Things I found in storage - Trainer Foam conversion and Build
- Thread starter SteveOBHave
- Start date
SteveOBHave
Senior Member
It actually ends up being significantly less work than trying to smooth finish epoxied glass. With the Fuselage I think I will use what they call the 'Lost Foam Technique' which does remove the foam. After you finish glassing and let it set, you then put a little bit of a solvent in and the foam dissolves into a gooey mess that you can easily remove. With the wings and control surfaces I think I will leave the foam in as it ends up being structural. The fuselage will get some dividers put in and an electronics tray. There's stacks of room in there once the foam is gone!
Yeah! I can imagine that, as it's only going to be an outer shell. So anyway, are you going to split the fuselage? Or do you have like a canopy you can remove?
SteveOBHave
Senior Member
You know I haven't thought that far ahead 
Not too sure - I don't think that I'll split it, I think a flush hatch on the nose would be best - give me access to all the important bits. My only concern will be the length of push rods to the elevators and rudder. I could use the glider way of spring loading and using string rather than wire. Having said that I still need to go hunt down some piano wire - the stuff is rarer than hens teeth here in Sydney...
Not too sure - I don't think that I'll split it, I think a flush hatch on the nose would be best - give me access to all the important bits. My only concern will be the length of push rods to the elevators and rudder. I could use the glider way of spring loading and using string rather than wire. Having said that I still need to go hunt down some piano wire - the stuff is rarer than hens teeth here in Sydney...
SteveOBHave
Senior Member
So a couple of weeks down the line...
I left my camera in the hanger so I didn't have any photos with which to update the build log but that has now been rectified.
Where I left off was with the landing gear in the mold. It wasn't the prettiest of efforts, mostly because getting even pressure on the mold was not able to be achieved with the tools at hand. However it did yield a very usable piece of glass and after band sawing off the flashing and a bit of eyeballing next to the sander we have this!
I took to a couple of small blocks of foam to have a go at making some wheel pants. My first attempts were ill conceived and the result less than satisfactory. mainly because, like many of my builds, I approached it with a mental image and not an understanding of how these things are actually approached.
Sculpting wheel pants has a pretty simple approach (kindly informed by my father on this one - he has the grace to allow me to make a hash of it the first time and then give me gentle nudges in the right direction, after all we learn better from our mistakes do we not?). Basically you take a symmetrical airfoil and scale it around a wheel - makes sense too as you don't want the pants skewing your airflow - hence the symmetrical airfoil!
The weather was pretty sweet so we ended up hanging up the tools and going flying for a few batteries and then that was pretty much that for the weekend.
I left my camera in the hanger so I didn't have any photos with which to update the build log but that has now been rectified.
Where I left off was with the landing gear in the mold. It wasn't the prettiest of efforts, mostly because getting even pressure on the mold was not able to be achieved with the tools at hand. However it did yield a very usable piece of glass and after band sawing off the flashing and a bit of eyeballing next to the sander we have this!
I took to a couple of small blocks of foam to have a go at making some wheel pants. My first attempts were ill conceived and the result less than satisfactory. mainly because, like many of my builds, I approached it with a mental image and not an understanding of how these things are actually approached.
Sculpting wheel pants has a pretty simple approach (kindly informed by my father on this one - he has the grace to allow me to make a hash of it the first time and then give me gentle nudges in the right direction, after all we learn better from our mistakes do we not?). Basically you take a symmetrical airfoil and scale it around a wheel - makes sense too as you don't want the pants skewing your airflow - hence the symmetrical airfoil!
The weather was pretty sweet so we ended up hanging up the tools and going flying for a few batteries and then that was pretty much that for the weekend.
SteveOBHave
Senior Member
Fast forward to this weekend and we'd managed to source a number of items that should lend themselves to vacuum bagging. Mostly from Bunnings (hardware store here in Aus) so not really specifically for the task but sourcing this stuff locally and cheaply has a lot going for it.
My Franken Glider has been disassembled for parts and all I was left with was the wing. So what to do with a wing? Well, make it fly of course! Over the week proceeding this weekend I threw together a fuse for just this purpose, mostly because I have a hankering for a hand/bungee launched glider. End result?
Granted, she's not pretty but it was functional (and I say was because in 20MPH winds there wasn't much room for error... err...). Suffice to say, the fuselage is now pretty flexible and a few inches shorter! Still nothing wrong with a proof of concept and despite some pretty wicked wing flap at high speed bungee launches it was a lot of fun.
With that small distraction out of the way and it being waaaay too windy to go flying a little foamy like the AXN, there was nothing left to do but work. With the motor glider pretty much ready for glassing I needed something to use as a test for the bagging technique. Luckily I had one that I prepared earlier!
At the start of this thread I talked about some balsa trainer kits and again about my lack of experience in building. I also showed a fuselage that I had put together out of foam board and subsequently some wing cores that we had hot wired, again very much as a 'feeling it out' process.
Once again the trainer has come to the fore, ironically in a training capacity! Here I have the three cores joined with a 2 degree dihedral only in the centre. I guess I could've given it polyhedral as it is in 3 sections but it's added complexity with the bagging and the aim here is to learn so why complicate the process?
Gorilla glue is pretty good stuff but I've found that I have to keep re-compressing the join as it foams out - am I doing this wrong or is there a better way to join wing cores?
Here is the same wing with the trailing edge cut.
And here mocked up on the trainer fuselage
My Franken Glider has been disassembled for parts and all I was left with was the wing. So what to do with a wing? Well, make it fly of course! Over the week proceeding this weekend I threw together a fuse for just this purpose, mostly because I have a hankering for a hand/bungee launched glider. End result?
Granted, she's not pretty but it was functional (and I say was because in 20MPH winds there wasn't much room for error... err...). Suffice to say, the fuselage is now pretty flexible and a few inches shorter! Still nothing wrong with a proof of concept and despite some pretty wicked wing flap at high speed bungee launches it was a lot of fun.
With that small distraction out of the way and it being waaaay too windy to go flying a little foamy like the AXN, there was nothing left to do but work. With the motor glider pretty much ready for glassing I needed something to use as a test for the bagging technique. Luckily I had one that I prepared earlier!
At the start of this thread I talked about some balsa trainer kits and again about my lack of experience in building. I also showed a fuselage that I had put together out of foam board and subsequently some wing cores that we had hot wired, again very much as a 'feeling it out' process.
Once again the trainer has come to the fore, ironically in a training capacity! Here I have the three cores joined with a 2 degree dihedral only in the centre. I guess I could've given it polyhedral as it is in 3 sections but it's added complexity with the bagging and the aim here is to learn so why complicate the process?
Gorilla glue is pretty good stuff but I've found that I have to keep re-compressing the join as it foams out - am I doing this wrong or is there a better way to join wing cores?
Here is the same wing with the trailing edge cut.
And here mocked up on the trainer fuselage
SteveOBHave
Senior Member
On to the exciting stuff!
Wing laid out on the prep table with glass getting cut to size. The plan here is to use one layer of unidirectional laterally the length of the wing with 45 degree bidirectional on the leading edges and tips. It's all experimental stuff to see how little we can get away with and still have a pretty robust wing.
The perforated 'Peel Ply' - really high tech stuff here, it's clear vinyl table cloth from bunnings - I have no idea how well it will work but this is why we're doing this on a test wing and not the pretty one!
Wetted out
Applying Peel Ply
Shiney...
It puts the wing in the bag...
It applies suction... You can see some epoxy already making its way out
It puts a tent up and takes the wing camping... wait... what?
Yes it is a tent - since it's pretty cold here at the moment and trying to heat a hanger is a little much for a fan heater, we shot down the road and for $19 got a 3 man tent to use as a bagging oven. In with the pump, a fan heater and a thermometer and we have a good constant 35 degrees C or 95F. The wing is chocked up for a couple of reasons - to keep the air circulating all around it and to help maintain the dihedral.
5-6 hours later out of the ove..ten...hmm tent oven! By this stage the epoxy has gotten pretty solid and as you can see quite a bit of it has come out which is exactly what we were after.
Unfortunately this is where I have to leave it. It will be a couple of weeks before I can update it again due to have prior commitments for the coming weekend involving a friends birthday and potentially a pretty decent hangover... yay!
It took a huge amount of restraint not to tear into the bag and check out the finish but apparently you shouldn't do that till about 12 hrs down the line. Not to say that we didn't open the bag and pull aside some of the wadding, despite the apparent lack of resin visible on the outside there was actually quite a bit around the outside of the peel ply, this is a good thing. The more on the outside of the PP, the less in the glass and the less weight we have in the wing.
I think a good place to leave it More in a couple of weeks!
Wing laid out on the prep table with glass getting cut to size. The plan here is to use one layer of unidirectional laterally the length of the wing with 45 degree bidirectional on the leading edges and tips. It's all experimental stuff to see how little we can get away with and still have a pretty robust wing.
The perforated 'Peel Ply' - really high tech stuff here, it's clear vinyl table cloth from bunnings - I have no idea how well it will work but this is why we're doing this on a test wing and not the pretty one!
Wetted out
Applying Peel Ply
Shiney...
It puts the wing in the bag...
It applies suction... You can see some epoxy already making its way out
It puts a tent up and takes the wing camping... wait... what?
Yes it is a tent - since it's pretty cold here at the moment and trying to heat a hanger is a little much for a fan heater, we shot down the road and for $19 got a 3 man tent to use as a bagging oven. In with the pump, a fan heater and a thermometer and we have a good constant 35 degrees C or 95F. The wing is chocked up for a couple of reasons - to keep the air circulating all around it and to help maintain the dihedral.
5-6 hours later out of the ove..ten...hmm tent oven! By this stage the epoxy has gotten pretty solid and as you can see quite a bit of it has come out which is exactly what we were after.
Unfortunately this is where I have to leave it. It will be a couple of weeks before I can update it again due to have prior commitments for the coming weekend involving a friends birthday and potentially a pretty decent hangover... yay!
It took a huge amount of restraint not to tear into the bag and check out the finish but apparently you shouldn't do that till about 12 hrs down the line. Not to say that we didn't open the bag and pull aside some of the wadding, despite the apparent lack of resin visible on the outside there was actually quite a bit around the outside of the peel ply, this is a good thing. The more on the outside of the PP, the less in the glass and the less weight we have in the wing.
I think a good place to leave it
More in a couple of weeks!
SteveOBHave
Senior Member
Aha - now then, I think I'd need to get a decent sized FliteTest sticker to do that wouldn't I? Would anyone know where I might get my hands on this fabled large FT sticker?
Send a picture of your white plane to Chad - and he'll send you a sticker!
SteveOBHave
Senior Member
Heh - guess I should get it finished then!
SteveOBHave
Senior Member
With all the promise and expectation of success it was with deep regret that we arrived at the hangar, grabbed the wing, and discovered that the vacuum bagging process had failed. There were a number of reasons for this. The primary reason, I believe, was using the wrong materials for the job.
Rather than using the correct perforated peel ply, I decided to give it a shot with some thin clear vinyl table cloth covering bought from Bunnings (Aus hardware store). In theory it could've worked but I suspect that due to the nature of the plastic, it didn't behave well in the tent/oven and expanded 'self healing' the perforations that I had put in it. Rather than allowing the epoxy to wick away from the glass layout, it trapped it in leaving us with exactly the opposite effect of what we were after.
As you can see the epoxy has pooled in spots and sits way too thick on both the leading and trailing edges. This made the wing quite heavy and meant that I was to spend the first day sanding the whole wing to strip back as much of the epoxy as I could. To add to the fun it also showed that some of the glass had lifted from the foam somewhere in the process and left us with peaks in the layup that when sanded left us with unacceptably thin glass. The solution to this? Cut it out
Luckily it was only half the wing that had the lifting glass, unsurprisingly the side that I had worked on. The side that my father had worked on was too all intents and purposes entirely workable. It shows what experience can do for you. I'm not too upset by this as it was my first glass layup on foam. However, is it too much to ask for for it to be perfect first time? Haha... obviously so...
Too cheer myself up I took an hour or so to chuck together a simple delta which turned out to be a bundle of laughs, if only in that it really keeps you on your toes when you're flying it. It may actually be the first plane that I've chucked together that will get a paint job!!! Big thanks to Dekan on RCGroups for posting this one - bloody genius in it's simplicity - what a cracker of a design. It is actually co-incidental that FT did the delta in their last episode, but a fun one non-the-less!
http://www.rcgroups.com/forums/showthread.php?t=867083
Rather than using the correct perforated peel ply, I decided to give it a shot with some thin clear vinyl table cloth covering bought from Bunnings (Aus hardware store). In theory it could've worked but I suspect that due to the nature of the plastic, it didn't behave well in the tent/oven and expanded 'self healing' the perforations that I had put in it. Rather than allowing the epoxy to wick away from the glass layout, it trapped it in leaving us with exactly the opposite effect of what we were after.
As you can see the epoxy has pooled in spots and sits way too thick on both the leading and trailing edges. This made the wing quite heavy and meant that I was to spend the first day sanding the whole wing to strip back as much of the epoxy as I could. To add to the fun it also showed that some of the glass had lifted from the foam somewhere in the process and left us with peaks in the layup that when sanded left us with unacceptably thin glass. The solution to this? Cut it out
Luckily it was only half the wing that had the lifting glass, unsurprisingly the side that I had worked on. The side that my father had worked on was too all intents and purposes entirely workable. It shows what experience can do for you. I'm not too upset by this as it was my first glass layup on foam. However, is it too much to ask for for it to be perfect first time?
Haha... obviously so...
Too cheer myself up I took an hour or so to chuck together a simple delta which turned out to be a bundle of laughs, if only in that it really keeps you on your toes when you're flying it. It may actually be the first plane that I've chucked together that will get a paint job!!! Big thanks to Dekan on RCGroups for posting this one - bloody genius in it's simplicity - what a cracker of a design. It is actually co-incidental that FT did the delta in their last episode, but a fun one non-the-less!
http://www.rcgroups.com/forums/showthread.php?t=867083
SteveOBHave
Senior Member
It's a little heart breaking to hack into all your hard work when the end result should've been an example of a well built and finished glass layout. But C'est la vie. Having pretty much compromised the strength of the wing by cutting out all the bad parts I had to learn a new skill. Fixing a composite wing! Honestly this is not something that I have a problem with. If there is anything that I have learned over the years it is that in fixing problems you pick up considerably more that if everything goes swimmingly.
As you can see from the previous pictures of the wing, park of what I had to cut out was directly across the 'saddle' of the wing. This is a pretty serious compromising of the centre of the wing where the majority of forces effect it's structure. We took this as an opportunity to add a design 'feature' and put a loop of bi-directional glass around the centre structure. All the holes, including the centre one were to have a single layer of uni-directional glass on them.
First step. Cut the glass to not only cover the holes but to overlap by an inch all around.
The next step is to get a dry microballoon mix (or micro) which is a very light epoxy based filler that has a consistency like cake icing. Yum... or not...
Step three is to fill in all the gouges that my glass excavation work left in the underlying foam and also to create a nice smooth transition between the good glass and the hole.
This done it was layup time and rather than using the vacuum bagging technique again we've opted for using a fabric peel ply.
Unfortunately this is where I will have to leave it for another week as the layup cures and hopefully the final work of finishing can get under way. Finishing will require more of that micro stuff being applied to the outside of the glass too fill in irregularities (of which there are many) and then being sanded back till we have a nice smooth surface for painting.
I also hope to have some things like wheels and possibly a more powerful motor and ESC to get this thing off the ground as I don't think that the park flier motors have the oomph to do it justice.
Like I said earlier, it would've been nice if it had been a straight forward example of how vacuum bagging can work but the reality has been a really valuable learning experience that I'm sure will come in handy further down the line.
As you can see from the previous pictures of the wing, park of what I had to cut out was directly across the 'saddle' of the wing. This is a pretty serious compromising of the centre of the wing where the majority of forces effect it's structure. We took this as an opportunity to add a design 'feature' and put a loop of bi-directional glass around the centre structure. All the holes, including the centre one were to have a single layer of uni-directional glass on them.
First step. Cut the glass to not only cover the holes but to overlap by an inch all around.
The next step is to get a dry microballoon mix (or micro) which is a very light epoxy based filler that has a consistency like cake icing. Yum... or not...
Step three is to fill in all the gouges that my glass excavation work left in the underlying foam and also to create a nice smooth transition between the good glass and the hole.
This done it was layup time and rather than using the vacuum bagging technique again we've opted for using a fabric peel ply.
Unfortunately this is where I will have to leave it for another week as the layup cures and hopefully the final work of finishing can get under way. Finishing will require more of that micro stuff being applied to the outside of the glass too fill in irregularities (of which there are many) and then being sanded back till we have a nice smooth surface for painting.
I also hope to have some things like wheels and possibly a more powerful motor and ESC to get this thing off the ground as I don't think that the park flier motors have the oomph to do it justice.
Like I said earlier, it would've been nice if it had been a straight forward example of how vacuum bagging can work but the reality has been a really valuable learning experience that I'm sure will come in handy further down the line.
SteveOBHave
Senior Member
I guess one thing to learn from this so far is that with composites, if you make mistakes early on, there is a great deal of work in fixing them. When you get it right, however, the rewards are hard to argue with.
Great stuff, Steve! I have fiberglass cloth on its way to my house to glass the flying wing I am building. Unfortunately, I don't have an experienced person to help me. I'm not planning on vacuum bagging it, but being real careful with the amount of epoxy I use to wet the glass.
What type of epoxy resing are you using?
I'm not planning on vacuum bagging it, but being real careful with the amount of epoxy I use to wet the glass.What type of epoxy resing are you using?
SteveOBHave
Senior Member
Good man. The epoxy that we're using is primarily West Systems I believe with a slow hardener. I think it's a 105 resin with a 209 Extra Slow Hardener. If you have questions I will pass them on to my father and he can fill us in but there is one thing that holds true regardless. The finish on the foam is what you're going to have to work with once you've applied the glass. Getting that looking good means that the final finish has a better chance of looking the same.
Thanks for the advice. I am using lightweight spackling to smooth the surface of the foam and fill in the dings and dents. Do you worry about really shallow dents or is it similar to prepping a car for painting?
Do you use any type of sealer on the foam surface or simply sand it with fine paper?
Do you use any type of sealer on the foam surface or simply sand it with fine paper?
SteveOBHave
Senior Member
with the shallow dents I'd use a long flat sanding block and sand at 45 degrees to the leading and trailing edge holding the sanding block parallel to the leading and trailing edges. The idea is to let the sanding block form the curve using the overall form to define the lines. Ideally you want to maintain a nice smooth airfoil and whacking some filler into the dent and then blending it down shouldn't add too much to it overall. Really small blemishes will likely get bridged buy the glass and you can of course use the finishing before painting to get a really smooth surface.
I've quickly drawn up this image to hopefully make it clear.
In reality the dents probably don't matter a whole bunch as at this scale the efficiency variables are far less than with a full sized plane and getting it wrong doesn't have the same life threatening end story. I didn't use any sealer on the foam for this wing and if done properly you shouldn't need to but as I've shown from my own lack of experience, it doesn't always work out the way it 'should'. I'd take whatever opportunities you can to get the practice in with finishing because it all adds up. The thing to keep in mind though is that everything you add to the build is weight that you'll have to fly later.
I've quickly drawn up this image to hopefully make it clear.
In reality the dents probably don't matter a whole bunch as at this scale the efficiency variables are far less than with a full sized plane and getting it wrong doesn't have the same life threatening end story. I didn't use any sealer on the foam for this wing and if done properly you shouldn't need to but as I've shown from my own lack of experience, it doesn't always work out the way it 'should'. I'd take whatever opportunities you can to get the practice in with finishing because it all adds up. The thing to keep in mind though is that everything you add to the build is weight that you'll have to fly later.
Thanks. I'm pretty handy with a sanding block as I've done autobody work in the past. I'm mainly filling in gouges from the rough cutting of the foam.
I'm planning on doing a single layer of 0.56 oz/ sq yd fabric. From everything I've read, the West System epoxies are about the best. I don't need the best, but it doesn't cost much more than any other epoxy system. There is a polyester resin product called Sytrosafe that is a good deal less expensive than epoxy and supposedly foam safe. But, The marketing of it is so poor that I'm not even sure where to buy it.
What I'm not sure about is whether to just leave it a single coat, or put on a gelcoat for finish. Its probably not worth it.
I'm planning on doing a single layer of 0.56 oz/ sq yd fabric. From everything I've read, the West System epoxies are about the best. I don't need the best, but it doesn't cost much more than any other epoxy system. There is a polyester resin product called Sytrosafe that is a good deal less expensive than epoxy and supposedly foam safe. But, The marketing of it is so poor that I'm not even sure where to buy it.
What I'm not sure about is whether to just leave it a single coat, or put on a gelcoat for finish. Its probably not worth it.
SteveOBHave
Senior Member
I'd say that a single layer is plenty but I'd consider putting another layer on the leading edge and wingtips to cover yourself from impact damage. Gelcoat is just extra weight for no real structural advantage in my opinion. I'd concentrate on power to weight ratios with a perfect finish as a very close secondary aim. You should be able to get the glass with a good enough finish with micro and primer to not need anything more than the glass finish.
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