Substituting tungsten for lead in counterweights, need ideas

[Danny7]

I've been thingking about this for a while, and don't know any more than before, other than material densities. I was wondering how much weigh loss could be attained by using a denser material for the counterweights and putting it as far out as possible, increasing the arm. If a blob of lead occupies a space 4 inches long in the axis of balance, could you use a denser material such as tungsten, move it as far out as possible (increasing arm) and reduce the overall weight? Is there an easy way to figure this out, i suppose i could run up to the Community college and ask a math prof. for the equations i need to use. other than structurally fixing it to the part, is there a reason other than cost i shouldn't look into this?

i realize adjusting weight would be harder, tungsten would not be a good material to try and drill to lighten while that is common for lead counterweights. I can get past that though.

[amilder]

No problem other than cost as you say. THe math is just like the moments you calculate to determine weight and balance:

moment = mass * distance, where distance is the linear distance from the center of your weight to the pivot axis. If you can increase the distance, you can reduce the mass:

m0*d0 = m1*d1 or m1 = m0*d0/d1 (m0 = original mass, d0 = original distance, and d1 is new distance)

keep in mind the tungsten alloys are typically 80-90% tungsten so the density isnt quite as high as pure tungsten (but still much higher than lead)
Andy

p.s. one issue is that you will be increasing the moment of inertia (=m*d^2), but I don't know if that makes much difference here.

[lostpilot28]

I'm not about to do the math on this (I'll let you do it and let us all know! ), but I'd be really surprised if you could save more than an ounce or two. Total.

Not trying to be a nay-sayer, but the moment arm you're referring to on the elevator and rudder are pretty short, and the difference in mass between tungsten and lead isn't significant.

Still, I'm curious to see what you come up with!

[hevansrv7a]

Take the elevator weights for example. The rib is designed with bolt holes placed for lead. In order to make the beneficial change you describe you would have to re-think the attach points. Hmm?

[frankh]

Bang for the headache buck IMHO...If your thinking bout this kind of stuff you'll never finish the airplane..Move on with lead is my advice.

Frank

[Danny7]

thanks frank, sonny and evan, but my emp is not dependent upon my wondering about this. Even if i could do the weight exchange tomorrow my emp would still take me months to finish.

Thank you Andrew for giving me the equation. without actually working out some of the numbers who's to say how much difference it could make?

also tungsten density is generally around 19.3 g/cc or 19300 kg/cu.m while lead is 11340 kg/cu.m the difference is large

[szicree]

You could definitely save some weight this way but at what cost? Suppose you could even shave half the stock weight, how would you attach it, adjust it, etc. That stuff is as hard as heck and super expensive. If I had my old -4 plans handy I could crunch the numbers in about five minutes, but my intuition says it's very little.

[RetiredRacer]

Using the same theory, I've installed Tungsten counterweights in my -9a elevators. I did keep a record of the weight saving in my note pad, but I can't seem to find it at the moment. You can't drill it, so I used a cutting disc to shape it to get the tungsten bar as far forward as possible. I put a slot in from each end (offset to the rear slightly to keep as much weight to the front as possible, but still allow some area at the rear of the bar for trimming) to mount it. I also drilled another two mounting holes further up into the nose. To work out a size to cut the Tungsten, I first fitted and trimmed a lead counterweight that I could weigh, and work from there with the Tungsten. I then kept slicing of the the rear of the Tungsten bar till I got the balance (the paint design has the elevators polished)
From memory it was something like a 30% weight saving. And the lead ballast I made first was a heavy sucker.

[Mike S]

Nagging bit of "red flag" going on here.

Prior comment about how hard this stuff is are correct. Counter weights must be mounted securely for safety reasons.

Flutter is usually determined by a combination of witness statements, and post crash analysis.

Yes, it is experimental, and what you are doing is right there in the spirit of it all.

Just think it through and understand what you are doing.

Please.

[RetiredRacer]

The plane is not flying yet (about two months away) Mike, if you know or can see something I may have missed, please explain. These are securely mounted (as secure as the lead mounts).