Posted by dannparks on Wednesday, January 31, 2007 @ 04:37 PM:
I know I am going to get flack for this since the little VWs are already fairly quiet compared to a Lycoming, but they are still straight-pipes. Has anyone looked at putting mufflers on them? I fly from an airpark with neighbors close by. Can I make the thing "stealth" quiet, like a car? So I can cruise around low and slow on a Sunday morning and not even think about disturbing anyone. The Rotax 912 uses a muffler and it is very quiet and neighborly. A 2-into-1 collector into some kind of short, narrow muffler on each side might work. Or maybe a SuperTrapp system.
Any ideas?
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Posted by Donald on Saturday, February 3, 2007 @ 09:08 AM:
I've sometimes wondered about this too but if you have the standard perforated mufflers and you really do mean 'low and slow' you may not be going to disturb anyone anyway. Flying at a low throttle setting is probably the most effective thing you can do here. On many occasions I have been puttering around maybe 1000ft over the field and folks on the ground have later remarked that they had not realised I was up there till I came in to land.
I also know that the standard mufflers are surprisingly effective. One time on take off the manacle clamp on one side came loose and the pair of mufflers that side departed. I sure knew they'd gone! That or I'd blown a hole in a pipe.
The sort of approach I think I would take if I weren't just too darn lazy would be something like a gun silencer on the end of each pipe. There are internet references for home-making that sort of thing out of tube and washers. One reason I haven't bothered, other than that I'm too lazy, is that all my flying friends remark upon how quiet the RF3 is, so why bother? Furthermore, from within the cockpit the noise I hear when I remove the headset seems to be more in the manner of mechanical engine noise rather than exhaust noise.
A final thought about the perceived quietness of my Fournier to those below. The standard pipes point back, not down so the 'muzzle velocity' is not aimed towards the populace and is very probably masked to a large extent by the wing root. Furthermore, the perforations face outwards from the fuselage in a more or less horizontal direction. In contrast, some of my friends' aircraft have pipes which point pretty much downwards from under the cowl and they always seem to be the noisy ones.
Posted by JamesB on Thursday, March 22, 2007 @ 01:02 PM:
The RF5B has a muffler. Most people say they it is quiet under full throttle and almost silent at cruise. We are not that far apart -- we can get together for you to take a look at it. I might have a reasonable picture.
Posted by patrick on Thursday, March 22, 2007 @ 07:39 PM:
Muffler / silencer for RF4 : Yes there are 2 certified mufflers ( similar to the RF5 system) for SAUER 1800 engines and for Limbach 1700 engine. Reason is, in Germany any new certification /STC must comply to the ICAO noise abatment limits MINUS 5 dbA !!!,
I have also seen a non certified modification made by a German RF4 owner: he confectionned 2 mini mufflers slipped on the 2 exhaust pipes along the fuselage.
I will make photos of the different versions and insert them on this forum.
But donīt forget the biggest noise emission does not come from the engine but from the PROP !!!!
The best way to reduce the noise is to reduce the prop revolution (with a reduction gear like rotax !!)
Patrick
Patrick
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Posted by Bob Grimstead on Monday, March 26, 2007 @ 04:54 AM:
Hi Folks,
A good way to reduce propeller noise if you have an engine capacity more than the original 1200cc is to go to a coarser pitched propeller, thus getting lower rpm.
I now have 1400cc pistons and cylinders on my Rectimo. When I first flew it with the original Hoffman HO-11 133s propeller, the prop tips were very noisy.
I now use a Hoffmann HO 11-145 B 80 L propeller (originally supplied for the early RF5 with the 1700cc Limbach motor). It is a little longer than the original, so there is slightly less ground clarance. I helped this by pumping up the main wheel tyre to a higher pressure, and fitting a smaller tailwheel.
To my amazement, not only was this propeller quieter, and greatly reduced the engine rpm, but it improved the climb rate and ALSO increased the top speed. Take-off roll is a little longer though (but still shorter than with the original 1200cc engine). Data below:
9th March 2006, Temp 30°C, QNH 1010 HPa, 1400cc engine. Standard Hoffmann 133/70 propeller, no spinner, 17 litres fuel (aerobatic weight)
Take-off rpm 3,200. Climb 500-1,500 feet 1:47 @ 60 knots and 3,200 rpm = 560 fpm. Max IAS 100 kts @ 4,000 rpm
Same conditions, new Hoffmann 145/B/80L propeller, no spinner, 16 litres fuel (aerobatic weight)
Take-off rpm 2,800. Climb 500-1,500 feet 1:34 @ 60 knots and 2,850 rpm = 638 fpm
9th March 2006, Temp 28°C, QNH 1010 HPa, 1400cc engine, Hoffmann 145/B/80 propeller, no spinner, 36 litres fuel (maximum weight)
Take-off rpm 2,800, Climb 500-1,500 feet 1:40 @ 60 knots and 2,850 rpm = 600 fpm, Max IAS 110 kts @ 3,600 rpm
Just for interest.
Yours, Bob
Posted by patrick on Sunday, April 8, 2007 @ 05:11 PM:
Muffler for Rectimo RF4
I knew that a German guy did such a mod and I finally found himt. Here is his muffler modification. The weight is approx. 2,5 kg more for both sides !
Patrick
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Posted by sericson on Wednesday, April 11, 2007 @ 08:26 PM:
Patrick
Any info on the ram air inlet he is using? Looks like he has added an airbox. Is that the stck carb?
Steve
Posted by patrick on Friday, April 13, 2007 @ 06:19 AM:
Answer : yes this is a Rectimo " special" with the ogirnal Zenith carb.
Franz has the stencil tools to cut the carb gaskets.
he installed an air box with a filter so that he normally flies with cold air and can close the entry to get warm air belwo the engine if advisable .
Patrick
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Posted by dannparks on Monday, April 23, 2007 @ 03:38 PM:
Patrick, thanks for the muffler photo. This is the what I was thinking of doing. Do you know where he got the muffler unit from? Is it motorcycle or VW aftermarket? Is it round or oval? Is it supported at the end, or just hanging from the engine?
It looks like the existing pipes could be used with the right muffler unit, and some skilled welding.
Thanks.
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Posted by patrick on Monday, April 23, 2007 @ 05:18 PM:
This RF4 Muffler is an own construction. As far as I remember the face is a triangle.
Will make better pic. whenever possible.
Patrick
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