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-   -   reinforcing motorbox/firewall (http://www.rcuniverse.com/forum/giant-scale-aircraft-3d-aerobatic-110/7316848-reinforcing-motorbox-firewall.html)

MetallicaJunkie 04-01-2008 01:09 PM

reinforcing motorbox/firewall
 
My brother has a 33% SD models extra 260, and we feel the the motor box and firewall are going to need reinforcing to meet our flying style demands.

What ounce weight of carbon fiber cloth is needed, and what is a good website to buy small quantities at a reasonable price?

Tired Old Man 04-01-2008 01:59 PM

RE: reinforcing motorbox/firewall
 
8-12 ounce unidirectional.

Try [link]http://www.fiberglasssupply.com[/link] in Bingen, Washington. I don't know their minimum quantities but the owner will work with people. It's worth taking a look. Bear in mind that carbon is not cheap.

Oh darn. Looks like he changed locations. Now I can't just walk next door for stuff when I'm at the office anymore[&o]

MetallicaJunkie 04-01-2008 02:27 PM

RE: reinforcing motorbox/firewall
 
thanks pat, i found another nice company while browsing here at work... http://www.uscomposites.com/carbonpage.html



sensei 04-01-2008 03:17 PM

RE: reinforcing motorbox/firewall
 
For just a fraction of the cost you could use balsa tri stock and thin CA and you would get the same results.
Just food for thought.

Bob

pe reivers 04-01-2008 03:41 PM

RE: reinforcing motorbox/firewall
 
hmm... not quite in the same league. Balsa shear force is very low. The motor box has to transmit all torque vibrations through the fuselage to the wings that act as a balancer. With larger engines, balsa just won't cut it any more.
In 100% aircraft, Balsa is used for filler blocks, not for contruction main parts. There is a reason for that. Light ply too is suspect in larger planes. The glue interface to the fuselage is no stronger than the weakest link, which is the wood.
With carbon reinforcement, the carbon will take ALL loads, and should be dimensioned as such. This is due to the large difference in strain properties, know as young's modulus. Before the wood is anywhere near decent load bearing strains, the carbon is at it's strain limits. This should be considered with carbon reinforcing.

Tired Old Man 04-01-2008 05:52 PM

RE: reinforcing motorbox/firewall
 
One other item to keep in mind. The engine pulls, and does not push unless you have a tail mounted engine. Reinforcing the outside of the box does more than working the inside. If you wet the carbon well and lay it up using vacuum bagging or pressure from another source to have it tight to the wood the stuff is stonger than steel for a minimal weight penalty. It sets ultra thin per layer when laid up tight. More epoxy than needed to fully wet the carbon is only excess weight when it dries and provides no additional strength.

If you are needing to do lap joints, think "tree" and it's branches. That's probably the strongest joint made in nature and if you overlap wet carbon layers similar to the joint between a tree trunk and a branch you will end up with a formidable lap joint.

as722 04-01-2008 07:08 PM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: MetallicaJunkie

My brother has a 33% SD models extra 260, and we feel the the motor box and firewall are going to need reinforcing to meet our flying style demands.

What ounce weight of carbon fiber cloth is needed, and what is a good website to buy small quantities at a reasonable price?

What kind of "flying style demands" will you put that 260 through to need carbon fiber cloth on the firewall ? Hard landings ?


Albert

Craven 04-01-2008 08:23 PM

RE: reinforcing motorbox/firewall
 
Hard landings? LOL....

Tired Old Man 04-01-2008 08:29 PM

RE: reinforcing motorbox/firewall
 
Just for informational purposes, the 35% SD Katana firewall without any extra help handles a BME 115 with no problems. The SD planes are pretty well made over all. Perhaps some fit issues here and there but not weak by any account.

sensei 04-01-2008 08:46 PM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: pe reivers

hmm... not quite in the same league. Balsa shear force is very low. The motor box has to transmit all torque vibrations through the fuselage to the wings that act as a balancer. With larger engines, balsa just won't cut it any more.
In 100% aircraft, Balsa is used for filler blocks, not for contruction main parts. There is a reason for that. Light ply too is suspect in larger planes. The glue interface to the fuselage is no stronger than the weakest link, which is the wood.
With carbon reinforcement, the carbon will take ALL loads, and should be dimensioned as such. This is due to the large difference in strain properties, know as young's modulus. Before the wood is anywhere near decent load bearing strains, the carbon is at it's strain limits. This should be considered with carbon reinforcing.
This is a nice story... (LOL) like I said, balsa tri stock will do the job just fine.

Bob

bzrogers 04-01-2008 09:28 PM

RE: reinforcing motorbox/firewall
 
Tri-Stock works fine on all my 40%ers with a DA-150!

mikec3d 04-01-2008 10:03 PM

RE: reinforcing motorbox/firewall
 
1 Attachment(s)
How about these...they work just fine....

1. 40% Carden 260
2. 40% SD Models Yak 54

Tired Old Man 04-01-2008 10:05 PM

RE: reinforcing motorbox/firewall
 
Pe's illustration implies that balsa will be stronger than carbon at the end of the paragraph. Sorry, but I have to dispute that. I fly 40 pound carbon airframes and no part of them would carry the load of another part if made from balsa of any type. The only component that could come close to carrying some of the wing loads would be of metal.

3DAP 04-01-2008 10:17 PM

RE: reinforcing motorbox/firewall
 
Most light weight army uavs are made from carbon fibre not balsa. Check out Air and Space and see what they are using carbon for. Also balsa may not prevent twist like mentioned before. Some of these guys have a lot more exp than other wise given credit for. Go far the Carbon or at least fibre glass. this stuff really strengthens joints or people would not be telling to use it.

mikec3d 04-01-2008 10:43 PM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: The glue interface to the fuselage is no stronger than the weakest link, which is the wood.
What would you epoxy the CF cloth to????
I guess since the vibrations are tranfered through the motor box to the wing tubes, then that all needs to be reinforced also, since it is all glued WOOD.

MetallicaJunkie 04-02-2008 12:18 AM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: as722


Quote:

ORIGINAL: MetallicaJunkie

My brother has a 33% SD models extra 260, and we feel the the motor box and firewall are going to need reinforcing to meet our flying style demands.

What ounce weight of carbon fiber cloth is needed, and what is a good website to buy small quantities at a reasonable price?

What kind of "flying style demands" will you put that 260 through to need carbon fiber cloth on the firewall ? Hard landings ?


Albert

no, just hard, wild, throwing the sticks type flying not necessarily 3d.... if i ever get concerned about hard landings, ill make a different thread

Tired Old Man 04-02-2008 12:22 AM

RE: reinforcing motorbox/firewall
 
I suppose I could say something about the length of the carbon weave extending back over a wood component. Longer moves the stress point accordingly, and long enough moves the stress point perhaps to another bulkhead which adds considerable "carry" to the other end. Or perhaps laminating back to a wood doubler which would pick up more torsional strength. You won't care if the wood breaks under the carbon because the carbon would continue to carry the load.

I have to agree that in most cases a simple piece of balsa tri stock effectively strengthens the firewall to fuselage joint, but what do you do if you think both the firewall and the sides it's attached to are too weak. Just adding a ply doubler inside the firewall will do nothing for the sides, right? Now there may be some grumbling about the weight of the carbon. No worries. That 8 ounce carbon is the weight for a square yard, and correctly planned an entire motor box covered in carbon should come in around 2.5 ounces or less after completion.

Don't limit your thinking to a single point.

sensei 04-02-2008 07:39 AM

RE: reinforcing motorbox/firewall
 
Guys,

What I stated was; balsa tri stock properly bonded in the corners of the motor box of a built up airframe is cost effective and strong enough to carry any flight loads you could induce upon it, it's that simple.

Bob


bzrogers 04-02-2008 08:06 AM

RE: reinforcing motorbox/firewall
 
How did a discussion about a 35% Yak turn into an argument about 40lb airplane?

[:@]

This is rediculous.

sensei 04-02-2008 08:09 AM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: 3DAP

Most light weight army uavs are made from carbon fibre not balsa. Check out Air and Space and see what they are using carbon for. Also balsa may not prevent twist like mentioned before. Some of these guys have a lot more exp than other wise given credit for. Go far the Carbon or at least fibre glass. this stuff really strengthens joints or people would not be telling to use it.
I think I will check out the Air & Space mag. so I can learn about composites...

Bob

T. Bob 04-02-2008 09:29 AM

RE: reinforcing motorbox/firewall
 
Quote:

just hard, wild, throwing the sticks type flying not necessarily 3d....

We gotta stick jammer here.

Matt_McCarty 04-02-2008 12:33 PM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: sensei


Quote:

ORIGINAL: 3DAP

Most light weight army uavs are made from carbon fibre not balsa. Check out Air and Space and see what they are using carbon for. Also balsa may not prevent twist like mentioned before. Some of these guys have a lot more exp than other wise given credit for. Go far the Carbon or at least fibre glass. this stuff really strengthens joints or people would not be telling to use it.
I think I will check out the Air & Space mag. so I can learn about composites...

Bob
LOL!.....guys his name is sensei for a reason......the balsa tri will work just fine.

MetallicaJunkie 04-02-2008 12:44 PM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: T. Bob

Quote:

just hard, wild, throwing the sticks type flying not necessarily 3d....

We gotta stick jammer here.

So what bobby?

as722 04-02-2008 02:51 PM

RE: reinforcing motorbox/firewall
 

Quote:

ORIGINAL: MetallicaJunkie


Quote:

ORIGINAL: as722


Quote:

ORIGINAL: MetallicaJunkie

My brother has a 33% SD models extra 260, and we feel the the motor box and firewall are going to need reinforcing to meet our flying style demands.

What ounce weight of carbon fiber cloth is needed, and what is a good website to buy small quantities at a reasonable price?

What kind of "flying style demands" will you put that 260 through to need carbon fiber cloth on the firewall ? Hard landings ?


Albert

no, just hard, wild, throwing the sticks type flying not necessarily 3d.... if i ever get concerned about hard landings, ill make a different thread

Now that I know we're dealing with wild throwing the sticks type flying but not necesarily 3d I would definetely wrap the entire engine box with carbon fiber cloth. Good luck with your plane.


Albert

T. Bob 04-02-2008 03:23 PM

RE: reinforcing motorbox/firewall
 
Quote:

Now that I know we're dealing with wild throwing the sticks type flying but not necesarily 3d I would definetely wrap the entire engine box with carbon fiber cloth. Good luck with your plane.
Hey Albert

I would'nt even take it out of the box.


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