Hi,
I''ve been practicing taking out the wrinkles in ARF covering with a covering iron. My test subject was an old not-great quality p-51 ARF (it looks like a wrinkled dog).

I used tips/instructions from the following post by krproton:
http://www.rcuniverse.com/forum/m_64...tm.htm#6494490
(may need to scroll down a bit after clicking to see it)

My practice session worked out well and was on the fuse with mostly plywood sheeting behind the covering.

My question relates to de-wrinkling a horizontal and vertical stab on my new trainer ARF (my actual immediate goal). They are made of relatively thick balsa sheets.

The above link is very good and informative, but does anyone have any specific tips for de-wrinkling balsa-sheet-stabs in particular?. My concern is that I might cause the stabs to bow even a little, which would be terrible. Any tips or elaborations on the technique specifically for avoiding that?

Thanks

p.s. The tail stabs were the only wrinkled parts in my trainer ARF. Everything else is really nicely covered.

Attach a flat metal plate to the side opposite the one you are working on, using clamps.

Use an iron or gun to eliminate wrinkles on the work side, moving the clamps as needed.

Let the covering FULLY cool before swaping it for the other side.

This should eliminate the potential for bowing or producing curves where unwanted.

OK thanks. I was also sort of looking for confirmation that there is a high likelyhood of bowing happening in that process... and I see that there is given your suggestions. I''ll do it that way.

When I assembled some trainers before years ago, I was so impatient that I just ignored flaws like wrinkles. On my last trainer, the whole tail plane was installed crooked My whole approach now is a bit more thoughtful.

Thanks

It depends upon the material, how much work you have to do ( or rather how many wrinkles you have to remove ) and how hard the underlying wood is.

I tackle this before building the plane, so I can lay the surface on a table and clamp it down to avoid bowing.

That way I can be a bit more agressive removing wrinkles.

Irons are great at making sure that the covering adheres properly to the underlying wood, but you can eliminate wrinkles quicker and with more ease using a heat gun.

I typically go over the entire surface with the gun first to shrink the covering, then go back and hit it with an iron to make sure the glue adheres.

That''s a good technique. Warp potential varies with the skill of the "shrinker" and construction of the stabilizer. If the stabilizer flops fairly easy then it is quite possible to shrink a warp in it. If it''s good and solid then the potential is less. For example, on a balsa electric I used the heat gun and covering to keep the rudder straight. On some of my other airplanes I would blow a hole in the covering before it shrinks enough to bend anything. If the stabilizer isn''t very flimsy and you use just enough heat to tighten it you won''t have a problem.

I wrote a reply to this earlier (responding to specific quotes), but it's dissappeared...

Anyhoo, part of what I said in the reply was that I don't have a heat gun and none of my LHS's have them for some reason.

I went ahead and tried to iron out the wrinkles with my covering iron... there were so many. It started out fine on one side, but the other side where there was A LOT of them and BIG ones... it just didn't work out.

To make a long story short, I ruined the horizontal stab [] It's got a nice little bow in it now front to back

Sooo, I'll need to get some same thickness balsa and cut and shape a new stab.

Question: What is the easiest type of covering to put on it for dolts who can't even wrap a sandwhich properly? Or better yet, what would be a good painting option? Is there something I could paint onto it to first make it smooth and then paint color on that?

Thanks

That's easily fixable, but you will need a heat gun...

A good place to purchase them is at a local hardware store.

They are frequently sold in the electronics or tools sections.

Anyway, take the STAB and place it on a flat surface.

Heat both sides with the heat gun and then press the stab down against the surface to straighten it out.

Clamp it in this position and apply heat to remove any remaining wrinkles let it cool fully while it is straight.

If it is still a bit bowed, reheat... remember that the heat will pull the covering taught so you want to adjust your attack accordingly...

You would thing that all you need to do is to heat the convex side, but you really need to heat both sides, to loosen one ( to let it streatch ) and to tighten the other ( to pull it taught )... thereby fixing the problem.

Oh thanks. Would be nice to be able to fix it... un-cluttsify my handy work

I thought those hardware store ones were too hot.... I was just looking at ones on the advantage hobby site... those ones are 1000 watts. Can it be much more than that in watts? Ordering from advantage will take 2 weeks or more so... I'll check the HW store then.

Cheers

I checked a major hardware store catalog. They only have 2000 watt models... lowest temp setting is 300 C (572 F). The hobby ones are only 1000 watts. Would 300 degrees C be way too much?

You can use a heat gun from a hardware store, but I really don't recommend them. Especially for people without a lot of experience with covering. These types of guns produce a lot more heat the heat guns we use for covering. While they can be used it's extremely easy to get the covering too hot and melt it with these. My advice would be to just order one from Tower hobbies, they are only $12.95. [link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJD39&P=ML[/link]

Ken

Thanks. I'll keep looking around. One of the hobby gun descriptions says that the nozzle gets to 400 F, so if I still find one that's about 1000 watt and has a 400 F setting, then perhaps that's an option.

If I order a heat gun (2+ weeks delivery time), then I thought I almost may as well get H9 replacement stabs also. But I'll hold off a bit and see if I could fix this latest masterpiece of mine.

I'm right now seeing what a block of wood and 5 kg's of weight would do... it's placed on it with the bowing-out side up. I'm too tired to bother with heat right now, but tomorrow I'll try first heating it with the iron and then adding the wood block and weights... and maybe try 10 kg's or more weight (actually that would be overkill... enough weight to straighten it is all that's needed).

Thanks for help

That's basically what I did.

My heat iron was purchased at a hardware store and has a dial that goes from 1 - 10.

I can dial the heat up from room temp to "too hot for covering!".

After a bit of experimentation ( the dial lies! ) I found that 6-7 gives me the best results.

Yeah there's gotta be something like that somewhere. Cooking thermometer probe could be used to test the setting.

I just upgraded by stab straightening apparatus to use two stone floor tiles and two 5 kg weights. It's a lot of weight but the tiles are perfectly flat and distribute the weight very evenly. That might just do it.

Remember that you DO need to heat the covering and then let it cool so the whole thing retains the desired shape.

After you've done all of this once or twice, you'll never face a bowed covered surface with trepidation.

It's really easy to do. I had to do this to a rudder on one of my airplanes last season. After leaving it out in the hot sun all day for the annual airshow I noticed it was a little warped when I went to put it away. I pulled out the heat gun and two minutes later it was good as new and no worse for wear. Like opjose mentioned, it won't work if you don't hold the piece straight until the covering is completely cooled.

Thanks a lot for all the help. I got a fully adjustable heat gun from the hardware store. It has stepless adjustment of heat from 100 C to 600 C. On scale of 1 to 10, I have it set to about 3. At that setting it contracts the wrinkles with the nozzle at just under 2 inches from the surface. Works great.

There were many really big wrinkles on the bottom surface of the stab and I got them all out. After the final step of bonding with the iron, I immediately put the stab under the stone floor tiles with 15 kg on top. The "inverse camber" bowing flattened out completely, but then I noticed a little anhedral. I think that resulted from having the weights too much toward the center. So after a second go with the heat gun and iron on the flip side, I distributed the weights evenly over the whole surface. Now both the camber and anhedral are gone. Whew!

But I find that it's necessary to always use the 15 kg even compression on it immediately after treatment (it's a solid balsa stab).

There are a few minor wrinkles on the vertical stab. I'll use the same process (with weight compression afterward) on that.

Cheers and thanks again

Excellent... now I'll just send you my plane parts to straighten out...

You sure about that? [winking smiley] (punctuation marks get messed up in the editor these days)

Looks like a standard heat gun is a good option as long as it has stepless adjustment and you take proper care to find the right setting. I practiced on an old really junky arf that I have and initially I started out at a distance of 5 inches or so and carefully moved in closer.

I suppose it could have use also for heating the crankcase of an engine to loosen bearings. 600 C ought to be enough for that I would think.

It's also quite useful when you are breaking in a brand new ABC engine.

Heat the cylinder head for a while first, crank the engine over by hand to get fuel into the head, and start it up.

This will prevent scoring and other minor problems, such as not being able to crank the engine over.

You also can use it to soften/remove epoxy, shrink heat shrink tubing, etc.

I rarely put mine away.

This can be quite an aggrevating process. I needed to do one more go on the bottom side to minimize some creases that I had caused yesterday with the iron. I accomplished that, but then after removing the weights, there was a slight anhedral again. Sooo, I heated up both sides with the heat gun (not as much as I would if removing wrinkles)... that significantly decreased the anhedral (after being under weights while cooling)... and now there seems to be a very very slight inverse camber again... very slight though... uhg.

I'll leave it under the weights over night.

It's basically like you have to keep doing this until you happen to get no bowing, then quit while you're ahead. But it's so slight now that maybe it's fine. The very slight anhedral might make leveling the horizontal stab a little harder, but... whatever. I guess I'll just have to keep at it.

Just another idea.
I have a Top Flite P51D that I am building. The whole plane is severely wrinkled. Needless to say I am very disappointed with this plane. Today I tried something new, as experiment. I put the horiz stab in the oven. Set the temp to 250, laid a small towel down on the rack and placed the stab on it. I let the oven heat up, keeping a close eye on it. As it heated up and got closer to 250, the wrinkles formed larger bubbles but smoothed out a bit. I took it out and rubbed it down with small towel. That got a lot of the wrinkles out. Then I used a covering iron over the whole thing. I tried the oven a few times then I used iron after each time I removed it. I would say it was about a 90% success. Unfortunely I can’t put large pieces in the oven.
The rest I’ll just have to do as others have discribed and hope for the best.
Shubova
[8D]