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Aug 15, 2014, 11:23 AM
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FliteMetal's Avatar
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Beating It Up... ;^)


Your DC-8 project sounds good. We are seeing more and more interest in scratch building larger and larger
EDF projects with integration of newer composites. Especially when the traditional materials are married
to new products. Thus far, we have been pleased with all our findings. The cost of scratch building keeps
shrinking with each new product discovered.

Polyurea Resin Polystyrene Foam Coating For RC Scale Models (4 min 11 sec)


Such is the case with the Polyurea resin.

1. Initially I will post images of test conducted with low density (white) beaded foam. These disclose the
overall acceptability of Polyurea for the general application to polystyrene from a cause and effect
standpoint.

2. All Polyurea test surfaces were "brushed" onto the least expensive white beaded foam after being
primered. To-be-coated surface was lightly sanded with sanding block to break loose and clean dust
of polystyrene which typically occurs as a result of hot wire cutting. Test planks were hot wired into
3.83" square x 1".

3. The Polyurea was applied in multiple thicknesses to illustrate the overall strength and durability of
each thickness. I did not have to conduct more than one test to arrive at my decision.

4. It was observed when one (1) coat of proper primer was brushed onto the foam surface and permitted
to dry X time...two brushed on coats of the Polyurea resin yielded a hard surfaced plastic coating 1/16th
of an inch thick with a level and smooth surface.

5. Note in the image with the plank turned vertically the multiple diameter of the expanded bead foam.
The individual beads of foam had an unusally brittle surface with the internal foam "shrunk back" within
the bead perimeter. This is the first time I have ever observed this. Usually beads simply pop loose from
each other when picked at; not the case here. I was told there were recycled beads in this test foam.

6. Clicking the images below will yield super sized detailed up close look at how tight and clean the foam
and Polyurea are as a sandwich not easily parted. Look closely at the wicking action of the proper "primer".
It wicked between beads inconsistantly but as deep as 1/4". Primer dries firm, but pliable.

7. For the impatient among you...though the Polyurea was "brushed on" note the nice smooth surfaces.
Lightly wet sand, prime & wet sand smooth prior to paint or my favorite natural
aluminum covering...

8. Next, impact and T/C testing videos...First impact testing.
Last edited by FliteMetal; May 08, 2018 at 08:57 PM.
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Aug 15, 2014, 05:09 PM
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FliteMetal's Avatar
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Posted the physical destructive test video and still closeups of 1/16th of an inch thick Polyurea Resin Coating
over EPS (white beaded foam).

There has been a decision to lighten our load while increasing durability with polyurea resin, PR. This instead
of balsa skin on fuselage, fuel tanks, inboard and outboard nacelles on both BuNo configs. The DB-47B-50-BW
anti-radiation drone fuselages will be PR'd as well.
Last edited by FliteMetal; Sep 13, 2014 at 10:49 AM.
Aug 16, 2014, 11:21 AM
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FliteMetal's Avatar
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Posted a replacement Polyurea Resin Coating Video:
Last edited by FliteMetal; Aug 16, 2014 at 04:52 PM.
Aug 16, 2014, 02:18 PM
Dont forget the velcro straps
corsair nut's Avatar
what happens under flexing? doesnt it crack?
Aug 16, 2014, 03:41 PM
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p901P901's Avatar
So what would happen if Polyurea Resin Coating was applied to a plug or mold instead of using fiberglass. Will it have enough strength and what is the weight per sqft?
Last edited by p901P901; Aug 16, 2014 at 05:47 PM.
Aug 16, 2014, 04:42 PM
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FliteMetal's Avatar
Thread OP
Just how much flex would you expect this B-47 to experience?

My initial test occured at the manufacturer's lab where my multiple two handed thrusts to a lab table's sharp
edge yielded absolutely "0" damage to another of these brush coated blocks with "0" tension and compression.
This with my weight behind six consecutive thrusts. Surface rebounded without deformation even though the
resin was brushed onto only one side of the "white beaded EPS".

The inventor of this resin smiled. I think he was a little taken back that I would press this heavily on his resin
with it at "0" tension and compression. There was no evidence I had impacted the surface except marring, no
scaring or scratching. Rebound was surprising. Very little energy absorbsion.

My fuselage is a facade, faux, non-load bearing structure comprised of three Dow Hi Load 60 Styrofoam sections.
Fuselage milling and hot wiring is performed on each half of the fuselage centerline from nose to end of rear turret
cavity.

Fuselage front halves are CNC'd internally then turned 180 degrees and their entire outside surfaces are CNC'd
back to the parting point between fuselage frontend and front of fuselage mid-section. The midsection extends
from just ahead of the wing front tangent back to virtually half way between wing rear tangent and end of 20mm
rear turret.

The rear portion of the fuselage is CNC milled internally then turned 180 degrees and its exterior surfaces CNC'd.
Internal truss cavity is epoxied to a 16th thick balsa plank laminated on both sides with carbon fiber vale on each
of its cavity surfaces.



Because the cavity is diamond shaped it will captively hold another truss shaped exactly the same as its upper &
lower sections with a slip fit tolerance between the two trusses. Trusses are minimum thickness to cantilever its
horizonal stab and vertical fin flight loads. Laminated with carbon fiber this is not anticipated to require much
thickness.





Because fuselage front contains only the forward navigator/bombadier station and upper cockpits, it will not be
of enough mass to weigh heavily on the telescoptic front truss.

In addition to the front fuselage telescoping into the center truss, there is an internal truss within the previously
described truss. This is suspended within the truss cavity with proper vertical slits into which a pair of wing spar
blades extend out into the wing inboard spar box. The spar blade is captive by hex head bolts entering in top and
bottom narrow edges extending outward with access from above and below through threaded brass seats.



Wing halves are two piece with outboard section from wing tip to outboard edge of receiving box for removable
inboard engine nacelle blade as illustrated in previous illustration. Each of the two portions of the wing halves
utilizes traditional spars and captive spar boxes on either side of the pylon parting point.

Outboard wing sections are formed from hot wired and balsa sheeted Hi-Load 60 Styrofoam. Inboard foam core
is low density white beaded foam to reduce over-all weight. strength of inboard wing design negates need for 60
pound density Styrofoam.

The outboard engine pylon is shaped like a short sided row boat and much wider at its base than inboard pylon to
assure narrow wing is not twisted from side force of outboard engine nacelle. Outboard EDF are 90mm 13 bladed
with 6.7# thrust on pair of 12kmah3s.

Last edited by FliteMetal; Sep 13, 2014 at 11:05 AM.
Aug 16, 2014, 06:16 PM
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FliteMetal's Avatar
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With the latest edit, the B-47 thread is up to date. The entire thread is within WattFlyer.
Last edited by FliteMetal; Sep 13, 2014 at 11:28 AM.
Aug 16, 2014, 10:33 PM
Official Boat Bum
Eddie P's Avatar
Good stuff... I am digesting it a little, bit by bit - that's because I'm on the road and not able to really pay much attention toward RC activities right now. Will go back and look at the video and re read your test summary in another day or two. Are you going to add any sort of fiberglass weave or wood under the Styrospray? Right now I have many sets of hot wired foam sections for my particular project - and the plan was to cover those in balsa and glass/resin. Then fill, sand, paint, etc. That has always been the "standard" composite scratch build construction glass job for me. I have been curious for some time, however, as to the possibility of using Styrospray as a compliment/replacement of the above procedure rather than a simple addition to it.
Aug 17, 2014, 01:14 AM
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Lt599's Avatar
I have used Styrospray 1000 directly over Dow Blue Core foam on scratch built 70mm EDF jets with great results. As you have shown it is extremely durable, One of the models is over 2 years old. It is a belly lander and has been flown many times with hard landings and even a couple of "mishaps" It has no stress crack or any signs of chipping or delaminating. I apply it with foam brushes but I would like to try and spray it with a HVLP hopper gun, just have to make sure you have the proper respiratory protection or it is lethal. I have not tried it but I believe it would work very well on plugs or molds in place of resin and glass, a person could build it up to a thickness that would be quite rigid. Very nice build you have going Greg
Aug 17, 2014, 08:23 AM
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FliteMetal's Avatar
Thread OP

Traditional Base Of Laminated Styrofoam With .6 Oz Glass Cloth


Thank you Greg, its getting there. I am afraid to spray wherein I believe you loose thickness control. I want the
thickness to stay around 1/16th...aka 0.0625. My wings, vertical fin, rudder, horizonal stab and elevator are
laminated with 1/16th balsa, .60 oz/sq.yd. glass cloth and Pacer Z-Poxy Laminating Resin diluted 30% with
denatured alcohol.

This is going to invoke traditional T/C. After preparing the lamnate in the traditional manner, pour and distribute
Polyurea Resin in multiple foam brush applied coats. You can see, though it's 158+ inches w/s, there are many
internal cavities for our mechanical operations.

For our complete Scratch Building How-To...from thought to takeoff, see three (3) threads in WattFlyer.com.
Key-in Google... 1:8.7669 Boeing B-47 and follow the multiple links...return here for short hand version as
we do final assembly and initial flight. I welcome all questions and advise you have to share when I paint myself
into a corner...
Last edited by FliteMetal; May 08, 2018 at 09:23 PM.
Aug 17, 2014, 11:15 AM
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Polyurea As A Molding Medium


Quote:
Originally Posted by p901P901
So what would happen if Polyurea Resin Coating was applied to a plug or
mold instead of using fiberglass. Will it have enough strength and what is the weight per sqft?
In my personal opinion I believe the Polyurea Resin is best used as a coating where its thickness can be
controlled. If used in a rotational mold there would be a uniform thickness, negating the reason for spraying.

From where I sit, spraying should be avoided for health reasons... PERIOD! At this time there is not an MSD
Sheet without requesting hardcopy of same.

I am sure there is a release agent which will permit Polyurea resin to be released from a mold...however this
will create a probable fault or weakness.
Last edited by FliteMetal; Sep 13, 2014 at 11:19 AM.
Aug 17, 2014, 11:53 AM
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Flexing...Cracking


Quote:
Originally Posted by corsair nut
what happens under flexing? doesnt it crack?
Brent,

Good question, however you need to more clearly define flexing and cracking. I am serious, not being curt.

For example, I expect each of my B-47's wing tips to flex/rise between three and four inches at ROG. This
is normal for a swept wing aircraft. Looking at any inflight images of a B-47 you easily see a four to five foot
flex.

As long as this does not manifest itself as an occilation and your wing laminate is not delaminated, you
should not have any issue. In George Maiorana's Tu-95 video wing tip flex/rise presents no issues. Aside
from being 44 inches narrower than my B-47, the Tu-95 is a mirror image of the planeform footprint.

Obviously you do not want occilation/flapping. The 1:1 experienced this in both the wind tunnel and in early
flight testing until vortex generators were installed on outboard wing sections ahead of the ailerons limited
the degree of flex.



Wing was too clean resulting in air traveling down the wing trailing edge from root to tip inducing turbulation
leading to loss of consistant lift resulting in excessive wing occilation.

Wing rise/flex is clearly seen in the wind tunnel at speed with the 1/10th scale B-47 test model.



Note the nose down attitude at speed. Look at the wing tip incidence at this time..., virtually "0".

Tell-tale flags show problem on the 1/10th wind tunnel model. Air is moving laterally across the wing in flight...

Last edited by FliteMetal; May 08, 2018 at 09:32 PM.
Aug 17, 2014, 01:46 PM
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Thread OP

XPS Vs. EPS


Quote:
Originally Posted by Lt599
I have used Styrospray 1000 directly over Dow Blue Core foam on scratch
built 70mm EDF jets with great results. Greg
Thank you Greg:

Beyond the over the counter Blue Dow Styrofoam here are the products which can provide greater tensile
and sheer strength with little to no gain in weight. Yes, Dow does manufacture an expicit product named
Surfboard Foam. It is used by a single surfboard manufacturer, who will sell the product if you want to go
to California for it. It is extremely expensive because of limited production.

Note the specifications for Surfboard Foam compared to Styrofoam Hi-Load 60. Its virtually the same, yet
Styrofoam Hi-Load 60 can be more easily hot wired since it does not have the1/4 inch vertical Styrene
Stran (filiment) layers within it.

Last edited by FliteMetal; Aug 17, 2014 at 08:42 PM.
Aug 17, 2014, 02:34 PM
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Polyurea Resin Weight Per SqFt?


Quote:
Originally Posted by p901P901
So what would happen if Polyurea Resin Coating was applied to a plug or mold instead of using fiberglass. Will it have enough strength and what is the weight per sqft?
I posted this earlier, easy to overlook since it is small.

Aug 17, 2014, 07:40 PM
Registered User
Lt599's Avatar
Quote:
Originally Posted by FliteMetal
Thank you Greg:

Beyond the over the counter Blue Dow Styrofoam here are the products which can provide greater tensile
and sheer strength with little to no gain in weight. Yes, Dow does manufacture an expicit product named
Surfboard Foam. It is used by a single surfboard manyfacturer, who will sell the product if you want to go
"tote de note" so to speak. It is extremely expensive because of limited production.

Note the specifications for Surfboard Foam compared to Styrofoam Hi-Load 60. Its virtually the same, yet
Styrofoam Hi-Load 60 can be more easily hot wired since it does not have the1/4 inch vertical Styrene
Stran (filiment) layers within it.

Thanks for posting this information, I am always interested in available foams and their properties. Greg


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