Hopping Up a Stock Medallion .049

You could also shorten your lines a few feet.

Thanks for the good words, gents. Looks like two votes for the #1 cylinder. I'd like to stay with the longer lines, Ken but will keep that in mind.

Regards,
Dave...

Also be prepared for more fuel consumption-- maybe 30% more.

I think Ken was suggesting that hopping up an engine to stay out on 42ft lines would be the same as shortening the lines and keeping the engine as is. In theory it would be the same speed and lap times would be equal. Generally 35’ is the standard for 1/2A as you probably know. 42’ is used when you have a plenty of power to spare.

Ron

Hi Dave. What propeller(s) are you running on the Medallion? Have you experimented with other propellers? I'm guessing "yes".. but there hadn't been any mention of prop-type or fuel-blend.

Ah, lots of good help being offered here! The additional dope: the prop is a 5x3; it's black and I'm not sure of the brand but I think it came from Cox International. Fuel is 18% nitro and 20% oil blend, mostly castor.

Agreed, 42 feet is a stretch for the Medallion. Yet we do get a reliable number of windless or low-wind time slots in the weather around here. My intent is to try flying on the long lines in anticipation of moving up to a Big Mig .061 ship that I've got in mind. If the Medallion with the #1 cylinder still doesn't cut it, then 30-lb. Spyder line is always around for shorter lines.

Thanks again, gents!

Mo...

Upping your nitro will help as well. Between the dual bypass cylinder and higher nitro, this will cut the run time down with the current tank

Very good, Ken. I've got room for a larger tank if need be. Much obliged!

Dave Mo...

Thought I'd give this thread a bump and a question. The #1 cylinder is installed on the Medallion body, 5x3 prop, and fuel with 25% nitro / 20% oil. The question concerns break-in time. So far, I've run maybe six ounces of fuel through the critter, and haven't gotten a nice even run yet. Still sputters a bit and varies in speed, though I tached it at 17,500 max. Is the sputtering and variability normal with a new old stock piston and cylinder with this amount of fuel through it?


Dave...

Dave, the break in shouldn't take more than a couple of tanks through the engine. However, your other symptoms are a bit of concern. Of course running it a little bit more is not going to hurt it prior to letting it loose on the plane. The concerning thing to me is the sputtering and rpm fluctuation. Are you currently running this on the plane? Silly question but if so, is the engine tight enough?

I would look closely at the piston relationship to the plug landing and insure it's not coming above.

Adding a additional 1-2 head gaskets due to the nitro increase and the fact it's a new cylinder. This could smooth things out and can be removed as needed.

If not currently new, a new plug can cause the erratic running. Just because it glows doesn't mean it's up to the job.

I'm not certain if you ever dismantled the engine to the point of removing the crankshaft. Old castor can become really built up on the shaft and in the bore of the case. This doesn't remove itself from running. A good cleaning is in order in this area as the old castor heats up and acts like a brake on the shaft when running. This can offer the symptoms you've mentioned.

Making 100% sure that your carb body has no cracks on it as well. This can really be responsible for erratic running and poor needling.

In general, make certain everything is properly tightened: backplate, carb body retention collar.

Ken:

Thanks for the input. It's mounted on a Baby Flite Streak. I just checked and found all is shipshape as far a being tightly mounted, etc. Will check out the rest of your recommendations and try the head gasket trick and get back to you. Yes, this is a bit weird.

Dave...

Ken Again:

Yup, another head gasket helped immensely. Much better with just a minor amount of sputtering. If I had another one, it'd go on. Instead, I'll try dropping the nitro to 20% this afternoon and see what happens.

Very good insight on your part. Many thanks.

Dave Mo...

I think your right on track with the nitro. More nitro usually isn't a problem. That being said, your dealing with a new piston and cylinder which can increase the compression. Shortly after break in though the compression might maintain but it could drop a touch as well. It's just that a over compressed engine can show symptoms of not being exactly happy especially when you start to lean it out. If one head gasket was a improvement, another certainly won't hurt. As mentioned, after a few flights you can remove one and see where your at. It certainly increases the glow plugs longevity by raising it. It could drop the power a little but you can dial it in a little more as far as leaning it to get that power back. This will offer a little bit better of mileage as well.

I suggest trying this
https://www.coxengineforum.com/t13187-049-black-widow-tuning#169574

Ken and Oz:

Well, I've finally got it running better thanks to the collective wisdom here! Three head gaskets and 15% nitro suit it so far. Outdoors for the bench run, weather was warmish and very humid. Still just a tiny bit of sputter, but maybe that will take care of itself when it unloads in the air. What do you gents think?

Many thanks!

Dave Mo...

I'm thinking it's go time. Report on how it works.

Oh yeah, Ken it does go! I had it out this evening on the 42-feet lines and she stays right out there. Still kind of sputtery as I didn't take time to lean it out properly. But then I ended up with quite an audience of youngsters and wasn't concentrating on the perfect run. Man-o-man, did they have lots of questions, and offers of "help"! Very fun interacting with the lads and lasses.

i take it that I am aiming for a completely sputter-free run when it's all leaned out? Not sure if I want to drop the nitro to 10%, but could easily do that. Will try again this week and will report back.

Dave...

As a homebrewer as well as modeller, I certainly know the importance of hopping up!

Hello All:

I'm back to the well again, seeking further advice on this Medallion. The fuel blend, prop, head gaskets, crankcase seals are all top notch and I get a great run on the bench. The problem is in the air where it really needs to perform a lot better! So, methinks 'tis a fuel tank problem.

The existing tank is a beat up homemade one, so I won't try to describe it. The Medallion is mounted on a profile Baby Flite Streak with about 2-1/4" of tank space between the leading edge and the back of the engine. Does anything strike you gents as to what might work in there? What tanks do you use on your profile TD and Medallion ships?

I'm open to a Texas Timers bladder tank, but am not sure how that could be mounted on an already built model. Sounds like it might just be what the doctor ordered for better fuel delivery though. I've never tried one.

Again, I await the collective wisdom ensconced in this fine board.

Dave Mo...

Dave, I can't recall my actual tank size but I use these on my Streaks. This is a Brodak version. Brodak purchased the tank line from Perfect. Perfect tanks are far from Perfect and Brodak's versions are in need of work equally. Perfect uses brass tubing which is not good due to it splitting internally. I use copper only. You will note that most wedge tanks has the pickup exiting the center right of the tank. This is not a good place as it has your fuel line going down under the cylinder and back up again. Many will say this is a non issue as the fuel seeks it's own level which is true but it can cause issues with maneuvering. This makes the fuel tubing longer than it needs to be and in maneuvers it cause the fuel line to flop which changes your engine run. I reroute the pickup and make it exit on the bottom of the tank which shortens the fuel tubing and offers a straighter shot to the spraybar.

The key to a good tank is cleanliness, no commercially available tanks are properly cleaned. They're soldered and packaged which leaves flux inside the tank which corrodes the plating. Older tanks especially are usually so bad they're not worth even using. I have even seen this with new tanks. The next thing is of the utmost importance and that's to solder the pickup in it's correct location in the tank. Some tanks have the pipe jammed into the end cap which is also incorrect as it can get solder balls in it. I generally place mine 1/8" to a 1/4" off the end cap.



I can get more info on this size but this one is 1 3/8" long 1" high. It might be 2/3 oz. I could be incorrect on that.



When I removed the front cap, I cut off the pickup tube and left the stub out of the front. I pinched it off and soldered it. Pulling it out and soldering the hole is not good enough. Many times when these tanks are used conventionally, the tubing going down under the cylinder causes the tubing to develop a split right where it connects to the pickup tube due to being stressed downwards. This type of split doesn't always show it's ugliness and can cause bad engine runs that can be misdiagnosed.

Ken:

Thanks for the great response (and for taking the time to shoot a couple of pics). That tank is beautiful in a sort of ugly way, but I bet it supplies the motor nicely. Looks like I'll have to get an order in to Brodak, and then plan on doing some work with the soldering iron per your suggestions.

Have you ever tried uniflow on the Cox Bee or rotary valve motors?

Thanks again!

Dave Mo...

Dave I make most of my tanks uniflow. Not the one I pictured in my last post. Traditionally, I run standard vent in most of my 1/2A's . Some of the speed stuff can really benefit from uniflow. One thing I found out is that I have never successfully worked out the bugs whenever I uniflow a wedge tank. I think it cause turbulence inside the tank and as the tanks head pressure drops, the funny business starts. I have noticed this more with the wedge styles. Uniflow is one of those things that doesn't always work on every plane. As much as I would like it to, vibrations can really disturb it's function.

The Streak is one of my favorites and they fly very well. I had a RSM Miss Ashley kit which I kit bashed into a Magician. That plane works extremely well due to modifying the fuse to get the tank inline with the TD spraybar. The TD does very well with my setup.

Here's a shot of the install






I had to get back into this tank after it was assembled. This was due to a side to side adjustment. I had to move the tank further outboard. This required the removal of the filler pipe and relocation of it to get t to shift further outboard. This is why the paint is missing on the front. I used a water based polyurethane to paint the tank. You can't get this stuff off without using a wire wheel. I have no more blue as I mixed it to get it as close as I could color wise to the Monokote.

Of the profiles I have mounted the tanks in this fashion, I have been very pleased with the results. It didn't come without trial and error though. You seem to have that same desire. I just say keep plugging away at it no matter how frustrating it can be.