D

Danny7

Well Known Member
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.
 
math

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.
 
Last edited:
I'm not about to do the math on this (I'll let you do it and let us all know! :D ), 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! :)
 
Design Issue?

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?
 
Not enough

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
 
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
 
Last edited:
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.
 
Have done it

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.
 
Last edited:
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.
 
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).
 
Danny,
Since you requested idea's, I would just sell the tail kit now and save yourself 10 years of frustration!
Sorry, it's midnight and I've had a few beers and even some "Jaaeger".
I'll probably delete this in the morning if someone else hasn't already!
 
amilder said:
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.
Click to expand...

You are increasing the moment of inertia and that makes a BIG difference. The RIGIDITY of the structure needs to be taken into account. You need a REAL Aeronautical Engineer for this one. I would not want to be the test pilot in this airplane without the Engineering to back up the change.

The RV-4 had a longer moment arm with less weight than the RV-6. I remember CRINKLED RV-4 elevators on one RV-4 that went too fast then the elevators started to flutter. The less weight with a longer arm without more structure created more flexing and problems.

I do not want to be the test pilot or the DAR that signs this change off.
 
jthocker said:
Danny,
Since you requested idea's, I would just sell the tail kit now and save yourself 10 years of frustration!
Sorry, it's midnight and I've had a few beers and even some "Jaaeger".
I'll probably delete this in the morning if someone else hasn't already!
Click to expand...

I've got the kit, i've got lots of other work keeping me busy so i don't get to work on it. Someday i'll get more spare time and i'll crank away on the kits. This is more of a mental exercise to keep my brain thinking, trying to retain some of that math i went to college to learn and apply it to aviation.
 
RV6_flyer said:
You are increasing the moment of inertia and that makes a BIG difference. The RIGIDITY of the structure needs to be taken into account. You need a REAL Aeronautical Engineer for this one. I would not want to be the test pilot in this airplane without the Engineering to back up the change.

The RV-4 had a longer moment arm with less weight than the RV-6. I remember CRINKLED RV-4 elevators on one RV-4 that went too fast then the elevators started to flutter. The less weight with a longer arm without more structure created more flexing and problems.

I do not want to be the test pilot or the DAR that signs this change off.
Click to expand...

Correct me if I'm mistaken, but isn't it the builder that determines design validity, and the DAR that determines whether the quality of the work is ok? I mean, is this any more risky than the first Harmon Rocket?
 
RV6_flyer said:
You are increasing the moment of inertia and that makes a BIG difference. The RIGIDITY of the structure needs to be taken into account. You need a REAL Aeronautical Engineer for this one. I would not want to be the test pilot in this airplane without the Engineering to back up the change.

The RV-4 had a longer moment arm with less weight than the RV-6. I remember CRINKLED RV-4 elevators on one RV-4 that went too fast then the elevators started to flutter. The less weight with a longer arm without more structure created more flexing and problems.

I do not want to be the test pilot or the DAR that signs this change off.
Click to expand...


And what was the eventual design result? Did Van's just up the part crinkling in thickness and it has been working ever since?
 
do the math

When I do the math in my head I think about 1 inch is the most you could move it. If the arm is 12 inches that is 1/12 th the weight between the metals. If the change is 50% lighter then you save 1/24 th the weight of lead. Is my math correct.
 
osxuser said:
Correct me if I'm mistaken, but isn't it the builder that determines design validity, and the DAR that determines whether the quality of the work is ok? I mean, is this any more risky than the first Harmon Rocket?
Click to expand...

This is a DESIGN CHANGE That needs an Aeronautical Engineer. I am an Engineer but NOT an Aeronautical Engineer. Alarm bells are going off in my head with this change. As such, I would want to see the design validated by an Aeronautical Engineer and consider it not airworthy till I see the data.
 
Danny7 said:
And what was the eventual design result? Did Van's just up the part crinkling in thickness and it has been working ever since?
Click to expand...

Lesson learned, DO NOT EXCEED the designer's recommendations. The aircraft went over Vne where the resultant flutter and pull BENT the elevator. There are limitations placed on products by designers for reasons. Exceed the limitations and one may not like the results.
 
RV6_flyer said:
Lesson learned, DO NOT EXCEED the designer's recommendations. The aircraft went over Vne where the resultant flutter and pull BENT the elevator. There are limitations placed on products by designers for reasons. Exceed the limitations and one may not like the results.
Click to expand...

oh, Exceeded Vne. For some reason i read your earlier post that it was one of the initial examples of the RV4 that simply "went to fast", and was a design problem not an exceeding recommendations. Thanks for clarifying that to me.
 
burgundyja said:
When I do the math in my head I think about 1 inch is the most you could move it. If the arm is 12 inches that is 1/12 th the weight between the metals. If the change is 50% lighter then you save 1/24 th the weight of lead. Is my math correct.
Click to expand...

Yeah, I'm not doing the math...but if you're right, this is what I was referring to in my earlier post. We're talking less than a couple ounces here because you can only move the arm a tiny bit.
 
I'm pleased that Danny asked the question. I have often thought to ask what others thoughts were on this modification.
For those of you that put forward your knowledgeable thoughts, thank you. I spent months thinking about this, studying the elevator and ballast arm. and tested the fitment and weight saving before I decided to replace the lead with the tungsten.
It's not a case of how much weight can be saved with this modification, its a case of every little bit of weight saving from nose to tail adds up to a total weight saving package.
My 9a is a quick build kit, and I can assure anyone that may be a bit concerned, the airframe is standard (there has been no lightening there). But the seats and instrument panel are RV12 copy's. The wheels are Magnesium. It's fitted with a 0-235 with conical mounts, Flytek started and P-Mags, with auto leads and plugs (yes I even weighed the weight saving difference there).
I've probably spent more time trawling the internet checking on weights of bolt on items, and weighing items than building. But I want a light plane.

Thanks guys
 
As I said before, it is something that I would not do without an Aeronautical Engineer reviewing the change.

I am afraid that the increase change in length needed to create the same moment, could lead to undesirable condition. I am afraid that I do not know enough about resonance and natural frequency oscillation but recognize that it could occur with this change. I ask myself, what changes would be needed in the arm to make it more rigid with the longer arm, same moment, with less weight?

The Tacoma Narrows Bridge is what comes to mind for me when you talk about lengthening the arm and using less weight. See this video.
 
RetiredRacer said:
I'm pleased that Danny asked the question. I have often thought to ask what others thoughts were on this modification.
For those of you that put forward your knowledgeable thoughts, thank you. I spent months thinking about this, studying the elevator and ballast arm. and tested the fitment and weight saving before I decided to replace the lead with the tungsten.
It's not a case of how much weight can be saved with this modification, its a case of every little bit of weight saving from nose to tail adds up to a total weight saving package.
My 9a is a quick build kit, and I can assure anyone that may be a bit concerned, the airframe is standard (there has been no lightening there). But the seats and instrument panel are RV12 copy's. The wheels are Magnesium. It's fitted with a 0-235 with conical mounts, Flytek started and P-Mags, with auto leads and plugs (yes I even weighed the weight saving difference there).
I've probably spent more time trawling the internet checking on weights of bolt on items, and weighing items than building. But I want a light plane.

Thanks guys
Click to expand...

OK, Bob, not to be critical - I am just curious - how much weight did you save by using tungsten instead of lead?
 
You must log in or register to reply here.