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-   -   how to sttrengthen without adding weight? (http://www.rcuniverse.com/forum/arf-rtf-75/11384920-how-sttrengthen-without-adding-weight.html)

ameyam 01-26-2013 08:57 AM

how to sttrengthen without adding weight?
 
Hi
earlier in the year 2012, I bought a GW (ARFMFG) Sbach 300 20cc. As you can see in the attached pics, the airframe is basically a frame. I need to strengthen without adding too much weight to keep it 3d. So I have 2 questions
1) Is this airplane suitable for a 20cc dle for 3d or do I need a more powerful dle 30? link is below
2) how to strengthen without adding too much weight? I need to fibreglass the firewall & reinforce the LG but besides that, how to reinforce the joints? Someone suggested CF tape to epoxy onto joints. I that good enough?

http://www.generalhobby.com/goldwing...lor-p-402.html
http://www3.towerhobbies.com/cgi-bin...&I=LXB964&P=ML
ameyam

ameyam 01-26-2013 08:59 AM

RE: how to sttrengthen without adding weight?
 
1 Attachment(s)
pics

sensei 01-26-2013 09:32 AM

RE: how to sttrengthen without adding weight?
 
Forget about the carbon tape, just get a 2 oz. bottle of both thin and medium C/A, carefully soak all the joints with thin C/A until you see slight pooling, keep moving fuselage around allowing the C/A to flow everyplace, then spray kicker. work small areas at a time until all areas are completed. Next go back over all non gusted areas with medium C/A, kick and your ready...

Bob

GaryHarris 01-26-2013 10:00 AM

RE: how to sttrengthen without adding weight?
 
What Bob said.

ram3500-RCU 01-26-2013 10:22 AM

RE: how to sttrengthen without adding weight?
 
With all due respect, I know CA is easy. but for truly light weight, it is not the best glue to use. There is a much safer (CA fumes), cheaper, and better way to do this. Professional builders who build really light use aliphatic resin emulsion adhesive like Titebond. They wipe all the excess out of the joints. No puddles of excess weight. This is a tremendously strong yet light glue joint.

Sometimes methods that have been used for years, really are still the best.

nitro wing 01-26-2013 10:22 AM

RE: how to sttrengthen without adding weight?
 
just make sure you dont get it all over your turtle deck, unless you have foam safe CA [X(]
Maybe add one stringer on the bottom. 1/16 th small ply gussets are very light, you could add a few in spots

ameyam 01-26-2013 10:33 AM

RE: how to sttrengthen without adding weight?
 
I realise best way to conventionally do it is to CA / Glue. I am concerned there isint enough bearing area of wood-to-wood contact for either glue to work. A friend who did up his version with 1/8" balsa sheeting in all open bays to strengthen, now suggests to use CF stringers laminated between the original (very thin) ply and 1/16" balsa formers. My concern is this will add weight. In his case, he is flying with a 120ax which would be more powerful than the dle20 I intend to use, so I want to keep the weight down. Frankly I am thinking to use 1/8" balsa sheeting with lightening holes in all bays and 1/4" tristock at all intersections

Ameyam

ram3500-RCU 01-26-2013 11:00 AM

RE: how to sttrengthen without adding weight?
 
Quote:

ORIGINAL: ameyam

I realise best way to conventionally do it is to CA / Glue. I am concerned there isint enough bearing area of wood-to-wood contact for either glue to work. A friend who did up his version with 1/8'' balsa sheeting in all open bays to strengthen, now suggests to use CF stringers laminated between the original (very thin) ply and 1/16'' balsa formers. My concern is this will add weight. In his case, he is flying with a 120ax which would be more powerful than the dle20 I intend to use, so I want to keep the weight down. Frankly I am thinking to use 1/8'' balsa sheeting with lightening holes in all bays and 1/4'' tristock at all intersections

Ameyam
If full scale airplanes were as overbuilt as most of our models, they would be so heavy they hardly would be capable of their intended uses.

600Bob 01-26-2013 03:20 PM

RE: how to sttrengthen without adding weight?
 
Yeah I think you are really worried about nothing.  Yes with an ARF ya want to check the factory glue job but that plane looks plenty strong to me, it IS a 3D plane after all, it doesn't look any different than others I have seen.  Carbon fiber blocks 2.4 gig signals so if you add a bunch of it then you can think about where you are going to mount the RX so the signal doesn't get shadowed.

nitro wing 01-26-2013 05:56 PM

RE: how to sttrengthen without adding weight?
 
carpenter glue wont soak into already glued joints, like thin CA followed by medium will.
Maybe do it outside so the fumes coming from the fuse wont knock you out.
Dont puddle it, its not needed, it will just run inside the covering and like horrible.

Truckracer 01-26-2013 05:59 PM

RE: how to sttrengthen without adding weight?
 
What Bob said +2. I fly a Goldwing 30 sized Yak 55 and other than saturating the glue joints with thin CA, reinforcing the firewall with aluminum corner brackets, and adding a few pieces of wood to the LG area, it has held together quite well over 2 seasons of hard flying.

Regarding aliphatic resin glues, I agree they are great glues but not for exterior application where little of the glue can penetrate the joint.

opjose 01-26-2013 07:10 PM

RE: how to sttrengthen without adding weight?
 
Quote:

ORIGINAL: ameyam

pics
Here we go again. You're over thinking it.

CA as suggested, maybe a BIT of CF and/or tri-stock at the landing gear and THAT'S IT!

Learn to improve the pilot, so you are not so concerned.

That plane was built with light ply purposely. What looks weak to you, is actually far stronger than you think.

Remember the balsa planes you are used to look more built up, but their structural material is weaker than the ply.

With planes of this type of build, as much far heavier ply is eliminated without sacrificing strength. Don't be tempted to "undo" the design you'll regret it.


Remember that if you make an area FAR stronger than before, you'll end up with breaks in a more difficult to repair area...

e.g. there are those who go nuts worrying about aluminum gear being weak, so they beef up the gear, and it rips the entire bottom fuselage out on a landing.
Had they left the "weak" gear in, the gear would bend out and absorb the load by doing so, or have resulted in far easier to repair damage.





ram3500-RCU 01-26-2013 07:19 PM

RE: how to sttrengthen without adding weight?
 
In 45 years of building scratch, kits, and ARFs, I have never had a plane fall apart in the air, under any circumstances. As they say, different stroke for different folks. I'll stick with what I have been doing, but that is not to say that other methods would work as well. On ARFs, I concentrate on the firewall, wing mounting structure, and landing gear mounts, with a little time spent on overall construction.

Also, no glue will "soak into" already glued joints. You are looking for joints with little or no glue, keeping the added glue to a minimum. CA is brittle and makes poor fillets.

Truckracer 01-26-2013 07:29 PM

RE: how to sttrengthen without adding weight?
 

Quote:

ORIGINAL: ram3500-RCU

In 45 years of building scratch, kits, and ARFs, I have never had a plane fall apart in the air, under any circumstances. As they say, different stroke for different folks. I'll stick with what I have been doing, but that is not to say that other methods would work as well. On ARFs, I concentrate on the firewall, wing mounting structure, and landing gear mounts, with a little time spent on overall construction.

Also, no glue will ''soak into'' already glued joints. You are looking for joints with little or no glue, keeping the added glue to a minimum. CA is brittle and makes poor fillets.
Agree for the most part.

Re: ARF glue joints, many times these have joints, especially in the plywood fuselage structure, where glue is applied to one side of a joint, leaving the other side only partly glued. Adding CA to these joints does complete the joint process. Also, thin CA can wick quite nicely into joints through the surface pores of the wood, especially where the all to common ARF glue (I don't know what it really is) just sort of sits on top of the wood. I can't think of any other kind of glue that can wick into existing joints like CA can.

chuckk2 01-26-2013 08:31 PM

RE: how to sttrengthen without adding weight?
 
How about a flexible glue like UHU Por? It has a great deal of flexibility, is kind to most coverings, and bonds to most surfaces quite well.
I've used it over CA, to help provide strength that is not really subject to cracking.

ameyam 01-27-2013 02:14 AM

RE: how to sttrengthen without adding weight?
 
Hi
I agree with Opjose. In the past, I have reinforced my models to the point they are much stronger than needed- case in point the GP Reactor bipe I am flying now thats also overweight. But its difficult to know where to stop and pilots dont improve overnight. In the meantime, I probably need to balance weight with sturdiness. In the Bipe, I strengthened ant then removed most of it with a dremel sander. There most of the weight was gained through use of standard servos

What we get in India is only thin CA. There is no kicker, the CA dries within seconds but also runs. I need to look for medium CA, I am told its available, so let me se
Ameyam

sensei 01-27-2013 07:17 AM

RE: how to sttrengthen without adding weight?
 
You don't want to build or strengthen to crash proof your airframe, you only need enough integrity to get the job done, just remember, the heavier the airframe is, the stronger it needs to be in order to carry the flight loads in the first place, and the higher the energy upon impact in the even of a crash, adding strength is adding weight and this is a vicious cycle, so be careful, weight goes on in grams and before you know it... [:o]

ARF designs themselves are pretty good but in many cases they can show up on your doorstep from the manufacturer and have dry glue joints, they are already covered making things tough to get to at times, sometimes even joints that appear to be glued are dry or have voids in or under them, so thin C/A followed by medium in areas at this point are the only adhesives that will flow into these areas clearly making this your very best path to lightweight and structural joints.

I design and build my airframes exclusively utilizing C/A adhesives for the assembly of all wood substrates, and I use the methods of assembly that I earlier explained because I know them to work very efficiently and to be the lightest possible way to build as I have demonstrated in many of my on a diet documented build threads over the years, no matter what adhesive you decide to use don't start adding a bunch of thing you don't need, you will be sorry in the end...;)

Bob




opjose 01-27-2013 12:07 PM

RE: how to sttrengthen without adding weight?
 

Quote:

ORIGINAL: Truckracer

Re: ARF glue joints, many times these have joints, especially in the plywood fuselage structure, where glue is applied to one side of a joint, leaving the other side only partly glued. Adding CA to these joints does complete the joint process. Also, thin CA can wick quite nicely into joints through the surface pores of the wood, especially where the all to common ARF glue (I don't know what it really is) just sort of sits on top of the wood. I can't think of any other kind of glue that can wick into existing joints like CA can.

Agreed.

That's the primary reason CA works so well for hardening and re-inforcing sometimes poorly glued ARF's, especially in hard to reach areas.

I'll also use a fuel proofing mix to get at more accessible areas too.


LDM 01-27-2013 05:03 PM

RE: how to sttrengthen without adding weight?
 
This is not for this plane as I agree with most said in this thread and its over kill .
I just wanted to add that when I do want to add very very light weight yet very strong material I have used flite skin. It can be used to line anything , it can be cut to line a simply stick wood frame.
You simply sand the side you want to glue add some CA and it will add incredible strength with very little weight .

ameyam 01-28-2013 12:13 AM

RE: how to sttrengthen without adding weight?
 
Correct me if I am wrong here- the load bearing areas are the point where the wing screws into the fuse, landing gear block and firewall. So, I plan as follows

1) In this airplane, the ply where the wing bolts on is so thin, when I tried to install the wing, the anti-rotation dowels were tight with the holes and the side of the fuse actually bent out of shape. I plan to use 1/16 birch ply there

2) The LG block is actually quite thick. But based on my buddy's experience with the same airplane, everytime he deadsticked, the LG pulled out. So I will add a couple of ply formers with CF sandwiched in between, then tristock on the side s where it meets the fuse. This will be 30 min epoxy, I cant see where I am working, just feel with my fingers

3) Another flier with the same airplane had his firewall comeoff in the first flight. So I will fibre glass / use CF woven sheet there for strength. Also, the engine box extends upto the fuse tube. That will be doubled with 1/16" birch ply there as well with lots of holes for lightening. I will use epoxy here as well for strength

4) For the fuse, I am going to wick in thin CA and then thick CA. I think the LHS has foam safe kicker on clearance sale. Most likely I wont use the 1/16 birch formers that I cut for the fuse. Even if I do, it will be mostly a frame with only 5mm rim all around and remaining part cutoff with a cross stringers left. That will keep weight at a premium.

5) Bottom of the fuse is just stringers. Since we transport the airplanes in a sedan with the front seat rolled back, this is the part that bears weight in transportation and most likely to crack. I plan to put in CF stringer sandwiched between the original and additional balsa strip. This will prevent cracking. Since rest of the bays are open, the 2.4G signal wont get blocked

An associated question- will the DLE20 give me similar power at 50% (hovering power) as a 120ax? My buddy flies with a 120ax and it flies well. I want to go gas with this one but I am not sure whether the traction will be sufficient for 3D

Ameyam

sensei 01-28-2013 04:36 AM

RE: how to sttrengthen without adding weight?
 

Quote:

ORIGINAL: ameyam

Correct me if I am wrong here- the load bearing areas are the point where the wing screws into the fuse, landing gear block and firewall. So, I plan as follows

1) In this airplane, the ply where the wing bolts on is so thin, when I tried to install the wing, the anti-rotation dowels were tight with the holes and the side of the fuse actually bent out of shape. I plan to use 1/16 birch ply there

2) The LG block is actually quite thick. But based on my buddy's experience with the same airplane, everytime he deadsticked, the LG pulled out. So I will add a couple of ply formers with CF sandwiched in between, then tristock on the side s where it meets the fuse. This will be 30 min epoxy, I cant see where I am working, just feel with my fingers

3) Another flier with the same airplane had his firewall comeoff in the first flight. So I will fibre glass / use CF woven sheet there for strength. Also, the engine box extends upto the fuse tube. That will be doubled with 1/16'' birch ply there as well with lots of holes for lightening. I will use epoxy here as well for strength

4) For the fuse, I am going to wick in thin CA and then thick CA. I think the LHS has foam safe kicker on clearance sale. Most likely I wont use the 1/16 birch formers that I cut for the fuse. Even if I do, it will be mostly a frame with only 5mm rim all around and remaining part cutoff with a cross stringers left. That will keep weight at a premium.

5) Bottom of the fuse is just stringers. Since we transport the airplanes in a sedan with the front seat rolled back, this is the part that bears weight in transportation and most likely to crack. I plan to put in CF stringer sandwiched between the original and additional balsa strip. This will prevent cracking. Since rest of the bays are open, the 2.4G signal wont get blocked

An associated question- will the DLE20 give me similar power at 50% (hovering power) as a 120ax? My buddy flies with a 120ax and it flies well. I want to go gas with this one but I am not sure whether the traction will be sufficient for 3D

Ameyam
Truth is, it's your airplane so do as you think best. Your opening statement reads: Correct me if wrong so... If you are going to add all that stuff to that little airplane then you are wrong! If the wing in not fitting properly to the fuse side, then see what the problem is and correct it, don't double up on the thickness of the fuse side, and if you land hard enough you will rip out the gear regardless how much epoxy and wood you place inside, it will find the weakest link and break. Now if the firewall falls out on the first flight, it is not because of the design, it is because of poor bond lines and the assembler of the ARF should have gone over everything in the first place. I am not beating on you so please don't take it that way, I am just giving you constructive criticism for your own growth bro...

Bob

raptureboy 01-28-2013 06:41 AM

RE: how to sttrengthen without adding weight?
 
I reinforce with bubble gum, preferably double bubblehttp://www.rcuniverse.com/forum/js/f...sn/biggrin.gif really though the airframe is supposed to be light and I would just look for those places that seem weak and reinforce them only. I have also used polyurethane glue very sparingly because it will foam up and attach itself to anything. Slightly dampen the area and then apply a little poy-u with a tooth pick and let it do it's magic. I like to use nylon bolts for landing gear so they shear off instead of taking the whole bottom out.

600Bob 01-28-2013 08:32 AM

RE: how to sttrengthen without adding weight?
 
On point #2 if the landing gear survived normal landings but came off on a dead stick then your friend needs to correct his dead stick landing technique.

#3 gas engines do vibrate more than glow, maybe it can stand to be reinforced a little or maybe it just didn't get glued properly, your call here. I don't mind beefing up this area because most all of my planes have needed extra weight up front to balance anyway so why not make it useful weight?

#5 I have a 1/4 scale Tiger Moth, it weights about 18 lbs, the bottom is just a few stringers and a little plywood and I transport it in my car with the seat back.  No issues.  And your plane looks like it is at least as rugged if not more so in some areas.

There is a reason a 3D plane is built light, if it doesn't look strong enough for you then maybe you need to practice with a plane that is built heavier for someone who is learning 3D, there are 3D planes that are built on the heavy side.

LDM 01-28-2013 12:43 PM

RE: how to sttrengthen without adding weight?
 
Ameyam , before you get torn apart quicker then your airfram lol , its really about what you are comfortable with .
You aksed a simple honest question that many of us can not answer because the typical 3D plane structure looks nothing like most planes , in fact I spend most of my time in the warbirds thread and many warbirds are on avg heavier in wing loading then the typical bird.
To accomplish what you want -stregnth and light follow the points so far .
1)CA will soak into the frame as seen in the pics
2)carbon fiber tape is good , some can be heavy
3)Flight skin is great if cut to size (in strips in your case ) and ca in place .
In closing if you want to nail down your plan and move on , state the current wing loading , that will give most guys who know 3D a idea if your current wing loading is low , mid or high and you can then determine your margin of error .

ameyam 01-28-2013 08:55 PM

RE: how to sttrengthen without adding weight?
 
Ok, I am going to start to build it soon, so I will figure out as I go along.

BTW, that deadstick landing that took off the LG was when the engine quit 10-12 off the ground in a hover. More of a controlled crash. He too has the bottom of the fuse reinforced as I described. In his case, he has sheeted the entire fuse upto the bay behing the canopy with 1/8" balsa

Anyway, can someone answer the engine question?

Ameyam


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