Hello, Im covering my 1st model. Problem, Monokote dips between ribs. When Im covering the wing as I iron between ribs without applying pressure just to heat monokote it dips between ribs. How do I prevent that? I want that hard flat finish. Thanks.

I'm new to the hobby, but have studied many planes in detail. Unless the wings are sheeted with balsa, there is going to be dip in between the ribs. From what I've seen, this is normal due to the tightness of the covering. Since i'm new to this, I could be wrong, but this is just what I observed on other planes. Also, I have an LT-40 and when I covered it, I noticed the same thing.

Exactly right!

Full-size aircraft covered with fabric are the same. The true airfoil is not obtainable.

Yes a little sag is allright,if you pull it tight and tack it down then do you shrinking it should come out right.

Hi all, thanks for the input. Im continuing to cover now. This helps me alot. I sounds like its unavoidable.

The only way to get the true airfoil would be to do a wooden or composite layup and actually form it. Covering materials have to be supported. As mentioned, this is true to fuel scale as well.

If you're looking for that flat look, what you can do in the future is omit the cap strips and sheet the wing. It adds a little weight, but gives that flat look. I've done it on a few of my planes.

Minn Flyer, I just finished the wings on my LT-40. I havent covered yet, but the wings are completely finished ready to cover. Is it too late to do what you said or not?

the covering material shrinks more in the longest direction...perpendicular to the roll. When you cover a wing, roll out the covering with the roll parallel to the fuselage and cut your wing-panel covering from the sheet like this. If you turn the sheet sideways, it shrinks front-to-back and dips deeply between the ribs. If you do it the right way, it shrinks along the span and dips much less between the ribs.

It makes a REALLY big difference on a wing that has an unsheeted front section.

No matter what you do, the Monokote will dip because of the curvature of the ribs themselves.

Jim Casey is correct, it makes a big difference in how you align the monocote, you must keep the grain going with the span of the wing.

Excuse me, folks, but I've been using Monokote for 28 years and I have yet to see a grain in the material. It is milar and, to the best of my knowledge, has no grain. You can put it on any direction with the same results. As far as sag goes, on an open bay wing, sag is normal, and as was said by 4*60, is found on full sized fabric covered aircraft. So, when using Monokote, tack it to the center section, pull it tight and tack it to the tip. Tack it to the leading edge at the middle of the span, pull it tight and tack it to the trailing edge. Keep pulling it tight as you continue to tack it all around the wing. When you've ironed it to all the edges, use the gun and it will look beautiful. The sag will be there, but not very pronounced.

You won't "see" the grain, but it's there.

When they extrude the plastic, the takeup roller runs faster than the stuff comes out of the extruder, stretching the film at the moment it "freezes" . This aligns the grain, or properties of the film. Little or no stretching occurs along the width of the film. When it shrinks, it's trying to return to it's unstretched state.

Try it for yourself. Cut one wing panel across the roll, and one lengthwise. Cover a left wing with one, and a right wing with another.

Where I learned about it was on patching wings. Grabbing a scrap out of the monokote box, it's hard to tell how it was aligned with the roll. When you get a dippy patch, you know it was sideways.

And yeah, I have been using monokote since before dirt was invented, too. Even before it was "Super".

Jim, I guess your reply shows that there's always things to learn, even for old dogs. I would guess that, since most wings would be covered with the Monokote's six foot length running spanwise, that the shrinkage would be the greatest and dips between ribs less pronounced. Consequetly, one would never see the reduced shrinkage from covering across the span. Thanks for enlightening me. That's one of the great things about this forum.

Frank T.

Experience is a great teacher. If I could just learn to stop blistering my fingers with a covering Iron, it would be great.

With all the small electrics these days, many have half-spans that fit nicely across a roll of covering instead of the traditional endwise layout. These also tend to have very lightly constructed wings with no sheeting. Ergo, a high chance for a sideways, dippy covering job. Also, since the wing depends on the covering film for strength or at least stiffness, a dippy covering job will sacrifice properties in that regard also. And it's already been pointed out in this thread that a dippy covering job deviates more from the intended airfoil--sacrificing flying performance.

The Covering material's direction oughta' be in the instructions, both for the covering material and for the airplane.

SmallFry,

It's never too late, but if your wing is ready to cover, you would have to remove all of the rib cap strips. Probably more hassle than it's worth.

I have a model at home that demonstrates the difference in shrink very clearly. I covered the bottom of the wing with the monocote grain running with the chord and the sag between the ribs is MUCH greater than it is on the top of the wing. The top is fairly smooth. As smooth as you could expect from an open bay wing. The bottom sags at least twice as much as the top and the only thing I did different was to cut the the bottom panels from the roll with the length of the roll running with the chord of the wing.

If you don't cut your control surface panels from the roll lengthwise, you will also run into more issues with the covering lossening up when you set the model out in the sun.

John

If this is your first kit, or even first model, I would suggest not pulling the cap strips off and fully sheeting the wing. Get the model in the air and build up some stick time. Worry about modifying kits once you get a couple under your belt and you have developed your building skills a little more.

just my .02
John

John is right.
An LT-40 flies GREAT as designed. Having the ribs visible in the covering is part of its charm. ALSO, the open wing structure can give a little and bounce back, and if necessary, it's easy to repair. All good traits for a trainer.

Do the sheeted wing when you are skilled enough to stay ahead of a fast plane, and not likely to bounce it off the graound.

hover your sealing iron over the sag ,allow it to cool then reheat do this until your sags are gone.

That will only work on areas that need to be reshrunk. If you apply the covering in the wrong orientation, no amount of reheating and shriking will change the fact that the covering dips between the ribs more than it would if applied properly.

John

If the kit is like my ARF, no capstrips on ribs.