Concept2 Forum

Does anyone have an explanation for the noisy and annoying  fluttering noise produced by the fan especially at level 1 ?
It sounds like the air is struggling to get out evenly.  It's a little disconcerting and now I can't unnotice it. It's also worse if you switch down from a higher level to level 1.

I've put the turbo fan into a model D Rower and the fluttering does not happen. I put the Rower fan assembly into the bike's and it flutters as well.
The flywheel covers appear to be the same size as the Rower giving the same  volume and shape as the  Rower. The only difference on the fan compartments therefore  is where  the 4 brackets are for the securing pan screws.  On the Rower they are at  11 o'clock and 1 o'clock  and 7 o'clock and 4 o'clock. Whereas on the bike they are approximately  every 90 degrees ( 11,2,5 and 8 o'clock).

Is there something else I'm missing?

Have you checked to see if there is something hanging loose inside the fan enclosure? What you're describing sounds like when I was a kid attaching playing cards to my bike frame to "flutter" against the spokes, which we thought was a cool sound.

Ahh the good old card trick. Happy days !

I have had the cover off loads of times and I can't see any foreign objects. C2 did suggest that also when I emailed them.

It sort of reminds me of when you turn a bottle of water upside down and the old water-goes-out-air-goes-in thing.  Or when your trying to pour  screen wash into a car. .if the bottle is tipped too high there is no way for the air to get in easily  until the pressure thing (insert science here ) causes the water flowing out to pulse or pause to let air in.
So when the Rower is on L1 the vent is closed so air going in has to go in through the perf assembly and battle against the air coming out ?

Because I have put the fan in a Rower  ,switched the perf assembly (ie the mesh ) I am assuming it has something to do with the fan pan and cover - particularly the location of the fixing brackets as that's the only difference I can think of. There doesn't appear to be any deformation  in the fan assembly.
I originally thought it was the fan assembly which was unbalanced /warped and c2 sent a replacement..


I have put the link to a video which shows  the comparison  between a bike turbo  fan in a bike erg and the same fan in a model d rower. (Playing cards would have worked here but as I was in the garage sandpaper was handy ).
https://youtu.be/Rw7SzOnW7xA?feature=shared

Is  this fluttering just my bikeerg?

There was a similar issue with Model C rowers- some of them exhibited a "puffing" sound at low damper settings. The fix was to block a bit of the exit perf (the metal screen around the perimeter of the flywheel) with a thick paint- maybe just a few square inches of perf area. You might try this on your machine with some tape on the stainless perf to see if it helps.

The theory as to how this works goes something like this: The fan pulls air into itself from the side through the inlet spiral and pushes it out the perimeter through the exit perf. When the damper is fully closed very little air is being allowed in, yet air is still being pushed out the perimeter. This creates a vacuum which builds up to a point before relieving itself with a resulting puffing noise. By reducing the exit perf area there is less of a vacuum build up and the puffing goes away. That's the theory anyway. A lot of Model Cs went out with this fix, with the thick black paint being applied to the bottom of the perf.

I note that something similar happens when I open only a rear window on my VW Tiguan while moving- a very deep thumping noise that I can hear and feel which goes away when I just crack a front window.

Thanks, I'll have another look. I put tape over the perf next to the brackets on the top last week to no effect, but if it's like the model c Rower then there might be a sweet spot/ specific area to cover.

It's most noticeable on L1-2 , I can go above that but when the garage temperature is near 0°c that wind chill on L2 +can be pretty painful on the left hand.

Incidentally, that VW phenomenon you mentioned seems to have got worse on the newer styles which have a more slanted front .

Having spoken to c2  the 'fluttering ' noise is  normal and all bike ergs have it.  If you are reading this and have a bike erg,  you have it.
Originally I didn't understand  why the row erg and bike erg sounded different and this made me concerned about the bike being faulty.  From my investigations the row erg D does flutter a little  but the difference between the 2 is caused by the vents on the flywheel cover.  When the vents are closed by being on L1 the fluttering is most pronounced  (due to air in/air out conflict). On the row erg on L1 the vents are never closed  so hardly any fluttering. 
If I want both ergs  to sound the same I now have to put a metal foil plate over the row erg to close off the vents. It is kept on by air pressure at the moment and falls of when the rotation stops . A bit inconvenient.  So I'll probably  look for a more permanent solution  down the line.
Video of foil plate on row erg:
https://youtube.com/shorts/z8fX-_grMrI? ... jzA-VW3X1b


Facetiousness aside , moving the damper up to L3 for 30secs and then down again to L1 sometimes reduces the fluttering.  So I guess  for the most part I'll have to put up with  train-like noises , or bike on a higher level.