Overly Low aspect ratio.

Overly Low aspect ratio.
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Overly Low aspect ratio. - 6/13/2009 10:19 AM

Rendegade

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Guys, I've just come back from the airfield, after flying me new "old" pattern ship. It's an australian design (crica 2000) but with some really strange things.

THe previous owner told me he'd added more sweep to the wing, to give it a more aft C of G, which i can beleive as it has a very G202ish profile and by accident planform now.

Having said that, it's like a G202 stretched in one direction only, length. I have to say it looks wierd in flight, it flies ok though but has very little roll damping which caused this thread.

It's a 2m ship but I took to measuring the wings and each panel is 750mm long. the fuselage is 180mm wide.

so thats's 760 + 760 +180 = 1700mm, a long way short of 2000mm don't you think?

Is there something I'm not aware of that would make this sort of design worthwhile? It has HUGE chord, much like a brushfire, so area's not a problem, Should I redo the wings, or am I just being a knob?

< Message edited by Rendegade -- 7/5/2009 3:04 AM >

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RE: Overly Low aspect ratio. - 6/13/2009 10:25 AM

tIANci

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Rendegade ... question is ... does she fly well?

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RE: Overly Low aspect ratio. - 6/14/2009 10:45 AM

Rendegade

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She does, but I have to say I find her a little "undamped" in roll, it need some work to try and get a perfect line though loops.

I think longer wings would help.

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RE: Overly Low aspect ratio. - 7/4/2009 12:30 PM

Taurus Flyer

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quote:

ORIGINAL: Rendegade

She does, but I have to say I find her a little ''undamped'' in roll, it need some work to try and get a perfect line though loops.

I think longer wings would help.

Rendegade, I see you do not get an answer anymore.

In the othrer thread, I see you have a Sagitta 900, see picture 1.
The Sagitta 900 has (normally) an old Eppler 205 airfoil, more tha 30 years old.
We do use another modern airfoil on our Sagitta's.
My advice, if you Sagitta airfoil is the old Eppler 205, use these wings on this old second hand airplane.
Make new wings for the Sagitta.

Some pictures (2009) of the ASK 18 span 4,5 m with the Eppler 205, Eppler 203 and Eppler 193 airfoils in the wings (strack?)
I did design this plane myelf 28 years agom with the Epplers!.
The pilot is not visible on the picture 2.

Cees

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RE: Overly Low aspect ratio. - 7/4/2009 2:21 PM

robert

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Out of interest, what do you mean by very little roll dampening? Does it get easily disturbed in roll by things like turbulence?

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RE: Overly Low aspect ratio. - 7/4/2009 7:19 PM

Taurus Flyer

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Robert,

Do you ask me? Taurus Flyer?

Cees

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RE: Overly Low aspect ratio. - 7/5/2009 2:57 AM

Rendegade

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What? I'm not talking about the Sagitta.

Robert, roll damping, simply put is like you say, how twitchy an aircraft is to disturbances, and how quickly it will stop and start the roll. Think of a little btit like the suspension on your car. My older aircraft had soft damping, which meant it would not be as affected by turbulence and hence took a little less effort to fly, but has the disadvantage of requiring more stick input to correct it. This is the same with a rolling manevure.

I was thinking that maybe I needed a bit more span to increase the roll damping, but having flown it a bit more I'm starting to tune into it's flying, I think I may have been a little bit overdramatic.

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RE: Overly Low aspect ratio. - 7/5/2009 8:40 AM

Taurus Flyer

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quote:

ORIGINAL: Rendegade

What? I'm not talking about the Sagitta.

Robert, roll damping, simply put is like you say, how twitchy an aircraft is to disturbances, and how quickly it will stop and start the roll. Think of a little btit like the suspension on your car. My older aircraft had soft damping, which meant it would not be as affected by turbulence and hence took a little less effort to fly, but has the disadvantage of requiring more stick input to correct it. This is the same with a rolling manevure.

I was thinking that maybe I needed a bit more span to increase the roll damping, but having flown it a bit more I'm starting to tune into it's flying, I think I may have been a little bit overdramatic.

Rendegade, you started the topic see post one on 6/13/2009.
My post was of the date 7/4/2009.
You edit your own post one (see bottom post 1) :< Message edited by Rendegade 7/5/2009 3:04 AM >

This is the reason I normally quote the post, just I did in the thread about : Glow vs. Electric. Let the discussion begin.
I did want to see what you would do in this case.

You write:

"I think I may have been a little bit overdramatic"

Never use : "I think, Probably etc ", because I start looking for facts. What is the topic name?

Cees

Because this is not my mother language I have to EDIt nearly always.
When the next post is made I do not change the structural content of my own posts because it is not fair!!
When I "launch" my edit post and see there was a later post after that, I check for the content to make excuses if necessary.

< Message edited by Taurus Flyer -- 7/5/2009 9:03 AM >

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RE: Overly Low aspect ratio. - 7/5/2009 2:59 PM

robert

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Rendegade I wish I had some of my notes with me as my brain is a bit rusty

I would have thought that increasing the sweep would have increased the dampening? Do you know what airfoil it is? I always imagined that an airfoil with a flat Cl alpha curve would be best for pattern so you don't get a large change in lift for any changes in alpha due to gusts or turbulence or whatever. I haven't bothered reasearching the airfoils being used though. I'll have a think about increasing the span too intuitively you'd imagine that the bigger span will be more damped and stable than a smaller span due to the larger restoring force?
I don't think it was anything to do with the low Re numbers as the length used to calcuate that is usually the chord length and I don't think it would have made much of a difference.

< Message edited by robert -- 7/5/2009 3:03 PM >

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RE: Overly Low aspect ratio. - 7/5/2009 3:33 PM

Taurus Flyer

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quote:

ORIGINAL: robert

Rendegade I wish I had some of my notes with me as my brain is a bit rusty
I would have thought that increasing the sweep would have increased the dampening? Do you know what airfoil it is? I always imagined that an airfoil with a flat Cl alpha curve would be best for pattern so you don't get a large change in lift for any changes in alpha due to gusts or turbulence or whatever. I haven't bothered reasearching the airfoils being used though. I'll have a think about increasing the span too intuitively you'd imagine that the bigger span will be more damped and stable than a smaller span due to the larger restoring force?
I don't think it was anything to do with the low Re numbers as the length used to calcuate that is usually the chord length and I don't think it would have made much of a difference.

Robert,
People might think why you write about the low Re numbers!
Have attention he did change the topic name and the complete first post of this thread.
Cees

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RE: Overly Low aspect ratio. - 7/6/2009 2:20 AM

Rendegade

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I changed the name of the thread as I felt is was misleading as we were really talking about aspect ratio not RE numbers. It was my mistake.

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RE: Overly Low aspect ratio. - 7/6/2009 7:23 AM

Taurus Flyer

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Rendegade:

This was the only post after post 1 of another member

quote:

ORIGINAL: tIANci

Rendegade ... question is ... does she fly well?

After that you only were thinking!

Now you write:

quote:

ORIGINAL: Rendegade

I changed the name of the thread as I felt is was misleading as we were really talking about aspect ratio not RE numbers. It was my mistake.

Where did you talk about aspect ratio? nowhere and you also did edit in the first post!
Do you see how easy it is to destroy the post of other people!

Next time you say: Sorry, it was a mistake I will never do it again. (You also may do it already now, then I can go to sleep!)

Success with looking for a sponsor.

Cees

< Message edited by Taurus Flyer -- 7/6/2009 7:30 AM >

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RE: Overly Low aspect ratio. - 7/6/2009 10:37 AM

matt13

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What am I missing here? The post started with a question relating to a Pattern model, not a glider?
Rendegade, have you tried using more expo to help with thr rolling issues?
I would certinally spend time trying to find a trimming solution before re-doing the wings. Matt

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RE: Overly Low aspect ratio. - 7/6/2009 10:46 AM

Rendegade

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Matt; Yeah, I did. I ended up with about 50% D/R to get it "grooving" but now that I've reset the linkages my low rate setting is around %70 and I need about 25% expo, but let me tell you, the ailerons only JUUUST move, and it's enough to get a good 270°/sec roll.

It does beg the question though, which was my main point before, and before this thread took a turn for the sideways, is why would make a designer clip the span and increase the chord, to end up with a very low AR. (not RE, got a bit muddled initially,) for an aircraft that really doesn't warrant it? Anyhoo, the plane doesn't know it's funny looking, it still flies pretty good!

< Message edited by Rendegade -- 7/6/2009 10:47 AM >

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RE: Overly Low aspect ratio. - 7/6/2009 1:08 PM

matt13

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Who knows why the builder thought that this would work, I bet he didn't do it the same on his next model. But still one has to try new things in design, some work, some don't, maybe you should fit a cannuliser thingy to it, you never know...?

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