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.

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

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

CT

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

CT

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

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

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

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.

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

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

CT