Tim Wiltse-RCU

Hello All,

This is my first post here! There is more 1/2a info here than I have ever seen!!!! My first plane was a Cox PT-19 at age 12 and I just love the darn things. I have a Norvel and it runs GREAT but Cox is where I stay.
I have an anodizing set-up and a small machine shop. I have been making Cox RR-1 clones. I have a test engine that I have been testing to see what I can get out of it. Running .093 tank venturi, 1702 hi-compression head, reground/balanced crank,#4 sub piston induction cylinder, 30% nitro, cut down Cox gray prop to 5x3 and so far have a best of 18,300 rpm. Am I in the ball park with these mods on this engine? I'm looking to make Venom level power. I know I need to do some piston/cylinder work and drill out the fuel pick up nipple on the tank back.
What kind of output are you all getting on reed valve engines? This looks like a great group of people and look forward to sharing thoughts/info with each other.

Tim

ZAGNUT

My Feedback: (1)

coincidence?

i was over at some vintage engine site and saw a collection of your custom anodized cox beauties. very nice work!

dave

BMatthews

18,300 sounds pretty hot to me. It's been years since I held a tach to any engines but as I recall most of the hotter twin bypass engines put out about 15000 to 15500 on a grey 6x3. I believe the 5x3 raised that to about 16000. And I think it took a hot TeeDee to break 20000 on a grey 5x3. But these are older memories.

I really only wanted to complement you on the nice ano job. And are those little turned ribs I see on the case nose?

Tim Wiltse-RCU

BM,

Yup... I start with a thick tapered crankcase and turn the RR-1 style ribs into it. I use a 8 cc stunt tank, pull the tubes and go to work on it. My goal with my RR-1 clones is to have the old school look and still have the power of a true rear rotor Cox.


Tim

MR Flyer57

I've only seen the rear rotor at a distance. Yours look as good as anything I've seen. If they run as good as they look you will have a norvel killer!!
Do the rrs use a different crank? I saw the plans for one but didn't really understand the crank set up.

Also I have seen the Venom but don't know much about it. Was it a reed or rr and what did it turn?
MR Flyer

ajcoholic

My Feedback: (10)

The original RR-1's have the same style cox crank but with an extended stepped crankpin that drives the rotor.

Thats excellent work! I have anodised a lot of cox engines myself, and one problem I had is that the cases are allready clear anodised on many of them, and when I remove the anodising with a bath in the caustic solution it also removes enough material from the inside of the crankshaft bore as to make the fit sloppy. Are the older tapered cases plain aluminum or are they anodised?

Are you also making a rear rotor conversion, or is the 18,000 rpm with a reed? Thats very impressive. I had the best reed valve mod I did get to about 16,000 with a modified porting and a lightened machined crank ala venom.

Would you be willing to share your work with us or is it "priveliged" info?? If it is I totally understand.

Andrew Coholic

Tim Wiltse-RCU

Thanks for the good words guys. I am not yet making a true rear rotor set-up. My clones are using reed valve intake. A real rear rotor remake in in the works!!!

Andrew,

I too have heard that even the plain case engines were clear anodized. I have found that to be not true. Other than polishing I don't strip plain crankcases. If they were indeed factory anodized they wouldn't do anything unless stripped first. As for what I have done to rework my test engine I have only done what I have listed so far. Maybe this one is a freak and I just got lucky! I will get to work on another test piece, maybe just a plain Babe Bee to see what I can get out of them!!

Tim

wild fred

My Feedback: (3)

zagnut; arrgh, haven't seen the energy cones in 20 years! did you know one of the members of devo writes the music for the rugrats cartoon show now? man, that makes me feel OLD!

Japanman

I have made a custom reed setup for my 049 cox reedys using more modern V shaped twin reed design, and mylar reeds. With this setup i saw a big jump in rpms with a 5.7 by 3apc but the really cool thing was when i made a metering carb, with a 7by 3apc it would idle down so low that you could almost see the prop turning. no real exhaust note. it was amazing! (and it would hold the idle without stopping..)

Those rr engines are cool, very sexy 50`s period stuff. I suspect they are restricted by the size of the valve window- not as big as a td, or other contempory engines. If you are making a special, you might like to address this.
There was a RR engine on ebay the day before yesterday, you might just catch it if you want it.
J.M

Msaint

My Feedback: (5)

Metered carb ?
Hmm sounds intresting.
Could you go into a lil detail.
I would love to get away from the exhaust throttles.

Japanman

Its a bit of a job, but it is worth it i think. (trust me, it is better than any exhaust throttle!
Have you seen a thermal hopper with no tank on the back, but a metal venturi sticking out?
this is kind of what it looks like when you are finnished. I would like to post a picture but my engine and carb are in N.Z while i am in Japan...
I`ll be a bit general here, because there is a bit of room for variations to get the same result.
What you want to end up with is a r/c carb (and obviously to get the super low idle a metered one is better if you have got the gear to make one/ modifiy another carb to become one) feeding a reed valve at the back of the engine.
I did this by making a 1.8mm (i would make this thicker, or from steel next time) brass backplate that is also the motor mount. (i made the original engine to go on a biplane, mounted on a plywood firewall with a hole cutout for the carb to poke through.)
onto the backplate on one side -that fits into the crankcase-i had a reedvalve setup and the other side a cone and tube to mount the carb onto.
An easy way to achieve this would be to use a stock reedvalve setup by using one of those killerbee (etc) backplates, binning the needlevalve setup (or recycling it on your carb!) and carefully boring and threading the plastic ventury -so as not to damage the reed valve seat/ arrangement- to take your carb. this should give a good idle depending on the carb.
I am want to note here that much depends on the carb.
mine was made from scratch, it started life as an air bleed carb- which worked o.k (if you compare it to a norvel carb, you would say it was excellent.. much lower idle, but i don`t think much of norvel 1/2Acarbs..)
but because of my reed valve design i could keep progressively boring it out to get more and more rpms. unfortunately i ran into the air bleed carb bogeyman- a when you run a big venturi for good high rpm power, you start to find excessive richness at about 1/4 too 3/4 throttle. this is why i converted to it to a metering carb with two needles. but really its not necesary if you stick with a std cox reed valve, as they offer a lot of down stream restriction anyway. - if you go to big on the venturi you will find you have fuel feed problems.
If you are keen, I would reccomend making the v shaped twin reed block. Yes, it`s a lot of work, but after i made mine i had an engine that has all the easyness of a reed engine. A bonus is that mine pulls about the same revs as my t.d. After i made my backplate mods i never used my T.D again.
If anyone makes one of these engines, please let me know, I`d love to hear how you get on. (and i can post a drawing to help if needed.)
And to all those engine designers out there who are reading this,
Yes, make us r/c reed valve engines please! just get the reed valve design right. (i see J.R makes a reedy engine for helicopters- no comment on the reed setup though..)
J.M

Msaint

My Feedback: (5)

Im maintenance manager for a rather large machine shop.
So I think I will make a go at doing some of these mods.
some drawing of your vblock reed mod would be helpfull.
The carb I think I can deal with no problem.

MR Flyer57

I am interested, but I do not have the insight into the machining that you do.

Your finished product would be fun to try. Please post any drawings or pictures that you can, and when you get back to New Zealand please favor us with a thread on this subject.
I don't know what the twin reed valve is and so I can't get a mental image of what it would look like or the way it would work.
Good stuff,
MR Flyer57

Msaint

My Feedback: (5)

i found a very nice website with pictures of all the old rear carb cox engines.

http://www.mh-aerotools.de/airfoils/cox_frameset.htm

I am now hooked!

Not quite yet ready to sell all my Norvels tho yet

DICKEYBIRD

Here's an engine mount/reed/venturi adaptor one I drew up a few years ago and friend Roger Armstrong machined for me. It uses a stock mylar reed, a bushed down TD venturi/needle assy. and an exhaust throttle sleeve. I called it the "Poor Man's Space Hopper."

It's neat looking but is heavy and doesn't run as well as a mod'ed TD plus has the rich low/mid range problems that I've always had trouble with on reed engines. You'd think a reed would have better fuel draw and metering down low but I've never been able to get them to run as consistently as a TD. The crankcase wear problem is always there as well....TD's do much better over the long term

Nitro-Nut

HI TIM,

I haven't played with my Cox engines in a while and this thread inspired me..

I just ran this Black Widow ... (see pic)

- 30%n/castor,
- 5x3grish,
- hacked cylnder from a Naboo fighter ( I ground the exhaust port thingys out with my dremel)
everything else is stock...

I have a few other modified cox 049 engines that go a bit faster... I have to dig 'em up and and run them again...

One of my PW .020's is running 22000 with a slightly reduced prop and my .010 peaking at 27000.

Japanman

Dickey Bird,
Thats interesting what you found running the stock reed setup and exhaust throttle.
I can`t comment about power output compared to a TD with a stock reed design.
But as reeds go they make much more sence with a r/c carburettor. In the early days of motorbike engine design the rotary vave ruled supreme. Then it was discovered that with good reed valve design there was little or no difference in peak power, but because of the totally varying induction timing a 30% increase in mid and low end power was realised. (this is similar to what i found with my engine. I is very easy to prop- it will swing a 7/3 just as happily as a 5.7/3.. )
This according to yamaha, who really developed the technology.

In this way Cox was ahead of its time and that is one of the reasons why texicos will swing big props at low revs and still produce good power, and their reed valve brothers with only a bit bigger ventury slightly different porting will scream on high nitro and small props.
In Model engines I think for peak power at high rpms the rotary valve setup may always rule supreme. (this is because the relative viscosity of the oils we use is so high, restricting the reeds slightly as the try to open). But with Cox engines I suspect an optimized reed valve setup may be able to outperform the rotary valve, this is because of the Cox`s porting configuration.

The Cox cylinder is very much a piece of classic 50`s contempory two stroke technology. The cox cylinder relys on very high transfer port gas velocitys to scavenge the cylinder. Engines with this layout benifit from high crank case compression ratios- this further increases the velocitys in the transfers and allows scavenging to occur at higher rpms= more power.
Now if you consider that (according to Jett eningeering) having front rotary valve induction reduces the crankcase compression ratio by a factor of about Two as compared to a rear induction rotary valve. (very similar comparable crankcase volume wise to the stock cox reed valve setup) ***note here to ultimate cox engine builders***contempory rear induction disc valve!****build the most powerful Cox ever!***
This poses a few questions about the stock reed setup. If the crankcase compression ratio is so much higher, and the porting configuration likes this, why doen`t it dance all over a front rotary valved engine? That reed valve starting to look like it is in need of an update?
Hope this has got you guys thinking!
J.M

ajcoholic

My Feedback: (10)

The rear disk rotary cox has been done. My good friend Roger Schroeder in Kansas designed this one.... I built it a number of years ago. Runs well but I never flew or tached it!

Andrew

Ragwing

My Feedback: (2)

Sorry this is off topic, but I just had to complement you Andrew on that good looking engine . Hope mine looks that good some day. I'm turning the crankcase now, and I've decieded to mill the mounting lugs into the case, instead of making 4 detachable mounting lugs that bolt on. We'll see. I can't wait till summer break (one more month!), so I can devote more time to modelling and working on engines.
There are some great threads going on right now, just thought I should compliment everyone on their ingenuity and resourcefulness. Wish I could be experimenting with all of ya. Keep up the good work!
Derek

ajcoholic

My Feedback: (10)

Thanks Dereck. Hope yours turns out good!

Instead of cutting the threads in the lathe, if you want to fool with cox cylinders a lot, make yoursefl a tap (just plain steel and case harden the cutting edges with casenit)

I have used this one LOTS on aluminum and it cuts a perfect thread for the cox 049, have one for the 020's also. Takes about 1/2 hour to make. Timesaver!

Andrew

Japanman

I am grinding my teeth here at not having access to a lathe...
That is one funky looking engine, Andrew!
I have taken to using a drill press on its side to do all jobs. It makins screw cutting something for those with a steady hand though....
Amazing how many of us are some kind of engineer, isn`t it?
i was working as an engineer before i came to japan.
I am getting bad lathe withdrawell (whats the spelling for that??) that i am looking at the proxxon lathe and fingering my wallet..
J.M

Ragwing

My Feedback: (2)

Yet another ingenious Coholic creation . At this point, with my limited experience, I probably should get practiced at cutting inside threads. But this summer I'll definetly look into making that tap. Looks like a real time-saver.
I've really been suprised by how many guys in the forum like-I wonder if that comes with the territoriy. 1/2A isn't as popular or developed as the bigger stuff so we gotta tinker. Thanks guys!
Derek

ajcoholic

My Feedback: (10)

YEs, I think in many ways the 1/2A guys (at least the ones here) are way more adept to engine and airplane tinkering and re engineering. Most "sport" flyers I know and communicate with (who fly the standard 40, 60 size) dont even like to dissassemble and clean their engines, never mind do anything more with them.

I persoannly think its too much fun NOT to experiment. Heck, its all good fun!

I wouldnt give up my lathe for anything...

Japanman, get it on credit! Get over that lathe withdrawl before you get too sick

Andrew

Nitro-Nut

just ran this up on 30%n/c... (pic)

mods-
1. Cox high compression head, two gaskets
2. Tee Dee cylinder
3. ground 1.5mm from bottom of piston
4. Killer Bee/ Venom crankcase assembly
5. Standard 049 plastic back, chucked the screen, venturi drilled to .25"
5. modified needle valve to look like a "needle"
6. chucked the nv spring and put a small piece of fuel tube to secure nv
5. 5x3 grish

MR Flyer57

Hey Nitro-Nut,
Did you do anything to the reed?
MR Flyer57