What is lighter?

[Gary Dowler]

Hiding grain in sheeted surfaces.  What will add less weight, covering it with silkspan, or filling with sanding sealer?
Posted this in building techniques, but wasn't generating any responses. Need to get on it soon.

Gary

[goozgog]

Hey Gary.
 
  It depends what you're building.  I prefer paper
since it adds a lot of stiffness and crash resistance
and that means I can make the structure lighter.

  I think all good finishes should add strength.
Sanding sealer just adds weight.

  On full size 600 sq/in stunters I use a lot of
glass/carbon-epoxy finishes..  It sounds heavy
but the finish is finished before I apply any
color.  It's light compared to a good dope finish.

Hope this helps.. - K


   

[Gary Dowler]

Hey Gary.
 
  It depends what you're building.  I prefer paper
since it adds a lot of stiffness and crash resistance
and that means I can make the structure lighter.

  I think all good finishes should add strength.
Sanding sealer just adds weight.

  On full size 600 sq/in stunters I use a lot of
glass/carbon-epoxy finishes..  It sounds heavy
but the finish is finished before I apply any
color.  It's light compared to a good dope finish.

Hope this helps.. - K


 

I like the idea of a little extra crash resistance. This is a scale project, which means it's already over weight....

[Air Ministry .]

Yea , Tissue & Dope weigh 2/10ths of 5/8ths of stuff all . . . .

One of Urtnowskis tapes has him ' Five Coats ' on the bare wood .

Doping till the timbers caught a gloss , theres less later coats , after the tissue . Maybe .
Ive got the local art store to get me some ' Unadultatrated Talc ' . The Babys bum stuff with the oil & scent will crack up & weighs a ton .
The Art Supplies stuff ( Maybe Drawing office supplies too ) is chalkyer & light and sands right off easy , hopefully just leaving it in the
cavities , or thicker for putty for dings .

You can throw multitudeinous layes of tissue on in places ( tho the Gloss Sided stuff dont like that ). SEVEN LAYERS on parts of a few things , seemingly with no weight penalty . Balsa without tissue is weak .
A Adamisin artical tho has pre coated polyester resin sheeting onto the ribs , then on the outside once adheared , a coat there .
Effectively double skined resin with a balsa core .

Extra layers / strips of tissue as filler and / or reinforcing , at emenage / fin - tailplne - fuse joints etc beef it up ,
if ' Dope Rich ' . i.e. pretty saturated at the end of the day .

Piling coats on when its not hot leads to problems tho , particularly with butrate . itll take forever to cure , continually deforming the structure
This is called WARPING to you and me .

The Dupli Colour Clear auto lacquer as top coat ( the big can ) is pretty fuel proof and compatable . Ive even alternated Dope & clear
with no issues .

A Urtnowski tape has you sanding each coat and 5.000 holes patched .
NOW I throw on Five Coats , knock off any lumps , a few more , dress flat quick and carefull with 320 , then clear top coat
or silver colour base .

[Steve Helmick]

.2 oz CF mat. It must be, 'cause all the stunt grunts use it.  Steve

[Dave_Trible]

How light is more about what you sand off than anything else.  Balsa will dry out and shrink over time as well as the dope or whatever medium will shrink, except perhaps epoxy.  With no type of covering the wood grain will reappear within a year or two.  The covering somewhat fills or otherwise hides a lot of that for an extended period.  If you simply fill the carbon or silkspan much of that weight will remain.  If you seriously sand each coat you will remove a good amount of the dope, silkspan or carbon each time.  On solid surfaces you might end up with half the original material thickness and weight but have have a better finish due to the sanding .  On my latest project I mostly filled the carbon with clear.  When I got real aggressive with the sanding-150, then 320, then 400 wet grits I sanded off over three ounces.  In places I sanded clear through the carbon and had to do some patching but the savings in weight matters....Wish I had originally done more sanding and less doping, however there were still areas of porosity in the carbon that had to filled with spot filler that couldn't be seen until base color was applied...one step forward, two back. 

Dave

[Doug Moon]

I have found old 00 silk span adds the least amount of weight to sheeted surfaces.  The older stuff is a little harder put on as it almost falls apart when it is wet.  BUT the ease of sanding it flat is a dream compared to other stuff. 

[Dennis Toth]

I think that you need to cover the bare wood with either silk, silkspan, carbon fiber vail or 1/2oz fiber glass (applied with dope). If you just fill the wood, as the finish ages it tends to open up the grain and crack.

Best,   DennisT