Hughes500E

My Feedback: (16)

What type of aircraft would benefit from a tuned pipe?
Are tuned pipes for speed only?

Steve

downunder

Tuned pipes have been used in RC pattern and are still used in CL stunt as a means of governing engine revs to maintain a more constant airspeed, especially in a dive, so they've got more uses than just sheer speed.

DarZeelon

Steve,


Some engines make a good benefit from a tuned exhaust system, that make the engine come on-the-pipe at lower than maximum RPM. Such are the control-line stunt engines that Brian writes about and in engines used for 3-D, you would want the engine just on-the-pipe during hover, with full launch power at full throttle.

A wide-band tuned silencer is usable for this, while a narrow band full length pipe cannot be used.

Most MVVS engines are bought with a tuned silencer and very few are used for sheer speed only.
Most, however, are used for 3-D and for sport flying.

Hughes500E

My Feedback: (16)

Thanks guys,
Dar, you know what I'm doing Mostly interested in hearing about 3D type aerobatic flying etc.
Any other comments?
Thanks

wildthing7037

I flew a 3D type model recently which had a rossi 45 on a full length pipe. To be honest it was a dog to fly.
It had a huge amount of power, it was just throttling which was no good. From idle up to half throttle, which was off the pipe, had hardly any power, then it jumped on the pipe and suddenly you had everything, which was too much, so you would throttle down a bit then it goes off the pipe....
I believe the pipe it has on it was more of a pattern/3D 'broad tuned range' type pipe, but still the jump on the pipe made flying around quite annoying. Probably what would of been better is a tuned muffler, or mini pipe set-up.

Stefan

Hughes500E

My Feedback: (16)

You nailed it Stefan, I believe you experienced my fear however, I think I am getting confused between a tuned pipe and what you speak of, a tuned muffler or mini pipe.

jaka

Hi!
I don't think that a long tuned pipe is good for 3D flying (hoovering and such) the problem with a long tuned pipe is the time lag before the engine responds. Using a tuned pipe will always slow down throttle action slightly compared to using a silencer...that's my experience.
The shorter minipipes (like MVVS) respond quicker but the noise is higher than that from a silencer/muffler...so I think I would go with a silencer instead.

Regards!
Jan K
Sweden

Ernie Misner

If you go to the Mac's website and look at the recommended header length, they always seem to be aimed at top rpm or speed. In the real world, most of the 3D or funfly planes here in the .32 size use the full 6 inches of the stock header length without cutting it before attaching the mousse can. The combat guys, on the other hand, run the headers short for WOT operation and rpms up to 20,000.

Ernie

wildthing7037

For tuned mufflers, check out www.jettengineering.com for Jett-Stream mufflers, and also www.pspec.com for Ultrathrust mufflers.
Both these mufflers are what you want for a 3D type model, they are just like a normal muffler, just are tuned so you get some extra power. As far as I'm aware there is no signifigant 'jump' on and off the pipe with these things.

Also check out the tower muffler which is similiar to the ones above, just less coin.

Cheers

Stefan

Flyboy Dave

My Feedback: (21)

Here's a long pipe tuned for low RPM and torque....see how long the header is ?
The object is to keep the engine at or near 11,400 rpm's (which is low for a .61)
when pulling straight up....it will not bog down.

The exhaust on the red prop jet is completely different. See how short the head pipe is ?
It will turn 18,100 on the ground, and over 20,000 in the air "on the pipe".

The engines porting specs are what dictates the rpm at which the engine will run,
the pipe keeps it there. If I was to switch the pipes on these planes, neither
one would run worth a hoot. []

FBD.

William Robison

My Feedback: (3)

FBD:

Looking at the vertical fin (left picture) it looks like that OS is still puking its guts. Or is that an old picture?

Bill.

Flyboy Dave

My Feedback: (21)

Unfortunatly Bill, that's the new (replacement) OS engine with the nickel liner
on the fast track to an early demise. []

But remember...."that's not a problem" according to Hobby Services. [X(]

Any bets on how long it will take to chuck the liner ?

Dave.

downunder

Flyboy Dave, I'll take a guess your long pipe is about 17.5" to the first baffle? That's close to the length and revs normally used in CL stunt and is what my 40VF had when I bought the complete model/engine from a friend of mine. It's useless as a competitive model because it's far too heavy (about 69 ounces) so I got it just to have fun with. I've never liked flying stunt at those revs so just for a lark I lengthened the pipe to 21.5" so it'd be tuned for around 8000 or so. At those revs the engine runs in a 4 stroke but what surprised me was that as I slowly leaned it out the engine got on the pipe with a much stronger 4 stroking sound. The change was almost as noticeable as when going from a 4 stroke to 2 stroke.

My second surprise was when I flew it set at that breaking point. Coming over the top of a loop when the engine unloaded it didn't simply keep the revs constant, the engine went completely silent as though it'd stopped. Naturally I chickened out on doing another loop so I pulled out level. The engine sound came back again! It did this time after time so I screwed up my courage and went for a consecutive loop. Sure enough, as soon as the nose went up the engine seemed to restart. Now I like to do this just to scare everyone

DarZeelon

I would generally agree, but only on a one-way basis.

If an engine has modest timing numbers, designed to peak (open exhaust) at, say, 11,000 RPM, even the best high RPM pipe in the world would not make it peak at 14,000, or 16,000 RPM.

If, however, an engine is designed to peak at high RPM, like 14,000-16,000 RPM with open exhaust, a good, low RPM tuned exhaust system can utilize its long breathing durations to to make maximum HP at a much lower RPM.

This is illustrate very nicely in this [link=http://www.supertigre.com/engines/supg0235-man.html]MAN Super Tigre review[/link].

To make the same HP, at a lower RPM, an engine must pass roughly the same amount of mixture at this lower RPM.