Why Washin ?

Why Washin ?

Postby CHE » Thu Nov 29, 2007 1:54 am

The convention on most models is to have washin on the inboard wing centre panel in order to provide thermal seeking. Why not use washout on the outer centre panel ? Has anyone tried it ? Is there any difference between the two and if so what, why and by how much ?

Obviously this question relates to models outside of FAI as well but I didn't want to double post.

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Postby John Lorbiecki » Thu Nov 29, 2007 9:52 pm

Good questions....

Many people do many things with wash. I know that some people have washed out a tip to do the same. However, I think that the feeling is that it takes more wash out (Leading edge down) to accomplish the same as a washed in panel- If a panel is leading edge down (wash out) there is less drag or change with the same amount put in than if you washed in the panel. As aspect ratios increased, there is less wash needed to produce the same result, because of increased moments.

One thing to think about is that a washed in panel not only increases lift but also increases the drag of that panel. So, the wing may not only lift but also yaw towards that panel. This is where it can get interesting when watching a model in power. It may look like it is turning right when in fact it is rolling left. In this case the model actually wants less incidence in the right panel. This is very common with FAI style models. We ran into this with our J models and kept adding rudder when what it actually wanted was a wash change. Look very carefully at what it is doing and then think about what is actually needed...

Hopefully that helps a small amount...
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Postby CHE » Fri Nov 30, 2007 1:52 am

John,

Thanks for you comments. Your note about the extra drag coming from washin on the inner panel is of course correct but if you had washout on the outer panel instead then the drag there would be less and you'd have the same effect wouldn't you ?

I take your point about power models. To be honest I was only really interested in the glide and thermalling effects so perhaps I should clarify that point.

Any other thoughts ?
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Postby John Lorbiecki » Fri Nov 30, 2007 9:13 pm

The answer to the question on the outer panel would probably be yes. But, I think it "may" take more to produce the same effect. Typical tapered tips would force more but then again because of the increased moment....Heck, what do I know....

The effects of wash in glide are, in my opinion, not as dramatic at normal speeds. However, the latest FAI models do use wash to enhance the thermalling capabilities. If I recall when talking to Eugene Verbitsky he stated that one reason he used wash out on the right center panel was to allow the model to tighten up from the model's normally large circle (we glide about 1 minute plus glide circles- in fact, one max that John had at the world champs was about 7/8 circle in 3 minutes). However, after we broke one model, Eugene said that it "can" happen because of the way that wing was washed. Here we are talking about .04-.06" wash total. Not much in light of the size of the model.

I know that I always used to wash out both tips a fair amount for stability in glide. The idea always was to make the tips stall after the center section. I have never been able to dismiss this concept as it seems to always work and many poeple do it.

Maybe this helps a little bit...
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Postby John Lorbiecki » Fri Nov 30, 2007 9:13 pm

The answer to the question on the outer panel would probably be yes. But, I think it "may" take more to produce the same effect. Typical tapered tips would force more but then again because of the increased moment....Heck, what do I know....

The effects of wash in glide are, in my opinion, not as dramatic at normal speeds. However, the latest FAI models do use wash to enhance the thermalling capabilities. If I recall when talking to Eugene Verbitsky he stated that one reason he used wash out on the right center panel was to allow the model to tighten up from the model's normally large circle (we glide about 1 minute plus glide circles- in fact, one max that John had at the world champs was about 7/8 circle in 3 minutes). However, after we broke one model, Eugene said that it "can" happen because of the way that wing was washed. Here we are talking about .04-.06" wash total. Not much in light of the size of the model.

I know that I always used to wash out both tips a fair amount for stability in glide. The idea always was to make the tips stall after the center section. I have never been able to dismiss this concept as it seems to always work and many poeple do it.

Maybe this helps a little bit...
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Washin vs washout to CHE, etal...

Postby sweepettelee » Sun Dec 02, 2007 12:22 am


CHE,

The answer in milliseconds is: MOX NIX!

IMHO, based on 50+ years of struggle with similar issues, whether the
wing washin is plus inboard or minus outboard is not important.
The AIRPLANE will seek trim equilibrium no matter which method is applied.
I have seen and had gliders with each setup work equally well as to thermalling ability.
Conversely, several of my F1A compatriats and I have tried flat
mains with ONLY tip differential and found them generally to
be dogs in thermal condition.
Therein lies one reason to have picked the right glider for any given flight.

DIFFERENTIAL is the key, i.e., having just the amount of positive incidence on the inboard wing to do the job you desire.
As John L stated on his answer to your post: 'As aspect ratios increased, there is less wash needed to produce the same
result, because of increased moments.'
Hence, I have found that a 2 meter glider can and must use more differential than a 2.5 meter glider.
Examples from my fleet: 2.1m Wishbone has about 0.4 deg washin, my 2.25m Li'l ALs have 0.2-.3 deg, my newest,
2.4m EOS has ~0.1 deg, while my 2.5m Buntero is about the same.
All the above is with flat main panels that have been trimmed using
wing wigglers, not panel twists.
Mind you, the ears have washout. Usually the left[I glide to right]ear
has a bit more than the right, or inboard ear.

This goes back to my comment above related to the job the glider is intended for.
Is it a thermal pig, where a bit more drag won't matter, or is it your ultimate FO bird, where any added drag
may mean enuf more sink to be an all-so-ran?

Ciao,
Leeper

FLY, MAX, WIN!
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Washin vs washout to Big John L, etal...

Postby sweepettelee » Sun Dec 02, 2007 12:58 am

Big John,
A small point of order, related to your " latest FAI models do use wash
to enhance the thermalling capabilities. If I recall when talking to Eugene Verbitsky...".
I believe you are specifically speaking of F1C models here, as
most F1As do use washin of inboard wing to enhance thermalling, with
less fear of spinning in from violent air.
I have been studying the use of washin on outboard wings, as used by
Andriukov-inspired F1B fliers. Now you indicate Verbitsky-inspired F1C
types are doing similar trim setup.

Hmmm...here is where I stick my neck out...my unsubstantiated idea is:

This is somehow caused by the extremely long tail moment positions
of the current B & C design. As a percent of wing span, B & C booms
are much longer than F1As, in general these day.
This leads me to believe there is a newish paradigm of forces which
create this turning lift from ourboard wing, coupled with the rudder
turning forces, which causes turn tightening from wide to speeding up
and turning into the lift.
The great 2-time A2 glider champion, Rudi Lindner is said to have used
such a trim in the 50s, but I saw some attempts to use the
so called 'Lindner trim' meet with less than satisfactory results, shall
we say...
Which leads me back to my synopsis that long moment arm and small
fin area somehow are combining with the wide circling of these ultra
clean[read 'low drag']design types, which I don't see it being a viable
trim direction for F1As, in current planform arrangements.

There, I have said it, so blast away at it, if you want... :P

Ciao,
Leeper
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Postby John Lorbiecki » Mon Dec 03, 2007 8:29 pm

Lee Buddy, et al....

Yup, I always look at it from what I have some experience in, which is F1J and F1C. We had one of our best models climb beautifully, bunt very well, and the proceed to do a slow right spiral into the ground- at the WC, of course- and, of course, it hit the road...Destroyed the aluminum fron end, broke the tail boom, bent up a wing and dinked the stab...Talked with Eugene about this and that is where I got the info, as this was one of his models and we flew it like it was set up. He said that the warps were in it primarily to help the thermal seeking capabilities but what happened to us "sometimes happens".

I do agree that there must be something to do with our somewhat largish rudders (fins), long tail booms, high aspect ratios. I would hate to take one of these models and really crank in some glide turn. We run, of course a minute or so circle and this helps keep the wings much more level than in a tighter turn. I have seen it too many times when these things tighten up and it looks like they are in the spiral/crash mode.

I also know that some folks have tried (somewhat ssuccessfully) offseting the dihedral break (slanting it so that the break is not parallel to the fuse centerline) to provide the wash in the tips. Dick Swenson did this in the 80's on his F1C models.

Everyone has his own deal, but I think we can pretty much state that we need the tips washed out some and possibly the inboard section could have some wash in (or out, depending on which side of the pond you are on). With many AMA gas model, low thrust models will have the tips washed out and the right center section washed in (to keep it up in power).


Hell, what do I know, it is the kid that does all the good flying!!
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Postby Dan Berry » Tue Dec 04, 2007 7:05 am

I have a penny

I am led to understand that the natural effect of airflow accrossa wing naturally creates wash-in and the tips need wash-out to counter this effect. Does anybody know differently?

To the subject of spinning in. If you have wash-in on the wing outboard of the glide circle and are very close to zero-zero on your decollatage, er, decalage, a nose nose down attitude will create a spin that the plane cannot recover from. The extra speed causes the stab to lift even more which causes the wash-in to lift even more which drives the beast into the ground. I understand the theory of wash-in on the outer panel to enhance thermal hunting, et al. When it bites you on the backside, there is nothing to do but watch in disgust.

I don't think the fin size or tail moment have any effect on the spin. Solve it with a bigger glide turn or more decalge. Or just glide toward the wash-in and never worry about it again.
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Postby John Buskell » Tue Dec 04, 2007 2:22 pm

I haven't flown a FAI model since the early 90's (and even then the model was about 6 years out of date), so take the following comments for what they are worth;

When I stopped FAI flying I was coming to the conclusion that wash-in was to be avoided (period). My older (wooden) F1C's with wash-in on the RH inner panel - for climb trim purposes - wandered away from lift (i.e. they straightened out) when gliding. Very noticeable on these old ships as the glide turn was so much tighter than the modern high a/r machines. But they never ever did the death spiral thing. I got around the straightening out by using a larger rudder off-set (glide posn.), and a little reverse tail tilt. With the tiny tails on modern models, I suspect this approach wouldn't work.
Wash-in on the outside wing or wash-out on the inside wing will for sure eventually produce what John Lorbiecki described. I guess it's the risk game, then; for very still/low lift conditions, the model with a touch of wash-in on the outer wing will turn toward a trace of lift and tighten ever so slightly into it - which is what you want. Fly the same model in more normal conditions, and look out below!!! I don't think it matters if you are flying near 0-0 - that is the tendency this set-up will induce. I flew rubber models right/left, and they did it, and they had plenty of decalage.

As an aside, the last F1C I built had 'all washed out' wings - i.e. washed out from root to tip, slightly more on the left wing for climb trim. I didn't fly it enough to tell if that was a good way to go.
John
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Washed UP?

Postby DaveEdmonson » Tue Dec 04, 2007 2:52 pm

At the 1956 NATS in Dallas Texas, I was 13 years old. I was testing a 1/2A Spacer on the day before the event. It had been flown previously in Minneapolis in a very nice right left pattern.

Flying it in Dallas it was going straight up in a beautiful pattern, and after some of the guys examined it, they told me it had wash in on the left panel, and washout on the right.

So when I saw Sal Taibi that night I had to tell him my secret on trimming the Spacer!! Sal was very gratious in listening, and I feel embarrassed to this day.

For anyone wanting to relive the past, those models were Jap tissue covered which is the worst junk in the world to keep a model trimmed with. The model continued to warp overnight and smashed on the first official flight!

It flew the 3 official flights without wingtips and I never much cared for that washin adjustment after that!

So maybe this subject is WASHED UP!

(I plan to build another 1/2 A Spacer with Ultracote light to see if the model can really hold a trim. I will power it with my Atwood Shriek from the 1956 NATS!)
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Washed UP?

Postby DaveEdmonson » Tue Dec 04, 2007 2:52 pm

At the 1956 NATS in Dallas Texas, I was 13 years old. I was testing a 1/2A Spacer on the day before the event. It had been flown previously in Minneapolis in a very nice right left pattern.

Flying it in Dallas it was going straight up in a beautiful pattern, and after some of the guys examined it, they told me it had wash in on the left panel, and washout on the right.

So when I saw Sal Taibi that night I had to tell him my secret on trimming the Spacer!! Sal was very gratious in listening, and I feel embarrassed to this day.

For anyone wanting to relive the past, those models were Jap tissue covered which is the worst junk in the world to keep a model trimmed with. The model continued to warp overnight and smashed on the first official flight!

It flew the 3 official flights without wingtips and I never much cared for that washin adjustment after that!

So maybe this subject is WASHED UP!

(I plan to build another 1/2 A Spacer with Ultracote light to see if the model can really hold a trim. I will power it with my Atwood Shriek from the 1956 NATS!)
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Postby Dan Berry » Tue Dec 04, 2007 9:31 pm

Ahhhhhhhh, Spacers

Look out! I'm about to launch a Spacer! They'll get you even after they've DT'ed.

The Spacer is a classic example of the washin on the right wing and gliding left. If it ever gets the nose down,- for any reason, you can expect it to spin in. Mine glides right and the CG is 3/4" for ward of the plans CG. I still NEVER trust it to do what it did on the last flight.

The tissue wasn't the problem. Think dope and only one spar. A recipe for trim constant changes.

My Marvals, in 3 sizes, will transition and glide in a straight line until finding the lift that I didn't launch into. Then, a little wiggle and up they go! Several timers have watched this action and at first said 'What's happened to your plane?" My reply - she's going to find the thermal. Its amazing to watch. Up, down and crosswind. Always Rt/Rt by the way.
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Postby John Lorbiecki » Tue Dec 04, 2007 9:51 pm

Never built a Spacer but saw one once when I was at a Holiday Inn...Sori...

The F1C stuff that we fly as well as the J models all have a CG at about 50%. With this, we typically have a "fair" amount of decalage. By this, it is definately above 0-0...The infamous crash was this really wierd somewhat low speed spiral of death. RC DT would have been a very nice thing right about then...

So, back to the Jack Daniels...
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Right-Right is for rubber models

Postby DaveEdmonson » Tue Dec 04, 2007 10:43 pm

Your Spacers were not consistent because you tried to fly them right right.

I built several 1/2A Spacers with the pylon in the rear position. They always flew well until the tissue/dope warped badly. With the pylon in the Atwood position and a 1/16 shim under the trailing edge of the stab, they were quite stable. Always flew them right left. Have fond memories of them up in big thermals!
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