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F2D Noise Reduction
Noise rules for F2D Combat
First published: 29/9 2010 - Last update: 1/2 2011

Some rules on noise reduction are already in the new rule book:
  • The warm up period will be reduced from 1 minute to 30 seconds
  • 6 mm outlet from the silencer
  • The heat will be terminated when all streamers are gone and the pilots must stop their engines and land
  • Probably even more restrictions to reduce the exhaust noise
  • Probably some kind of rules to reduce the propeller noise
  The 2011 Rule book:

30 second warm up:
4.4.9 e

6 mm silencer outlet:
4.4.5 c

Silencer verification:
4.4.6 c
How will the new rules affect Combat:
The 30 seconds starting period from 2011 will not be a problem

The 6 mm silencer outlet from next year will probably be a problem for some pilots.
Most engines will slow down a little but some will have big problems with the higher back pressure from the 6 mm silencer.
The higher temperature may also affect the life time for some engines.

In the proposal for the 2011 rules the heat should be terminated and the pilot lands right after all streamers were gone. At the CIAM meeting in the spring this rule was taken out of the 2011 rules and postponed to 2013.
There has been a lot of confusion on how this rule should be understood. I have posted my view on this rule at the Yahoo forum. It will not be mandatory to use the shut-off system or another device to stop the engine. If a pilot is asked to stop the engine he can just fly the model to the ground.

2013 Rules:

From 2013 there will probably be some new restrictions on the exhaust noise.
This could be mandatory use of a double chamber silencer or homologated silencers.

Another approach could be to set a minimum effectiveness for silencers and check them with an acoustic noise generator. More information on how the silencer effectiveness can be measured on the flying field in a few minutes.
  More info and How To

How to change
the silencer outlet
from 8 to 6 mm

How to use the shut-off to
stop the engine at will

Noise reduction
by shut-off

A special device for

My interpretation of the
stop the engine rule

The paper on noise
reduction by a
homologation process
from Hungary
2013 Rules based on effectiveness:
If the noise reduction for 2013 will be based on verification of the silencers effectiveness the rules can be made very simple and clear:
  • The silencer must be able to reduce the noise with at least 12 dB when it is tested on the acoustic noise generator. The actual value might be set to another value when some tests and experiments have been done.
  • To prevent pilots from building tune pipes the maximum length of the exhaust system could be set to 150 mm. This is the same restriction as we have today.
  • The design, function, choice of material, etc. will be completely free.
    Only the silencer must be able to demonstrate that it can reduce the noise.

Propeller noise:

When the exhaust noise is reduced the propeller noise will be dominant. This noise can be reduced by reducing the propeller tip speed.
A way to go could be to set a minimum propeller diameter that is so high that the engine will not be able to turn the propeller more than e.g. 20,000 RPM.

Another solution could be to certify propellers in some kind of homologation process. A description of this process can be found in this paper from WC in Hungary.

See how the
silencer test
can be done

The equipment for
testing effectiveness:

Acoustic noise generator

Sound level meter

F3D Pylon Race:
The acoustic noise generator has been used in F3D Pylon Race to verify silencer in a homologation process. The equipment and the testing procedures have been developed by Rob Metkemejer.
F3D Pylon Race has used this technique for a year now. The noise problem in F2D Combat is similar to the problem F3D Pylon Race had earlier. It would be easy for F2D to learn from Pylon Race and copy equipment specifications and the testing procedures from them.

Some of the best silencers for Pylon Race reduce the noise by 30 dB without affecting the engines! These silencers have been developed with the acoustic noise generator. The only change the noise rules have causet to Pylon Race is that the exhaust noise is gone!

  The rules for Pylon Race
have a special section on noise
See the Annex 5P on page 17-19:
F3D rules

A good description of the method used
for mufflers in Pylon Race can be found here         < 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 >