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Old Jan 24, 2015, 06:48 AM
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How about adding a couple of fuselage booms to an X8!

Something different!

I decided to modify my X8 to possibly improve the tendency to tip stall and make the beast a bit more stable in the process! so here it is - my cure for (some) of the handling problems with the X8 flying wing.

I reasoned that by extending the elevator to a more conventional moment arm and doing away with the elevons, replacing them with conventional ailerons, would have to make the model a more enjoyable and easier to control machine. Perhaps not quite so touchy in the pitch attitude and with the aid of reasonably sized flaps make the X8 easier to land as well.

It will be equipped with a FY-41AP Lite, Dragonlink RC, 10,000 mah for motor, plus 3300 for OSD, cams, VTX and RX. (total weight around 5.5kg)

It has not been flown yet but almost ready to fly and should be an interesting maiden flight when finally finished and weather is suitable for that first nervous flight.

I have flown many small and large scale model planes and currently fly a Penguin with RVOSD, pan tilt, lights etc and had a lot of enjoyable flights up to a max of nearly 7 klms, so pretty confident I can handle this machine. Will take some video and post here in due course. I'm calling it an X10 ( X8 + 2 booms!)

Any thoughts from you experts about whether the CG should be any way different from an (unboomed) X8 - I would appreciate your thoughts and suggestions..
Cheers,
Supcub
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Last edited by supcub; Jan 24, 2015 at 06:51 AM. Reason: Transferred from "FPV Equipment" to this more appropriate thread
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Old Jan 24, 2015, 06:19 PM
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Old Jan 13, 2015, 09:24 PM
The following Posts were copied from the original thread under the "Equipment" heading.

That thread is now closed.

My apologies to all for any inconvenience caused!

supcub


#2
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Heppy Ket
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Interesting indeed. I sure hope you have lots of long grass where you are I'm not sure how you would go at sorting out the CG, it will surely be forward of where it is, do please post some videos.
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Old Jan 13, 2015, 10:42 PM

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Dogdude
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Looks cool
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Old Jan 14, 2015, 02:19 PM

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Quote:
Originally Posted by Heppy Ket View Post
Interesting indeed. I sure hope you have lots of long grass where you are I'm not sure how you would go at sorting out the CG, it will surely be forward of where it is, do please post some videos.

Supcub
Thanks Heppy Ket, Yes I know what you mean, but will be ultra careful when the time comes to fly!

Supcub
The balance point can be seen here, tell me what you think - is this gonna be OK, or should it be somewhere different to this (to start with) ?
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Old Jan 14, 2015, 02:37 PM

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fOaMmaSh87
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Looks like a stealth plane! Nice.
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Old Jan 14, 2015, 05:09 PM

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Daemon
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It may work, but not likely be as efficient as a conventional plane.
A normal conventional plane does all of its lifting with the main wing which
has a cambered airfoil which generates all the upward lift, plus a
negative pitching moment (pulls the nose down).
The CG is usually placed well back from that of a flying wing airfoil, but
still in front of the center of lift which also causes a negative pitching
moment.
The horizontal stab and elevator back at the end of the tail boom/s then
must provide negative lift to create a positive pitching moment countering
the negative moment of of both the cambered airfoil and CG.

A flying wing normally has no elevator at the end of a long boom, so the wing
as a whole must have both camber and reflex so it can generate lift with the forward
portion of the airfoil, and counter its own positive pitching moment with
the reflex. A flying wing airfoil is usually a bit less efficient for this reason,
but usually makes up for it with lower platform drag (no fuse, tail boom or tail).

The problem with adding a tail boom or booms to a flying wing, is that
you've still got the original lower efficiency flying wing airfoil with built
in reflex plus your adding more platform drag with the booms and tail group.
The center of lift of a flying wing airfoil is pretty far forward, so you
can't move the CG back nearly as far as you would with a conventional airfoil,
so the horizontal stab has to run close to zero angle of attack
which doesn't provide a lot of inherent stability (makes it very pitch sensitive).

For your rig, I would start with the CG pretty close to stock recommended (rear
end of front finger holes), and keep the decalage (relative angle of
horizontal stab versus that of main wing) pretty close to zero, with a pretty
low elevator rate. I wouldn't be surprised if you find it challenging
to find the initial working angle of the horizontal stab and elevator.
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Old Jan 14, 2015, 07:08 PM

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Supcub
Quote:
Originally Posted by Daemon View Post
It may work, but not likely be as efficient as a conventional plane.
A normal conventional plane does all of its lifting with the main wing which
has a cambered airfoil which generates all the upward lift, plus a
negative pitching moment (pulls the nose down).
The CG is usually placed well back from that of a flying wing airfoil, but
still in front of the center of lift which also causes a negative pitching
moment.
The horizontal stab and elevator back at the end of the tail boom/s then
must provide negative lift to create a positive pitching moment countering
the negative moment of of both the cambered airfoil and CG.

A flying wing normally has no elevator at the end of a long boom, so the wing
as a whole must have both camber and reflex so it can generate lift with the forward
portion of the airfoil, and counter its own positive pitching moment with
the reflex. A flying wing airfoil is usually a bit less efficient for this reason,
but usually makes up for it with lower platform drag (no fuse, tail boom or tail).

The problem with adding a tail boom or booms to a flying wing, is that
you've still got the original lower efficiency flying wing airfoil with built
in reflex plus your adding more platform drag with the booms and tail group.
The center of lift of a flying wing airfoil is pretty far forward, so you
can't move the CG back nearly as far as you would with a conventional airfoil,
so the horizontal stab has to run close to zero angle of attack
which doesn't provide a lot of inherent stability (makes it very pitch sensitive).

For your rig, I would start with the CG pretty close to stock recommended (rear
end of front finger holes), and keep the decalage (relative angle of
horizontal stab versus that of main wing) pretty close to zero, with a pretty
low elevator rate. I wouldn't be surprised if you find it challenging
to find the initial working angle of the horizontal stab and elevator.
Thanks for your excellent advice there Daemon. I can see that you have given this a lot of thought and that is the sort of information I was hoping to get by creating this hybrid wing/ twin boom model
and posting here on RC Groups.

I also had similar thoughts about this modification, but the way I figured is if I make the stabilizer a full flying tailplane, with less camber on the upper surface (10%) than a fully symmetrical unit the result would be at least somewhere near stable. I anticipate having to make whatever changes needed to trim the flying stab to suit level flight especially at cruising speed.

I admit to not actually crunching the full numbers on this, but have drawn on more "gut instinct and a lifetime of experience with models" than anything more than basic aerodynamics.
So its just a bit of a combination of hope and good luck if it does fly with the sort of good manners and ease of control we all look for in our models... Time will tell!

All opinions and input much appreciated!

Supcub

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fOaMmaSh87
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Have you flown it yet?
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Old Jan 14, 2015, 10:03 PM

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supcub

Quote:
Originally Posted by fOaMmaSh87 View Post
Have you flown it yet?

Not Yet Ben, too many other priorities atm.. not enough hours in the day. Also weather here in SA not suitable for the first flight anyway.

I will post a video of the flight when the time comes.
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Last edited by supcub; Jan 15, 2015 at 08:54 AM.
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Old Jan 22, 2015, 08:56 AM

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Supcub
Update Jan 22 15:
Ongoing delays because of problems with electronics. Mainly problems with FY-41AP Lite. unable to be easily resolved, so am in process of fitting RVOSD G5 in its place.
First test flight anticipated this coming weekend if autopilot performs as it should and depending on weather of course...
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Last edited by supcub; Jan 25, 2015 at 06:19 AM. Reason: Transferred from "Equipment" thread to this more appropriate thread
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