double covering

[Bootlegger]

  About 50 year ago I double covered a Road Runner wing with Japanese tissue, today I double covered a wing on  Twister profile with some silkspan, I left it loose so that hopefully it will not split when I dope it down, hope to have some "successful" pictures soon..

[Gerald Arana]

  About 50 year ago I double covered a Road Runner wing with Japanese tissue, today I double covered a wing on  Twister profile with some silkspan, I left it loose so that hopefully it will not split when I dope it down, hope to have some "successful" pictures soon..

Gil,

Bummer! Why you ask? I double covered my Trivial Legacy with Jap tissue and I'll never do that again! Every time I put a coat of dope on it, it wrinkled up. Very disappointing to see that happen. Plus it was a PITA.

It's poly span for me from now on!

Jerry

[Larry Renger]

As I recall, proper double covering was water shrunk silkspan with one coat of dope overlaid with Japanese tissue shrunk over it. The result was very torsion resistant and required not a lot of dope to seal.

Never did it myself, so take that as only rumor.

[Air Ministry .]

If you put the second layer on dry , with thinned dope , its just possable to remove it when you notice all the wrinkles , if you slap more dope on
as solvent . 

Er Um . ! We wont say how we know this  , .

One HAS to put it on WET , & use thinner , going from the middle outward .

Helps to pin it in a place or two . Can slide around so dont pre cut to tight on the outline .
Conversely its awkward to pull it around , damp . to align BEFORE the thinner goes on .

After that your stuck .

Youll also have well doped hands from smoothing it down out through and across , maybe lifting it in places as you go to avoid misalignment / wrinkles .

This only leaves the problem of blushing / Milky Colour from the moisture . Likely the thinners better for evaporateing it , thinned dope'd trap it ?? .

[Larry Renger]

The top covering was applied dry, bonded only on the perifery, then water shrunk. Then the dope would bond top and bottom layers to make a composite covering of great strength and minimal dope to seal.

This was a standard technique for large free flight models that needed torsional strength and warp resistance,
Hmm, could that apply to CL stunt?

Gee, does that sound a bit like SLC over Polyspan? See the thread on the finishing and paint section.

[Jim Kraft]

I double cover all thin surfaces like the stabilizer on the Humongous. I use medium silkspan first, then silk over that. Silk by itself on thin open structures is not very stiff. But with silkspan under it becomes very strong. It adds very little weight if any, as with a couple of coats of dope on the silkspan, it seals and then the silk does not take so much dope to fill. I use high shrink dope for the first coat or two, then switch to low shrink. Still looks great after years of flying. Dope is all brushed including the clear coats.

[paw080]

As I recall, proper double covering was water shrunk silkspan with one coat of dope overlaid with Japanese tissue shrunk over it. The result was very torsion resistant and required not a lot of dope to seal.

Never did it myself, so take that as only rumor.

Hi Larry, you are correct about torsional strength and I'll add the much lighter and puncture resistance

compared to a single layer of silkspan. I'd also like to add that I haven't seen good quality silkspan like

the kind included in most 1940's- mid-1950's kits. I consider the silkspan from GM(?) totally worthless.

I have double covered 1/2A combat models with "real" Japanese tissue(stockpiled for years going back to 1955).

The models, enlarged(From 160 to 195sq"s) Hoffelt 1/2A Monobooms , withstood two entire seasons of Combat,

with only minor tissue repairs.  I double covered some FAI power, two A2 Nordics  and one Starduster 900 FF ships.

As for covering a stunt model with double layers of Japanese tissue; it would really depend upon the type of wing

construction encountered.

Tony G