Profile fuse flexing

[Paul Taylor]

I have been searching as I know this has been talked about before. I have not found a thread.

Will adding two layers of silk on a profile fuse prevent flexing or just add extra weight?

Thanks
Paul

[John Rist]

I am no expert but I had some luck with carbon vale for stiffing.

[Dan McEntee]

  The issue isn't necessarily "flexing" but twisting. You want to keep the stab level. Applying any kind of laminated material around the whole fuselage will add a"shell" to the balsa that will resist twisting. Sil, silkspan, carbon veil will all work to different levels.
   Type at you later,
     Dan McEntee

[Serge_Krauss]

My short answer is that one layer, with threads diagonal should help. I believe that .56-oz glass filled with epoxy is better, since it is light and much less flexible

I've made very stiff profile fuselages by triangulated-truss tail arms, with 1/16" balsa lamination to close the box and .56-oz fiberglass epoxied on with 45^o biased weave. These fuselages are very stiff and torque resistant. The glass/epoxy can be as light as or lighter than dope and silkspan or CF, IF you apply to a very thin (wiped with card) base coat of epoxy to keep it from floating (you can roll it in), followed by a coat to fill the weave, after the base coat has set to a tackiness. The glass doesn't seem to take as much epoxy as, say, medium silkspan

I know you didn't ask, but I've included pictures of the simple truss-work too.The biased glass/epoxy application can be a real mess, if not very carefully done. One hint is to roll the cloth carefully ahead of time, so that it can be carefully un-rolled over the base coat. Taping the edges helps a LOT, because it keeps the weave at 90 degrees, preventing it from stretching in any direction. Any attempts to re-position or adjust the glass can be really frustrating or futile, unless those edges are stabilized.

Using dope with the glass is easier, but the dope is softer and moreflexible, and it keeps shrinking to reveal the weave for a long time. I think the dope can float the glass, when subsequent coats soften/dissolve earlier ones, adding weight.The epoxy is better. You can paint over slightly roughed up glass/epoxy with butyrate for final finishing. I patched together some photos that show some of what I have said. The plane was flown several times this summer, and the Brodak butyrate dope has adhered fine, as long as shielded by enough clear final coats. There is no mechanical separation of dope from glass/epoxy. A big advantage is that, if you do it right and wet sand with 400-600 just down to the weave, you're about ready for color coats.

If you use two layers of silk, it's probably advantageous to have one with longitudinal and vertical weave and the other biased. It sounds as though it could be kind of heavy. The single layer of glass is sufficient to make a big difference in the "hand-twist" test.

SK

[James Holford]

1/64 ply

Sent from my SAMSUNG-SM-G891A using Tapatalk

[fred cesquim]

My short answer is that one layer, with threads diagonal should help. I believe that .56-oz glass filled with epoxy is better, since it is light and much less flexible

I've made very stiff profile fuselages by triangulated-truss tail arms, with 1/16" balsa lamination to close the box and .56-oz fiberglass epoxied on with 45^o biased weave. These fuselages are very stiff and torque resistant. The glass/epoxy can be as light as or lighter than dope and silkspan or CF, IF you apply to a very thin (wiped with card) base coat of epoxy to keep it from floating (you can roll it in), followed by a coat to fill the weave, after the base coat has set to a tackiness. The glass doesn't seem to take as much epoxy as, say, medium silkspan

I know you didn't ask, but I've included pictures of the simple truss-work too.The biased glass/epoxy application can be a real mess, if not very carefully done. One hint is to roll the cloth carefully ahead of time, so that it can be carefully un-rolled over the base coat. Taping the edges helps a LOT, because it keeps the weave at 90 degrees, preventing it from stretching in any direction. Any attempts to re-position or adjust the glass can be really frustrating or futile, unless those edges are stabilized.

Using dope with the glass is easier, but the dope is softer and moreflexible, and it keeps shrinking to reveal the weave for a long time. I think the dope can float the glass, when subsequent coats soften/dissolve earlier ones, adding weight.The epoxy is better. You can paint over slightly roughed up glass/epoxy with butyrate for final finishing. I patched together some photos that show some of what I have said. The plane was flown several times this summer, and the Brodak butyrate dope has adhered fine, as long as shielded by enough clear final coats. There is no mechanical separation of dope from glass/epoxy. A big advantage is that, if you do it right and wet sand with 400-600 just down to the weave, you're about ready for color coats.

If you use two layers of silk, it's probably advantageous to have one with longitudinal and vertical weave and the other biased. It sounds as though it could be kind of heavy. The single layer of glass is sufficient to make a big difference in the "hand-twist" test.

SK

what a neat and clean  build Serge, and beatifully shaped fuselage! congratulations.
i have been using .56 fiber and finish resin on scale and F3A r/c models for ages, but have my doubts about weight for control line use.
do you think that fiber/resing finish turns out as light as dope/carbon veil?
regards
Fred

[Bill Morell]

Serge, what kind of epoxy are you using and what is the "working" time of it? Thanks in advance.

[Paul Smith]

Profile fuselages are best used on 1/2A's and maybe up as high as 35-size models.

The bigger "profiles" now in use are something of a rules-beating scheme to invade the so-called "simplified" events with larger and more elaborate models. These complex honeycomb structures with high tech composite siding are a long stretch from the original concept of "profile" as a point of relief for full-bodied construction.

I'm sure some sea lawyer will read me The Rule Book and prove that "profile" with a piped 75 is not illegal.  But it's far stretch from the rationale for P-40.

[Robertc]

Larry Cunningham wrote "Building a Better Profile" where he talked out that very question.   The last profile fuse he built, I have and it is VERY stiff.
Basically 1/2" balsa till around the back of the wing, then 1/2 x 1/2 balsa top and bottom to the back with diagonal bulkheads in between, BUT his are
very slightly convex.  This is covered with 1/64 ply.  1/2" block in the area where stab goes.    I have all his files.  If you want to read the lengthy file,
let me know and I'll send it to you.

[Serge_Krauss]

Fred - Yes, I have experimented while building and can say without doubt that I have actually saved weight with Epoxy/glass laminates. The two fuselages shown are for similarly sized planes. The horizontal tails for each were finished differently. The older one's stab/elevator was finished with doped CF veil on the Stab part and weighed marginally more than (about the same as) the one finished with glass and epoxy. The glassed one is stiffer. That is because the glass took less epoxy than the amount of dope needed to fill the veil. Dope weighs less, as far as I can tell, but I seem to need more of it. My original primary Force fuselage had more, but lighter balsa (really good 5-lb stuff) in it than the fuselage shown being built (7-lb +/-). When finished with dope and the newer (lousy) silkspan, the original PF fuselage weighed 4.6 ounces more than the new one. I believe this is because successive coats of dope raised ('floated') the silkspan, as more coats dissolved the earlier coats, and I ended up with more dope than I should have needed. The epoxy, applied as I described, kept the glass down against the fuselage surface, so that only enough to fill the fine weave was necessary to bring it to a smooth sheen, without grain showing. I'll attach a picture I took of the new fuselage against the original P-Force plan so that you can judge how mush less balsa I used, but remember that the P-Force did not have the cowl-cheek tripler.

Bill - I used West Systems 105 Epoxy with 206 hardener.It has a reasonable working life, but becomes too viscous, if you take too long getting the surface coat on and scraped thin (almost invisible) and glass oriented and rolled out.right. That is, you have to work diligently an quickly before the viscosity works against you. Time? H-m-m-m-m,...maybe 10 minutes of thin enough viscosity. The stuff is usable for other tasks for a longer time, but we're trying to save weight here. I wish I could remember this better, but I'm only talking "ballpark" figures, when it comes to workability for this particular task. I like this resin, but as I said, it can become a real mess, without precautions. If the resin is left unevenly applied, work is multiplied in getting the finish right.

I agree with Paul on profiles, but have to say that this particular trussing took minimum time to make (just time to scroll-saw the opening, cut and white-glue the diagonals), except that laminating three pieces (two 1/16" sheets on the 1/2" core) to make the 5/8" thick fuselage takes more time. However, using 1/16" plywood for the nose makes a seamless transition along this significantly stiffened fuselage. Don't underestimate how much torsionally stiffer these few simple diagonals alone make the structure, especially when the box is completed with the sheeting. Even the small opening saved  significant weight in the right place (I weighed after each step).

The 1/64" plywood route makes a VERY stiff and torque-resistant fuselage, but that great stuff is much heavier. That''s something you can compute ahead of time in your decision making.

[Gerald Arana]

My short answer is that one layer, with threads diagonal should help. I believe that .56-oz glass filled with epoxy is better, since it is light and much less flexible

I've made very stiff profile fuselages by triangulated-truss tail arms, with 1/16" balsa lamination to close the box and .56-oz fiberglass epoxied on with 45^o biased weave. These fuselages are very stiff and torque resistant. The glass/epoxy can be as light as or lighter than dope and silkspan or CF, IF you apply to a very thin (wiped with card) base coat of epoxy to keep it from floating (you can roll it in), followed by a coat to fill the weave, after the base coat has set to a tackiness. The glass doesn't seem to take as much epoxy as, say, medium silkspan

I know you didn't ask, but I've included pictures of the simple truss-work too.The biased glass/epoxy application can be a real mess, if not very carefully done. One hint is to roll the cloth carefully ahead of time, so that it can be carefully un-rolled over the base coat. Taping the edges helps a LOT, because it keeps the weave at 90 degrees, preventing it from stretching in any direction. Any attempts to re-position or adjust the glass can be really frustrating or futile, unless those edges are stabilized.

Using dope with the glass is easier, but the dope is softer and moreflexible, and it keeps shrinking to reveal the weave for a long time. I think the dope can float the glass, when subsequent coats soften/dissolve earlier ones, adding weight.The epoxy is better. You can paint over slightly roughed up glass/epoxy with butyrate for final finishing. I patched together some photos that show some of what I have said. The plane was flown several times this summer, and the Brodak butyrate dope has adhered fine, as long as shielded by enough clear final coats. There is no mechanical separation of dope from glass/epoxy. A big advantage is that, if you do it right and wet sand with 400-600 just down to the weave, you're about ready for color coats.

If you use two layers of silk, it's probably advantageous to have one with longitudinal and vertical weave and the other biased. It sounds as though it could be kind of heavy. The single layer of glass is sufficient to make a big difference in the "hand-twist" test.

SK

Serge,

I agree with you on the bias aspect of the glass cloth however, I've never had any success on coating the cloth first before applying it.

Because of the bias, the cloth stretches or shrinks and (for me at least) becomes very hard to work with as well as being messy.

A better way (AFAIC) is to use toilet paper.
My method: Put a couple coats of 50/50 dope, lightly sanded, on the part first to keep the resin from soaking in.

Step one; wet out the part to be glassed.

Step two, apply the cloth dry and smooth it out, slather it with resin, lots of it!

Step three; take 4-5 sections of TP and BLOT off as much resin as you want and yes, you can remove to much! Might have to do this a couple times.

I like to think of it as a nylon stocking on a freshly shaven leg (Yes, LADIES!!!)

Let the resin cure to the "green" stage, then trim off excess. For those who don't know what the green state is, it is the point where the resin is firm enough to cut but not completely hardened.

Cheers, Jerry

[Brett Buck]

A better way (AFAIC) is to use toilet paper.
My method:
Step one; wet out the part to be glassed.

Step two, (smooth it out) slather it with resin, lots of it!

Step three; take 4-5 sections of TP and BLOT off as much resin as you want and yes, you can remove to much! Might have to do this a couple times.

    This is more or less what I do for any fiberglass applications, but I roll the toilet paper across it. Just leave it on the roll and roll it across - the direction it DOESN'T unroll, of course. It works very well, particularly for the very like 1/2 ounce glass. The heaver stuff will not lay down flat nearly as well and you would do better blotting up the excess and then vacuum-bagging or somehow compressing it.

    Brett

[Fred Cronenwett]

I have been building profile fuselages with the method SK described for over twenty years.

One of the first that I did was over 20 years ago, had 1/16 balsa sides from nose to tail with 1/2 x 3/4 sticks in the truss structure covered with Sig Koverall, and then dope.  The model is still together and has no signs of cracking or damage. The 41" span F7F has over 400 flights on it. The secret is that the outer skins take the bending and twisting loads.

My lastest project that has been flying for four years now is over 72" long (B-29) and was built with 1/16 balsa skins, 1/2 x 3/4 stick truss structure with 3/4 ounce fiberglass cloth and resin on the entire model. I also have some carbon fibre cloth (dry) that was epoxied to the inside of the fuselage skins before creating the box. Between the fiberglass cloth & Resin on the outside, balsa skins and the carbon fibre on the inside of the skins that fuselage is very stiff.

I have also built sport models with profile fuselage with the typical engine on the nose. I don't have any plywood doublers on the fuselage only the fiberglass skins and balsa skins and have had no problems.

I will post some pictures later today

Fred

[Mike Griffin]

A few years ago when I kitted Larry Cunningham's MoBest, as Robert has already said, when I built the model as a test build I found it to be the stiffest profile fuselage I had ever built because I kept it exactly as Larry designed it.  Just as a point of interest, Eric Rule at RSM told me when he cut the kit for me that there was more balsa in that model than in the Thundergazer.  Mike Nelson in Great Britain has built a couple of MoBest and if he reads this thread maybe he will add his thoughts.

Mike

[Perry Rose]

I built the Mo' Best and since then I have used 1/64 ply on all my built up profile fuselages. Whatever weight difference there is isn't enough to make a difference. One coat of poly crylic, one coat of primer and it's ready to paint. I also use a support under the stab. Hollowed 3/4 triangle stock.

[Fred Cronenwett]

The 1/16 balsa that I used worked but 1/64 plywood would have been easier to handle, I had splice 4" wide balsa sheets together which had to be sanded out. the 1/64 plywood can be found thru National balsa in large sheets that can easily cover the fuselage

Fred

[Serge_Krauss]

Gerald- 'sorry to be late responding, but I think you misunderstood what I do. I do not  put resin on the cloth before applying. That would defeat my purpose greatly. After a coat or two of dope - with sanding - to seal the wood, I apply a very thin resin coat, scraped down to a thin sheen, to the wood. I roll the glass onto the wood, roll it tight under waxed paper (finger pressure in concave or convex places), and wait for the resin to tack some. Then I apply another coat of resin just to fill the weave. The glass does not float up. I remove the excess resin by the card method and  - IF I have applied that resin right - sand down to the weave later.

The last time, I rolled the glass after taping the edges to prevent what you've described. Believe me, I know what you mean; what a mess, if the glass is allowed to stretch!! The first side of the second fuselage had to be cleaned off and redone, after the glass did that. It's a delicate operation, but you can get the job done with minimum resin this way. I'm always really tired, after that operation - takes concentration!

If memory serves (!), my calculations, and one trial weighing, showed me that I could save over an ounce of weight using 1/16 balsa and FG/Epoxy instead of 1/64" plywood, but I love the ply and probably would use it sometime for this purpose. It's much easier. - SK

[Don Chandler]

I recently scratch built  Banshee/Impala and had to settle for a slab of balsa way to light to be a one piece fuselage so I coated it with silk on both sidse. By the time I finished sealing and painting the fuse ended up being quite rigid and the plane flys well.

[Brett Buck]

Profile fuselages are best used on 1/2A's and maybe up as high as 35-size models.

The bigger "profiles" now in use are something of a rules-beating scheme to invade the so-called "simplified" events with larger and more elaborate models. These complex honeycomb structures with high tech composite siding are a long stretch from the original concept of "profile" as a point of relief for full-bodied construction.

I'm sure some sea lawyer will read me The Rule Book and prove that "profile" with a piped 75 is not illegal.  But it's far stretch from the rationale for P-40.

   Given that there is no generally-agreed "rule book" for profile, yes, that is legal. I would also point out that you can use the *pipe* as a structural member, 75, 40 or otherwise and greatly stiffen the fuselage.

    The effort to make so-called "simple" events invites the sort of technology race you describe. It's still a competition, and people want to win, so *someone* will go to whatever length it takes to do it. The more restrictions you put on it in the rules, the more dominant the experts will become and the more success will depend on knowing the latest tricks. That's happened in nearly every attempt to "simplify" these events - look at B Team Race - Rat - slow Rat. There were things hanging on slow rat engines that even *I* didn't know what they were doing or why.

    The only way to prevent this is to either ban experts, or somehow make it unappealing to experts. I think that is more-or-less a lost cause, but it works for a while. One thing for certain, DO NOT make your "simple" event an AMA Official event. As soon as that happens, there will be a national championship at stake, and all efforts will be expended to win it.

   This is why stunt - the real, essentially unrestricted original event - has been so successful when all the other events have more-or-less died. Get right down to it, there aren't any consequential technical rules for stunt at all, literally anything goes as long as it fits in a 70' circle.


    Brett

[Dave Harmon]

I spray a thin mist of 3M77 on the fuselage vertically from about 3'. This prevents the cloth from sliding around and holds it in nooks and crannies etc etc.
It takes just a little to hold the cloth.

Then I put my hands in plastic baggies to avoid snagging on the glass....then drape the glass (cut to size first using a slip sheet) right on the work.
Then apply the epoxy...I use Bob Smith Finish Cure epoxy (the thin stuff) and use a plastic squeegee from SIG to spread it out.
Their squeegee is far better than a plastic card because it has a smooth radius that can't snag the cloth.
Use the toilet roll to sop up any excess....then the squeegee again and so on and on until it looks like there is no epoxy on the glass....no puddles and not shiny anywhere.