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FF2017 Int. Racers: Crosby CR-4

#42
When you glass the foam are you doing multiple fill coats? Or are you just doing one coat to wet out and adhere the glass to the foam? I'm getting ready to tackle Wilson Man's Bloody Ripper. I have some 1.4 oz cloth and it took me three coats of epoxy to get the weave filled in and smooth on some test pieces.

If so do you do the multiple coats on both sides?
 

earthsciteach

Moderator
Moderator
#43
Personally, I wouldn't fill the weave on the Bloody Ripper. But, if you want a nice, painted finish, you can apply a 50/50 mix of WBPU and baby powder. This fills the weave pretty well without adding a tremendous amount of weight. If you really wanted to lighten the weight of the fill, you could mix microballoons and WBPU. I've never done this, but I don't see why it wouldn't work.
 
#44
Personally, I wouldn't fill the weave on the Bloody Ripper. But, if you want a nice, painted finish, you can apply a 50/50 mix of WBPU and baby powder. This fills the weave pretty well without adding a tremendous amount of weight. If you really wanted to lighten the weight of the fill, you could mix microballoons and WBPU. I've never done this, but I don't see why it wouldn't work.
Yes, I've considered going the WBPU direction, but I'm looking at the Ripper as a tool to improve my fiberglass/epoxy skills as I have my eye on a larger, more complex project that I want to glass (I need a lot of practice :)). I do have some .7 glass that I imagine would take only two coats of resin to fill.

I am curious for those who glass the DT foam if they do multiple coats on both sides until the weave is filled, or one coat on both sides, or one coat on pieces that will be on the interior of the craft, and then enough coats to fill exterior pieces.
 

willsonman

Builder Extraordinare
Mentor
#45
Generally, the idea behind using DTFB is to keep things light for smaller models. The glass is not necessarily there for strength but for hangar/field rash. The smoothness is to make a prettier finish. Adding epoxy on these smaller models is only adding weight. The WBPU and baby powder formula just works, as you know.
 

HilldaFlyer

Well-known member
#46
Good points from all. I've never "filled" the fiberglass weave so I don't have any experience with that. Maybe it is just me, but the 0.73 oz cloth has a pretty small weave, hardly noticeable by eye (maybe I'm going blind). So the answer is, no, I do not use fill coats. Every coat of anything adds weight... even paint.

It is true that if you want a car-like finish, filling and sanding is in order. On this race model, I'm trying to keep it as light as possible because the wings are so small. I'm not making the 1/4 scale any lighter by adding retracts either. I hope it flies...period.

Adding fiberglass does provide more strength. If you peel the paper, overlay with 0.73 oz cloth and squeegee the epoxy off really well, the foam sandwich comes in about 10% lighter than with the paper. It has its pros and cons. I like the way fiberglass stiffens the foam. Having said that, fiberglass will not prevent damage in a crash, it kind of rips apart whereas paper will fold and bend - the same outcome in a crash is plane destroyed. However, the true benefit of fiberglass is that it is waterproof, will not warp and does a great job of preventing hanger rash. If you want you models to last longer than _____________ (fill in the blank like one dewy day, a week in a humid hanger, sudden rain) then fiberglass skins are the real deal. I've actually used the water hose to wash mine... Can't do that with paper!

I am curious for those who glass the DT foam if they do multiple coats on both sides until the weave is filled, or one coat on both sides, or one coat on pieces that will be on the interior of the craft, and then enough coats to fill exterior pieces.
Sorry if I don't understand the question... are you referring to coats as layers of fiberglass or overcoats to fill weave? If you are asking about coats to fill the weave, others who have done that will have to answer. I've never put more than one layer of fiberglass onto the foam unless I am adding structural support. Most of the panels in the planes I've built are single layer of fiberglass on both sides of the foam with no filling overcoat. Over this past summer I made a super light wing with one layer of 0.73 oz cloth on the outside surface of the foam. It was really light and flew like lightning!

Weighs 14.2 oz.

Looks like this now:

Lost elevon control in a steep dive going full throttle... spiral of death was really exciting!


 

HilldaFlyer

Well-known member
#47
Crosby CR-4 1/4 Scale

Progress is slow... but sure
This is the wing of the 1/4 scale Crosby.


Installing the aileron servos.



Installed the flap servo.



Taped the two wings together.



Hanging one wing over the edge of the table so Gorilla glue can be applied to the joint.



Flap panels installed. I won't glue the top wing panel down until after I fit it to the fuselage. So it will wait in this condition for a bit.

 

HilldaFlyer

Well-known member
#48
Crosby CR-4 1/6th scale

Redesigned the ⅙ scale plans using formers to make the shape. There will be a former every 5 cm or so.


Cut out the fuselage profile pieces and skinned them with fiberglass.



Mounted the tail servos and installed the control rods.



Cut the vertical fuselage profile where it meets the horizontal fuselage plate and made guides to help in the gluing process. At this point I had another thought about making a box fuselage and sliding formers over it…. so I played with another design. At the end of this process I might have a few planes built.
 

PsyBorg

Wake up! Time to fly!
#51
That wing alone looks like it soaked up a few hours to put in retracts, hidden flaps and all the support structure. That's some nice design work

You said you wanted to do a wing for he endurance competition to. Think Star Trek with the saucer section that separates. Just make the wing so it separates then the fuse can be recovered rocket style with parachutes and you can go from the races right into the enduro. (I am kidding for those that don't get me)

Have you found the snoopy head to hide the mobius in for cockpit footage yet?
 

HilldaFlyer

Well-known member
#53
Crosby CR-4 1/6th scale

Things are progressing. Good thing Joshua mentioned the deadline... I didn't read the rules close enough and so I thought I had until May.:black_eyed:

So, yesterday was a build DAY...
I redesigned the fuselage to be easier to build - box frame with skin formers. Here goes nothing...



Here is the fuselage cut from nose to tail, the blue masking tape marking the location of the foam joint. If you look close you will be able to see vertical lines. These are where the formers will be located.



Box fuselage glued with Gorilla glue.






Made the cowl from insulation foam. Leaving a little gap for air cooling on the NTM 3536 1400kv motor and 100A Plush ESC.



The motor mount is a bit bulky, but should hold the motor from flying off. The plywood panels slide into the slot in the fuselage.



All the major parts completed (minus the skin). I’ve made the cockpit removable to enable adding FPV to the pilot’s seat. The battery hatch lines up with panel lines. The main wing houses the receiver and slides into the bottom of the fuselage along the block guide. It will be held in place with skewers that slide through the fuselage and block guide. The tail will be permanently mounted, of course...



Holy cow… it almost looks like a plane. The inside of the fuselage was fiberglassed to add support. When the skin gets put on, it should be ready to fly. Haven't decided on the battery size... thinking 2200 mAh 3S because with 3S 9x4.5 APC propeller produces 68 oz static thrust and 60 Amp draw.


 

FAI-F1D

Free Flight Indoorist
#56
This is a pretty epic project. Can't wait to see it finished. You might want to program the ailerons into partial spoiler mode for starting out because that thing looks like a tip stall queen. Probably get someone to launch it for you and do so over tall grass.

It just looks scary!

And it looks awesome!
 

rockyboy

Skill Collector
Mentor
#57
I'm really loving the way this is turning out. While I designed my Caudron with a more traditional flight test folded slab fuse for simplicity, I really think this style results in a better body shape and am eager to both build this one, and learn how to design plans this way.
 

HilldaFlyer

Well-known member
#58
Thanks for all the kind comments and encouragement. It is appreciated.

I really think this style results in a better body shape and am eager to both build this one, and learn how to design plans this way.
You should probably wait to see how the skinning goes first... and to see if this thing actually flies. Funny thing about scratch design, the fuselage went through 3 or 4 designs and ended with the one that came to my mind at first - box tube with formers. I guess that will teach me to try harder stuff first. The profile "+" style is really easy to build, but finding wing attachments and battery locations becomes hard. I'll probably finish it too, just for fun.

You might want to program the ailerons into partial spoiler mode for starting out because that thing looks like a tip stall queen. Probably get someone to launch it for you and do so over tall grass.
Josh, how about deep snow? Thanks for the suggestion. Could you explain the partial spoiler thing because I'm not sure I grasp that. If both ailerons are slightly up, doesn't that reduce lift? Thanks.
 

FAI-F1D

Free Flight Indoorist
#59
Josh, how about deep snow? Thanks for the suggestion. Could you explain the partial spoiler thing because I'm not sure I grasp that. If both ailerons are slightly up, doesn't that reduce lift? Thanks.
Snow works great!

You are correct that deflecting the ailerons up decreases lift. It also lowers the angle of attack of the tips. Another approach might be to combine that with a little bit of flaps. Say 1/4" of flaps and 1/8" up aileron. Just something to make the wingtips be more effective.

As they say, your mileage may (will?) vary, but the bottom line is that the CR-4 is a pretty extreme design. I know some folks have built free flight ones, but I've never been able to get a flight report on one.
 

HilldaFlyer

Well-known member
#60
. I know some folks have built free flight ones, but I've never been able to get a flight report on one.
I knew that all of these speed demons would be a handful to fly because they aren't built to go slow. In the beginning I was going for as light as I could to lower the wing loading, but after building the wings and noticing the fuselage is twice as big... going for speed is the only way to keep it up. I know with the power setup that this plane will fly straight up. Maybe I'll launch at 70 - 80 degrees just to make the first flight last longer than 10 feet. :applause: The maiden will be fun regardless of the outcome. And boy, what a learning experience. So far so fun!