JNorton

My Feedback: (2)

I'm going to start building my Somethin' Extra. As most of you probably know it has wash-in built into the wing. My question is do you think it is worth while to build it straight without the wash-in? As I understand it wash-in will effect how the aircraft handles inverted verses upright.
Thanks,
John

tommy s

My Feedback: (55)

I don't know why any plane would need wash-in. Wash-out on the wing tips is to improve low
speed performance. It makes the center of the wing stall before the tips lessening the possibility
of stalling the plane when landing etc.

tommy s

Tall Paul

The SE "washin" is the result of a blunder in the construction method.
The rationalization for it by SIG makes no sense at all.
Build it straight.
You are also aware the c.g. on the plan is very conservative, and many fliers move it back a lot?
This helps the excessive noseweight situation that arises when the plane is assembled and the c.g. is placed per print.

JNorton

My Feedback: (2)

Tall Paul,
How far past the indicated CG would you put it for an average non-3D sport flier flier? 3/8" inch?
Thanks,
John

Tall Paul

3/8" is a modest change. The kit c.g. is at 25% mac, when placed 3-1/2" back from the leading edge.
4-1/2" moves it to 32%, and I've people say theirs is even further back.
I had a lot of lead at the back of mine, and it could still use more, as it won't do a decent snap or flat-spin..
Start say 1/2" back and work from there, expecting to go even further aft as you get experience with the plane.
When properly set up, these are good 3D planes.

JNorton

My Feedback: (2)

Paul,
Thank you for your information. I thought 3/8" was a fair amount. Would never have started at 1/2"!!! Thanks also for your web site. I've gleaned quite a bit of useful information. Didn't there used to be a page on the Somethin Extra? Think I may have saved the page somewhere!

The problem with computers and ever increasing hard drives is having the information available when you need it. I think I need a Dewey Decimal system with a card file to keep track of all this junk!

Thanks again,
John

David Cutler

You should build it straight.

It's a great flier, capable of very slow landings without snapping, and a wing of that shape doesn't need anything other than being as square as possible.

-David C.

JNorton

My Feedback: (2)

Straight it is. Thanks David.

Red B.

I'm not sure whether SIG made a mistake in the construction or not but depending on how you want the aircraft to behave, wash-in may be a good thing.

It is usually assumed that the lift distribution of a wing is elliptically shaped, i.e., the inner portion of the wing does contribute more to the total lift than the outer portion. As a result, if one wants all parts of a wing to contribute equally much to the lift, an elliptical plan-form is considered ideal.
When a stall occurs it is most likely to start at the part of the wing that does most of the lifting work. With a rectangular wing, where the outer portion of the wing has "excess area" compared to an elliptical plan-form and is consequently rather lightly loaded, the wing root is likely to stall before the wing tips. This is usually a good thing as it produces safe stall characteristics. The downside of this is that spin and snap roll entries may be less clean
With an elliptical wing all parts carries the same load and thus a stall can start anywhere and with a highly tapered wing, the tips carries a higher load than the root and thus tip stalls are likely to occur.

If a rectangular wing has some wash-in added, the stall characteristics may be altered, making the aircraft more prone to tip stalling. From an aerobatic point of view this may be a good thing as it helps with positive spin and snap roll entries.
When inverted, the wash-in effectively becomes wash-out making for a plane that will be very nice for high angle of attack flight (inverted harriers) but may have slightly worse negative snap-roll entry characteristics.

I have built my SE according to the instructions and the aircraft does exhibit the behavior described above, but only to a small extent. For me this is a good thing as I love inverted harriers and my snap rolls are mostly positive.

/Red B.

RCaillouet3

I built mine straight and the airplane flies great!!! Only one problem I have with it. The RUDDER is not big enough! I can't get the airplane to hold a decent knife edge and flat spins are none existent!! I have broken it down to the rudder being just to smal for the airplane to fly the way I want it. My "proof" in this was when a friend of mine asked me to build one with him. He had very little building experience and wanted out of the ARF world. His airplane was build as mine was. The only change was that the rudder was scratch built with another 3/4" of rudder length at the top and 1" at the bottom. The powerplant, receiver, servos, and battery pack were all identical. The only differences in the 2 is that I used transparent monokote, he used ultracote solids, and of course the rudder.

I was the person who put the airplane in the air for the first time. I flew it around the pattern for a few times getting a feel for the airplane and trimming it out. I then proceeded with a stall with no problems. Then power was set to full and pointed skyward! UP UP AND AWAY!!!!!!! I had the owner there standing next to me and I asked for permission to "ring her out a little." He was so excited he immediately answered with a "YES!!!!!!!!!!!" Well as for what happened next was enough for me to go home and enlarge my rudder as well! NOW the extra FLIES!!!!!!!!!!!

Thanks,

Reg