Lafayette

Hello and I am a scratchbuilder. I am building an airplane right now and I am having my first experience with heat-shrink material. It is going pretty well, I am learning quickly, but it turns out to be I have 4 or 5 major areas with maybe 6-7 1 mm or 0.5 mm wrinkles in the wing covering. My question is, even with wrinkles would the airplane be able to lift off? Please don't post "repair the wrinkles" because I did as much as I could wihtout damaging the covering, just please say will the wing have pretty much teh same properties or not? Would the wrinkles affect the flight majorly ot the lift producedf? I know drag will be there, but since the wrinkles are at the trailing edge where lift is not present and air detaches from thew wing, will the plane fly pretty much the same as without wrinkles?

Thank you,
Yishht87.

Nathan King

Technically it will increase parasitic drag, or more specifically skin friction drag; however, I don't know a modeler that would feel the difference on our small models.

mboland

They WILL have an effect. The size, number and position will determine what sort of effect.

Some pics would help

Should not affect lift but may affect trim

An example, a club member changed his aerial location on a Bobcat by putting an aerial tube under the left wing about 10mm from the leading edge.
He could not work out why he suddenly had to hold HALF FULL RIGHT AILERON to maintain level flight.

Lafayette

wait let me get pictures please

Lafayette

here are pics

Rodney

It is highly unlikely to effect flight characteristics of your model. Now, on some wings, turbulators are deliberately installed near the leading edge of the wings and are claimed to improve performance so I guess it depends on the location and severity of the wrinkles.

mboland

It looks like it will fly OK, but I have to ask, have you heat shrunk it yet?

We have covered wings with worse wrinkles but the good ol' heat gun disguises quite a few sins.

Its just that the covering looks very slack. It is a built up wing I am assuming from the pics.

propbuster

My Feedback: (1)

Put a heat gun to it

Nathan King

Like I mentioned above, wrinkles of that size will not markedly effect performance. Have you tried a heat gun?

da Rock

Depends on what performance you're worried about.

Covering can add strength to structures. When the covering is loose, it certainly won't.

On wings, it actually helps resist wing flex. It won't give, and that can provide something.

da Rock

What is the covering?

Almost every covering can be applied such that the wrinkles will come out with the heating our irons can provide.

So why not iron them out? If raising the heat a little at a time doesn't do it, then it's worth the lesson to pull it off and apply fresh covering. Apply tightly enough that it's shrinking ability removes the remaining wrinkles.

Why would you want to leave wrinkles that might iron out. And if they won't, it's worth your effort to learn to cover without wrinkles. And to produce a model with a covering job that will actually add strength and not cause drag. The added strength isn't a lot, and the drag isn't huge. But you'd cut a better piece out of balsa if the 1st wasn't large enough wouldn't you?

crasherboy

If it were me,I ,would try to heat the wrinkles out. If I could not do that,I would recover. It will by no means help your flight characteristics to leave them in there.It would still fly I think,I also think it would act better if you took care of the wrinkles.

Lafayette

guys. what's a heat gun? I am afraid of touching the wrinkles because at the top i hadd to recover some parts because the covering just wrinkled and hasn't shrunk due to too much heat. I am using Solartex/film by the way- and I quite hate it actually wince it don't shrink much >(.

mboland

Heat gun, or hot air gun, you can even use a hair dryer, but unless they have a dial in temp setting you have to be very careful.

For ages I just used a standard clothes iron.
adjust the heat settings very slowly, starting low, until you get a satisfactory shrink. If you have it too hot you will get a hole.
Try using some scrap on a piece of balsa or other material to get your temp right. Low setting should give you stick without much shrink, slightly higher gives the shrink you will require.

Lafayette

Wel I used a slightly higher setting this morning on my wing, tried the hair dryer- too cold for shrinking. Went back to ironing with higher temperature at about 150 degrees celcius. I successfully removed about 90 percent of the wrinkles that you see on the pictures of the yellow covered bottom part of the wing. The material is now very tight, although in the process I accidentally got some colow out of the wing- about 3 to 4 places about 1 mm in diameter. Although, I asatisfied because the wing is like a drum now, makes a banging sound when i touch it. Glad thats over, , but Istill got another wing and fuse coming up, with the tail it will probably be a disaster. But who knows, I am just happy for that this wing is all good. I am visiting an old man's house on saturday, I have got to ask him a couple of questions about my plane design, since he's been building his own planes for about 30 years now and nowadays hes about 80 years old :-S . I think he has a lot to tell me about my plane, i will do my best since on my plane the wings require a hammer and a drill to get my servos out. Damn, I was designing this plane so that in a crash a repair would require another crash on the work bench. Lets just hope this will turn out fine .

Yishht.

Guys, please could you post pictures on ehre of your own scratchbuilt models and especially their covering? I would like to see what you guys are up to.


Thank you,
Yishht.

da Rock

Good to hear of your success.

Part of the trick to getting a good covering job is the first attachment of each piece of film. When you're first starting to learn to cover, it really is worthwhile to have another pair of hands. If you don't have a way to talk the hand's owner into helping you, then it's good to have a way to hold the model or piece securely. You need to work the iron in one hand and slightly tension the covering with your other hand. You don't have to put it down wrinkle free from the start, but you do need it to be somewhat flat and without big wrinkles.

Sorry to hear about the color changes. That suggests the covering isn't Monokote or Ultracote, or that the iron was too hot. Some brands of covering really won't stand heat.

Since it sounds like you have a way to check the temperature of the iron face, take a look at the recommended heat for whatever covering you're using. Rolls of covering often have instructions that include that information.

When a covering mfg mentions that their covering can be attached at xxx temp and it shrinks at yyy temp, you can use that info to your benefit. Tack the covering along the spar for example at the low temperature. Then the covering won't shift around as you pull it flat and tack along the trailing edge, working from mid-span to tip and from mid-span to the root. Then do along the LE the same. You'll wind up with a decently flat piece of covering tacked in place and with no wrinkles. (or only just a few) Keep the low heat setting and work around all the areas where wood is underneath. Iron down all the solid areas. When the covering is tacked in place with few wrinkles, those solid areas will iron down with only small wrinkles. Now turn the iron up to the recommended shrinking temp and go over the open areas. And then go over the solid areas to shrink that covering. There are wrinkles hidden in covering that wasn't shrunk. The sun will bring them out first time you go fly the new airplane.

Lafayette

Thank you da Rock. You really gave a lot of info, I must say a huge thank you for that . My way of checking is by what the info sheet tells- use a scrap piece of covering and test how fast or slow it shrinks. Slow shrnking is recommended temp, while fast shrinking is hih temp. I figured out that what I was doing wrong when covering is some of the covering film was no tacked onto the fram. As soon as that was done, the coveruing easily shrunk with no loops and wrinklish parts. I am hoping on a better next wing, and an even better fuse. Today as I was walking down the street with the completed wing, it was quite windy and I heard my wing just simply buzz and voluntarily lift by about 50 degrees. I take that as a good sign, since a wing that can lift half of iself two wings wil lift a whole wing in simply wind only. Now with the engine, I am launching for the full plane, since the wind was about 10-15 km per hour and my flying speed will be 60-70 km per hour.


Again let me confirm please. If I have a wing which is not perfect and has patches of wrinkles here and there, will the amount of lift produced be afected? Will there be an efect on performance other than a need on trimming the control surfaces? I know that there will be more drag, but will anything else flight-important be affected such as the amount of lift? My plane is wingspan 1.4 meters and length 1 meter. Will this plane fly having a comsiderable amount of wrinkles on the wings? My plane's weight is 2 kg, powered by a .46 O.S. engine.

Lafayette

someone pleas reply to this.


If I have a wing which is not perfect and has patches of wrinkles here and there, will the amount of lift produced be afected? Will there be an efect on performance other than a need on trimming the control surfaces? I know that there will be more drag, but will anything else flight-important be affected such as the amount of lift? My plane is wingspan 1.4 meters and length 1 meter. Will this plane fly having a comsiderable amount of wrinkles on the wings? My plane's weight is 2 kg, powered by a .46 O.S. engine.

Thank you, I really need an answer,

Yishht.[8D]

mboland

With a plane that weighs only 2kg and a .46 in it, I don't think you will have trouble getting it to fly.
Trimming and handling is another matter entirely. Though you haven't mentioned a wingspan.
Work out your wing loading, weight/wing area, that usually gives an INDICATION on how things are going to go.
More wing loading = more speed to fly, higher stall speeds, etc.

Add enough power and you can get a brick to fly.

Lafayette

here are specs of my aircraft.

Aircraft Specifications

Wingspan- 148 cm

Length- 93 cm with nose cowl

Length- 84 cm w/o nose cowl

Maximum height- 24 cm

Wing Area- 2590 cm^2

Dry Weight- 1143 g w/o battery, receiver, fuel, and engine.

Wing Reynolds Number- 423.293 K

Wing Loading- 81.082 g/dm^2

Will it fly? My wing loading is quite low for an aircraft my size, no? And I have a lot of wingspan to make up for wrinkles, plus a very light airplane. Will it fly?

mboland

In a word - Yes

The plane will, how about the pilot, that's the unknown factor

da Rock

It's going to be impossible to predict how much effect wrinkles should have.

I have a number of excellent airfoil books that have references to the surface condition of the airfoil and it's effect on performance. Back during WWII the US did a bunch of work trying to get a clear picture on the problem. They wanted to see just how much or how little time they had to spend on that part of the manufacturing process. But they really did not go into surface imperfections that would actually equate to battle damaged surfaces. They only looked at what we would call smooth surfaces versus rough textured surfaces.

So there really isn't any scientific guidance for your question.

It is interesting to note that one of my books shows a rough surface test with Reynolds numbers that run into our range. And the L/D actually goes favorable for us. They didn't expand on it, however. I noticed that back in the 80s and did a little experimenting. It appeared to me that for the difference in Reynolds between the wing of a larger RC glider and it's horizontal tail, there was probably a benefit to covering the tail with a textured covering like SolarTex. And I tried using SolarTex on the wings aft the max thickness line. Never saw enough difference with that to draw any conclusions. ("conclusions" is not actually a good choice for what I was drawing...... w.a.g. is more correct )

da Rock

OK, this Sagitta actually has one of my scratchbuilt wings on it. The horizontal tail is probably one of mine also, but I'm not positive about that. All my gliders wound up with way more than one set of wings built for them. Detachable wings are perfect for experimenters like me. If an airfoil caught my eye, I could whip out a wing with that new, magic airfoil before the next weekend. I'm pretty sure the wing in the picture is based on an Eppler family. One profile at the root progressing to another in the family at the dihedral break progressing to a 3rd at the tip. I was also trying upturned Hoerners versus downturned about the time Epplers hit the scene.

A wing with the identical airfoils was covered with Monokote so I could compare surface textures. By building what was as close to identical wings that differed only in the texture of the covering, I had at least a fighting chance of having a sensible test setup. Unfortunately, testing out in the world blows that fighting chance. I knew that, but it was still fun to pretend that I'd be able to tell a difference if it was significant enough. Yeah, right.......

Lafayette

Guys, if any of you have flown airplanes with significant wrinkling in the covering, please post pictures. I wanna see just how bad the covering can go for an rc airplane. If any of you have web site addresses with flying rc airplanes which have wrinkles covering, or if you possess any pictures, I would very much appreciate it if you would share it with me to cheer me up a bit. I teared half my top section of the wing accidentaly today and I have to recover it, plus the bottom section was recovered. Bottom section is smooth except for singinficant wrinkling around the futaba servos- about 3-4 cm in diameter wrinkles, in two parts of the wing as the wing carries two servos each.

Lafayette

hm, well I have recovered the whole bottom section of the wing, and now it is very smooth and very tight :/ sounds kinda wrong... oh well... anyways my wing is very smooth now and in my 20 mile per hour wind, my wing actually just lifted itself up again now the full way and just kinda glided along with my arm holding noto it so it doesnt fly off.