Elevons and Elevator

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wtsidney
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Joined: Wed May 09, 2012 6:46 pm

Re: Elevons and Elevator

Post by wtsidney »

Modified a Lethal Weapon. Less drag / Less weight and smaller target with a flying stab.

Not sure what to expect. Havn't flown it yet.
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Bill Sidney
Round Rock, Texas
RCCA 1036
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Blue Note
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Re: Elevons and Elevator

Post by Blue Note »

Looks good, but watch your throws. The stabulator is much more sensitive than a traditional elevator. Usually only about 1/2" up and 1/2 down measured at the aft end, probably less to start with until you dial it in. Too much throw can really cause you problems in the beginning. I also suggest about 25% expo to smooth things out. Without it, it may feel very twitchy, especially when coming in to land. Good luck.
Chris Gunter
East TN
RCCA #954
wtsidney
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Joined: Wed May 09, 2012 6:46 pm

Re: Elevons and Elevator

Post by wtsidney »

All too many questions and not enough stick time - but here we go:

How do you size the stabilator? What happens when it is to small? Is there a rule of thumb for the size?
Bill Sidney
Round Rock, Texas
RCCA 1036
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Blue Note
Posts: 221
Joined: Tue Aug 12, 2008 1:02 pm
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Re: Elevons and Elevator

Post by Blue Note »

wtsidney wrote:All too many questions and not enough stick time - but here we go:

How do you size the stabilator? What happens when it is to small? Is there a rule of thumb for the size?
My Tomahawks are very similar in size ( front to back ) with what you are using, so the comparison is basically direct. Trial and error certainly work, but maybe with some grief. Looking at it, the stabulator appears to be sufficiently large. Mine are similar in design at 12" across, 2" at the tip, and 3.25" at the root. My wings carry more area than a Lethal Weapon or Battle Axe and I still have plenty of authority. If it is too small, you just have enough authority to adjust for the pitch change. Again, CG is the key for really unlocking it's potential. With the plane properly balanced, the stabulator just influences the pitch enough to change it, otherwise it just helps maintain some stability so the pitch doesn't drift. With the CG too far aft you are out of control, but too far forward and you just can't overcome the imbalance and fight it by riding the elevator input. If properly balanced, the stabulator should be perfectly parallel with the rails. Assuming your incidence on the wing is correct ( neutral for my symmetrical wigs ) as well as thrust angle, any pitch deviation should be adjusted at the flaperons, not at the stabulator. Being that my wings are symmetrical, there are slight differences, but not much. Here is a link to a build thread of how I build my planes which may help answer some questions. It is a bit in depth, but intended for a novice builder, so just pass over the basics as you see fit.

Build Thread

http://rccombat.net/forum/viewtopic.php?f=31&t=13700


Image

Here is a video showing the flight differences of elevator to stabulator. Although there are also some airfoil and planform variations, it still should demonstrate the comparison.

Chris Gunter
East TN
RCCA #954
wtsidney
Posts: 30
Joined: Wed May 09, 2012 6:46 pm

Re: Elevons and Elevator

Post by wtsidney »

Thanks Chris - Great Looking plane with incredible docs and details.

Flew the modified Lethal Weapon and was surprised. This is an existing air frame that was setup and flying with a neutral horizontal stab and no elevator trim. Did not adjust the CG - it balances on the spar.

Had to add 3 1/2 turns of reflex to get the flying stab parallel to the rails. The reflex is very noticeable now on the semi-symmetrical wing. Dialed the throws in so it didn't snap out of a loop and put three flights on it.

Thinking of putting a shim under the trailing edge should reduce the required reflex.

I don't think the added reflex slowed the plane down. Was able to fly inverted and perform outside loops. Otherwise the flight characteristics didn't really change, thought they would.
Bill Sidney
Round Rock, Texas
RCCA 1036
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