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Old Nov 20, 2012, 02:49 AM
FLY IY, BREAK IT, FIX IT,
Hampshire, United Kingdom
Joined Jun 2005
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Quote:
Originally Posted by xviper View Post
This has been done by a few of us already. The problem with going up high is that unless you've got a cameraman who can track the plane and zoom in at the appropriate times, all you see is a spec in the sky. In this first video, I took it up very high as I half believed all the doom and gloom from those who post here about a stall being the harbinger of death for an X8. So, I went out and purposely stalled it over 1/2 dozen times just to see what would happen. Well, nothing! In all cases, I just made sure the throttle was off and I let go of the sticks. In most cases, it just flopped over and pointed nose down and when the airspeed was enough, I just pulled out without power. In 2 of those stalls, I purposely put it into a spin and with throttle closed, I let go of the sticks. (It would not go into a spin on its own.) It stopped spinning very quickly, pointed itself nose down and I pulled out when the airspeed was sufficient. In every case, the X8 recovered on its own in 50 - 100 feet of altitude. You can't really see all the times it stalls or spun. You just have to believe me -- or not. I have my X8 slightly nose heavy, with the CG set at about 15mm in front of the published recommended place. Most, if not all of the death stalls/spins we've seen were with FPV or autopilot flown X8s.
..................
I'm flipping glad yo posted that - I was thinking about leaving mine in its box having been petrified by all the "spin" stories..........
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Old Nov 20, 2012, 05:14 AM
Registered User
United Kingdom, Gt Lon
Joined Feb 2007
125 Posts
spin spin sugar

X8 thread - more spin than an EU press conference...

However, the descriptions and results are not particularly counter-intuitive when you take the time to understand what's happening. One wing stalled + one wing flying = sharp yaw in direction of stalled wing. If the CoG is slightly forward, the nose will drop causing a dive, speed will increase & stalled wing will fly again, she recovers with no input (assuming neutral control surfaces). Which is exactly what xviper demonstrated.

If the CoG is slightly aft, the spin will develop into a stable configuration - locked in by the centrifugal force of the spin. In this case, to get the stalled wing to fly again we have to force the nose down by (ideally) leaving the stalled wing elevon neutral & applying down elevon on the flying side. Which is exactly what daemon demonstrated.

There is one consistent solution regardless of CoG position - don't stall the bloody plane

It's very easy for me to say all of that - I've yet to maiden my X8
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Old Nov 20, 2012, 05:26 AM
FLY IY, BREAK IT, FIX IT,
Hampshire, United Kingdom
Joined Jun 2005
816 Posts
Quote:
Originally Posted by wolfaroo View Post
don't stall the bloody plane

:

Stalling a plane is one of my standard maiden "tests" to see how it behaves. Normally I can get out of it, but not too sure I will follow my typical maiden protocol on this one....
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Old Nov 22, 2012, 04:34 PM
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Joined Sep 2012
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Quote:
Originally Posted by Daemon View Post
There's no "rudder" action at all, so it's just not applicable in this context.
On a flying wing you have ailerons and elevator combined into elevon, and if you apply full
down + full opposite roll (opposite the spin direction as you're implying by
suggesting an analog to rudder input) and look at the control
surfaces, you'll find the one on the outside wing (the only one flying) is level or even above
level (depending on relative aileron/elevator rates) which is exactly
the wrong way it needs to be. It needs to be below level as far as possible, so
this one flying wing can pitch the nose down to built airspeed, get the other wing flying, and
then you can center the stick and pull out. The only way to get it into that state is full down
elevator and roll input *into* the spin direction. No power is necessary at any time during X8
spin recovery, and will make the situation worse.

Just to be clear, the control inputs do not resemble a conventional aircraft spin recovery, at all.
It's not the intuitive thing to do either which means you have to think about what you're
doing, and get it right, or it *can* just spin all the way to the ground.

ian
Ian - so from onboard the x8 (or looking from above) nose is spinning right (clockwise spin) you add down elevator and stick right (so right wing elevon higher than left elevon) with no throttle...? Is that correct?

Thanks
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Old Nov 22, 2012, 04:36 PM
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Joined Sep 2012
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Hi - does any on have a few screen dumps of there APM pid settings?

Something like the image in this page....?

http://code.google.com/p/ardupilot-mega/wiki/Tuning

Thanks
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Old Nov 22, 2012, 04:38 PM
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Quote:
Originally Posted by Impailer View Post
Stalling a plane is one of my standard maiden "tests" to see how it behaves. Normally I can get out of it, but not too sure I will follow my typical maiden protocol on this one....
Yes - 4 of my 5 flights have resulted in stall spins... Just getting on top of it now with CG, elevon limits and working in Ian and JetPilots spin recovery methods.....

When it is flying - it is such a cool bird and looks so menacing in the sky...
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Old Nov 22, 2012, 05:51 PM
Wats the worst that can happen
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Canada, BC, Surrey
Joined Jan 2009
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Quote:
Originally Posted by VizBizTas View Post
Ian - so from onboard the x8 (or looking from above) nose is spinning right (clockwise spin) you add down elevator and stick right (so right wing elevon higher than left elevon) with no throttle...? Is that correct?

Thanks
Wouldnt that mean down elevator, and full left? If the plane is spinning clockwise, the outer wing (or lef) is 'flying', thus is the surface that hopefully will respond to control movement.

I'm fairly certain Daemon specified to jam the sticks top left corner even.
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Old Nov 22, 2012, 05:54 PM
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United States, GA, Cumming
Joined Dec 2001
203 Posts
Airframe finished, on to electronics

Here is a picture of my Skywalker X-8. It is covered in auto vinyl. It is black on the bottom, purple, gold, (LSU Tigers colors) and Pewter on top.



Outboard on the left wing is the 1.2Mhz Video Transmitter, with heat sink and BlueBeam CP antenna. The right wing has a corresponding amount of weight (1.5 ounces) at the same location.

The motor is a Turnigy Aerodrive SK3 4240 740KV which will be run on 4S 5000MAh. During bench testing it turned the 13X6.5 prop 8,800 rpms, drew 44amps, and hit about 600 watts.

Guidance will be Dragon Link UHF, and it will have a Dragon Link OSD V2. Two cameras will be used- one for FPV on tilt and pan and a fixed position GoPro for flight recording.

Planning to make a catapult launcher even though I have a lot of hand launch experience. The carbon fiber prop in the back of this thing would cut furrows across my arm and hand if I have a bad launch, so a catapult will be readied.

Looking forward to extended time and range flights soon.



If anybody in North Georgia reads this and can suggest some places to fly I would like to hear about them. I will do the LOS flights at my AMA club's field but cannot do long range FPV from there.
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Old Nov 22, 2012, 06:18 PM
Team Park Pilot - Airborne
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Australia, NSW, Sydney
Joined Nov 2006
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Nice job Lou - Can you tell me how much Auto vinyl you needed to cover it ? Also, that little stand could be made in to a ground based dolly if it were just a bit higher and add some wheels. I will be looking into that if I ever get around to starting my 8 !
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Old Nov 22, 2012, 06:35 PM
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United States, GA, Cumming
Joined Dec 2001
203 Posts
G-Forced,
2X4 feet of purple and gold, 2X4 feet of black for the bottom and 3X4 feet of pewter for the fuse top and bottom. The pewter is 3M Di Noc but I wouldn't spend the extra money to get it were I to do it again. The secret to application is a heat gun. It doesn't take much heat to make it very flexible and it will go around curves nicely. I got the vinyl from a company called Metrostyling. They had good selection and reasonable prices.

In the 60s I flew control line speed planes out of three wheeled dollies. As they gained enough speed to fly they would lift with the dolly to about a foot and the dolly would then drop away. A bungee ramp launcher is easier to build and I believe more effective. We'll see.
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Old Nov 22, 2012, 06:38 PM
Team Park Pilot - Airborne
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Australia, NSW, Sydney
Joined Nov 2006
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Thanks Lou - My field is very flat so I think a dolly would work well. But for most, not very practicle but very easy to make.
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Old Nov 22, 2012, 06:50 PM
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Canada, MB, Brandon
Joined Jan 2003
434 Posts
Quote:
Planning to make a catapult launcher even though I have a lot of hand launch experience. The carbon fiber prop in the back of this thing would cut furrows across my arm and hand if I have a bad launch, so a catapult will be readied.
I realize the X8 is big....but.....has anyone tried launching it by resting one wing on the ground, grasping the leading edge of the other wing, do a 1/2 circle and "fling" the X8 into the air? Of course you'll be adding throttle with the other hand as you're doing this......

Bill
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Old Nov 22, 2012, 07:39 PM
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Quote:
Originally Posted by BillyM View Post
I realize the X8 is big....but.....has anyone tried launching it by resting one wing on the ground, grasping the leading edge of the other wing, do a 1/2 circle and "fling" the X8 into the air? Of course you'll be adding throttle with the other hand as you're doing this......

Bill
Somewhere there is a video of an X8 being launched "discus" style from a small ledge (Australia?), but I did a media search tonight and can't find it.
I have to assume it was light build by the way he handled it. I can't picture trying to launch my 8 lb wing that way.
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Old Nov 22, 2012, 09:12 PM
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Lakewood, Colorado
Joined Aug 2002
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Quote:
Originally Posted by TheCure View Post
Wouldnt that mean down elevator, and full left? If the plane is spinning clockwise, the outer wing (or lef) is 'flying', thus is the surface that hopefully will respond to control movement.

I'm fairly certain Daemon specified to jam the sticks top left corner even.
right (clockwise) spin requires full down elevator, full right aileron.
With mode 2, that'd be stick in upper right corner.
You have to look at how roll and pitch inputs mix together for elevons to understand why.
Right aileron input drops the left elevon.

ian
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Old Nov 22, 2012, 09:14 PM
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Quote:
Originally Posted by Daemon View Post
right (clockwise) spin requires full down elevator, full right aileron.
With mode 2, that'd be stick in upper right corner.
You have to look at how roll and pitch inputs mix together for elevons to understand why.
Right aileron input drops the left elevon.

ian
Yip - for it...
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