serious power

Hi Matt,
I'm hoping that the veil on both sides will help that - and it's no worse than ribs anyway as they suffer the same ripple effect.
So maybe veil on the inside and 'whatever' on the outside will minimise it anyway - we'll see.

Brian

serious power

Hi,
Rudder core at 10g before honeycombing and 6g after.
A lot of work for 4g.
However the total foam (15Kg/m\3 variety) removed was 37.7g per wing panel x 4 panels, 8g per tail panel x 2 panels and 4g from the rudder.
That's 170g total in the bin.
Six Futaba BLS 173's weigh 168g.

Tail panels are at 27.5g sheeted.
The first skin took nearly 2.5cc of PU (Gorilla).
The 2nd took 2cc and the 3rd and forth skins took 1.5cc each to apply. I just had to get the nozzle size correct so as to control the quantity used.
Ready to try a wing panel now.

Brian

MTK

Many might argue that specific point but few will understand. It's not often you can remove 40% the weight of anything in our toy planes. If I could eliminate 40% of my body's weight, well, then I'd be down to fighting weight, LOL.

My 20.5x10 APC prop weighs about the weight savings you realized. That's a bunch! That's why I'm going through the effort of creating a mold and molding the prop from carbon. The carbon unit will weigh half that of the plastic APC.

BTW, how do you like the tail panel stifness?

serious power

Hi Matt,
It is impressively stiff.
Considering that when honeycombing the tail cores I had decided to experiment with a diamond pattern with very narrow remaining walls it is even more impressive.
What it is going to be like when the outside is done as well remains to be seen but it is shaping up to be incredible - almost !
I will keep you informed as this develops
I have something cooking using your undercarriage recipe as well.
More later.

Brian

serious power

Hi,
Have skins on the first two wing panels - top wing.
They weigh 85.5g
That's ;
Core - 27.5g (top wing)
Skins - 25g x 2
Glue - 8g - ; = 4g per skin.
There is some more sanding to do on the skins while the facings are being prep'd. So Maybe 80g equivalent is possible for these top panels.
The bottom ones will be 7g to 10g more.
A little concerned re finishing method after the discussion on the 'post a photo thread' just now.
Some quantitative testing req'd over the next few days.

Brian

serious power

Hi,
Just a little on method for applying the skins.
- Using the veil on the inside eliminates the need for additional structure ; spars, carbon straps etc.
- I dispense the PU with a syringe and a lab,, calibrated sampling nozzle. This measures that used and I cut the tip back on the nozzle to give the desired bead size.
- I roll a 'damp' emulsion roller across the core before applying the glue bead. I then roll it over the skin/carbon veil just before positioning it. I do not wet anything - just leave a residue.
- Using PU on pre-sealed surfaces means that one skin can be applied at a time as there is no wetting of the wood. This makes accurate alignment easier as it is critical for the application of the 2nd skin only.

Brian

serious power

' Hi Brian,

Is that Fumed Silica? It is very fine, extremely fluffy material. But I don't think it's a good filler that sands easily. I don't think it will do the job on the finish that you are looking for but I don't know for certain. I would test first.

I don't use microballoons in the finish either. Much too coarse and needs extra filling so paint can stick without pinholes or bubbles. I don't recommend it as a top coat. Great underlayment tho.

So that we are not accused of highjacking this thread, maybe we should this take this discussion to your other thread?? What do you think? '
( Quote from the 'post some pictures' thread.)

Matt,
Good thinking
http://www.westsystem.com/ss/410-microlight
I can't find a data sheet or spec.
I think it's a synthetic 'balloon' a bit like the brick red phenol ones but this is easy to sand according to a friend ,Dave, who is helping when he has time.
On a test piece just now it, mixed 50/50 with a dope thinner 50/50 mix, it has filled 0.3oz veil all but completely in one coat.
There are pin holes/air bubbles in it alright - very small though.
I'm thinking that if I thin the dope more and use less 410 that it will fill in layers and I can start to add talk progressively in layer 2 and 3.
I will do samples first.

Brian

najary

Hi Brian,

I saw the beautiful job you are doing here and was struggling with myself if I should tell you what I am going to tell you now:

About 20 years ago I built a plane named Vortex with wings structure about the same as you are building here.
That plane crashed in it fourthly flight!!!

The wing had broken in the air about were the aileron servo was.

As I analyzed what happened: in positive G force the lower skin is pushing against the foam and the upper skin is try to disconnect from the foam.

As a result of the lake of foam area the foam itself could not held the tension forces.

Just a sad story.

Good luck,

Isaac Najary

serious power

Hi Isaac,
Thanks for the concern - much appreciated.
I have been honeycombing like this since the mid 1980's.
Everything has to be right ; foam quality/work, wood grain orientation, bonding of wood to foam and stress focal points must be avoided/managed.
With a diamond pattern there is sheer web at all chord depths by the full length of the panel so if the foam and the bonding is good such a failure will not happen - unless there is some stress focusing.
Also I am creating a composite skin.
I believe it will be ok.
Thanks again.

Brian

MTK

Brian,

406 is what I was thinking of. That's fumed silica. It's a terrific thixotrope and results in a very smooth finish. That's what I use as my surface coat in building molds. This material admixed into epoxy thickens the epoxy quickly

I have not used 410 but looks like it's a worthwhile material to have around.

MTK

I think so too. A couple key points (making the assumption that Najary built a monoplane with retracts).....
1- the stressed skin used takes quite a bit of load both in compression and especially tension.
2- it's a bipe; each wing's load is considerably lower than that of a monoplane's. Same g's load each wing significantly less, at least 35% less.
3- Years ago chances are we were dealing with retracts which always compromised the lower skins unless proper reinforcements were added.
4- The servo cutout also compromises the lower skins. However, one only needs to extend the facings of the aileron cutouts some 3-4 inches towards the root to greatly reduce the sharp load by distributing the stress riser over a longer arm.

serious power

Matt,
I will try various blends of this ,glass spheres and powder and see how it works.
It is compatible with the dope (does not break down) and makes a very smooth slurry for brushing.
It is very light.
We'll see !

Brian

serious power

Hi,
Have all the panels sheeted now.
The bottom wing panels are at 100g - they are a little bigger ,have less foam removed at the root and I used a little more glue each skin (6.5g/skin)
So the weights with the skins applied to the cores are;
Rudder 21g
Tail half 28g
Top wing half 86g
Bottom wing half 100g

Matt,
Have spent a lot of time in the last few days working out a method for finishing the carbon veil - if ever I get that far !
I have had a look at both the 0.2oz and the 0.3oz veil.
The .2 is a bit feeble over the soft balsa - it is usable but is soft and easily cut through, I would have to bury it in dope to avoid cutting through it while blocking over the honeycombed foam walls.
I like the strength and resilience of the 0.3 so I have decided to give some weight back by using it.
The lightest and shortest path I've found is ;
Apply the veil to unsealed wood using this mix; Dope 1 part, thinner 1 part and west 410 1 part.
This all but fills the veil and the 0.3 is happy being put down this way - but it is full of pin holes.
Then two coats if sanding sealer - fairly thin.
This seems ready for wet sanding then priming - see pic;

Brian

MTK

Brian, I like the 0.3 veil too. But it is thicker. It will build an even stiffer panel. BTW, how are you planning to mate the halves? Carbon Joiner Tubes of glass cloth? If glass cloth, consider applying that with nitrate dope too. Probably 2.4 oz bias cut is more than enough.

I've tried the "shortest path" before and wasn't happy with the result. It had a tough time sealing, needing way too many coats to do so. For wet sanding that is. But wet sanding is not the only option.....

I don't think it will hold up to wet sanding. It doesn't sound like enough sealing coats went on. But what the heck! And you always have dry sanding available which should work well enough for primer. One thing certain, the primer will show every flaw you can't see at the veil stage.

The weights you are seeing are on par with my honeycombed panels, area for area. Definitely lighter than non-honeycombed. Glue weight savings is considerable; my regular 530 square panels take about 40 grams of epoxy top and bottom skins. Yours are taking half or less area for area. Another way to say that honeycombed panels expose about half the foam area to the wood. Sounds like the early weight estimates for the wings that we kicked around should be very close to the real thing. I still see around 10-12 ounces per wing ready for equipment.

serious power

Matt,
The test pieces seem water tight - I will check some more as this is my first time using dope.
Re the joining/mating of the panels ;
I should get to that next week or the week after and will show it here.
Having attached the root faces with a minimum of PU (some people use excessive amounts of glue here and all it is is weight,a waste and useless) my plan is to first overlap the veil - as you have said there is some substance to it - actually the 0.3 with the 410 and dope is as hard as epoxy and 1/2oz glass ,maybe harder.
Anyway I've tested the veil on a lot of samples and even the 0.2oz supports the balsa enough that, with the veil on the tension side, the balsa always(100%) fails in compression. When tested the other way around, ie with the veil on the compression side the balsa always failed in tension on that side.
I will do a small overlap on the top wing, both sides, and on the bottom of the bottom wing. I will extend the overlap past the wing seat on the top side of the bottom wing.
This overlapping will simply continue any tension that is in a panel skin under load past centre to the other side.
Then I will use 0.6oz glass to back that - first a wide piece then a second narrow one. Wide of course will be relative to location. I think that will be sufficient. I will load the wing to check.

Yes I'm impressed with the tensile strength of the dope and intend to use it for the 'bandaging'. Again no abrupt change in load bearing characteristics by continuing through with the dope also.

Brian

tuny

I have a little F3A biplane experience and I can suggest that dont under estimate the flight loads on a biplane wings. My point is, you dont need 300g wings, yo need STRONG wings. Your craftmanship looks very good!

Just my 2c

serious power

Hi Tuny,
Thanks. I will be trying to avoid any.underestimating. That is why I want to use the 0.3oz veil to complete the wing skin sandwich. Skin strength is key to building wings this way.

Actually with regard to wing loads on these bipes ; Normally they should be a lot lower than on a mono. This is in part why I'm asking about incidences in the other thread. If the wings are set at very different incidences there will be some very funny things happening ,load wise, as various manoeuvres are performed depending on conditions.

I wish I could get 300g wings - 350g to 400g is my real target.

Brian

Edit;
Hi again Tuny,
Perhaps you could post some details from your new bipe on the ' Biplane Wing Incidence ' thread !
What wing incidence v downthrust ??
Are both wings the same or how much difference ??
Thanks again.

MTK

350 gram wings are realistic. The stressed skin composite covering the foam is very stout. What I have observed so far indicates the wings will easily support the loads to at least to 12-15 g.

Having "built" a 12 pound all balsa Extra a couple years ago, with open bay wings, and 1200 squares and powered with a piped DLE55 (35 lbs of thrust), I realized how overbuilt most of these models are. Granted, those 550 square inch panels weighed 18 ounces (500 grams) RTF, but still, they were well designed and constructed to hold up to the wild gyrations of that crate. Some may need to recalibrate their thinking in regard to weight versus the task.

Poorly built wings, the types we saw a few years ago coming from some reputable manufacturers, can weigh double and still fail.

serious power

Hi,
Making progress,slowly, with this.
Have panels ready now for two models but will take one only forward from this point Better to see how one goes first .
They are all faced except for the elevator roots which will be done after fitting to the model to suit the fin/rudder.
Using 1/8 balsa for the wing and tail hinge TE's and 1/4 for the aileron and elevator LE's.
This lot represents 16 wing panel skins, 8 tail panel skins and 4 rudder skins.

Brian

serious power

Hi,
The alignment of tail halves and the importance there-of was mentioned recently in an other thread and quite correctly.
Back in the day,when we were producing our OD stuff we came up with the following to deal with this ;
We made the tail halves as if they were for a one piece tail, going through the fuz,, .
We then joined/glued them having jigged them up for perfect alignment (as close as possible anyway).
Then the outer tubes are dropped in from the top (or bottom) having been boxed in balsa first.
The tubes/boxes are put parallel to each other in plan and end views. This assure ease of assembly there-afterwards.
Then cut the halves apart again (two cuts), face with a root rib and discard the middle piece. Rejoin with inner tubes for that 'perfect' alignment !
Finish the boxes to profile and they are ready for covering - a 15g glass patch over the top is a good idea, but not required, if using film.

The adjustable tube is run through a box in a box and shims are used to adjust. This is stiff and not subject to loosening up or pivoting even if using a YS.
The foam former is plenty stiff enough and is not subject to popping loose if jarred. It and the boxes weigh 9.5g. The equivalent in a factory job (the screw in the fuz,, type) weighs between 20g and 30g not including the tubes.

Brian

serious power

Hi,
Some progress;
Old school meets new school ;

serious power

Hi,
Some more.
May have a good option for the Monokote/Oracover users - will talk about this later today hopefully.

MTK

Brian,

Am I looking at the wing on the last photo? The weight is very good for a 700 square wing, just under 8 ounces with covering on.

Have you had a chance to sand the 410 filler? How did that go. I bought some a few weeks ago but have not tried it yet.

serious power

Matt,
Yes that is the top wing - a little smaller than the bottom one and a little more foam removed near the centre.
I am going with the 0.3oz veil all around.
It will take more to fill than the 0.2oz, quite a lot more, but I think it is worth it for this project. I am still working on getting a good sequence of materials and sanding to get the best out of it.
The 410 sands very easily but if too much is used too soon it gives a lot of pin holes etc.
However this 0.3oz (actually 0.35oz) adds so much stiffness and strength it is hard to believe. It also gives quite a hard surface.
Also the 0.3oz takes a lot extra per coat - it really sucks the material out of the brush as you try to wet it.

That wing has a sealing coat and 3 heavy coats of 1:1 dope/thinner , the first of which put the carbon down.
It looks like it will be ;
1 Sealing coat
4 coats (heavily applied) 1:1 dope.
Light sanding
2 coats dope and 410 ; - 2 parts dope / 1 part 410 / 4 parts thinner
A better sanding - maybe wet ?!!
2 coats of sanding sealer
Full wet sanding.

I am using the 410 to lighten nearly all the adhesive I'm using at this stage - 410 + epoxy and or 410 + PU - both are easy to work , sand and carve etc.

Brian

PS; The aileron in the 2nd photo above is sanded after the two coats of 410 mix - waiting for sanding sealer and is at 16.5g as is.
There re no ailerons on the scales with the wing.

serious power

FOR MONOKOTE;
While experimenting with lay-ups I wondered about using this carbon veil method for film.
I think this will work;
.- Use whatever core you prefer ! - Balsa ribs/spar/sheer web - foam ribs/spar - foam core - honeycombed foam.
.- 1mm comp grade balsa for skins - will suffice for both mono and bipe wings.
.- 0.2oz carbon veil applied with two coats of 1:1 dope on the inside of the skin having pre-sealed the skin with a single coat of dope.
.- 0.3oz carbon veil applied after skinning the core - one seal coat then apply the veil with two coats of dope/west410/thinners 1:1:1
.- Sand moderately with 600gt.

Based on the wing above this would be ready for film at 230g - all hard points,woodwork etc completed. The wing above is stronger and stiffer than my Midrex wings.
The surface would be as hard as 0.6oz glass and epoxy. If 0.2oz was also put on the outside, instead of the 0.3oz, it would be a little softer but still harder than just balsa.
It would NOT be sealed so should film well. The surface has a texture and firmness similar to non gloss card material (like the inside of a greeting card)
Most Monokote colours cover everything however if you had a feeble colour the surface could be covered with a dust coat of a primer.

I have not tried this and do not have time or material right now - maybe someone has ??

If it works wings for a bipe would be finished and ready for equipment at 300g

Brian