I'm trying to get the NP Explorer 60L (aka low wing trainer) ready for flying in the next week or two, and need advice from anyone with experience removing air bubbles from the covering film NP uses on their models. What's the recommended temperature for this material?

I posed this question to Nitroplanes' customer service, and got this response:
"We do not have that kind of info as we have never had a problem like this before. You can try out rcuniverse.com and perhaps one of their members can refer you to a solution."

Thanks!

PJ

Yup you asked a "build" question, not a question about a problem with a shipment. They only field the latter which is why you were referred here.

Re: Temp

A set temperature is not good to go by as if I give you a setting it may be either too cold or too hot depending upon your own technique.

What you should do is apply heat until you notice a slight discoloration of the covering. At this point you found the right temp. ( the normal color will return when it cools ).

Note that this point is right on the edge. A bit more and you can start damaging the covering, a bit less and it will have no effect.

That said, just a bit beyond where the discoloration occurs the material begins to shrink, a bit beyond that and it will tear.

You also need to be sure to first heat the seam areas with an iron. Get these affixed first. Then let them cool and get the surrounding areas, making sure NOT to get near the seams again. If you don't do this, the covering will pull away from the seams, exposing the wood under it, or just making it look poor.

I typically hit the seams with an iron, then I use a heat blow gun to get the rest of the plane.

I apply heat until the bubbles seem to INCREASE, then I continue in a widening circle which causes these bubbles to flow together. Once you have only a larger bubble, I pierce the covering if needed, with a pin to let out the air, or I merely let it cool, as the plastic shrinks when it does so. As it cools I smooth the covering with a heat glove. The glove is merely to make sure that the adhesive is pressed against the underlying wood.

The results can be spectacular... a wrinkly plane ends up looking like it has a fine finish.

No manufacturer is immune to wrinkles... I recently put together a Giant Scale U-Can-Do-3D that looked horrid out of the box. I spent a good 2-3 hours getting rid of the wrinkles on all of the parts and tightening up the covering.

One other caveat.

When doing smaller surfaces ( such as the elevator and rudder ) and control surfaces, place the item down on say a work pad on a flat surface.
Work on one side and as you go over the material make sure the item stays FLAT. Ideally clamp it down so it cannot bow out, etc.

As you heat up the covering the item can and will warp as the covering pulls tight. You want to be sure that this does not change it's shape. by flattening the surface, etc. as you start to remove heat. It's important to keep the item flat until it cools. Be careful with this.

Thanks for the detailed answer, opjose ... I'll post some pix when we git'r done.

I was pointed to this handy tech guide on the Hobbico/Great Planes website. It tells you how to "sneak up" on the best temperature if your covering is not MonoKote:

http://manuals.hobbico.com/top/tighten-covering.pdf


PJ

I've only had so-so success with that technique on NP's covering, although it depends upon which plane and which covering.

That guide does NOT advise letting the bubbles meld together nor letting the covering come up a bit.

I find that I need to do exactly that to get a good taught covering that will not wrinkle again later.

The "Bubbles over the sheeting" heat setting is exactly what I am looking for.

If I fear that there may be adhesion problems I go over the covering with a slightly colder iron later.

Your results may vary.

In any case NEVER forget about the possibility of warping the surface in all of this, else you will be kicking yourself for doing so.

Hint: With Nitrplanes covering...

Top Flight Clear Coat is your friend.

Use it ( or something similiar ) or loose your covering in a short time due to fuel attacking the adhesive and seeping in, causing all of the covering and trim to let go.

It's a cheap fast safeguard.

Apply several light coats on your finished plane with any and all clear plastic parts removed.

Thanks for the follow-up.
The iron at 325 is doing a good job of lifting the wrinkles ... they swell up a bit, then settle down ... after which I can go back over the finish with firm pressure and bond the film to the wood.
I tried one patch with the heat gun, and the risk of damage (from my clumsy effort)became apparent quickly.
I'll give the clear coat a try ... usually I seal Monokote edges with clear (laquer) nailpolish. I also go over the entire plane with Meguiar's 'Deep Crystal' automotive polish, which not only gives a fanastic sheen to the plastic film, but affords some protection from exhaust residue.
Cheers!

PJ

Nailpolish is OK, but a bit localized. You typically don't get the entire plane with it.

Automotive polish makes the finish look good, but does not really seal the edges all around.

You can use something like Krylon clear coat, or anything else that might be fuel proof.

I'd recommend that you do this before your first flight. It makes a huge difference to how the covering holds up.

Something to add to opjose's excellent explaination. On some of the N/P's birds they are painted over the covering. You may not see a change in color as it's painted over, when you heat them up.