Van's Air Force
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Weight Savings From Creating Lightening holes on the V-S Spar Stiff.
- Thread starter briand
- Start date
I didn't weigh mine, but it didn't seem very significant at the time. The small things may not seem worth the effort, but I have taken the position that I'm going to take advantage of all of the 'recommended' weight-saving measures that are in the plans, and I have so far (unless I've missed one or two). I figure all of the little things will all add up to something a little more significant. And almost everyone I have talked to with RV experience says "built it light" and "build it per the plans." So I am. And then I won't feel as guilty when I add something to the panel that I'd like to have there.
Just my 2 cents' worth.
Just my 2 cents' worth.
AntiGravity
Well Known Member
Weight saving
I cannot believe someone would be sad enough to care. Oh wait, no I was!
I weighed the VS before I started, and then weighed it again when I was doen. Total saving a whopping 95g! Still, if you can save small amounts in many places you can overall save a large amount. All helps. Of course, I probably added this back in primer but what the heck, a saving is still a saving, right
I cannot believe someone would be sad enough to care. Oh wait, no I was!
I weighed the VS before I started, and then weighed it again when I was doen. Total saving a whopping 95g! Still, if you can save small amounts in many places you can overall save a large amount. All helps. Of course, I probably added this back in primer but what the heck, a saving is still a saving, right
95 grams translates to .209 pounds. Not much weight however, it may be noticeable on the CG as it has a large arm.
People talk of building light and many often consider that to mean removing mass from the design wherever possible. Well, after going through all major components, I've come to the conclusion that this view is marginally misguided. If you avail yourself of all the areas where Vans highlights the option of trimming material for weight reduction, you may save 1.5 pounds, possibly 2. Don't eat that burger on your Saturday flight or you will put that back on. If you start trimming areas not identified by the engineers, then you are assuming responsibility for structural integrity in a manner you may not be qualified for.
Building light means watching what you add to the airframe, not looking for meaningless extra mass to trim. Heavy primer (excess) will add more weight than you can possibly trim away. 3 coats of color followed by 3 layers of clear coat may look very nice but, that's a lot of weight (not to mention a significant aft CG shift). Prop and engine choice - big impact. Panel decisions? See where this is going?
For me, the biggest target for weight reduction is my waistline. I can trim away 80 pounds of excess material without compromising the airframe.
Jekyll
People talk of building light and many often consider that to mean removing mass from the design wherever possible. Well, after going through all major components, I've come to the conclusion that this view is marginally misguided. If you avail yourself of all the areas where Vans highlights the option of trimming material for weight reduction, you may save 1.5 pounds, possibly 2. Don't eat that burger on your Saturday flight or you will put that back on. If you start trimming areas not identified by the engineers, then you are assuming responsibility for structural integrity in a manner you may not be qualified for.
Building light means watching what you add to the airframe, not looking for meaningless extra mass to trim. Heavy primer (excess) will add more weight than you can possibly trim away. 3 coats of color followed by 3 layers of clear coat may look very nice but, that's a lot of weight (not to mention a significant aft CG shift). Prop and engine choice - big impact. Panel decisions? See where this is going?
For me, the biggest target for weight reduction is my waistline. I can trim away 80 pounds of excess material without compromising the airframe.
Jekyll
It really does come down to WHERE you're trimming the weight. Especially on a -7, anything you can do to get that CG forward is going to help. If I were building an -8, I'd probably not cut them out.
The way I did mine, I cut them out a little smaller than called for in the plans. This just made the measuring easier (i.e. you can be a little sloppy and not sweat it too much....sloppy in my case was I got it in the right position, centered to within about 1/32...I could do better, but no need).
All in all, they added about 1 1/2 hours to the build time for me, including deburing and stuff.
The way I did mine, I cut them out a little smaller than called for in the plans. This just made the measuring easier (i.e. you can be a little sloppy and not sweat it too much....sloppy in my case was I got it in the right position, centered to within about 1/32...I could do better, but no need).
All in all, they added about 1 1/2 hours to the build time for me, including deburing and stuff.
Rick6a
Well Known Member
Significant
http://www.vansairforce.com/community/showthread.php?t=2445
Rick Galati RV-6A "Darla"
RV-8A empennage done
Yep, check out this thread for my before and after weight observation.briand said:
http://www.vansairforce.com/community/showthread.php?t=2445
Rick Galati RV-6A "Darla"
RV-8A empennage done
My earlier post sounded like I don't remove material where recommended. To the contrary, I do act on those recommnedations when possible. I just don't anticipate much net reduction and realize that my ultimate weight control is in watching what I add. I've got a QB so some of those parts with optional trimming have already been assembled and the factory didn't always do the trim. I am pleased that they made some of the trims. I'm not interested in dissassembling the QB to do those optional trims they passed on.
Back to the waistline issue....... My flight surgeon seconds my weight reduction concept.
Jekyll
Back to the waistline issue....... My flight surgeon seconds my weight reduction concept.
Jekyll
AntiGravity
Well Known Member
Trim yourself!!
Jekyll, this is very true. Not flying yet, but skydiving and I've always been a fast faller. As a jumpmaster it just doesn't look good when gravity takes priority and you leave a student floundering on their own in mid-air . Losing 10kg has helped enormously! I sometimes wonder how my wife and I will fair when we get the -8A built, from a CG perspective. We're only 70kg and 54kg; I guess we'll cross that bridge when we get there! Meanwhile though, I'll save weight where I can, so longer as structural integrity and safety are not compromised...
Blue Skies!!
Jekyll, this is very true. Not flying yet, but skydiving and I've always been a fast faller. As a jumpmaster it just doesn't look good when gravity takes priority and you leave a student floundering on their own in mid-air
. Losing 10kg has helped enormously! I sometimes wonder how my wife and I will fair when we get the -8A built, from a CG perspective. We're only 70kg and 54kg; I guess we'll cross that bridge when we get there! Meanwhile though, I'll save weight where I can, so longer as structural integrity and safety are not compromised...Blue Skies!!
How to cut lightening holes...
I used Greenlee punches. Unibit to drawbolt size (3/4") and Greenlee "slugbuster" conduit punch to 2" and 1 3/8". Very simple and easy if you have access to the punches (know an electrician?).
I think most people use a flycutter, but I couldn't locate the one I'm pretty sure I bought years ago in anticipation of building a plane...
If you've never used a flycutter, read all instructions and be very carefull - they are wicked tools that will mess you up if you get in their way!
I used Greenlee punches. Unibit to drawbolt size (3/4") and Greenlee "slugbuster" conduit punch to 2" and 1 3/8". Very simple and easy if you have access to the punches (know an electrician?).
I think most people use a flycutter, but I couldn't locate the one I'm pretty sure I bought years ago in anticipation of building a plane...
If you've never used a flycutter, read all instructions and be very carefull - they are wicked tools that will mess you up if you get in their way!
AntiGravity
Well Known Member
Hole saw / drill press
Hole saw / drill press ; since I already had it. Slow and careful, but it worked...
Hole saw / drill press ; since I already had it. Slow and careful, but it worked...
I was wondering if a hole saw would work. I'll see if I have any that'll fit the size needed.. might end up with the fly cutter since it's adjustable. Thanks for the info everyone!
(The slug busters look pretty darn slick, too bad I don't know anyone that would have one!)
(The slug busters look pretty darn slick, too bad I don't know anyone that would have one!)
I used a fly cutter on mine too. I found it worked well to cut a little more than 1/2 way through on one side, and then flip it over and finish it off from the back.
I didn't know at the time that they made hole saws designed for going through metal. I just found this out about a week ago (how could I now know this, right??? I've mostly done woodwork in the past, so I guess I just never looked). No question about it...if I had to do it again, I'd use a hole saw.
I didn't know at the time that they made hole saws designed for going through metal. I just found this out about a week ago (how could I now know this, right??? I've mostly done woodwork in the past, so I guess I just never looked). No question about it...if I had to do it again, I'd use a hole saw.
rzbill
Well Known Member
If you plan to use a fly cutter on the 1/8" reinforcement, I'd recommend going to the trouble of beg/borrow/stealing the use of a drill press with a LOW rpm setting. The common cheapo bench units (I own one) are usually limited to about 500 RPM minimum. More expensive floor models will get below 200.
I've found no difficulty using the bench models for cutting thin skin at 500 RPM, but when I did the heavy gage VS part, the cut was deep (even flipping the part) with a lot of chatter. On the last hole, the fly cutter broke. Days later I noticed the press spindle was bent. The local merchant (Lowe's) was gracious enough to provide a free trade-in repair on the press. (I went in asking to buy repair parts).
I've found no difficulty using the bench models for cutting thin skin at 500 RPM, but when I did the heavy gage VS part, the cut was deep (even flipping the part) with a lot of chatter. On the last hole, the fly cutter broke. Days later I noticed the press spindle was bent. The local merchant (Lowe's) was gracious enough to provide a free trade-in repair on the press. (I went in asking to buy repair parts).
Don?t underestimate the benifit
I believe every ounce you can save is beneficial. I read an article in one of the magazines where a guy went through his plane and tried to remove any unnecessary weight. He even shortened the wires behind his panel. In the end I don?t remember exactly what he removed but it was a few pounds total.
If your goal is performance weight is critical. It even has more of an impact on performance than horsepower at some point.
My problem is I am building an 8 and I am already concerned about C.G. issues. I weigh 255 pounds so I?m trying to keep weight off of the front. For this reason I have decided not to cut the lightening holes in the rear spars.
I will definitely take advantage of any weight savings on the front end of the plane. I?m moving my batteries to the rear to improve the C.G. but I regret the additional battery cable required.
My desire is to have the best vertical performance possible. After flying Cessnas and Cherokee's I long for the climb out of my RV. Weight has a greater affect in V.S. than it will the overall top speed. (to a point)
Donald
RV-8 Empennage
N-2845 Reserved.
I believe every ounce you can save is beneficial. I read an article in one of the magazines where a guy went through his plane and tried to remove any unnecessary weight. He even shortened the wires behind his panel. In the end I don?t remember exactly what he removed but it was a few pounds total.
If your goal is performance weight is critical. It even has more of an impact on performance than horsepower at some point.
My problem is I am building an 8 and I am already concerned about C.G. issues. I weigh 255 pounds
so I?m trying to keep weight off of the front. For this reason I have decided not to cut the lightening holes in the rear spars.I will definitely take advantage of any weight savings on the front end of the plane. I?m moving my batteries to the rear to improve the C.G. but I regret the additional battery cable required.
My desire is to have the best vertical performance possible. After flying Cessnas and Cherokee's I long for the climb out of my RV. Weight has a greater affect in V.S. than it will the overall top speed. (to a point)
Donald
RV-8 Empennage
N-2845 Reserved.
jferraro17
Opulence, I has it...
Every little bit...
I too am concerned about the CG in my -8, but don't you think ANY savings in weight is benificial, and you can work out the CG issues later?
My point is, I'm into the wing kit with about a million decisions still to be made--from the engine to the panel, fixed pitch or wood prop, from which landing/taxi lights I'll use to what kind of seat covering material. Heck, I haven't even decided -8/8A! ALL of this will have a bearing on the W/CG. So my attitude at this point is to build the parts I'm currently building now as light as possible.
Some decisions seem like no brainers now (battery in back), but the rest? Man, so much could change over the years of building, why lock in now, at the VS stage? Just build it lite, and worry about the CG when you realize you need balast in the back! Just my opinion.
Joe
I too am concerned about the CG in my -8, but don't you think ANY savings in weight is benificial, and you can work out the CG issues later?
My point is, I'm into the wing kit with about a million decisions still to be made--from the engine to the panel, fixed pitch or wood prop, from which landing/taxi lights I'll use to what kind of seat covering material. Heck, I haven't even decided -8/8A! ALL of this will have a bearing on the W/CG. So my attitude at this point is to build the parts I'm currently building now as light as possible.
Some decisions seem like no brainers now (battery in back), but the rest? Man, so much could change over the years of building, why lock in now, at the VS stage? Just build it lite, and worry about the CG when you realize you need balast in the back! Just my opinion.
Joe
Decisions Decisions
Joe?I understand your views and even though it seems that I am locked I frequently find myself changing ideas. I am locked on not lightening my tail section though. I have flown in 8?s and talked with those that own them. Due to my size I will be using ballast during solo flights. Due to the fact that the tail section is so far out on the arm from the C.G., if I save ounces there it could require a pound behind the back seat to compensate. I am speaking in generalities because I haven?t actually done a weight and balance on an 8 but I know the theory to be true.
I do agree with your belief that we should build everything as light as possible. Thanks for your input.
By the way??Build the 8! Looks way cooler. Just my opinion. (Plus in my case moves the weight of the 3rd wheel from the front to the back)
Donald
RV-8 Empennage
N-284DP Reserved
Joe?I understand your views and even though it seems that I am locked I frequently find myself changing ideas. I am locked on not lightening my tail section though. I have flown in 8?s and talked with those that own them. Due to my size I will be using ballast during solo flights. Due to the fact that the tail section is so far out on the arm from the C.G., if I save ounces there it could require a pound behind the back seat to compensate. I am speaking in generalities because I haven?t actually done a weight and balance on an 8 but I know the theory to be true.
I do agree with your belief that we should build everything as light as possible. Thanks for your input.
By the way??Build the 8! Looks way cooler.
Just my opinion. (Plus in my case moves the weight of the 3rd wheel from the front to the back)Donald
RV-8 Empennage
N-284DP Reserved
briand said:I wonder if vans ever tried any stress tests on the vs808pp lightened and not lightened to see the diff. in strength. Not that I believe the extra strength is needed, if vans says o.k. to lighten I trust them, just curious. Too bad their engineers don't hang out here.
Without getting into technical gobblygook, you can cut out the lightening holes without much strength penalty. It essentially works the same way as hogging out side channels in a solid block of steal and calling it an "I" beam.
