Hey combat guys,
I am organizing some club combat for this year. Several of us in my club are going to get Avengers this year and fly some informal club combat. We would like to stick to the Open B class restriction of a .28 size engine. We fly at 5,000 ft altitude and we need all the power we can get. I'm wondering what's the best engine/muffler combo for us for optimum power.

Thanks, Jim

It's hard to beat the Webra .25 with a mousse can muffler right now.

However, for someone's first combat plane, the OS .25FX is almost as powerful and is a lot easier to run and keep running reliably. You can't fly combat if you're fiddling with your engine all the time.

Also if you decide later to try "limited B" or other speed-limit classes, the Webra is horrible for that, while the OS does quite well. The Webra is timed for high RPM operation, and doesn't run well with larger props at lower RPM.

Jim, it's great to hear you are getting some combat going! We do club combat the 1st Saturday of every month (weather permitting) at Mile-Hi RC Club in Aurora. Let us know when you are flying and maybe some of us could make the trip up. We'de love to have you guys come to ours plus we will have 2 NPS meets this summer. Airpark Elite will have some NPS events as well.

A lot of us run the OS25FX with a Combat Can on 25% fuel. We turn in the high 18s and low 19s rpm. A couple of guys are running the Webras on Combat Cans and probably hitting 20k.

The FX is a solid, tried and true performer. The Webras seem a bit more finnaky to me but I don't own one. There are some Norvels still flying from the days when they were available. There are a few Irvines too, they seem strong.

Thanks for the replies guys.
Randy, there's a good possibility we can get together one way or the other sometime this year. Let us get some practice first so you don't obliterate us.
What is a combat can?

Thanks, Jim

Combat Can is a tuned pipe that meets the 8" max length RCCA rule. It is a Mac's header with some kind of an alum can with an exhaust stinger JB Welded into it fitted onto silicon tubing on the Mac's header pipe - tuning adjustable by sliding the can up and down. There's a pic somewhere, I'll look for it.

r

How does the Combat Can compare in performance to an Ultrathrust muffler or a Jett Stream muffler?

Thanks, Jim

The can produces a little less power than those mufflers in most cases. However, I don't think those are tuneable, where the can is. Also, the can is lighter and a heck of a lot less expensive. And in combat useage, having something cheap and light is usually a win since mufflers often take damage and you'll want to have several of them.

here's a pic

Thanks guys

Jim

I have two mouse can mufflers i would like to get rid of they are for 25fx's, the club quit flying combat. just sitting around Darrell

Hey Gump......How much you want for those cans???[sm=wink_smile.gif]

I would let them go for $55 shiped, these are perfect they have been flown but not much. and pay pal would be the best way to pay

RH, are the stingers required for rules compliance? I have 2 mousse cans that I got from Marv way back but they just have a hole in the side without a stinger added. If so maybe I will have to add them.

RP

I have an aluminium "bottle" muffler on my 46 fx. Do you need to play with the mixture much to get it to run right?, It will idle fine and power up okay but then fades and dies when it reaches peak revs. Seems that it is leaning out. Havent tried it again after first attempt, might have another go at it this weekend if I get a chance. Any thoughts?.

Thanks.

RP, not ignoring you, just missed this one a couple months ago [:@] No stinger required, just meet minimum length requirements [8D]

pjbass, not sure what your aluminum bottle muffler is for sure but with any hi-perf mods you always have trade offs. A tuned pipe motor runs like a banshee when you are "on the pipe" but idle reliability suffers or goes out the window completely . I always set the needle for max performance at wide open throttle and don't even try to get an idle (this is on competion combat rigs). I start at about half throttle, rarely throttle back less than that until ready to kill the motor and land. The motor loads up too bad at low rpms and will probably die when you are tuned to run on the pipe.

For these reasons, I run stock mufflers on my sport planes.

r

What do you mean by "tuning" the mouse cans. I have two on Norvel .25's but used em right out of the bag from Flying Z hobbies. Don't know what I'm tacking but the engines sure seem like screamers on 9x4MA and 15% nitro.

You can slide the can back and forth a bit, which changes the point where the engine comes on pipe. If the can is too far down the header the engine will come on pipe too soon, and you won't get much power. If it's too short, you won't get on the pipe at all.

The default length is pretty good for most engines though. So I usually don't mess with it unless an engine isn't doing what I expect it to.

Thanks Kirk--What RPM range should I expect with this set up? Any guesses?

RPM depends on a lot of factors such as the nitro %, air temp and humidity and so on, as well as engine tolerances and how you broke the engine in. And I don't run Norvels, so I can't be too sure.

However, I have seen them tached at 19k+ on several occaions. Some guys claim higher, and I don't have reason to doubt them. A good norvel can out-turn an OS, but Norvels have a reputation for being a bit tricky to keep running right.

Greg,
A good Norvel AME .25 on 15% nitro, after break in, should turn a MA 9X4 about 16,400 rpms on normal muffler with baffle removed. This is what Rick Fraley, Jim Bodnar, and others were getting in your neighborhood. With a Flying Z Hobbies Mousse can your rpms should immediately top 18K and depending on temp and humidity, as Kirk said, jump over 19K.

That is the good news. Now for the bad news part. With a mousse can your fuel consumption will go up and you will need 6 ounces to make a five minute heat with a little time for start up. The worst thing though is the vibration you will pick up with the mousse can. It will cause your fuel to foam so badly you will not be able to get a consistent run. Putting Armorall in the fuel, loosening the tank from its mount, adding a porous clunk or oversize filter to the tank or line will not get rid of the problem. You will have to go to some form or bubbleless tank. Bladders won't work because the Norvel needle valve will leak with the high pressure. The most effective tanks I found were the Jett Bubbleless tanks. A lot more information on Norvel's can be found here:

http://www.georgiacombat.com/RunningNorvels.htm

Good luck.