I just built a SPAD and its my first build. Should the ailerons move an equal amount, just in opposite directions? For instance, should the left move up two inches and the right down two inches? On my wing the pull aileron moves up say two inches and the push aileron moves down maybe a half inch.

Thanks!

That is probably ok. A trainer (PT- 40) I built was like that. The Instruction book said that is gave the plane better rolling performance. I think it helps the plane to roll without dropping altitude, however, I cannot tell the difference between it and any of my other planes. Good luck, maybe someone alse will have some better info.

depends on the wing design.....

xray328, you have built a trainer aircraft, so it is in your best interests to have equal amounts of up and down movement in your ailerons. To achieve this you have to position your servo arm { if it is a straight one } parallel to the aileron, so you then have equal amounts of push and pull, with the aileron in the neutral position when the control on your radio is also in neutral position . That includes the trim levers as well. Only when you are advanced enough to fly high performance aircraft will you need to program differential control surfaces.

Aileron differential is used to prevent adverse yaw. When the ailerons are deflected, say for a left turn, the right aileron is dropped and the left aileron is raised. The dropped aileron has more drag than the raised one, so sometimes the nose of the plane will yaw to the right. This creates a very ugly turn and also usually raises the nose, which may cause a stall in the turn. Added rudder input in the direction of the turn is also used to prevent adverse yaw.

Aileron differential is NOT used to prevent the nose from dropping in a turn. That's the job of the elevator.

Unless your plane shows this adverse yaw, it's probably good for the ailerons to deflect the same amount. If your SPAD has that much difference in deflection, and all linkages are at 90 degrees to each other, and your radio is set for equal movement each side of center, then you have binding somewhere. That is never good, and should be corrected.

The statement you make "the push aileron" leads me to believe binding may be the cause. Linkages will bind in "push", and seldom bind in "pull".

Dr.1

I agree with DR1. I'll also go on to say that differential can be a good thing in a trainer to alleviate adverse yaw. I don't know if your SPAD is considered a trainer or not. Certainly a real SPAD isn't! Differential can affect how symmetrical your rolling maneuvers are and if this is important to you, work towards equal up and down aileron movement.

I agree with Dr1Driver also. I have a Hobbieco Superstar 40 and the ailerons do not go up and down equal amounts. It is stated in the manual that come with it the exact reason that Dr1Driver incicated to you.


Poppy2

Mark-

I assume his "SPAD" that he is referring to is a Simple Plastic Airplane Design, or coroplast and gutter pipe creation, not a WWI fighter. Otherwise, good advice.

I recognized your screen name in another post of yours. Hope all is well up in PR. I might be up next weekend and if the weather's good I'll head out to the field.

-Scott Johnson
(TCRC)

Dr1 explained the reasons and effect of differential very well. As far as the application, as a general rule that I use, and of course there are exceptions, differential is often beneficial for wings with flat bottoms, or semi-symmetrical wings. For fully symmetrical wings however, differential generally isn't used. That is, the ailerons deflect the same amount for both up and down.

DaveB

Scott, Good to hear from you! I rather thought he was talking about a Simple Plastic Airplane Design SPAD as opposed to a "Societe Anonyme pour l'Aviaton et ses Derives" SPAD. See ya!

Mark

Mark-

I should have given you more credit. Sorry. Now I'll quit hijacking Xray's thread and let it get back to a discussion of aileron diff. I might send you a PM to ask about the Cub project though.

-Scott

On all my SPADs, the ailerons should move about the same up and down. This is xrays first SPAD, and I think he's building a Debonair. In that design, there is a single servo driving both ailerons. The Servo is on top of the wing, so it pulls the elevator up, and pushes down. My guess for the cause of the differential is that the push rods are flexing. Try using a number 4 rod (4-40) if you're not already. Also, work the aileron hinges to their extremes a few times to loosen them up a little. Make sure you have completely removed the strip of coro where you cut your hinge.

Brad

As stated above in post#7, my Hobbieco Superstar 40 is a trainer, and it does have a flat bottom wing and it does have aileron differential. I should have been more clear about the flat bottom. DaveB has given some very good information in his post to make the picture much clearer.

Poppy2

Sorry, yes it is a Deboniar. Heres a couple things I've noticed. The inside of the aileron moved more than the outside, I think because the control horn is on the inside. Being a plastic coroplast aileron could it be flexing? Does that matter? The second thing is that it seems like the push rod is stiff. Do to the fact that the top of the wing is curved, the rod had to flex to meet the control horn. Its not much but it is there. Not sure on the rod diameter, but I had to drill out the servo arm holes to get it to fit. I'll post a picture when I get home. The wing is in fact a flat bottom. Thanks!

The inside of the aileron moved more than the outside, I think because the control horn is on the inside. Being a plastic coroplast aileron could it be flexing?

Yes it could, and that's not good. Most of your roll control is on the outside half of the wing. You might want to replace them with hard balsa. Before you do that, however, check your hinges and make sure they all move freely.

The second thing is that it seems like the push rod is stiff.

That's a straight-run pushrod that's completely outside the wing. It should move freely. Angle the horns so they match the angle of the pushrod.

Dr.1

I think the stiffness is coming from my Z bends. It seems like the middle of the "Z", where the control arm sits isn't tall enough for the arm. I'm using Z bend pliers (hobbico), not sure what to do where. Maybe the push rods are too thick? Again, I have to enlarge the hole to get them to fit. Thats more the stiffness I was talking about. It never actually touches the wing. I'll post some pictures of all ths later.

If you're using 4-40 rods, the Z bender you mention (same one I use) will make a Z bend that's too short for the servo arm thickenss. You can still use this tool, however. Make the bend and insert the rod in the servo arm. Look at the angle the rod sits in the servo arm with the other end free. Bend the rod so it's level with the arm, about 1" from the end. I've done that a lot, and it works well.

Dr.1

Well at least its not a total waste of money.

Just to be sure I'm clear here...

So go ahead and make the Z bend like normal? Heres a picture of how that looks. Notice the angle? So to fix this I bend the servo arm end or the clevis end? Why would Hobbico make it like this???

Is this whats responsible for my aileron problem? I've been sort of forcing it together like this. [:@]

yes it probobly is you should cut that off so it sticks thriough the servo arm just a little bit hope this helps

Oh yeah, I'm not using it like this, I just extended it to show the angle better. My point was that the Z bend was too short which wasn't allowing the push rod to lay flat.

Make the bend about 1" away from the Z bend so the rod is parallel with the servo arm. Hobbico designed this bender for 2-56 rods. It's sturdy enough for 4-40, so it's used there a lot. Hobbico should make a bender for 4-40 rods. If you force the rod down to the horn, you'll twist the servo arm, causing the binding. The bend in the rod eliminates that problem.

Dr.1

Any binding in the transmission of force to the control surface should be minimized as much as possible. Even then there may be to much, in which case a different approach may be warranted; change to snapper keepers, ball links or clevis). Z-bends are great, when they are correctly made and fit right. I always come up through the servo arm so the point of the Z-bend doesn't rub on the servo case. Any loss of transmitted force should be minimized as much as possible (Aileron twist, servo arm or horn hole to large, etc.) Take a systemic approach to the whole mechinism and try to make it work the best it possibly can. I've seen SPAD type airplanes when aileron input is generated, it actually warped the wing in the opposite direction due to a flappy wings. The plane flew and the owner didn't care, so what the hey!!