IS this legal in the USA?  
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IS this legal in the USA? - 4/17/2007 2:35:47 PM   
j.duncker



Posts: 1228
Joined: 6/22/2004
From: Where I park the RV, AK, USA
Status: offline 		In SCC combat is the MVVS 21 set up as rear exhaust with the black silencer legal in scale combat. I fly in the UK and Europe and this is OK in most countries on this side of the pond.

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< Message edited by j.duncker -- 4/17/2007 2:36:59 PM >

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RE: IS this legal in the USA? - 4/17/2007 2:51:54 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		SSC is a limited class of combat that requires a .15 size engine with normal muffler, so no, it's not legal on that class.

There are 2 scale classes in the US, 2610 and 2548.

In 2610, the engine can be up to a .26 and the exhaust can not be longer than 8 inches. So it should be legal in that class.

2548 is a limited class, with only expansion mufflers allowed, so a tuned exhaust like that would not be allowed there either.


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Kirk Montague Adams
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RE: IS this legal in the USA? - 4/19/2007 12:15:14 AM   
pe reivers



Posts: 3018
Joined: 1/23/2002
From: Arcen, , NETHERLANDS
Status: offline
quote:

ORIGINAL: Montague

SSC is a limited class of combat that requires a .15 size engine with normal muffler, so no, it's not legal on that class.

There are 2 scale classes in the US, 2610 and 2548.

In 2610, the engine can be up to a .26 and the exhaust can not be longer than 8 inches. So it should be legal in that class.

2548 is a limited class, with only expansion mufflers allowed, so a tuned exhaust like that would not be allowed there either.


Please explain the "normal muffler" and "expansion muffler" bit
In my opinion, the mufflers as supplied with most engines are made up of:
1) a straight section of pipe that connects the engine cylinder to a chamber
2) the beforementioned chamber
3) an end restriction where the gasses can exit

1) + 2) +3) is exactly a Helmholtz resonator that will sing to a certain tune

The black MVVS muffler consists of:
1) a straight section of pipe that connects the engine cylinder to a chamber
2) the beforementioned chamber
3) an end restriction where the gasses can exit

In all honesty, I cannot see the difference between the two. Both these systems sing to a predefined tune, which is volume and pipe length dependant. The Helmholtz Q-factor defines the power bandwidth of the system.

OTOH,
A tuned reso pipe consists of:
1) a section of pipe that connects the engine cylinder to a exhaust system
2) a diverging section that amplifies the pressure wave
3) a straight section that stabilizes the pressure wave (not always present)
4) a converging section or baffle plate that reflects the pressure wave back
5) a stinger pipe that exhausts the system and controls the system's back pressure, about as long as the converging part.

The power band location (rpm-wise) is dependent on the total system length. The power bandwidth depends on both diverging and converging section's construction and section lenths and stinger pipe dimensions.



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RE: IS this legal in the USA? - 4/19/2007 4:41:50 AM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		Like I said, SSC class is limited to .15 displacement.

For 2610 scale, is it shorter than 8 inches long? then it's legal.

For 2548, there is the rule out of the RCCA rules:
quote:


3.2.5 Exhaust Systems.
Exhaust systems designed to increase performance through a "tuning" effect or use of an internal
pipe or similar arrangement, are not allowed. Examples include, but are not limited to, tuned pipes
and mousse cans. The front of the muffler must be closed and “flow through” mufflers are not
allowed.


So, if the muffler provides a boost in RPM through a tuning effect, it's not legal.

Also note that in 2548, the engine must turn an APC 10x3 or MAS 10x4 prop and is limited to 14,500RPM measured on the ground.


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Kirk Montague Adams
RCCA 560

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RE: IS this legal in the USA? - 4/19/2007 4:51:56 AM   
Fred420



Posts: 128
Joined: 6/23/2003
From: Sunnyside of Louisville, IN, USA
Status: offline 		Kirk ....... I am going to use an .25 MVVS in Limited B and have the same type stock pipe on it as J. does. Is it leagel in Lim B?

Thanks,
Dave

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Dave "that red-headed stepchild" Davis

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RE: IS this legal in the USA? - 4/19/2007 1:49:29 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		If you're using the specified prop and under the RPM limts, then probably, as long as that muffler isn't tuned to boost RPM. I'm not sure if it is or not, but it looks like it might be.

Even with the rpm limit, a tuned exhaust can be a problem if the engine is set up to come on pipe in the air, but not on the ground. The result is an engine that unloads more than the others and gives a power advantage. The point of 2548 and limited B is to keep everyone at about the same available power in the air. So, anything that gives you noticeable power above and beyond is going against the spirit of the rules if not the letter, and if it's not illegal now, it might be in the future.


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Kirk Montague Adams
RCCA 560

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RE: IS this legal in the USA? - 4/19/2007 8:49:36 PM   
j.duncker



Posts: 1228
Joined: 6/22/2004
From: Where I park the RV, AK, USA
Status: offline 		Thanks for all the info but I am still a little confused.

Is scale combat limited to 15 size engines in the US. The RCCA site sems to say that the 21 is OK.

quote:

2105: 3.4. Maximum total nominal displacement for single engine designed aircraft shall be .21 cu. in. Tuned pipes are not allowed.

2610: 3.4. Maximum total nominal displacement for single engine designed aircraft shall be .26 cu. in.

3.4.1 Maximum total combined nominal displacement for multi engine designed aircraft shall be .30 cu. in. Multi engine model aircraft must have more than one functioning engine as per its full scale counterpart. Designs which utilized 2 engines contained in the fuselage may employ a single functional engine, but must comply with all single engine aircraft restrictions in this section.

3.4.2 A muffler or tuned silencer is required and may not exceed 8" in length.


I have my MVVS 21 engines sorted out and would bring them over with me.

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< Message edited by j.duncker -- 4/19/2007 8:56:20 PM >

_____________________________

The dreamers of the day are dangerous men, for they may act their dreams with open eyes, to make it possible.

(in reply to Montague)
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RE: IS this legal in the USA? - 4/19/2007 9:56:27 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		There are 2 classes of scale combat in the US, both allow up to a .25 engine. (actually, one allows a .26, but close enough).


_____________________________

Kirk Montague Adams
RCCA 560

(in reply to j.duncker)
       Post #: 8

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