greenboot

My Feedback: (1)

Does Monocote stretch and shrink the same in both directions? On my last covering job, I decided to always cut the long dimension of every piece along the length of the roll. That seemed to work better. Of course on the big wing pieces you have no choice.

Has anyone ever taken a piece like 3x3" and just put it in an oven to see how much it really shrinks? I wonder if it would still be square.

Tom

SALMONBUG

My Feedback: (1)

as far as I know, there is no "direction" in the monokote

JWN

My Feedback: (42)

Yes, Monokote shrinks more in the direction of the length of the roll than across. You should always cut the material to maintain the length of the roll with the length of the part. If you ever cover a wing with the roll length orientated with the chord of the wing, you will find the covering dips further between the ribs than it would if applied with the span. I have a model at home that drove this point home very clearly.

On a solid surface, you will have greater sag/wrinkle issues with temperature changes.

John

capthis

My Feedback: (67)

I have a freind that has built many airplanes for people and such and is an excellent builder. He swears there is a direction, to the stuff. Of course he can also tell you what covering you have by smelling it? Sound weird I thought so too but he sure enogh can tell the major brands apart by the smell! I tell him he has sniffed to much glue!

greenboot

My Feedback: (1)

Funny that nobody ever mentions this! Maybe THIS is the "hidden" secret.

Tom

SALMONBUG

My Feedback: (1)

I learned something, but I have to admit it won't change my covering technique, the diference of shrink regarding the direction should not be very hig......

JWN

My Feedback: (42)

It shouldn't be, but it is. If you are looking for the best covering job you can do, you'll pay attention to the "grain" of the covering.

John

SALMONBUG

My Feedback: (1)

I just made a "live experiment", went to my workshop, cuted a square small piece of oracover, removed the protective paper, and gave it to my wife with a magnifier. My wife couldn't tell me how I cuted it.

JWN

My Feedback: (42)

Apply heat to it and see the results.

You cannot "see" the difference without applying heat.

John

SALMONBUG

My Feedback: (1)

live experiment part two.

went to my workshop, picked up my ironing tool, ironed the small square part on the kitchen table, still look square, but I admit that the piece is maybe too small to allow to see a diference.....

JWN

My Feedback: (42)

How about an even better experiment? Cover the top of the wing in one direction, and the bottom in another. Compare results.

Then, cover one side of an elevator in one direction, an the other side in the other direction. Place in the sun, compare results.

John

SALMONBUG

My Feedback: (1)

There is no reason to not thrust you, if you tell it it's certainly thrue
I will pay atention to that in the future

BingoFlyer

Unfortunately it does have a grain and shrinks more in the length direction than in the width. I was trying to skimp on MonoKote and thought that being plastic there would not be a difference in shrinkage. I didn't save anything as I had to do it over (the more heat I applied the bigger the sag between ribs).

Then I remembered my engineering background, it is caused by the way it is rolled between rollers during manufacturing (sheet metal does the same thing and causes problems in stamping because it stretches different).

MinnFlyer

My Feedback: (4)

The direction can affect the color as well as the shrinkage. Several years ago a friend covered a P-51 with Aluminum MonoKote. Near the tail-feathers, he sort of pieced it together with lots of small pieces to go around the dorsal fin. Out in the sunlight, you could see every little scrap as the sun reflected differently on them.

pinball-RCU

Even if it does shrink significantly more in one direction than the other (which seems unlikely to me), I don't see how that would make any difference in your covering job.

Suppose you are covering a square. Why would it matter which way shrunk more? Now suppose it's a rectangle? Why is it better to be tighter one way than the other? Loose is loose, no?

Please explain. I just finished a wing in which I ran the alleged grain chordwise on the wing. It worked great. Did I do the right thing, or was I just lucky?

Rodney

The difference is quite large, just cover a wing with the long way of the roll accross the cord. I'll bet you have to redo it unless you like big sags between the ribs.

rajul

My Feedback: (58)

John, thanks for the greeeeeeaaaat tip ! (you can see the word stretches more in one direction too LOL !). I think it is technically sound to expect anisotropic shrinkage in the film as the carbon backbone of the polymer molecules are oriented in the direction of the extrusion. It's kinda like miniscule springs arranged in one direction .

AlStack

My Feedback: (1)

I understood what you said, but I think I hurt myself doing it! Great tip, Who Knew???

Holeshot

Probably the GREATEST tip that I've seen since I learned to keep my fly zipped!!!

big max 1935

My Feedback: (9)

I think a lot depends on how tight you pull it when you are tacking around perimeter. Never could see any difference. The stuff only shrinks so much & if you don`t pull it tight when installing you will get sag. Way back in my mind I some times have a little guy that tells me things. One that if it did have a direction the manufacture would have told us! As much as they have sold they would want it installed right! May be a difference , but I bet it would be so slight it`s not noticeable!
>>>>>>>>>>>>>>big max 1935>>>>>>>>>>>>>>>.

SMALLFLY-

My Feedback: (19)

Yet another reason not to use monokote. I have never had an orientation problem with ultracoat, but like discussed before orientation while applying is subjective to how you want to cover it

cknaack

My Feedback: (1)

MonoKote does shrink more in the direction of the length of the roll. This is true of all thermoplastics. The film is produced most likely from one of two methods, blown film, or cast film. In either case, the process orients the molecules in a fashion that yields slightly more shrinkage in the length direction.
The downstream lamination and adhesive processes will also contribute to this effect.
Last but not least, the pigment used to produce each color reacts slightly different, causing yet another possible shrinkage change.
Although the shrinkage is measured in thousands of an inch (.001") it will add up when covering a longer wing panel. I agree with the suggestion to keep the length of the roll consistent with the length of the wing panel.

JWN

My Feedback: (42)

Sigh .......

Looks like I'm going to have to post pictures.

How tight you pull the covering makes no difference in the dips between ribs when the covering shrinks more across the chord than it does across the span.

John

Sky Chief

Thanks to all: Being new to this hobbie any tips I can get are gratefully appreciated

pinball-RCU

I measured a piece of yellow Monokote as close to 6" square as I could get it. I then mounted it in the jig shown below. I used rubber bands to provide a very gentle tension on the Monokote. I hit it with the heat gun, as if it were a wing panel. I measured the results. Each way was as close to 5-15/16" as I could measure.

I know this isn't the most precise science, but I think it shows that if there is a difference in shrink factor, it is subtle. It is certainly not like it shrinks twice as much in one direction as the other. Given the limits of my measurements, it could certainly shrink say 20% more in one direction than the other, but I doubt it would be noticable, given that you might pull the cold Monokote tighter in one direction than the other much more than the 20%.

To really get a good take on this, you'd probably have to use a 24" square piece, which I'm not ready to sacrifice until I see some more science from those of you who say it shrinks dramatically more in one direction than the other.

Until then, I say, put in on the wing in the way that minimizes your waste. That's what I do.