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Old Jan 09, 2013, 02:34 PM
Fit to CFIT
vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
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If you're holding outside aileron throughout the turn on some reasonably well behaved plane you are apparently also holding inside rudder. So either a rudder mix or differential will require you to hold a little more rudder in this case. That said, it's often beneficial to avoid holding outside aileron - either by using less inside rudder or more dihedral.
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Old Jan 09, 2013, 03:24 PM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
Joined Dec 2004
1,739 Posts
If your goal is coordinated flight, you will typically need a bit of top aileron (aileron stick towards the higher wing). The lower the wing loading, the higher amount needed. Increasing the dihedral will allow the plane to circle without top aileron, but it will not be the minimum drag solution.

In circling flight, there is a yaw rate, and the vertical tail gets some "push" towards the center of the circle. With zero rudder, the result will be that the nose is pointed away from the center of the thermal circle. Hence, the "in-rudder" to place the fuselage closer to the average flow.

As the inboard wing is moving slower, it has to generate more lift. This can be achieved via either fuselage nose out and dihedral with the fuselage in a steady state sideslip, or via "in-rudder" and "out-aileron", with the fuselage having no sideslip.

This effect is more pronounced with larger aircraft (longer fuselage) and with lower wing loading (smaller diameter circles).

One airplane that highlighted this to me 30+ years ago was a super light Mirage that I had built. I got it down to 18 oz (more of a 3m dlg, not meant for winch launch with 1/8"x1/8" spars). In a steady state hands off circle the fuselage was pointed something like 20 degrees nose out.
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Old Jan 09, 2013, 03:59 PM
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vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
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Yes, but perfect coordinated flight minimizes fuselage drag whereas a slight slip minimizes wing drag. So something between the two should be closer to ideal, especially with skinny model fuselages.
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Old Jan 09, 2013, 04:15 PM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
Joined Dec 2004
1,739 Posts
I'm uncertain about your premise regarding "slight slip minimizes wing drag". Can you walk me through this one?

One important thing to remember, is that for light wing loadings there can be a significant difference in section lift coefficient between the inboard and outboard wing. My premise is that the higher lift coefficient inboard wing is likely to benefit from increased camber (out-aileron) just as the outboard wing should benefit from reduced camber with its reduced lift coefficient. It isn't only about fuselage drag.
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Old Jan 09, 2013, 06:06 PM
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vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
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I was assuming that aileron deflection would distort the lift distribution but you're right Joe -- in a steady turn the inboard and outboard wings produce equal lift at different airspeeds so cambering accordingly can reduce drag. There's still some intersection drag at the ends of the ailerons and some hinge kink drag but it's very small. There's also the drawback of pushing the inside wing closer to stall by deflecting the aileron downward but that's just a piloting problem. Lastly, when circling tightly, the majority of the fuselage is sideslipping in one direction or the other anyways due to the curvature of the relative wind so the condition of "coordinated flight" really only means that the wing saddle is aligned with the flow as shown here. A slight slip would align the middle of the fuselage with the flow instead of the wing saddle so the drag penalty of slipping could be extremely small.

So I think on a miniscule and theoretical level a very slight slip is most efficient and does offer some stall-prevention benefits but I'm surely splitting hairs here.

As usual, Drela did a great writeup of all this and reinforces your statement.
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Old Jan 09, 2013, 08:47 PM
RIP MC
fnnwizard's Avatar
United States, CA, Midway City
Joined Dec 2003
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We should be trying to align the wing to the airflow. Iit doesn't really matter what the fuse is doing as long as the aforementioned is true.

So, unless somehow the fuse can be curved with the airflow, the nose will always be "slipping" and the tail "skidding".
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Old Jan 09, 2013, 09:27 PM
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lesterpk's Avatar
Australia, WA, Perth
Joined Oct 2003
860 Posts
I'm no aerodynamic guru and I guess I consider myself to be a lazy pilot who gets good results so heres how I do it.
My models are setup with ail>rud mix always on for all thermalling modes. I probably did play with various amounts of differential and rudder mix when I first started flying Supra but now I've been flying them for 6 years, I've pretty much forgotten any of that setup work.

My general rule of thumb when setting up a model is 2:1 diff and some rudder mix, CG to suit and fly it, then fly it some more, make a few adjustments if neccesary and then leave it alone. I find these days I have to call my own air in contests as well as be able to keep an eye on whats others are doing. That means I need a model thats stable in a turn and doesnt start doing anything silly while I'm not looking at it for a while. It also makes it easy to fly at long distance. My left thumb generally only comes into play when low and slow and I want to flick the tail around a bit without disturbing the wing surfaces too much.

At a recent contest I was being timed by a guy new to soaring so was trying to give some tips while we flew, he mentioned I was circling smoothly and I said I wasnt even on the sticks. The model was in light lift and doing lazy 75ft circles and for nearly a minute I had no reason to make any control corrections, and when I did it was quick blip of out aileron as the model was slowly steepening the turn.

Maybe my diff setup isn't ideal, but I know that if I can leave the sticks alone and not induce any more control drag then I'm probably ahead. Like someone who knows about these things once told me, set the model up for max scoring, not max performance.
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Old Jan 10, 2013, 12:36 AM
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bOjO's Avatar
Santa Barbara - California
Joined Aug 2004
238 Posts
Target, if you want and if Mike is ok with it of course, could you give us a summary of the discussion ? I'm sure all of us will be interested to know more about Mike's way to set up his sailplanes (maybe I should also check if Mike already post on this subject...).

This is a recurring subject for sure but it certainly helps to come back and think again about setups we sometimes do automatically without thinking much...



Quote:
Originally Posted by FLY F3B View Post
Hey Target, from the practical side of flying our RC sailplanes, I can and have answered that question many times. If you are really willing to listen and learn my approach I'd be happy to share it with you.

Is it needed? Yes.

All the time? NO.

Does it help make it easier to fly the plane in a more coordinated manner with less pilot work load? Yes.

More detail, PM me.

Mike
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Old Jan 10, 2013, 09:44 AM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,291 Posts
Hi, Joel-

I hope you are doing well.

The fact that Mike wants me to PM him means that he'd rather not just post it here, and having me post my interpretation of what he's trying to share with me can only be worse, not better.
If I do a PM chain with him, I CAN include you also, and I doubt that he will have any problem with that.

R,
Target
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Old Jan 10, 2013, 10:35 AM
LSF V aspirant
tewatson's Avatar
United States, CA, Orange
Joined Oct 2006
2,405 Posts
http://www.rcgroups.com/forums/showt...highlight=diff

Tom
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Old Jan 10, 2013, 11:22 AM
or F, J, K, or even TD
FLY F3B's Avatar
Joined Jun 2007
2,898 Posts
I have no problem with that at all Target. And Tom, thanks for sharing that link. It does a great job of exposing the differential issue, but I can describe a clear cut procedure for glider set up based on my philosophy of being a lazy pilot that wants the best performance and handling with the least effort possible.

Regards,

Mike
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Old Jan 10, 2013, 01:58 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,291 Posts
Hey, I want to be a lazy pilot!
I'm not, only because I cannot afford to be when flying with all these good guys, I need to be on my toes.
I DO know that most of these planes stay aloft with LESS pilot input than more, usually.

R,
Target
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Old Jan 10, 2013, 02:37 PM
JimN8UAY
United States, OH, Medina
Joined Oct 2004
585 Posts
Quote:
Originally Posted by FLY F3B View Post
I have no problem with that at all Target. And Tom, thanks for sharing that link. It does a great job of exposing the differential issue, but I can describe a clear cut procedure for glider set up based on my philosophy of being a lazy pilot that wants the best performance and handling with the least effort possible.

Regards,

Mike
Hi Mike! Is this the same set-up as filmed on Paul Naton's RCA videos? Thanks for your efforts.
Jim
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Old Jan 10, 2013, 02:38 PM
Where did my plane go???
HHARRIS's Avatar
United States, CA, Tustin
Joined Nov 2008
638 Posts
Quote:
Originally Posted by target View Post
Hey, I want to be a lazy pilot!
I'm not, only because I cannot afford to be when flying with all these good guys, I need to be on my toes.
I DO know that most of these planes stay aloft with LESS pilot input than more, usually.

R,
Target


I'm just sayin....

HUGH (missin Target)
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Old Jan 10, 2013, 02:57 PM
or F, J, K, or even TD
FLY F3B's Avatar
Joined Jun 2007
2,898 Posts
Quote:
Originally Posted by Jimn8uay View Post
Hi Mike! Is this the same set-up as filmed on Paul Naton's RCA videos? Thanks for your efforts.
Jim
Hi Jim, pretty much the same, but with perhaps a clearer understanding as to why it works so well according to the way I believe (and have proven through competition) gliders should fly and be flown.

Its going to be a few days until I have something written up that is concise and fully comprehensive.

Mike
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