Hopping Up a Stock Medallion .049

Dave, my tank mounting was actually due to using a TD. I'm quite certain you've heard that a TD doesn't draw fuel on suction as well as a Medallion does. This is really due to the placement of the tank vs the function of the engine. I had all intentions of using my plane to fly the pattern. My initial flight inverted caused issues and I had to raise the tank which in turn had me hogging out a little material. I started with only a slight protrusion through the fuse knowing that the more I moved it outboard, the higher the tank would rise. Yes, I had to put a little thought into it and most of the time the tank needs to be raised, not all the time.

The wheels are quite simple, 3 discs of 1/32" ply with a o-ring wheels. I Monokoted the discs. As for the bubbles, unless they're causing engine issues I wouldn't be concerned. I put 2 spritzes of Original Armor All in my fuel. Despite what the naysayers will tell you, it helps and it doesn't cause any issues in the 20 years I have been doing it. If that still doesn't help, I use a inline Dubro filter. I have also seen bubble wrap around the tank prior to securing it. I use rubber bands most of the time, the integral mounted tank is just spotted into the fuse with epoxy.

Greetings all:

Well, the modified Medallion and I spent some running time in the garage this eve, and we both sounded like sputtering fools! But before I launch into the unpleasant details, let me thank Ken for his post above, again offering some great design and setup ideas.

So here 'tis: maximum RPM is 16,700 but it's not a steady run. Unfortunately nothing much new here in comparison to prior runs. The 16,700 was on 5% nitro; upping the nitro in one jump to 25% gave me 11,200 RPM. Beautiful motor on a beautiful airplane. I'm confounded, but I do get one-flip starts!

So I did a quick calculation of the possible number of permutations given these variables: two different props, two different tanks, uniflow and non-uniflow setups, shims from zero up to three, and four nitro levels in the fuel (all 20% castor oil) from 5% to 25%, and came up with 196 combinations. I bet I've tried at least 60 of them and not a good run yet. Can't seem to establish much of a pattern in any of this, but then I didn't keep records.

I'm almost embarrassed to report this here as I suspect you all question either my sanity or my methods. But there you have it.

I don't have a high compression head as I didn't really want to go that route. Bringing back the standard one-port Medallion cylinder looks tempting.

Oh, it's still fun, but not as much when this sort of thing happens!

Dave Mo...

A stock Medallion ought to get at least 16K on 5% nitro on a 6-3 Cox black prop

DaveyMo wrote:Greetings all:


So here 'tis: maximum RPM is 16,700 but it's not a steady run. Unfortunately nothing much new here in comparison to prior runs. The 16,700 was on 5% nitro; upping the nitro in one jump to 25% gave me 11,200 RPM. Beautiful motor on a beautiful airplane. I'm confounded, but I do get one-flip starts!



I don't have a high compression head as I didn't really want to go that route. Bringing back the standard one-port Medallion cylinder looks tempting.

Oh, it's still fun, but not as much when this sort of thing happens!

Dave Mo...

I don't see how 5% fuel gives you 16,700 and then adding nitro loses at 11,200. The 16,700 is really pretty good for the low compression head. I don't even use them. If your crankcase is hot, it may be a bit too tight and need lapping. However if it has too much slop it could be leaking air, giving an erratic run as you mentioned. My Medallion seemed pretty slow compared to every other .049 I have. Even the Wen Mac was faster.

I can't believe that someone would make such a confession on Medallion vs. Wen Mac. We're going to have do an INQUISITION on that.

You should have added gaskets when going from 5 to 25%. Rule of thumb is one per 10% of nitro.

That’s more than likely why you lost RPM.  Too much compression is just as bad as low compression.

A Cox engine requires a bare minimum of 15% for a steady run and easy needling. You are wasting time with 5%. They may run, but never very well.

Keep on with the 25% and use 2-3 head shims, you should be much happier.

Ron

Thanks, gents, for the good feedback. Will follow Ron's advice on my next run. And knowing that I should expect RPM over an unmodified Medallion's 16,700 will be helpful. Onward.

Tico, go easy on Aspeed when it comes time for the auto da fe!

Dave ...

Not to worry, I'll be his abogado pro bono publico

Uncle, he cries! I got one good run with the latest advice last evening, but just can't get it to start today. Back to the original, single-port #2 cylinder setup; I'll just have to live with the possibility that I missed the one or two correct combinations in all of the 196. It's been fun, I've certainly enjoyed the dialogue here, and have picked up some great suggestions. Will certainly return with more Cox problems in projects in the pipeline.

Thanks to all!

Dave Mo...

DaveyMo,

This should have been an easy hop-up. Something must be wrong.

How old is your fuel? Still using 25%? Battery condition?

Even a good glowing glow plug can actually be bad.

Good fuel, good glow plug and good compression is all you need.

Have you had the carb/venturi assy off? Sometimes people will drill the case for pressure, it can wreak havoc when running conventionally.

Ron

Ron:

I've gotta think you're right. For now, the #2 cylinder will let me get it into the air on shorter lines to recharge my spirit. Swapping it back to the #1 when I'm ready to give it another go won't be hard. Thanks for the suggestions and encouragement.

Dave...

Ron et al:

So I left the #1 cylinder on, and put some padding around the fuel tank. With the 25% fuel and lines of 42 feet, I got four-second laps. That's cooking along well enough by my standards. A bit of a bugger to start and thirsty to boot, but am quite happy with the results. Methinks the padding was needed all along, though I did learn a few things in the process.

Thanks to all for hanging in there with me!

Dave Mo...

DaveyMo wrote:Ron et al:

So I left the #1 cylinder on, and put some padding around the fuel tank. With the 25% fuel and lines of 42 feet, I got four-second laps. That's cooking along well enough by my standards. A bit of a bugger to start and thirsty to boot, but am quite happy with the results. Methinks the padding was needed all along, though I did learn a few things in the process.

Thanks to all for hanging in there with me!

Dave Mo...

That’s good news Dave! Sounds like you had fun!

DaveyMo wrote:Greetings:

Calling Rockin' Rusty or anyone else in the know. I'd like just a bit more snort out of this beautiful engine for my Baby Flite Streak...

Dang, Dave, I just now saw this thread pop up. Can't believe you gave me a callout and I missed it. But about the time it was posted, all heck broke loose on my side and I've been completely out of action. I wish I could have jumped in, but you were in great hands anyway.

I need to go back and re-read your thread in detail and see if I can add anything. I'd love to get you started with a pressure bladder, and probably have a few bits of hardware for you that could be helpful, so stand by. Keep in mind, I am still running on a very slow clock these days, but I ain't going away any time soon.

Also, if you haven't watched these videos yet, here's a bladder primer... no, it's not a beer.
https://www.youtube.com/playlist?list=PLg0IjwkivQPD-4_0aESC17zpy9FuhHWLa

I was a noob when I made those two videos, so it's much less complicated than I made it seem

Rockin' Rusty

Rusty:

Hey, quite OK my good man. Thanks for picking up the thread now and for the links. And I too know that Father Time can be less than kind to us, so hang in there.

From time to time, I get sorely tempted by the bladder tanks. For the existing bird (already built), I just don't know how a bladder could be worked in.

All the best to ya!

Dave Mo...

Rusty:

As I wipe the egg off my face, I see that you've got the same Baby Flite Streak that I have, and that you've shown how to mount the bladder. Well, my order to Texas Timers will go out today.

Great videos. Many thanks!

Dave Mo...

DaveyMo wrote:Rusty:

....For the existing bird (already built), I just don't know how a bladder could be worked in...

Dave, once I got over the fugly aesthetic issue, I just lay it on the wing right over the CG behind the engine and secure both ends of the container... if I'm lazy, I don't even use a container. Once you go Bladder, you'll never go back!

I put a check valve in its rear end, lol, for quick filling. I found that a little air bubble will not get sucked in until it's running out of gas. Also the bladders last much longer than I realized at the time. I've used the same one for several flights over a week or more. I was a noob retread back then.

That was the Brodak kit, and it's the first plane I ever flew that seemed like a real airplane... meaning aerodynamics, glide, etc. Texas Timers seems to be dropping some of his CL stuff. The NVs and backplates are gone now. Not sure about the Fourmost 1-way(check) valves.
Rusty

P.S. Here are a couple of videos of my Baby Streak and Refried Bean in action.
https://www.youtube.com/playlist?list=PLg0IjwkivQPCoNcNxt2XEdvrgunWyDVWl

I have some bladders that are a few years old that are still usable. Maybe the oil preserves them. Some unused tubing has dried up from age. I have heard of some Chevy check valve being used for bladders/pressure systems. Maybe from vacuum lines or something. Don't know any part #. I have also heard rumors of a pressure regulator working for a bladder. Makes starting simpler. Maybe the vibrating opens the valve instead of using hemostats? IDK, I would like to try something like that. I really hate bladders but they give a nice run. I seem to have got a lot of F2D planes lately that would be good victims for experimenting.

Rusty: Ah, good to hear that you've endorsed the check valve in that location. Texas Timers still has them and i was on the bubble with ordering one; I'll put one on the docket for sure.

Next question was about the mesh container for the setup. Not sure where you got your material, but I see the stuff on beach bags. Any other source? Knowing that it is optional makes bladder life a bit easier.

I took a peek at your flying videos. Looks to me like you've got a hornet on a string (three-second laps and all). Lots of fun, eh?


Sir Aspeed: It seems that you've got mixed feelings on bladders. I can understand the lack of aesthetics as a down side to their use. Any other disadvantages?

Thanks much!

Dave Mo...

Bladders give a great even run.  When they get to the end of the tank, they go rich, rather than going lean with an already hot engine. Some argue that they are lighter.  You can run a huge venturi for more power.The other side of the coin is that occasionally they burst, which makes a mess,  a fine thread needle valve is needed, which are hard to find,  and are fiddly to fill.  In my case, I really am not fast enough to run off the prime, and get to the hemostats or clip to release the fuel.  It takes a few tries.  Some guys can squeeze the fuel line with the thumb, while flipping but I am not one of them.  I have problems with hard tanks sometimes too, but for the most part can solve them.  I will keep plugging away with methods to use bladders.  The F2D arm type shutoffs are kind of handy for starting.

Aspeed:

Many thanks for your comments concerning the bladder system. Two tips are most enlightening - the fine needle valve requirement and the quick action with the hemostat. Will have to work both of them into my routine.

Dave Mo...

Dave, the fine needle valve is a must. These can be sourced from product backplates and can be adapted to the carb body. However, you can forego the needle valve on the carb body eliminating the cross through spray bar and use the needle assembly remotely. I started out with hemostats  which is too cumbersome and dangerous. They weigh too much, they can get caught in the prop if you slip and they just don't offer easy ability to do several things. The real problem is they lock and you don't want that. It works great when holding back the pressure but after that one can struggle. I start most of my bladder equipped planes between my knees. Pretty much one flip starts and off into the air. I make lightweight pinchers from bass using a sewing bobbin in the middle. These are 4" long and light.

  I paint them with high vis colors in case I drop them.

I remember reading in an old magazine about using an electrical toggle switch to pinch the tubing and then just flicking it over when it runs off the prime. I could never visualise actually fabricating it. I have 9 F2D planes that I want to use more often. I only fly a couple when there is someone useful at the one distant field and they are really my favourite planes, even more so than rc stuff. The Fora is great, but even the slower .15s are good for an old fart like me.