NZ Scythe

I have a problem...

My 72" Edge 540 has a tendancy to drop a wing and go into a spin when you pull on high G's.

I have balanced the model and it flys ok doing big manouvers, but if you fly too slow or pull on the G's it will snap dropping its right wing.

I checked the lateral balance and had add a bit of tip weight to the left wing, but still there is no real improvement..

Is there anything else I can do to stop this from happaning?
I am putting it down to a poorly designed model.

Cheers

3D_FLYER-RCU

are you high speed stalling it??? (to much elevator to quick)
back the elervator thow off and try
good luck michael

Post Hole

Sounds like you are experiencing "snapping". This happens when a wing stalls, usually in slower flight and at high angles of attack. Certain airfoils are better than others at flying at certain speeds. Your symetrical wing will stall and snap much sooner than a flat bottom (trainer) wing at low speeds.

Your Edge is a high-performance airframe with an airfoil to match and that wing needs a certain amount of airflow over it to fly. High rates and low speed = stalling. If you have a 72" Edge I am betting you have a computer radio as well. I recommend using dual rates and switching to low rates when you are going to do slow-speed maneuvers. Keep turning down the low rates until the snapping stops at the speed you want to fly. Of course, too slow and you won't fly at all so I hope you have plenty of power and the correct prop to pull you out of trouble.

We fly combat, we build our own planes and cut our own wings. We just built some Sellig 8036 airfoils and they turn GREAT. We just keep turning up the rates on the elevator until the aircraft snaps out of a turn, then back off the rates a notch or two.

David Cutler

Along with the other excellent suggestions here, make absolutely certain your elevator halves are exactly in line, (assuming you have separate linkages for them) throughout their whole travel. This includes making sure the geometry of the linkage is identical (e.g. the servo arms are parallel throughout the range of movement).

Good luck!

-David

fishgod

My Feedback: (13)

I second what David said. I have a 73 inch Cap and while entering a high alpha manuver the thing would tip to the left all the time even with spoileron. After scratching my head and walking around in circles I decided to check the differential of the elevators. I found this tip on a pattern website and I made the gauges. Really easy to make and makes it easy to check differential throughout the whole range of elevator travel.

An Idiot Proof Elevator Differential Gauge

If you have split elevators a very simple way to test for elevator differential is to get two stadard clothes pegs and epoxy in two straight piece of piano wire (as in the diagram). Clip the cloths pegs to your elevator's at an angle so the ends of the wire are almost crossed, then move your elevator up and down. If the wires stay the same vertical distance throughout the movement, you have perfect elevator movment! but if the wires change their distance apart you need to (if you have a computer radio) mix in some opposite aileron to couteract the elevator differential. I found this out after two years of flying a pattern plane that when ever you did loops you had to hold in right aileron.

Guy McCaldin (design John Payne)
Australia email: [email protected]

Post Hole

Wow fishgod! Great tip! I will have to remember that one.

Thanks!

NZ Scythe

Thanks for the tips,

I will re check my throws tonight, I do however think I may have just a tad too much up elevator programed in - what should a model of this size have on the elevator? the instructions are very brief..

Cheers

fishgod

My Feedback: (13)

Believe it or not about 16 mm up and down for low rate. Mesured furthest inboard.

jabowil-RCU

My Feedback: (9)

My GP Giles 202 (1/4 scale) recommended elevator throw is 1/4" up and 1/4" down. When I set it up I thought was not enough, but its plenty.

GMM

It sounds to me like your plane may be too nose heavy. I know this goes against conventional wisdom, but believe it or not nose heavy aircraft are much more "snappy" than properly balanced aircraft. If you have alot of throw and the plane is not very pitch sensitive, try moving the CG back a bit, and reduce the elevator throw. I usually set a plane up with the CG towards the rear of the manufacturer's recommended range, then shift things around after flying it some to suit my tastes. When I get finished, sometimes I'm way behind the recommended range. Most manufacturers are very conservative with the CG locations. Next time you go out to fly move your battery or reciever back or add lead to the tail, and see if that helps. In my opinion, nose heavy airplanes are much harder to fly than slightly tail heavy planes.

Greg

NZ Scythe

GMM,

That is an interesting thought...

I know it is a tad on the nose heavy side and by the sounds of it I have way too much elevator movement. I will add a little tail weight and decrease my throws and hopefully it will be a much better plane.

Thanks for all the help

David Cutler

I had a similar situation with my GP 300s. It was snapping all over the place before I made certain the elevator halves were in line throughout their travel and reduced the throw to, what looked like, a ridiculously small movement.

There seems to be a close correlation between the thickness of the wing section and the snappiness of a model. For example, I can't get my SIG Somethin' Extra to snap without using the rudder, and that has a thick section, whereas the GP CAP snaps if you just try a tight loop, and that has a very thin section.

-David

Thunderbolt47

My Feedback: (8)

i had the same problem with a 40 extra 300 and it was the differential in the elevator. I was using one servo on a Y push rod and it would get more than a 1/4 inch off at full throw. This made it barrel roll in a tight loop. I connected the elevator haves together with a piece of piano wire. It solved that problem. I don't know if this will work on a 120 size but central hobbies sales an elevator bell crank that eliminates differential throw. If your servo are in the tail then, never mind , try a match box.