipper; 04-05-2019 at 02:19 PM.
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Old 04-14-2019, 12:30 PM
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Default New mount



From the front

The finished product, it isnít machinists quality, but I thought it pretty good for free hand
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Old 04-14-2019, 01:21 PM
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Great effort-especially with your limited tool range. Looks the part and no doubt will serve the purpose admirably.

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Old 04-14-2019, 03:12 PM
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Just thought I would mention that I made up a turbo head for my newly acquired G Mark.061. I don't think I put it here yet. 15% fuel and a 4 1/4-4 APC was 18,300 stock head. Turbo head 24,000. With a 6-4" MA 14,400 and the turbo head 17,500. Pretty happy with that, sort of beats a TD. Mine is the control line version unfortunately. I passed up an .03 at Toledo for $20 or $35 or whatever it was. Too windy here for the little guys. One of the above posts mentioned better timing and a turbo head would help. It sure does. I didn't spend the time raising the cylinder as it seemed pretty good. The muffler did not seem to reduce power much, these numbers were unmuffled but the difference was like 300 rpm.
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Old 04-14-2019, 03:18 PM
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Well done that man-you're nicely confirming Mike Billington's prediction that 'there was potentially more power to be extracted from the basic design. I hope Greg Kamysc will be persuaded to offer this head in due course as part of his range of aftermarket accessories. That being said-those a VERY impressive power gains you're reporting....I think your R&D work may result in a lot of people revisiting the G-Mark-I certainly will-none of mine are currently actually earning their keep in models-but I've always had a soft spot for them-while their design owes much to Cox, I think they were made 'up to a standard' rather than 'down to a price'-and based on my past running of them-will probably well outlast a TD....and now that you've demonstrated they can outperform a TD as well....

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PS can you post some drawings and photos?

Last edited by ffkiwi; 04-14-2019 at 03:27 PM. Reason: Additional info request
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Old 04-14-2019, 07:03 PM
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OK, I used a centre drill that I ground a ball onto but a 100 degree or even a 90 degree countersink works good too.I made a bunch of blanks with the turbo plug end finished and 1/2" diameter step .100" deep. The step was to grab on a collet to finish the combustion chamber side which are all a bit different for each engine. The OD I made a few of many stock sizes. 3/4", 1", 1 1/4" etc. (In this case the 1/2" step interfered with the bolt holes so I turned it a bit smaller when it was done.) The third pic is the stock head.



Stock head

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Old 04-14-2019, 07:15 PM
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Some more pics of the blanks I made a few years ago. Hardinge chucker lathe was for high production in 1952.



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Old 04-14-2019, 08:28 PM
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Are the dimensions-as per the notebook sketch-the final ones you used in terms of spigot depth, bowl depth and squish band? And what size ball mill did you use? [I have a range of ball mills -plus ER25 collet chuck-so I can probably duplicate what you've done fairly closely...]

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