COX .15 Throttling

I have. My first own design R/C was a 6ft motorglider. Single wheel landing gear. It sort of reminded other folks of an open cockpit RV-4. After seeing pics of a Fournier, it wasn't that pretty! This was in the early '90's. It was powered with an old TD .09 that my StepDad had shown me how to fit the ring to it. I had given an older gentleman in the club $20 for it. It was my first and only experience with an exhaust throttle. Man, was it smooth. I was amazed. I understand that it should not matter how it gets the fuel/air mixture when considering the exhaust throttle. But, I don't have any experience with reed valve engines or .15 Cox engines, so I thought I would ask.

I have been watching the slew of Olympics on evilBay. I don't understand the logic process behind $300+ when the market is flooded with them! Same seller has Sportsmans for even higher than the Olys! He hit a motherlode, somewhere... I'm bidding on one of the few Olympics that is NOT being sold by him and is in an auction format. It's used, but looks good.

Are you interested in selling your cylinder/throttle ring?

C.T.

The Medallion throttle ring won't fit the Olympic engines cylinder.
This aftermarket ring does. It might be possible to swap out the
piston / cylinder from a Medallion RC.

Thank you! Is it the spacing of the ports to case or the diameter of the cylinder? Are the internal bypass ports the same/similar enough between the two cylinders to be compatible? I wonder about the power difference, too. I presume the Medallion front rotor engine will be more powerful?
Maybe I am overcomplicating my idea... I have an old Peck's Prairie Bird, and I wanted to mount a throttled Olympic on it. Probably be better off sticking an Enya .15 on it and being done... but, it sure would pull with the Olympic on there.

CT

The OD of the cylinders are different. The Olympic would have a cool look and sound
given the large reed. Unique in size with the upside of bearings.

Are the aftermarket Olympic rings available anywhere besides finding one as a needle in the haystack?

CT

I just watch ebay from time to time and spot juicy finds.

Yup, needles! We be searching, alerting and schtuff! Thanks!
BTW, I am still only halfway through the Speed thread...

CT

Providing the cylinder base threads match (and not all 15 cylinders do...trust me on this..I found out the hard way!) there is no reason that a medallion 15 RC cylinder wouldn't work well in an Olympic. The RC cylinders have twin transfer flutes-just like the olympic, in contrast to the std Medallion which only has one. Without a careful side by side comparison I could not say with certainty the transfer TIMING is the same-but I suspect it is...given the Olympic dates from an era before Cox stated using boost ports. About the only difference would be the thicker cylinder wall in the Medallion R/C cylinder.

Now without a full tear down, I can't be certain about the crankpin size...which is about the only other area where you might get caught...but I can check that....

ChrisM
'ffkiwi'

There is a third choice for a RC Olympic using this version of a cox slide exhaust throttle.

Wow, thanks, both of y'all! With tools, skills, and ingenuity... the possibilities are endless! I can't even imagine the smooth throttled scream of that Special MkII !
CT

I wonder what type of cylinder the Olympic model uses it is similar to a sportsmans and the sportsman uses a different smaller cylinder compare a larger medallion Cannot be installed on the sportsman !

Well, shoot, that is going kill my first plan of swapping a throttled Medallion cylinder to the Olympic block. Thanks for the info, though.
I am going to post on the Wanted board for a ring for the Olympic. I have three differently worded searches on the evilBay set on wake me up! So, I can fire on one, should it rear its head!
CT

sorry to report that I've pulled down an Olympic, and a Medallion R/C cylinder will not fit the Olympic crankcase....the diameter of the Medallion threaded base is larger than the ID of the Olympic crankcase cylinder locating thread. Bummer!   The only option-and its not one I'd recommend-as it will irreversibly alter the Olympic-would be to get a skilled model engineer to machine out the opening and rethread it to the Medallion cylinder base thread. The difference in thread diameter is not trivial, being of the order of 1/16" larger diameter in the Medallion cylinder.*  The crankpin diameter however is still OK and the piston rod unit fits nicely on the Olympic shaft....

Contrary to my earlier post-the Olympic cylinder DOES use boost flutes in the transfer ports, BUT the Medallion R/C cylinder has more transfer depth than the Olympic-and a slightly increased exhaust depth-so IF the Medallion cylinder could have been fitted I would expect a slight improvement in performance over the Olympic, at full throttle

ChrisM

* the Medallion R/C cylinder tried is a fairly late production one-thickwalled, and with spanner flats milled on the top fin-and a spacer fitted to the gudgeon pin to centre the conrod. It is possible that a Cox Special 15 Mk1 cylinder might fit-with the thicker wall you might be able to grind the OD  for an exhaust throttle...but you might still have to settle for a two piece throttle unit...

ffkiwi wrote:sorry to report that I've pulled down an Olympic, and a Medallion R/C cylinder will not fit the Olympic crankcase....the diameter of the Medallion threaded base is larger than the ID of the Olympic crankcase cylinder locating thread. Bummer!   The only option-and its not one I'd recommend-as it will irreversibly alter the Olympic-would be to get a skilled model engineer to machine out the opening and rethread it to the Medallion cylinder base thread. The difference in thread diameter is not trivial, being of the order of 1/16" larger diameter in the Medallion cylinder.*  The crankpin diameter however is still OK and the piston rod unit fits nicely on the Olympic shaft....

Contrary to my earlier post-the Olympic cylinder DOES use boost flutes in the transfer ports, BUT the Medallion R/C cylinder has more transfer depth than the Olympic-and a slightly increased exhaust depth-so IF the Medallion cylinder could have been fitted I would expect a slight improvement in performance over the Olympic, at full throttle

ChrisM

* the Medallion R/C cylinder tried is a fairly late production one-thickwalled, and with spanner flats milled on the top fin-and a spacer fitted to the gudgeon pin to centre the conrod. It is possible that a Cox Special 15 Mk1 cylinder might fit-with the thicker wall you might be able to grind the OD  for an exhaust throttle...but you might still have to settle for a two piece throttle unit...

Chris, thank you for getting them out and going to all that trouble! I have to agree, I don't think machining the crankcase is a logical option. One mis-cut and it's ruined. With all the other variables that could be detrimental to power, smoothness, and reliability, plus the expense and lack of easy replacement parts... with maybe a boost in flow of the fuel/air mixture due to the later model cylinder.

I may need to sell some of my other stuff to purchase the Olympic with the air choke/throttle wannabe block thing sticking waaaay out the back of it. I am afraid that it would lag worse than an under powered Turbo. But, it sure looks neato. Almost like a velocity stack or a single high-rise intake on a side draft carburetor! I wonder if it has any (even tiny,infinitesimally small) effect on torque?! Not a measurable amount, anyway. Next wild idea: Anyone ever see a diesel head on a Cox .15 of any flavor? Not Conquest. Whew! Talk about expensive machining!!! But, it could be swapped out, easily. If it is the same diameter pin as the TeeDee and the Specials... I know that does not mean the metallurgy is not different. The final three models and the Rear Rotor .15's are probably hardened and polished...
Who is the gentleman that made diesel heads? I have been binge reading the forum so much, trying to learn and absorb it ALLLLLLL! Greg, maybe? I can't remember the screen name... why does it want to be Kazakhstan in my head? I could have sworn he was in Illinois!

There is no logic behind my obsession with throttling an Olympic .15. It's over complicating something because it would a) look cool; b) sound cool; c) be fun to make it happen and WORK, with reliability, convenience, and power!

What do you experts think? Would I be better off trying to adapt a carburetor off something else (installed at the needle valve position) or make a throttle sleeve/ring based on the aftermarket ones that @1/2anut (sp?) showed us? Or I could just be patient and hope the cosmos will crap a ring/sleeve or slide throttle on evilBay? Is there a carb that is easily adapted like the plastic cased Perry's? If I could find someone willing and able to machine a contrapiston and head, would I need to make the venturi/throat smaller (or use a smaller carburetor to start with?) to account for the smaller f/a charge needed for diesel?
I can't tell from the seller's pics if it is a drum valve or butterfly in the choke/throttle block below. Next, crazed brain flatulence, if it's a drum, I wonder if a needle valve (or a jet and remote valve) could be drilled through it?

I did say there isn't really any rational reason for any of these options. Just a desire to make it work, the way I want it to... not necessarily what it was designed to do and be!

CT

Boats...re the diesel thing...yes its been done. A guy in Australia-Ilya Leydman-was marketing diesel versions of the Medallion 15 a few years back...he was I believe of Russian extraction and had contacts with the various Russian model engine manufacturers...he traded under the name 'Mach East'-and sold a number of different russian made-mainly sport engines.  I don't know how many Medallion engines were produced/modified....he must have located a number somewhere to make the project worthwhile. I presume they were done in a similar fashion to the Mecoa 049 and 09 diesel heads...the photos I recall-in the Australian magazine 'Airborne' appeared to show a normal Cox 15 glowhead fitted with a compression screw and compression screw lock....all atop an apparently standard Medallion. I don't recall reading any reviews-but Airborne probably published one somewhere along the line.

Cox engines are known for being a bit fragile when dieselised-the reed valve 020 and 049 ones particularly so...whether that would apply to the .15 size reed valves I could not say-since to my knowledge there have never been any commercially available conversions. That being said someone will have tried it....and if they ended up with a broken crank or a snapped conrod for their trouble-they probably didn't boast about it.  Now 'surferkris' sings the praises of dieselised Queen Bees....and the dieselised 09s seem to work OK...so perhaps the 09s and larger have sufficient material strength to cope with the rigours of diesel operation. Its not a hugely difficult job to make a diesel head using a burnt out glowhead if you have machining skills-and experience has shown that the 'contrapiston' doesn't have to be full bore diameter-quite a few of the larger glow to diesel conversions use a setup where the adjustable contraspiston is in the form of a smaller slug-usually O-ring sealed- within the wider head....still adjusted by a compression screw in the normal way-but well less than the full bore diameter-allowing things like the squish band to be retained....which may or may not have a beneficial effect on running...

I would of course be a little bit chary of fitting a diesel conversion head to an Olympic, Sportsman or TD15-mainly because of the ball joint conrod....I'm not sure the little end would cope very well....this of course is not an issue with the Medallion as the later ones have a conventional wrist pin and conrod.

We have a few Australian members here-they may well be able to provide a bit more info on the Medallion 15 diesel.....jump in guys, if you can....

ChrisM
'ffkiwi'

Chirp, chirp... chirp, chirp...

Well, I too was hoping the diesel experts would chime in...
Should I copy and paste, and post in the diesel board?

And a bit of thread drift, here...

Does anyone have a Olympic 15 aftermarket throttle sleeve they find to be redundant, surplus or just in the way? I do have a brand spanking new Medallion .15 with a throttle sleeve on it for trading fodder. It comes with an admittedly rough jewel box and cardboard insert with a rough cardstock cover sleeve. If no one want to trade ill put it up on evilBay. Maybe even sell the exquisite Olympic I have and buy the airchoked one that was pictured above. The seller is stuck on $275 for it, though. I know, none of it is simple, nor is it urgent.
I wish MauricioB needed a throttled Medallion .15, I'd trade that for an aluminum throttle ring from his Lathe! Man, have you seen his work? That .049 muffler he made is beautiful, cool, and quiet! But, I watched his videos of his in flight...

C.T.

1/2A Nut wrote:There is a third choice for a RC Olympic using this version of a cox slide exhaust throttle.




 

This version of silencer would be perfect finding it can be difficult don't be discouraged you will definitely find Somting

Another option is to fly 2 channel (rudder/aileron and elevator, or all 3) and use a pylon fuel cutoff device:

https://www.coxengineforum.com/t17191-want-to-buy-cox-medallion-09-with-exhaust-band-throttle-found-one-thank-you#222518

https://www.fourmostproducts.com/our-products/fuel-fittings/


On pylon racing models, a quick blip of full down elevator pulls a string that snaps the fuel cutoff, glide her in.

davidll1984 wrote:

1/2A Nut wrote:There is a third choice for a RC Olympic using this version of a cox slide exhaust throttle.




 

This version of silencer would be perfect finding it can be difficult don't be discouraged you will definitely find Somting

There is one of these for sale on evilBay, right now, but it has the spray bar rotator with it and a .Medallion I don't need. I should micrometer the upper cylinders and see, but I think they're different diameters, too.

CT

GallopingGhostler wrote:Another option is to fly 2 channel (rudder/aileron and elevator, or all 3) and use a pylon fuel cutoff device:

https://www.coxengineforum.com/t17191-want-to-buy-cox-medallion-09-with-exhaust-band-throttle-found-one-thank-you#222518

https://www.fourmostproducts.com/our-products/fuel-fittings/


On pylon racing models, a quick blip of full down elevator pulls a string that snaps the fuel cutoff, glide her in.

Not to sound whiny, but I want to do touch and goes with this one.

CT

Boats13 wrote:Not to sound whiny, but I want to do touch and goes with this one.

Well, you still can do touch and goes, albeit very fast.

I would run out of altitude and ideas... but not airspeed!

CT

This is up for grabs with throttle sleeve.

https://www.ebay.com/itm/256400583998?itmmeta=01HS1DABYFSAB5F9HJ92XR68F8&hash=item3bb2aa6d3e:g:U0sAAOSwMKNlv1IM&itmprp=enc%3AAQAJAAAAwOdBWNnF9eAsBZZHWKUpR09pHiZfA17XBmTXxEcH78R2mQWrGx08suSZ4L5m%2FAArVcFNMCe4DQe9p5OSx2u5IGbZ9t%2FF9P2X1Z8thq8U7g0kZPjt86%2B96blWO4kz5N6daBhsoQGoxdqa6VjdBSu9awaOSCy5TQKd4vjAjO3v3Onhfx1uAmQqWN1drSgKtpWd%2FzCRaMU28xkFwIKlWaWv0W6%2BMdr96ADaE4uwt1np7eiT%2Be%2FQn3v9bCUDQXvmS09fSQ%3D%3D%7Ctkp%3ABk9SR7i_qa3IYw


and this

https://www.ebay.com/itm/404797292896?itmmeta=01HS1DABYFZBNTT67HQRSSPS56&hash=item5e3fcc8160:g:A2QAAOSw3tBlUog7&itmprp=enc%3AAQAJAAAAwIM9uatljXjeydO%2BeuIrcI5oi%2FBR930YRqced5m9R7ovzVXO1cskAxAyPeVKqw2j80yCqpdlL4dy2v6J%2FmhINwyWEwwGt%2BkN4OEkZ0AxXwd0uubrKYHnQmH%2BaS9zLZLCFFmj118SvfnR%2FuVa35BXreB9dGq04UhWDmvFdzMI45hA79bfEM19Qv7Sk7xihAoZPjzjRiHSOnSyd84M4XsGJpCey54NRsXfiAtYTCXmeSv2vxxBP6Q%2FUhgJRA4eSljN7g%3D%3D%7Ctkp%3ABk9SR7i_qa3IYw