I would like axial rolls on new build.

[reacher10]

I'm making a plane using a a foam GWS Piper Cub fuselage and using a wing with a S3022 airfoil @ 12% thickness, 6.5" constant cord and 32" wing span.
This is a rather thin wing

I would like very axial rolls.

What are some major factors to achieve this.

I can make it a high, mid or low wing.

With wing mounted on top but a little lower then standard and no dihedral the battery will be in the bottom of the plane. How much does the batt being so low and away from the wing effect roll? My guess is quite abit. Is it possible to just modify it so the battery is at centered top to bottom?

With the mid wing, no dihedral the batt will be mounted low but right against the bottom of the wing or it could be mounted right on top of the wing. My guess is a lot less.

With the low wing the batt will be centered top to bottom and I will add a few degrees of dihedral. My guess is this is ideal.

With out getting into indepth design I am looking for input from more experienced flyers, builders and designers.

On either the low or mid wing config how does dihedral affect axial rolls.

I have a stock GWS Cub that I mounted a thick wing with ailerons. The small 2S 900 mah batt is mounted low. It does spiral rolls, not axial, that are very squirly. The wing is very high lift. My feeling is both the low CG because of the battery and the very high lift wing is the cause of this. There is no dihedral and also no diferential on the aileron throws. This plane flys great but rolls stink and inverted fight is a bear.

I also have a GWS P-51 that does perfect axial rolls. The battery is mounted just about centered top to bottom. No differential on the ailerons. This plane flys great all around.

Some feed back would be great. I've done a lot of reading here about this but this is only my third plane and first big mod so even though I've tried to educate myself about wing mounting and CG I'm going by just what makes sence to me and is really just a good guesstimation.

It would be a shame if it has the same tendencies as the other cub.

Thanks

[vintage1]

go pattern ship.
Mid wing, symmetrical section, equal fuselage area above and below, zero dihedral and a fin with as much area above as below the center line, thrustline zero zero and bang in the middle.

[reacher10]

go pattern ship.
Mid wing, symmetrical section, equal fuselage area above and below, zero dihedral and a fin with as much area above as below the center line, thrustline zero zero and bang in the middle.

Ok? I guess thats along the lines of how do I get a million dollars...be born rich...I see how easy it is now.

So I guess more axial rolls are not possible with this plane and nothing I can do will help.

Thanks

[slipstick]

I'm guessing you want completely axial rolls with just aileron control. With a cambered airfoil if you want anywere near axial rolls you're going to have to fly them. The right management of aileron and elevator control throughout the roll will get you quite close.

Getting everything set at 0 incidence with the wing, stab and thrust line as near as possible in one straight line will help a bit as will concentrating all the weight, including the battery, as close to that line as you can to avoid any pendulum effects.

But basically V1 is right. If you really want a plane that flies like a pattern plane it's going to have to be designed like one. Probably the most important factor is to get rid of that cambered airfoil. There are good reasons why aerobatic planes, even full size, use zero camber (symmetrical) airfoils.

Steve

[reacher10]

I'm going to move the battery centered top to bottom. I think that prolly has biggest affect and still keep it simple with a high wing.

I'm not shooting for a pattern plane but I don't want the screwy rolls the first cub has and to get better inverted flight.

The whole reason for doing this is it's really really cheap, it's fun getting it to come together and I might end up with a neat flying plane.

Thanks

[Dan Baldwin]

If inverted flight is a bear, you need to move the CG aft. A very forward CG will also make it more difficult to do axial rolls. Only move the CG back a little at a time. A tail heavy plane is difficult to fly, especially if your a low timer.

Dan

[eflightray]

I'll add my 2 cents.

A true axial roll need to be very fast if just aileron input is used.

A slower axial roll will need correction during the 'knife edge' part. That dreaded gravity thing gets involved. (And probably the 'P' factor as the nose is raised).

I recently put together a profile Edge 540, (very cheap foamie sheet kit), for 'playing' at 3D. Playing, as I have never really been into aerobatics other than the usual simple stuff.

The difference in roll between the Tx rates in and out is quite amazing, (to me). The roll looks totally axial with max aileron deflection, but then they happen so fast.

And certainly it's 'symmetrical' wing section, flat sheet, lets it go where ever it's pointing, including straight down. It's fun, but I wouldn't want to be in a real one.

[BMatthews]

One of the flat foamie 3D models will do what you want for cheap as well. You're fighting City Hall in trying to get what you have to do really GOOD axial rolls.

But if you're in this for the challenge of making this "thing" work as well as you can make it then I agree with the posts above about moving the CG back until it won't level itself out from a 40 degree dive but doesn't want to tuck to vertical. When it's at that point it's on the edge (CG is at or very close to the neutral point) and moving the CG back much further is not a good idea.

Also for slow axial rolls all models require some top rudder at each 90 point and a whisper of down when inverted as they do their roll. It's just the way it is and you need to learn this to do good ones.

[vintage1]

..and rip out the dihedral altogether, if it has any.

[reacher10]

Thanks for all the input guys.

With my P-51 it snap rolls no prob with just ailerons.

This is what I've decided to do. Mid wing.

http://www.rcgroups.com/forums/showthread.php?t=1066041

I'm going to start with the CG @ 30%. I DL'd compufoil3d and it tells me this is 2 1/8" from the LE. It tells me the ideal AOA is 1.08 deg so I laid this out carefully, I hope I got it right. From what I have read is that the horz. stab. being the datum line and then adding the incidence from there. This wing goes straight thru the fuse...no dihedral. I'm not sure how big of an effect the battery will be not having it in line but it will be right against the wing. I'll just wait and see.

Being very new to flying I'm going to ROG for the maiden as there is no telling what tendencies this plane will have and with my very limited exposure to different planes I would hate to drill it into the ground on the first toss.

If I understand things correctly and make sure I build the plane true it should fly.

What got me going was that I put the Super Cub wing with ailerons on the GWS Cub and the plane came alive, this was after I figured out the AOA was way off.

I then saw foam wing cores from Steelhead products @ $22.00 for 2 wings and thought with what I've learned from the first Cub I should be able to make something that will fly well and be a good all around plane, good speed...fast and slow, plenty of power and good aerobatics.

I don't have a computer radio but I've read how the control horn can be positioned to achieve differential throws.

I'm really having a blast flying my other 2 planes and I'm having a blast figuring this one out.

When I first started sailing I was reading everything I could find and was thinking what the heck do I need this or that for? Then I started crewing on race boats and was like...Oh, I need that and I'm gonna have to have this, must have new sails. all new blocks, etc. I took a basic sailboat and turned it into a boat I could race and was a pleasure just to go sailing on.

So I'm pretty much in the same mode here. I could have just bought a J-22 and raced it but I had more fun putting mine together.

If you guys have any ideas or see some pitfalls with what I'm doing I would welcome your input as I really appreciate all the input so far.

The build itself is nothing major so I'm not going to put every little detail about how I did things and if anyone has any questions then I can explain in more detail.

Thanks All
Rick

[reacher10]

I can get half way decent rolls from the cub when I input up elevator so I'm getting better at it and I've been working on knife edge. It's coming along. I haven't crashed in quite awhile and confident more and more eveytime I fly.

Inverted is easier when I have a fresh batt and more speed. I'm going to move the CG back...one quarter at a time...lol. I had 4 now I'm down to 2. :p

I still get a little nervous with the P-51 only because I have to basicly shoot carrier landings on a basket ball court from only one available direction and avoid the backboard post and the park benches along the sides.

I have good command of it and I am waiting for some 3s batts to arrive as right now I have one very lame 2S batt to use in it. The new ones I already have just will not fit in it.

So i'm figuring I will be able to have control of this one when I take it up.

This should be quite the blast!

[BMatthews]

WOW! That gives it a WHOLE new look!

Assuming that one is yours or if you're also going to reshape the wing to the same sort of airfoil then I think you're on the right track for getting the absolute most out of this collection of parts that you'll manage to get.

You're still trying to "make a silk purse out of a sow's ear" but that's half the fun of this hobby.

Since this will be intended as a serious aerobatic model and that you'll be trimming the CG back closer to the neutral point I would suggest you toss out that angle of incidence and make the wing and stabilizer set to 0-0. I'd also suggest just put the firewall at 0 as well and for the first few flights add a washer to shim in a skosh of downthrust. Work the CG back using the dive test to check for progress until it almost wants to continue in a steady angle to the ground (pull out before it plants :D) That'll be as close to the neutral stability point as you'll want to get. At that point you'll likely find you can remove the last of the downthrust and that you'll have as aerobatic and axial a model as you're going to get with this collection of bits.

[reacher10]

Same plane, same wing.

Let me see if I have this right.

Wing incidence is a line from the very point of the leading edge to the very point of the trailing edge?

Decalage is the difference between the horz. stab and the wing incidence?

The AOA is stated by compufoil3d to be 1.08 deg. So I take a line from the horz. stab. and then lower the rear or raise the LE to change wing incidence by 1.08 deg. and this should give me the optimum AOA.

I made a quick drawing, do I have this correct?

Thanks

[Dan Baldwin]

The 1.08 degrees you are showing is wing incidence, or angle of incidence. AOA or angle of attack is not a static measurement, it is dynamic. It is the angle of the relative wind in flight with regard to the wing cord. It can be anywhere from perhaps -20 degrees to +20 degrees, depending on the conditions of flight.

Dan

[reacher10]

At level flight I should have according to compufoil3d "Ideal angle of attack of 1.08 deg." if I set the wing as per that sketch?

Correct?

Here is a screen shot.

[BMatthews]

The angle Compufoil is giving you has to be a preffered angle of decalage between the wing and stabilizer. As Dan mentioned there is no "ideal" angle of attack for a model airplane. The angle of attack at any moment during a flight is based on the speed and any elevator inputs. At most the angle of attack will stay constant for no more than a very few seconds while flying straight and level.

As for the reference line to take the measurements from you got it right. It's from the extreme forward point on the leading edge radius to the intersection of the trailing edge lines just as you showed.

We tend to get all wrapped up in some ficticious "reference line" when setting up angles. But really the wing center line is the only reference line that has any merit at all. By setting the wing incidence to +1 degrees (good luck setting it to spot on 1.08 or even setting it to 1.1 if you round it off) you're automatically adding in 1 degree of downthrust as well. All in all though +1 at the wing with 0 for the thrust line and 0 for the stabilizer would not be a bad place to start. Although if it were me I'd just set the model up for 0-0-0 and click in a few clicks of up trim in the elevator for the first flights. After all, 1 degree at the wing is likely equal to about 3'ish degrees of elevator up trim.

[reacher10]

Cool, thats exactly what I needed to know. I just eyeballed it @ just a tick under an 1/8" and set it at that angle which should be fine. I layed it out in autocad and it was like .11". I went out on the web and found the same thing about AOA being dynamic. I wonder why Compufoil3D states that info like that. I'm sure it makes perfect sence but with my limited knowledge I'm not seeing it. But I am learning!

I'm just learning about a lot of this stuff kind of at once and didn't really think about adding a little elevator trim but I just didn't want to step in any bear traps.

Now I'm starting to grapple with washout and doing a bunch of reading on that. Add it, don't add it, how much to add. I do want the plane to be pretty stable and not some herky jerky twitchy handfull.

Thanks BM

Rick

[BMatthews]

For a model that will be flown at lower speeds a bit of washout is a good thing. But it becomes less important the a)faster you fly b)the lower the aspect ratio and c)the more truly aerobatic you want the design to behave.

What washout does for you is to help you avoid tip stalls during slower flight. But keep in mind that you can induce a perfectly stable and well behaved model into tip stalling if you jam in a bunch of aileron at low speeds. When flying slow and closer to the stall with any airplane aileron inputs need to be kept small and just wait a bit more for the model to SLOWLY bank into the turn. Try to jam it and you'll suddenly think you have a hellspawn model but in reality you just broke a pretty common rule. So start without any washout. Get up about 4 mistakes high and fly at idle or only a couple of clicks open and get a feel for what you can get away wtih. If it gets ugly then land using a bit more airspeed and add a skosh of washout. Keep it small or none at all on an aerobatic model though. It messes up any amount of inverted flying.

[Ralph Walton]

Just a couple of points that havn't been touched on are to do your rolls at a reasonable airspeed, ie faster is better.

If you reflex (raise) your ailerons slightly, possibly up to 3mm, you can reduce the effect of camber built into the wing. The plane will take a bit more power to keep in the air but the rolls should be more axial.

I've seen a couple of different setup sheets, sort of a flowchart , used to help setup your plane to be well behaved for aerobatics (someone may have a link to one). It will give you alot of handy hints on how to get the most out of what youve got.

The goal is to make your plane flying neutral in any orientation, vertically up and down , upside down right way up etc, then you fly it to do what ever manouver you want without tendancies to nose up or down or corkscrew etc

You can learn alot playing around like this.

Good luck!

[Ralph Walton]

This is the kind of thing I was talking about

http://www.geistware.com/rcmodeling/aerobatics/setup.htm

[reacher10]

This is the kind of thing I was talking about

http://www.geistware.com/rcmodeling/aerobatics/setup.htm


Thats great stuff Ralph. I'm about to post some pics and I'm ready to close the fuse and get it flight ready. I was waiting for some 3S batts but its been two weeks and there is no telling if they will ever get here.

Take a look at the thread see what you think.

Thanks everybody for some great information. I was kind of holding my hands out in front of me and feeling my way around...at least now I have a flashlight and can see things better :p

Here is the thread for the build/Assy:

http://www.rcgroups.com/forums/showthread.php?t=1066041

Thanks!

[reacher10]

I'd like to say thanks for the feedback on this.

Took it up tonight for a proper shake down and it flew on rails and the rolls are perfect.

Thanks

Rick

[BMatthews]

We need pictures or this never happened.... :D

[reacher10]

We need pictures or this never happened.... :D

It's funny. My GF gave it a try with the Piper Cub and the only thing she got was, me "did you get that fly by" and on the recording is an excellent video of her shoes...LOL.

Another day one of the kids at the school had a super nice camera and I asked could he take videos with it, he gave up in about 30 seconds, I'm sure he got some awsome video of the sky...again...LOL

I am working diligently on finding some one with a decent camera that knows how to use it.

Watch it'll prolly be me with a brand new cam duct taped to my head.

I am amazed at how well this thing flys! It caught me off guard, I pictured it being a dirt digger but really when I stepped back and looked at it I said to myself it should fly...how well, didn't know, but it should fly.

One video of duct tape covering a lense coming up! :)

[BMatthews]

LOL, I'll be looking for that one... :D

Yep, everyone thinks that because they have a camera that they are now a photographer. As you've seen there's a HUGE amount more to it.

[reacher10]

I've flown the "Sport Cub" quite a bit. Inverted flight hands off. One click right aileron which is almost imperceptible when you look at the actual control surface.

The plane flies better then I could ever have hoped for. I'm working on outside loops. Bigger motor, more amps, bigger prop, more thrust...I need it damn it!!! :eek:

However right hand rolls are true and crisp but I am getting just the smallest bit of barrel roll on left rolls.

My next purchase will be one of those cheapo 2.4ghz radios, really low on funds, unemployment sucks. At least I should be able to dial in the servos even if it needs to be done on a computer.

Could it be the aileron servos have different travel on left rolls?

Any info on this would be very helpful.

http://www.rcgroups.com/forums/showthread.php?t=1066041

Thanks

[Brandano]

most likely an effect caused by the prop and its slipstream. possibly you have to add a little rudder and/or elevator to the rolls when rolling left. In any case, when doing a slow axial roll you have to correct with elevator and rudder all the way through it

[reacher10]

Thanks.

I'm going to add alittle right thrust and see if that helps. It's only noticable by me and it is very sensitive to control surface deflections. I can live it NP.

[Ralph Walton]

Sounds like you're havin fun Reacher10. Its pretty normal for planes to roll different left and right. A little bit of diffence in mechanical linkages, a bit of wing twist, aileron flex, any number of things, and yes, servos, can contribute to it too.

Often, servos that don't have the arms parallel when flying straight and level, are to blame.

You seem to be "on the journey" and asking all the right questions and doing the right things. Good luck!

[reacher10]

Sounds like you're havin fun Reacher10. Its pretty normal for planes to roll different left and right. A little bit of diffence in mechanical linkages, a bit of wing twist, aileron flex, any number of things, and yes, servos, can contribute to it too.

Often, servos that don't have the arms parallel when flying straight and level, are to blame.

You seem to be "on the journey" and asking all the right questions and doing the right things. Good luck!

Thanks For the feed back.

I did throw a better motor on it...it's more efficient..put it that way...less amps same performance and I was able to put a 10x10 prop on it and it lit up...lol...but only for a few minutes as it spit the prop....it was a park zone prop anchored to a prop saver...bad combo.

I got my AMA and was able to fly at a good and true field today.

I am still waiting for the 2.4 gig radio however I have flown this plane quite abit in a small field and being able to get it out in the open in front of me was a real treat.

There were 3 old codgers scoping me out and I flew the crap out it for them...and me.

I'll give a more in depth post tomorrow or there abouts as it's late right now.

And again thanks for the feed back.

Renegade airlines flight 5050 out!

Reacher