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For those of you who have read my threads you know that I've recently maidened an Extra 300 .60. I've noticed however, that the plane behaves really odd when I give it more than half elevator on high rates during a turn. I start to turn left, I let the plane drop the wing until it's almost perpendicular to the ground and then proceed to add elevator to make the turn. As soon as the elevator input exceeds about half travel, the plane violently turns to the opposite side to which I'm turning as if it was on an autopilot system leveling the flight or something. If I input even more elevator the plane sort of snaps. I can't really figure out what's going on. The CG is as instructed by the manual, but it could be slightly aft. Anyone who has flown this type of aircraft have any idea?

GRANT ED

Sounds like your pulling too much elevator and causing a snap roll.

bbbair

I cannot say for sure until you give me some more information about YOUR Extra.

BUT!

I have an Extra 300 that was a kit made in the ealy 1990s (another story) if our two AC have the same Elevator hook up I MAY be able to help you... (bear with me)

I have a single servo that uses a pushrod to a 'Y' arrangement to the TWO elevators.
- the servo is located on the right side of the fuse
- because of the location of the servo, the LEFT Elevator push rod is LONGER than the RIGHT pushrod.
- the servo action is circular and it only moves the elevators in a linear fashion for about 30 degrees (+/- 15) which is gentle flight.

When I EXCEED the linear motion of the servo the pushrod moves the left and right elevators at a different rate - and I get what appears to be some SLOPPY manouvers. [:'(]

MY Solution to this is to add a second servo and pushrod for the Left elevator and slave them together.

So what sort of Elevator arrangement do YOU have?

DMcQuinn

My Feedback: (13)

Most aerobatic planes will snap on high rates if you pull too much. I think Grant Ed has it right. If the plane is fairly heavy this is even more likely.

Stickbuilder

Sounds as if you are inducing a stall with the elevator. I have seen several designs that will really show this when you apply excessive elevator. If the plane tucks under and then departs the flight path on an opposite heading, this is what is happening. You will often find this occurring when on the downwind leg too. Your speed over the ground is high, but your relative airspeed is lower. You give aileron input, and the low wing is travelling slower than the top wing, and then you horse in the elevator, and away it goes. Try setting your elevator rates a little lower, and get used to not giving full stick commands. There is nothing wrong with your plane.

Bill, AMA 4720
WACO Brotherhood #1

Jester241

Your definetly stalling the wing. This is when the airflow around the wing is interupted for some reason(or something like that). My edge 540 does it all the time if I yank the elevator too hard in a turn. Theres really nothing you can do about it except not turn so hard. It can be VERY dangerous,so be careful. Its best to set your throws on low rates so that they wont exceed the limit that induces this stall effect. And then just be careful on high rates.

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I do have the same setup you had although I thought about this before installing the servo so I have it in the middle. Both halves move equally throughout all the travel. I do want to use a second servo to be sure.

I think this is what sounds like my problem. I can notice it only on the downwind turn so I figure this must be the answer. I still don't understand the aerodynamics behind what's happening. Why should the plane snap in opposite direction to where I'm turning? It's a fairly violent snap which in some cases gets the plane in totally the opposite direction.


I thought of this originally but if this was the case, the plane would tend to fall towards the "dropped" side but it does the total opposite, it briefley returns to level flight and tends to roll to the other side.



I should add that if I fly level and apply full elevator, the plane wont climb but it rather does a weird "hop". It kinda drops the tail slightly and gets sluggish. Can't all this be due to a tail heavy setup?

flyinrog

My Feedback: (1)

I should add that if I fly level and apply full elevator, the plane wont climb but it rather does a weird "hop". It kinda drops the tail slightly and gets sluggish. Can't all this be due to a tail heavy setup?

sounds like nose heavy to me,,,,nose heavy has to fly fast to compensate, tail heavy you would find you'd need to trim in down elevator to fly level and that is minor tail heavy, ...Rog

Stickbuilder

You must remember that when you stall the plane in a turn, one wing is still moving a little faster than the other one. Sudden application of elevator stalls the wing even further, and with the small amount of aileron, that you have inputted, you experience adverse yaw. We see this a lot with giant scale models of Cubs and Biplanes. When one aileron is more effective than the other, the more effective wing really speeeds up, while the other one slows down, and the airplane tries to fly on a different heading. Watch sometimes when someone is flying these kinds of models and does not have aileron differential (more up than down) dialed in. The plane will bank left, begin to turn left, but the nose starts pointing right.

In you case, you are flying at a lower airspeed, due to being on the downwind leg, and you begin to bank left. To facilitate the turn, you yank in a bunch of elevator, which changes the angle of attack of the wing, creating a stall (the attitude, lack of airspeed and AOA change kills the wings ability to provide lift). As the airplane continues to roll, you will have backed off the elevator input, and the plane is now inverted, or close to it. But, it has changed heading from the original flight path.

This was prevalent with some full scale planes (P-51 Mustang especially) due to wing designs. The pilots called it. "The Thing". My Father flew these planes and had it happen to him on several occasions.

What you are experiencing is not abnormal, but you might want to either plug in a little less elevator authority, or practice not using full stick deflection.

If you are flying 3-D, you normally won't experience this, since your airspeed is not as high, and you are using thrust to keep the model airborne. Ask someone at your field who flies 3-D if they ever experience this when flying non 3-D, but are flying fast aerobatics. Bet they will tell you that their planes do it too.

The, "Hop", that you experience when you hit full elevator from level flight again is from you stalling the wing. You spoil the speed differential over and under the wing, and it quits flying RIGHT NOW. Before you do too much adjusting on the model, recheck the balance, and if like the previous post said, check for a nose heavy condition. You want the balance to be right in the middle of the suggested range until you become comfortable with the plane. Then you can begin to slowly move the Balance point to the rear (DO THIS IN SMALL INCREMENTS). I know that all caps are considered yelling, but whatever it takes.[8D]

Bill, AMA 4720
WACO Brotherhood #1

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Thanks guys, I'm off to the field right now and will check the CG.

Sourkraut

I don't think there is anything wrong with your plane. My BME Cap 232 Maniac and my Funtana S 40 both do the same thing on high rates with full elevator at higher than average speeds. At slower speeds the snap is way less noticeable.

Curt

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Update on this issue:

It turns out that I was the luckiest guy for one day. I found out that the battery pack had unfastened from the velcro strap and was dangling towards the rear of the plane. It threw the CG back more than 2". It was only secured by the connection to the power switch. Any harsh movement would have disconnected the battery in flight and I would have lost this kit built bird. I corrected the error and now the elevator issue has almost disappeared. Phew!