CARBON FIBER DISCUSSION

[Piotrsko]

As someone that's BTDT, to mount stuff on top of the rudder, you need to build a structurally beefy rudder that's very stiff in a couple of axises. Mounting brackets could be as simple as a pair of bent tin brackets, notably if it is full flying. However full flying is prone to severe flutter in a couple dimensions. Then there's the issue of keeping it out of the wing wake. Yes it's more theoretical efficient, and has that sexy way cool visual effect, BUT.........BUILDING it is a whole can of worms. What's wrong with a flerkin style for up to 250 mph?

Your wing profile is probably good, but building it without skin structure doing most of the strength means it has to be solid CF or really thick

Take any of your current planes up until it's a spec, push it into a dive, wait a bit then pull up. If you don't fold the wings, you build much better than me

 

[Zoom Master]

As someone that's BTDT, to mount stuff on top of the rudder, you need to build a structurally beefy rudder that's very stiff in a couple of axises. Mounting brackets could be as simple as a pair of bent tin brackets, notably if it is full flying. However full flying is prone to severe flutter in a couple dimensions. Then there's the issue of keeping it out of the wing wake. Yes it's more theoretical efficient, and has that sexy way cool visual effect, BUT.........BUILDING it is a whole can of worms. What's wrong with a flerkin style for up to 250 mph?

Your wing profile is probably good, but building it without skin structure doing most of the strength means it has to be solid CF or really thick

Take any of your current planes up until it's a spec, push it into a dive, wait a bit then pull up. If you don't fold the wings, you build much better than me

I’m gonna have foam core wings and yes I’m starting to regret putting the stab on the top. Putting the stab on top opened up a lot of problems for me so for the foam board version I might just put it on the bottom and yes my wings will be foam core so they won’t bend under all that pressure.

 

[Zoom Master]

As someone that's BTDT, to mount stuff on top of the rudder, you need to build a structurally beefy rudder that's very stiff in a couple of axises. Mounting brackets could be as simple as a pair of bent tin brackets, notably if it is full flying. However full flying is prone to severe flutter in a couple dimensions. Then there's the issue of keeping it out of the wing wake. Yes it's more theoretical efficient, and has that sexy way cool visual effect, BUT.........BUILDING it is a whole can of worms. What's wrong with a flerkin style for up to 250 mph?

Your wing profile is probably good, but building it without skin structure doing most of the strength means it has to be solid CF or really thick

Take any of your current planes up until it's a spec, push it into a dive, wait a bit then pull up. If you don't fold the wings, you build much better than me

Ill probably manage building it and ill see what I can do to make my wings stronger.

 

[telnar1236]

Another thing to consider is control linkages. Having them in open air with no fairing adds some drag and you need enough space for the servo so wherever the elevator is, you need to consider where the servo for it will be mounted. T-tails might be more efficient, but you might lose all that efficiency again by having a thicker vertical stabilizer to mount hardware.

 

[telnar1236]

For 200 mph a couple strong carbon fiber spars through the wing should be totally fine and significantly lighter than making the skin thick enough to avoid buckling even with a foam core. That said, it's worth looking at the 0 lift drag coefficient of the airfoil you choose. In general, you want something thin, but too thin and sharp isn't always better since it can cause flow separation.

 

[Zoom Master]

Another thing to consider is control linkages. Having them in open air with no fairing adds some drag and you need enough space for the servo so wherever the elevator is, you need to consider where the servo for it will be mounted. T-tails might be more efficient, but you might lose all that efficiency again by having a thicker vertical stabilizer to mount hardware.

True all the control linkages wont be out in the open and my servo for the T tail will be in the fuselage. And as for the vertical stabilizer being thick....that is sort of what im gonna do not to think but it is gonna be a bit thick so I can get some control links through and mount my horizontal stab.

 

[Zoom Master]

For 200 mph a couple strong carbon fiber spars through the wing should be totally fine and significantly lighter than making the skin thick enough to avoid buckling even with a foam core. That said, it's worth looking at the 0 lift drag coefficient of the airfoil you choose. In general, you want something thin, but too thin and sharp isn't always better since it can cause flow separation.

Yea im gonna put like 2 carbon fiber spars through the wings and a thin one that will go through the vertical stab. And yes I'll look at the airfoils once again but.....for the foamboard version im not using any airfoils.......

 

[Houndpup Rc]

Im also gonna be making the wing pretty thin. So im planning on using a pretty thin airfoil for the plane something like this.
View attachment 252313
And also im gonna order the parts and get started building my speedwing soon ! (hopefully) So now im gonna go and finalize my design and finalize all the parts for the airplane and then order them !

Keep in mid that the thinner you make it the faster you will have to fly to keep the airplane in the air.

 

[Houndpup Rc]

Yea im gonna put like 2 carbon fiber spars through the wings and a thin one that will go through the vertical stab. And yes I'll look at the airfoils once again but.....for the foamboard version im not using any airfoils.......

You mean you are just going to have a single layer of foam for the wings and no airfoil?

 

[Zoom Master]

You mean you are just going to have a single layer of foam for the wings and no airfoil?

Well no not a single sheet im basically gonna do what Joshua Finn did with his wings.....where he used 2 peices foam sheets to make the wings.

 

[Houndpup Rc]

Well no not a single sheet im basically gonna do what Joshua Finn did with his wings.....where he used 2 peices foam sheets to make the wings.

Make sure to put a CF spar in

 

[Zoom Master]

Make sure to put a CF spar in

I will 👍

 

[Zoom Master]

As someone that's BTDT, to mount stuff on top of the rudder, you need to build a structurally beefy rudder that's very stiff in a couple of axises. Mounting brackets could be as simple as a pair of bent tin brackets, notably if it is full flying. However full flying is prone to severe flutter in a couple dimensions. Then there's the issue of keeping it out of the wing wake. Yes it's more theoretical efficient, and has that sexy way cool visual effect, BUT.........BUILDING it is a whole can of worms. What's wrong with a flerkin style for up to 250 mph?

Your wing profile is probably good, but building it without skin structure doing most of the strength means it has to be solid CF or really thick

Take any of your current planes up until it's a spec, push it into a dive, wait a bit then pull up. If you don't fold the wings, you build much better than me

Well then why do some of the worlds fastest rc planes all have T tails ?

 

[Piotrsko]

Didn't imply it COULDN'T be done, just implied it's tough to do at these speeds when the mechanism is halfway engineered. These guys are using solid CF rudders on thick skin big diameter booms and probably experienced every failure you can get. You'll notice they all have smallish moving surfaces. Wonder why? ( I actually know why)

 

[Zoom Master]

Didn't imply it COULDN'T be done, just implied it's tough to do at these speeds when the mechanism is halfway engineered. These guys are using solid CF rudders on thick skin big diameter booms and probably experienced every failure you can get. You'll notice they all have smallish moving surfaces. Wonder why? ( I actually know why)

Why ?

 

[Piotrsko]

Oh by the way, you want your pushrods to be pull for up.

 

[Piotrsko]

Why ?

Instant spontaneous disassembly if the servo can actually get full deflection. Mostly something load bearing fails at these speeds don't forget metal geared servos

 

[Zoom Master]

Oh by the way, you want your pushrods to be pull for up.

Noted 👍

 

[Zoom Master]

Instant spontaneous disassembly if the servo can actually get full deflection. Mostly something load bearing fails at these speeds don't forget metal geared servos

Hmm interesting….ill look into it…..and btw does one really need metal gear servos for 200 mph ?

 

[Zoom Master]

Hmm interesting….ill look into it…..and btw does one really need metal gear servos for 200 mph ?

I was sort of planning on just using 2-3 9 gram non metal servos……