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Old 05-11-2008, 07:24 AM   #1
Wrench66
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Default Undercambered wing with ailerons? OK??

I built my new Zero with undercambered wing and used 70% width ailerons, normal size to the plane (no 3d stuff). I am happy with it's performance for the most part.....at times though it seems that the aileron response is very slow or non exsistent, such as stall recovery and take offs. It has no rudder control...only elev and ailerons.
What are your opinions?

thanks,
Ray

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Old 05-11-2008, 08:31 AM   #2
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Its not really a good combo, you would need like a flat bottomed airfoil, or a fully symmetrical airfoil, or even a flat airfoil(also KF airfoil) for ailerons to work well with and have the wings flat. Undercambered is for low speed, heavy load carrying. LIke the slow stick. They have lotsa dihedral for the rudder.

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Old 05-11-2008, 01:36 PM   #3
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Wrench66, Aileron effectiveness is dependent on airspeed.

The faster the plane goes the more effective the ailerons are.
Ailerons don't work well with stall recovery because that's about as slow as you can go.

3D planes fly very slow, that's one of the reasons they use such large control surfaces.

If you want your ailerons to work at slower speeds, enlarging them would help.
If you don't have a lot of throw on them already, then increasing the throw might also help.

Hope this helps.
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Old 05-11-2008, 03:07 PM   #4
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Wrench - what wingspan is it? What kind of performance do you want out of it? That makes a big difference as to whether undercambered would be appropriate or not. For a very small plane, a 4-40 undercambered wing is probably ideal. Getting larger, a KF airfoil would be good to use. Above that, you'd want a more "real" airfoil.

So, the answer is... it depends.

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Old 05-12-2008, 09:22 AM   #5
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Originally Posted by magic612 View Post
Wrench - what wingspan is it? What kind of performance do you want out of it? That makes a big difference as to whether undercambered would be appropriate or not. For a very small plane, a 4-40 undercambered wing is probably ideal. Getting larger, a KF airfoil would be good to use. Above that, you'd want a more "real" airfoil.

So, the answer is... it depends.
What is a 4-40 wing anyway??
Oh, OK well I don't really run my planes that fast......a 1000K outrunner with 8x6 prop direct, on 2s is not a rocket by most stds I am mostly concerned with stability and the less twitchy the better. I just fly around at 1/2 - 3/4 thr 90% of the time with an occasional loop and a cool roll now and again......I have done some Cuban-8's and that's a neat trick too. It's WS is 30in, length 25.5 and it weighs 13oz now with the wing sheeting added.
I went ahead a mounted a pair of thin sheets under the wing for a flatbottom effect (thanks Ace). It added a couple of oz's to my AUW, but if it allows a better flight personality then they will be worth it

I also went ahead and gave her a quickie paint job......should fly better huh??! hehehe

gonna try again in the morning......wish me luck!

best to all,
Ray


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Old 05-12-2008, 11:26 AM   #6
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Looks great, should fly well, make sure it balances right. Nice paintjob too!!
hope it works out man.

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Old 05-12-2008, 01:19 PM   #7
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Originally Posted by Wrench66 View Post
What is a 4-40 wing anyway??
Hi Wrench -

A 4-40 wing is an undercambered airfoil that is bent into a foam wing. It has a 4% rise in curvature at 40% of the chord. See diagram below.



Originally Posted by Wrench66 View Post
Oh, OK well I don't really run my planes that fast......It's WS is 30in, length 25.5 and it weighs 13oz now with the wing sheeting added.
Here's a good article that details how to determine if your plane is "small" and is a good candidate for a 4-40 airfoil.

http://jef.raskincenter.org/published/airfoil.html

If it's larger than what the Reynolds number indicates is appropriate, you could graduate to a KFm (Kline Fogelman modified) airfoil. There's a couple good variations of it which would probably work well for you if the 4-40 isn't right.

Hope that helps!


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Old 05-12-2008, 05:09 PM   #8
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Wow, that's an eye opener........those PDF filed airfoils are much shallower than my "bend it like this.....yeah, that looks bout right eh?" guessing!
My chord is avg between 7.75in and 6.5, which airfoil would be correct for me in that bunch? Also, is my chord too large for the plane??
You get an idea of what camber I came up with by looking at the pics below, what would too much camber cause the plane to react like?

BTW.....I flew it again this morning in some tricky winds, more than I would've liked about 10mph and changing direction, and it did OK all things considered. The ailerons had much more to say than before, prolly would have rolled easily if I had let it (the wind again, just trying to keep it off the ground ) I did manage to break off part of the right outer elevator tip during a landing attempt (comes in very nicely btw) as the high grass bit it off. No bother though as the elev has boo-koo authority and can stand a bit of trimming. The orig Zero's didn't have as large a surface anyway so paring it down a might is just adding to the scale look of it.
The take offs are the most nerve racking now....one time it does beautifully and pulls up right off the ground fairly straight, the next it wants to turn left as it's nearing flight speed
Maybe it does need a rudder after all? The two tosses I have given it before have ended with me not getting my hand back to the stick in time before the big crunch. Although it does glide well when thrown power-off. So am much more comfortable ROG'ing it off the short grass or pavement.
My CG is directly at the highest part of my airfoil.....if not a touch forward.

thanks for help, I'm definitely learning something.

regards,
Ray


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Old 05-12-2008, 06:19 PM   #9
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Originally Posted by Wrench66 View Post
Wow, that's an eye opener........those PDF filed airfoils are much shallower than my "bend it like this.....yeah, that looks bout right eh?" guessing!
My chord is avg between 7.75in and 6.5, which airfoil would be correct for me in that bunch?
Well, there are three different sizes that will all work for your tapered wing. The PDF file is drawn to scale, so you could print it out and check your wing where it is 6.5", 7.0" and 7.5" chords. Just cut the paper you print it on right over the curved airfoil line, and you can push those up underneath your wing at the appropriate chord lengths. At least by checking it in three spots, you'll be able to "see" if the airfoil is consistent - assuming, of course, you want to try that airfoil in the first place. Jef's article does a good job of explaining how to determine if your plane is "right" for it or not.


Originally Posted by Wrench66 View Post
Also, is my chord too large for the plane??
I'm not sure there's really a 'right' or 'wrong' chord for a given plane. It's really a matter of how you want the plane to perform, and the chord will alter the flight characteristics.



Originally Posted by Wrench66 View Post
You get an idea of what camber I came up with by looking at the pics below, what would too much camber cause the plane to react like?
Well, I used that 4-40 airfoil on three planes once. The planes all had a similar design, but were just scaled to different sizes. The two small ones worked very well. The largest one flew fine if I flew very slowly, but anything above about 2/3 to 3/4 throttle, and it would nose DOWN!!! The only way to keep it from being a lawn dart was LESS throttle (up elevator didn't really help at that speed).

Truly a good example of the idea that "a plane can stall at ANY speed." You may be stalling your wing with your current camber at a higher speed. I know from that experience above that it can happen.

Hope that helps.

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Old 05-12-2008, 11:29 PM   #10
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Wow is the CG really suppose to be on top of the curve of a wing? i never knew that, i always keep my planes extra nose heavy just in case, and they glide excellent as if they have the motor on on idle.

hey Ray, glad it performed pretty well(from what i hear)

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Old 10-11-2011, 03:04 AM   #11
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Originally Posted by GreenAce92 View Post
Wow is the CG really suppose to be on top of the curve of a wing? i never knew that, i always keep my planes extra nose heavy just in case, and they glide excellent as if they have the motor on on idle.

hey Ray, glad it performed pretty well(from what i hear)
CG should be 1/3 of the way into the wing, measured from the front. If the wing tapers it's either done at the average width or at the fuse (widest part of the wing).

oving the weight forward gives more stability, back less - aka, more responsive - to a point of course.
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Old 10-11-2011, 06:24 AM   #12
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Welcome to Wattflyer Professor We always like when new members jump right in, you picked a post of mine that must of had so many many pages of newer posts ahead of it...LOL. I was (if I can remember what that little plane flew like three + years ago) able to finally get comfortable with the plane and enjoy it until I lost it in the sun and it went in Thanks for trying to help out
Your message regarding CG is an extremely variable number......33% is a very reward number to a majority of the planes that aren't 3D......even 30% is sometimes pushing it but for the most part if you are dealing with a new build or just an unknown ship you would be safe recommending a start of 25% at the wing root. Your recommendation of a forward CG giving stability is helpful.

Keep up the good work, thanks again and welcome

--Ray

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Old 10-11-2011, 06:27 AM   #13
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The correct CG isn't necessarily at the top of the wing curve (in fact it rarely is) and it also isn't necessarily at 1/3 wing chord (though for normal looking planes it's usually somewhere close to 1/3rd). To work CG out accuratly you need to take into account both wing and tail and the length of the fuselage (tail moment arm), along with other factors like wing and tail aspect ratio. There are some simple to use online calculators that do a good job: http://adamone.rchomepage.com/cg_calc.htm. With such calculators available IMHO there is no point using guesswork which is all rules such at 1/4 or 1/3 chord really are.

On the subject of ailerons. for slow flying models large ailerons are best even if you don't want to do 3D stunts. however you should get better response from the ones you have if you build in lots of differential, that is the up-going aileron should move further than the down-going one. You achieve this by offsetting the servo arms, or if you have two servos on separate channels and a programmable radio you can do it electronically. Differential is especially important on under-cambered wings, you should aim for at least the up aileron to move twice as far as the down one.

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Old 10-11-2011, 06:41 AM   #14
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Hi Steve,
In the intervening 3+yrs I had learned many lessons from all the planes we've built, the majority scratchbuilt from blue foam and Depron, but the one that stays up in the fore light is that CG can vary from what the calculations say. Not MUCH but it does happen So now I build with adjustments in weight in mind.
The undercambered wing with ailerons question was finally solved by sheeting the bottom of the wing with thin foam or on this particular plane, card stock paper. With the elimination of that air trap up against the undercamber the ailerons came to life and gained a lot of response. It flew well and taught me lots of what I still use (or don't..LOL) in my current projects.

thanks for your post

--Ray

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Old 10-11-2011, 08:04 AM   #15
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Ray, what you did with the card stock was reduce the camber of the wing. The same as if you flattened it out.

If you follow Steve's advice and use differential, you could keep the camber and still have effective ailerons - without having to give up some of your slow speed performance.

Im assuming you guys are doing the undercamber wings for improved slow speed flying. There really isnt any other reason to bend the wings other than structural stiffness.

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Old 10-11-2011, 08:07 AM   #16
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By the way, Id highly recommend paying close attention to any suggestions Steve/JetPlaneFlyer makes.

He really does know one or two things about this aerodynamics stuff

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Old 10-11-2011, 08:30 AM   #17
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Thanks Larry but remember this thread is over 3yrs old ...LOL.
The little Zero is long long gone but the experience gained is used in most everything I build nowadays.

Never thought this thread would get dug up.....nice it might help someone though.


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Old 10-11-2011, 12:12 PM   #18
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Originally Posted by Wrench66 View Post
Hi Steve,
......CG can vary from what the calculations say. Not MUCH but it does happen So now I build with adjustments in weight in mind.--Ray
Ray, i could not agree more. The CG calculators are just an estimate, fine tuning should be done with flight testing.

The good thing about the calculators is that at least the estimate should be quite close meaning the plane will be safe to fly and only take minor tweaking to optimise. Other 'rules of thumb' might in some cases be miles out and there might sometimes never be a second flight.

There are some more accurate calculators around that the one I linked. These complex versions in my experience produce extremely accurate results but they need a bit more time spent on data input and most people cant be bothered, the simple ones are usually good enough.

Steev
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Old 10-11-2011, 01:58 PM   #19
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I found this thread through google and only after I posted did I notice it was 3 years old...sorry 'bout that!

Good, useful info though. I am seriously considering designing a plane...cheaper and faster to get it than ordering one although I do have to find the time to do it (something I'm woefully short of most of the year).

The discussion on the wing cambering and aileron differential is most enlightening and useful.

I read over this http://adamone.rchomepage.com/cg_calc.htm and it makes sense...but I have a question or two...

If you balance the plane it's wing on the bench what is 'level'? I assume you want the horizontal stab surfaces parallel to the bench and the wing at 0 deg incidence (unless the design call for something else). Now as you move the weight around won't all that change? If the horizontal stab gets out of 'level' then you'll need to add some elevator during flight to correct it and that will induce unnecessary drag (and perhaps other issues)
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Old 10-15-2011, 11:56 PM   #20
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Without reading through to see if it is already here:
The issue with ailerons on an undercamber is increased drag. On planes with large span/short tail moments, the adverse yaw will literally cause aileron reversal. As long as you have the ability to adjust differential, then there's no reason you can't do it. Mixing with rudder makes life much easier when you have this situation. I would start with considerable differential, with an undercambered aileron setup.
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