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Author Topic: how to stiffen a profile fus  (Read 27668 times)

Offline Paul Allen

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how to stiffen a profile fus
« on: July 19, 2014, 05:59:24 AM »
I have fitted two rows of carbon fibre tape to both sides of the fus with epoxy
then covered with carbon tissue applied with nitrate dope. This has stiffened the fus
is there a better way to run the carbon tape for more twist resistance?
Thanks
Paul
In OZ

Offline BillLee

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Re: how to stiffen a profile fus
« Reply #1 on: July 19, 2014, 07:40:03 AM »
I have fitted two rows of carbon fibre tape to both sides of the fus with epoxy
then covered with carbon tissue applied with nitrate dope. This has stiffened the fus
is there a better way to run the carbon tape for more twist resistance?
Thanks
Paul
In OZ


Diagonal. Like the ribs in a geodesic wing construction resists the twisting of the structure.
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Offline Phil Krankowski

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Re: how to stiffen a profile fus
« Reply #2 on: July 19, 2014, 07:41:11 AM »
Like bridge trusses, make triangles.

Phil

Offline BillLee

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Re: how to stiffen a profile fus
« Reply #3 on: July 19, 2014, 09:46:30 AM »
Like bridge trusses, make triangles.

Phil

Yes. Diagonals.  :)
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Offline Dennis Toth

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Re: how to stiffen a profile fus
« Reply #4 on: July 31, 2014, 06:39:00 PM »
Paul,
I just finished up on a revised Tutor II that had a really twisty fuse. The fuse is 5/8" at the front that tapered to 3/8" at the tail. What I did was to add some formers down the length of the fuse to increase the thickness to 5/8" then added 1/64" plywood sides. I put a slight oval shape to the formers (back to the original thickness on top and bottom). It is now very stiff and I was also able to increase the size of the elevator/stab to about 23% which really helped the ship corner smoother.

Best,          DennisT

Offline Avaiojet

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Re: how to stiffen a profile fus
« Reply #5 on: July 31, 2014, 07:56:01 PM »
Dennis,

Where did you get the 1/64 plywood?

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Offline Perry Rose

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Re: how to stiffen a profile fus
« Reply #6 on: August 02, 2014, 12:31:05 PM »
Michaels the craft store has 1/64 ply as does National Balsa and probably other wood vendors.
I may be wrong but I doubt it.
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Offline Tom Niebuhr

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Re: how to stiffen a profile fus
« Reply #7 on: August 08, 2014, 07:27:59 AM »
I could never understand the love of profiles. The PERCEIVED simplicity of building is not there. When you start adding the plywood doublers, carbon, trusses, etc.  that help some, you are putting more work into the project. Add to this that almost all profiles have thin tail surfaces you sill have a platform that twists,  wobbles and vibrates in flight.

With all the effort to improve profiles, you will have a much easier build with a simple box fuselage like the "Hobo".  This is more stable, will not twist around and will always yield better, and more consistant engine runs.

Add to this the fact that almost all the profiles available as kits are simply remakes of old airplanes with thin airfoils and short moments. .

Over the years when someone tells me that they "are not ready" for a better airplane, in reality it is the airplane that is holding them back, not their ability.
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Offline john e. holliday

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Re: how to stiffen a profile fus
« Reply #8 on: August 08, 2014, 09:27:19 AM »
Is the Hobo still available or do I need to get plans from the AMA?
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Offline Tom Niebuhr

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Re: how to stiffen a profile fus
« Reply #9 on: August 08, 2014, 10:53:52 AM »
Doc,
Since I had the Bypass surgery I have stopped doing kits. I realized that I have not built a Pampa ship for myself in about 14 years, so I am now being selfish and am building an "Impala" in honor of Ed Elasick who was my old flying partner, for Classic at VSC. I have also started a new design Pampa ship that will be very different than anything you see today.

I have the updated kit plan for the "Hobo" for $15.00 + $7.00 shipping.

I am still doing vinyl graphics, since I can turn that around fast and I have my own cutter.

Again I want to emphasize that a good profile is not easier to build and is not better than an airplane with a fuselage. Even a simple box fuselage provides a better platform. I have not stated this to sell anything.
« Last Edit: August 09, 2014, 10:36:19 AM by Tom Niebuhr »
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Offline Paul Allen

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Re: how to stiffen a profile fus
« Reply #10 on: August 31, 2014, 10:57:06 PM »
This is what I have done on a Pathfinder, Dave Brown carbon fibre strip
applied with epoxy, covered with carbon  tissue, has stiffened fus nicely.
Paul
In OZ

Offline Chris Wilson

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Re: how to stiffen a profile fus
« Reply #11 on: August 31, 2014, 11:50:05 PM »
Surely torsional resistance is best with spiral wrapped carbon fiber rather than diagonals that suffer from cuts at every length?
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Offline Paul Allen

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Re: how to stiffen a profile fus
« Reply #12 on: September 01, 2014, 01:31:30 AM »
Chris
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Paul

Offline Chris Wilson

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Re: how to stiffen a profile fus
« Reply #13 on: September 01, 2014, 01:56:31 AM »
Fair enough Paul, that's all that counts.

Just wondering how treating the fuselage sheet would work if done in the same manner as a drive shaft i.e.

Tracing the main fibres from the high point above the wing root to the low point at the tail and vice a versa to form a flat 'X' shape.
Then spiral wrapping that in both positive and negative directions keeping the wrap as close to 90ş to the main fibres as possible.

Massive overkill I know but that would be the ultimate.

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Offline phil c

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Re: how to stiffen a profile fus
« Reply #14 on: September 01, 2014, 06:42:00 PM »
Keep it simple, during construction just cover the sides with .2-.4 oz. carbon veil.  To do a better job don't taper the fuselage- round the edges and maybe taper the canopy, but leave the main sides intact.  Prop the fuse up on a brace, about 8 inches off the board. After applying the veil clamp it with a thin sheet of builders poly sheeting, no more than 4 mil thick.  Make it 2-3 inches larger all around and hang weights around the edges(get a helper).  You can also use rubber bands down to screw hooks in a base.  It doesn't take a lot of pressure.  Before the epoxy dries ( I use West Systems 2hr) gently push any excess epoxy to the edges and wipe it off.  Make sure the plastic is pulled down smoothly.  Let it cure, clean up the edges, turn it over and do the other side.

You can just spread epoxy and squeegee the veil in place.  A bit heavier and it will require more sanding and filling, but it will stiffen the fuse the same way.

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Offline Mike Lauerman

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Re: how to stiffen a profile fus
« Reply #15 on: September 05, 2014, 02:10:54 PM »
'Crane lacing'. In ribbon...

Offline Tim Wescott

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Re: how to stiffen a profile fus
« Reply #16 on: October 27, 2014, 07:37:39 PM »
What I find I like most about profiles is the easy access to engine, fuel tank and control system.  I can't remember if the Hobo hangs the controls on the outside -- if it doesn't, then for a beginning flyer it probably should.

Be that as it may, if you want to compete in a profile class, you gotta have a profile...
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Offline John Kelly

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Re: how to stiffen a profile fus
« Reply #17 on: October 27, 2014, 07:49:22 PM »
   ...
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Offline Gene O'Keefe

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Re: how to stiffen a profile fus
« Reply #18 on: October 28, 2014, 07:45:36 AM »
"When" I build a profile, I always use 1/64" plywood as stated in one of above replys -- works really great.
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Offline Garf

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Re: how to stiffen a profile fus
« Reply #19 on: October 28, 2014, 02:05:36 PM »
What would painting the fuselage with CA glue do to strength (resistance to breaking)?

Offline FLOYD CARTER

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Re: how to stiffen a profile fus
« Reply #20 on: October 28, 2014, 02:31:04 PM »
If you look at all the offerings by Brodak, you might think that a profile model is the "only way" to go!

The advantage of a profile model is the perceived simplicity of building. That is not always the case, but the idea appeals to many modelers.

They look OK from the pilot's point of view inside the circle.  On the ground, looks is quite another matter.

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Offline Garf

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Re: how to stiffen a profile fus
« Reply #21 on: October 28, 2014, 03:00:10 PM »
I have always liked the side mount engine and easy access tank. I have long since cured the separation problem at the front of the wing to fuselage joint. Now if I can only cure the broken fuselage at the rear of the wing problem.

Offline Tim Wescott

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Re: how to stiffen a profile fus
« Reply #22 on: October 28, 2014, 03:22:45 PM »
What would painting the fuselage with CA glue do to strength (resistance to breaking)?

Probably not nearly as much as other treatments of the same weight.  CA is quite brittle, particularly in shear.  So if it DID stiffen the fuse, it probably would break down fairly quickly.

For best stiffness you probably want the CF tow, or CF cloth.
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Offline RknRusty

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Re: how to stiffen a profile fus
« Reply #23 on: October 31, 2014, 12:00:10 AM »
What if you rip the fuselage in half lengthwise and sandwich a 1/2"x1/16" or 1/2"x1/8" strip of spruce or hardwood and laminate it all beck together? Or even make two rips, each 1/3 of the fuse height from top and bottom and laminate two strips of stiffer wood into it?
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Offline Serge_Krauss

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Re: how to stiffen a profile fus
« Reply #24 on: October 31, 2014, 11:11:47 AM »
I have found that .56-oz. fiberglass applied with minimum amount of West Systems epoxy is marginally lighter than CF veil applied the same way. I dope the fuselage surface to seal it from epoxy penetration and light sand. Then I apply a thin coat of resin and wipe it off with a card, leaving almost too little to see. I apply the glass with threads biased 45o to the fuselage direction. This difficult, but I've found some ways to limit the mess. I then roll the glass into the epoxy and wait for it to tack. This prevents the glass from floating and taking more epoxy. At this point I reapply resin to fill the rest of the weave, carding the surface, but leaving a sheen over the weave. After the resin has cured to some hardness, I wet sand with Dupont Prep-Sol to smooth it down to the glass, but not into it. I have to admit that I have not perfected this skill and have spent time repairing. You can fill the weave with dope instead, but as the dope shrinks (forever), the weave returns. So that requires many applications and sanding.

This has stiffened my profile fuselages greatly and made them especially resistant to twisting. I've done the calculations and, even though the 1/64" plywood is much easier to apply and works quite well, it is significantly heavier.

I agree with Tom that profiles aren't as good as full fuselages. I'm particularly at fault here, because my profiles have been somewhat complex lately. I do cut out an area behind the wing and truss it with diagonals. That has been shown to actually stiffen the thing while saving weight. I've been using 1/16" plywood doublers in the engine area, with 1/16" balsa doublers behind, closing the trussed area. One could save a lot of work by sandwiching the glass or CF between the 1/16" balsa and the 1/2" fuselage core. Then sanding and finishing the stuff would not be the pain that it is. Really stiff? You might try inside and outside CF or FG laminations. It would probably still be lighter than using the 1/64 plywood. But I haven't tried that. I apply a 1/2” – 5/8” Cheek tripler on the left side of the nose. It fairs nicely into the non-stepped fuselage side.

Offline Tim Wescott

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Re: how to stiffen a profile fus
« Reply #25 on: October 31, 2014, 11:16:46 AM »
What if you rip the fuselage in half lengthwise and sandwich a 1/2"x1/16" or 1/2"x1/8" strip of spruce or hardwood and laminate it all beck together? Or even make two rips, each 1/3 of the fuse height from top and bottom and laminate two strips of stiffer wood into it?
Rusty

You could, and it would make the fuselage stiffer, but you get the most bang for the buck by putting a thin shell of something stiff on the fuselage.
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Offline Howard Rush

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Re: how to stiffen a profile fus
« Reply #26 on: October 31, 2014, 01:30:45 PM »
Mark Scarborough brought his new, pretty profile Impact to our September contest.  I thought I saw the fuselage twisting in maneuvers, so I commandeered the airplane--my prerogative as CD--and duct-taped a movie camera to it.  The result was interesting.  The fuselage did twist a little, but the main effect we saw was the fuselage deflecting toward the outside of the circle on the downwind side and toward the inside of the circle on the upwind side in level flight.
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Offline Dennis Saydak

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Re: how to stiffen a profile fus
« Reply #27 on: October 31, 2014, 06:03:46 PM »
Oh phooey! It's obvious to me your suggestions are far too complex when a couple of capsules of Viagra in clear dope will make it plenty stiff.  y1 y1 y1  ~>
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Offline Howard Rush

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Re: how to stiffen a profile fus
« Reply #28 on: October 31, 2014, 06:38:19 PM »
If your fuselage is still stiff after four hours, consult a structural engineer right away.
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Re: how to stiffen a profile fus
« Reply #29 on: October 31, 2014, 07:58:53 PM »
Tom Morris has been building profile Cavaliers for years using a built up fuselage and sheeting it with 1/64 plywood.  He has done well in contests flying one of these in electric.  The problem with 1/64 plywood is the cost.

Mike

Offline Serge_Krauss

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Re: how to stiffen a profile fus
« Reply #30 on: November 01, 2014, 01:03:01 PM »
Yes, it's VERY expensive - way overboard! It's great stuff and easy to use (even cuts with scissors), but it is dense and measurably heavier than glass/resin/balsa laminates over large areas like fuselage sides. That having been said, I may well use it on a simpler project aimed at faster-build and durability. It can take the place of thicker plywood on the nose when using engine pads of sufficient size and cheeks. That makes a seemless side.

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Re: how to stiffen a profile fus
« Reply #31 on: November 01, 2014, 01:18:47 PM »
I am curious.

If you had a piece of Carbon Fiber that measured 1/2" thick  4" wide and 36" long nd a piece of balsa the same dimension, which would weigh the most?

Mike

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Re: how to stiffen a profile fus
« Reply #32 on: November 01, 2014, 01:21:19 PM »
Yes, it's VERY expensive - way overboard! It's great stuff and easy to use (even cuts with scissors), but it is dense and measurably heavier than glass/resin/balsa laminates over large areas like fuselage sides. That having been said, I may well use it on a simpler project aimed at faster-build and durability. It can take the place of thicker plywood on the nose when using engine pads of sufficient size and cheeks. That makes a seemless side.

Serge, what if you took a built up profile and sheeted it with 1/16 balsa applied at a 45 degree angle.  Would it be strong as the 1/64 plywood?

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Re: how to stiffen a profile fus
« Reply #33 on: November 01, 2014, 02:47:36 PM »
I am curious.

If you had a piece of Carbon Fiber that measured 1/2" thick  4" wide and 36" long nd a piece of balsa the same dimension, which would weigh the most?

Mike

Mike,

Your plank of carbon would weight a little under 65oz, if it's of good prepreg.
The correct way yo do it would be to use honeycomb in the middle (that's about 29kg/cubic metre) and use thin carbon sheet skins. A good skin might consist of 76g cloth at +/-45 degrees and 1-2 layers of 16g(/m2) UD lenghtwise. That would be lighter than 1/2" balsa fuselage, and several times stiffer.
But then you could also make a simple box from 1/8" balsa sheet..
Personally I don't understand why profile fuselages should be taken seriously. They are good enough for trainers and if you want more performance, make a built-up fuselage.
Of course if we want, we could use our carbon/boron hybrid prepreg and make a fuselage 1/8" thick and stiffer and propably lighter than anything ever built but that would be against the original idea of profile class.

To keep it classical, a good solution might be to skin balsa core with 1/128" 2-ply aircraft plywood, at +/-45 degrees. It's available at special order I think. At least I've seen it at the factory.

Lauri

Offline Tim Wescott

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Re: how to stiffen a profile fus
« Reply #34 on: November 01, 2014, 03:20:07 PM »
Personally I don't understand why profile fuselages should be taken seriously.

At least around here, if you can consistently put in over 500 points a flight, you're too good to stay in Advanced.  If you can't hit 580 or 590, you don't have any hope of placing in Expert.

But if you can hit 520 or higher with a profile, you can place in Profile Expert.

So -- there's why profile fuselages are taken seriously around HERE!
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Offline Serge_Krauss

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Re: how to stiffen a profile fus
« Reply #35 on: November 01, 2014, 03:51:07 PM »
Hi, Mike-

I'm sure that the plywood would be a lot stronger. The diagonal balsa would give some pretty good resistance to twisting torques, which is important, but going in only one direction per side, it might well contribute to fuselage warping. I believe that Larry Cunningham encountered that, after advocating the biased grain, and then rejected using it in only one direction. On the other question, such a thick piece of carbon would weigh much more than the balsa. You could probably anchor houses on such stuff.

I weighed some parts made with thin CF veil and FG layers filled with epoxy resin, and they were very light. The FG was a bit lighter in practice on a horizontal tail, probably because it absorbed less resin. A 2-layer CF veil test sample epoxied over 2lb/ft2 pink foam weighed about .008 oz/in2. I don't know how accurate it would be to say that one layer would weigh .004 oz/in2. That's pretty light for fuselages though. My old notebook, in which I list data from weighing my own stock, shows 1/64" plywood to weigh .0079 - .0087 oz/in2, or over twice as much as a layer of CF/resin as applied to the pink foam. The density of 1/64" plywood is twice to three times the density of spruce and about eight times the density of "average" (7-lb) balsa. The main point to remember when deciding among carbon veil, .56 oz glass, or similar laminates is that their weight is really negligable compared to the epoxy or dope used to fill them.

My rough calculations say that my current fuselage for a .25-powered stunt plane would have required 1.5 oz (not counting glue) of 1/64" plywood lamination, while the biased .56-oz fiberglas and epoxy added .25 oz to one such fuselage and closer to .3 oz to the other to cover about 7/8 the total side area (including cockpit) plus the fins, top/bottom, and cheek convexity. So, if you build light like Tom, the extra ounce wouldn't be a problem, especially for the stiffness and savings in labor. My total fuselage weight is about 5.9 oz. For comparison, the Cardinal ARC fuselage weighs 9 ounces, even with cutouts. So for larger fuselages, you're looking at a bit more weight difference.

The nice thing here is that with a little (relatively) easily measured data, you can approximate the weight gains from using various materials and make your best decision before building.

SK

Offline Jim Dincau

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Re: how to stiffen a profile fus
« Reply #36 on: November 01, 2014, 04:53:54 PM »
never mind
Unless it's crazy, ambitious and delusional, it's not worth our time.

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Re: how to stiffen a profile fus
« Reply #37 on: November 01, 2014, 05:08:43 PM »
Serge,

Ever hear about the "toilet paper" method? The TP is used as a blotter to remove the excess resin and to push the FG down against the surface being glassed.

Simply put the TP on and rub it gently. Then remove it by pulling it off against itself. Can be done a couple times......with fresh TP of course! And YES! You can take off to much resin so be careful!

Good luck, Jerry

Offline Tim Wescott

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Re: how to stiffen a profile fus
« Reply #38 on: November 01, 2014, 06:12:25 PM »
CF plate is about 100 pounds per cubic foot [1].  Balsa would weigh between 4 (crazy light) to 20 (crazy heavy).  So making the fuselage out of solid CF would not result in joy, I think.

Making a hollow fuselage with sides made from balsa "plywood" may work, but you'd want to check on the stiffness to weight ratio of balsa vs. your plywood (taking glue weight into account).

On laying CF onto a fuse -- I suspect the least-weight way to do it is to vacuum bag the stuff, but I've never done it, and doing so is just hugely over the top.

Serge seems to have done this way more than anyone else on earth, but I'm going to guess that if you really wanted a super-rigid, super-light profile fuselage, and if you didn't mind the effort or the fact that the thing will burst into a million pieces in a crash, the best thing to do would be to make a profile out of foam, with a balsa perimeter and various inserts in the nose for strength, then CF vacuum bagged onto that.

[1] http://www.rockwestcomposites.com/ckeditor_assets/attachments/106/Uni%20Panel%20Specifications.pdf
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Offline phil c

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Re: how to stiffen a profile fus
« Reply #39 on: November 01, 2014, 08:15:37 PM »
If you're building from scratch the easiest way to stiffen a profile fuselage is to make it thicker.  A half inch thick layer of white styrofoam with 1/16in. balsa sides is plenty stiff for a 46 powered plane.  For something a bit bigger go to 3/4 in thickness.  No glass or carbon fiber is required, but would stiffen it even more.  It is important to keep the thickness back to the stab leading edge.       Tapering the the fuselage along its length makes the tail area much more flexible.

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Offline Tim Wescott

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Re: how to stiffen a profile fus
« Reply #40 on: November 01, 2014, 08:24:50 PM »
If you're building from scratch the easiest way to stiffen a profile fuselage is to make it thicker.

The stiffness goes up by (roughly) the square of thickness if you stick to one size of sheeting -- i.e., a 3/4" thick fuselage will be roughly twice as stiff as a 1/2" thick fuselage, IF you stick to your 1/16" sheeting (or plywood, or whatever).

In the Northwest, the competition regulations call out a fuselage that's no thicker than 3/4" at the flap TE.  So that sets your maximum around here.  Different regions have different rules, though -- there's no country-wide definition of "profile".
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Re: how to stiffen a profile fus
« Reply #41 on: November 02, 2014, 01:26:24 AM »
Just wondering if pre-tensioning carbon strands or mat would work here?

(Has anyone run tension guy wires from the wing tip to the the tailplane  and from the rudder top to the canopy 's silhouette? Kinda like making a 'box kite' out of it.)
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Online Lauri Malila

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Re: how to stiffen a profile fus
« Reply #42 on: November 02, 2014, 02:27:46 AM »
We do tensioning for the free flight spars, either just by pulling the rowing in mold or in pultrusion process.
But for forces that you have in a profile fuselage.. Not necessary.
Besides, you need very little carbon to do the work at tension side, the specs I gave in the earlier post will result in a skin thickness of less than 1/128" with good resin/fibre ratio, meaning that handling the compression side is much more important.
If I had to do it, I would use 1/2 (or even thinner) Kevlar honeycomb core, it is much, much light than even lightest balsa and does much better work at handling the compression & shear forces. L

Offline Serge_Krauss

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Re: how to stiffen a profile fus
« Reply #43 on: November 02, 2014, 09:18:23 AM »
Gerald- No, I haven't used the TP method, although I've seen it mentioned before. I like the plastic cards, but have to admit that if I'd used the TP around the compound curves I have, I might have done it easier. I'll keep that in mind.

As Tim pointed out, vacuum bagging would be the best way to lay the fiberglass (or CF) up. Not only will it apply more pressure than shown by all the "erudition" stacked up in my humerous (but real) shot, but I think that it will give the smoothest surface. Whatever fraction of atmospheric pressure (14.7 lb/in2 at SL) is chosen will be more even and can exceed anything I can do with those books, bottles, and cans.

Phil once sent me pictures of his styrofoam fuselage structure, and I intend to try it, since he's built many successful medium-powered profiles that way. The reason I built my second of the two fuselages in my pictures the same way as the first is that I wanted a comparison, extending the first design to a different plane. I think my method is not all that hard to do, but it is certainly more labor intensive than called for by most profiles. I like to "sculpt" the sides some, so I've used a few unorthodox methods, like milling the balsa to recess the vertical stabilizer, tank openings, and landing gear opening behind the nose cheek. These are just aesthetic and "hobby"-related affects that do not get me into the air the quickest. So in this thread I was just addressing stiffening methods on a primary level (trusses), with emphasis on the biased glass preference. I don't necessarily recommend the rest of my structure!

SK
« Last Edit: November 02, 2014, 09:41:46 AM by Serge_Krauss »

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Re: how to stiffen a profile fus
« Reply #44 on: November 02, 2014, 05:33:58 PM »
Lauri where in the world do you buy Kevlar Honeycomb Core Material?

Mike

Offline Steve Helmick

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Re: how to stiffen a profile fus
« Reply #45 on: November 02, 2014, 06:53:47 PM »
Mike...Google it, and you'll find some sources...I just did.  H^^ Steve
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Offline Howard Rush

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Re: how to stiffen a profile fus
« Reply #46 on: November 02, 2014, 11:48:24 PM »
If I had to do it, I would use 1/2 (or even thinner) Kevlar honeycomb core, it is much, much light than even lightest balsa and does much better work at handling the compression & shear forces. L

You mean Nomex?  Compression is not Kevlar's forte.
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Offline Howard Rush

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Re: how to stiffen a profile fus
« Reply #47 on: November 02, 2014, 11:59:30 PM »
Dad gum.  I did Google it.  It exists.   It's new stuff.  Where can you get thin Kevlar honeycomb in tiny cell sizes?  Is it as enjoyable to work with as Kevlar cloth?
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Offline Howard Rush

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Re: how to stiffen a profile fus
« Reply #48 on: November 03, 2014, 12:05:57 AM »
Personally I don't understand why profile fuselages should be taken seriously.

Neither do I.
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Online Lauri Malila

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Re: how to stiffen a profile fus
« Reply #49 on: November 03, 2014, 01:02:45 AM »
Howard,

One good source for Nomex is R&G in Germany. Other than that, they have everything you need fot this kind of construction.
It is quite amazing but Nomex honeycomb can be sanded to shape. I mean to shape like airfoil. Robert Leško has won the last World- and European champs in F1A with a model with spreadtow carbon skin molded around sanded Nomex core. He made an interesting article about it, it can be found at least ifrom "F1A Flappers" group in facebook.
If you want to make it stiffer and perhaps lighter, you really must pay attention to the core material. Using balsa in the usual way (but hollowed to reduce weight) or styrofoam you can only improve stiffness/weight ratio but not really improve stiffness. compression resistance is the key.
Perhaps easier to work with than honeycomb, and nearly as good in use would be Rohacell foam. The lightest Rohacell is about 30kg/m2. It resembles roofmate foam but compression resistance is better.
It allows for really light carbon skin, the ones that we use in our wings now have have just one layer of about 1oz/sq.yd spread tow at +/-45 degrees. And then a good spar to take care of bending.
« Last Edit: November 03, 2014, 01:33:22 AM by Lauri Malila »


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