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Old Jan 30, 2012, 05:54 PM
Team JR
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Medford, NJ
Joined Jan 2004
322 Posts
Quote:
Originally Posted by RCvehicleGuy View Post
So... Just because of my curiosity of aerodynamics. Exactly what does having a upward angled wing-let thing under the wing do? All I see is a device that is not aerodynamically symmetrical, which can only mean one thing. It is to compensate for some other aerodynamic flaw that makes the plane knife edge funny. They get rid of coupling, right? And I guess they cause a little drag that helps slow the plane down in a dive. Plus you can make the plane look more scale I think...
?
I dunno, just tell me what its for!

Chris G.
It is a spade...common aerodynamic counterbalance on full scale aerobats. The slight angle of the horizontal portion does not affect KE, but it does put a small amount of preload on the ail control system, and add a bit of overall drag (as you noted).

Regards,

Dave
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Old Jan 30, 2012, 07:47 PM
Mr. Foam, Tape, and Carbon
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Joined Feb 2011
292 Posts
How does the preload help? With a dual servo setup the preload only is active on one direction. And it would cause unnecessary stress in the other. And with a single servo setup the preload would be not noticeable at all. You are forgetting that it is an angled piece of something or other that resembles a spoiler on a car, it should only be able to provide force in one direction. And since it is angled up it should displace air down, providing an upward force on both ailerons during level flight.
Any more detailed response I could have?

Chris G.
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Old Jan 30, 2012, 08:27 PM
Oly crap.. Deese ease not gud!
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USA, NC, Kernersville
Joined Nov 2006
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The spades aren't to compensate for anything. They do not "get rid" of coupling by themselves in any way. They do add a translational force on the airplane as a whole, but that can't eliminate a rotation-inducing coupling force. When properly trimmed and with the right CG, this airplane has negligible roll and pitch coupling with rudder or at normal beta angles, with or without the spades. I'll admit by themselves they theoretically add a negligible rotational force in pitch... but really too small to notice.

However, the spades do load the ailerons. We don't run a dual-servo setup, however it doesn't particularly matter how many servos we use, as they still have the same effect. They do not provide an upward force on the ailerons as you say, because the spade plates are in front of the hingeline... They actually load the ailerons downward (at the trailing edge). This tends to flex the ailerons a bit and add some camber to the wing, making the fuselage fly at a more level angle and making the airplane present a straight line better.

In knifeedge, naturally they have the same effect. However, more importantly, they add a small amount of side area. This is enough to add some stability while flying knifeedge. Coupling isn't effected much, but the airplane does tend to be more pitch stable while on knifedge.

Try it with and without... see what you think!

RJ
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Old Jan 30, 2012, 08:41 PM
Mr. Foam, Tape, and Carbon
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That is a much more straightforward answer. And thanks for the info. I have been designing my own planes for almost a year now and I have always gotten them to fly with no gizmos on the wings at all. My newest one, flies a nice straight line in a knife edge as long as you don't try and make it go too slow in one. And it needs close to no rudder input for the knife edge to happen, it does need a tap here and there though. It tends to hold an angle of attack in knife edge and lock in there, whether its pointed slightly up or slightly down. It even holds it as you decrease throttle. Though then it stalls and gets a little weird. Its funny how ailerons do close to nothing in a high alpha knife edge. I would like to start experimenting with airbrakes, because there is nothing more annoying about a five ounce foamie than the difference between forward flight speed and dive speed. It will just crawl along like a feather till you point it down and then its a rock, almost no time to get any neat tricks in.
I actually don't have the MX2, well, I got a wrecked one in the basement that I was given for carbon and depron scraps... but that is all. I have not bought a kit foamie since I got the Yak 55m from Fancy foam back last March. I have had too much fun coming up with my own stuff!
I am just on here criticising this airplane because of those funny Spades that are on it, I wanted to know what they do.

Chris G.
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Old Jan 30, 2012, 09:10 PM
Oly crap.. Deese ease not gud!
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USA, NC, Kernersville
Joined Nov 2006
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No problem, a lot of people ask about the spades. They're just a nice little addition. The airplane flies quite well without them... but I prefer it with them!

Just as a general comment, I always prefer an airplane that takes a definite rudder input to maintain knifedge. Some people prefer them so neutral that they don't require any rudder, but that tends to make for an awkward feeling airplane. Since they also tend to be directionally unstable, they also end up needing somewhat unpredictable rudder inputs through other maneuvers, and don't "lock in" well. An airplane tends to need positive stability to "lock in".

Ailerons really should have good control power through a normal beta range (beta is like alpha in knifedge, it's the slip angle of the airplane) because the wing is not approaching/past stall, or even loaded for that matter. If they lose control authority, there's likely some other reason for it, such as some sort of very disturbed flow from the fuselage over one wing, or a coupling force that doesn't present itself until some alpha is present (just as the plane rolls away from pure high-beta knifeedge).

Anyways, I'll step off my foamy design soap-box now! Try an MX2 if you ever get a chance, you might like it!

RJ
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Old Jan 30, 2012, 09:33 PM
Mr. Foam, Tape, and Carbon
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I have noticed a definite instability with the rudder. That is why I am on my third version of the airplane! The first was pretty good. The second was a step forward and a step back, it was just too silly with the rudder. Then v3 is super close. Like I said, it does not need much rudder to knife edge, just a tap here and there. I do agree that no rudder input for a knife edge is awkward indeed. I plane on a longer tail moment for the rudder and the horizontal stab in a fourth version. To rid this airplane of its flippyness. Plus I hope to make it not pull to the outside all by itself in a partial knife edge. It does do that, though it is not too great.
The ailerons have power to spare, you know when you are about 45-50 degrees angled in a knife edge and the elevator rolls the plane better than the ailerons do? And the plane starts to get a little floppy? That is what I am talking about, because the ailerons are almost sideways at that point. The airplane itself that I made has the most responsive ailerons of any plane I have flown yet, mostly because it has more aileron area than wing area and the ailerons go about 60 degrees. LOL! Anyways, the airplane does not tend to stall out of a knife edge on its own. It can pull tight knife edge loops that are closer to flips without flipping out. It is when you have to turn the airplane in a super high "Beta" knife edge that it does not like. Then again all planes I have flown were like that. It just requires lots of coupling. Normal knife edge flight where the plane is at an AOA of around 10-30 degrees it feels great in.
Plus it hovers really nice, like, REALLY nice.
Don't worry about getting geeky on the foamie talk. It is some of my favorite stuff, cause it is all my budget can afford! I just get my foam and carbon from my friend than I go to town!
I got a thread up of my plane if you wanna take a look, I have been looking for a more professional opinion of the thing.
I always take a chance to fly OPP, the best kind of flying. That is when I try new tricks! The MX2 looks like a splendid airplane and I would love to get a demo of one if I come across the chance. I like just about anything that flies!

Chris G.
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Old Jan 31, 2012, 11:29 AM
DFC~ We Do Flyin' Right
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USA, GA, Atlanta
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Hey RJ, are you going to head down for SEFF this year? I would enjoy watching you fly
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Old Jan 31, 2012, 06:30 PM
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You would enjoy it more at joe nall !!!!!!!!
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Old Jan 31, 2012, 10:37 PM
Oly crap.. Deese ease not gud!
hpapilot's Avatar
USA, NC, Kernersville
Joined Nov 2006
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I love SEFF, but I think school is going to get in the way this time around. We'll see!!

Count on Joe Nall though... that's right after exams and I wouldn't miss it!
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Old Feb 02, 2012, 11:27 AM
DFC~ We Do Flyin' Right
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I will try to make Nall, but not as likely

Out of curiosity, how old are you? What are you studying?
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Old Feb 02, 2012, 01:08 PM
Oly crap.. Deese ease not gud!
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Nall is a blast!! It's really worth trying to attend.

I'm 21 and studying Aerospace Engineering at NC State University. I'm stuck with this airplane stuff for good!

RJ
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Old Feb 02, 2012, 02:09 PM
DFC~ We Do Flyin' Right
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lucky dog!
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Old Feb 02, 2012, 08:21 PM
OSMBuddha
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KC Mo
Joined Mar 2007
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Got mine painted, and received Axi motor and Mamo stuff.......now for the build. I hate building, even if it's easy.
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Old Feb 03, 2012, 10:24 AM
DFC~ We Do Flyin' Right
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Paint-job looks fantastic!

Well Done!
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Old Feb 03, 2012, 11:02 AM
OSMBuddha
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Thanks, cheap aerosol airbrush kit! Need to get a decent one some day......
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