How do you build light ?????

[Paul Taylor]

So I picked up two profile planes this past Saturday that belonged to my flying buddies. One was Profile Shark the other a little Scrapper. I think both had a Fox engine on it. 35 I think, but could have been smaller. Any way these planes felt lighter then the little Scrapper I am building, and I do not even have an engine on mine yet.
What is the secret to building a light plane? For some unknown reason (at least to me) all my stuff comes out heavy.
 

[wmiii]

What has helped me the most is, glue is not a gap filler, all joints must be tight, sandpaper is your best friend. As Bob Geiski said, use only enough glue to do the job.

 Walter

[Randy Powell]

There was an article in a recent Stunt News that Pat Johnston wrote about how to build light (Design Column). His basic words were: use light wood and remember, air weights less than wood or paint. Any place you can not have wood, you lighten the plane. So, hollowing blocks, cutting out extra wood in leading and trailing edges, etc. tends to lighten the project. Use enough paint to cover, but no more. We all tend to over build planes when we start out. Just takes time to learn the tricks of where you can remove wood and where you need it for structural rigidity.

The biggest single thing to remeber is,  use light wood.. I had to use some 7lb wood for a top block on my current project. It's hollowed out as far as I dare. Sucker is just about transparent. It's still heavier than the bottom block that was 4lb wood and isn't hollowed out nearly as much.

[Clancy Arnold]

Paul
I sent you an E-mail but then realized that others might want to have the information. 
Attached are two charts that I made up to help me select the right wood for my models.

To use the charts you go down the left column to the wood size you are weighing. 
Go across to the weight of the wood you are weighing in oz or grams.
Go up to the top to read the density.
For example: a sheet of 1/16 x 3 x 36 weighs .62 oz (17.6 grams).  What is its density?  Go down to 1/16 x 3 x 36, go across to .62 oz, go up to read density is 10 lbs per cubic foot.
Leave that piece for the R/C fliers.

I have this in an MS Excel file if anyone wants it.  Much easier to read.  Just send me an E-mail or maby someone here will put it in the download file.

Clancy

[James Lee]

Another thing to do, although it is a bit cold hearted, is to do a thorough post mortem on your broken models.      By examining what did and didn't break, you can lighten the unbroken parts and improve what did break.  Back when, all my models would basically break into four pieces -  wing panels and front and back half of the fuselage...  eventually I realized that the wings were overbuilt and the fuselage could be lightened...  A common comment is that if it doesn't break something on a hard landing it's overbuilt....   Some truth to that!!!
Years ago my Magnum went straight into the concrete at the Nats....   flopped over onto its wheels and sat there....   Looking rather undamaged...   the prop wasn't even scratched!!!  It wasn't particularly overweight (62oz with Saito 45) but definately overbuilt!!!  And yes the wing was actually broke in half and the fuselage split.  But it was a learning experience, in more ways than one!!!
Good luck!!  
Jim

[wmiii]

As Randy said use the best wood you can get, to paraphrase Jim, model
airplanes should not be built to survive crashes .

 Walter

[peabody]

Noel "We have the Technology" Drindak has a terrific piece on building light in the next STUNT NEWS.....Noel creates 52 ounce Buso Kestrals powered by PA .65's....so he knows from light.
Very, very interesting....

[phil c]

If I had to rank things, I'd put it wood, paint, building, and glue as the ways to build weight fast.  The balsa density calculation sheet is great.  Just think, on a typical big stunter that might weigh 25 oz. or so bare bones built with excellent wood would be so easy to pork up to 35 oz. or more just through poor wood selection.  Just grab some 8lb wood instead of 5 lb.  Paint is next.  One solid coat of paint(or filler) can easily add two ounces or more that have to be sanded off before the next coat goes on.  7 or 8 oz. excellent paint jobs are possible, but just a few careless passes with the spray gun or hitting "just a few extra spots" can add ounces that are invisible.  Dope isn't so bad 'cause it takes so many coats to get a good film it's often easier to stop one too soon than ten too late.

Take a note from Sparky's excellent photo presentations.  If the wood work underneath is excellent the finishing is always a lot easier and lighter.

Epoxy glue especially can add weight fast, fast, fast.  Be very careful.  Gorilla glue or similar polyurethanes can do just about everything epoxy does(once you learn how to use them) except fuel proof the tank compartment.  It only takes teeny, tiny dabs for most joints and any excess foams up and sands or cuts off easily.

[peabody]

Balsa/wood is just 1/4 of the weight of a typical stunt plane....

[RC Storick]

Balsa/wood is just 1/4 of the weight of a typical stunt plane....

Well lets see. 23-28 oz hardware. Engine,spinner,prop,pipe,header,tank,coupler,bell crank,lead outs,wheels,LG wire,tail wheel. Now come the covering and finish. It is possible to finish at 7-8 oz but most will finish at 10-12 for a 700 sq inch airframe.

I can finish a plane like this at 57 oz but most will do it in the mid 60tys. so we'll say 65-66 oz.  66-40= 26oz Who here has built an airframe at 26oz ready to paint?

That's how I figure final weight. Start backward.

[RC Storick]

Well Sparky...

My new Genesis Extreme is ready for color at 22 ounces! It has all the fillercoat on and sanded and should require only a couple of ounces more in color and clear. I'm aiming at 48 ounces Bob Hunt

Thats a good weight! How many SQS? Is it 690-700?   Like you said there is no need for heavy fuel proofing with electrics. You weren't included in my thoughts when I posted this and you models are not of the type I was thinking of. All this combined with you being a world class builder leaves little to wounder why your plane will be light!

[peabody]

Electrics do not need the internal fuel proofing either....

[Dennis Moritz]

No cg change during flight. Also worth something (a lot) in terms of weight/aerodynamics interplay. Not precisely an issue of lightness, but related.

[Paul Taylor]

As Randy said use the best wood you can get, to paraphrase Jim, model
airplanes should not be built to survive crashes .

 Walter

I guess I found part of my problem. I build them to surive crashes. 

Good stuff in this thread.

[Bill Little]

Hi Paul,

Build them to fly, not crash if you want maximum performance.  I think it was Billy Werwage that told me that if it doesn't turn into tiny pieces on a crash, it was too heavy and overbuilt.

Wood selection, fits, and types of glues are the starting point.  CA glue is one of the heaviest ones we use along with epoxy!  When wanting to save every gram, Ambroids, Sigment, Duco, Elmer's Glue All, etc., are lighter.

Sanding everything properly is also a great factor and hollowing blocks kill a lot of ships.  If I cannot see a bright light through the wood, it ain't thin enough.

Once you have built the airframe as light as you can, the finish can be the other killer.  Only enough paint/filler should be left on the plane to make it look right.