Ogriv

I am tired of cleaning so much fuel off of my plane. I have seen the Du-Bro extensions that are available, but they don't appear to be long enough to have any great effect. Is there something readily available at the local hardware store that I could use? What does everybody else use? Would extending the exhaust port affect the back pressure on the engine? BTW I have an OS 61FX engine.




Thanks

Stick Jammer

You would be surprised what a silicone extension can do, pointed in the right direction of course.
They work great on 2-strokes, not so great on 4-strokes.

Montague

Long tubes on the exhaust can cause an excess of backpressure which can lead to a noticeable drop in performance, and in the extreme, overheating problems.

Rick Lindsey

I seem to remember hearing that diesels don't suffer from the same problems with back-pressure... is this true?

Ogriv

Montague,

How long is "too long" ? What clues should I look for if I'm getting too long?


You all don't have to beat around the bush, just tell me what works and what doesn't.





Thanks,

Mike

Stick Jammer

For the couple of bucks that a silicone extension costs, give it a try.

snowwave83

Dubro makes a great extention and their cheap. I think 6 bucks with 2 plastic wraps and thats all you need. I used it on my .46 OS and it was significantly less fuel on the side of the plane. Of course nothign can prevent ALL fuel from getting on your plane but for a few bucks those silicone extentions are very useful. Just makes sure to point it down and away when you put it on, clean off the metal with alcohol so that no fuel or oil will allow it to slip off.

Steve

moparcolt

My Feedback: (2)

A small metal hose clamp from the auto part store works great for holding those silicone extensions on. The plastic ties they come with just don't cut it.[8D]

photoniq

I agree that you need something more than the plastic ties that come with the extension. I lost mine on my first flight. Thinking of buying another one but will either cut a groove in to my exhaust pipe for that plastic tie clip to cut in to or will buy metal clamp thingy as suggested above.
Photoniq

Ogriv

Thanks, I'll give it a try.




Mike

snowwave83

moparcplt, photoniq - You probaly lost your extention because you didnt clean the metal with alcohol or something to get all the fuel and oil off. I could be wrong, but I cleaned mine semi-good and I havent even seen it slip at all. Regardless those dubro's extentions safe me TONS of time wiping fuel off my plane.

steve

LouW

The outlet of most mufflers can be rotated to direct the exhaust away from the airplane, which is usually enough to keep it relatively clean. However where that is not enough, an extension may be used. The two photos show examples of extensions from my fleet. The first is on a PAW 19 diesel. Diesels are particularly dirty with oil that is dark brown. Before fitting the extension I found myself leaving this airplane at home more often than not because cleaning it was such a pain. With the extension, the bottom of the elevator is the only place to collect much oil.

The second picture shows an extension fitted to an MDS 46 engine. I have flown it for several years without the extension, and now have another year with it installed. I’m sure if I carefully measured the rpm with a tach, or if the aircraft was underpowered in some particular maneuver, I might notice some slight reduction in performance, but as a practical matter, it has made no noticeable difference in performance. Again, the only place to collect oil is the underside of the stabilizer.

In both cases, the extension is made from aluminum tubing available at Home Depot, Lowes, etc. The internal diameter is a little larger than the exhaust opening in the muffler, and I don’t believe the back pressure is increased any substantial amount. I have seen no increase in operating temperature in either case.

Ogriv

Thanks for the pictures!



Mike

Montague

Yes, that's true (as far as I know). I've seen diesels with tubing going all the way to the tail. Now that's clean.

I'd have said that one in the picture above would be too long . However, the truth is that if the engine runs fine and shows no loss of power or tendancy to do funky things, then it's not too long. That's really the point, right?

Lou pointed out that the tubing is of a larger diameter than the exhaust outlet, and that's key. I'm not sure, but I'm guessing Lou also isn't trying to get max power out of his engines either. If you run it a bit rich, and go easy on the WOT, then you'll have better luck than if you always roar around with your tail on fire. Also, I suspect (but haven't exactly gone around and tested) that some engines are more sensitive to this than others. I did "fix" a guys engine at my field one day by just taking off his home-made diverter. It was smaller than the ones Lou showed, but it made a HUGE difference in the air. Also, to further confuse things, take a look at tuned pipes. The're awfully long, but actually add power. (not the same thing though, I know. Still I've seen home-made pipes as well).

Anyway, the best way to tell is to run the engine and set the needle to a good setting. Then install your diverter. If you can't tell the differnece in the engine performance, then you're fine. If you notice a change, then you might want to adjust the diverter. If you've been flying with a diverter and you're suddenly unsure, fly a flight with it, then take if off for a flight and see if you notice a difference.

Ogriv

Good advice! I called a friend and he is loaning me a Du-Bro extension. I'll give it a try. I update the thread with my results.




Mike

Stick Jammer

The plastic tie wraps have worked fine for me on 2-strokes. As mentioned already, make sure the muffler end is clean first. My experience has been that they will not work on 4-strokes. Too much heat, even for the silicone.

LouW

I tune just slightly rich so that the engine peaks in the air. I use WOT a lot. The extension should be a little larger in diameter than the exhaust outlet, and the longer, the more open it should be. I don't notice any reduction in power, but the fact is that most R/C airplanes are so overpowered, that a little loss is not a big problem if there other benefits to be had.

You may have to adjust your needle valve when installing the extension. If the extension adds any back pressure, it will increase tank pressure making the mixture a little rich. Leaning it will restore most of the power loss if any. If the needle setting dosen't change, that in itself is a good indication that it hasen't added much back pressure.

Woodpile

I use Ty-Gon tubing available at your local hardware/home center for about $.35 per foot. Ten dollars gives you a BIG supply. Plastic wire ties hold it on perfectly with no slippage, if you tighten them with diagonal cutters before trim the tag ends to size. The other thing you have to do is slot the end that goes over the muffler outlet. Since the Ty-Gon is clear, you can easily see the oil and fuel residue streaming through the tubing so you you can better gauge how much oil is coursing through the engine. I have successfully used a long enough extension that I tie-wrapped it to the main gear down by the wheel to keep it out of the way of a camera pod I built for one of my planes with no ill effects. Usually, I just cut it long enough to extend about 1/2" (5cm) past the bottom of the fuse. That keeps almost all the oil off the fuse, but it does collect on the bottom of the stab. If you want to be really technical, buy two sizes, one just large enough to slip over the muffler outlet and one just large enough to slip over the first size. This way, you make your extension from two different sizes of equal length and reduce the backpressure. Personally, I haven't seen the need to do this, but if it makes you feel better about engine performance, go for it! With three sizes, you could probably run it all the way to the tail without increasing engine backpressure significantly.

2thfxr

Lazy bee with a norvel 15 aluminum pipe slightly larger than outside diameter of muffler tie waped to fuse and conneced to muffler with vinyl gas line hose. Pipe extendes length of plane and exit down below stabilizer. Craft stays very clean idle speed increased, no noticable loss of power or over heating. Also have made extentions for 4 stoke saito 45 (still a dog) and magnum 91 out of brass tubing split with a dremel and fastened with small gear clamp. These are only 3-4 inches long.

MinnFlyer

My Feedback: (4)

I once had an extension that went all the way to the tail with no problem.

Another time, I added the little Du-Bro, and lost lots of RPM. However, cutting only 1/2" off it brought the RPM back up.

So try it, and if it looses power, try shortening it.