|Sep 17, 2008, 02:24 PM|
Lets talk about the lay out of the gear a little more.
For those that have not viewed any of the other MCW building threads, it is very important to try to balance the model as close as possible to the CG now as once you start cutting out the gear you will have no option to move it like your std arf model.
try to lay the gear on the wing where you expect it to go and then pick it up at the cg and see if it seems to balance at that point. Close is fine . . just TLAR it now before you start finalizing your radio layout and spars.
once you have this done, lay the gear in the position it will go and with a ball point pen, trace the battery, servos, receiver ESC and motor mount in place.
Take the pen and make an oval over the servo control arm that is 1/4" wide and 1" long. This will allow the servo arms to move once installed.
|Sep 17, 2008, 02:37 PM|
make the keel
There is nothing more frustrating than getting your fingers caught in the prop on launch - or worse. The reality is that the "problems" with wings is that they can be challenging to launch.
Ive been flying wings for a long time and the easiest way of fixing this conundrum is by adding a keel to the center of the wing to grip the plane by while you are launching it.
Here is my method of doing it, takes a little time and patience BUT it pays off 100X the first time you try to launch with any wind....
take a piece of 1/8" lite ply
lay the root core on the ply and draw around it leaving a little space between the wing and pen for "cutting errors"
take the wing off and draw a 1/2" skid below the airfoil shape and curve it in at the back.
take the wing and extend the lines from the radio gear set up down into the wing then transpose those marks onto the keel . .add marks for spars too.
Using a coping saw or jig saw, cut the keel out then cut the radio gear slots out.
fit to the wing
take the motor mount area and CAREFULLY mark it on the keel then the center line marks
add your "down" thrust here against this line....
carefully cut it out.
fit it to the wing and check again to make sure everything lines up
I like to use a dremel tool with a sanding drum to make these small changes and keep them straight. It is a bear to try to do it with a saw on this small a scale.
you are done.
Mine took 15 minutes to complete with the assist of my scroll saw . .first time you are looking at about 30-45 depending on your saw choices. either way . . .take your time!
|Sep 17, 2008, 02:50 PM|
joining the wing
take gorilla glue (i used the fast dry to do this on this build but do not recommend it for doing it on yours. . .use the amber stuff . it works a little better)
work it into both wing halves as well as the keel.
do not use too much glue as you will have a foaming mess if you do. . . gently rub it in an rub the pieces together to work it in more...
join the halves with the keel then weigh the wing down to prevent it form moving.
check the wing every 10 min to make sure that the foam is not going crazy and that the joint is remaining solid and there is NO FLEXING or TWISTING in the joint.
Let it sit about an hour then check again then let it sit for a few more to make sure the glue dries well.
check for any warping after the wing has sat for no less than 6 hrs. . . . this ensures that the glue has dried.
check for warps or twists or misalignments now
|Sep 17, 2008, 03:06 PM|
I like using a razor blade to do this as it gives better control. I use a flat #11 blade to cut the corners out
use the lines you marked initially to cut out the motor mount. Make sure you cut the depth and test fit everything
mark the prop area to allow for at least 1/2" between the prop blade and the back of the wing.
mark the approximate diameter of the prop and cut out the area to clear by no less than 1/4" at the tips of the largest prop you will use on your motor choice and cut it out with a razor blade.
I like to do this when none of my kids are around as the motor mount takes a little bit of patience to work.
|Sep 24, 2008, 12:38 PM|
ready for the next step . . . cutting it all out!
you can see in the pictures that the motor mount was cut down to the keel so that the mount rests on it (not all the way though the wing) and the prop clearance is cut out to accommodate up to an 8" prop. The initial cuts were set up for a 6" prop as I anticipated adding a screamer on here. Since we are changing that to more of a hybrid, the largest prop that these tower pro motors fit is an 8" prop . . . 8X6 is recommended. In anticipation, I picked up 8x4 and 8x6 thin and an 8x4 and 8x6 slow flyer props from apc. I plan on trying these out on my watt meter once I get them and find the best mix. As I am running a 30 amp esc, I have some room to push it.
Now it is time to cut all of the motor and radio stuff out.
For a complete explanation, go to this post, specifically post 35 to start:
|Sep 24, 2008, 12:42 PM|
take your time - please
cutting this stuff out is not hard, it just takes a little time and patience.
remember that the epp cuts slower than the virgin foam . that means that you need to be especially careful on the transitions between the leading edge and the main wing.
The virgin foam is very easy to work with, just take your time and work slowly, especially in the depth department
|Sep 24, 2008, 12:48 PM|
the battery compartment on these wings is traditionally a weak point.
after you have carefully cut out the battery box (mine was cut out for that largest of my 4 s packs (3300 20c 3s)) and you pack fits snugly, cut a small hole on the back side for the power connector to slide into the radio bay.
Make sure that your charge leads have a place to go, I ended up making a small cut to accommodate the wire and connector in the wall behind the battery.
I give credit on this tip the CK and paul . .battery support mod
One of the most frustrating things to happen is to have the battery box collapse on hard landing or impact. CK and Paul came up with a tip to solve some of this and give additional support to the box without adding a lot of weight.
cut a piece of henry's 183 to fit in the battery box and a piece on the underside of the wing that extends 1" beyond the sides of the box. Use Gorilla Glue white glue (fast dry low foam) as the glue to hold it in.
Place the cloth in the box and cut the corners so that it wraps around all sides.
Run a bead of glue in the compartment and rub (use a latex glove to protect your finger as this stuff is a bear to get off skin) thoroughly around the compartment. Lay the cloth down and add a little more glue to wet the cloth.
take wax paper and place it over the hole then press your battery down into the hole and use light pressure to keep it in place.
turn the wing over and wet the area under the battery box then place the cloth in position.
Place a piece of wax paper over this then lay the whole wing in the core beds to apply even pressure.
Lay weight over your battery to apply pressure in the box.
Let this sit for 15 minutes and check to make sure that the foam is wiped down . . do not allow it to build...wipe/smooth it out with a piece of wax paper . let it sit 15 more minutes and check it again . . . .do this every 15 minutes for about an hour...
If you live in an arid climate it is not an issue, but if you live in a humid one, this stuff makes foam like a rabid dog!
Make sure your battery will come out after the first hour then put it bakc and let it sit for about 2 hrs more . . . .
Lay a piece of henrys a little oversized for the battery box on the bottom and coat it and the underside of the battery box with the gorilla glue and let it sit under pressure with wax paper protecting it from the core bed. Check often to make sure the foam doesnt go nutty.
onto the next step.
|Sep 24, 2008, 12:52 PM|
mount them servos!
get out those glue guns y'all!
I discovered my wife's glue gun a few weeks ago . . .Ive been using a cheapo from micheals I picked up for 3.00. It has thin glue stick that have worked great . . . . . . but my wife has a real nice one she uses for her holiday wreaths and drape making . . . . .. . .
This one is a little more expensive but the company makes two different temperature sticks, either of which go on a lot hotter than my little glue gun..This give a little more time to work the material AND the material dries a little harder than the cheap stuff.
You do need to exercise a little more restraint as the material comes out hot enough to burn the foam if you slip and squeeze out too much glue. . but overall, I like it a lot more than my cheapo for radio install.
Take the servos and test fit them before you start.
take the servos and wipe them clean with denatured alcohol to remove all the finger oils.
re check the center point on all servos and zero trims (make sure you start with a fresh programming model on your radio so you know all the mixing and sub trims are zeroed out!
make sure you servo wire reaches the bay and make sure it fits down into the slot!
apply a circle of hot glue in the hole and one around the three corners of the base of the servo (not where the horn goes ) and gently and quickly press the servo into the glue applying firm pressure until the glue dries.
Lift the servo wire from the base of the servo and apply a small dolup of glue in the slot then press the servo wire into the slot applying firm pressure to the wire while the glue dries.
pull the servo wire at the end and press the length of the wire firmly into the slot applying a small dolup of glue and the mid point then one at the end... keep light tension on the servo wire while you do this to ensure that it is at the bottom of the trench.
once the glue is dry take a small piece of depron or fan fold and trace the outline of the servo hole on it . .cut it out and fit it to the size of the servo hole...not over the control arm, just the servo.
Once this cover is fit to size, take either hot glue or goop (you can also use this for the servo install but I like the hot glue as it is a little faster)
apply a small drop of glue to the top of the servo and a small bead of glue around the edges of the servo hole.
Press the plate onto the top of the servo and hold until dry.
|Sep 24, 2008, 12:55 PM|
Take a piece of music wire . . .I use 1/16"
take a z bender and bend one end of the wire and see if it fits in your servo arms.
If it doesnt, take a drill and - gently - drill the second hole down from the top of the servo arm out to accommodate the wire.
Do not use the top one as it WILL break too easily. It weakens the servo arm.
cut the wire 3" past the trailing edge
leave the other end open for now
|Sep 24, 2008, 12:58 PM|
spackle spackle everywhere and not a chore in sight ;)
I use the stuff I got a home depot when I picked up my henrys . . . cheap . . light and fast drying with minimal shrinkage!
Here you can see my "ugly spar" job!
Take your finger and dig into this stuff and start working it deep into the servo wire slots and the servo cover edges.
Work it into and around the spar slots and anywhere you have dings or dents.
You can do one heck of a lot of fix up with this stuff and the foam holds it very well.
take a spackle tool and run it along the top of the surface to knock off any extra and also to level the rough areas.
let the first coat dry at least overnight, if you live in a humid climate, a full day!
once dry, take 120 grit paper and a block and start sanding. Work the servo covers lightly with 80 grit first to knock them down to the wing level (about 1/8" worth is what I had to sand off) take it slow our you will gouge the cover and the wing . . . .
sand those servo wire slots with the 120 and let it sit.....if the spackle pulls it is not dry enough and needs to sit a little longer.
Once you have finished, check and see where else you need the filling and lay another level of spackle.
Use as many coats as you need as you are sanding off almost all of what you are putting down and the stuff has little weight to begin with.
The EPP sometimes gets big dents and airholes in it. I use the stuff to pack them and make it smoother...epp is by its nature bumpy so dont get too carried away . . .this is what makes it so shock absorbent!
|Sep 24, 2008, 01:07 PM|
lay the elevon out so it comes even with the edge of the prop cut out
mark the end with a ruler to get a nice line
cut even with the wing tip using a saw
|Sep 24, 2008, 01:13 PM|
Take a piece of 1/8" ply and trace the wing tip on the ply with the grain going front to back.
Leave yourself a little on the top and bottom of the trace out to assist you in cutting them out.
I take the template I have made and make a rectangle around it so that I add 1" onto the back to accommodate the elevon.
Make 1" long lines 1/16 high 1/2" back from the leading edge top and bottom and just in front of the elevon on the back of the rectangle and cut with a dremel thin router tip or coping saw to accommodate the tape that will hold the tips to the wing.
Shape it the way you want.
I have included the pics from the 36" tips so you can see the difference. My 48" tips go slightly below the tip as well as above and add a little length on the back to protect the elevon more. I also add weight way back by doing this so . . if you are tight with an aft cg to begin with . . make your tips closer to the elevon tip!
If you are going to paint the elevons and tips, buy some cheapo wood sealer and paint from your local hardware store and paint away.
I like two coats of sealer or primer - lots of sanding with 120 then 400 grit sand paper followed by the color.
The tape for the elevons and tips bonds well to this method of finish whereas just a coat of paint will peel off!
|Sep 24, 2008, 01:25 PM|
We have arrived in that point of the build that the "building" is done
- - pat yourself on the back
we now resume the process and work on the finish!
At this point, without any finish or radio and motor gear, we are at a delightful 5.6 oz for the airframe minus the tips!
I am very happy at this point as I am well under the 7oz I wanted to be.
At this point, you can whip out the rolls of packing tape and finish as I posted in the 36" thread
|Sep 24, 2008, 01:36 PM|
Kellys vs tape
As I mentioned in the 36" thread, the tape is fast and easy - - also cheap!
Slap a layer tape, then econocoat over it and within 2 hrs you are ready to fly!
For this build I decided that I would try two newer building techniques:
water based poly over .75oz glass cloth
3M spray 77 over Kellys 183 cloth
As I build the two 48" MCW birds, I am trying some new techniques and ideas on each of the builds to - well . . .try new things and keep these threads interesting to you and me as well as help those that are new to building a model find out how to find their way.
On the builds (running concurrenly) I have opted to use Water Based Polyurathane and .75 oz fiberglass cloth -what I thought would be the heavier technique - on the starfire and a modified "rite method" using Kellys 183 cloth & 3M Spray 77 (the virgin foam is NOT compatible with the 3M spray 90 that the Rite folks are using on the EPP - Spray 77 is!)- what I though to be the lighter technique for the MCW 48"...
I have been using fiberglass cloth and epoxy or polyester resin as a finish as well as for construction for a loooooooong time (70's). I am so familiar with the use and abuse that it is almost a non event . . weights and the like havent changed much in a long time as the materials have not changed in that long!
I have been a long time subscriber to the Rite building thread as well as others that have used the Kellys cloth but was skeptical. It looks brittle and rough and a bear to "fill" to the point of making a nice base for covering. Spray 3M glues have traditionally been the bane of my existence. The fumes are belligerent (read the can some time) and the stickiness is hard to overcome with all but time. It works with the tape but . . . . . . . a pain in the tail-feathers!
I have also been reading in many different forums about the use of water based polyurethane sold by minwax and others through lowes and home depot for a few years now but never really could wrap my arms around something that was not as "durable" as finish type epoxy or resin have proved to be over the years. so I was not sold from what I had read nor from what I had heard from local folks as most were trying it from the standpoint of a newbie trying glassing for the first time!
I was highly sceptical but . . ..
I was chatting with a buddy of mine from a long while ago about the technique and my rational for swaying away from either. He pointed out that - like in the old days of electric when we were taking common kits and tossing the aircraft ply and lite ply for for balsa ply and or straight balsa, there is no "durability issue" with an electric model.
You have no fuel eating at it, no compatibility issues with materials as the glues and the fuels are a non issue, you have no cleaning solutions attacking it when you finish flying because . . . there is no fuel on it or dirt . . it is electric and doesn't need the "durability" that a fuel model does...it just needs to bond the cloth to the structure and be able to be filled to hide the weave of the cloth then hold the paint!
Well . .. . .have I received an education.....
I was wrong on two points:
with the application of heat (car trunk) for a work day spray 77 sheds a lot of the transporter and is much lighter after dry. It also looses a good bit of it's tackyness over the course of two days to the point where it is workable.
It does not come off the attatched pieces of cloth even after being left in a car trunk for two weeks in the middle of the North carolina summer (mainly clear and hot the week I tested it)
The end weight is almost twice that of water based poly over glass cloth BUT its ability to keep a model airplane in tact in a crash is superior!
This adds considerable strength to the structure while the water based poly provides the best weight savings and best finish. the glass cloth and poly does not add as much strength to the overall frame as the kelly;s does as it is very brittle in relation to the Kellys and 3M....
Lets start with the basic set up.
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