weight variations?

[13brv3]

Greetings,

I've spoken with people who say their LE is close to the weight limit, and others who say it's more than 100 lbs over the limit.  The extra weight doesn't seem obvious, and in fact I had an Airbike that was 350 lbs.  If I tried real hard, I probably could have trimmed 20 lbs off that with different wheels, lighter paint, etc, but no way could I have ever gotten it down to the weight they originally claimed. It was N numbered, so not a legal issue, but it always baffled me that it was so heavy.   

This makes me wonder how much extra weight isn't obvious.  For example, say one builder lays on the epoxy heavy, where another uses just enough.  How much of a difference would that likely make?  I imagine wood selection is likely a bigger factor.  How much variation do you think there could be between the lightest and heaviest wing? 

Same question to some extent with welding.  If someone makes nice TIG welds, and another leaves a much larger weld using MIG or OA, I wonder how much that would add up to over the whole fuselage. 

I guess I'm just trying to grasp how some planes can make weight, while others are far above it, even without any obvious differences.  It would be nice to know a target weight for the fuselage and wings.  I'm always on the lookout for a local project, but I'd hate to find one that had wings that were so heavy that there's no hope of making the legal weight. 

Thanks,
Rusty

[IflyHG]

I don't have a set of plans (yet) and have not built one, I had hoped builders would have chimed in here.  I share your frustration, I would like to know how I'm doing against either a standard, or at least the average of what other builders have achieved.  I can't find it now but there used to be a separate website (blog) that was written by a few of the early builders of the LEUL.  In it they documented at least what they ended up with for weights of all the major components.

If you are going to build a plans built ultralight, especially the LE where so much is left up the imagination of the builder, in my opinion, you have to weigh everything, and I mean everything, that makes up the plane as you build, in order to stay under your weight budget.

My plan is to redraw the entire plans and build the plane in CAD for multiple reasons.  1st, I think it will help me visualize how every piece goes together.  Builders have reported studying the plans over and over and still not understanding all the details or not being able to find important information, or finding conflicting information.  2nd, I think it will help uncover discrepancies in the plans.  I have read several build blogs where builders have discovered missing dimensions or dimensions that cause interferences or other problems and parts have to be remade to work correctly.  Also, builders have discovered the materials list is inaccurate, wrong length bolts and the like.  By redrawing in CAD I hope to uncover these types of issues and develop a more accurate materials list so hopefully I will end up with less unusable material and fewer orders/trips to suppliers for parts.  3rd, and this goes to your point, I plan to put the material densities in for all the parts so that I have a prediction of what parts and assemblies "should" weigh.  Accounting for things like adhesives, polyurethane, primer, paint, and powder coat will be harder but the containers do have coverage estimates and CAD can handle that so it should be possible.  As I build I can check what the real parts weigh against the CAD prediction and make corrections as I go.  If I find parts and assemblies coming in overweight I can stop and re-evaluate and think about how to build lighter while maintaining strength.  I also plan on buying some excess materials to use to practice new skills.  I can use these practice materials to check some of the estimates.  By using this approach I should know as I build, that I'm going to make weight, and not have an ugly surprise at the end.  Also, by knowing what all the parts weigh I can verify weight and balance is going to work out correctly. 

In reviewing build blogs I have seen some clever ideas about how to make parts that still are functional and strong enough but lighter.  Every little bit helps, I plan on implementing these ideas and some of my own.  This is another area where I think building in CAD will help.  I can see what the plans built version should weigh, and what a modified version should weigh, and how it will impact CG.  All aircraft are a trade space between being strong enough, with margin, to get the job done, and being light.  Building light costs more, either in time to lighten a part with material removal, or money, to buy a lighter material to begin with.  I have always heard lighter flies better.

I suspect overweight ultralights are built by builders with the wrong mindset.  In one blog a committee of builders built a LEUL.  It came in at 371 lbs.  The author admitted that when individuals decided "it really needs to have this..." no one pushed back so the outcome was predictable.  For example, a builder might think "real aircraft have dual magnetos, I want a starter so I don't have to hand prop, and I want an alternator so I don't have to keep recharging the battery".  Leonard's 1/2VW doesn't have any of this and weighs less as a result.

I agree, that if the plans included weight targets for significant assemblies, that would be very helpful.  For the wings, what should a rib weigh, what should a spar weigh, what does the wing weigh before and after polyurethane, after covering, after priming and painting?  What does the fuselage weigh when just tacked together just out of the jig, after completing all of the welds, after adding all of the tabs and guides, after painting/powder coating, after covering, priming/painting?  Same for empennage, main landing gear, wheels, tail wheel assembly, fuel tank, spar assemblies, wire bracing, control wires, engine (firewall forward full solution), brakes, gauges, windshield, main wing gap cover, etc.

If any builders have schedules of weights like this it would be great if they would post them.  I plan on building a spreadsheet with these schedules of weights for my LEUL when I build it.

[13brv3]

Wow, that sounds like a really ambitious project!  I've really been spoiled by modern CAD drawn plans, and an update to the plans for the LE would certainly be welcome.  Realistically, I'll probably start with a project, so I don't expect to need the plans as much as someone starting from nothing.

I do remember seeing a page where someone documented wing panel weights and such, but with a sample of one, I'm not sure if it was on the high or low side.  I have enough Oratex, and a Hirth F-23 engine that I'd use, and that would help keep the weight down.  I still wouldn't feel completely confident it would make the 254 lb weight limit, and there would be some anxious moments when it comes to the final weigh-in :-)

Rusty 

[Dan_]

http://www.angoraaffaire.com/leu/whatdoesitweigh_.htm

[13brv3]

That's a great site!  Thanks for the link.
Rusty

[Chuck in Indiana]

I built the lightest Sonerai 2L ever to the best of my knowledge. 500 lbs. at certification. I weighed the old girl again a few years ago, and like all old girls  she had picked up 20 lbs. from fuel system changes, dual ignition, seat cushions..
What I'm saying is it ain't my first rodeo and I gave it my best shot on Bullet. (looking over my shoulder to see if the FSDO is looking) 277 lbs.
The heaviest part by far is the covering because I used Poly fiber. The coat of Poly brush that fills the weave adds a lot.. If you can afford it and want the look of it, Oratex would be the way to go.
Leonard used light fabric and just rolled one coat of house paint on his. No rib stitching. The wood that came in the materials kit was 10% over sized. I don't have a planer, and just went with it.That doesn't sound like much, but it makes a difference.
Another place is the engine. Yes, the Verner weighs a little less than the half V dub..comma but..in needs a fairly substantial engine mount, oil tank, and *hoses.* Those suckers are heavy and you don't want light ones.
So. While Bullet doesn't meet the letter of the rule, she certainly meets the spirit.
Part 103 came about because people were flying heavy ultralights with big fuel tanks and in many cases two seats (!) without training, knowledge of rules of the air, etc.
In reality, the FAA doesn't care if your ultralight is a *few* pounds over weight. Just the same, I have never posted it anywhere but here, and I'd appreciate it if it doesn't become general knowledge. 

[13brv3]

I appreciate the weight information.  Is yours a LEU, or LE-XL? 

Making the weight would be an interesting challenge.  I stumbled across someone selling 31 meters of Oratex a few years ago for only $1000.  That should save some weight, and save me from the dreaded task of painting.  I also have a Hirth F-23 engine which I'd trust at least as much as a half VW.  It's 78 lbs complete with electric start (plus battery and wiring), and maybe 74 lbs with pull start that wouldn't require a battery.  CG would be a concern for the lighter engine, so maybe some extra weight required in a longer mount.  I'd expect performance to be much better than a half VW, though fuel consumption would be much worse.  I'd make as many items removable as possible so they wouldn't count as empty weight.

I'll keep looking for an affordable project near east TN. 

Thanks,
Rusty
 

[Dan_]

If you are going to run a 2 smoker, cover the air filter with a plastic bag after each flight. Else dust will clog it, and you will be up in the air wishing you were on the ground. If you ask how I know, I won't tell you...