Fuel pump noise

Tnx a lot, I will do that!

I got this explanation and suggestion from the manufacturer:

We know about the noise problem and Rotax knows about it too. But, we can not make any non-authorized individual modifications or improvements of fuel pumps. Unfortunatelly, Rotax does not offer any solution. Also, there is no limits for noise level established for fuel pumps, so Rotax can consider it individually. At least we put a piece of molitan foam over it to damp the noise, but it does not help too much. As mentioned, we can not take responsibility for any non-authorized  modifications which could affect the correct operation of the engine. We must do the installation according to Rotax instructions. Write to Rotax like many others did, and same as we did. Hopefully it can help and Rotax will make some arrangements to solve it. That is all we can do in this time.

I have the same plane Faeta NG (also very satisfied) and the same problem. There are 2 reasons for the noise:

a)       The plane has the pumps directly “in” the cabin, meanwhile the others have mostly it in close to the engine, behind the firewall. It has advantages, but all the vibrations and noise goes directly to your ears.

b)      I was talking to the manufacturer directly (it is only 30 minutes from our airport) and he said, that the previous pumps were not so noisy, so he didn’t solve it before. His demonstration plane with old pups was quieter than mine. I was told that Rotax has probably changed the producer and the pumps generate more sound, but I who knows..

We have tried to find some solution. I firstly placed some acoustic foam from above of the pump deck, but it did not help so much. After few months I was talking to the manufacturer again and he had tried to fill the box with pumps with the foam strips completely. He said it has helped much more. But I did not want to dissemble everything again to do I too, so I will probably wait for the next pump maintenance and then I will do it to...

Hi Martin, 

Very interesting.

Could it be that certain foam is better for certain frequencies and for such, the right foam needs to be identified to minimise the "screaming" noise? It's a real pain to listen to. I also recall the demo plane, it was not at all so bad, but then one I ended up getting delivered the noise level was truely horrible and given Ill now get another one build again, I want to make sure this screaming noise is less or completely gone!

Ive send you a PM on FB.

There are surely differences between the foams, but I took the firs “acoustic” foam (ca. 15mm) I have found an I gave it also to the manufacturer (but I do not know if he used the same later). But there are surely many types of them. I placed it on the upper carbon deck above the box with pumps, but it did not help much, because the sound goes also in other directions.

The manufacturer told me he opened the box with pumps and filled the space with the foam completely, co the pumps are covered with it. But I did not want to spend several hours with it yet. I have good headphones, so it is not so bad.

I got the plane 2 years ago and the sound was not so bad. But then I got new pumps from Rotax (there was some bulletin) and since then the sound was much stronger. You probably got the plane with the new pupms…