|This photo is of the prototype during the
earlier phases of construction.
January 18 2017 2.0hrs - 3094.0 total. Sanded edges of forms with emery cloth, top and
bottom where it will contact plexi. Cleaned throughly with acetone. Put down two lines of
high temp silicone on top form piece. Went to the store and got a large piece of 1/8" plexi,
they didn't have any 3/16". Started to layout to cut plexi piece that will go in mold. Started
planning how to install air fittings. Cold out today, -51F at 11:30pm.
January 19 2017 1.0hrs - 3095.0 total. Measured and cut a piece of plexi. Trial fit in
mold. This is only 1/8" and is so flexible it fits right in there without having to be heated.
I'm expecting to need to do this in two stages with thicker material: first heat and bend to fit
into mold, second heat and inflate. Discovered I need some more pieces for the air fitting.
|Ran two beads of high temp silicone
across contact surfaces on top form piece.
|Heater and humidifier running
full blast in the garage trying
to maintain 70 degrees and
|Trial fitting 1/8" plexi in mold.
January 21 2017 5.5hrs - 3100.5 total. Tried to put the form into the oven. Realized I didn't account for the broiler coil occupying about an
inch of the top of the oven. So the form won't fit in the oven... Decided to try seeing what I could do with the heat gun. Picked up some
more air fittings and installed. Removed plastic from plexi sheet, clamped into form, heated the edges with the heat gun and it quickly and
easily flowed into shape to allow the form sides to clamp nicely into position. Hooked up the air fitting, applied pressure, and started heating
with the heat gun to see what would happen. Was working a little, but plexi was flowing as if no air pressure on the inside? Switched to the
big compressor - which required two more trips to the store for fittings. Got it hooked up, started heating, and no difference. Figured out
that the small piece of copper tubing I was using, because I expected it be inside the oven, was severely restricting the flow. Another tip to
the store for more fittings and now I had a full size air hose providing pressure. With that turned on with the higher pressure, several air
leaks became obvious. Clamped the frame pieces together more securely, using lots of clamps, and eliminated most of the air leaks. Started
heating again with the air gun, and got nice results. The only issue is that the gun creates relatively small areas of heat, even if I wave it
around quite a bit, I still get hot spots, which turn into bulges. You'd think you could work the heat gun around enough to smooth everything
out, but its not easy. If you keep the gun moving, it doesn't heat up enough, but if you slow down, you get nothing, nothing, then suddenly it
starts to bulge. On one of my trips to the store today I picked up some thicker plexi. Maybe I'll try it tomorrow with the thicker stuff and
see if it is any easier to work. Plan B will be to try to make the form into a heater itself.
|Plexi clamped into mold
before any heat applied.
|Closer view of un-heated plexi showing
how it doesn't seat into the mold edges.
|After heating the edges
with a heat gun to get it
to seat into the form.
|After heating all over with
air pressure inside.
|After rough trim. Set on
fuselage to see how it looks.
February 1 2017 1.5hrs - 3102.0 total. OK, Plan B it is. Started enclosing the sides. Went to the thrift shop and bought some 3 X 5
picture frames and took out the glass so I can use it to put little view ports in the sides of the enclosure. Found a cheap electric "hot
plate" at Walmart. Tested it - should do well.
February 3 2017 2.0hrs - 3104.0 total. Continued working on closing in the bottom part of the form. Almost done.
February 4 2017 3.5hrs - 3107.5 total. Finished up the sides, made up a top and added a hinge. Ready to give it a try! Will give it a
try without insulation first. Will probably need a fan to keep the temperature constant throughout. Might need to add some temperature
February 6 2017 3.0hrs - 3110.5 total. Clamped the form to the bench so that it extended out over the edge. Placed sheet metal on the
bench and various surfaces for heat shielding. Set the hot plate on a couple of milk crates -again with sheet metal shielding. Tried
heating up the form. Realized the meat thermometer I stole from the kitchen only goes up to 220 so went to the store and bought a
thermometer for a BBQ grill. Drilled a hole and mounted it on the form base. Started heating it up again with the hot plate. Could only
get it up to about 175 - used digital thermometer I had for calibrating a fabric iron, and verified that the new BBQ grill thermometer is
off by at least 100 degrees - waste of time and money. Using the little digital one, was able to watch the form heat up to about 175, but
no more. Noticed a lot of heat loss around the base, so wrapped some aluminum foil around the large gap I had intentionally left before.
Temp went up to about 225, but hot plate kept shutting off. It was getting too hot inside the foil so repositioned foil so that radiant
element is inside, but body of unit is outside. It still shuts off occasionally, but now the temp inside gets up to above 250. It takes
about a 1/2hr to get the entire interior space above 200. Stuck the sample windscreen piece in the mold to see how soft it will get. The
radiant heat is very strong so the lower portion, closest to the hot plate is about 20 to 40 degrees warmer than the upper area. Once it
was warmed up, reached in and poked it with a piece of wire. Its very soft at the bottom and barely soft at the top, but the longer I left
it in there, the more uniform the softness became. Looks like it might work! This piece was trimmed off so it would fit on the
fuselage, so I couldn't get a good air seal on it to try blowing it.
February 11 2017 5.5hrs - 3116.0 total. Traced template onto new sheet of plexi. Cut to shape. Clamped into form. Turned on the hot
plate and waited. Edges weren't bending into shape inside clamped area so used the heat gun, works very well for this and is fast.
Continued to wait for inside of form to heat up, but just wasn't getting to temp. Draped several layers of heavy towels over the top and
sides and sealed bottom better with aluminum foil. A little better, but still not enough. Also tried blowing the heat gun into it for a while.
Very bottom was warm enough to try so gave it some compressed air and got a little distention, but only where plexi was closest to hot
plate. Turned everything off and went and bought another hot plate. Turned it all back on, wrapped it back up with the towels, etc.
Now it gets nice and worm and plexi gets very soft. The problem is that the areas closest to the hot plates is much softer than the rest
of the plexi, no matter how long I let it all heat soak, because of the radiant heat from the hot plates. Need to put in a heat shield to
protect this area. Went ahead and gave it some more air now that was nice and soft, but the bottom area is too soft and distends
disproportionately. Also noticed I was using a lot of air, but most of it seemed to be leaking out? Shut it al down and removed the plexi.
Noticed that most of the JB Weld glue joints in the form top section had cracked and broken loose. The high temp silicon glue was fine,
so used a bunch of it to re-glue and seal the broken JB Weld joints. Will have to see how well this works?
|Starting to close in the sides.
Finished enclosing the form base. Top closed - top open.
|Not too pretty, but it
might actually work!
|New "twin engine" power plant.
|2nd attempt. Getting there...
February 12 2017 7.5hrs - 3123.5 total. Made up a small piece of aluminum and clamped in place to act as a heat shield for the portion
of the plexi closest to the heat source. Traced pattern onto thicker 3/16" plexi, cut to shape and clamped to bottom of form. Its much
stiffer so had to heat it up with the heat gun a little to get it to seat into the bottom of the form. Put the top of the form in place and
started to clamp it down and more of the JB Weld joints broke. Its says on the box its good to 550, but I don't see how it got
anywhere above maybe 400 at the most, but all the joints are very brittle and just shatter if they are stressed at all. Heated the whole
thing up to about 275 to 300, plexi got fairly soft, but when air pressure was applied, it didn't inflate very much. Lots of air leaks.
Turned it all off and went to lunch to let it cool down. Picked up 2 more sheets of 3/16" plexi while I was out. Nice clear, sunny -33F
day. Once unit had cooled down, glued more of the broken joints with high temp silicon. Gave it an hour to dry, then heated it all up
again. This time when air pressure was applied, got a slightly better "inflation". A surprising problem is that it takes quite a while to get
everything warmed up to the same temp so all the plexi is uniformly soft, so when the air is blow in, it quickly cools down the plexi
from the inside. The air is pretty cold as its expanding coming out of the compressor tank. So the technique is to wait about 5 or 10
minutes for the plexi to get uniformly soft, then give it some air, it expands a little, then if you leave the air on - or turn it off - the plexi
starts to shrink back about 50% to 75% of the progress you just made. Also, turns out the heat shield worked a little too well and made
a slightly cooler area than the rest. So this time it distended too little. In my attempts to get it to expand, I actually over-extended the
rest of the areas. It was all smooth and even, so if I wasn't go for scale accuracy, it would be completely usable. Its very optically
smooth, without the wiggles and distortions, and since it wasn't in contact with anything - as in male mold suction form - there are no
surface marks or texture. Took it all apart. Put masking tape over the outer surface and trimmed it to shape so I could trial fit it on the
fuselage. The over-inflation is very obvious with it sitting in place. The top part of the mold continued to disintegrate so went ahead and
glued all of the remaining cracked JB weld joints with silicon. I have a plan on how to get this to work once and for all. It involves
making a plate in the male portion of the mold that will press the flat windscreen portion into position. That will make the rest of it
much easier to shape.
February 15 2017 2.5hrs - 3126.0 total. Cut out flat plate for male portion of mold. Trimmed and sanded to correct shape. Riveted it in
place on bottom edge. Started working on the bracing to hold it at the correct angle. Kind of ironic that I had this piece in the original
plans I drew up, but thought I wouldn't need it and removed it once I started building the mold.
February 18 2017 1.0hrs - 3127.0 total. Finished up the bracing for the new flat plate. Ready to give it a try.
February 19 2017 10.0hrs - 3137.5 total. Clamped "try #2 piece" back into the form to test. Heated it up and messed around with the
fit, clamps etc. Laid out and cut new piece of 3/16" plexi. Used the heat gun and clamps to press into onto the male portion of the
form, then clamped it into the female portion and heated it up. Over the course of the next several hours installed and removed piece
three or four times to see how it was going. Nice thing about this is its not a one time deal. If you need to blow or bend it more, just
heat it up again - but if you go too far - there' no undoing it! At one point drilled out some rivets and changed the angle on the male
plate. Also one of the pieces of glass in the mold side broke, so went to the thrift store and bought another 3X5 frame for $.99,
removed glass, tried to install it, but the glass was about 1/32" larger so I ended up drilling out some more rivets, grinding down some
aluminum pieces and re-riveting to get the glass in place. Once plexi was close to what I wanted, I had a difficult time getting the last
bit of shape. Made up some larger pieces of shielding, repositioned the hot plates, and dug out an old 4" muffin fan, soldered a cord to
it, mounted it into the top of the form, and heated the form up again. Could get it to about 260 to 280, but it wasn't quite enough.
Wrapped a couple more towels and blankets around it for insulation. That got it up to 280 to 300. Was able to blow it to just about
perfect shape. I could see how you could do this 100 times and never get exactly the same shape. This one looks very usable. Have
another piece of 3/16" plexi so I think I'll make a spare while I'm all set up.
February 20 2017 2.5hrs - 3140.0 total. Experimented with sanding plexi for final shaping - works fine. Sanded the plexi from
yesterday a little to see if I could get it to fit in place on fuselage - not quite there yet. Went ahead and cut out last piece of plexi I had
on-hand. This time pressed it into female portion of mold and used heat gun to soften it till it fit in place with no clamps. Marked line
across top of frame, where it has the most intense compound curve, and trimmed it right up to the outside edge of the form. Clamped
into form with male half, applied heat, and kept tightening the clamps. Worked really well. With all the extra blankets and towels the
form heats right up. Took about 1/4 of the time of the last one. Once the entire piece was blown to about where I wanted it, removed
the shielding over the tight compound area, let it soften and blew that area a little more. Let it cool and removed from form. Looks
even better than the last one!
March 6 2017 2.0hrs - 3142.0 total. Decided to make two more windscreens while I've got this all set up and remember how to do it.
Picked up two more pieces of thick plexi. Traced template onto them and cut out with bandsaw. Formed one into female mold with
heat gun. Ready to clamp male portion on and fire up the burners. Don't have time to do that today so spent a little time trimming the
previous one. Masked it off first then trimmed it back a little. Not done trimming yet. Its definitely usable.
March 9 2017 1.5hrs - 3143.5 total. Put top portion of form in place. Used heat gun to form plexi around edge to allow form halves to
be clamped together. Heated up the form, applied more clamps all around once plexi was soft to get better air seal. Removed shielding
pieces, allowed it to heat up the area closest to the burners more than the rest then applied air pressure. Once it looked good, left the air
pressure on but quickly removed heat source, towels, etc. to get it to cool quickly while still holding the correct shape. Let it cool a little
then removed it from form. Has a couple of spots where it wasn't hot enough so didn't take on correct shape. Need to get it to temp
and leave it for a while to allow entire piece to get uniformly soft before blowing it. Rushed it tonight and went too fast. No problem
though, as I can reheat this piece and keep going with it. All of the bad areas are under formed - not over formed - so I can continue to
March 11 2017 5.0hrs - 3148.5 total. Re-heated and formed try#6 a couple more times and got it looking pretty good. Cut a small
piece out of the form base that was acting as a heat shield on one side of the portion closest to the burners. Am satisfied I can only
mess it up if I keep working on it, so masked it off, set it aside, and started on the last thick piece that I'm planning to do for the
windscreen (try#7). Clamped it into the lower half, heated it with the heat gun to get it to hold the basic shape, marked trim line,
removed from base, trimmed on bandsaw, clamped back into base then loose clamped top part of form in place. Ready to heat up and
blow this last one.
March 12 2017 4.5hrs - 3153.0 total. Tried just heat without adding any air to see how it would tun out. The sides were almost
concave. Part across the top was OK, but not shaped well. Tried just heating one of the sides with a heat gun. Made a mess of it.
Decided to go ahead and heat it and give it some air to see if it would fix it. After two heatings and moving the shielding around, finally
got to the point I could tell it was good enough, and I'm just getting tired of doing these! I think I could do five or ten more before I
got one I was totally satisfied with. These last four are all usable, though I can see problems with each of them. I'm hoping that once
they are installed with the window frames, most of the imperfections will be covered up or not noticeable.
March 13 2017 2.0hrs (not counting toward the total) Not counting this time as I spent it cleaning up the shop. Stored the
windscreen form in the basement and cleared away much of the clutter that has accumulated during this plexiglass form building
phase. Am going to work on building the windscreen out of either try #5 or #6 and wait on trying to do the canopy. Also will see if I
can get the rudder and elevator finished up and covered before May.
March 17 2017 1.5hrs - 3154.5 total. Measured, marked and trimmed #5 down to just about final shape. Started to layout for
fiberglass layup of the frame. Need to get some plastic wrap to put on the plexi surfaces where the epoxy will be so it won't stick.
Don't want to use packing tape on the plexi.
March 18 2017 5.0 hrs - 3159.5 total. Picked up some stretch plastic at the store. Removed masking tape from areas where frame will
go and covered with stretch plastic. Covered some other areas with plastic packing tape. Covered fuselage area with plastic and other
masking material. Aligned windscreen and taped in place with packing tape - holds it in position and works as mold release for epoxy at
the same time. Measured and cut a bunch of 6 oz fiber glass and laid up in place on the windscreen. Used three layers in all areas as
called out in the plans. I'm expecting to fill, sand and add at least this much more again as another layer before its done.
|3rd attempt. Thicker plexi this time.
|3rd attempt. After trimming and
masking. Can't see it very well here,
but its very "bulbous". Too much so.
|Starting to install flat plate
in male portion of mold.
|Fan to keep the heat evenly distributed.
|More towels and blankets
|Looks like my trusty old shop light
can't handle 300 degree heat.
|Right out of the mold, untrimmed,
but looks pretty good!
|Masked and rough trimmed - looks usable!
|Try #5 - 3rd thick one.
They keep getting better.
|Try #5 - 3rd thick one.
Masked and partially trimmed.
|Try #6 - 4th thick one.
Just going into the form.
|All 7 windscreens - most
recent one on the left.
|#5 trimmed, masked, covered in
plastic, and clear taped in place.
|3 layers of 6 oz fiberglass on
all frame locations.