Fiberglassing stunter noses

Why are full fuse noses usually fiberglassed, but profile noses are not? I'm at the point where I need to make a decision whether or not to glass the nose of my chip. Currently the nose is raw balsa. Do I seal the balsa first with dope, or glass it the way it is so more resin soaks in? Do I use 3/4oz or 1/2oz glass, or does it really matter? This plane will probably weigh 45oz, so weight is a factor, it's a kit built, hanger rashed, mutilated, rashed, rebuild (sort of a crash repair before it'll ever see flight), and I'm AT LEAST the 3rd owner (but the first who will ever see it fly!) so longevity really isn't the highest priority. It'll have a 40FP, which I understand isn't the shakingest motor out there if that changes anything.

As usual, any help will be well received and appreciated.

I assume you also have some plywood doublers on that profile nose!

I believe in fiberglassing ALL fuselages, built up or profile, and I use unthinned nitrate dope as a binder, with .56 oz glass cloth. This is sanded very lightly, then more coats of nitrate are added, and silkspan over that. This lamination is light and strong, it doesn't sand away the fiberglass strength, and the silkspan provides a nice surface to fill and prefinish. And it doesn't weigh much.

I know, I know. People like to use epoxy for fiberglassing.. And people have trouble with nitrate dope.. And it isn't fuel proof..

No reason why epoxy finishing resin can't be used as well. As for added stiffness and strength, the aft profile fuse area will probably benefit more than the nose. If your rudder is in place, you can do it at the same time.

L.

I covered my Pathfinder fuselage from nose to tail with 0.5 oz FG cloth held down with dope. No silkspan, however. It filled with three coats of clear and a coat of butyrate/talc. It is pretty slick for a finishing impaired builder like me. And it seems pretty stiff.

Oh, by the way, I was really thinking of NOT fiberglassing a full fuse nose. But the consensus seems to be that it really doesn't weigh much, so I'll probably go ahead and do it.

Didn't think about doing the tail. My Banshee REALLY suffers from tail wiggling problems, AND I have tail weight back there, SO...

Back to fiberglassing in general. I guess then that the binder doesn't really matter? Would regular dope work as well as nitrate? I have nothing against nitrate, in fact I like it a lot, but not sure if I have any on hand right now. Been using NOTHING but Brodak dope for the last couple planes in an effort to avoid compatibility problems I've had. So, now that that problem is gone, I can reintroduce a thing here and there and see if the problems come back, when (if) it does, I'll know what did it. I have a feeling the real problem I was having was age related and thinner related, but to save time and money, just went straight to a reliable set of circumstances.

Also, since it is a built up fuse with a removable tank compartment, dope proofing is important. If I use resin, is the tissue important? I did do a plane once with glass and resin and remember it sanding to a nearly completely filled surface right away. Couple coats of dope and that was it.

Thanks,

You are right, if you fiberglass (or use carbon fiber on) the nose, you don't need silkspan over it. If you use epoxy resin, it is possible to fill it to a glass smooth finish. This may prove a bit heavier, however, if you fill it all the way. I believe a resin application will give you greater strength than dope, however, even if you do a final fill with dope.

Some say Nitrate dope sticks better (to bare wood, who cares?) and that it fills better. I am not so sure that the Brodak butyrate doesn't fill as well, however. Nitrate might stick better over a polyester resin, but, remember, we are now introducing compatibility problems again. Have you ever seen underlayer colors bleed through a finish? If you put nitrate dope down first and then butyrate over it, there will be a mixing of dope--especially if you use retarder. The thinner will melt down and bring up the bottom layer into the top layer. That means the Nitrate underlayer is going to bleed into the Butyrate. The same thinner works on both dopes.

Matt had some bleed through of yellow into his white weeks after the finish was finished. The top will skim over, but the bottom layers remain active for a long time.

Leonard Neumann

Tools:

I have had some conversations with several fairly smart folks who advocate using epoxy to adhere glass cloth... they hold that, properly applied, not too much weight will be gained, while the strength will increase (over dope) by huge amounts.

See Ya

LAST EDITED ON May-21-02 AT 08:21 AM (CST)

Those of you with unused gallons of the evil nitrate dope, please email me. I'll pay the shipping to take it off your hands..

I'd be interested in some definitive data on strength versus weight for fiberglass cloth bound to a surface with epoxy versus nitrate or butyrate dope. No fair talking about multilayer carbon fiber composites with special resins cured at high temperature..

(Got a bet here, Bobaloo! How do we measure "strength"? Stiffness? Puncture resistance? Tensile properties?)

L.

PS

BTW, Leonard, I was advocating use nitrate dope to actually adhere the fiberglass. Not over fiberglass bound with something else. That might not have been clear.

(The use of nitrate with fiberglass was first suggested to me by Bob Hunt.)

Rich,

You bring up an interesting point - HUGE amounts of strength increase.

I'm all for that. But if we have two items, both more than adequately strong and durable, both the same weight, and one with a factor of 10 overkill, produced at considerable cost and effort, which one to use?

I see Windy making $600 carbon fiber wings that are EXTREMELY strong, like a surf board. They are fantastic, of course, and I don't doubt that they suffer absolutely zero flexing. (Was flexing a problem, however?)

But if we can make a surf board wing, isn't there some way to make a wing that is only twice as strong and half the weight of a conventional wing? Wouldn't that be a better application of new technology? Do we really need to use the $100 a yard CF cloth and resin that is post cured for 16 hours in an oven?

I love and respect Windy and do not fault his efforts in any manner. I'd just point out that he's well into overkill. Ask him!

Along the same lines, I wonder why we might need carbon fiber wheel pants versus fiberglass wheel pants? Same deal with a molded cowl or wing tip. Isn't fiberglass plenty adequate, cheaper, and much easier to use?

Same with carbon fiber arrowshaft control rods, when a fiberglass one is stronger than needed by a factor of at least 10. (Maybe the CF unit is lighter?)

The craze for diagonal ribs is another questionable area for me. Are such wings really lighter, stronger, or somehow markedly superior? Diagonal members definitely contribute strength by forming triangles. But in a wing structure, exactly where is the strength being added? It seems to me that it is in a direction where we don't have any strength problems to start with. Diagonal ribs are LONGER ribs. They're still made of balsa, and some of them very thin, soft, and light balsa. Do they really contribute any twist resistance to the wing? What strength do they add, compared to covering the wing in silkspan, and shrinking it tight with a dope finish? The main thing making the wing rigid is its covering, which is in strong tension.

I know. I know. The free flighters use diagonal ribs. They also use super light little spindly wing structures, which AGAIN depend on the covering for the major strength. They seldom have a planked leading edge like we do.

I did figure out two potential advantages to diagonal wing ribs. 1)they might "turbulate" airflow a little, and 2) they're HIP!

Speaking of worthwhile technical articles, it would be nice to actually measure such things, and tell us the results.

L.

"I keep tryin' to think, but nothin' happens.." - Curly Howard

Hmmm, cool discussion.

Back to the original question, however, maybe the answer has been implied, do I really need to glass the nose at all? Would dope and tissue be adequate for a OS 40 and a model that is going to be used to introduce me introductory local level intermediate class stunt?

Larry made it clear he thinks so, even for profiles. I'm beginning to think it may be more necessary for those over built up fuses. By the way, Larry, I do use ply doublers. When I built a new fuse for my Banshee I made extensive use of the series of articles you published in SN about 96 or 97. Didn't glass the nose, though, never even thought of it. Did sand the thing too much, which is why the tail is too light and wobbly! But, it still flies a tad better than I do, so it's alright for now. This Chip only has to be somewhat better than the Banshee, and so on... Don't want to spend too much time and only have ONE plane that is REALLY good, and no back up. Besides, I know better than to believe I could do that in only one attempt. I've already made the necessary gains I had envisioned in this model, so it's time to get it flying so I can resume construction on a Super Chip which is scratch built (should be noticeably lighter) and more extensively modified (rather than converted after construction began).

Later, thanks for all the replies.

I have glassed fuselages using epoxy and it works well and is tough as a boot. The price is in some increased work of sanding it, and likely an increase in weight. Having done both dope and epoxy, I think the dope is plenty good, at least for my purposes. My goal is a tough ding-resistant skin with a minimum of work. If the fuselage picks up stiffness, that's a nice bonus. Stiffness is certainly more of an issue with profiles than built-ups.

Tools,

A Super Chipmunk does not really need any glassing on the front end, unless you are planning on it lasting 1000 flights or more. I built three super chips, two doped and one monokoted.(No glass noses). The noses held together under FP 40 power for a maximum of 120 flights before they disintegrated. They disintegrated because I hit the ground, and glass won't help you there. When you go straight in under power the front end vaporises no matter what its made out of. If you are still learning the useful life expectancy of the model is probably 200 flights or less-and dope and tissue combined with reasonably proper construction will do fine. Something else to consider: built stock with an FP 40 you will find the chip to be nose heavy-if you are adding weight (glass and epoxy) you are going to be adding tail weight and be looking at a heavy airplane with alot of mass in the nose and tail.
Another note: My Sig Akrobat (sister ship to chipmunk with identical construction) has over 200 flights with no unrest in the unglassed nose. No problems there. And my CL-3 Chipmunk had no problems with BALSA nose doublers and a silk and dope finish. When it crashed the all-balsa front end powdered, but remarkably the damage stopped exactly where the doublers ended, and the engine survived the spectacular disintegration of the front end a-ok (a first for me). It seems to me the fragility of the nose, while strong enough for a great engine run, was able to absorb the impact forces totally and not transmit impact forces to the engine or the rest of the airframe-sort of like an Indy car flying apart while the guy inside is ok.
When I have stunters live long enough to see cracks appearing in the nose, then I'll glass the front end. Till then, I'm not going to worry about it....

>
>I'd be interested in some definitive
>data on strength versus weight
>for fiberglass cloth bound to
>a surface with epoxy versus
>nitrate or butyrate dope. No
>fair talking about multilayer carbon
>fiber composites with special resins
>cured at high temperature..
>
>(Got a bet here, Bobaloo! How
>do we measure "strength"? Stiffness?
>Puncture resistance? Tensile properties?)
>
>L.

I would be interested in this, too. What we would need here is someone to make up some test strips, and, either break them under a bending test, or puncture them with a calibrated punch (like used to test fabric on a real airplane). Of course, the break test is more relevant since we are talking strength here. Stiffness as to the amount of beinding under a certan load could enter in, however.

>PS
>
>BTW, Leonard, I was advocating use
>nitrate dope to actually adhere
>the fiberglass. Not over fiberglass
>bound with something else. That
>might not have been clear.
>
I was thinking of it in terms of sticking it down and filling between the pores. Some use polyester or epoxy resins to stick it down and use this thin while they fill with dope (lightest) and some use the resins to actually fill the fiberglass (strongest, I would assume, but heavier, definitely).

>(The use of nitrate with fiberglass
>was first suggested to me
>by Bob Hunt.)

Bob has tried a number of things, some that worked some that didn't (I have tried some things, too, but just didn't tell anyone about them). Bob used epoxy resin, lightly scraped into the pores of bare wood and then scraped off with no silkspan over this. Makes for a fast, light finish, but the grain did sink over time. It was a good idea, however. Bob tried carbon veil stuck down and filled with CA glue. Quite expensive, and I don't remember the full results, but this was later abandoned as not the perfect solution, either. I do believe that the nitrate dope might stick better to the ployester resin (epoxy isn't as much of a factor) and some have used it on fillets for the same reason, but we haven't had any problems with Brodak's butyrate sticking, and, therefore, don't see a reason to use nitrate as a base. The butyrate fills quite good, too.

>"I keep tryin' to think, but
>nothin' happens.." - Curly Howard
>

In Curly's favor, and you can take heart all you who can't grow hair, it has been shown that it takes a layer of fat in the scalp in order for hair to grow. So baldheads are not fat heads. (Bad logic, but it is cute).

I have never glassed one fuse nose ever. On your chip you donot need to do this. The FP will not shake it out and it wont hurt to go without the glass. You said logevity was not a factor anyway so why add the extra work. You want the nose to be strong on full fuses? Follow this trick and you will never half to glass one. Run your motor mount(maple) bearers all the way from the wing to the nose ring. Set it up so that the motor mount is carved to the shape of the top of the wing. When you set the wing into the saddle the motor mounts tie into the wing. This really makes it strong. Now move to the front. make sure that your bearers run all the way to the nose ring. The ring is glued onto the maple mounts. This will be so much more stronger than cutting the mounts short and adding a balsa block. I have seen so many designs like this and it makes me crazy. Adding the mounts out the ring helps make a boxfor the motor to sit in. This really helps stop the shaking. Glassing the nose seems to be making up for design.

DMoon

Nitrate has no gloss hardener in it. That is why it penetrates better than butyrate and attaches stuff better. Just thin the butyrate down and it will work just as well.

A carbon fiber pushrod can be a bit thinner and still retain its stiffness. If we don't make it thinner, however, we gain nothing (or little. Most of the weight is in the epoxy). Same with wheelpants or cowls. And wings need to be strong enough to bear the weight of the flight forces in flight and not to flex. They don't need to be strong enough to stand on. So, maybe the next generation will be a little thinner wing with less costly materials (and even less weight). The first generation products usually are a little heavier and stronger (and costly) than needed.

Windy's wing will be used for many years to come. Since he always builds the same wing he now never has to again unless he crashes it. Now that is nice. Just move it from plane to plane. Repaint it and move on. He uses technology to his advantage.

>Along the same lines, I wonder
>why we might need carbon
>fiber wheel pants versus fiberglass
>wheel pants? Same deal with
>a molded cowl or wing
>tip. Isn't fiberglass plenty adequate,
>cheaper, and much easier to
>use?

Yes fiber glass is adequete but the carbon is lighter and people want it light. Having the option is good. Carbon fiber wheelpants are lighter and stronger and resist rock chips and general damage alot more so that FG pants that are the same weight. Getting them same weight makes them very flimsy at best. Yes there is a noticable advantage to having an object on your plane that has no aerodynamic advantage if it is very light. This is why I dont have them. There is no need for big bulky pants for appearance when they are just added weight. I hear some guys cry about verticle CG but then they have wheel pants. Come on.

>
>Same with carbon fiber arrowshaft control
>rods, when a
>fiberglass one is stronger than
>needed by a factor of
>at least 10. (Maybe the
>CF unit is lighter?)

The CF unit is stronger. This means it lasts longer. The tow in the new central hobbies shafts runs lengthwise. It is not spun like arrow shafts. This resists flexing better than arrow shafts ever thought about. Also they come with fitted Titanium inserts that are threaded making setup a snap. There is no special building or construction. My grandma could get it right on the first try and it will last forever.

Again with technology helping out.

>
>The craze for diagonal ribs is
>another questionable area for me.
>Are such wings really lighter,
>stronger, or somehow markedly superior?
>Diagonal members definitely contribute strength
>by forming triangles. But in
>a wing structure, exactly where
>is the strength being added?
>It seems to me that
>it is in a direction
>where we don't have any
>strength problems to start with.
>Diagonal ribs are LONGER ribs.
>They're still made of balsa,
>and some of them very
>thin, soft, and light balsa.
>Do they really contribute any
>twist resistance to the wing?
>What strength do they add,
>compared to covering the wing
>in silkspan, and shrinking it
>tight with a dope finish?
>The main thing making the
>wing rigid is its covering,
>which is in strong tension.
>
>I know. I know. The free
>flighters use diagonal ribs. They
>also use super light little
>spindly wing structures, which AGAIN
>depend on the covering for
>the major strength. They seldom
>have a planked leading edge
>like we do.
>
>I did figure out two potential
>advantages to diagonal wing ribs.
>1)they might "turbulate" airflow a
>little, and 2) they're HIP!

Wow you must have read my mind about 6 months ago. Then I built two wings side by side. They are identical designs. One with geo ribs and one with straight ribs. The geo wing was stroger and less resistant to twisting earlier in the process of building it. It actually was strong and really less twist resistant before any of the sheer webbing or cap strips were added.

The straight rib wing took about 80% of the sheer webbing to be installed before it had the some of the rigidity that the geo wing had without the sheer webbing. This wing waas not really strong until it was completed. This would make it alot easier to build in a twist or a warp since it would not get strong until the end. I used to think they were strong early on but now I know differnt.

When both were completed before covering the geo wing was still stronger. Keep in mind all the same thickness wood was used in all the same area of construction.

This means that the wing is relying less on the covering to be strong and more on its inturnal structure.

The real seller is that the geo wing was 1.5oz lighter in the end.

>
>
>Speaking of worthwhile technical articles, it
>would be nice to actually
>measure such things, and tell
>us the results.
>
>L.
>
>"I keep tryin' to think, but
>nothin' happens.." - Curly Howard
>

It is always a good idea and should be a pricipal to question technology and advancements. However make a good comparison and you will often see that technological advancements are our friends.

I have known for sometime now that you feel we over build our models. I dont follow this at all having built and excellent stunter that was supposed to be for one season. I under built it on purpose to keep it real light. Well this gave me best plane ever at the time. Well I built another plane it wasnt as good. I had to go back to other one again. Now it is hurting on the apearance and covered in cracks. I built another one and the same thing happened. I had to fly it the third year in a row and the appearance cost me at the Nats. Please build as strong as humanly possible but keep the wing loading to a minumum. Over build the structure and under finish the plane. You know less colors/clear(weight) and it will last. Under built and shinny it wont last unless you cut back on flying it.

DMoon

Good points, Doug.

And the only thing I might balk on a little is having the CF control rod somehow "lasting longer" - I've yet to see any of these arrowshaft control rods actually wearing out. I think they're extreme overkill. And I went to the bow shop several years ago and got a big assortment of flawed fiberglass and aluminum arrowshafts. I have some VERY LIGHT ones!

I do like the idea that we could get Doug's 'nanny to build this stuff for us! I can testify that the control system hardware he is talking about is beautiful stuff. (Wish I could get you guys to build some CF Expocranks for me..)

1.5 ounces is a lot of wood, do you think it was accounted for strictly in terms of the difference in the surface area of the ribs? Do you use 1/16" sheet for ribs?

Anyway, I'm glad someone has done some definitive comparisons here.

(You'll notice that my old StuntRib program DOES do diagonal ribs, so I'm not completely against the idea..)

I've got to try out the new Brodak dopes.

And yes, Bobby Hunt did try out some interesting finish techniques. One was fiberglass smoothed into place over 3M 77 and then saturated with thin CA. Then sanded. It sanded off with a powdering action, looked good, and seemed tough. But Bob pointed out that it was actually a little brittle.

As for covering fiberglass with silkspan, I do it for two reasons. First, I don't like to sand into the fiberglass trying to get it filled and finished. Second, like balsa grain, fiberglass weave can be almost impossible to completely fill. Yet silkspan covers the grain/weave easily, is cheap, doesn't weight much, forms another composite layer, and presents a very friendly surface for filling and prefinishing. The best of both worlds.

I dunno. Maybe I'm just a cheapskate.. Or maybe my 55 years are kicking in, so I'm resisting technology or something.

Anyway, thanks to everyone for this wonderful discussion. I really like sitting around the fire (or A/C) with you guys and talking about such stuff!

L.

"I keep tryin' to think, but nothin' happens.." - Curly Howard

PS

Leonard, God made a few perfect heads. The rest have hair on them. I'm a ~pelon'~ myself. So Curly and I reach on multiple planes..

<...>
>I have known for sometime now
>that you feel we over
>build our models. I
>dont follow this at all
>having built and excellent stunter
>that was supposed to be
>for one season. I
>under built it on purpose
>to keep it real light.
> Well this gave me
>best plane ever at the
>time. Well I built
>another plane it wasnt as
>good. I had to
>go back to other one
>again. Now it is
>hurting on the apearance and
>covered in cracks. I
>built another one and the
>same thing happened. I
>had to fly it the
>third year in a row
>and the appearance cost me
>at the Nats. Please
>build as strong as humanly
>possible but keep the wing
>loading to a minumum.
>Over build the structure and
>under finish the plane.
>You know less colors/clear(weight) and
>it will last. Under
>built and shinny it wont
>last unless you cut back
>on flying it.
>
>DMoon

One question here, though, Doug.

I thought you were just advising someone NOT to fiberglass a nose. Yet you are talking about your ships that cracked and failed.. Maybe you SHOULD try fiberglassing. It's nearly FREE strength.

And, you're right, of course. It is definitely possible to build too light. We've all seen a ship fold a wing sometime. Building adequate strength is definitely NOT over-building.. But a wing that is 10 times as strong as necessary IS over-building.

Cheers,

L.

Larry:

My bet is that if folks took the time (sanded until it was really smooth) and used the resin / epoxy sparingly (as directed, actually), they would find that the weight was only slightly more than a dope application....especially when factoring in the fact that less material or filler needs to be applied to achieve a reasonable finish.

The bass guys search high and low for weight, that their boats will accelerate fast to stalk the fish, and, with the huge amounts of money in that sport, I would bet that the boat builders would offer a hull molded in glass and dope if they thought that one would make it across the lake.

See Ya

Rich,

Think of the bass you could get with a carbon fiber/post cured epoxy resin'ed boat!

L.

I am new to this forum, an old model flyer from the 50's and 70's but more recently an EAA builder of a Lancair 360 composite aircraft,(the real thing). this bird flies at 200 Knots true air speed on 180 hp lycoming IO360. Pertaining to this thread on fiberglass fuselages, I offer the following thoughts for consideration from the full scale realm.

Epoxy or any bonding agent to glass is used to hold the fiber layers or composite materials close together so the forces and stresses can be transfered to the other materials, thus roughing up the surfaces for mechanical friction, improves adhesion. Physical contact is important for the materials to accumulate their addative strength properties. The epoxy to glass ratio is optimal at about 50/50 weight to weight, more glass and it is not wetted enough and looks white. More epoxy and it is heavy, brittle, looks wet and weaker because it is the glass, not the epoxy, that has the strength. The epoxy is there to hold the glass in place. In more detail any epoxy above the highest fiber in a layup is a waste of epoxy and adds weight. Use the lighter fillers here, whatever that may be. Take equal volumes of the fillers, weigh them wet, weigh them dry and make your choice for weight.

As to the bonding of dopes, epoxies or other binders here are a few thoughts.

Epoxies are weak in tension, in fact most glues are weak in tension, but rather strong in shear. For a simple strength test, take equal size fiberglass patches and glue the same area
with epoxy and other tests with the other glues or dopes. Then use a peel test to lift the fiberglass off the attached surface. Make your own conclusions.

Surface preparation is important. A fully prepared bonding surface, properly cleaned, sanded and roughed up and properly wetted surface are all important. Also proper bonding of the glass to mechanically come in contact with the bonding surface is important. Try rolling and or squeegee the glass and remove as much epoxy or bonding agent from the surface leaving the glass relatively dry. This will make the lightest and strongest situation. Then fill the weave, or cover with silkspan etc.

As to models I have silkspanned over wood, painted the fuselage and flown profiles. Interesting I have used double sided foam tape to secure the fuel tank in position. Often times when removing the tank the foam tape lifts the silkspan which was doped to the plywood. This indicates to me that dope is a weak bonding agent or a poor prepped surface. Draw your own conclusions.

One final thought. In the lancair we always apply glass bid tapes when joining two pieces on a 45 degree bias thus every fiber is across a joint and fully utilized in compressing or tension. I would recommend that the glass be applied on the 45 degree bias to the fuselage to eliminate twisting. applied normal to the fuselage axis is inefficient because the vertical fibers are poorly utilized in a crash and are useless in twisting. Only the horizontal strands are useful in bending and compression. the 45 degree bias will utilize all fibers in bending, compression, twisting and tension.

Bob Smiley

>One question here, though, Doug.
>
>I thought you were just advising
>someone NOT to fiberglass a
>nose. Yet you are talking
>about your ships that cracked
>and failed.. Maybe you SHOULD
>try fiberglassing. It's nearly FREE
>strength.

I know it sounds like I am talking out of both sides of my mouth. I also stated earlier in the post you mentioned about how to build the nose and engine crutch area so that glass is not needed. I built a Saturn that way by the original numbers. Then I hollowed out the nose and somehow fit a Saito 72 in it. It never shook or cracked or nothing because the internal structure was strong enough to hold the motor. If not FG isnt gonna help much. It will still end up shaking apart from the inside.

The other reason I told him not to Glass it was because he said he using an fp 40. They dont need to be glassed for that motor. I had one and flew it for along time and crashed it many times too. Never glassed it and it never needed it. The fp is a smooth runner not a shaker like a Tiger or a FOX. Also he said logevity was NOT a concern.

If the internal structure is strong then there is no need for glass and all that filler and extra work. If you build a crutch with only one former and balsa block between the bearers and the nose ring and use just a standard 1/4" piece of balsa to fill the bearer area then you might want to glass it. FG on the outside wont make the internal structure any stronger. It just strengthens the topblock and the joint to the fuse. If the crutch is still weak then you will be in for some shaking.

>And, you're right, of course. It
>is definitely possible to build
>too light. We've all seen
>a ship fold a wing
>sometime. Building adequate strength is
>definitely NOT over-building.. But a
>wing that is 10 times
>as strong as necessary IS
>over-building.

Trouble here is how do you know what 10X to strong is as opposed to 2X to strong. You see I would rather make a little or alot for that matter to strong then a little to weak. I build with a scale on my bench at all times. I go until it gets to a weight I like and then stop there and move on. I also finish with a scale on my bench. That is why most of my paint jobs are just letters and numbers nothing to special.

The 1.5 oz was from wood and glue. This wing is pretty big, 63". 714 sqrs with flaps so it is pretty big.

>
>Cheers,
>
>L.
>
>"I keep tryin' to think, but
>nothin' happens.." - Curly Howard

Motor crutch building is one of the most important parts of the whole building process. When done correctly it is plenty strong and glassing the nose would be OVERKILL(he he he) This is how I build mine. It is built with 3/8 by 3/8 or 1/2 by 3/8 maple bearers that extend from the nose ring all the way back past the leading edge of the wing. Build the formers F1 and F2 out of 1/8" plywood so that the bearer has a 1/8" drop from the top. This meaning that the motor mount actually lays 1/8" below the top edge of the fuse side when it is glued in. I will tell you why in a minute. As for the area between the motor mounts scrap the big balsa chaunk and go with three pieces of 1/16" balsa laminatied together with thin CA with the grains going in opposite directions. This helps resist twisting better than a big chunk of balsa. The grains must go in different directions. Even it is just a few degrees it makes a big difference in strength. Now you have your mounts glued into the Formers F1 and F2 with and open area in the middle. Before you glue in the laminated balsa use small 1/4" pieces of triangle stock in each of the four corners of that open area on the inside, glue these in with epoxy. This really helps tie in the maple to the formers. Now trace out the outline of the open area onto the laminated 1/16" balsa wood. Now cut this out and glue it in with epoxy keeping it level with the top of the mounts. Remeber that little 1/8 area above the mounts now it should look nice and flat in there. Glue this crutch to your fuse sides with epoxy. Do them one at a time it makes it easier to line it up at the front. I also build it upside down on my flat table on wax paper. Now flip it over and you have this little 1/8" area between F1 and F2 where you can take a piece 1/8" balsa and fit it perfectly to this area. Make it a tight press fit. Grain direction at this point doesnt matter because all the other grains are going in different directions. Use a smooth layer of epoxy and press fit it in there. Now fit on the nose ring onto the maple mounts. I tack them in with thin CA then come back with some epoxy. Thin I fill in the front behind the ring on the top with a small peice of 1/8" balsa that goes back to the blind nuts. This makes fairing the nose later alot easier. If you look at your wing hole you will see maple mounts hanging down in there in the way. Pull out the trusty old dremel and shape them the be a part of the wing saddle. When you glue the wing onto them you just made a bullet proof joint that can really handle stress. I only use 5 minute epoxy. I cant stand 20 minute it takes to long to setup. As long as your joints are good and solid 5 minute is plenty strong and fast. I know alot of this is old newes to some but I thought it would be helpful to see how I overbuild the heck out of my crutch so that FG is not needed and any motor can be fitted in there and I dont have to worry as much about it shaking around or twisting and flexing. Tieing in the nose ring to the motor mounts was one the biggest strength gainers to date, then the laminated balsa in the middel really helps it resist twisting.

Remeber when you sand FG or CF and you cut the weave you have just weakend it considerably. Putting glass on just so you can sand it off makes no sense. Now if you do like Larry and put the galss or carbon on then cover it with Silkspan or something and then sand it you have retained all the strength of the glass or carbon.

Question to Larry Cunningham ----- Is there a problem using buterate dope to apply fiberglass? I recently applied fiberglass to a Nobler cowl with buterate, and it seemed to work fine.

I think butyrate dope works fairly well. Fiberglass is amazingly friendly and easy to use, and when it gets properly wetted, it adheres.

Good points have been made about the superiority of epoxy for adhering fiberglass. In terms of absolute strength, epoxy is the way to go. I'm sure that with proper surface preparation, you can get dope or lacquer to stick adequately well over an epoxy surface too. (Or, do the fuselage paint job in epoxy..)

But I have found that you can treat fiberglass like you do silkspan, dope DOES adhere it.

I personally find nitrate dope a little stickier than butyrate, and I'm told it is slightly lighter and have observed that it shrinks less. Meanwhile, butyrate is (sorta) fuel proof, while nitrate clearly isn't at all. (But I didn't feel that the layers immediately over the raw balsa wood needed to be fuel proof..)

And I know that folks have had problems with compatibility between nitrate and butyrate, which is a good reason to do it all in butyrate. I've personally not had such problems (knock on wood), and I like the nitrate better for adhering things and prefinishing. That's all. I've been getting away with it.

I can understand how someone who experiences a compatibility problem could be very gun shy about using nitrate. That's fine, I understand.

I once foolishly tried to paint a (butyrate) dope color coat over a fuselage nose that I had smoothly prefinished using K&B epoxy filler/sealer. It was beautiful. However: that paint couldn't get either chemical nor mechanical purchase on the epoxy filler/sealer, and it just peeled and rolled off! My friend Bill Melton got a real horse laugh out of that one..

So I come back to the practical old low tech composite method of dope/silkspan under dope or lacquer or epoxy color finish. And all I do to modify that is insert a layer of light fiberglass under the silkspan. It works ADEQUATELY well for me, and it definitely adds strength, with just the tiniest increase in weight.

L.

I agree with Larry you can use butyrate to stick it down. I used it to stick down polyspan and it even says not to. But i did not want to mix and match brands(sig and brodak)and I had already started with Brodak.

Windy says if you thin the butyrate it will penetrate better when used as a binder. I tried this and it works. You may have to put more coats on but since it is thinned it ends up being the same amount.

Butyrate has a gloss hardener in it to make it fuel proof this also adds to the shrinking. This also makes it a bit thicker and it wants to sit on top each layer. Thinned and it will penentrate better. Nitrate has no gloss hardener in it. Therefore no fuel proof. I truly love it for prefinish. This stuff sticks and it will really dry out and become really light.