Ailerons on the KR2S

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StRaNgEdAyS

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I've been reviewing all the data I can find on the KR2S since I got the opportunity to purchase a set of plans.
Of the things I have noticed that could do with some modification, cabin width is an easy one, I'll only need an extra 2 inches to make it nice and comfy. But in the matter of the controls, I have noticed a couple of things that could stand some scrutiny.
The control surfaces are, for all I have been able to discern from the avaliable data without having the plans here just yet, unbalanced, and the ailerons appear not to be differentially linked? Is this so, can anyone else verify this?
If it is so, then this is an area in which I will be putting some thought into before building them.
Careful balancing of the control surfaces can and has shown a significant improvement in the Vne on many other completed KR's, and I feel that giving the ailerons some differential may also improve the handling somewhat.
 

orion

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I used to have the same plans set (although I can't seem to find them now). I also remember the lack of balance and differential movement.

However, before you doo much work in that direction, it is best to look at the application. The differential movement is used when trying to improve the roll adverse yaw responce. Given the small size and short span of the KR wings however, it is unlikely that the adverse yaw will be significant enough to really cause a problem. Yes, if you wish you can incorporate the differential linkage but before you do, I'd suggest flying someone's airplane to make sure it's worth it.

The balacing of the surfaces is also a good idea but given the rather limited performance of the airplane and the rather small surfaces, the construction and controlls are most likely stiff enough that the balancing was not considered critical to the deisgn by the original designer.

Personally though, I do recommend a static control surface balance for any airplane.
 

StRaNgEdAyS

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I've noticed some KR's with mass balanced ailerons, but those I've seen (online) are fairly rudimentary, sizable weights attached out in front of the aileron. I'm sure these can be done in a cleaner fasion.
One of the motivating forces behind the project is to try some of my ideas out on a more forgiving airframe before I start building any of my other planes.:whistle:
 

Falco Rob

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Balancing Control Surfaces

Just read the comments on balancing KR2 ailerons and thought I'd throw in a little more confusion.

The Falco has differential and balanced ailerons, but the question here is "define balanced!"

I've always thought that "balanced" meant just that . . . when suspended from their hinges they neither rose nor fell.

The Falco's ailerons, however (and the elevator and rudder as well) must be "balanced" to within a specified range.

From memory the elevator, for example, must be in the range of 22 to 26 ozs positive when measured at a nominated point on the trailing
edge. You set it up in the horizontal position then place a scale under the point and it should read somewhere between 22 - 26 ozs.

In the case of the elevator it's weight distribution is such that it comes out about right, however the ailerons need some additional mass (lead shot, or similar) added to the leading edge to achieve the required "weight" at the trailing edge.

The rudder is balanced by laying it on it's side and repeating this process.

I suspect it means that so long as a control surface is not too biased in any direction (ie. too nose heavy or vice versa) then it don't really need to be be perfectly"balanced"!

Any ideas on this theory?

Rob




Whiltsst they
noticed
 

wsimpso1

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OK, first why balancing is supposed to do, then why 100% balance is not always needed...

Balancing is supposed to keep control surfaces from contributing to flutter. Imagine an aileron with all of its weight behind the pivot point. If you get a distrubence (gust) that drives the wing upward, the aileron will lag behind because of its mass, and in so doing will increase the lift of that wing, causing the tip to continue to accelerate upwards until it is slowed by the stiffness of the wing, then the tip will start to accelerate back towards its neutral position, as it does this the aileron will lag behind again (this time above) , greatly reducing the lift of the wing, so the tip will overshoot... This will drive energy into the surfaces and cause them to oscillate at the natural frequency of structures. When you put energy in at the natural frequency, the oscillation will grow, and cause the airplane structures to fail.

So if you balance the control surfaces by placing weight forward of the pivot, when the initial movement occurs, the aileron stays in its original angular position relative to the wing. No added energy, and the oscillation just dies out.

Now, do you need 100% balance to prevent the addition of energy? Maybe not... First, there is some aerodynamic resistance to control surfaces deflecting in this way. Second, there is structural resistence to control surfaces deflecting this way. Third, there is some friction in the air passing over the surfaces that resists the oscillation. There are probably more reasons... These all work against flutter oscillation increasing freely, which reduces the need for balance.

So, some airplanes do not need 100% balance. The reasons to balance less than 100% are to save weight, and that the extra weight might push some other natural frequencies together and cause other flutter problems, and so on... Since homebuilts are small and have relatively stiff wings, tails, and fuselages, 100% is easy, only adds a ounces, can not excite other vibrations easily, and so that is what we tend to do.

Billski
 

orion

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Confusion is right! I'm not sure what the Falco is trying to achieve.

Basically, there are two forms of balance - static and dynamic. Dynamic balancing takes a bit of calculation as it tries to account for the mass distribution of the surface, chordwise and spanwise. Actually, there is a pretty good cookbook procedure for doing this in the manual for most Glasairs. See if you can dig one up and it will have the procedure listed.

Actually, if anyone on this board has a set of these plans, if you can copy that part to here I'm sure it would be appreciated.

The static balance is just that - you hang the surface from the hinge line and add weight until the part's chord line hangs level.

From the parts I've seen, the dynamic balace tends to result in slightly less wieght - the static balance on the other hand is a bit more conservative. I tend to use the latter in most of our work.
 

pylon500

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G'Day StrangeDays,
How much of this KR-2S do you want to build?
If you want to get some pre-made bits, you could ring one of my club members who is kitting assorted bits for his "JOEY 2"
I think he supplies a differential aileron kit as well.
I don't know what he does about mass balancing, not sure he uses any?
Call him on 02 9534 8776.
His name is Garry.
As for 100% balancing, most of the Beechcraft I work on don't fully balance, (the elevators at least) probably because the mass weights become too heavy to hang off the end of the tailplane!
Here is a classic example of flutter (deliberately controlled, but scary all the same);
http://www.AirAndSpaceMagazine.com/asm/Web/Site/QT/TCFlutter.html
Arthur.
 

StRaNgEdAyS

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Oct 20, 2003
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The KR actually serves a few purposes.
It is a nice and simple plane, that Sarah and I can both fly, that she can help build, this is going to be her plane after all's done...:gig:
It is also kind of an active test bed for some of my ideas. Not so much for plane #2, but for #3 :whistle: I can easily change aspects of the design post build. So I guess We'll be making pretty much most of it, some bits a couple of times...:p:
Having said that, there are probably a couple of bits I'll want to source from other places. No sense reinventing the wheel if I don't need to. As of yet I don't know what they'll be. Thanks for the info. :D
still waiting for that movie to cache... (one disadvantage of living in the sticks... no DSL :wail: )
 
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