crash bandicoute

i posted this in the aerodynamics forum also, but it always seems pretty dead over there, so i'm going to post it here as well, and see who responds to it. what is wash-in and wash-out and what does it do and how do i build it in? i just got a set of plans to scratch build an extra 3.25 from rich urivitchand was curious about this. the plane builds pretty light anyway, wing span 47", right around2.75-3.5 lbs, wing loading 19-23 oz./sqft, 340 sq. in., powered by my trusty .32 from o.s.,so i'm curious if tip stalling is going to be a big deal with it.don't be afraid to throw it all at me.just never really thought about wash-out before. the only thing i know about it, is it has to do with the root of the wing stalling vs. the tip, or before at least, keeping the ailerons active. any other assistance would be great with figuring out this "mystery".

vpresley

My Feedback: (162)

As I recall, washout is where, at the wing tips, the trailing edge is reflexed up, slightly higher than the leading edge. better flying and stability habits. Helps with Wing Tip Stalling.



Vince

crash bandicoute

how much should be adjusted into it and would you do this by intentionally building in a twist, per se, in each wing? maybe a couple degrees, or a 1/4 inch up on the trailing edge of the tip?

Tony Hallo

2 to 3 degrees.
I would believe the plane you're building does not need any wash out. Normally highly loaded scale planes do. Just built it straight. As stated the purpose of wash out is to force the wing to stall near the fuselage before the tip, this prevents auto rotation. As the wing stalls, speed increases moving away from stalled condition. Hope this makes sense?

crash bandicoute

makes perfect sense. thanks. i was curious if it should be something to think about while building the plane, as to do it in the process.

majora

Based on the name of the model, it is a 3D type machine. With this in mind, the wing should be as straight as you can get it because the wash-out will become wash-in when you are inverted. I would think that inverted tip stalls would be un-good.

Cheers
Gordon
K4SD

Gray Beard

My Feedback: (-1)

Rich never mentioned 3-D in the MAN article when he designed the plane, it's just a small fun scale Extra. When these planes are designed the designer builds test planes and puts them through there paces, makes any mods or changes needed then sells the plans. The Extras aren't a design that tip stalls anyway but if Rich discovered this plane needed any wash he would have put it in the plans. I have built a few of his designs over the years, one thing I have noticed is he tends to build them a bit on the heavy side but I have never had one of his planes fall apart on a rough landing. The wings even stayed on with the bipes he designed, when I built them my landings really needed some help!!

gmohr

Wash-out is an intentional decrease in angle of incidence across a wing span from root to tip. This is intended to decrease the tip angle of attack (AoA), which will cause a stall to develop first at the wing root and later at the wing tip. Because the lift developed by a wing *decreases* with increased AoA after the point of stall, an asymmetric stall at one wing root cause less of a rolling force than a stall at the tip. And a straight ahead stall will be less likely to develop into a spin than a stall compounded by an unwanted rolling tendency.

One might wonder how a wing can stall on one half asymmetrically and not on both wing halves at the same time (don't both wings have the same incidence, and therefore AoA?). The answer is relative airflow. If one wing is dropping relative to the airflow, that wing will will experience a higher AoA. So for example if the airplans is rolling left on base-to-final, and close to the critical angle of attack, that left wing panel has a higher AoA and will stall sooner than the right side. If that wing has washout, the stall will happen inboard rather than outboard, and will contribute less to an uncontrolled roll into a spin.

pmw

My Feedback: (1)

Crash,

As mentioned above, do not build wash out if you plan to fly inverted. I've got a 1/4 scale GeeBee with 3 degrees of wash out at the tips. Although it will not tip stall, it also simply will not fly inverted. Full down elevator inverted will not stop it from sinking. Tip wash out is not used for aerobatic aircraft, either full scale or models.

crash bandicoute

then it's settled. no wash-out. i'm glad, cuz i don't really want to try building it in. sounds like a pain in the butt. i was just curious if it was necessary and more curious of what the actual effects from it were. or how it worked, i guess.

Gray Beard

My Feedback: (-1)

Usually if it's needed the designer will draw tabs on the bottom of the wing ribs so it is built in when you build the wing flat on your building board then you just remove the tabs when complete. You will see this on a number of kits when wash is required. True scratch builders have to do the math, those of us that build kits and from plans don't need to think about it.

crash bandicoute

sweeeeeeet... andi thought the tabs on the bottom were just to keep the wing aligned properly to avoid twists or a warp. like on the topflight warbird kits. i didn't know it was intentional for inducingtwist for the washout. that's cool. you learn something new everyday. do you happen to remember the issue that he wrote the article in for the extra 3.25? i would like to read a little more about it if i could get ahold of it.

GAP-RCU

Yes, the tabs primarily do exactly as you thought. However, when washout is part of the design, the length of the tabs on the outboard portion of the wing are adjusted as needed. The aft tab will be a little longer, and the leading edge tab a little shorter. On a straight, constant cord wing, the altered tab sizes are easy to see with washout. For a tapered wing, it's not so obvious, since the tabs will be different for each wing rib anyway, with or without washout.

Gray Beard

My Feedback: (-1)

I may have cut it out and kept it?? When I get some time I will go out to my shop and see if I have it, if so I can send it to you in a file. At the time you could buy the cowl, canopy and pants from him, just molded plastic but it beat looking around for it. Most of the plans I buy are for older planes and the sources for glass parts or a canopy are long gone so I have to search for ARFs of the same size. I have gotten lucky with Fiberglass Specialties a lot of times too.

crash bandicoute

yeah, i'm deffinitely going to buy them from him. the bunch of it comes with the ABScowl (not impressed with that), the canopy and ABS wheel pants. not impressed with them either, but the whole set up is 20 USD. not bad at all. plus i've been experimenting with fiberglass, so i could probably reproduce a glass cowl. i checked at fiberglass specialties, and they don't have a cowl for the plane, but the wheel pants, if i decide to get some, are fairly descent priced. or i could balsa the pants. none of it too difficult. i'd probably pay 20 bucks for the canopy alone. i would greatly appreciate the article if you happen to find it. i enjoy reading about all of them, often wanting to try one. but lately, i've been hung up on the extra. i think i saw the plane a couple years ago in a plans listing.

Gray Beard

My Feedback: (-1)

Not only do I have the article but I have the plans too!!! I thought I did but wasn't all that sure. These were featured in the 1993 MAN and back then magazines would often have what they called pull out plans so you got yourself a set of free plans with the article. When you buy plans from MAN or RCM they toss in the article with the plans to help you build the plane, for the most part just tips but the copy is usually so bad you can't see any of the photos when they are trying to show you something.
Hit me with a PM and I will send you the files when I get your address.

Gray Beard

My Feedback: (-1)

I just read the building instructions and Mr. U does have wash out in the wing plus he has a partial flat bottom airfoil section to keep this little plane from being a complete hand full in the air. He covers how the wash is automatically built in on step #11, very easy.

crash bandicoute

PM sent. thanks a million.