L

Loman

Well Known Member
I think this stuff is worth a try. What interests me is that you only need to cover 10% or more of the area to get effective vibration damping - just a strip or two in the center of each panel will do. At 0.17 lbs / sq ft that should not add much weight. Even if you used a whole roll of 36 yards, that's only just over 3 lbs. I am thinking of putting some in the center of every skin panel from the baggage bulkhead to the firewall as well as both of those bulkheads. The cabin interior lining will cover it.

There are two very different issues that I haven't figured out:

1. Fire performance. This is not an aviation product so it does not seem to have been tested to any aviation standard. However, it is comprised of 10 mils of aluminium foil and 5 mils of "viscoelastic polymer" with some strong adhesive. How bad could it be?

2. It is supplied in cases of 5 rolls (likely to be enough for 10 aircraft) and 3M in this country won't sell individual rolls. Does anybody have half a roll or more left over that I could buy?
 
McMaster Carr has something that sounds just like what you are looking for;
http://www.mcmaster.com/#sound-control-tape/=e1ewhj
The iPhone has a DB meter app which I have used in my rv7. It measures 99db in 160 mph cruise. That would be a tool you could use to try to measure any benefit you get by applying this tape.
If you do it please let us know your results!
 
McMaster Carr no longer ship overseas

Unfortunately, I heard McMaster Carr no longer ship outside the US. Pity - I had used them several times. Also, the local 3M branch won't sell less than a full case. This stuff is used by the likes of laundry machine manufacturers, who have all long since departed the emerald shores, so there is not much call for it here.

I did notice that 3M in the US sell a single roll on-line but I gather from the order form that they envisage US addresses only.

I am still hoping to get hold of some. If I do, I will certainly post the cockpit noise level using that app - when I eventually fly.

Using a sound meter app could be a great way of establishing a measurement against which we could discuss the effectiveness of sound deadening measures. However, we need standard conditions. How about straight and level at 8000 DA with 23/2300 and anything else you guys think should be controlled for?

How about the fire performance of the 2552 tape? Do any of our chemists have a comment on how viscoelastic polymers as a class behave when exposed to heat or flame? Is the adhesive a concern?
 
This stuff will help a bit with the first mode of panel vibration. With a bit broader coverage (more of the panel) it might help a little with the second mode too. The higher modes generally don't have as much energy associated with them and aren't usually as critical.

However, typically flat aluminum panels have such a low natural frequency that they aren't a significant source of noise - for example, a 20" square panel, .025 thick, has the first three modes under 1 hertz. You'd feel it but not hear it. A 10" x 4" panel has its second mode at about 20 Hz, so that might start to be audible. Note that adding mass, such as primer or damping tape, will lower the frequency.

Of course, curved panels have a higher natural frequency.

What you will have for a noise source is all that engine noise and aerodynamic noise. The engine noise starts at about 40 Hz and the aero noise seems to start at 2,000 or 3,000 Hz. The exhaust pulses come at about 80 Hz for 2,400 rpm and will vibrate whatever is available, of course. Looking at a plot of noise magnitude versus frequency, there's a series of spikes at the engine frequencies, then a large white noise region for the aerodynamic noise.

Based on that, it wouldn't hurt to use this tape in the cabin area, especially in the floor area. If nothing else it'll cut down on potential cracking from vibration. In general, though, you won't be hearing much panel resonance.

But routing the exhaust away from the cabin (if at all possible) and sealing against leaks will pay bigger dividends.

Dave
 
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