RE: CMP 120 Zero ARF Build thread
 

ZERO-322 , I have again to tell you that your job on weathering is amazing.

One thing that concern's me is exhaust/muffler pipe. I was talking with friend who makes exhaust pipes for cars,
and he said to me that he can make any kind of pipe but does not recommended it for this type of engines.
Engine has to be reliable in every condition of flight, and it is, for us very important.

That make me to consider my idea to make working, replica exhaust, for Zero, and did little search on the web.
I have found this article by author Bud Connolly (hope he won't mind for quoting him)

[b]The engines we use for flying do not have a true expansion chamber but rather a semi-expansion chamber and muffler combination.
You can imagine what happens when the positive pulse arrives at the piston a bit too early or too late.
The benefits of a tuned exhaust in enhancing the retention of the fuel charge are not fully realized.
When it's just right, however, it will push some or most of the fresh fuel charge that has started to exit
the exhaust port right back into the cylinder just before the exhaust port closes.

The exhaust side is semi-tuned since we use a muffler and not a true expansion chamber.
The most highly tuned 2-strokes will have an individual exhaust pipe and expansion chamber for each cylinder,
and the resulting increase in horsepower output will be dramatic, but only in a narrow band.
This is not good for a wide power band like we need on aircraft engines. Also, the noise would be unacceptable for use in local flying.

The exhaust manifold on our 2-strokes almost always joins into a Y on the 2 cylinder models, and this creates a further problem.
The pulse will travel down the pipe, but when it returns it will try to go back up both pipes in the Y.
At certain RPM ranges it will be causing more harm than good relative to conservation of the fuel charge.

Rotax spent a lot of time and trouble in designing the exhaust system for their engines.
While it's not a pure tuned exhaust such as used in racing, it is nevertheless tuned,
and the shape and distance from the exhaust port to where the elbow enters the muffler chamber is very important.

The shape of the exhaust pipe is not simply that of a constant diameter pipe, such as on a 4-stroke engine.
The pipe on our tuned 2-strokes is gradually expanding in diameter from the engine to the point where it enters the muffler.
It is shaped like an elongated cone when viewed from the side. That shape is an important part of the exhaust tuning.

The length of the exhaust pipe, prior to the muffler, is another important factor due to the speed of the pressure waves mentioned earlier.
The length must be such that the exhaust pulse can travel to the end of the cone and be reflected back up the
pipe to arrive at the exhaust port just before it closes.

Higher RPM will require a shorter pipe and lower RPM a longer pipe to produce the maximum effect at the RPM we want to
use for maximum horsepower. It's not practical to vary the pipe length, so we compromise with some specific
length that will deliver the best push at near top RPM.

The Max continuous RPM for the Rotax 447 and 503 is 6,500. (The 582 is rated for only 6,000 Max continuous.)
I don't remember the exact distance from the exhaust port to the end of the cone on the 447 and 503, but I think it was
set by Rotax at about 29 inches. Technically, that is a centerline distance and not just the measurement of the exterior surface of the curves on the pipe.

The shape and distance is critical and can't be ignored or changed without changing the Rotax power band numbers published on their graphs.
So when people change these exhaust systems on their own, they are unknowingly changing the design power curves.
Unless they know exactly what they are doing and why, they will likely end up with less power at 6,500 RPM, or unpleasant
operating characteristics that are no longer suited to what they are trying to use it for.

As you know, common homeowner 2-stroke engines don't use any exhaust tuning. Chain saws, weed whackers, and the like, usually just have a
little muffler box bolted to the side of them, which is not exhaust tuning. This works just fine but misses out on the additional "push" we could
get from the engine by tuning the exhaust.

The physics of a 2-stroke engine is very complex compared to that of a 4-stroke when we are trying to optimize horsepower, reliability,
and reasonable width of the power band. The 500 cc 2-stroke racing motorcycles that used to be popular in the 500GP races would produce
peak power output of around 180 HP, but in a very narrow RPM range. In order to get that same amount of horsepower from a 4-stroke racing engine,
it has to be about 1,000 cc. However, the 4-stroke does have a much flatter torque and horsepower curve and is better than the 2-stroke at pulling hard from lower RPM's.

As someone said, it all gets pretty complex with a lot of compromises. There are times when a two-stroke engine acts rather strange,
and it's all related to both the intake and exhaust tuning with the major influence coming from the semi-tuned exhaust system.

Author: Bud Connolly
[/b]

RE: CMP 120 Zero ARF Build thread
 

Misha take a look at this and see what you think. http://keleo-creations.com/
They have building custom muffler similar to this for years.

RE: CMP 120 Zero ARF Build thread
 

@Whisting Death,
I am not saying that it can not be done. Lot of company's are making maybe better than original.

I am only saying that it should be done with lot of calculations. Nobody want to know that it won't work
at 100m high in the air. where conditions are not same, like on the ground.
Mirce has made fully functional replica of exhaust pipe for his Hellcat, and it worked well on the ground,
and looked more better when smoke was coming from places it should come. It was phenomenal.
Motor had maybe 200 revs less then with original, but it never was in the air because motor has been changed later.

http://www.nsmodelers.rs/hellcatapril222010.htm

I know that I will fly it wit original first and, when everything comes in place, than maybe will consider
to make replica.

RE: CMP 120 Zero ARF Build thread
 

Wow, the work on that Hellcat was superb!

RE: CMP 120 Zero ARF Build thread
 

Interesting re the tuned exhaust, but we are not dealing with race planes or engines here. Like the weed wackers etc. as long as it works good enough then that is ok. I have used original exhaust, the pitts muffler were it lost about 100 rpm, and the straight pipe where it gained about 50 - 100 over stock. All worked fine in the air and on the ground. Start with an engine that has a little excess power and a little loss in power by having scale like exhaust won't matter.

RE: CMP 120 Zero ARF Build thread
 

The engine i have been considering is a dle 30 which has more then enough power to fly this bird
also using a 26 cc crrc i did do some bench testing with quite a few configurations of the exhaust and discovered the full exhaust ring with 7 outlets was the poorest performance, backfired and would get really really hot also a drop in rpm was evident at idle

running the exhaust as I've set it up as a u shape and 6 outlets and running it from the muffler instead of a straight pipe solved all of the above issues also the exhaust is a half inch diameter bigger then what the muffler exit is

this configuration gave me a much smoother idle and transition to full was flawless also got a little over a 200 rpm increase, now thing May change when the engine is Swaped for the dle or at altitude time will tell

RE: CMP 120 Zero ARF Build thread
 

Zero - The standoffs are small strips of thin steel and no insulators are used between it and the firewall...and after three years of use, there is no damage to teh firewall. I think the surface area of the standoffs allow them to cool enough where they meet the wood. Also, the standoffs are all silver-soldered to the exhaust ring....except for the one closest to the exhaust inlet. I ended up brazing this standoff onto the ring because it did get hot enough to melt the solder on early flight tests.

http://i293.photobucket.com/albums/m...s/IMG_0130.jpg

RE: CMP 120 Zero ARF Build thread
 

Pilot perhaps you could share any some insight as to performance did it increase decrease or stay about the same? Besides cool factor is there a benefit to running the scale setup were attempting being that you have experience?

RE: CMP 120 Zero ARF Build thread
 

Zero - I never ran or tach'd the Saito 125 with the stock muffler, so I really do not have a base line for comparison.....but, with the Saito 125, performance is "spirited" with a 16x6 APC Sport prop, 15% Cool Power and...the airplane weighs 17 lbs less fuel. The only reason I did the scale exhaust was for the cool facotr...and because I had never tried it before, so it was a challenge.

RE: CMP 120 Zero ARF Build thread
 

@Zero, glad to hear that you have run test, and that is all well with that kind of setup.
Since L16Pilot's motor is Saito four stroke, custom exhaust should not make any difference in engine performance.

RE: CMP 120 Zero ARF Build thread
 

Zero - I just got the J-tec exhaust back from the welding shop....can't wait to mount it and check the fit. Will post pics....but might not be until Thursday night.... :D

RE: CMP 120 Zero ARF Build thread
 

LOL I think for once I'm a little ahead of you, got everything assembled and mounted starting routing the exhaust tips out the cowl only to discover I MADE IT BIG ! ERRR ! I made the width about a 1/2" too wide not a big deal but its easier to make a new one then to fix the one I started, also I think I'm going to use the 3/8" copper instead of the 1/2" it looks better coming out the cowl to the fuse and I think it might be better for the diameter tubing to stay the same from beginning to end

Pilot I know your doing the M3 but I'm still hoping you post some pic soon

RE: CMP 120 Zero ARF Build thread
 

Okay, couldn't wait til tomorrow to check the fit....really nice. Don't have time to trim the pipes or fit the cowl, but I'm liking it a whole bunch.

http://i293.photobucket.com/albums/m...o/IMG_0681.jpg
http://i293.photobucket.com/albums/m...o/IMG_0679.jpg

RE: CMP 120 Zero ARF Build thread
 

Not sure....but from the second photo it looks like you will have to rotate the carb 180 to get to the HS and LS needles.

RE: CMP 120 Zero ARF Build thread
 

Yup....that was one of the compromises I had to make to get the throttle and choke linkage on top, (actually bottom of the engine). However, in the many gas engines I've run from G23s to G-62s, once set, I rarely had to make adjustments. hopefully, the same will hold true with teh DLE-20.

RE: CMP 120 Zero ARF Build thread
 

Looking good buddy ! I took the plunge and ordered a DLE 20 should be here hopefully before the weekend, these are the pic I took before realizing the width of the exhaust was too wide by about a 1/2" but this is pretty much the direction I'm heading

My plan is to route the exhaust from the muffler to the main structure using the high temp silicone tubing this would give me a little more wiggle room to get everything fitting properly, I have the new structure built out of the 3/8" copper "this time I measured 3 times" and the JB weld is setting as I am typing this, should have the tips out of the cowl done tomnarow night

RE: CMP 120 Zero ARF Build thread
 

hey!! that looks good....

RE: CMP 120 Zero ARF Build thread
 

Nice looking, both of you. I am finishing wing today, and starting assembly on fuselage..
Will post some pictures later.

RE: CMP 120 Zero ARF Build thread
 

Pilot on the dle 20 is it possible to run the stock muffler pointing up instead of down can the muffler be reversed? Im waiting for mine to come in and looking at this it might work out better if i could route it from the top

RE: CMP 120 Zero ARF Build thread
 

Well, this part of wing reconstruction is finished. After little bit of sanding, I have glued two parts
on the end of wing for screw reinforce. Because I think that original ply is soft, new one is made
from 5 layer 3mm ply. As this ply is thicker than original have to send it's end little bit.

http://img251.imageshack.us/img251/9866/dscn1932qn.jpg

http://img25.imageshack.us/img25/2710/dscn1933z.jpg


After that, plastic mask is glued at top of that and gap between it and wing was filled with filler,
to make smooth surface. Tomorrow I will make air bottle, pressure servo and ventil holder.

http://img828.imageshack.us/img828/589/dscn1938me.jpg

http://img40.imageshack.us/img40/747/dscn1940t.jpg

Complete wing (wood parts) with flaps and servo covers weights 1300g or about 46oz.
Will se how much weight will add glasing, paneling and painting.

http://img219.imageshack.us/img219/9720/dscn1945.jpg

http://img42.imageshack.us/img42/9774/dscn1941b.jpg

RE: CMP 120 Zero ARF Build thread
 

Zero - Here's the stock muffler mounted as you indicated. With the stock cowl, the muffler rests on the inside of the cowl...not sure how your modified Yellow cowl will fit. Also, the exhaust pipe is really close the engine mount rail...might be able to relieve the mount without sacrificing the strength.

Hope this helps.

http://i293.photobucket.com/albums/m...o/IMG_0683.jpg
http://i293.photobucket.com/albums/m...o/IMG_0684.jpg

RE: CMP 120 Zero ARF Build thread
 

L16 scale exhaust would look better

RE: CMP 120 Zero ARF Build thread
 

perfect ! I'm going to search and see perhaps if there is a spacer available if not i could always space it a little with some heavy gasket

RE: CMP 120 Zero ARF Build thread
 

Okay, got the cowl clearanced for the exhaust....not completely scale, but definitely happy with the results.

http://i293.photobucket.com/albums/m...o/IMG_0685.jpg
http://i293.photobucket.com/albums/m...o/IMG_0686.jpg

...can't cut me a break, can ya?....looking forward to see how you do the exhaust on that Ziroli P-38...:)

RE: CMP 120 Zero ARF Build thread
 

Misha looking great ! see you've got quite a bit done on the wing. What glassing method will you be using ? I've gotten a little side tracked from glassing mine working on the exhaust but hopefully should be able to get back at it soon

I'm going to be trying out the polycrilic water based method I've some really nice results using this in the past plus its fast easy, odorless and who doesn't like water cleanup ?