• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Winter Build 2018/19: Hangar 9 P-47D Razorback

willsonman

Builder Extraordinare
Mentor
The oven worked. popped the part in for 5 minutes and it cam out hot but I could still handle it. Not a smoldering pile of goo either. I was able to massage the part into the shape I wanted. With the plastic hot, there is less likelihood of it breaking so I was able to over-bend the part so that it would cool to a relaxed state in the right shape. Unfortunately, the perfectionist in me wants to do more but I'm trying to let go. It was good enough to do the glass work so I prepped. Over-sized doors were cut from scrap and taped. I drew reference lines around the perimeter. One single spot is my reference spot to locate the part after it is done and the hole opened back up. I'll go over that later. All she needs is some plastic wrap and about 30 minutes to lay some glass. should be fairly easy stuff.
IMG_7729.JPG
 
To understand this proces better:
am I correct in assuming that you haven't cut the bays in the wings yet, but you are first making the doors. And to be on the safe side, you're making them a little bigger than the bays you're going to cut. So next steps would be: cutting the wing and then cutting the doors.
Correct?
 
Oh and can you please take me through the glassing process?
What steps do you take? (for example: covering with foil? how many layers? do you go from heavy to light glass, or inverse?
I am a 100% noob when it comes to glassing, but I want to do the same gearmod you're doing... So I am struggling with the how.
Any explanation would be greatly appreciated!
 

willsonman

Builder Extraordinare
Mentor
Yes, I've not cut out any wood in the wing for the inner doors. I want their final shape first and then I'll trace them and cut. If you nice in the images, there is a recess in the wing's outer balsa skin down to a ply plate. I plan to mimic this for the inner doors. So, for now the glass door will be over-sized a bit for me to trim them up once cured and positioned with the cover from the glass work removed. This way I can also shape the area that will meet the outer door too. I'll likely put on a 1/64" ply lip to close this gap too.

So, the process is pretty simple. To protect the wing. I'll stretch a piece of plastic wrap over the area where I'll be glassing. THen, I'll cut glass cloth for the area. The first two layers will be 6oz. cloth from the hardware store. The first layer applied and the second will be at a 45-degree bias for increased strength and rigidity. Then another two layers of 0.75oz. cloth to finish. Again, I'll use the 45-degree bias here. It makes them very stiff yet thin. After that, I'll apply another layer of plastic wrap and make it as smooth as possible. I'm using epoxy with a 60-minute pot time. This long time means I need a full 24-hours to cure out. With the long cure time and my humid climate there is a high level of risk that the epoxy will do something called "flashing." This is where the moisture in the atmosphere settles and condenses on the epoxy as it cures and separates the resin from the hardener. The epoxy will partially cure out and be a holy sticky mess. The last layer of plastic wrap prevents this from happening. I'm in MD and the erratic fluctuations in humidity here dictate that I do this every time I do a layup. Annoying but a necessary evil.

A couple of additional pointers here. Some folks prefer to thin their mix with denatured alcohol to make it less of a syrup consistency. The reason for this is to avoid air bubbles in the glass. You want the epoxy to fully wet out all the fibers of the cloth and sometimes that gets air bubbles in the layup. Personally, I put on gloves and physically use my fingers to massage the epoxy into the fibers for each layer. This also prevents the epoxy from running all over the place and making a somewhat messy process becoming an ungodly mess. SOme folks even go to the extent of mixing their pot of epoxy and having a special lid and pulling a vacuum on that mix to remove as many air bubbles as possible before you apply it. And then there are the crazy sailplane guys who put their layups in in a vacuum bag. This pulls all the air out but also squeezes out any extra epoxy to save every gram of weight. This involves mylar skins and paper towels in the bag, fancy gauges so your vacuum is not too strong so that it crushes your layup, and a myriad of other things.

Really what I want to end this on is that glass is a rabbit hole. The deeper you go the more complicated it gets. I'm like 12" down. The key here is to just TRY the technique. Make mistakes and learn from them. If you want to dab a toe into glass work I highly recommend you follow this link.
https://forum.flitetest.com/index.php?threads/fiberglass-foam-a-tutorial-and-discussion.23228/
Lots of good info there to get you started. Once you can work with WBPU, instead of epoxy, approaching epoxy becomes a lot easier. I taught a couple of classes on these basics at FFOH 2016. It was well-attended and a lot of folks realized really how easy it is to do.
 
Fantastic info. Thanks a million. And I will look at the thread you mention for sure.

Just two final questions:
- you mention 6oz and 3/4oz cloth. I am dealing with metric suppliers (stating gram/m2). Is your cloth 6oz per m2, or something yard-like?
- You mention 3 layers of cloth (applied diagonally). Do you let it cure each time after one layer, or do you apply multiple layers in one go?
 

willsonman

Builder Extraordinare
Mentor
Yes. the weights are per square-yard. So you would be looking for gram per square-meter.
Go back... 4 layers. 2 6oz and 2 0.75oz. One layer of each is on a bias. All 4 layers applied all in one go.
 

willsonman

Builder Extraordinare
Mentor
I cut my cloth before I mix my epoxy. Mixed up 12 oz of the stuff and went at it. Some people prefer to use the pour and squeegee around method. I prefer a good old fashioned brush. The disposable kind from the hardware store works just fine. All of $0.89. I brush on a bit at a time, working the epoxy into the fibers. I use a stippling technique to poke into the fibers to work the epoxy well into the first layer. The second goes on top and the extra underneath is pushed in first. Then all more epoxy to soak. The next two layers go on and no additional epoxy was needed. I covered up the layup with plastic wrap and used a scrap piece of balsa to squeegee out the air bubbles. Pretty simple. Hope to pull these off this afternoon.
IMG_7730.JPG
 
Well, the result is less than I hoped for. The epoxy cured okay, but the objects are not becoming stiff.
I used 4 layers: 2 x 200gr/m2, 1 x 80gr/m2 and 1 x 50gr/m2, all in one go.
The objects became transparent when I applied the epoxy, so I am guessing I used enough of that.
And the epoxy itself (leftover in a cup) became a rock hard, so nothing seems wrong with the epoxy itself.

What am I doing wrong?
 

willsonman

Builder Extraordinare
Mentor
Epoxy in the cup may have cured faster than the layup. My guess is that you are expecting the part to be super stiff and may also not be fully cured. If your part is out of the plastic wrap, let it cure more (another day at least) and see where you end up. This number of layers is still going to have some bend to it. It's not likely, as your cup cured hard, that you did not mix your epoxy thoroughly enough. I mix mine for at least one minute before I use it. Again, this is not likely. If the part is still even slightly tacky it needs to cure more. Heat, even from a lamp, will help it along.
 
Hmm... the only thing I didn't do was the plastic wrap and squeezing. And maybe I didn't soak the layers enough... (i didn't do the stippling, just 'painting' the layers)... I'll give it another go.
 
Another pile of cloth and epoxy are curing as we speak... I did the stippling and seem to have used more epoxy. Also I did the wrapping.
A nasty job altogether, but let's hope the result is better this time.
 
Results are in.
It's better than the previous time. Still not superstiff, but I am understanding -from Willson- that is not to be expected with so few layers.
I am guessing it will be useable as is.
Next time i will use 1 or 2 layers extra.
 

willsonman

Builder Extraordinare
Mentor
Depending on how stiff you want it, you can add some carbon fiber tow. I can cover that if you want. My parts may need it just for some insurance. It would be lighter this way anyway without going full on CF. More layers will make it more stiff but keep in mind that stiff mean that when it breaks, it is likely to be a catastrophic failure. You almost always want some flex.

I had a productive weekend so let's go over the mix of photos I have.
First up is the rough trimmed door. I put it back in place with the hole exposed. I properly traced the full outline of the door area and then drew a third line inside of that for the final shape of the door. I also drew the line where the two doors meet. I intentionally drew this one dead on so that I could sand to fit later.
IMG_7731.JPG
Next I cut out the shape of the door recess and removed extra balsa. I also had to re-shape some of the ply underneath but the dremel made quick work of that. Just minor stuff. OI then cut the door to its mostly final shape and sanded the flat edge with my sanding bar. I just used scissors here. I cut on the outside of the marker and then sanded into the marker line for the final edge. Again, some shape work will still be needed.
IMG_7732.JPG IMG_7733.JPG
What I did not capture in a picture is some initial hinge work. I printed out a couple of different one and settled on one but somehow is not looking right to my eye. More on that later when I get it sorted.

Next up we have some additional room in the fuselage beneath the battery tray. As mentioned a while back, I installed a piece of balsa here for the second resonator for the sound system. We have additional volume from this and it is tucked out of the way and forward of the CG.
IMG_7734.JPG

As I will need more than the supplied 8 channels of the X8R, I received a S.Bus to PWM converter in the mail. This breaks out the S.Bus output of my receiver into all 16 channels (20 available on this unit). I started mounting these electronics as well as routing the wiring from some of the existing electronics. It was fun seeing the cowl flaps, oil cooler doors, wastegate valve, and the intercooler doors all working at once. Then I coupled that with the sound module. Good fun. Obviously there is a lot more to do with installation of more flying servos (Elelvator, Aileron, Flap, Gear, Gear doors, etc.) but it's a good practice to tidy as you go. I finally put the battery tray back in too. It still needs a proper strap but it's back in.
IMG_7735.JPG IMG_7736.JPG
 

willsonman

Builder Extraordinare
Mentor
There are pros and cons to it. The pro is the simplicity of it. Run the S.Bus to the converter and you instantly have access to all the channels. If you opted to go with a secondary RX8 you would still have access to all 16 channels but you would have independent reception of the signal. One would receive ch 1-8 and the other 9-16. There is NO redundancy of signal reception so there is not really any advantage IMO to do this. I save a bit less than $10. I just prefer the cleaner install.
 

rockyboy

Skill Collector
Mentor
Love looking at how clean your wiring is inside the fuse :D

I've got to say that those wooden glued on servo arm extensions look a little suspect though - are they at least epoxied? I don't know that I'd trust something like that without wrapping the joint in thread and covering in epoxy... :cautious:
 

willsonman

Builder Extraordinare
Mentor
Meh, Honestly, I'm not the best at wiring jobs. I more or less try to route them simply and out of the way so that none of the moving stuff inside touches them. Thanks though.
 
Can you add a photo from the cut wheel well, in the direction of the wing root? I am wondering how far you've cut and if you have removed the wing rib that is nearest to the wing root. Also, I am wondering is there is space for a hinge.

I do wonder what you mean with the carbon fiber tow. You mean like a carbon fiber cloth (and epoxy), or more like a carbon rod?
 

willsonman

Builder Extraordinare
Mentor
I can try to grab those shots for you. There is plenty of room toward the wing root. I've not cut into the root rib at all. Plenty of room for a hinge.

Carbon Tow is basically just strands of carbon fibers bunched together. The K rating relates to the the strength of the bunch. I have been using 12K for awhile now to add strength here and there. You can always remove a few strands if you feel its overkill. I used it to reinforce the nose of the Bugatti and it worked very well. I also used tow to reinforce the 3D printed tail gear parts for my Corsair. The cool part about it is that you can tack it down with a little bit, like a drop or less, of medium CA and then flood it with thin CA and the fibers will wick the glue along and make the carbon as hard as a rock. Fun stuff to work with.