Coyote`s X8

[Zeeflyboy]

only small, and really big.

What size motor shaft are we talking? I would think it must be relatively easy to re-purpose either a large heli tail or a smaller heli head (though tail would be easier).

The biggest tail assembly you'll easily find is from the Mikado Xxtreme - that's a 6mm shaft.

http://szene.litronics2000.de/wp-content/uploads/2011/03/IMGP94271.jpg

could then use heli blades like these http://www.ebay.co.uk/itm/15pcs-200mm-Main-Rotor-Blade-Walkera-4F200-RC-Heli-/270728425686 for props.

those are 200mm, so total blade disc would be about 450mm, or a little bigger than the 16" you're currently swinging. Obviously you'd need to check blade root thickness - if It's thinner than the tail grips then it'b be easy to shim out.

[Coyote]

Wont the problem be a hollow motor shaft for the control rod to go through ?

[Zeeflyboy]

no, the heli doesn't have a hollow tail shaft... that's the appeal of adapting it to work.

you may need an extended motor shaft, but I think it'd probably work with typical lengths... you only need half as much travel as a heli tail since you don't need the negative portion of the pitch. Just need a servo to push/pull the tail slider forwards and backwards.

To be clear, the tail hub and blade grips would be attached to the end of the motor shaft, the slider between the hub and the motor bell.

You then just need to make a small servo mechanism for pushing the slider back and forth.


These blades would be great btw http://shop.spinblades.com/index.php?option=com_virtuemart&page=shop.product_details&flypage=flypage.tpl&Itemid=82&category_id=&product_id=128

Spin asymmetric blades. More efficient in one direction (forwards in this case!)... 3mm root would fit most larger heli tail blade holders (except the Xxtreme, which is 4m root i believe, but two 0.5mm shims would fix that).

Of course it could end up complete bollocks, but that's half the fun isn't it?

[Coyote]

16x8 prop turned up, 658 watts at 40 amps static test

[Coyote]

Yes ages ago :)

[markvanhaze]

Any news on motor and prop combo?

[Coyote]

No rain all week, back to work tomorrow but going to try it in the afternoon if I can

[Coyote]

After my spin the other week a few patterns have been appearing in the X8 thread on RCG.

More and more people stalling into a spin and not being able to recover it.

Spun my X8 all the way to the field:
- good news: no damage to the plane
- not so good news: it is possible to spin this plane so that it does not recover

I was doing extreme slow flight testing today. Flew with power on at high angle of attack and kept the plane straight with elevons. All was ok. I was thinking it is not possible to spin the X8 and it is almost stall proof.

Then I repeated the same with zero power. Obviously keeping the plane level with ailerons is the recipe of getting it to spin, and it seems X8 is no exception. At stall angle of attack, I expected it to recover by dropping the nose. Nope. Instead it dropped immediately to fully developed spin. Elevons were completely ineffective, and adding power had no effect, it continued spinning the same direction like a falling tree leaf.

Same as I had, elevons had no effect

[markvanhaze]

Ok that's one to look out for then. I guess the rule is not to fly too  slow. It would be interesting to know the air speed and ground speed when it happens.

[Zeeflyboy]

After my spin the other week a few patterns have been appearing in the X8 thread on RCG.

More and more people stalling into a spin and not being able to recover it.

I thought that was a fairly common trait with flying wings? to get into a spin you have to stall the airframe, and due to the nature of the design the flight controls have very little authority to pop you out of it, and no vertical stabiliser/rudder to help arrest the spin.

speaking of spins, you made me look for my old video of upset training where I first learned to do them! Upset training - spin

[FPVSteve]

Definitely means that getting a good launch is critical though doesn't it, when airspeed is very low.

[markvanhaze]

After my spin the other week a few patterns have been appearing in the X8 thread on RCG.

More and more people stalling into a spin and not being able to recover it.

I thought that was a fairly common trait with flying wings? to get into a spin you have to stall the airframe, and due to the nature of the design the flight controls have very little authority to pop you out of it, and no vertical stabiliser/rudder to help arrest the spin.

speaking of spins, you made me look for my old video of upset training where I first learned to do them! Upset training - spin

Very interesting video! Scary but how do you recover then correctly? Obviusly its about regaining airspeed but what else is needed to stop the spinning? Im assuming the spinning does not allow for proper airflow over the wings which is why the aeleron deflection is not working efficiently?

[Zeeflyboy]

The normal recovery technique is a boot of rudder in the opposite direction to the spin, while centralising the controls or adding forward stick.

You do have some flow over the controls during a spin, and indeed for most (well designed) light aircraft they have to be held into a spin with full back stick, and usually aileron. Just releasing the controls will sometimes recover, albeit not as quickly as using opposite rudder and some aircraft need the rudder input. The trick comes from ascertaining your spin direction - not as easy as you may think sometimes, especially if you managed to get into an inverted spin!

On a flying wing, the "elevators" don't have as much authority due to close positioning to CG, and you have no vertical stabiliser to help stop the spin. In a simplified way of thinking about it, Imagine a flat spin if you will - a big tail sticking up is going to be acting as a big drag force stopping the spinning motion, on a flying wing there is no such force trying to stop the spin.

[Pasty]

What Rich said, if a wing enters a spin via a stall and it flattens out or starts to you are indeed screwed and become a passenger.

Having said that if the wing loading is kept low and you're carrying a good cofg it should recover easily with a good waggle of the sticks and a boot of throttle if needs be.

My thoughts about this X8 stuff is that people are running them too heavy, the wing loading is too high inducing early stall and once stalled or in a spin that heavy wing loading makes it harder or indeed impossible to recover.

Heres an example...

An X8 is 50% bigger than my scout, Ians X8 as an example is 125% heavier than my scout....

It would be interesting to know what the wing loading is of these spinning X8's.

Ians is around 18.4 oz/sqft.

[markvanhaze]

That makes sense.