Re: RSM P51d build

**Cribbs74** Thu Apr 16, 2015 11:06 pm

Well, that was kind of what I was expecting to see after your previous post. That's an expensive lesson on dope. Hope it gets better.

But, whoah! That's one tough wing eh?

ian1954 Fri Apr 17, 2015 4:45 am

Cribbs74 wrote:Well, that was kind of what I was expecting to see after your previous post. That's an expensive lesson on dope. Hope it gets better.

But, whoah! That's one tough wing eh?

It was an expensive lesson but it could have been worse. I have three other models awaiting covering and I was tempted to do them as a batch following my pleasure with the initial progress. It is a good job that I didn't. I would be more than miffed now!

Still, I hope it is a warning/guide to other members. The dope I used was "modeling" dope but the shrinking variety widely available here. It is a bit of a conundrum - was it the dope, the wood or the tissue I used.

It is difficult to find the details chemicals used for plasticisers and retarders here or commercial products. It will be a matter of trial and error but not on this scale. Whatever happened to the Humbrol dope I remember?!!

I have to say though that the kit was superb and enjoyed the build. It was my finishing that ruined it Sad

The wing was extremely strong. I laid it on the floor and stood on the centre section to remove the bellcrank. It did not break! I had to stamp on it using my heel.

Once the covering was torn a punctured with a screwdriver the wing was then easy to break. One thing I have learned it that the tissue, silk and dope finish is far stronger than the iron on stuff and adds a great deal of strength to the wing.

You live and learn!

getback Fri Apr 17, 2015 9:06 am

Man That SUCKS AIR !! I see you had your Pulse checker out and the outside stove I love it , I want one but don't know why Rolling Eyes

I am glad you didn't go for the other airplanes covering while waiting . I have had a lot of problems with warping lately But for the whole plane to be demolished is a real killer . Ian if you want I will see if I can get this Flexall and send it to you ! I have been wanting to do another silk span but I just don't know what I may get myself into Surprised

Eric

ian1954 Fri Apr 17, 2015 1:22 pm

Thank you for the kind offer Eric.

Send liquids to the UK and they will be confiscated. Especially if Her Majesties Customs & Excise combined with Border Force (or whatever they are called these days) don't understand what it is! (this is also not likely)

Then the Coup de grras - Royal Mail won't handle liquids, lipo batteries or anything potentially flammable. We live in strange days!

Ken Cook Sat Apr 18, 2015 6:44 am

Ian, I've had to discard many of the pieces using traditional finishes on laser cut kits. Dope isn't the same as you mentioned nor is the coverings used. Silkspan is no longer available at least the type that you see Windy using. I have about 12 sheets left of the old Sig silkspan. Laser cut kits with a dope finish is very susceptible to twisting. While your observations initially proved that the wing was exceptionally strong, it's short lived. The dope unless plasticized becomes what I call the potato chip stage. UV rays quickly and I mean within 2 months of use render the covering so brittle that if it doesn't split on it's own, it will even tear with a tough weed on landing or high grass. I don't have this problem with Sig dopes when I use Sig Lite Coat as a final. Sig Lite Coat is the lowest shrinking dope currently out there and in my opinion is the clearest of clears in dope. I probably have anywhere from 12-14 coats of dope on a wing when complete which is a variety of brushed and sprayed coats the majority of them being sprayed. All attachment coats are brushed. Another issue is like I mentioned is the taughtening part, while the outer pieces of the structure on a laser cut kit has a lot of integrity, the shrinking that takes place with the lighter laser cut wood can just explode the ribs internally. If they don't break, they bow very badly. This is very common with silk due to it's ability to really shrink and crush the model. Polyspan is something many of us switched to and I have done so myself and I find it stronger than silkspan, cheaper and I also found that it does have some elasticity to it which is a benefit. My Brodak Oriental https://www.facebook.com/PhillyFliersCL/photos/pb.513140418756097.-2207520000.1429357046./840692392667563/?type=1&theater needed some tweaking and nursing along the process of doping due to various pieces wanting to twist. I very rarely build from kits for this reason, this kit was given to me so I built it. The cost of dope finishes for me totally outweighs the need to use it in my opinion if one is sport flying. The health hazards is another. While many enjoy Windy's videos, what most people don't understand is how it did have a negative impact on his health. Many of his earlier paint jobs was experimenting with newer and far more dangerous products. If I have a silkspan plane that is in need of covering, I find all of my crap iron on covering and go right over it. Ken

JPvelo Sat Apr 18, 2015 2:50 pm

Ken,
I am currently building a corsair that will be covered with polyspan and sig lite coat. I plan on shooting it with primer and paint after the poly is sealed with dope. Should I use a plasticizer?

Jim

Ken Cook Sat Apr 18, 2015 7:28 pm

Jim. Sig Lite Coat will be fine. I believe it already is plasticized and it doesn't shrink like Sig Supercoat. It won't shrink open bays however. You must use Supercoat first and then use Sig Lite coat to stabilize . Sig Lite Coat is also great to use on lighter structures like free flight. Sig Lite Coat can be used on planked surfaces from start to finish. It comes in the bottle like syrup and really needs to be thinned out. I highly recommend using Sig thinner as it's the slowest of them all. Ken

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