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tonybroad - n/a
15-Feb-08, 05:03 PM
The new F3 craft hovered properly for the first time today with both Rotax Max 125 kart engines running in tandem



I can't repeat what my students said but AWESOME was the second word, the first began with F



with the silencers in the plenum, the noise of the fan and chain transmission to the driveshaft seem to dominate and it sounds very meaty for a pair of 2 strokes



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a few weeks and we'll be ready to test 'in the field'



thanks for all the comments and questions, it's still going to be a development year for us but it's a sound start



Tony

jon_curtis - n/a
15-Feb-08, 05:35 PM
looks mental tony http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif

Keith Oakley - n/a
15-Feb-08, 09:14 PM
Well done you seem to have an air intake silencer box, but don't forget to curve the splitter plate (like a flow straightner)or that'll be high on the noise source list. When you put the flow straightners in make sure theres a 100mm + gap between them and the fan or they'll add to the din too!

tonybroad - n/a
16-Feb-08, 08:27 AM
All of the above already on the to-do list Keith, i want to be one of the first visitors to web-cam this season - the target is sub 90dB



the standard kart silencers are rated at 92dB but are inside the plenum, there is a specific replacement silencer wadding for them so no more loft insulation or fibreglass scraps



no doubt we'll have a chat at the AGM



cheers



Tony

Keith Oakley - n/a
16-Feb-08, 09:05 AM
Great stuff - good to hear you've got some decent stuffing material. In the longer term however I think we need to move from that kind of absorbtive silencer to a reactive one. Below is a graph from next weeks noise lecture at the AGM. If you look at the performance curve for a typical stuffing material in the graph you'll see that it has an attenuation of around 7db at 165hz. (Thats the frequency of a single TZR cylinder doing around 9900rpm) A typical reactive silencer offers a 25db attenuation at 165hz. The absorbtive silencer is a bit more reasonable at taking out the harmonics at 330hz 495hz etc which is why a well stuffed silencer does cut out the higher pitched crack, but it does little to reduce the fundamental 165.



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nickyd - n/a
18-Feb-08, 02:10 PM
Rock and Roll!!!!

Jamie Lewendon - n/a
19-Feb-08, 10:08 PM
Rumour has it, the Bucknall boy is planning on going racing this year, so it may be good to see what you can do Tony!!!!!!!!!!!



(I'm baseing this rumour on the fact that he has stolen his poncy exhausts back!)



Jamie

nickyd - n/a
19-Feb-08, 10:20 PM
Well he better get either the camper or the craft to at least one meeting this season!! http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif